CN112464589B - Simplified numerical simulation method for aerodynamic resistance of power transmission conductor - Google Patents
Simplified numerical simulation method for aerodynamic resistance of power transmission conductor Download PDFInfo
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Abstract
The invention discloses a simplified numerical simulation method for the aerodynamic resistance of a transmission conductor, which is carried out according to the following steps: determining N types of transmission conductors, corresponding transmission conductor parameters and a test scene of a wind tunnel test; defining a formula of the resistance coefficient of the transmission conductor, carrying out wind tunnel test on N types of transmission conductors, and obtaining the relation between the pneumatic resistance coefficient of the transmission conductor and the wind speed; selecting a lead as a target transmission lead, and simulating to obtain a geometric model of the target transmission lead; simplifying a conductor groove in the target transmission conductor geometric model to obtain a target transmission conductor geometric simplified model; presetting an aerodynamic resistance coefficient influence factor, and carrying out numerical simulation on the aerodynamic resistance coefficient of the power transmission conductor of the target power transmission conductor geometric simplified model by adopting CFD software to obtain the relation between the target power transmission conductor and the wind speed; the aerodynamic drag coefficient influencing factor is locked. Has the beneficial effects that: a wire simulation method is provided, and calculation data and difficulty are greatly reduced.
Description
Technical Field
The invention relates to the technical field of power transmission conductor simulation, in particular to a simplified numerical simulation method for the pneumatic resistance of a power transmission conductor.
Background
Wind load is dominant in all loads of the power transmission line, and has a great influence on the strength design of a tower foundation and a tower. The calculation of the wind load of the transmission line in the project depends on the value of the resistance coefficient suggested in the corresponding design specification to a great extent. With the rapid construction of the scale of the power grid and the continuous change of the climate and the environment, the wind disaster of the wires is increasingly serious. It is therefore important to accurately calculate and reduce the wire drag coefficient, especially in high wind environments. The wind resistance can be realized by only improving the structural strength of the power transmission line under the condition of strong wind and needing a large amount of investment, and the wind resistance has certain limitation. Conventional Aluminum Conductor Steel Reinforced (ACSR) wire is the most common wire, and its outer layer is generally circular in cross-section. The method optimizes the pneumatic appearance on the basis of the ACSR structure, develops the special-shaped lead with smaller resistance coefficient and has wide application prospect.
Previous studies have shown that the drag coefficient of a single wire is mainly influenced by factors such as the reynolds number, the incoming wind direction, the turbulence level, and the surface structure form (roughness) of the wire. For multi-split conductors, it is also influenced by the number, spacing and angle of the sub-conductors. However, they are all studies on specific wires, and there are few systematic analyses of the effects of different surface structure forms (roughness) of wires, which are far from satisfactory for engineering applications.
The wire may be viewed as a rough cylinder with a plurality of helical strands or grooves on the surface. The flow around a rough cylinder has smooth-cylinder-like properties (Achenbach, 1971: the resistance coefficient is basically unchanged in the subcritical region and is not influenced by roughness. The critical zone minimum drag coefficient increases with increasing relative roughness K/D. Roughness can lead to premature boundary layer separation, reducing the critical reynolds number. The coefficient of resistance in the supercritical region increases with increasing K/D. Helical wires or grooves have been extensively studied as an omnidirectional damping device (Law and Jaiman,2018, ishihara and li, 2020). (Szalay, 1989, tanaka et al, 2012, tang et al, 2013, kim et al, 2015) and the like have conducted experimental studies on the forces and responses of polygonal cross-section straight and spiral high-rise buildings, which may provide reference for the study of novel wires.
Based on the technology, in the aspect of calculation of the aerodynamic resistance coefficient of the wire, the defects of complex calculation data, large calculation amount and the like still exist, so that the calculation is difficult, and the progress of the wire simulation technology is greatly hindered.
Disclosure of Invention
Aiming at the problems, the invention provides a simplified numerical simulation method for the aerodynamic resistance of a transmission conductor, which is used for carrying out wind tunnel test research on the conductor to obtain the law of the resistance coefficient changing along with the wind speed. CFD simulation was then used to model and simplify the conventional wire geometry. A simpler wire simulation method is obtained, and the calculated amount is greatly reduced.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
a simplified numerical simulation method for the aerodynamic resistance of a power transmission conductor comprises the following key steps:
s1: determining N types of transmission conductors and corresponding transmission conductor parameters, and determining a test scene of a wind tunnel test;
s2: defining a formula of the resistance coefficient of the transmission conductor, and carrying out wind tunnel tests on the N transmission conductors to obtain the relationship between the aerodynamic resistance coefficient of the transmission conductor and the wind speed;
s3: randomly selecting one conductor from the N kinds of transmission conductors as a target transmission conductor, simulating the target transmission conductor by adopting CFD software, verifying the simulation accuracy and obtaining a geometric model of the target transmission conductor;
s4: simplifying a conductor groove in the target transmission conductor geometric model to obtain a target transmission conductor geometric simplified model;
s5: according to the test scene of the wind tunnel test in the step S1, presetting an aerodynamic resistance coefficient influence factor, and carrying out numerical simulation on the aerodynamic resistance coefficient of the power transmission conductor of the target power transmission conductor geometric simplification model by adopting CFD software to obtain the relation between the target power transmission conductor and the wind speed under the action of the aerodynamic resistance coefficient influence factor; and locks the aerodynamic drag coefficient influencing factor.
According to the scheme, wind tunnel test research is firstly carried out on all the wires, and the change rule of the resistance coefficient along with the wind speed is obtained. And then, simplifying the traditional lead geometric model by adopting CFD simulation. One of the novel wires is selected, and the influence of the groove depth and the groove number on the resistance coefficient is researched. A wire simulation method is provided, and calculation data and difficulty are greatly reduced.
According to a further calculation scheme, the parameters of the power transmission conductor at least comprise the cross section area of the conductor, the number of outer stranded wires, the diameter of the outer stranded wires, the shape of the outer stranded wires and the outer diameter of the conductor; the test scene of the wind tunnel test at least comprises the following test parameters: the method comprises the following steps of testing a lead, measuring the space size of a backflow wind tunnel, a wind tunnel wind speed threshold value, turbulence, a wind speed nonuniformity value, a sampling frequency of a pneumatic resistance coefficient of a power transmission lead and a sampling time of the pneumatic resistance coefficient of the power transmission lead.
In a further calculation scheme, the formula of the resistance coefficient of the power transmission conductor is as follows:
wherein C is D Is the wire drag coefficient; f D Is the average of the measured resistance forces exerted on the wire; ρ is the air density; u is the wind speed perpendicular to the wires; l is the wire length; d is the wire outer diameter.
In a further calculation scheme, a shear stress transfer model is adopted by the target power transmission conductor geometric simplified model; the model calculation domain is: the center of the wire is taken as the origin of coordinates, and the width and the depth of the wire are respectively 30D and 40D; calculating the spanwise length of the domain to be 5D, rotating each stranded wire by 180 degrees along the spanwise length L =5D, and establishing a centrosymmetric and periodic model, wherein D is the outer diameter of the wire; the model network is as follows: the wire groove adopts a wedge-shaped grid; the wall surface of the stranded wire adopts hexahedral meshes, and the stranded wire far away from the wall surface adopts wedge-shaped meshes; the grid in the lead flow field is a spiral stranded wire grid formed by sweeping a two-dimensional grid along the spanwise direction and simultaneously twisting the grid; the external part of the lead flow field is directly swept along the span direction, and the grid in the lead flow field is connected with the grid outside the lead flow field through a non-matching grid.
In a further calculation scheme, in step S4, the content of simplifying the conductor groove in the geometric model of the target power transmission conductor is as follows:
performing equivalent replacement on the geometric model of the target transmission conductor within the test wind speed range by adopting the equivalent roughness of the conductor surface to obtain a geometric simplified model of the target transmission conductor; the calculation formula of the wire surface equivalent roughness is as follows:
where R (θ, z, t) is the local radius, representing the distance from the center C of the section to a point on the surface, as a function of the angle θ on the cylinder, the axial position z along the cylinder, and time t;
d is the outer diameter of the wire; r is the radius of a circumscribed circle of the lead, and D =2R;
if err (θ, z, t) is equal to 0 at every point, the cylinder is circular and constant in cross-section.
In a further calculation scheme, in the step S5, the preset aerodynamic drag coefficient influence factors at least comprise the depth of the wire grooves and the number of the wire grooves; the aerodynamic drag coefficient influence factor is the wire groove depth.
The invention has the beneficial effects that: the depth of a prototype which can be reasonably simulated is found, the pneumatic resistance coefficient influence factor is the depth of the groove of the wire, and the simulation finds that the resistance coefficient is firstly reduced and then increased and then stabilized along with the change of the depth of the groove. The shape of the conductor having the best effect of reducing the drag coefficient is obtained.
Drawings
FIG. 1 is a schematic view of a wire pattern
FIG. 2 is a schematic cross-sectional view of a conventional lead (top) and a novel lead (bottom) corresponding thereto
FIG. 3 is a mounting layout of wind tunnel test model
FIG. 4 is a resistance coefficient C D Comparing the drag reduction rate with the change rule of the wind speed;
FIG. 5 is a schematic diagram of a wire calculation domain;
FIG. 6 is a schematic diagram of a conventional wire grid;
FIG. 7 is a schematic view of groove depth;
FIG. 8 is a graph illustrating the variation of the drag coefficient of a conventional wire with wind speed;
FIG. 9 is a graphical representation of the comparison of test values of coefficient of resistance to simulated values;
FIG. 10 is a graphical representation of the drag coefficient as a function of groove depth;
FIG. 11 is a schematic of a mean flow chart;
FIG. 12 is a schematic boundary layer profile;
fig. 13 is a flow chart of the method of the present invention.
Detailed Description
The following provides a more detailed description of the embodiments and the operation of the present invention with reference to the accompanying drawings.
A simplified numerical simulation method for the aerodynamic resistance of a transmission conductor is carried out according to the following steps:
s1: determining N types of transmission conductors and corresponding transmission conductor parameters, and determining a test scene of a wind tunnel test;
the parameters of the power transmission conductor at least comprise the cross section area of the conductor, the number of outer stranded wires, the diameter of the outer stranded wires, the shape of the outer stranded wires and the outer diameter of the conductor;
the test scene of the wind tunnel test at least comprises the following test parameters: the method comprises the following steps of testing a lead, measuring the space size of a backflow wind tunnel, a wind tunnel wind speed threshold value, turbulence, a wind speed nonuniformity value, a sampling frequency of a pneumatic resistance coefficient of a power transmission lead and a sampling time of the pneumatic resistance coefficient of the power transmission lead.
In this embodiment, N =3,3 transmission conductor types are respectively: JL/G1A-630/45, JL/G2A-720/50 and JL1/G2A-1250/100.
In table 1, cross-sectional parameters of six actual wires corresponding to the wires in 3 are listed, and a rigid model of the wire was prepared by a geometric scaling ratio of 1. The model wire is made by sleeving a 3D printed wire shell on a hard aluminum tube. The shell is made of PLA plastic, is accurately printed and is tightly attached to the hard aluminum pipe, and the rigidity of the model is ensured by the hard aluminum pipe. All the wires have the pitch-diameter ratio of about 11 and rise spirally anticlockwise.
Wherein the groove depth h of JLX2/G1A (DFY) -720/50 is the distance between the groove bottom and the wire circumscribed circle. The effective length of the pattern wire is 1.7m. The wire pattern and cross-sectional shape are shown in figures 1 and 2.
TABLE 1 conventional conductors and their corresponding low wind pressure conductor parameters
The test scene of the wind tunnel test is as follows:
the wind tunnel test is carried out in a wind tunnel laboratory high-speed test section of Shijiazhuang railway university, which is a closed backflow wind tunnel. The test section is 5m long, 2.2m wide, 2m long and 80m/s maximum wind speed. At 63m/s, the turbulence is less than 3% and the wind speed non-uniformity is less than 1%.
To simulate an actual wire, end plates were mounted at both ends of the model. The end plates are arranged on the sleeves at the two ends and are fixed on the wall of the wind tunnel through the external support, so that the end plates and the wires are stressed separately. The end plates are 8mm thick and 260mm in diameter and are made of a stiff wood plate, the thickness being sufficient to provide out-of-plane stiffness. In order to reduce the influence of cross wind vibration and flow field of the end plate to the maximum extent, the edge of the end plate is inclined at 45 degrees. Six-component high-frequency force measuring balances (HFFB) are horizontally arranged at two ends of the aluminum pipe, the sampling frequency is 1500Hz, and the sampling time is 20S. Referring to FIG. 3, the final test setup in the wind tunnel is shown.
S2: defining a formula of the resistance coefficient of the transmission conductor, and carrying out wind tunnel test on the 3 transmission conductors to obtain the relationship between the pneumatic resistance coefficient of the transmission conductor and the wind speed;
the formula of the resistance coefficient of the power transmission conductor is as follows:
wherein C D Is the wire drag coefficient; f D Is the average of the measured resistance forces exerted on the wire; ρ is the air density; u is the wind speed perpendicular to the wires; l is the wire length; d is the wire outer diameter.
In this embodiment, seven uniform wind speeds are considered, with wind speeds ranging from 10.0m/s to 44.8m/s.
As can be seen from the combination of FIG. 4, the resistance of three groups of conventional wires and the corresponding novel wires thereof in the wind speed range of 10m/s to 44.8m/s is measured in the test to obtain C D And the law of the drag reduction rate changing with the wind speed. Drag reduction rate = (new wire drag coefficient-traditional wire drag coefficient)/traditional wire drag coefficient.
Three kinds of traditional wires and C of corresponding novel wires D the-U curves are descending and ascending and finally tend to be smooth, which is consistent with the previous test results. C of conventional wire D The wind speed corresponding to the minimum value is between 15m/s and 20m/s, and the novel wire resistance systemAnd the wind speed value corresponding to the number minimum point is more than 25m/s. The drag reduction rate of the three novel wires is reduced firstly and then increased until the drag reduction rate is stable. When the wind speed is small, the drag reduction rates of the three novel wires are very small, even less than 0, and the drag reduction effect cannot be achieved. When the wind speed is more than 15m/s, the drag reduction rate is gradually increased; over 25m/s, the resistance is always positive, and obvious resistance reduction effect is achieved. Among the three novel wires, (e) the wire has a more obvious effect of reducing the resistance coefficient, and the maximum resistance reduction rate is 36.98%.
S3: randomly selecting one of the 3 transmission conductors as a target transmission conductor, simulating the target transmission conductor by adopting CFD software, verifying the simulation accuracy and obtaining a geometric model of the target transmission conductor;
in this embodiment, the conducting wire JLX2/G1A (DFY) -720/50 is selected.
The target power transmission conductor geometric simplified model adopts a shear stress transfer model; the model involves two transport equations, one for the kinetic energy of the turbulence and a specific dissipation ratio. An Unsteady Separation Algorithm (USA) was used in the analysis. The coupled velocity expression is processed with the SIMPLE algorithm and a second order implicit scheme is employed for the instability case. The second order solution is used for the convection terms in the k- ω transport equation and the momentum equation.
As can be seen in connection with fig. 5, the model computation domain is: the center of the wire is taken as the origin of coordinates, and the width and the depth of the wire are respectively 30D and 40D; calculating the spanwise length of the domain to be 5D, rotating each stranded wire by 180 degrees along the spanwise length L =5D, and establishing a centrosymmetric and periodic model, wherein D is the outer diameter of the wire;
during simulation, the aerodynamic force of the long cylinder can be effectively predicted by adopting symmetrical boundary conditions at two ends of the cylinder. The cylinder is located downstream 15D of the inlet. Uniform velocity conditions are adopted at the inlet boundary, U =19.5m/s, and the Reynolds number Re = UD/v ≈ 4.8 × 10 based on the outer diameter of the wire 4 . Pressure outlet conditions are used at the outlet boundary. Symmetric boundary conditions are applied to the top, bottom and lateral surfaces of the computational domain.
The traditional flow field net comprises local grids, wall local grids and steel strand wall local elevation grids. See figure 6 for details. Because the depth of the grooves between the strands is small, high resolution is required to accurately capture the flow field characteristics.
In this embodiment, the model network is: the wire groove adopts a wedge-shaped grid; to ensure the accuracy of the complex geometry of the strands.
The wall surface of the stranded wire adopts hexahedral meshes to form boundary layer meshes;
the stranded wires are far away from the wall surface and adopt wedge-shaped grids; to avoid meshes of excessive slenderness ratio.
The entire flow field uses a hybrid grid system and is divided into two regions, an inner region and an outer region. The grid in the lead flow field is a spiral stranded wire grid formed by sweeping a two-dimensional grid along the spanwise direction and simultaneously twisting the grid; the external part of the lead flow field is directly swept along the span direction, and the grid in the lead flow field is connected with the grid outside the lead flow field through a non-matching grid.
The meshes on both sides of the interface are similar in size, so that the accuracy can be maintained. The grid system not only helps to generate reasonable grids, but also allows for faster computation speed with sufficient accuracy using a smaller number of grids. The same meshing strategy is also adopted by the novel wire.
The convergence of the grid is verified by several dimensionless aerodynamic parameters of the wire, namely the drag and lift coefficients root mean square and Strouhal numbers. Strouhal number S t ＝f v D/U represents, wherein f v Indicating the vortex shedding frequency obtained by spectral analysis of the lift force on the cylinder. Table 2 shows the average resistance system C for different resolution grids D Root mean square of lift coefficient C Lrms And S t . The grid resolution gradually increases from grid 1 to grid 3. Results between grid 2 and grid 3 were less than 2%, and both were less than 2% compared to the experimental results, which is acceptable for engineering application convergence. Therefore, the grid 2 is used in the following simulation in consideration of accuracy and efficiency.
TABLE 2 grid independence verification
| Grid mesh | Number of grids | C D | C Lrms | S t |
| Grid 1 | 2,845,040 | 1.028 | 0.70 | 0.23 |
| Grid 2 | 4,192,560 | 0.945 | 0.51 | 0.22 |
| Grid 3 | 5,746,800 | 0.934 | 0.49 | 0.23 |
| Test values | 0.929 | 0.47 | 0.22 |
S4: simplifying a conductor groove in the target transmission conductor geometric model to obtain a target transmission conductor geometric simplified model;
as can be seen from the grids near the wall surface of the stranded wire in fig. 6 (b), if the conventional wire flow field is directly subjected to grid division, the number of the grids will be particularly large. Especially inside the grooves between the strands, the mesh is not only numerous but also small, which leads to difficulties in convergence during the calculation and not necessarily to correct results. According to the basic assumption of viscous fluids, the fluid itself near the angle is close to each wall surface, so that the fluidity is poor, the flow resistance is large, and the speed is almost 0. And according to the previous reduction of the sharp angle of the groove of the traditional wire, the relative roughness change of the surface of the wire is not large, so that the influence on CD is not large.
Therefore, the grooves of the conventional wire JLX2/G1A (DFY) -720/50 shown in FIG. 2 (b) are simplified to find a depth that reasonably simulates the prototype wire.
Because the resistance coefficient of the wire is related to a plurality of parameters such as the diameter, the number and the diameter of the wire of the outer layer,
in step S4, the content of simplifying the conductor groove in the geometric model of the target power transmission conductor is as follows:
performing equivalent replacement on the geometric model of the target transmission conductor within the test wind speed range by adopting the equivalent roughness of the conductor surface to obtain a geometric simplified model of the target transmission conductor;
the calculation formula of the equivalent roughness of the surface of the wire is as follows:
where R (θ, z, t) is the local radius, representing the distance from the center C of the section to a point on the surface, as a function of the angle θ on the cylinder, the axial position z along the cylinder, and time t;
d is the outer diameter of the wire; r is the radius of a circumscribed circle of the lead, and D =2R;
if err (θ, z, t) is equal to 0 at each point, the cylinder is circular and constant in cross-section.
S5: according to the test scene of the wind tunnel test in the step S1, presetting an aerodynamic resistance coefficient influence factor, and carrying out numerical simulation on the aerodynamic resistance coefficient of the power transmission conductor of the target power transmission conductor geometric simplification model by adopting CFD software to obtain the relation between the target power transmission conductor and the wind speed under the action of the aerodynamic resistance coefficient influence factor; and locks the aerodynamic drag coefficient influencing factor.
In the step S5, the preset aerodynamic resistance coefficient influence factors at least comprise the depth of the wire grooves and the number of the wire grooves; the locking aerodynamic drag coefficient influence factor is the wire groove depth.
As can be seen from FIG. 7, the use of concentric circles of different diameters reduces the depth of the grooves, their roughness and the corresponding C D See table 3 for details.
TABLE 3 steel strand C at different groove depths D
| Numbering | Groove depth h (mm) | Equivalent roughness K e /D(％) | C D | C Lrms | S t |
| Experiment of the invention | 2.525 | 1.533 | 0.929 | 0.47 | 0.22 |
| Simulation 1 | 2.115 | 1.527 | 0.945 | 0.51 | 0.22 |
| Simulation 2 | 1.715 | 1.492 | 0.945 | 0.51 | 0.22 |
| Simulation 3 | 1.315 | 1.395 | 0.947 | 0.52 | 0.22 |
| Simulation 4 | 0.915 | 1.198 | 0.936 | 0.47 | 0.22 |
| Simulation 5 | 0.715 | 1.047 | 0.990 | 0.57 | 0.22 |
| Simulation 6 | 0.515 | 0.850 | 1.098 | 0.80 | 0.24 |
The traditional wire has small width in the deep part of the groove and deep width in the shallow part, so the reduction of the depth of the groove at the beginning has little influence on the equivalent roughness. When the equivalent roughness is 1.198%, the drag coefficient of the simplified lead is very close to that of the original lead. When the equivalent roughness is further reduced, the result varies greatly. The law of the change of the resistance coefficient along with the depth of the groove is analyzed in detail in the following research of the groove of the novel wire. CFD simulation of this conventional wire was performed over the range of test wind speeds using this equivalent roughness. The simulated values for the drag coefficient are very similar to those tested herein and are detailed in FIG. 8.
The new wire JLX1/G1A (DFY) -680/45 of FIG. 2 (e) was selected and its aerodynamic force was further studied. According to the test results, the lead can effectively reduce the resistance coefficient of the lead. Firstly, CFD simulation is carried out on the wind speed sensor in a test wind speed range, the change rule of the resistance coefficient along with the wind speed is shown in 9, the simulation result is basically consistent with the test result, and the simulation precision meets the requirement. The groove depth and the number of the grooves of the novel wire are changed, and the wire is wound at a wind speed of U =30m/s, with Re being approximately equal to 7.1 multiplied by 10 4 Simulation analysis was performed.
Referring to fig. 10, a curve of the resistance coefficient of the wire along with the depth of the groove is shown, wherein the depth of the groove is 0.29mm, which is the original depth of the novel wire. It can be seen that the resistance coefficient of the novel wire increases with the depth of the groove, and when the depth of the groove is 0.5mm, the resistance coefficient even exceeds the traditional wire corresponding to the low wind pressure wire.
Average flow charts for smooth cylinders and three different groove depth wires, see fig. 11.
The average flow velocity of the wire across the mid-section is shown in fig. 11. The right enlarged view is the boundary layer separation position (red frame region). The wake consists primarily of a pair of symmetrical vortex rings, the length of which is commonly referred to as the recirculation length. The cylindrical surface roughness can significantly affect the wake morphology, and the wake recirculation length of the wire is significantly increased relative to a smooth cylinder. Fig. 11 (d) shows that there is a small vortex inside the groove due to the local separation of the fluid inside the groove. The separation point can be found by drawing a boundary layer profile. Fig. 12 is a boundary layer profile near the cross-sectional separation point across wires of different groove depths. It can be seen that the boundary layer profile changes from L-shape to S-shape, indicating the presence of an inflection point, i.e., a separation point. Exact split point position θ s And a recirculation length L r The results are shown in Table 4. The smooth cylinder has a separation point of 88.6 deg., and a shallow groove would move the separation point backwards, resulting in a reduced coefficient of resistance, but when the groove is deep enough, separation would occur at the edge of the groove and the coefficient of resistance would increase instead.
TABLE 4 different groove depths wire recirculation lengths and separation point locations
The number of grooves has little effect on the coefficient of resistance of the wire, with only a slightly decreasing tendency. When the number of sides is large, the influence of changing the number of sides is small, which can be confirmed from an experiment of a regular polygon. The larger the number of sides, the closer to a smooth cylinder, so the drag coefficient is reduced.
From the above analysis, it can be seen that the polygon is most effective in reducing the drag coefficient. Thus, by varying the number of sides, CFD simulations were performed on the pairs 16, 18, 20 of polygons, with the drag coefficient decreasing as the number of sides increases. See table 5 for details.
TABLE 5 resistance coefficient of wire with different number of edges
| Number of edges | 16 | 18 | 20 |
| C D | 0.765 | 0.720 | 0.690 |
The three low wind pressure leads can play a role in reducing the resistance coefficient when the wind speed is more than 25m/s, but the effect is not obvious when the wind speed is low, and even the resistance coefficient is increased.
The simplification of conventional transmission lines found that when the equivalent roughness Ke/D > 1.198%. The geometric model of the traditional transmission line is simplified, the difficulty of grid division and the number of grids can be greatly reduced, and therefore CFD simulation analysis can be accurately carried out.
The resistance coefficient is firstly reduced, then increased and then stabilized along with the depth change of the groove.
It should be noted that the above description is not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art should also make changes, modifications, additions or substitutions within the spirit and scope of the present invention.
Claims (5)
1. A simplified numerical simulation method for the aerodynamic resistance of a transmission conductor is characterized by comprising the following steps:
s1: determining N types of transmission conductors and corresponding transmission conductor parameters, and determining a test scene of a wind tunnel test;
s2: defining a formula of the resistance coefficient of the transmission conductor, and carrying out wind tunnel tests on the N transmission conductors to obtain the relationship between the aerodynamic resistance coefficient of the transmission conductor and the wind speed;
s3: randomly selecting one conductor from the N kinds of transmission conductors as a target transmission conductor, simulating the target transmission conductor by adopting CFD software, verifying the simulation accuracy and obtaining a geometric model of the target transmission conductor;
s4: simplifying a conductor groove in the target transmission conductor geometric model to obtain a target transmission conductor geometric simplified model;
the content of simplifying the conductor groove in the geometric model of the target transmission conductor is as follows:
performing equivalent replacement on the geometric model of the target transmission conductor within the test wind speed range by adopting the equivalent roughness of the conductor surface to obtain a geometric simplified model of the target transmission conductor;
the calculation formula of the equivalent roughness of the surface of the wire is as follows:
where R (θ, z, t) is the local radius, representing the distance from the center C of the section to a point on the surface, as a function of the angle θ on the cylinder, the axial position z along the cylinder, and time t;
d is the outer diameter of the wire; r is the radius of a circumscribed circle of the lead, and D =2R;
if err (θ, z, t) is equal to 0 at each point, the cylinder is circular and constant in cross-section;
s5: according to the test scene of the wind tunnel test in the step S1, presetting an aerodynamic resistance coefficient influence factor, and carrying out numerical simulation on the aerodynamic resistance coefficient of the power transmission conductor of the target power transmission conductor geometric simplification model by adopting CFD software to obtain the relation between the target power transmission conductor and the wind speed under the action of the aerodynamic resistance coefficient influence factor; and locks the aerodynamic drag coefficient influencing factor.
2. The simplified numerical simulation method of power transmission conductor aerodynamic resistance according to claim 1, characterized in that: the parameters of the power transmission conductor at least comprise the cross section area of the conductor, the number of the outer layer stranded wires, the diameter of the outer layer stranded wires, the shape of the outer layer stranded wires and the outer diameter of the conductor;
the test scene of the wind tunnel test at least comprises the following test parameters: the method comprises the steps of testing the length of a wire test section, the size of a space of a backflow wind tunnel, a wind tunnel wind speed threshold value, turbulence, a wind speed nonuniformity value, a sampling frequency of a pneumatic resistance coefficient of a power transmission wire and a sampling time of the pneumatic resistance coefficient of the power transmission wire.
3. The simplified numerical simulation method of power transmission conductor aerodynamic resistance according to claim 2, characterized in that: the formula of the resistance coefficient of the power transmission conductor is as follows:
wherein C is D Is the wire drag coefficient; f D Is the average of the measured resistance forces exerted on the wire; ρ is the air density; u is the wind speed perpendicular to the wires; l is the wire length; d is the wire outer diameter.
4. The simplified numerical simulation method of power transmission conductor aerodynamic resistance according to claim 1, characterized in that: the geometric simplified model of the target power transmission conductor adopts a shear stress transfer model;
the model calculation domain is: the center of the wire is taken as the origin of coordinates, and the width and the depth of the wire are respectively 30D and 40D; calculating the spanwise length of the field to be 5D, rotating each stranded wire by 180 degrees along the spanwise length L =5D, and establishing a centrosymmetric and periodic model, wherein D is the outer diameter of the wire;
the model network is as follows: the wire groove adopts a wedge-shaped grid; the wall surface of the stranded wire adopts hexahedral meshes, and the stranded wire far away from the wall surface adopts wedge-shaped meshes; the grid in the lead flow field is a spiral stranded wire grid formed by sweeping a two-dimensional grid along the spanwise direction and simultaneously twisting the grid; the external part of the lead flow field is directly swept along the span direction, and the grid in the lead flow field is connected with the grid outside the lead flow field through a non-matching grid.
5. The simplified numerical simulation method of transmission conductor aerodynamic drag according to claim 1, characterized in that: in the step S5, the preset aerodynamic resistance coefficient influence factors at least comprise the depth of the wire grooves and the number of the wire grooves; the locking aerodynamic drag coefficient influence factor is the wire groove depth.
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