CN111291457B - Method for predicting water depth average two-dimensional water flow direction of curved compound river channel with submerged vegetation on beach - Google Patents

Method for predicting water depth average two-dimensional water flow direction of curved compound river channel with submerged vegetation on beach Download PDF

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CN111291457B
CN111291457B CN201810806011.7A CN201810806011A CN111291457B CN 111291457 B CN111291457 B CN 111291457B CN 201810806011 A CN201810806011 A CN 201810806011A CN 111291457 B CN111291457 B CN 111291457B
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刘超
单钰淇
刘兴年
张斌
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Sichuan University
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Abstract

The invention discloses a method for predicting the average two-dimensional water flow direction of the depth of a curved compound river channel with submerged vegetation on a beach, which can predict the average two-dimensional water flow direction of the depth of any section between a curved section and a curved top section of the curved compound river channel only according to the relative vegetation depth, the geometric form of the curved section and the position of the section to be predicted of the curved compound river channel with the submerged vegetation on the beach, has higher prediction efficiency and accuracy, does not need to carry out flow velocity measurement work or other exploration work, and has wide universality in the field.

Description

Method for predicting water depth average two-dimensional water flow direction of curved compound river channel with submerged vegetation on beach
Technical Field
The invention belongs to the field of hydraulics and river dynamics, relates to prediction of the water depth average two-dimensional water flow direction of a curved river channel, and particularly relates to a prediction method of the water depth average two-dimensional water flow direction of a curved compound river channel with submerged vegetation on a beach.
Background
The riverway is usually evolved and developed into a more stable curved riverway in order to keep the scouring and silting balance of the riverbed. In most of the time every year, the upstream inflow is small, the water body moves downstream along the curved main riverway, and the two sides of the water body do not overflow on the beaches. Because of the proximity to water sources, beaches are ideal habitats for vegetation, and therefore, a large amount of vegetation grows on beaches. When the flood season comes, the upstream inflow flow is increased, the water depth is increased, the water flows over the curved main river channel to submerge the vegetation on the beach land and the beach land, and the curved compound river channel with the submerged vegetation on the beach land is formed.
In a single curved river channel, water flows downstream along the curved main river channel, and the law is simple. However, in curved compound channels with vegetation on the beach, the water flow direction no longer flows in the direction of the curved main channel. This is because in the compound river course, the water body exchange between the main river course water flow and the beach land water flow changes the development process of the main river course on-way secondary flow, resulting in the change of the water depth average two-dimensional water flow direction in the curved main river course. If the depth-average two-dimensional water flow direction of the main curved channel can be accurately predicted, the method is greatly helpful for numerical simulation calculation of the depth-average two-dimensional curved compound channel and prediction of channel evolution trend.
The shape of a curved compound river with submerged vegetation on the beach is shown in figures 1 and 2. Research shows that the included angle theta between the two-dimensional water flow direction of the main bent river channel of the compound river channel with submerged vegetation on the beach land and the relative vegetation water depth Drv, and the included angle theta between the curved section (the section of the curved river channel with the initial position vertical to the water flow direction of the main river channel) and the curved top section (the section of the curved river channel with the central position vertical to the river flow direction of the main river channel)geoAnd an included angle theta between the section at any position x between the curved section and the curved top sectionxThree elements are related: (1)
Figure BDA0001738184750000011
wherein H is the main river depth of the bent compound river, HfThe depth of water in the beach hvFor the height of the vegetation on the beach, the smaller the relative vegetation depth is, the smaller the influence of the water flow above the height of the vegetation on the water flow of the main river channel is, and the smaller the influence on the average two-dimensional water flow direction of the depth is; (2) thetageoThe larger the difference between the flow direction of the water flow of the curved main riverway and the flow direction of the water flow of the beach land is; (3) thetaxThe larger the section position is, the closer the section position is to the curved section, the larger the influence of the beach on the water flow direction of the main river channel is, and otherwise, the larger the influence of thetaxThe smaller the section position is, the closer the section position is to the curved top section, and the smaller the influence of the beach on the water flow direction of the main river is.
Although research indicates that the depth of the main curved channel with submerged vegetation in the beach land is Drv, the curved section and the curved topAngle theta between the facesgeoAnd an included angle theta between the section at any position x between the curved section and the curved top sectionxThe three elements are related; however, at present, few studies on curved compound riverways with submerged vegetation on beach areas are developed at home and abroad, and no further study is provided to provide a method for predicting the average two-dimensional water flow direction of the water depth of the curved main riverway, which has a clear mechanism, a simple structure and accurate calculation.
Disclosure of Invention
The invention provides a method for predicting the average two-dimensional water flow direction of the water depth of a bent compound riverway with submerged vegetation on a beach, aiming at the current technical situation that the current riverway water flow direction of the bent compound riverway with the submerged vegetation on the beach is short, wherein the method is characterized in that the transverse average value of the average two-dimensional water flow direction of the water depth is directly obtained by using relative vegetation water depth parameters and the form of the riverway between a bent end face and a bent top section, so that the average two-dimensional water flow direction of any section between the bent end face and the bent top section of the bent compound riverway with the submerged vegetation on the beach is predicted, and the predicted water flow direction is the average two-dimensional water flow direction of any section between the bent end face and the bent top section of the main riverway with the submerged vegetation on the beach.
The invention provides a method for predicting the average two-dimensional water flow direction of the depth of a curved compound river with submerged vegetation on a beach, which comprises the following steps:
(1) judging whether the bent compound river water flow is turbulent flow or not according to the Reynolds number Re of the bent top section; if Re is more than 1000, the water flow is turbulent flow, entering the step (2), and if Re is less than or equal to 1000, ending the procedure;
Figure BDA0001738184750000021
q is the over-flow of the section to be predicted of the bent compound riverway, A is the area of the section, R is the hydraulic radius,
Figure BDA0001738184750000022
x is the wet cycle, v is the viscosity coefficient;
(2) judging whether the bent compound river channel is a medium bent river channel or not; if the bending degree 1< s <1.6 of the bent compound river channel is less than the bending degree 1, the bent compound river channel is a medium-bending river channel, and the step (3) is carried out; if s is more than or equal to 1.6, the bent compound river channel is a large-curvature river channel, the bent compound river channel is not in the application range, and the procedure is ended;
(3) judging whether the beach vegetation is high-density submerged vegetation or not, if ahv> 0.1 and hv<hfIf the vegetation on the beach land is high-density submerged vegetation, the step (4) is carried out, otherwise, the procedure is ended; a is the unit water-blocking area a of the submerged vegetation group n x d, n is the vegetation number of unit area of the beach, d is the diameter of the single vegetation, hvSubmerging vegetation height of beach land hfThe depth of the beach water;
(4) according to the included angle theta between the section to be predicted of the bent compound river channel and the bent top sectionxJudging whether the position of the section to be predicted is between the curved surface and the curved top section, if thetax≤θgeoIf the position of the section to be predicted is between the curved surface and the curved top section, the step (5) is carried out, otherwise, the procedure is ended; thetageoIs the included angle between the bending-in section and the bending-fixing section;
(5) according to
Figure BDA0001738184750000031
Calculating to obtain a transverse average value theta of the water depth average two-dimensional water flow direction of the section to be predicted of the main channel of the bent compound channela(m)Completing the prediction of the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach; drv is the relative vegetation water depth,
Figure BDA0001738184750000032
wherein H is the main channel depth of the bent compound channel.
The method for predicting the average two-dimensional water flow direction of the curved compound riverway with submerged vegetation on the beach land aims at the flow speed U0>The 0cm/s bending compound river channel enters any section between the bending section and the bending top section, so whether the water flow in the bending river channel is fully expanded turbulent flow is judged at first; in addition, the prediction method provided by the invention is only suitable for the river channel with medium curvature and high-density submerged vegetation, and is not suitable for the river channel with large curvature and the river channel with non-high-density submerged vegetation beachThe application is as follows.
According to the method for predicting the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach, the wet circumference X in the step (1) is a boundary line of the contact between fluid on the overflowing section of the bent compound riverway and the riverway. The value of the viscosity coefficient v is 0.01cm at the water temperature of 20 DEG C2/s2。
In the method for predicting the average two-dimensional water flow direction of the depth of the curved compound riverway with submerged vegetation on the beach, the curvature of the curved compound riverway in the step (2) refers to the actual length (L) of the main riverway of the curved compound riverway targeted by researchw) Length of straight line (L) with the river reachv) In a ratio of
Figure BDA0001738184750000033
The method for predicting the average two-dimensional water flow direction of the water depth of the curved compound riverway with submerged vegetation on the beach comprises the step (5) of determining the transverse average value of the average two-dimensional water flow direction of the water depth of the section to be predicted of the main riverway of the curved riverway
Figure BDA0001738184750000034
Can be obtained by the analysis of a bent compound riverway water tank test. Firstly, from the definition of the water depth average two-dimensional water flow direction, a relational expression of the water depth average two-dimensional water flow direction and the height of a secondary stream vortex group of a bent compound river channel section is given, and then the water flow direction of a secondary stream vortex area and an included angle theta formed by the area section and a bent top section are determined according to a water tank testxBased on the relationship between the water depth average two-dimensional water flow direction of the cross section of the bent compound river channel and the height of the secondary stream vortex group, the transverse average value theta of the water depth average two-dimensional water flow direction of any cross section of the bent compound river channel is obtaineda(m)And the prediction of the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach is completed.
Firstly, defining the water depth average two-dimensional water flow direction of the main channel of the bent compound channel in any section vertical direction, the water depth average two-dimensional water flow direction of a secondary stream vortex group area and the water depth average two-dimensional water flow direction of an area above the height of the secondary stream vortex group:
(i1) the depth-average two-dimensional water flow direction of the main channel of the bent compound channel at any section vertical direction is defined as
Figure BDA0001738184750000041
In the formula [ theta ]zIs the local water flow direction h of a bent compound river channel main river channel0The height of the secondary stream vortex group at any section of the main river channel;
(i2) the water depth average two-dimensional water flow direction of the secondary flow vortex group area of the bent compound riverway is defined as
Figure BDA0001738184750000042
The water depth average two-dimensional water flow direction of the area above the height of the secondary flow vortex group of the bent compound riverway is defined as
Figure BDA0001738184750000043
(i3) Obtaining the depth-average two-dimensional water flow direction of the main riverway vertical to any section of the bent compound riverway according to (i1) and (i2)
Figure BDA0001738184750000044
The transverse average value of the water depth average two-dimensional water flow direction of any section of the bent compound river channel is
Figure BDA0001738184750000045
And b in the formula is the width of the main river channel at any section position of the bent compound river channel.
In the basin test, establish three-dimensional coordinate with crooked compound river course main river course section central point as the origin of coordinates, the tangential direction of the river course position that the origin is located is followed to the x-axis, and the y-axis is along the horizontal river course width direction that is of river course section, and the z-axis is along the vertical river course section that is of river course direction of height, obtains the horizontal average value of the water depth average two-dimensional water flow direction of the section of waiting to predict through the basin test and includes following step:
(I1) carrying out a plurality of times of bending compound river channel working condition tests with submerged vegetation on the beach land with different water depths by utilizing a water tank, measuring flow velocities of M different sections for each working condition test, selecting N different vertical directions for each section of the main river channel along the transverse direction, and measuring time average flow velocities U, V, W of water flows along three directions on each vertical direction, wherein U is the time average flow velocity along the axis parallel to x, V is the time average flow velocity along the axis parallel to y, and W is the time average flow velocity along the axis parallel to z;
(I2) drawing a plane distribution diagram of the secondary vortex group with different sections by using the time average flow velocity V parallel to the y axis and the time average flow velocity W parallel to the z axis in different sections of the main river in the step (I1), acquiring the heights of the secondary vortex groups with different sections from the diagram, summarizing the heights of the secondary vortex groups with different sections obtained under different working conditions, and obtaining the height of the secondary vortex group according to the summarizing test result
h0＝H-k(hf-hv) (4)
In the formula
Figure BDA0001738184750000051
(I3) According to
Figure BDA0001738184750000052
And (I1) calculating to obtain the vertical local water flow direction theta in any section of the main river channel by using the time average flow speed U parallel to the x axis and the time average flow speed V parallel to the y axis in any section of the main river channel in the step (I1)z；
(I4) According to
Figure BDA0001738184750000053
And h obtained in steps (I2) and (I3)0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of any vertical secondary flow vortex group area on any section of the main river channelcell(jl)J is 1,2,3, …, M, l is 1,2,3, …, N; n different verticality angles in the same working condition and the same sectionWater depth average two-dimensional water flow direction theta towards secondary flow vortex group areacell(jl)Averagely obtaining the water depth average two-dimensional water flow direction transverse average value of the secondary flow vortex group area of the same working condition and the same section
Figure BDA0001738184750000054
The water depth average two-dimensional water flow direction transverse average value theta of the secondary flow vortex group areas with different sections under the same working conditioncell(m)Further averaging to obtain the water depth average two-dimensional water flow direction transverse average value theta of the secondary flow vortex group areas with different sections under the same working conditioncell(m)And the water depth average two-dimensional water flow direction of the secondary flow vortex group area with different sections under different working conditions is used as the transverse average value thetacell(m)The average value of the water depth average two-dimensional water flow direction transverse average value theta of the secondary flow vortex group area of the arbitrary section of the main river channel is obtained according to the summary test resultcell(m)＝0；
(I5) According to
Figure BDA0001738184750000055
And h obtained in steps (I2) and (I3)0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of any vertical secondary flow vortex group on any section of the main river channelupper(jl)(ii) a The water depth average two-dimensional water flow direction theta of the area above the height of the secondary flow vortex group in different vertical directions in the same working condition and the same sectionupper(jl)Averagely obtaining the water depth average two-dimensional water flow direction transverse average value of the area above the height of the secondary flow vortex group of the same working condition and the same section
Figure BDA0001738184750000061
The water depth average two-dimensional water flow direction of the area above the height of the secondary flow vortex group with different working conditions and different sections is subjected to the transverse average value thetaupper(m)Divided by the angle theta between the respective section and the curved roof sectionxThen summarizing, and taking theta of an area above the height of the secondary flow vortex group in the same vertical direction in any section of the main river channel according to the summarized test resultupper(m)＝θx；
(I6) Will be provided with(I2) H determined by (I4) and (I5)0、θcell(m)、θupper(m)Substituting the formula (3) into the water depth average two-dimensional water flow direction transverse average value of the main river channel arbitrary section of the bent compound river channel
Figure BDA0001738184750000062
The transverse average value theta of the water depth average two-dimensional water flow direction of the section to be predicted of the main channel of the bent compound channel is obtained through the water tank testa(m)In the process, the step (I7) may be implemented by the step (I7'):
(I7') according to
Figure BDA0001738184750000063
And h obtained in steps (I5) and (I6)0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of any vertical secondary flow vortex group area on any section of the main river channelcell(jl)J is 1,2,3, …, M, l is 1,2,3, …, N; the water depth average two-dimensional water flow direction theta of the same vertical secondary flow vortex group area in the same working condition and different cross sectionscell(jl)Averaging to obtain the average value of the water depth average two-dimensional water flow direction of the secondary flow vortex group area on the same working condition in the same vertical direction; collecting the average value of the water depth average two-dimensional water flow directions of the secondary vortex group areas in the same vertical direction under different working conditions, and taking the water depth average two-dimensional water flow direction theta of the secondary vortex group areas in any vertical direction on any section of the main river channel according to the collected test result cell(jl)0; the water depth average two-dimensional water flow direction transverse average value of the secondary flow vortex group area of any section of the curved river channel
Figure BDA0001738184750000064
The transverse average value theta of the water depth average two-dimensional water flow direction of the section to be predicted of the main channel of the bent compound channel is obtained through the water tank testa(m)In the process, the step (I8) may be implemented by the step (I8'):
(I8') according to
Figure BDA0001738184750000065
And h obtained in steps (I5) and (I6)0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of any vertical secondary flow vortex group on any section of the main river channelupper(jl)(ii) a Dividing the average two-dimensional water flow direction of the water depth of the area above the height of the secondary flow vortex group on the same vertical direction of different sections under different working conditions by the included angle theta between the corresponding section and the curved top sectionxThen summarizing, and taking the water depth average two-dimensional water flow direction theta of the area above the height of the secondary flow vortex group on any vertical direction of any section of the main river channel according to the summary test resultupper(jl)＝θx(ii) a The water depth average two-dimensional water flow direction transverse average value of the area above the height of the secondary flow vortex group of any section of the main river channel
Figure BDA0001738184750000071
In addition, the analysis can also be used for obtaining the water depth average two-dimensional water flow direction of any vertical direction of any section of the main river channel
Figure BDA0001738184750000072
That is, the average two-dimensional water flow direction of the depth of water in a certain vertical direction on a certain section of the main river channel is only related to the depth of the water relative to the vegetation, the geometric shape of the curved river channel and the position of the section, so that the average two-dimensional water flow direction of the depth of water on a certain section is the transverse average value
Figure BDA0001738184750000073
The method for predicting the average two-dimensional water flow direction of the depth of the curved compound riverway with submerged vegetation on the beach is used for researching the actual length (L) of the main riverway of the curved compound riverwayw) And the linear length (L) of the river sectionv) Depth h of beach land waterfHeight of submerged vegetation hvThe depth of main river channel water H, the curved section and the curved roofAngle theta between sectionsgeoAngle theta between the section to be predicted and the curved roof sectionxThe parameters such as the area of the section to be predicted, the wet circumference X and the like can be obtained by measuring a geometric form diagram of the main channel of the bent compound channel.
The method for predicting the average two-dimensional water flow direction of the curved compound riverway with submerged vegetation on the beach land comprises the following steps ofzThe angle between the direction of local water flow in the vertical direction of the main river cross section and the tangential direction of the central position of the main river cross section is thetacellThe angle between the average water flow direction of the secondary flow vortex group area in the vertical direction of the section of the main river channel and the tangential direction of the central position of the section of the main river channel is thetaupperThe angle between the average water flow direction of the area above the height of the secondary stream vortex group in the vertical direction of the section of the main river channel and the tangential direction of the central position of the section of the main river channel is formed, and the thetaaThe mean water depth average two-dimensional water flow direction on the vertical upper part of the main river channel section forms an angle with the tangential direction of the central position of the main river channel section, and the angle is thetaa(m)The angle is formed between the transverse average direction of the water depth average two-dimensional water flow on the vertical upper part of the main river channel section and the tangential direction of the central position of the main river channel section.
The method for predicting the average two-dimensional water flow direction of the water depth of the bent compound river channel with submerged vegetation on the beach can calculate the included angle theta between the curved section and the curved top section by using a plan view of the bent compound river channel or the water tankgeoAnd the included angle theta between the section at any position x between the curved section and the curved top section of the main channel of the curved compound channel and the curved top sectionx. The general test water tank is built according to the comparison rule, and the theta is easily determined according to the comparison rulegeoAnd thetax. For natural channels, the morphological changes are more complex, and the general determination method is as follows: firstly, selecting a bending section aiming at research, and putting an inscribed circle with the largest area on the inner side of the curve by using a bending curve of the bending section; then determining a curved top section and a curved entering section according to the position relation between the river channel curve and the inscribed circle, and if the river channel curve is partially overlapped with the line of the inscribed circle, the central point of the overlapped line is the curved top section, and the curve at the upstream side of the overlapped line is just separated from the inscribed circleThe point (d) is a curved surface; if the curve of the river channel is not coincident with the inscribed circle, two intersection points are required to fall on the inscribed circle, the middle point of the two intersection points on the curve is a curved top section, and the intersection point on the upstream side of the two intersection points is a curved entering section. After the curved top section and the curved entering section are determined, measuring the included angle between the curved top section and the curved entering section to obtain thetageo(ii) a Selecting a section to be predicted, and measuring an included angle between the section to be predicted and the curved top section to be thetax。
Compared with the prior art, the method for predicting the average two-dimensional water flow direction of the depth of the bent compound river channel with submerged vegetation on the beach provided by the invention has the following outstanding advantages and beneficial technical effects:
1. the method for predicting the average two-dimensional water flow direction of the depth of the bent compound river with submerged vegetation on the beach can predict the average two-dimensional water flow direction of the depth of any section between the curved section and the curved top section of the bent compound river only according to the relative vegetation depth, the geometric form of the curved section and the position of the section to be predicted of the bent compound river with the vegetation on the beach;
2. the invention discloses a method for predicting the average two-dimensional water flow direction of a water depth of a bent compound river channel with submerged vegetation on a beach, which is used for analyzing the average water flow direction of the depth of an area inside and above a secondary vortex group from the change of the water flow direction of the secondary vortex group between a bent section and a curved top section of the bent compound river channel with the vegetation on the beach along with the vertical height of the bent compound river group, simplifying the prediction process of the average two-dimensional water flow direction of the water depth based on the analysis, and improving the prediction efficiency while ensuring the accuracy of the flow direction prediction;
3. the method for predicting the average two-dimensional water flow direction of the depth of the bent compound river channel with submerged vegetation on the beach only needs to measure the depth of the main river channel, the depth of the beach, the height of the vegetation on the beach, the included angle between the curved section and the curved top section and the included angle between the section to be predicted and the curved top section, does not need to carry out flow velocity measurement work or other exploration work, and has wide universality in the field;
4. the method for predicting the average two-dimensional water flow direction of the curved compound river channel with submerged vegetation on the beach can determine the included angle between the curved section and the curved top section and the included angle between the section to be predicted and the curved top section by only utilizing the river channel plane graph, thereby being beneficial to improving the efficiency and the accuracy of flow direction prediction.
Drawings
Figure 1 is a curved compound channel geometry with submerged vegetation on the beach.
FIG. 2 is a transverse cross-sectional view of the curved compound channel curved roof section of FIG. 1 with submerged vegetation on the beach.
Fig. 3 shows the distribution of secondary vortex masses in a curved compound river channel with submerged vegetation on the beach in the curved section CS5(a), the middle section CS6(b) and the curved section CS7 (c).
FIG. 4 is a comparison of predicted and measured secondary flow vortex heights of different cross sections.
Fig. 5 shows the distribution of the local water flow direction in the central region of the secondary vortex group in the vertical direction (N is 7 vertical direction in fig. 2), where (a) corresponds to the section CS5, (b) corresponds to the section CS6, and (c) corresponds to the section CS 7.
Fig. 6 is a schematic diagram showing comparison between a predicted value (obtained by the prediction method provided by the present invention) and an actual value of a water depth average two-dimensional water flow direction applied to a curved compound river channel with submerged vegetation on different beaches.
Detailed Description
The embodiments of the present invention will be given below with reference to the accompanying drawings, and the technical solutions of the present invention will be further clearly and completely described by the embodiments. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the disclosure of the invention without any inventive step, are within the scope of the invention.
Example 1
The embodiment describes a formula for predicting the average water depth two-dimensional water flow direction of any section between the curved compound river channel curved section and the curved roof section of the beach with submerged vegetation, which is obtained through a curved compound river channel water tank test.
Purpose of the test
The vertical development process of the secondary stream vortex group between the curved compound river channel bending section and the curved top section of the submerged vegetation on the beach is analyzed through a water tank test, the distribution rule of the height of the secondary stream vortex group on different sections is determined, the depth average water flow direction relational expression of the area inside and above the secondary stream vortex group is determined through test results, and the transverse average value prediction formula of the water depth average two-dimensional water flow direction of any section between the curved compound river channel bending section and the curved top section of the submerged vegetation on the beach is provided.
② test equipment
The main equipment is shown in table 1 below.
TABLE 1 flow velocity measuring apparatus for test of submerged vegetation curved compound river channel from curved section to curved top section on beach
Figure BDA0001738184750000101
Experimental condition
The test was carried out in a curved compound channel 35 meters long, 4 meters wide and 1 meter high. The geometry of a curved compound channel with submerged vegetation on the beach is shown in figure 1. The total flow (Q) in a curved compound channel with submerged vegetation on the beach is measured by a triangular weir mounted in front of the flume. The curvature of the main channel is defined as the actual length (L) of the curved main channelw) And the linear length (L) of the river sectionv) I.e. s ═ Lw/Lv1.381, satisfies the range of moderate and below tortuosity river channels (1)<s<1.6). The slope (S) of the river in the beach land is 1 per thousand, and the slope of the bent main river is 0.7 per thousand (S/S). The width (b) and depth (h) of the curved main channel were 0.7 m and 0.14 m, respectively, and the resulting b/h was 5. The inside radius (r) of the curved top section is 0.9 m. The geometric angle theta between the curved-in section (CS5) and the curved-top section (CS7)geoIs 60 degrees. The main riverway bed and the side walls at two sides of the beach land are all coated with concrete, and the Manning roughness coefficient of the main riverway bed and the side walls at two sides of the beach land is n ═ 0.015.
In the embodiment, three working conditions (MV1, MV2 and MV3) are set, and the water depths (H) of the main riverway are respectively 25.6cm,21.7cm and 18.8 cm. The water flow in the river is fully developed.According to
Figure BDA0001738184750000102
A is the cross-sectional area of the curved top section, R is the hydraulic radius of the curved top section (A/X), X is the wet cycle (B +2H), B is the whole river width (4 m), and v is the kinematic viscosity (0.01 cm)2Calculated and obtained the Reynolds numbers Re of 15,311 to 33,023 under three working conditions(s) (/ s)>1000) And the water flow in the riverway under the three working conditions is fully developed turbulent flow. The opening of the tail water gate can be adjusted to ensure that the slope of the water surface is parallel to the slope of the river valley, and a quasi-uniform flow condition is established. The test parameters of the curved river channel with submerged vegetation on the three working conditions of the beach are shown in the table 2.
TABLE 2 bending composite channel water tank test basic parameters with submerged vegetation on beach
Working conditions Q(m3/s) Re H(cm) hf(cm) hv(cm) Drv
MV1 0.149 33,023 25.6 11.6 2.8±0.2 0.34
MV2 0.093 21,065 21.7 7.7 3.5±0.2 0.19
MV3 0.067 15,311 18.8 4.8 4.1±0.2 0.04
Note that: q is upstream flow, Re (QR/Av) is reynolds number of river water flow, v is viscosity coefficient, H is main river depth, Drv (H) (H ═ QR/Av)f-hv) and/H) is relative vegetation water depth.
Flow rate measurements were made in CS5, CS6 (bend break) and CS 7. The three-dimensional coordinate is established by taking the center position of the main river channel section of the bent compound river channel as the origin of coordinates, the tangential direction of the river channel position where the origin of x axis is located is followed, the y axis is along the transverse river channel width direction of the river channel section, the z axis is along the vertical direction of the river channel section, the flow velocity measurement of three working conditions (relative vegetation water depth Drv is 0.04,0.19 and 0.34) is respectively carried out on each section, and 13 measurement vertical lines are sequentially arranged from left to right in the bent main river channel, as shown in figure 2. The lateral positions of these measurement perpendiculars are 5,10,15,20,25,30,35,40,45,50,55,60 and 65cm, respectively. In the three working conditions, the distance between any two measuring points in the vertical direction is 1.5 cm. The ADV uses two probes up and down for complete recording of flow rate at each vertical, with the ADV sampling frequency of 50Hz and duration of 30 s. The instantaneous flow rate data in three directions are then processed using ADV-resident data processing software to obtain the time-averaged flow rates (U, V, W) in the three directions (x, y, z), respectively.
Analysis of test results
In curved compound channels with submerged vegetation on the beach, the secondary vortex mass consists of two components, the enhanced primary secondary vortex mass and the upstream beach water flow component, which is closely related to beach vegetation characteristics (see Liu, c., shann, y., Liu, x., Yang, k.,&liao, H. (2016.) The effect of flow display in The flow characteristics of networking channels journal of Hydrology 542-17). Because of the influence of the beach land water flow on the secondary flow vortex group of the bent main groove, the height (h) of the secondary flow vortex group at different sections0) Is different. Height (h) of secondary vortex group on curved top section0) The same as the water depth (H), and the height (H) of the secondary fluid vortex group at the elbow inlet section0) Equal to the height (h + h) from the riverbed of the main river channel to the vegetation canopyv) Therefore, consideration must be given to the inside of the secondary flow vortex (0. ltoreq. z. ltoreq. h)0) Depth-averaged water flow direction (θ)cell) And the height of the vortex mass is higher than (h)0<z is less than or equal to H) depth-averaged current direction (theta)upper). Therefore, in the embodiment, based on the secondary flow vortex mass distribution, a method for obtaining a transverse average value of the water depth average two-dimensional water flow direction between the main channel curved section (CS5) and the vertex section (CS7) is provided, and based on the obtained result, a transverse average value prediction formula of the water depth average two-dimensional water flow direction of any section between the main channel curved section and the vertex section is provided.
In this embodiment, a method for obtaining a lateral average value of a water depth average two-dimensional water flow direction between a main channel curved section (CS5) and a vertex section (CS7) is further described in combination with test acquisition and data processing processes of operating conditions MV1-MV 3.
(1) Determining the height of a secondary flow vortex group:
the method is characterized in that the change of the secondary flow vortex group height is analyzed by adopting test data of the working condition MV1 in CS5, CS6 and CS7, and the specific steps are as follows:
step 1, drawing a plane distribution diagram of secondary flow vortex lumps of different sections in sections of CS5, CS6 and CS7 by using the time average flow velocity V of the main river channel under the MV1 working condition along the y axis and the time average flow velocity W along the z axis, as shown in FIG. 3;
step 2, obtaining the height h of the secondary flow vortex group from the graph0And it can be seen that the secondary stream vortex group fully develops in the region (z is 0 to h) below the main river channel depth of the curved section, occupies the region below the main river channel flood bank height, and h is0H; on the curved top section, the secondary flow vortex group fully develops on the whole section h0H; on the middle section of the curved section surface and the curved top section surface, the secondary flow expands upwards in the vertical direction, and the height of the secondary flow vortex group becomes h0＝H-0.5(hf-hv)。
The height h of the secondary flow vortex group obtained by three groups of working conditions0The results are summarized (see Table 3) to give
h0＝H-k(hf-hv) (4)
In the formula (I), the compound is shown in the specification,
Figure BDA0001738184750000121
TABLE 3 height variation of secondary vortex mass between curved section and curved top section under different water depth conditions
Figure BDA0001738184750000122
Fig. 4 is a comparison between the predicted and actually measured secondary vortex group heights of different cross sections, wherein the abscissa is the secondary vortex group height predicted by using the formula (4), the ordinate is the actually measured secondary vortex group height of different cross sections under three working conditions, the solid line represents an ideal result that the actually measured value is the same as the predicted value, and it can be seen from the figure that the formula can accurately predict the secondary vortex group height between the curved section surface and the curved top section surface of the secondary flow.
(2) Determining the local water flow direction theta of the secondary flow vortex groupz：
According to
Figure BDA0001738184750000123
Calculating to obtain the flow direction theta of the vertical local water flow in the arbitrary section of the main river channel by using the time average flow speed U parallel to the x axis and the time average flow speed V parallel to the y axis in the arbitrary section of the main river channelz. The local water flow direction of a certain vertical direction in any section of the main river channel is obtained. Further according to the local water flow direction theta of different sections in the same vertical directionzThe vertical distribution diagram of the local water flow direction of different cross sections can be drawn along with the change of the vertical position z, as shown in fig. 5, fig. 5 is the vertical (7 th vertical) local water flow direction distribution diagram of the central regions of the three cross sections CS5, CS6 and CS7 under the condition of MV 1.
(3) Determining the water depth average two-dimensional water flow direction transverse average value theta inside the secondary flow vortex group areacell(m). In the embodiment, the water flow distribution of three working conditions MV1, MV2 and MV3 in CS5, CS6 and CS7 secondary flow vortex block areas is analyzed in two ways, and the water depth average two-dimensional water flow direction transverse average value theta in the secondary flow vortex block areas with universal conclusion is obtainedcell(m)。
The first realization mode is as follows:
according to
Figure BDA0001738184750000131
And h obtained previously0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of any vertical secondary flow vortex group area on any section of the main river channelcell(jl)，j＝1,2,3，l＝1,2,3，…，N；N＝13。
Taking three working conditions as an example, the three cross-section central regions of CS5, CS6 and CS7 have vertical (l is 7) local water flow direction distribution, as shown in fig. 5. According to
Figure BDA0001738184750000132
And h obtained previously0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of the main river channel three-section vertical direction l ═ 7 secondary flow vortex group areacell(j7)J is 1,2,3 specific water depth average two-dimensional water flow direction valueSee table 4; the water depth average two-dimensional water flow direction theta of a secondary flow vortex group area with the vertical direction l equal to 7 in the same working condition and different cross sectionscell(j7)The average value of the water depth average two-dimensional water flow direction of the secondary flow vortex group area on the same working condition vertical direction l is 7 is obtained on average, and is shown in table 4,
Figure BDA0001738184750000133
(operating mode MV2, Drv 0.19),
Figure BDA0001738184750000134
(operating mode MV3, Drv 0.04); collecting the average value of the water depth average two-dimensional water flow directions of the secondary vortex group areas on the main river channel in any vertical direction according to the collected test result, and taking the water depth average two-dimensional water flow direction theta of the secondary vortex group areas on the main river channel in any vertical direction according to the collected test resultcell(jl)0; the water depth average two-dimensional water flow direction transverse average value of the secondary flow vortex group area of any section of the curved river channel
Figure BDA0001738184750000135
TABLE 4 Theta at different water depth conditions and section positionscellAnd thetaupperValue of
Figure BDA0001738184750000136
Figure BDA0001738184750000141
Note that: the number in parentheses being θupper/θxA value of (1), where Drv is 0.04upperNo value is taken because the distance between two measuring points in the vertical direction is larger than the distance between the top end of the vegetation and the water surface.
The second implementation manner is as follows:
according to
Figure BDA0001738184750000142
And h obtained previously0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of any vertical secondary flow vortex group area on any section of the main river channelcell(jl)，j＝1,2,3，l＝1,2,3，…，N；N＝13。
Taking three working conditions as an example, the three cross-section central regions of CS5, CS6 and CS7 have vertical (l is 7) local water flow direction distribution, as shown in fig. 5. According to
Figure BDA0001738184750000143
And h obtained previously0And thetazAnd calculating to obtain the water depth average two-dimensional water flow direction theta of the secondary flow vortex group area with any vertical three sections of the main river channelcell(jl)J-1, 2,3, l-1, 2,3, …, N; n-13. The water depth average two-dimensional water flow direction theta of the same working condition and the same section in N-13 different vertical secondary flow vortex group areascell(jl)Averagely obtaining the water depth average two-dimensional water flow direction transverse average value of the secondary flow vortex group area of the same working condition and the same section
Figure BDA0001738184750000144
b main channel width, as shown in table 5; the water depth average two-dimensional water flow direction transverse average value theta of the secondary flow vortex group areas with different sections under the same working conditioncell(m)Further averaging to obtain the water depth average two-dimensional water flow direction transverse average value theta of the secondary flow vortex group areas with different sections under the same working conditioncell(m)The average values of (A) are shown in Table 5,
Figure BDA0001738184750000145
(operating condition MV1, Drv 0.34),
Figure BDA0001738184750000146
(operating mode MV2, Drv 0.19),
Figure BDA0001738184750000147
(operating mode MV3, Drv 0.04); and the water depth average two-dimensional water flow direction of the secondary flow vortex group area with different sections under different working conditions is subjected to the transverse average value thetacell(m)OfThe mean value is summarized, and according to the summary test result, the water depth average two-dimensional water flow direction transverse average value theta of the main river channel arbitrary section secondary flow vortex group area is takencell(m)＝0。
TABLE 5 Theta at different water depth conditions and section positionscell(m)And thetaupper(m)Value of
Figure BDA0001738184750000148
Figure BDA0001738184750000151
Note that: the number in parentheses being θupper(m)/θxA value of (1), where Drv is 0.04upper(m)No value is taken because the distance between two measuring points in the vertical direction is larger than the distance between the top end of the vegetation and the water surface.
(4) Determining the horizontal average value theta of the water flow direction of the area above the secondary flow vortex group heightupper(m). In the embodiment, the water flow distribution of three working conditions MV1, MV2 and MV3 in CS5, CS6 and CS7 secondary vortex block areas is analyzed in two ways, and the water depth average two-dimensional water flow direction transverse average value theta of the area above the secondary vortex block height with universal conclusion is obtainedupper(m)。
The first realization mode is as follows:
according to
Figure BDA0001738184750000152
And h obtained previously0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of any vertical secondary flow vortex group on any section of the main river channelupper(jl)，j＝1,2，l＝1,2,3，…，N；N＝13。
Taking two working conditions as an example, the two cross-section center regions of CS5 and CS6 are obtained to have vertical (l is 7) local water flow direction distribution, as shown in fig. 5. According to
Figure BDA0001738184750000153
And h obtained previously0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of the secondary flow vortex group with the vertical direction l of the two sections of the main river channel being 7upper(j7)The average two-dimensional water flow direction value of j ═ 1 and 2 specific water depth is shown in table 4; the water depth average two-dimensional water flow direction theta of a secondary flow vortex group area with the vertical direction l equal to 7 in the same working condition and different cross sectionscell(j7)Divided by the angle theta between the respective section and the curved roof sectionxThe results are shown in Table 4; according to the summary test result, the water depth average two-dimensional water flow direction theta of the area above the height of the secondary flow vortex group on any vertical direction of any section of the main river channel is obtainedupper(jl)＝θx(ii) a The water depth average two-dimensional water flow direction transverse average value of the area above the height of the secondary flow vortex group of any section of the main river channel
Figure BDA0001738184750000154
The second implementation manner is as follows:
according to
Figure BDA0001738184750000161
And h obtained previously0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of any vertical secondary flow vortex group on any section of the main river channelupper(jl)，j＝1,2，l＝1,2,3，…，N；N＝13。
Taking two working conditions as an example, the two cross-section center regions of CS5 and CS6 are obtained to have vertical (l is 7) local water flow direction distribution, as shown in fig. 5. According to
Figure BDA0001738184750000162
And h obtained previously0And thetazCalculating to obtain the water depth average two-dimensional water flow direction theta of the area above the height of the secondary flow vortex group with the vertical direction l of the two sections of the main river channel being 7upper(j7)The average two-dimensional water flow direction value of j ═ 1 and 2 specific water depth is shown in table 4; different in the same working condition and the same sectionWater depth average two-dimensional water flow direction theta of area above vertical secondary flow vortex group heightupper(jl)Averagely obtaining the water depth average two-dimensional water flow direction transverse average value of the area above the height of the secondary flow vortex group of the same working condition and the same section
Figure BDA0001738184750000163
b main channel width, as shown in table 5; the water depth average two-dimensional water flow direction of the area above the height of the secondary flow vortex group with different working conditions and different sections is subjected to the transverse average value thetaupper(m)Divided by the angle theta between the respective section and the curved roof sectionxThen summarizing, and taking theta of an area above the height of the secondary flow vortex group in the same vertical direction in any section of the main river channel according to the summarized test resultupper(m)＝θx。
(5) The transverse average value of the water depth average two-dimensional water flow direction of any section between the main river channel entry curved section and the curved top section can be obtained through the steps (3) and (4)
Figure BDA0001738184750000164
From the above analysis, it can be seen that the water depth average two-dimensional water flow direction of a certain vertical section of the main river channel is only related to the relative vegetation water depth, the geometric form of the curved river channel and the section position, so that the horizontal average of the water depth average two-dimensional water flow direction of a certain section is equal to the water depth average two-dimensional water flow direction of any vertical section of the corresponding section, that is, the water depth average two-dimensional water flow direction of a certain section of the main river channel is equal to the water depth of a certain section of the curved river channel
Figure BDA0001738184750000165
Example 2
The method for predicting the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach provided by the embodiment comprises the following steps:
(1) for flow rate U0>Judging whether the water flow of the bent compound river channel is turbulent flow or not according to the Reynolds number Re of the cross section of the bent top of the bent compound river channel of 0 cm/s; if Re is more than 1000, the water flow is turbulent flow and enters the step (2), if Re is less than or equal to 1000,the program is ended;
Figure BDA0001738184750000171
q is the over-flow of the section to be predicted of the bent compound riverway, A is the area of the section, R is the hydraulic radius,
Figure BDA0001738184750000172
x is wet cycle, v is viscosity coefficient value of 0.01cm2/s2(ii) a The wet perimeter X refers to a boundary line of contact between fluid on the flow cross section of the bent compound river channel and the river channel;
(2) judging whether the bent compound river channel is a medium bent river channel or not according to the bending degree s of the bent compound river channel; if s is more than or equal to 1.6, the bent compound river channel is a large-curvature river channel, the bent compound river channel is not in the application range, and the procedure is ended; if 1<s<1.6, bending the compound river channel into a medium-bending river channel, and entering the step (3);
Figure BDA0001738184750000173
Lwactual length of main channel of curved compound channel, LvThe length of the bent compound river reach is a straight line;
(3) judging whether the beach vegetation is high-density submerged vegetation or not, if ahv> 0.1 and hv<hfIf the vegetation on the beach land is high-density submerged vegetation, the step (4) is carried out, otherwise, the procedure is ended; a is the unit water-blocking area a of the submerged vegetation group n x d, n is the vegetation number of unit area of the beach, d is the diameter of the single vegetation, hvSubmerging vegetation height of beach land hfThe depth of the beach water;
(4) according to the included angle theta between the section to be predicted of the bent compound river channel and the bent top sectionxJudging whether the position of the section to be predicted is between the curved surface and the curved top section, if thetax≤θgeoIf the position of the section to be predicted is between the curved surface and the curved top section, the step (5) is carried out, otherwise, the procedure is ended; thetageoIs the included angle between the bending-in section and the bending-fixing section;
(5) according to
Figure BDA0001738184750000174
Calculating to obtain a transverse average value theta of the water depth average two-dimensional water flow direction of the section to be predicted of the main channel of the bent compound channela(m)Completing the prediction of the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach; drv is the relative vegetation water depth,
Figure BDA0001738184750000175
wherein H is the main channel depth of the bent compound channel.
The method for predicting the average two-dimensional water flow direction of the curved compound riverway with submerged vegetation in the beach by the embodiment is adopted to predict the average two-dimensional water flow direction of the section water depth (CS5, CS6 and CS7) under the working conditions of the embodiment 1(MV1, MV2 and MV3), and the prediction result and the actual measurement result are shown in FIG. 6. And the actual measurement result of the water depth average two-dimensional water flow direction is obtained by averaging the water depth average two-dimensional water flow direction on each vertical line of the section to be measured along the transverse direction.
Application example
In order to test the accuracy of the method for predicting the average water depth two-dimensional water flow direction of any section between the curved compound river channel entry curved section and the curved top section with submerged vegetation on the beach, the model is verified by using the test data of published academic papers. The application example collects test data from 4 different sources (see table 6), and the details are as follows:
(1) marti i Vide et al (2008) conducted tests in a curved compound river with submerged vegetation on a beach 18.7 meters long and 1.7 meters wide, with a river slope of 9.4 per mill (S). The water flow of the whole river channel meets the quasi-uniform flow condition (namely the water surface gradient is approximately equal to the river bed gradient) through controlling the downstream tail gate. The geometric angle theta of the flood plain river channel between the curved section and the curved top sectiongeo17 deg. The main river width (b) and depth (h) were 40cm and 3.8cm, respectively, and b/h was 10.5. High water level (Q ═ 0.171 m)3S) and low water level (Q ═ 0.0189 m)3/s) of the water depth, and respectively provides a calculation method of the average two-dimensional flow velocity of the water depth, therefore, the data of the two groups of working conditions are adopted as the prediction provided by the embodiment 2The method predicts the basic data of the water depth average two-dimensional water flow direction. The beach vegetation is modeled by plastic strips with the height of h v8 +/-2 cm, and m 0.07 steps/cm2(i.e., the number of vegetation per unit area of the beach n in the present application), the width of the individual vegetation is d 2 ± 1mm, and thus a is 0.14cm-1And ahv1.12, satisfies the definition of high density vegetation (ah)v＞0.1)。(MartínVide J.P.,MoretaP.J.M.,LópezQuerol.S.,2008.Improved 1-D modelling in compound meandering channels with vegetated floodplains.Journal of Hydraulic Research,46,265-276.http://dx.doi.org/10.1080/00221686.2008.9521860)。
(2) The test by Shiono et al (2009) was carried out in a curved compound channel with submerged vegetation on a beach with a channel slope of 2% o, the channel being 13 metres long and 2.4 metres wide. The water surface gradient is approximately equal to the bed surface gradient by adjusting the baffle at the tail part of the water tank, so that the condition of quasi-uniform flow is obtained. The curvature s of the main river channel is 1.38. The width b of the main river channel is 40cm, the depth h is 4cm, and therefore b/h is 10. Relative vegetation water depth Drv of two groups of measuring working conditions in the curved main river channel is 0.47 and 0.35 respectively, and corresponding flow is Q-0.0353 m30.0157 m/s and Q3And s. The beach vegetation is simulated by a golf artificial lawn, and the density is m ═ 6.5 steps/cm2And the width d of the individual plant is 0.4mm, so that a is 0.26cm-1. Height of vegetation is hv0.7. + -. 0.1cm, so, ahv0.18, satisfies the definition of high density vegetation (ah)v> 0.1). The measured flow rate was used as The basic data for predicting The water depth average two-dimensional water flow direction using The prediction method provided in example 2 (Shiono, K., Chan, T.L., Spooner, J., Rameshwaran, P., Chandler, J.H.,2009.The effect of flow in roughness on flow structures, after forms and separation rates in mechanical channels with overhead flows: part I.journal of Hydraulic Research 47,5-19.http:// dx.doi.org/10.3826/jhr 2009.2944-I).
(3) Gunawan et al (2008) conducted field survey experiments in 300 meter River banks in River Black Water, UK. The average slope of the river bed of the river reach is 1 per mill. The geometric angle of the curved section and the curved top section of the river reachθgeo40 ° is set. The curvature(s) of the main river channel is 1.18, and the slope of the main river channel is 0.85 per thousand. The width and depth of the main channel are 4.25m and 0.75m respectively, so b/h is 5.7. This area was flooded for 5 hours 1 month in 2008. The bending main tank water depth H is 1.1m, and the beach water depth is 0.35 m. The height and the density of the vegetation on the beach land are h respectivelyv20 + -10 cm and a-0.31 cm-1Therefore, ahvSatisfy the definition of high density vegetation (ah) 6.2v> 0.1). The vertical flow velocities into the curved section and the curved top section are measured. The flow rate change during this time is within 10%. The measured flow rate is used as the basic data for predicting the average two-dimensional water flow direction of the water depth using the prediction method provided in this example 2 (Gunawan, b., Sun, x., Sterling, m., Knight, d.w., Shiono, k., Chandler, j.h., Rameshwaran, p., Wright, n.g., Sellin, r.h.j., Tang, x., Fujita, i.,2008.An integrated and non-integrated approach to estimation the vessel capacity of the River black water, Proceedings of the origin International Conference on Hydro-Science and Engineering, nagaya, Japan, pp.).
(4) Ismail (2007) developed series tests and numerical simulations in a curved complex river channel with submerged vegetation at the beach with a length of 13 meters and a width of 2.4 meters at the university of Lapfburg, England. Geometrical angle theta of the run-in and the bend-top sections geo60 degrees. The width and depth of the main river channel are 0.38m and 0.04m respectively, so that b/h is 9.5. The radius of the internal circle bend at the apex section is about 57.5cm and simulates a high water level condition (Drv 0.36) and a low water level condition (Drv 0.11), respectively, and the measured flow rates are used as the basic data for predicting the water depth average two-dimensional water flow direction using the prediction method provided in example 2 (Ismail, z.,2007.a study of overflow flows in non-sampled and sampled flows in a comprehensive mechanical channels).
TABLE 6 published summary of parameters of a bent complex river channel with vegetation on a beach
Figure BDA0001738184750000191
Figure BDA0001738184750000201
Note that: s is the main curvature of the river; s is the slope of the flood river; smc(S/S) bending the main river slope; r is the inner radius of the testing bending section; and b is the width of the main river channel.
According to the analysis of the four documents, the models in the four documents meet the requirements of the prediction method from the step (1) to the step (3) of the depth-average two-dimensional water flow direction of the curved compound river channel with submerged vegetation on the beach in the embodiment 2, namely, the water flow in the main river channel of the model is fully expanded turbulent flow, the river channel is medium-curvature and cannon, and the vegetation on the beach is high-density submerged vegetation.
According to the data provided in the above four documents, the water depth average two-dimensional water flow direction of any section between the main channel curved section and the curved roof section is predicted by using the formula for predicting the water depth average two-dimensional water flow direction of the curved compound channel with submerged vegetation in the beach provided in example 2, and the predicted value and the measured value of the water depth average two-dimensional water flow direction provided in the document are shown in fig. 6.
From comparison of the measured value and the predicted value, the method for predicting the water depth average two-dimensional water flow direction of the curved compound riverway with submerged vegetation on the beach can accurately predict the water depth average two-dimensional water flow direction of any section between the curved section and the curved top section of the curved compound riverway in different riverways.

Claims (2)

1. A method for predicting the average two-dimensional water flow direction of a curved compound river with submerged vegetation on a beach is characterized by comprising the following steps:
(1) judging whether the bent compound river water flow is turbulent flow or not according to the Reynolds number Re of the bent top section; if Re is more than 1000, the water flow is turbulent flow, entering the step (2), and if Re is less than or equal to 1000, ending the procedure;
Figure FDA0003502773640000011
q is a bent compoundThe cross section overflow of the river to be predicted, A is the cross section area, R is the hydraulic radius,
Figure FDA0003502773640000012
x is the wet cycle, v is the viscosity coefficient;
(2) judging whether the bent compound river channel is a medium bent river channel or not; if the curvature of the bent compound river channel meets 1< s <1.6, the bent compound river channel is a medium-curvature river channel, and entering the step (3); if s is more than or equal to 1.6, the bent compound river channel is a large-curvature river channel, and the procedure is ended;
(3) judging whether the beach vegetation is high-density submerged vegetation or not, if ahv> 0.1 and hv<hfIf the vegetation on the beach land is high-density submerged vegetation, the step (4) is carried out, otherwise, the procedure is ended; a is the unit water-blocking area a of the submerged vegetation group n x d, n is the vegetation number of unit area of the beach, d is the diameter of the single vegetation, hvSubmerging vegetation height of beach land hfThe depth of the beach water;
(4) according to the included angle theta between the section to be predicted of the bent compound river channel and the bent top sectionxJudging whether the position of the section to be predicted is between the curved surface and the curved top section, if thetax≤θgeoIf the position of the section to be predicted is between the curved surface and the curved top section, the step (5) is carried out, otherwise, the procedure is ended; thetageoIs the included angle between the bending section and the bending top section;
(5) according to
Figure FDA0003502773640000013
Calculating to obtain a transverse average value theta of the water depth average two-dimensional water flow direction of the section to be predicted of the main channel of the bent compound channela(m)Completing the prediction of the average two-dimensional water flow direction of the water depth of the bent compound riverway with submerged vegetation on the beach; drv is the relative vegetation water depth,
Figure FDA0003502773640000014
wherein H is the main channel depth of the bent compound channel.
2. The method for predicting the average water flow direction of the curved compound riverway with submerged vegetation on the beach of claim 1, wherein the step (5) is carried out to determine the transverse average value of the average water flow direction of the water depth of the section to be predicted of the main riverway of the curved riverway
Figure FDA0003502773640000015
Obtained by bending a compound riverway water tank test.
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