Turbine cascade runner based on NURBS curved surface and blade modeling method

Abstract

The invention relates to the technical field of axial flow turbine aerodynamic configuration design, in particular to a turbine cascade runner and blade modeling method based on an NURBS curved surface, and the turbine cascade runner and blade modeling method comprises the steps that the geometrical shape of an original cascade runner is generated; extracting the runner section of the original cascade runner; representing the original cascade flow channel as a flow channel control parameter; and generating a target flow channel geometric shape. According to the invention, through rich and limited flow channel control parameters, the accuracy and flexibility of flow channel geometric control are improved, so that the previous design difficulty is reduced. By utilizing the advantages of the NURBS curved surface, the smooth continuity of the flow channel curved surface can be realized under the condition of not introducing additional constraint conditions; the design process is simplified, it is ensured that the aerodynamic performance can be effectively improved when the flow channel is optimized, and potential problems caused by complex constraints are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of axial flow turbine aerodynamic shape design, and in particular to a turbine blade cascade flow channel and blade modeling method based on NURBS surfaces. Background Art

[0002] Aerodynamic design is a key step in the design process of axial flow turbines. The design of the cascade flow channel ensures that the blades can effectively guide and control the airflow. The control of the airflow can be attributed to two aspects: on the one hand, the direction of the airflow is turned, and on the other hand, the expansion and acceleration or compression and deceleration of the airflow are realized. The turning of the airflow direction is achieved by the bending of the center line of the cascade flow channel, and the expansion or compression of the airflow is achieved by the change of the cross-sectional area of ​​the cascade flow channel. Through the precise design of the cascade flow channel, the dynamic characteristics of the airflow can be effectively optimized to ensure the smooth flow of the airflow inside the turbine. Reasonable flow channel design can not only reduce flow losses, but also improve the aerodynamic performance of the turbine, thereby meeting the needs of various engineering applications. Aerodynamic design also needs to consider the geometric shape of the blade, including the degree of curvature of the blade, thickness, and spacing between blades. In addition, the inlet and outlet velocities of the blades need to be accurately calculated to ensure that each blade can evenly distribute the mass flow of the inlet and outlet.

[0003] Traditional blade shaping is achieved through radial stacking of two-dimensional blades, while achieving blade shaping through the design of cascade flow channels is an innovative idea. On the one hand, this idea can start from the design source and more effectively integrate the aerodynamic relationship between turbine blades, end walls and flow channels, overcome the problem of deterioration of flow in the blade / end wall corner area in traditional design methods, achieve refined organization and regulation of flow in the corner area, and weaken or avoid separation in the corner area; on the other hand, it can control the transformation law of the cascade flow channel section to make the flow channel wall surfaces such as blades and end walls merge smoothly at a high order, avoid problems such as discontinuous curvature of blade surface brought about by traditional design methods, and effectively improve the internal flow of the turbine.

[0004] 3D surface modeling focuses on creating and editing surfaces in 3D space. This technique usually involves using mathematical models to define the shape of the surface, such as B-spline surfaces and non-uniform rational B-spline (NURBS) surfaces. These surfaces can effectively describe complex geometric shapes, such as the outer contours of cars, airplanes and other industrial products. A key feature of 3D surface modeling technology is its precise control of the local and overall geometric features of the surface, which enables designers to flexibly adjust the shape of the surface to meet specific design requirements. Through parametric modeling technology, designers can achieve precise control and optimization of 3D surfaces in computer-aided design (CAD) software. For example, free-form surfaces are modeled using NURBS technology, and the shape optimization and deformation of the surface are achieved through parameter adjustment, thereby improving the expressiveness and functionality of the design.

[0005] However, although the existing technologies involve geometric parametric modeling of the flow channel or its S3 surface, there are still certain limitations in the flexibility of shape control. These technologies usually involve multiple control variables, which makes the optimization process more complicated. In addition, additional constraints are often required to achieve smooth continuity of the surface, thereby improving aerodynamic performance and design feasibility. Therefore, how to simplify control variables and constraints while maintaining design flexibility has become a key issue that needs to be urgently solved in the current field of turbine flow channel design and blade modeling.

[0006] Therefore, it is necessary to provide a turbine cascade flow channel and blade modeling method based on NURBS surfaces to solve the above problems. Summary of the invention

[0007] The present invention provides a turbine blade cascade flow channel and blade modeling method based on NURBS surfaces to solve the problem of how to simplify control variables and constraints while maintaining design flexibility.

[0008] A turbine blade cascade flow channel modeling method based on NURBS surface of the present invention adopts the following technical solution, including: Generate the geometric shape of the original blade cascade flow channel according to the parameter information of the original blade cascade and the coordinates of the two-dimensional blade profile discrete points; Through the third kind of relative flow surface theory, the flow section of the original blade flow channel is extracted according to the given flow section number, wherein the flow section includes: the leading edge section, each section in the middle of the flow channel and the trailing edge section; The original blade cascade flow channel is fitted by using a double third-order NURBS surface, and the original blade cascade flow channel surface is characterized as flow channel control parameters, which include: flow channel cross-sectional shape control parameters, flow channel centerline shape control parameters and leading edge shape control parameters; The shape and direction of the original cascade flow channel surface are modified using the flow channel control parameters to obtain a modified target flow channel geometry.

[0009] Preferably, the parameter information of the original blade cascade includes: blade height, blade pitch, chord length, axial chord length, geometric inlet angle and geometric outlet angle.

[0010] Preferably, the steps of extracting the flow channel cross section according to the given flow channel cross section number by the third kind of relative flow surface theory are: The plane enclosed by the leading edge lines of two adjacent blades and the end wall lines between the two adjacent blades is taken as the leading edge section of the flow channel; The plane enclosed by the trailing edge lines of two adjacent blades and the end wall line between the two adjacent blades is taken as the trailing edge section of the flow channel; According to the third kind of relative flow surface theory, the interpolation calculation of the third kind of relative flow surface is carried out between the leading edge section and the trailing edge section to obtain the sections in the middle of the flow channel.

[0011] Preferably, the double third-order NURBS fits the original blade cascade flow channel so that the original blade cascade flow channel surface u Xianghe v The directions have second-order continuity, and each group u The control polygon is composed of a closed control polygon composed of control points in the direction of the blade. The control polygon is used to control the shape of each section of the blade flow channel. The center line of the flow channel is used as the "guide line" to control the flow channel surface in v Directional position and size.

[0012] Preferably, according to the cross-sectional shape of the original cascade flow channel, each group of double third-order NURBS surfaces is obtained. u The control points in the direction form a closed control polygon as a control rectangle; the four vertices of the control rectangle are used as the first target control points, and the point between the midpoint of each side of the control rectangle and the adjacent vertex is used as the second target control point.

[0013] Preferably, the flow channel cross-sectional shape control parameters, the flow channel centerline shape control parameters and the leading edge shape control parameters all include: dimensionless parameters for changing the position of the second target control point and a weight factor of the first target control point, the weight factor of the first target control point being used to adjust the chamfer of each cross-sectional shape of the blade flow channel; the dimensionless parameters being used to adjust the position of the second target control point.

[0014] Preferably, a cubic seven-point NURBS curve is used to fit the center line of the flow channel.

[0015] Preferably, the step of obtaining the modified target flow channel geometry is as follows: by modifying the weight factor of the first target control point and the dimensionless parameter of the second target control point, the leading edge cross-section of the original cascade flow channel is adjusted to the leading edge cross-sectional shape of the target flow channel, the trailing edge cross-sectional shape of the original cascade flow channel is adjusted to the trailing edge cross-sectional shape of the target flow channel, and the middle cross-sections of the original cascade flow channel are adjusted to smoothly transition between the leading edge cross-section of the target flow channel and the trailing edge cross-section of the target flow channel.

[0016] Preferably, the leading edge cross section of the target flow channel geometry is elliptical, and the trailing edge cross section is rectangular.

[0017] A turbine blade modeling method based on NURBS surface comprises: arraying the flow channel geometry of the present invention along the end wall to form a flow channel array, physically filling the area enclosed between adjacent flow channels in the flow channel array, that is, filling the leading edge and the trailing edge to obtain a complete blade geometry.

[0018] The beneficial effects of the present invention are: First, the parameter information of the original blade cascade and the coordinates of the two-dimensional blade discrete points are used to obtain the precise geometry of the original blade cascade flow channel. The original blade cascade flow channel is fitted using the NURBS surface. After parameterization, the geometry of the original blade cascade flow channel can be characterized as three types of flow channel control parameters (flow channel cross-sectional shape control parameters, flow channel centerline shape control parameters and leading edge shape control parameters), so that the inlet cross-section of the fitted target flow channel is elliptical and the outlet cross-section is rectangular, in order to effectively control the secondary flow in the end area of ​​the turbine blade cascade. In addition, compared with the prior art, the present invention improves the accuracy and flexibility of the flow channel geometry control through rich and limited flow channel control parameters, thereby reducing the previous design difficulty. By taking advantage of the NURBS surface, the smooth continuity of the flow channel surface can be achieved without introducing additional constraints. This feature not only simplifies the design process, but also ensures that when optimizing the flow channel geometry, the aerodynamic performance can be effectively improved, avoiding potential problems caused by complex constraints. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a flow chart of a turbine blade cascade flow channel modeling method based on NURBS surface of the present invention; Figure 2 A two-dimensional blade profile schematic diagram of a certain type of turbine blade cascade used in an example of the present invention; Figure 3 Schematic diagram of a double third-order NURBS surface in an example of the present invention; Figure 4 A schematic diagram of the shape change rule of the cross section of the NURBS surface in an example of the present invention; Figure 5 is the NURBS surface in the example of the present invention u Schematic diagram of the control polygon; Figure 6 This is a meridian comparison diagram of the original blade and the FLOvane blade in the example of the present invention; Figure 7 A comparison diagram of the leading edge lines of the original blade and the blade of the new configuration in the example of the present invention; Figure 8 is a schematic diagram of the centerline shape of the blade; Fig. 9 The central curve (NURBS surface) obtained by using three-dimensional seven-point NURBS fitting in the example of the present invention vSchematic diagram of the "guide line"); Fig.10 is a geometric structure diagram of the original blade grid in the example of the present invention; Fig.11 A geometric structure diagram of a NURBS surface cascade obtained by the method of the present invention; Fig.12 Generate a blade geometry diagram through a flow channel in an example of the present invention; Fig.13 The geometric structure diagram of the blade constructed by NURBS surface in the example of the present invention; Fig.14 Schematic diagram of the total pressure loss distribution of the outlet cross section of the original blade cascade flow channel in the example of the present invention; Fig.15 The figure is a schematic diagram of the total pressure loss distribution of the outlet cross section of the target flow channel obtained by the method of the present invention. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] An embodiment of a modeling method for a turbine blade cascade flow channel based on a NURBS surface of the present invention is as follows: Figure 1 As shown, including: S1, generating the geometry of the original cascade flow channel; Specifically, the geometric shape of the original blade cascade flow channel is generated according to the parameter information of the original blade cascade and the coordinates of the two-dimensional blade profile discrete points.

[0023] In an exemplary embodiment, the extracted coordinates of the two-dimensional blade profile discrete points of the original blade cascade are ( x i , y i ), the parameter information of the original cascade is known, that is, Figure 2 As shown, the original blade parameter information includes blade height h , Pitch d , Chord Length C , axial chord length C x , geometric inlet angle α1 and geometric outlet angle α2, where the parameter information of the original blade cascade is shown in Table 1.

[0024] Table 1

[0025] S2, extracting the flow channel section of the original cascade flow channel; Specifically, the flow channel section of the original blade flow channel is extracted according to the given number of flow channel sections through the third relative flow surface theory, wherein the flow channel section includes: a leading edge section, each section in the middle of the flow channel and a trailing edge section.

[0026] In an exemplary embodiment, the steps of extracting the flow channel section of the original blade flow channel according to a given number of flow channel sections are as follows: taking the plane enclosed by the leading edge line of two adjacent blades and the end wall line between the two adjacent blades as the leading edge section of the flow channel; taking the plane enclosed by the trailing edge line of two adjacent blades and the end wall line between the two adjacent blades as the trailing edge section of the flow channel; and according to the third relative flow surface theory, performing interpolation calculation of the third relative flow surface (S3 flow surface) between the leading edge section and the trailing edge section to obtain each section in the middle of the flow channel.

[0027] S3, characterizing the original cascade flow path as flow path control parameters; Specifically, a double third-order NURBS surface is used to fit the original blade cascade flow channel surface, and the original blade cascade flow channel surface is characterized as flow channel control parameters. The flow channel control parameters include: flow channel cross-sectional shape control parameters, flow channel centerline shape control parameters and leading edge shape control parameters.

[0028] That is, the double third-order NURBS fits the original blade channel so that the original blade channel surface u Xianghe v The directions have second-order continuity, and each group u The control polygon is composed of a closed control polygon composed of control points in the direction of the blade. The control polygon is used to control the shape of each section of the blade flow channel. The center line of the flow channel is used as the "guide line" to control the flow channel surface in v The orientation and size in the direction; according to the cross-sectional shape of the original blade flow channel, each group of u-direction control points of the double third-order NURBS surface is obtained to form a closed control polygon as a control rectangle; the four vertices of the control rectangle are used as the first target control points, and the point between the midpoint of each side of the control rectangle and the adjacent vertex is used as the second target control point.

[0029] In an exemplary embodiment, the flow channel cross-sectional shape control parameters, the flow channel centerline shape control parameters and the leading edge shape control parameters all include: a dimensionless parameter for changing the position of the second target control point and a weight factor of the first target control point, the weight factor of the first target control point is used to adjust the chamfer of each cross-sectional shape of the cascade flow channel; the dimensionless parameter is used to adjust the position of the second target control point. Figure 5 As shown, Figure 5 The first target control point is , , , ; By adjusting the weight factor of the first target control point, the chamfer of the flow channel cross-section shape (rounded rectangle) is adjusted. Adjusting the weight factor of the first target control point can directly affect the shape of the NURBS surface, making the geometric features of the flow channel more flexible and in line with the design requirements; Figure 5 The second target control point is , , , , , , , .

[0030] It should be noted that the definition of NURBS surface is extended from the definition of NURBS curve. The difference is that NURBS curve is defined by a feature polygon, while NURBS surface is defined by a group of feature polygons. The control points of the group of feature polygons constitute the control grid of the NURBS surface. The order has n A NURBS curve with +1 control point is defined as:

[0031] In the formula, is the position vector on the curve; is the weight factor of the control point; is the control point; Defined at the node vector The irrational B-spline basis function on can be obtained by the De-Boor recursive formula as follows:

[0032]

[0033] In the formula, is the node vector The A vector of nodes.

[0034] In an exemplary embodiment, a Xiang Wei Step, Xiang Wei The control point grid is ( n +1) ×( m +1) is defined as follows:

[0035] In the formula, The coordinates within the NURBS control grid are control points; is the weight factor corresponding to the control point, and is defined at the corresponding node vector , node vector Irrational B-spline basis functions on , where (u,v)∈[0,1] × [0,1], the knot vector and The value of is:

[0036]

[0037] In the entire cascade channel, the flow channel geometry of the blade end wall integrated configuration needs to have a smooth transition from the inlet section to the outlet section. k The NURBS curve has a C k-1 According to the properties of NURBS surface, this embodiment also adopts u Xianghe v The shape of the flow channel is characterized by a bi-triple-order NURBS surface. Figure 3 A schematic diagram of a third-order NURBS surface is given.

[0038] The turbine blade cascade is redesigned using the blade end wall integrated modeling method. First of all, it is necessary to consider the shape changes of each cross-section of the turbine blade cascade flow channel. Compared with the original blade cascade rectangular cross-sectional flow channel, the blade cascade flow channel after the blade end wall integrated design needs to ensure a smooth transition between the blade and the end wall, that is, the blade cascade flow channel cross-section is a rounded rectangle or elliptical.

[0039] In the definition of NURBS, the weight factor is equivalent to the "gravity" of the control point. The larger its value, the closer the curve is to the control point. Therefore, the shape of the NURBS surface section can be changed by adjusting the weight factor of each control point. Figure 4 A schematic diagram of the change in the cross-sectional shape of the NURBS surface when the weight factor is changed while the control points remain unchanged is given. A set of control points of a NURBS surface, whose spatial positions are fixed, are connected to form a control polygon. Since NURBS has the characteristic of convex hull, the cross-sectional curve of the NURBS surface is always inside the control polygon. , , and , the weights of these four control points must be 1, and the weights of other control points ( , , , ) as the first target control point, the weight factor of the first target control point Can be adjusted according to needs.

[0040] In order to further improve the freedom of NURBS surfaces, Figure 4 Section control points in On the basis of adding 8 second target control points, that is, in the adjacent Add a movable second target control point between , the weight factors corresponding to these second target control points are set to 1, forming a new cross-sectional shape control polygon, such as Figure 5 As shown, the original quasi-elliptical cross-sectional shape (L0) design can be changed to a quasi-elliptical design combined with straight line segments (L1).

[0041] according to Figure 5 , which can characterize the NURBS surface section shape control parameters. Specifically, the first target control point , , and The weight factor is , the second target control point The position of can be expressed as a dimensionless parameter, defined as , The expression is:

[0042] In the formula, The second target control point To the first target control point The modulus distance; The first target control point To the first target control point The modulus distance.

[0043] According to research, the flow of air in the turbine blade flow channel needs to realize the deflection of the airflow direction and the expansion and acceleration of the airflow. The cross-sectional shape of the turbine blade flow channel affects the flow capacity of the airflow. The deflection of the airflow direction is achieved by the bending of the airflow channel. Therefore, the shape of the entire flow channel can be regarded as the accumulation of each cross section along the S3 direction. Based on the above ideas, the NURBS surface The control points of each section correspond to the S3 flow surface. By matching the direction with the flow direction, a flow channel with an integrated configuration of the blade end wall can be obtained.

[0044] In an exemplary embodiment, the leading and trailing edge of the new integrated blade end wall configuration is still constructed using a cubic NURBS surface. Figure 6From the FLOvane design shown, we can see that in conventional blade designs, the leading and trailing edge lines and the upper and lower end wall lines have obvious turning angles, while the blade design with a new configuration of integrated blade end wall achieves a smooth transition between the three, making the turning angle smoother. When the airflow flows through a rounded corner, compared with flowing through a right angle, the gradual change in velocity and smooth change in flow direction when the airflow flows through a circular cross-section can effectively reduce airflow resistance and reduce losses that affect fluid dynamics performance. Therefore, the design of the leading and trailing edge cross-sectional shape of the new configuration of integrated blade end wall draws on the design method of the FLOvane leading and trailing edge, and the leading and trailing edge cross-sectional shape is still regulated by the weight factor and dimensionless parameters of the control point. Figure 7 Schematic diagram of the leading and trailing edge profiles of the turbine cascade blade end wall. Figure 7 The leading edge line of the new configuration in corresponds to the control point of a section of the NURBS surface. is the control point, , , and is the movable first target control point, and its spatial position is determined by the dimensionless parameter Decide, and It is consistent with the inlet angle direction of the cascade. The expression of dimensionless parameters is as follows:

[0045] Wherein, the subscript le represents the leading edge.

[0046] By adjusting the control points and weight factors near the boundary, a smooth connection between the leading edge surface / trailing edge surface and the blade body surface can be achieved.

[0047] After determining the geometric shape of the entire cascade channel, it is necessary to fit the line connecting the centroids of each S3 flow surface. The determination of the centerline function constraint condition is based on the inlet airflow angle of the cascade channel. , Cascade channel outlet airflow angle , the leading edge point (0,0) and the point of maximum deflection defined and axial chord length It is determined that under the condition that these parameters are known, the shape of the center line cannot be accurately expressed, and additional control parameters need to be added. Therefore, in this embodiment, a cubic seven-point NURBS curve is used to characterize the shape of the center line, such as Figure 8 and Fig. 9 As shown, Figure 8 is a schematic diagram of the center line shape. Fig. 9 Schematic diagram of a cubic seven-point NURBS fitting curve.

[0048] Depend on Fig. 9 It can be seen that M 0- M6 is the control point of the NURBS curve, M 2- M 4 is in a straight line with x Axis parallel. M 0 and M 6 is the centroid of the inlet and outlet sections of the cascade flow channel, M 3 is the maximum deflection point of the center line In order to meet this requirement, it is necessary to introduce the tangent vector conditions of the first and last control points of the NURBS curve. and The first and last tangents x The angle of intersection of the axis direction, M 1 and M 5 is in the direction of the tangent vector at the head and the end. The accurate fitting of the centerline shape can be achieved by only determining the positions of the remaining control points, so the centerline of the cascade flow channel is accurately expressed by adding 4 additional dimensionless parameters, namely the control points M 1. M 2. M 4 and M 5. You can use dimensionless parameters The essence of determining the dimensionless parameters of the centerline control points is the distance between the control points and the axial chord length. The ratio of is normalized so that the value range of dimensionless parameters is 0-1. The expressions of the four dimensionless parameters are as follows:

[0049] In summary, the geometric control parameters of the cascade flow channel can be summarized into three categories: (1) leading edge shape control parameters; (2) flow channel cross-sectional shape control parameters; (3) flow channel centerline shape control parameters. It should be noted that the control process of the flow channel shape by the above modeling parameters is realized through a self-compiled program.

[0050] S4, generating a target flow channel geometry; Specifically, the shape and direction of the original blade cascade flow channel surface are modified using the flow channel control parameters to obtain a modified target flow channel geometry, wherein the original blade cascade flow channel surface is as follows: Fig.10 As shown in Fig.11As shown, the leading edge section of the target flow channel geometry is elliptical, and the trailing edge section is rectangular; according to the expressions of the various flow channel control parameters in step S3, the flow channel control parameters are modified to achieve the modification of the shape and direction of the flow channel curved surface, thereby obtaining the modified target flow channel geometry. That is, by modifying the weight factor of the first target control point and the dimensionless parameter of the second target control point, the leading edge section of the original blade flow channel is adjusted to the leading edge section shape of the target flow channel, the trailing edge section of the original blade flow channel is adjusted to the trailing edge section shape of the target flow channel, and the middle sections of the original blade flow channel are adjusted to smoothly transition between the leading edge section of the target flow channel and the trailing edge section of the target flow channel.

[0051] A turbine blade modeling method based on NURBS surface includes: forming a flow channel array by arraying the flow channel geometry along the end wall, physically filling the area enclosed by adjacent flow channels in the flow channel array, and filling the leading edge and the trailing edge to obtain the following Fig.12 The complete blade geometry is shown; that is, half of the cascade flow passage is the suction surface SS of the blade body, and the other half is the pressure surface PS of the blade body. Fig.13 A schematic diagram of the blade geometry generated by the flow channel is given.

[0052] Fig.14 is a schematic diagram of the total pressure loss distribution at the outlet section of the original cascade flow channel. Fig.15 is a schematic diagram of the total pressure loss distribution of the outlet cross section of the target flow channel in this embodiment, from Fig.14 and Fig.15 It can be seen that the cross-sectional area of ​​the turbine blade cascade flow channel based on the NURBS surface of this embodiment is consistent with the original blade cascade flow channel to maintain the same flow capacity and effectively reduce the secondary flow loss.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A turbine blade cascade flow channel modeling method based on NURBS surface, characterized in that: include: Generate the geometric shape of the original blade cascade flow channel according to the parameter information of the original blade cascade and the coordinates of the two-dimensional blade profile discrete points; Through the third kind of relative flow surface theory, the flow section of the original blade flow channel is extracted according to the given flow section number, wherein the flow section includes: the leading edge section, each section in the middle of the flow channel and the trailing edge section; The original blade cascade flow channel is fitted by using a double third-order NURBS surface, and the original blade cascade flow channel surface is characterized as flow channel control parameters, which include: flow channel cross-sectional shape control parameters, flow channel centerline shape control parameters and leading edge shape control parameters; The shape and direction of the original cascade flow channel surface are modified using the flow channel control parameters to obtain a modified target flow channel geometry.

2. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 1, characterized in that: The parameter information of the original blade row includes: blade height, blade pitch, chord length, axial chord length, geometric inlet angle and geometric outlet angle.

3. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 1, characterized in that: Through the third kind of relative flow surface theory, the steps of extracting the flow channel section according to the given flow channel section number are: The plane enclosed by the leading edge lines of two adjacent blades and the end wall lines between the two adjacent blades is taken as the leading edge section of the flow channel; The plane enclosed by the trailing edge lines of two adjacent blades and the end wall line between the two adjacent blades is taken as the trailing edge section of the flow channel; According to the third kind of relative flow surface theory, the interpolation calculation of the third kind of relative flow surface is carried out between the leading edge section and the trailing edge section to obtain the sections in the middle of the flow channel.

4. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 1, characterized in that: The double third-order NURBS fit of the original blade flow channel makes the original blade flow channel surface u Xianghe v The directions have second-order continuity, and each group u The control polygon is composed of a closed control polygon composed of control points in the direction of the blade. The control polygon is used to control the shape of each section of the blade flow channel. The center line of the flow channel is used as the "guide line" to control the flow channel surface in v Directional position and size.

5. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 1, characterized in that: According to the cross-sectional shape of the original blade flow channel, each group of double third-order NURBS surfaces is obtained. u The control points in the direction form a closed control polygon as a control rectangle; the four vertices of the control rectangle are used as the first target control points, and the point between the midpoint of each side of the control rectangle and the adjacent vertex is used as the second target control point.

6. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 5, characterized in that: The flow channel cross-sectional shape control parameters, the flow channel centerline shape control parameters and the leading edge shape control parameters all include: dimensionless parameters for changing the position of the second target control point and the weight factor of the first target control point, the weight factor of the first target control point is used to adjust the chamfer of each cross-sectional shape of the blade flow channel; the dimensionless parameters are used to adjust the position of the second target control point.

7. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 6, characterized in that: A cubic seven-point NURBS curve is used to fit the center line of the flow channel.

8. The method for modeling turbine cascade flow passage and blades based on NURBS surface according to claim 1, characterized in that: The steps of obtaining the modified target flow channel geometry are as follows: by modifying the weight factor of the first target control point and the dimensionless parameter of the second target control point, the leading edge section of the original cascade flow channel is adjusted to the leading edge section shape of the target flow channel, the trailing edge section of the original cascade flow channel is adjusted to the trailing edge section shape of the target flow channel, and each middle section of the original cascade flow channel is adjusted to smoothly transition between the leading edge section of the target flow channel and the trailing edge section of the target flow channel.

9. The method for modeling a turbine blade cascade flow channel based on a NURBS surface according to claim 1, characterized in that: The target flow channel geometry has an elliptical leading edge section and a rectangular trailing edge section.

10. A turbine blade modeling method based on NURBS surface, characterized in that: include: The flow channel geometry described in any one of claims 1 to 9 is arrayed along the end wall to form a flow channel array, and the areas enclosed between adjacent flow channels in the flow channel array are physically completed, that is, the leading edge and the trailing edge are completed to obtain a complete blade geometry.

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