CN111275792B - Method for drawing axial surface streamline of mixed-flow turbine - Google Patents
Method for drawing axial surface streamline of mixed-flow turbine Download PDFInfo
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Abstract
The invention provides a new method for drawing axial flow lines of a mixed-flow water turbine, which is divided into three steps, wherein the first step is to draw equipotential lines in a flow channel, the second step is to draw flow lines in the flow channel, and the third step is to check and correct the flow lines. The concept of straight bending and the principle of perpendicular to the upper crown and the lower ring are adopted to draw equipotential lines, so that the equipotential lines meet the design requirement; on the premise of drawing equipotential lines, drawing axial surface streamline by means of the principle that the streamline is perpendicular to the equipotential lines. By improving the axial flow line drawing method, the design process of the runner blade of the mixed-flow water turbine can be optimized, and the influence of experience of a designer on the axial flow line drawing quality is reduced.
Description
Technical Field
The invention belongs to the field of hydraulic mechanical engineering, and relates to a drawing method of axial surface streamline of mixed-flow hydraulic machinery.
Background
The runner blade of the mixed-flow water turbine is a core component of the mixed-flow water turbine, has the function of realizing energy conversion, and the working principle of the runner blade is that the energy of water flow is converted into the power potential energy of rotary machinery, and the overall efficiency of the mixed-flow water turbine unit is directly influenced by the advantages and disadvantages of the performance. The blade is an important component of the rotating wheel, and the design process comprises the steps of drawing a hydraulic calculation graph, drawing a wood pattern graph and three-dimensional modeling, and has the defect of an axial surface streamline drawing method. When the axial flow line is drawn according to the existing axial flow line drawing method, the quality of the first drawn flow line directly influences the workload of axial flow line correction, and the quality of the first drawn flow line mainly depends on experience of a designer, and has instability factors, so that the repeatability of axial flow line correction can be increased to a certain extent.
Disclosure of Invention
Aiming at the problems, the invention improves the drawing method of the axial flow line, provides a method for drawing the axial flow line of the mixed-flow water turbine, and weakens the influence of experience of a designer on the drawing quality of the axial flow line.
A method for drawing axial surface streamline of a mixed-flow water turbine is characterized by comprising the following steps: the method comprises the following steps:
1) Drawing equipotential lines in the flow channel: the first equipotential line is a drawn vertical line taking the point K of the intersection point of the lower circular arc and the inlet section of the flow channel as a starting point; drawing a second equipotential line in a straight-substitution curve mode, so that the equipotential line is perpendicular to the crown and the lower ring of the rotating wheel; and the equipotential lines should be smooth curves;
2) Drawing a streamline in a flow channel: firstly, dividing points of a runner outlet and a runner inlet, and drawing a streamline by using spline curve commands in AutoCAD on the basis of finishing the dividing points of the runner inlet and the runner outlet, wherein the drawn streamline is vertical to an equipotential line and has the characteristic of smooth flow direction;
3) Checking and correcting a streamline: firstly, determining intersection points of equipotential lines and streamline lines on two sides by using a method of drawing circles, drawing an equipotential line group by using a method of sequentially connecting spline curves, and correcting the drawn streamline lines and equipotential lines by using equal flow between two adjacent flow surfaces as a theoretical basis.
Further, in the step 1), the drawing mode of the straight-substitution curve is as follows: the intersection point of the equipotential line and the lower ring is selected in the arc section, two points A and B which are optionally close to each other are connected at the lower ring position of the rotating wheel, the points A and B are marked as a straight line section AB, the points C are marked as points C, the points C are crossed to form a perpendicular line of the straight line section AB, the point C at the middle point of the straight line section AB is used as a starting point of a spline curve, spline curve fitting commands are used for drawing the equipotential line along the perpendicular line direction of the straight line section AB, after a plurality of fitting points are crossed, the drawn equipotential line is perpendicular to the crown of the rotating wheel, drawing of one equipotential line is completed, and the drawing of the rest equipotential lines is completed by repeating the process.
Further, in step 1), the selection range of the number of fitting points in the drawing process of each equipotential line is set to 5-7 points, including a start point and an end point.
Further, in step 1), the number of equipotential lines drawn is 6 to 9.
Further, step 2) completes the drawing according to the following steps:
2.1 First, the separation point of the flow channel outlet and inlet: dividing the inlet of the runner into n parts by using a fixed number equal division command, and marking each node from the upper crown to the lower ring with the numbers 0, 1, 2, 3, … and n in sequence; the intersection point of the outlet straight line segment EF of the lower ring of the rotating wheel and the extension line of the central axis is marked as M points; selecting a radius circle drawing command, drawing a circle by taking M points as circle centers and taking a straight line segment EM as a radius, and marking the intersection point of the drawn circle and a central axis as N points and overcurrentThe E point of the lower ring end point of the channel outlet is a perpendicular to the central axis, the intersection point of the perpendicular and the central axis is a D point, and a straight line segment between the E point and the D point is recorded as an outlet straight line segment ED; dividing the outlet straight line segment ED into n parts by using a fixed number equal division command, making a vertical line of the outlet straight line segment ED through each node, and making a vertical line corresponding to each node and an arc segmentEach intersection point from the central axis to the lower ring outlet section is marked by the number 1', 2', 3', …, (n-1)' in sequence, and the number marks at the intersection points are in one-to-one correspondence with the number marks at the inlet;
2.2 Drawing a streamline: drawing a streamline by using spline curve commands in AutoCAD, drawing a spline curve which is sequentially perpendicular to each equipotential line by taking 1 point in points separated by the inlet of the runner as the starting point of the streamline, taking the end point of the spline curve as 1 'point separated on the outlet of the runner corresponding to the selected starting point, and marking the intersection point of the spline curve and the straight line segment ED of the outlet as 1'; drawing the rest n-1 streamline according to the method, and marking the intersection points with the outlet straight line segment ED as 2', 3', …, (n-1) '; after the streamline drawing is completed, the arc section needs to be deletedAnd uses the trimming command to trim the streamline, mainly trimming the arc segment +.>And a streamline section 1 'cut between the outlet straight section ED 2' and 3', …, (n-1)' (n-1) ".
Further, the number of streamlines drawn is 5, including an upper crown streamline and a lower annulus streamline.
Further, the method for drawing the equipotential line set in the step 3) specifically includes: initially defining a group of equipotential lines on two sides, wherein the distances S are 13, 13.2, 13.4, 13.6 and 13.8, selecting a radius circle drawing command, and drawing a circle by taking the intersection point of the equipotential lines and the streamline as the circle center and S/2 as the radius; after the circle is drawn, the intersection points of the circle and the streamline are sequentially connected by using a spline curve.
Further, the specific method for correcting the streamline and the equipotential lines in the step 3) is as follows:
on the basis of completing the drawing of the equipotential line group, breaking the streamline and the equipotential line from each intersection point of the streamline and the equipotential line by using a breaking-in-point command in AutoCAD; for the straight line segment or the distance between two points, linear labeling is adopted to measure the length of the straight line segment or the distance between two points, and for the curve segment, a list command is input to check the length of the curve segment; sequentially measuring the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential centerline between two adjacent axial surface streamlines and the distance R between the intersection point of the streamlines and the equipotential centerline and the central axis, wherein the distance R between the midpoint of the equipotential centerline between the two adjacent axial surface streamlines and the central axis is the average value of R at the endpoint of the equipotential centerline;
then MATLAB is used for autonomous programming, an automatic correction process of drawn streamlines is completed through for circulation, the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential centerline between two adjacent axial surface streamlines and the distance r between the midpoint of the equipotential centerline between two adjacent axial surface streamlines and the central axis are reasonably output, and the intermediate axial surface streamlines are converted into an AutoCAD graph;
the basic content of autonomous programming with MATLAB is: and (5) finishing correction calculation of the axial surface streamline by using the for-loop body statement. According to the measured original data, an error value delta can be calculated, whether the error value delta meets the requirement or not is judged, and if the error value delta does not meet the requirement, the length of an equipotential centerline between two adjacent axial surface streamlines is corrected by the error value delta, namely: Δb Correction =Δb× (1- δ), and the difference Δb×δ between the correction value and the original data is equally divided, to the length Δb of the equipotential centerlines of the remaining segments, where Δb: the length of an equipotential center line between two adjacent axial surface streamline; the length delta Lm of the intermediate shaft surface streamline and the distance r between the midpoint of the equipotential center line between two adjacent shaft surface streamlines and the central axis can be calculated through a similar conversion method by using the formula (5) and the formula (6);
r correction ＝(R 2 -R 1 )×(1-δ)+R 1 (5)
ΔLm Correction ＝ΔLm×(1-δ) (6)
In the above formula: Δb Correction : referencing Δb after correction value adjustment of the calculated Δb;
R 1 ，R 2 : the distance from the intersection point of the equipotential center line and the axial surface streamline to the central axis;
criteria to be followed in correcting the axial flow line:
the length of the equipotential centerline is not changed, namely: Δb 1 +Δb 2 +Δb 3 +Δb 4 ＝const；
The length delta b of the equipotential center line between the streamline of the two adjacent axial surfaces meets the relationship of orderly decreasing from the upper crown to the lower ring, namely: Δb 1 >Δb 2 >Δb 3 >Δb 4 ；
The length delta Lm of each section of intermediate shaft surface streamline should satisfy the relationship of decreasing from the upper crown to the lower ring in sequence, namely: Δlm 1 >ΔLm 2 >ΔLm 3 >ΔLm 4 。
Compared with the existing design method, the invention has the advantages that:
the invention relates to a method for drawing axial surface streamline of a mixed-flow water turbine, which adopts the idea of straight-substitution curve and the principle of perpendicular to an upper crown and a lower ring to draw equipotential lines, so that the equipotential lines meet the design requirement; on the premise of drawing equipotential lines, the axial surface streamline is drawn by means of the principle that the streamline and the equipotential lines are mutually perpendicular, so that the influence of experience of a designer on the drawing quality of the axial surface streamline is weakened.
Drawings
FIG. 1 is a contour plot of a method for streamlining a francis turbine according to the present invention.
FIG. 2 is a plot of flow channel inlet and outlet split points drawn by the method for drawing the axial flow line of the mixed-flow turbine.
FIG. 3 is an axial flow chart drawn by the method for drawing axial flow lines of a francis turbine according to the present invention.
FIG. 4 is a corrected axial flow chart using a method of francis turbine axial flow line mapping according to the present invention.
FIG. 5 is an enlarged view of the C equipotential line set in a method for drawing a francis turbine axial flow line according to the present invention.
Detailed Description
The invention will be further described with reference to the drawings and the specific embodiments, but the scope of the invention is not limited thereto.
The invention relates to a method for drawing axial flow lines of a mixed-flow water turbine, which is characterized by comprising the following steps of: the method comprises the steps of drawing equipotential lines in a flow channel in the first step, drawing streamline lines in the flow channel in the second step, and checking and correcting the streamline lines in the third step. Spline curve fitting, dividing equally, radius rounding, trimming, deleting, breaking in points, labeling, list and other commands are used in AutoCAD software to complete the drawing of streamline and equipotential lines.
The invention relates to a method for drawing axial surface streamline of a mixed-flow water turbine, which specifically comprises the following steps.
The first step is to draw equipotential lines in the flow channel: after the flow channel cross-sectional area is checked without errors, the spline curve command in AutoCAD is used for drawing equipotential lines. The starting point of the first equipotential line is selected at the point K of the intersection point of the lower circular arc and the inlet section of the flow channel, and the inlet of the flow channel is a straight line section, so that a perpendicular line of the inlet straight line section is made through the point K. The intersection point of the equipotential line and the lower ring is generally selected in an arc section from the second equipotential line, and the equipotential line is drawn by applying the idea of straight-substitution curve in order to ensure that the equipotential line can be mutually perpendicular to the lower ring of the rotating wheel. The implementation process of the idea of "replacing starter with starter" will be described with reference to fig. 1. And two points A and B which are optionally close to each other at the lower ring position of the rotating wheel are connected, the points A and B are marked as a straight line segment AB, the middle point is a point C, and a perpendicular line of the straight line segment AB is drawn through the point C. The drawing process of the equipotential lines is described with reference to the equipotential line diagram drawn by the drawing method of the axial streamline of fig. 1. Taking the midpoint C of the straight line segment AB as the starting point of the spline curve, and using spline curve fitting commands to draw equipotential lines along the vertical line direction of the straight line segment AB, wherein the drawn equipotential lines are vertical to the crown of the rotating wheel after passing through a plurality of fitting points. The above process is repeated, the remaining equipotential lines are plotted and marked in sequence with a, b, c, d, e and f equipotential lines from the entrance.
The number of the equipotential lines directly influences the result of correcting the streamline, the number of the equipotential lines is more, the correction result of the streamline is correspondingly more accurate, so that the streamline is more close to the streamline in actual flow, and when the number of the equipotential lines exceeds 9, the accuracy of the correction result of the streamline is limited; if the number of equipotential lines is small, the correction result for the streamline is not ideal, and the error in the correction result is amplified when the calculation of the axial flow velocity and the wrap angle is performed. In order to ensure ideal streamline correction results and reduce errors of subsequent designs, the number selection range of the equipotential lines is determined to be 6-9 equipotential lines by referring to the existing design method. The fitting points are points which are arranged for finely adjusting the curve to enable the curve to meet the requirement, the number of the fitting points is too large, the drawing difficulty is increased, the number of the fitting points is too small, the curve is difficult to meet the requirement, and the selection range of the fitting points is set to be 5-7 points, including a starting point and a terminal point, from the aspect of considering both the drawing difficulty and the quality of the curve.
The equipotential lines drawn must be perpendicular to the crown and ring of the wheel; and the equipotential lines are smooth curves, and if the uneven parts appear, the equipotential lines can be adjusted through fitting points so as to be smooth. Since the flow situation at the circular arc of the lower ring of the rotating wheel is complex, in order to ensure that the actual flow situation is approached, it is required that the starting point of the equipotential lines should be optimal at a position perpendicular to the circular arc of the lower ring of the rotating wheel.
Before axial flow line drawing, the separation points of the flow channel outlet and the inlet are needed to be carried out. The process of the flow channel inlet and outlet split point is described by combining the flow channel inlet and outlet split point diagram drawn by the axial flow line drawing method of the figure 2. The flow channel inlet split is described below using a number of split commands to split the flow channel inlet equally into 4 parts, each node from the top crown to the bottom ring being labeled with the numbers 0, 1, 2, 3 and 4 in sequence. The process of the flow path outlet split is described below, with the outlet straight segment EF of the runner lower ring and the central axis extending to intersect, and the intersection being marked with M. Selecting a radius circle drawing command, drawing a circle by taking M points as circle centers and taking straight line segments EM as radii, and combining the circle M with a central axisThe intersection point is marked as N point, the E point of the lower ring end point of the outlet of the flow passage is marked as a vertical line of the central axis, the intersection point of the vertical line and the central axis is marked as D point, and the straight line segment between the E point and the D point is marked as an outlet straight line segment ED. Dividing the outlet straight line segment ED into 4 parts by using a fixed number equal division command, making a vertical line of the outlet straight line segment ED through each node, and making a vertical line corresponding to each node and an arc segmentEach intersection point from the central axis to the lower ring outlet section is marked with numerals 1', 2' and 3' in turn, and the numerical marks at the intersection points are in one-to-one correspondence with the numerical marks at the inlet.
And step two, drawing a streamline in the flow channel: and on the basis of completing the division points of the inlet and the outlet of the flow channel, a spline curve command in AutoCAD is used for drawing the flow line. The process of drawing the axial streamlines is described with reference to fig. 3. Because the streamline and the equipotential lines have the characteristic of being mutually perpendicular, 1 point in the points separated by the inlet of the runner is selected as the starting point of the streamline, a spline curve which is sequentially perpendicular to each equipotential line is drawn, the end point of the spline curve is the 1 'point separated on the outlet of the runner corresponding to the selected starting point, and the intersection point of the spline curve and the straight line segment ED of the outlet is recorded as 1'; drawing the remaining two streamline lines according to the method, and marking the intersection point of the streamline lines and the outlet straight line segment ED as 2 'and 3'; after the streamline drawing is completed, the arc section needs to be deletedAnd uses the trimming command to trim the streamline, mainly trimming the arc segment +.>And streamline sections 1'1 ", 2' 2" and 3'3 "cut between the exit straight section ED.
The flow line is an imaginary curve existing in the flow field and represents the flow condition in the flow field at a certain moment. Because the design of the runner blade of the mixed-flow turbine adopts the omega=0 binary design theory, the drawn streamline is vertical to the equipotential line, and the streamline has the characteristic of smooth smoothness. For the concave-convex part of the streamline, the streamline can be smooth by adjusting the vertical position of the streamline and the equipotential line. A large number of practices prove that when the number of the streamline is more than 5, the precision improvement on the design of the runner blade of the mixed-flow turbine is very limited, and a large amount of time is consumed in the process of correcting the streamline; the number of streamlines is 5, including the crown streamlines and the annulus streamlines.
Before the axial flow line is inspected and corrected, the equipotential line set is drawn, so the description of the equipotential line set drawing process is given with reference to fig. 4. Since the equipotential line set generally includes three equipotential lines, distances from the equipotential lines on both sides to the equipotential line on the middle are equal, and the equipotential line set has a horn shape from the lower ring to the upper crown, intersection points of the equipotential lines on both sides and the streamline are determined by using a method of drawing circles, and the equipotential line set is drawn by using a method of sequentially connecting spline curves. The distances S of a set of equipotential lines on two sides are 13, 13.2, 13.4, 13.6 and 13.8, a radius circle drawing command is selected, and a circle is drawn by taking the intersection point of the equipotential lines and the streamline as the circle center and S/2 as the radius. After the circle is drawn, the intersection points of the circle and the streamline are sequentially connected by using a spline curve.
Since the primarily drawn streamlines may have large errors, inspection and correction of the drawn streamlines is required, and is based on the following theory. Since the axial flow is a potential flow, the flow between two adjacent flow surfaces is required to be equal, namely:
ΔQ＝const (1)
the flow rate between two adjacent flow surfaces is as follows:
ΔQ＝2πrΔbVm (2)
and:
Vm＝ΔΦ/ΔLm(3；
for the same set of adjacent equipotential lines, ΔΦ=const, Δq is equal, as can be seen from the combination of equations (1) (2) (3):
rΔb/ΔLm＝const (4)
wherein: Δb: the length of an equipotential center line between two adjacent axial surface streamline;
Δq: flow between adjacent two axial flow lines;
ΔΦ: potential differences of equipotential lines on two sides in the equipotential line group;
r: the distance between the midpoint of the equipotential center line and the central axis between the streamline of the two adjacent axial surfaces;
Δlm: the length of each section of intermediate shaft surface streamline.
Correcting the axial flow line by correcting the value of delta b, correcting the position of the axial flow line and the corresponding equipotential line group according to the correction value, thereby obtaining a second approximate axial flow network, and repeating the calculation until the axial flow network meets the requirement.
And thirdly, checking and correcting a streamline: the process of correcting the axial flow line will be described with reference to fig. 4 and 5. On the basis of completing the drawing of the equipotential line group, a break-in-point command in AutoCAD is used for conveniently measuring each parameter, and the streamline and the equipotential line are broken from each intersection point of the streamline and the equipotential line. For straight line segments or distances between two points, linear labels are used for measuring the length of the straight line segments or distances between two points, and for curve segments, list commands are input to check the length of the straight line segments or distances between two points. Sequentially measuring the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential centerline between two adjacent axial surface streamlines and the distance R between the intersection point of the streamlines and the equipotential centerline and the central axis, wherein the distance R between the midpoint of the equipotential centerline between the two adjacent axial surface streamlines and the central axis is the average value of R at the endpoint of the equipotential centerline. On the basis of completing measurement of original data, MATLAB is used for autonomous programming, an automatic correction process of drawn streamline is completed through for circulation, the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential center line between two adjacent axial surface streamlines and the distance r between the midpoint of the equipotential center line between two adjacent axial surface streamlines and the central axis are output reasonably, and the distance r is converted into an AutoCAD graph, so that errors caused in the process of repeatedly adjusting the streamline are reduced.
The basic content of autonomous programming with MATLAB is: and (5) finishing correction calculation of the axial surface streamline by using the for-loop body statement. According to the measured original data, the error value delta can be calculated, and whether the error value delta meets the requirement or not can be judged, if not, the error value delta is used for the adjacent twoThe length of the equipotential center line between the axial surface streamline is corrected by delta b, namely: Δb Correction =Δb× (1- δ), and the difference Δb×δ between the correction value and the original data is equally divided to the length Δb of the equipotential centerlines of the remaining segments, and the length Δlm of the intermediate axial surface streamline and the distance r between the midpoint of the equipotential centerlines between the adjacent two axial surface streamlines and the central axis can be calculated by the equation (5) and the equation (6) by the method of similar conversion.
Taking an enlarged diagram of the equipotential line set of the axial flow line drawing method C of fig. 5 as an example, the following description will be given of the formula (5) and the formula (6):
r correction ＝(R 2 -R 1 )×(1-δ)+R 1 (5)
ΔLm Correction ＝ΔLm×(1-δ) (6)
In the above formula: Δb Correction : referencing Δb after correction value adjustment of the calculated Δb;
R 1 ，R 2 : the distance from the intersection point of the equipotential center line and the axial surface streamline to the central axis;
criteria to be followed in correcting the axial flow line:
the length of the equipotential centerline is not changed. Namely: Δb 1 +Δb 2 +Δb 3 +Δb 4 ＝const。
The length delta b of the equipotential center line between the streamline of the two adjacent axial surfaces meets the relationship of decreasing from the upper crown to the lower ring. Namely: Δb 1 >Δb 2 >Δb 3 >Δb 4 。
The length delta Lm of each section of intermediate shaft surface streamline should satisfy the relationship of decreasing from the upper crown to the lower ring. Namely: Δlm 1 >ΔLm 2 >
ΔLm 3 >ΔLm 4 。
The examples are preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments, and any obvious modifications, substitutions or variations that can be made by one skilled in the art without departing from the spirit of the present invention are within the scope of the present invention.
Claims (7)
1. A method for drawing axial surface streamline of a mixed-flow water turbine is characterized by comprising the following steps: the method comprises the following steps:
1) Drawing equipotential lines in the flow channel: the first equipotential line is a drawn vertical line taking the point K of the intersection point of the lower circular arc and the inlet section of the flow channel as a starting point; drawing a second equipotential line in a straight-substitution curve mode, so that the equipotential line is perpendicular to the crown and the lower ring of the rotating wheel; and the equipotential lines should be smooth curves;
2) Drawing a streamline in a flow channel: firstly, dividing points of a runner outlet and a runner inlet, and drawing a streamline by using spline curve commands in AutoCAD on the basis of finishing the dividing points of the runner inlet and the runner outlet, wherein the drawn streamline is vertical to an equipotential line and has the characteristic of smooth flow direction;
3) Checking and correcting a streamline: firstly, determining intersection points of equipotential lines on two sides and streamline lines by using a method of drawing circles, drawing an equipotential line group by using a method of sequentially connecting spline curves, and correcting the drawn streamline lines and equipotential lines by using equal flow between two adjacent flow surfaces as a theoretical basis;
the drawing mode of the straight-substitution curve in the step 1) is as follows: the intersection point of the equipotential line and the lower ring is selected in the arc section, two points A and B which are optionally close to each other are connected at the lower ring position of the rotating wheel, the points A and B are marked as a straight line section AB, the points C are marked as points C, the points C are crossed to form a perpendicular line of the straight line section AB, the point C at the middle point of the straight line section AB is used as a starting point of a spline curve, spline curve fitting commands are used for drawing the equipotential line along the perpendicular line direction of the straight line section AB, after a plurality of fitting points are crossed, the drawn equipotential line is perpendicular to the crown of the rotating wheel, drawing of one equipotential line is completed, and the drawing of the rest equipotential lines is completed by repeating the process.
2. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 1, wherein the method comprises the following steps of: in the step 1), the selection range of the number of fitting points in the drawing process of each equipotential line is set to 5-7 points, including a starting point and an end point.
3. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 1, wherein the method comprises the following steps of: in the step 1), the number of the equipotential lines drawn is 6-9.
4. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 1, wherein the method comprises the following steps of: step 2) drawing is completed according to the following steps:
2.1 First, the separation point of the flow channel outlet and inlet: dividing the inlet of the runner into n parts by using a fixed number equal division command, and marking each node from the upper crown to the lower ring with the numbers 0, 1, 2, 3, … and n in sequence; the intersection point of the outlet straight line segment EF of the lower ring of the rotating wheel and the extension line of the central axis is marked as M points; selecting a radius circle drawing command, drawing a circle by taking an M point as a circle center, taking a straight line segment EM as a radius, marking an intersection point of the drawn circle and a central axis as an N point, drawing a perpendicular line of the central axis by passing through an E point of a lower ring end point of a runner outlet, marking an intersection point of the perpendicular line and the central axis as a D point, and marking the straight line segment between the E point and the D point as an outlet straight line segment ED; dividing the outlet straight line segment ED into n parts by using a fixed number equal division command, making a vertical line of the outlet straight line segment ED through each node, and making a vertical line corresponding to each node and an arc segmentEach intersection point from the central axis to the lower ring outlet section is marked by the number 1', 2', 3', …, (n-1)' in sequence, and the number marks at the intersection points are in one-to-one correspondence with the number marks at the inlet;
2.2 Drawing a streamline: drawing a streamline by using spline curve commands in AutoCAD, drawing a spline curve which is sequentially perpendicular to each equipotential line by taking 1 point in points separated by the inlet of the runner as the starting point of the streamline, taking the end point of the spline curve as 1 'point separated on the outlet of the runner corresponding to the selected starting point, and marking the intersection point of the spline curve and the straight line segment ED of the outlet as 1'; drawing the rest n-1 streamline according to the method, and marking the intersection points with the outlet straight line segment ED as 2', 3', …, (n-1) '; after the streamline drawing is completed, the arc section needs to be deletedAnd uses the trimming command to trim the streamline, mainly trimming the arc segment +.>And a streamline section 1 'cut between the outlet straight section ED 2' and 3', …, (n-1)' (n-1) ".
5. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 4, wherein the method comprises the following steps of: the number of streamlines drawn is 5, including the crown streamlines and the annulus streamlines.
6. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 4, wherein the method comprises the following steps of: the method for drawing the equipotential line group in the step 3) specifically comprises the following steps: initially defining a group of equipotential lines on two sides, wherein the distances S are 13, 13.2, 13.4, 13.6 and 13.8, selecting a radius circle drawing command, and drawing a circle by taking the intersection point of the equipotential lines and the streamline as the circle center and S/2 as the radius; after the circle is drawn, the intersection points of the circle and the streamline are sequentially connected by using a spline curve.
7. The method for drawing the axial flow line of the mixed-flow water turbine according to claim 6, wherein the method comprises the following steps of: the specific method for correcting the streamline and the equipotential lines in the step 3) is as follows:
on the basis of completing the drawing of the equipotential line group, breaking the streamline and the equipotential line from each intersection point of the streamline and the equipotential line by using a breaking-in-point command in AutoCAD; for the straight line segment or the distance between two points, linear labeling is adopted to measure the length of the straight line segment or the distance between two points, and for the curve segment, a list command is input to check the length of the curve segment; sequentially measuring the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential centerline between two adjacent axial surface streamlines and the distance R between the intersection point of the streamlines and the equipotential centerline and the central axis, wherein the distance R between the midpoint of the equipotential centerline between the two adjacent axial surface streamlines and the central axis is the average value of R at the endpoint of the equipotential centerline;
then MATLAB is used for autonomous programming, an automatic correction process of drawn streamlines is completed through for circulation, the length delta Lm of each section of intermediate axial surface streamline, the length delta b of an equipotential centerline between two adjacent axial surface streamlines and the distance r between the midpoint of the equipotential centerline between two adjacent axial surface streamlines and the central axis are reasonably output, and the intermediate axial surface streamlines are converted into an AutoCAD graph;
the basic content of autonomous programming with MATLAB is: finishing correction calculation of the axial surface streamline by using the for cyclic body statement; according to the measured original data, an error value delta can be calculated, whether the error value delta meets the requirement or not is judged, and if the error value delta does not meet the requirement, the length of an equipotential centerline between two adjacent axial surface streamlines is corrected by the error value delta, namely: Δb Correction =Δb× (1- δ), and the difference Δb×δ between the correction value and the original data is equally divided, to the length Δb of the equipotential centerlines of the remaining segments, where Δb: the length of an equipotential center line between two adjacent axial surface streamline;
and the length delta Lm of the intermediate axial surface streamline and the distance r between the midpoint of the equipotential center line between two adjacent axial surface streamlines and the center axis
Calculation can be performed through a similar conversion method through a formula (5) and a formula (6);
r correction ＝(R 2 -R 1 )×(1-δ)+R 1 (5)
ΔLm Correction ＝ΔLm×(1-δ) (6)
In the above formula: Δb Correction : referencing Δb after correction value adjustment of the calculated Δb;
R 1 ，R 2 : the distance from the intersection point of the equipotential center line and the axial surface streamline to the central axis;
criteria to be followed in correcting the axial flow line:
the length of the equipotential centerline is not changed, namely: Δb 1 +Δb 2 +Δb 3 +Δb 4 ＝const；
The length delta b of the equipotential center line between the streamline of the two adjacent axial surfaces meets the relationship of orderly decreasing from the upper crown to the lower ring, namely: Δb 1 >Δb 2 >Δb 3 >Δb 4 ；
The length delta Lm of each section of intermediate shaft surface streamline should satisfy the relationship from the upper crown to the lower ringThe secondary decreasing relationship, namely: Δlm 1 >ΔLm 2 >ΔLm 3 >ΔLm 4 。
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