A method and system for extracting lift and drag coefficients of a rotor blade section

Abstract

The present invention provides a method and system for extracting lift and drag coefficients of a rotor blade section, belonging to the field of helicopter aerodynamics. The method for extracting lift and drag coefficients includes: for the nth iteration, determining the nth blade micro-segment according to the section position and the width of the nth micro-segment, and classifying each grid cell according to the position relationship between the center coordinates of each grid cell and the position of the nth blade micro-segment; determining the pressure difference force according to the category of the grid cell, the cell area and the absolute pressure; determining the lift and drag coefficients on the nth blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vector; when n≠N, increasing the width of the nth micro-segment by a set increment for the (n + 1)th iteration until n = N or the width of the (n + 1)th micro-segment is greater than the set threshold, and determining the optimal lift coefficient and the optimal drag coefficient according to the lift and drag coefficients on the 1st to Nth blade micro-segments. The error existing at the boundary position of the blade micro-segment is reduced, and the calculation accuracy of the lift and drag coefficients is improved.

Description

Technical Field

[0001] The present invention relates to the field of helicopter aerodynamics, and particularly to a method and system for extracting lift and drag coefficients of a rotor profile. Background Art

[0002] Currently, CFD (Computational Fluid Dynamics) technology has been widely applied in the aerospace field. A complete CFD calculation generally includes three parts: preprocessing, solver, and postprocessing. Each module has different functions: First, preprocessing is some preparatory work done before the calculation, such as modeling the geometric model, constructing the computational domain based on the model and dividing the grid, checking the grid quality, etc., to ensure that subsequent calculation work will not encounter errors, divergence, etc. Second, the formal calculation work is carried out based on the solver. In this technical field, the solver generally solves the Navier-Stokes equation (abbreviated as the N-S equation) to obtain the flow field information in the entire computational domain, such as density, pressure, velocity, etc. Third, postprocessing is the visualization processing of the velocity field, temperature field, pressure field, and other parameters.

[0003] In the analysis of helicopter aerodynamics, the lift and drag coefficients of the rotor profile are very crucial quantities, which can effectively evaluate the aerodynamic performance of the rotor. Therefore, it is very necessary to accurately calculate the profile lift and drag coefficients. However, in the rotor CFD calculation, the blade surface has been discretized into many grid cells. To calculate the lift and drag coefficients of the profile, a micro-segment needs to be selected for investigation. This micro-segment may include complete grid cells or incomplete grid cells. Currently, it is considered that the error caused by selecting the micro-segment width is relatively large, so the calculation result will have unpredictable errors. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for extracting lift and drag coefficients of a rotor profile, which can eliminate the error caused by artificially selecting the micro-segment width, correct the grid cells at the micro-segment boundary, and improve the calculation accuracy of the lift and drag coefficients.

[0005] To achieve the above purpose, the present invention provides the following solution:

[0006] A method for extracting lift and drag coefficients of a rotor profile, comprising:

[0007] Obtaining the central coordinates, cell area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor; the grid model includes a plurality of grid cells;

[0008] Determining the profile position and initial micro-segment width in the grid model;

[0009] For the nth iteration, determine the nth blade micro-segment in the grid model according to the profile position and the width of the nth micro-segment, where 1 ≤ n ≤ N and N is the iteration number threshold; the width of the first micro-segment is the initial micro-segment width;

[0010] Classify each grid cell according to the position relationship between the center coordinates of each grid cell and the position of the nth blade micro-segment;

[0011] For any grid cell, determine the pressure difference force of the grid cell according to the category, cell area and absolute pressure of the grid cell;

[0012] Determine the lift and drag of the nth blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell;

[0013] Determine the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift and drag of the nth blade micro-segment;

[0014] Judge whether n is equal to N. If so, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients from the first blade micro-segment to the Nth blade micro-segment. Otherwise, increase the width of the nth micro-segment by a set increment to obtain the width of the (n + 1)th micro-segment;

[0015] Judge whether the width of the (n + 1)th micro-segment is greater than or equal to the set threshold. If so, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients from the first blade micro-segment to the nth blade micro-segment. Otherwise, perform the (n + 1)th iteration.

[0016] Optionally, the categories of grid cells include internal grids, first cross grids, second cross grids and external grids;

[0017] The classifying each grid cell according to the position relationship between the center coordinates of each grid cell and the position of the nth blade micro-segment specifically includes:

[0018] For any grid cell, if the center coordinates of the grid cell are located inside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, the category of the grid cell is an internal grid;

[0019] If the center coordinates of the grid cell are located inside the blade micro-segment and part of the area of the grid cell is outside the blade micro-segment, the category of the grid cell is a first cross grid;

[0020] If the central coordinate of the grid cell is located outside the blade micro-segment and a part of the area of the grid cell is inside the blade micro-segment, the category of the grid cell is the second cross grid;

[0021] If the central coordinate of the grid cell is located outside the blade micro-segment and there is no intersection between the grid cell and the boundary of the blade micro-segment, the category of the grid cell is the external grid.

[0022] Optionally, the category of each grid cell is the internal grid, the first cross grid, the second cross grid or the external grid;

[0023] Use the following formula to determine the pressure difference force of the k-th grid cell:

[0024]

[0025] where F k is the pressure difference force of the k-th grid cell, p k is the absolute pressure of the k-th grid cell, A k is the cell area of the k-th grid cell, b k is the distance between the central coordinate of the k-th grid cell and the boundary of the blade micro-segment, i = 1 indicates that the category of the k-th grid cell is the internal grid, i = 2 indicates that the category of the k-th grid cell is the first cross grid, i = 3 indicates that the category of the k-th grid cell is the second cross grid, and i = 4 indicates that the category of the k-th grid cell is the external grid.

[0026] Optionally, use the following formula to determine the lift and drag of the n-th blade micro-segment:

[0027]

[0028] where dL n is the lift of the n-th blade micro-segment, dD n is the drag of the n-th blade micro-segment, k max is the number of grid cells in the n-th blade micro-segment, F k is the pressure difference force of the k-th grid cell in the n-th blade micro-segment, is the unit surface normal vector in the x direction of the k-th grid cell in the n-th blade micro-segment, is the unit surface normal vector in the z direction of the k-th grid cell in the n-th blade micro-segment.

[0029] Optionally, use the following formula to determine the lift coefficient and drag coefficient on the n-th blade micro-segment:

[0030]

[0031] where, is the lift coefficient on the nth blade micro-segment, is the drag coefficient on the nth blade micro-segment, dL n is the lift of the nth blade micro-segment, dD n is the drag of the nth blade micro-segment, ρ is the air density, chord is the chord length, width is the micro-segment width, V ∞ is the far-field oncoming flow velocity.

[0032] Optionally, determining the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and the drag coefficient on the 1st blade micro-segment to the lift coefficient and the drag coefficient on the Nth blade micro-segment specifically includes:

[0033] Determining the mth error value according to the lift coefficient and the drag coefficient on the mth blade micro-segment, and the lift coefficient and the drag coefficient on the (m + 1)th blade micro-segment, so as to obtain N - 1 error values; 1 ≤ m ≤ N - 1;

[0034] Determining the minimum error value from the N - 1 error values;

[0035] Determining the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and the drag coefficient on the two blade micro-segments corresponding to the minimum error value.

[0036] Optionally, the following formula is used to determine the mth error value:

[0037]

[0038] where RMS m is the mth error value, is the lift coefficient on the mth blade micro-segment, is the drag coefficient on the mth blade micro-segment

[0039] Optionally, the following formula is used to determine the optimal lift coefficient and the optimal drag coefficient:

[0040]

[0041] where C l is the optimal lift coefficient, C d is the optimal drag coefficient, is the lift coefficient on the mth blade micro-segment, is the drag coefficient on the mth blade micro-segment, and m is the serial number corresponding to the minimum error value.

[0042] To achieve the above object, the present invention also provides the following solution:

[0043] A lift and drag coefficient extraction system for a rotor profile, comprising:

[0044] A data acquisition unit for acquiring the central coordinates, unit area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor blade; the grid model includes a plurality of grid cells;

[0045] A position width determination unit, connected to the data acquisition unit, for determining the section position and the initial micro-segment width in the grid model;

[0046] A blade micro-segment determination unit, connected to the position width determination unit, for determining the nth blade micro-segment in the grid model according to the section position and the nth micro-segment width for the nth iteration, where 1 ≤ n ≤ N and N is the iteration number threshold; the width of the first micro-segment is the initial micro-segment width;

[0047] A classification unit, connected to the blade micro-segment determination unit and the data acquisition unit, for classifying each grid cell according to the positional relationship between the central coordinates of each grid cell and the nth blade micro-segment;

[0048] A pressure difference force determination unit, connected to the classification unit and the data acquisition unit, for determining the pressure difference force of any grid cell according to the category, unit area, and absolute pressure of the grid cell;

[0049] A lift and drag determination unit, connected to the pressure difference force determination unit and the data acquisition unit, for determining the lift and drag of the nth blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell;

[0050] A coefficient determination unit, connected to the lift and drag determination unit, for determining the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift of the nth blade micro-segment and the drag of the nth blade micro-segment;

[0051] A first judgment unit, connected to the coefficient determination unit, for judging whether n is equal to N;

[0052] A first optimal coefficient determination unit, connected to the first judgment unit and the coefficient determination unit, for determining the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients from the first blade micro-segment to the Nth blade micro-segment when n is equal to N;

[0053] A width increase unit, connected to the first judgment unit, for increasing the nth micro-segment width by a set increment to obtain the (n + 1)th micro-segment width when n is less than N;

[0054] A second judgment unit, connected to the width increase unit, for judging whether the (n + 1)th micro-segment width is greater than or equal to a set threshold;

[0055] The second optimal coefficient determination unit, connected to the second determination unit and the coefficient determination unit, is configured to determine the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and the drag coefficient on the first blade micro-segment to the lift coefficient and the drag coefficient on the nth blade micro-segment when the width of the (n + 1)th micro-segment is greater than or equal to the set threshold;

[0056] The iteration unit, connected to the second determination unit and the blade micro-segment determination unit, is configured to perform the (n + 1)th iteration when the width of the (n + 1)th micro-segment is less than the set threshold.

[0057] Optionally, the categories of the grid cells include internal grids, first cross grids, second cross grids, and external grids;

[0058] The classification unit includes:

[0059] The internal grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the central coordinate of the grid cell is located inside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an internal grid;

[0060] The first cross grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the central coordinate of the grid cell is located inside the blade micro-segment and a part of the area of the grid cell is outside the blade micro-segment, then the category of the grid cell is a first cross grid;

[0061] The second cross grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the central coordinate of the grid cell is located outside the blade micro-segment and a part of the area of the grid cell is inside the blade micro-segment, then the category of the grid cell is a second cross grid;

[0062] The external grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the central coordinate of the grid cell is located outside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an external grid.

[0063] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention: classify the grid cells according to the positional relationship between the central coordinates of the grid cells and the positions of the blade micro-segments, determine the pressure difference force of the grid cells according to the categories, cell areas and absolute pressures of the grid cells, determine the lift and drag of the nth blade micro-segment according to the pressure difference forces of the grid cells and the unit surface normal vectors of the grid cells; determine the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift and drag of the nth blade micro-segment; if n is equal to N, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients on the 1st to Nth blade micro-segments, otherwise increase the micro-segment width by a set increment to obtain the width of the (n + 1)th micro-segment, if the width of the (n + 1)th micro-segment is greater than or equal to the set threshold, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients on the 1st blade micro-segment to the lift coefficients and drag coefficients on the nth blade micro-segment, otherwise perform the next iteration, increase the micro-segment width by a set increment through iteration, correct the grid cells on the boundary of the blade micro-segment, reduce the error existing at the boundary position, and improve the calculation accuracy of the lift and drag coefficients. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0065] Figure 1 It is a flowchart of the method for extracting the lift and drag coefficients of the rotor profile of the present invention;

[0066] Figure 2 It is an overall flow schematic diagram of the method for extracting the lift and drag coefficients of the rotor profile of the present invention;

[0067] Figure 3 It is a schematic diagram of the grid cell;

[0068] Figure 4 It is a schematic diagram of the module structure of the system for extracting the lift and drag coefficients of the rotor profile of the present invention.

[0069] Symbol Explanation:

[0070] Data acquisition unit - 1, position and width determination unit - 2, blade micro-segment determination unit - 3, classification unit - 4, pressure difference force determination unit - 5, lift and drag determination unit - 6, coefficient determination unit - 7, first judgment unit - 8, first optimal coefficient determination unit - 9, width increase unit - 10, second judgment unit - 11, second optimal coefficient determination unit - 12, iteration unit - 13. Detailed implementation manners

[0071] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0072] The purpose of the present invention is to provide a method and system for extracting lift and drag coefficients of a rotor profile. By iteratively increasing the micro-segment width by a set increment, the grid cells on the boundary of the blade micro-segment are corrected, reducing the error existing at the boundary position and improving the calculation accuracy of the lift and drag coefficients.

[0073] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0074] As Figure 1 and Figure 2 shown, the method for extracting lift and drag coefficients of the rotor profile of the present invention includes:

[0075] S1: Obtain the central coordinates, cell area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor. The grid model includes a plurality of grid cells.

[0076] First, the required data is output through CFD calculation: the data of the entire flow field can be obtained through the calculation of the pre-processor and the solver. Then, the central coordinates (x k , y k , z k ), cell area A k , unit surface normal vector and absolute pressure p k of the grid cells on the blade surface are output, where the subscript k represents the cell number, and the superscripts x, y, z represent the components in three directions.

[0077] S2: Determine the profile position and initial micro-segment width in the grid model.

[0078] S3: For the nth iteration, determine the nth blade micro-segment in the grid model according to the profile position and the nth micro-segment width, where 1 ≤ n ≤ N, and N is the iteration number threshold. The width of the first micro-segment is the initial micro-segment width.

[0079] S4: Classify each grid cell according to the positional relationship between the central coordinates of each grid cell and the position of the nth blade micro-segment. The categories of grid cells include internal grid, first cross grid, second cross grid, and external grid.

[0080] Further, step S4 includes:

[0081] S41: For any grid cell, if the central coordinate of the grid cell is located inside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an internal grid.

[0082] S42: If the central coordinate of the grid cell is located inside the blade micro-segment and a part of the area of the grid cell is outside the blade micro-segment, then the category of the grid cell is a first cross-grid.

[0083] S43: If the central coordinate of the grid cell is located outside the blade micro-segment and a part of the area of the grid cell is inside the blade micro-segment, then the category of the grid cell is a second cross-grid.

[0084] S44: If the central coordinate of the grid cell is located outside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an external grid. As Figure 3 shown are the schematic diagrams of various types of grid cells.

[0085] S5: For any grid cell, determine the pressure difference force of the grid cell according to the category, cell area and absolute pressure of the grid cell. In this embodiment, the categories of each grid cell are internal grid, first cross-grid, second cross-grid or external grid.

[0086] Specifically, use the following formula to determine the pressure difference force of the kth grid cell:

[0087]

[0088] where, F k is the pressure difference force of the kth grid cell, p k is the absolute pressure of the kth grid cell, A k is the cell area of the kth grid cell, b k is the distance between the central coordinate of the kth grid cell and the boundary of the blade micro-segment, i = 1 indicates that the category of the kth grid cell is an internal grid, i = 2 indicates that the category of the kth grid cell is a first cross-grid, i = 3 indicates that the category of the kth grid cell is a second cross-grid, and i = 4 indicates that the category of the kth grid cell is an external grid.

[0089] Since the internal grid is completely inside the area of the blade micro-segment, the pressure difference force calculation is performed for the entire grid cell. The first cross-grid and the second cross-grid use a weighted method to calculate the pressure difference force: The grid cell is equivalent to a square with a side length according to the area For a square, the pressure difference force considered is that of the equivalent square within the blade micro - section region. Since the overall external grid is not inside the blade micro - section, its pressure difference force is zero.

[0090] S6: Determine the lift and drag of the nth blade micro - section based on the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell.

[0091] Specifically, use the following formula to determine the lift and drag of the nth blade micro - section:

[0092]

[0093] where dL n is the lift of the nth blade micro - section, dD n is the drag of the nth blade micro - section, k max is the number of grid cells in the nth blade micro - section, F k is the pressure difference force of the kth grid cell in the nth blade micro - section, is the unit surface normal vector of the kth grid cell in the nth blade micro - section in the x - direction, is the unit surface normal vector of the kth grid cell in the nth blade micro - section in the z - direction.

[0094] S7: Determine the lift coefficient and drag coefficient on the nth blade micro - section based on the lift of the nth blade micro - section and the drag of the nth blade micro - section.

[0095] Specifically, use the following formula to determine the lift coefficient and drag coefficient on the nth blade micro - section:

[0096]

[0097] where, is the lift coefficient on the nth blade micro - section, is the drag coefficient on the nth blade micro - section, dL n is the lift of the nth blade micro - section, dD n is the drag of the nth blade micro - section, ρ is the air density, chord is the chord length, width is the micro - section width, V ∞ is the far - field incoming flow velocity.

[0098] S8: Judge whether n is equal to N.

[0099] S9: If n is equal to N, then determine the optimal lift coefficient and optimal drag coefficient based on the lift coefficients and drag coefficients from the 1st blade micro - section to the Nth blade micro - section.

[0100] S10: If n is not equal to N, increase the width of the n-th micro-segment by a set increment to obtain the width of the (n + 1)-th micro-segment.

[0101] S11: Determine whether the width of the (n + 1)-th micro-segment is greater than or equal to a set threshold.

[0102] S12: If the width of the (n + 1)-th micro-segment is greater than or equal to the set threshold, determine the optimal lift coefficient and the optimal drag coefficient based on the lift coefficient and drag coefficient of the first blade micro-segment to the lift coefficient and drag coefficient of the n-th blade micro-segment.

[0103] S13: If the width of the (n + 1)-th micro-segment is less than the set threshold, perform the (n + 1)-th iteration.

[0104] Denote the initial micro-segment width as width 1 , and the lift coefficient obtained at this time is The drag coefficient is

[0105] Increase the micro-segment width linearly with an increment of Δwidth:

[0106]

[0107] Similarly, denote the micro-segment width as width n and the lift coefficient calculated at this time is The drag coefficient is

[0108] Further, in step S9, determining the optimal lift coefficient and the optimal drag coefficient based on the lift coefficient and drag coefficient of the first blade micro-segment to the lift coefficient and drag coefficient of the N-th blade micro-segment specifically includes:

[0109] S91: Determine the m-th error value based on the lift coefficient and drag coefficient of the m-th blade micro-segment and the lift coefficient and drag coefficient of the (m + 1)-th blade micro-segment to obtain N - 1 error values; 1 ≤ m ≤ N - 1. That is, the error generated when the micro-segment width is increased by one step after obtaining the lift and drag coefficients of N micro-segment widths.

[0110] Specifically, use the following formula to determine the m-th error value:

[0111]

[0112] where, RMS m is the m-th error value, is the lift coefficient of the m-th blade micro-segment, is the drag coefficient of the m-th blade micro-segment.

[0113] S92: Determine the minimum error value from N - 1 error values.

[0114] S93: Determine the optimal lift coefficient and the optimal drag coefficient according to the lift coefficients and drag coefficients on two blade micro - segments corresponding to the minimum error value. Specifically, find the minimum error value among the N - 1 error values, and record its corresponding serial number m, indicating that the micro - segment width at this time is suitable for the calculation of lift and drag coefficients at the current profile position.

[0115] Take the calculation results of the micro - segment widths at the m - th step and the (m + 1)-th step, and use their average value as the optimal lift coefficient and the optimal drag coefficient.

[0116] Specifically, use the following formula to determine the optimal lift coefficient and the optimal drag coefficient:

[0117]

[0118] where, C l is the optimal lift coefficient, C d is the optimal drag coefficient, is the lift coefficient on the m - th blade micro - segment, is the drag coefficient on the m - th blade micro - segment, and m is the serial number corresponding to the minimum error value.

[0119] Furthermore, the method for extracting lift and drag coefficients of the rotor profile of the present invention further includes:

[0120] S14: Determine the aerodynamic performance of the rotor according to the optimal lift coefficient and the optimal drag coefficient.

[0121] The present invention proposes an adaptive extraction method for calculating lift and drag coefficients in the post - processing of computational fluid dynamics. It can adaptively adjust the micro - segment width, avoid the errors caused by manually selecting the micro - segment width, correct the grid cells on the micro - segment boundary, reduce the errors existing at the boundary position, improve the calculation accuracy of lift and drag coefficients, and thus effectively improve the reliability of rotor aerodynamic performance evaluation. In addition, the applicable scope of the present invention is wide, and it is effective for both structured grids and unstructured grids.

[0122] As Figure 4 shown, the system for extracting lift and drag coefficients of the rotor profile of the present invention includes: a data acquisition unit 1, a position width determination unit 2, a blade micro - segment determination unit 3, a classification unit 4, a pressure difference force determination unit 5, a lift and drag determination unit 6, a coefficient determination unit 7, a first judgment unit 8, a first optimal coefficient determination unit 9, a width increase unit 10, a second judgment unit 11, a second optimal coefficient determination unit 12, and an iteration unit 13.

[0123] Among them, the data acquisition unit 1 is used to acquire the central coordinates, cell area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor; the grid model includes a plurality of grid cells.

[0124] The position width determination unit 2 is connected to the data acquisition unit 1, and the position width determination unit 2 is used to determine the section position and the initial micro-segment width in the grid model.

[0125] The blade micro-segment determination unit 3 is connected to the position width determination unit 2. For the nth iteration, the blade micro-segment determination unit 3 is used to determine the nth blade micro-segment in the grid model according to the section position and the nth micro-segment width, where 1 ≤ n ≤ N and N is the iteration number threshold; the width of the first micro-segment is the initial micro-segment width.

[0126] The classification unit 4 is connected to the blade micro-segment determination unit 3 and the data acquisition unit 1. The classification unit 4 is used to classify each grid cell according to the positional relationship between the central coordinates of each grid cell and the nth blade micro-segment. Specifically, the categories of grid cells include internal grid, first cross grid, second cross grid, and external grid.

[0127] The pressure difference force determination unit 5 is connected to the classification unit 4 and the data acquisition unit 1. For any grid cell, the pressure difference force determination unit 5 is used to determine the pressure difference force of the grid cell according to the category, cell area, and absolute pressure of the grid cell.

[0128] The lift and drag force determination unit 6 is connected to the pressure difference force determination unit 5 and the data acquisition unit 1. The lift and drag force determination unit 6 is used to determine the lift and drag of the nth blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell.

[0129] The coefficient determination unit 7 is connected to the lift and drag force determination unit 6. The coefficient determination unit 7 is used to determine the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift of the nth blade micro-segment and the drag of the nth blade micro-segment.

[0130] The first judgment unit 8 is connected to the coefficient determination unit 7. The first judgment unit 8 is used to judge whether n is equal to N.

[0131] The first optimal coefficient determination unit 9 is connected to the first judgment unit 8 and the coefficient determination unit 7. When n is equal to N, the first optimal coefficient determination unit 9 is used to determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficients and drag coefficients from the first blade micro-segment to the Nth blade micro-segment.

[0132] The width increasing unit 10 is connected to the first determination unit 8. When n is less than N, the width increasing unit 10 is configured to increase the width of the n-th micro-segment by a set increment to obtain the width of the (n + 1)-th micro-segment.

[0133] The second determination unit 11 is connected to the width increasing unit 10. The second determination unit 11 is configured to determine whether the width of the (n + 1)-th micro-segment is greater than or equal to a set threshold.

[0134] The second optimal coefficient determination unit 12 is connected to the second determination unit 11 and the coefficient determination unit 7. When the width of the (n + 1)-th micro-segment is greater than or equal to the set threshold, the second optimal coefficient determination unit 12 is configured to determine the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and the drag coefficient on the first blade micro-segment to the lift coefficient and the drag coefficient on the n-th blade micro-segment.

[0135] The iteration unit 13 is connected to the second determination unit 11 and the blade micro-segment determination unit 3. When the width of the (n + 1)-th micro-segment is less than the set threshold, the iteration unit 13 is configured to perform the (n + 1)-th iteration.

[0136] Further, the lift and drag coefficient extraction system for the rotor blade profile of the present invention further includes an aerodynamic performance determination unit. The aerodynamic performance determination unit is connected to the first optimal coefficient determination unit and the second optimal coefficient determination unit. The aerodynamic performance determination unit is configured to determine the aerodynamic performance of the rotor blade according to the optimal lift coefficient and the optimal drag coefficient.

[0137] Further, the classification unit 4 includes: an internal grid determination module, a first cross-grid determination module, a second cross-grid determination module, and an external grid determination module.

[0138] Among them, the internal grid determination module is connected to the blade micro-segment determination unit 3 and the data acquisition unit 1. For any grid unit, if the central coordinate of the grid unit is located inside the blade micro-segment and the grid unit has no intersection with the boundary of the blade micro-segment, the category of the grid unit is an internal grid.

[0139] The first cross-grid determination module is connected to the blade micro-segment determination unit 3 and the data acquisition unit 1. For any grid unit, if the central coordinate of the grid unit is located inside the blade micro-segment and a part of the area of the grid unit is outside the blade micro-segment, the category of the grid unit is a first cross-grid.

[0140] The second cross-grid determination module is connected to the blade micro-segment determination unit 3 and the data acquisition unit 1. For any grid cell, if the central coordinate of the grid cell is outside the blade micro-segment and a part of the area of the grid cell is inside the blade micro-segment, the category of the grid cell is a second cross-grid.

[0141] The external grid determination module is connected to the blade micro-segment determination unit 3 and the data acquisition unit 1. For any grid cell, if the central coordinate of the grid cell is outside the blade micro-segment and there is no intersection between the grid cell and the boundary of the blade micro-segment, the category of the grid cell is an external grid.

[0142] Furthermore, the first optimal coefficient determination unit 9 includes: an error value determination module, a minimum error determination module, and an optimal coefficient determination module.

[0143] Among them, the error value determination module is connected to the first judgment unit 8. When n is equal to N, the error value determination module is used to determine the m-th error value according to the lift coefficient and drag coefficient on the m-th blade micro-segment and the lift coefficient and drag coefficient on the (m + 1)-th blade micro-segment, so as to obtain N - 1 error values; 1 ≤ m ≤ N - 1.

[0144] The minimum error determination module is connected to the error value determination module. The minimum error determination module is used to determine the minimum error value from the N - 1 error values.

[0145] The optimal coefficient determination module is connected to the minimum error determination module and the coefficient determination unit 7. The optimal coefficient determination module is used to determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficient and drag coefficient on the two blade micro-segments corresponding to the minimum error value.

[0146] Compared with the prior art, the lift and drag coefficient extraction system of the rotor profile of the present invention has the same beneficial effects as the above-mentioned lift and drag coefficient extraction method of the rotor profile, which will not be elaborated here.

[0147] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0148] In this article, specific examples are used to elaborate on the principles and implementation modes of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation modes and application scopes. To sum up, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A method for extracting lift and drag coefficients of a rotor profile, characterized in that, the method for extracting lift and drag coefficients of the rotor profile includes: Obtaining the central coordinates, cell area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor; the grid model includes a plurality of grid cells; Determining the profile position and initial micro-segment width in the grid model; For the nth iteration, according to the profile position and the nth micro-segment width, determine the nth blade micro-segment in the grid model, 1 ≤ n ≤ N, where N is the iteration number threshold; the width of the first micro-segment is the initial micro-segment width; Classify each grid cell according to the position relationship between the central coordinates of each grid cell and the nth blade micro-segment; For any grid cell, determine the pressure difference force of the grid cell according to the category, cell area, and absolute pressure of the grid cell; Determine the lift and drag of the nth blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell; Determine the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift and drag of the nth blade micro-segment; Judge whether n is equal to N. If so, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficient and drag coefficient from the first blade micro-segment to the Nth blade micro-segment. Otherwise, increase the nth micro-segment width by a set increment to obtain the (n + 1)th micro-segment width; Judge whether the (n + 1)th micro-segment width is greater than or equal to the set threshold. If so, determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficient and drag coefficient from the first blade micro-segment to the nth blade micro-segment. Otherwise, perform the (n + 1)th iteration.

2. The method for extracting lift and drag coefficients of a rotor profile according to claim 1, characterized in that, The categories of grid cells include internal grid, first cross grid, second cross grid, and external grid; The classifying each grid cell according to the position relationship between the central coordinates of each grid cell and the nth blade micro-segment specifically includes: For any grid cell, if the central coordinate of the grid cell is located inside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, the category of the grid cell is an internal grid; If the central coordinate of the grid cell is located inside the blade micro-segment and part of the area of the grid cell is outside the blade micro-segment, the category of the grid cell is a first cross grid; If the central coordinate of the grid cell is located outside the blade micro-segment and part of the area of the grid cell is inside the blade micro-segment, the category of the grid cell is a second cross grid; If the central coordinate of the grid cell is located outside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, the category of the grid cell is an external grid.

3. The method for extracting lift and drag coefficients of a rotor profile according to claim 1, characterized in that, The categories of each grid cell are internal grid, first cross grid, second cross grid, or external grid; Use the following formula to determine the pressure difference force of the k-th grid cell: Among them, F k is the pressure difference force of the k-th grid cell, p k is the absolute pressure of the k-th grid cell, A k is the cell area of the k-th grid cell, b k is the distance between the center coordinate of the k-th grid cell and the boundary of the blade micro-segment. i = 1 indicates that the category of the k-th grid cell is an internal grid, i = 2 indicates that the category of the k-th grid cell is a first cross grid, i = 3 indicates that the category of the k-th grid cell is a second cross grid, and i = 4 indicates that the category of the k-th grid cell is an external grid.

4. The method for extracting the lift and drag coefficients of a rotor profile according to claim 1, characterized in that Use the following formula to determine the lift and drag of the n-th blade micro-segment: where dL n is the lift of the n-th blade micro-segment, dD n is the drag of the n-th blade micro-segment, k max is the number of grid cells in the n-th blade micro-segment, F k is the pressure difference force of the k-th grid cell in the n-th blade micro-segment, is the unit surface normal vector in the x-direction of the k-th grid cell in the n-th blade micro-segment, is the unit surface normal vector in the z-direction of the k-th grid cell in the n-th blade micro-segment.

5. The method for extracting the lift and drag coefficients of a rotor profile according to claim 1, characterized in that Use the following formula to determine the lift coefficient and drag coefficient on the n-th blade micro-segment: Among them, is the lift coefficient on the n-th blade micro-segment, is the drag coefficient on the n-th blade micro-segment, dL n is the lift of the n-th blade micro-segment, dD n is the drag of the n-th blade micro-segment, ρ is the air density, chord is the chord length, width is the micro-segment width, V ∞ is the far-field incoming flow velocity.

6. The method for extracting the lift and drag coefficients of a rotor profile according to claim 1, characterized in that Determining the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and drag coefficient on the first blade micro-segment to the lift coefficient and drag coefficient on the N-th blade micro-segment specifically includes: Determine the m-th error value according to the lift coefficient and drag coefficient on the m-th blade micro-segment and the lift coefficient and drag coefficient on the (m + 1)-th blade micro-segment to obtain N - 1 error values; 1 ≤ m ≤ N - 1; Determine the minimum error value from the N - 1 error values; Determine the optimal lift coefficient and the optimal drag coefficient according to the lift coefficient and drag coefficient on the two blade micro-segments corresponding to the minimum error value.

7. The method for extracting the lift and drag coefficients of a rotor profile according to claim 6, characterized in that Use the following formula to determine the m-th error value: Among them, RMS m is the m-th error value, is the lift coefficient on the m-th blade micro-segment, is the drag coefficient on the m-th blade micro-segment.

8. The method for extracting the lift and drag coefficients of a rotor profile according to claim 6, characterized in that Use the following formula to determine the optimal lift coefficient and the optimal drag coefficient: Among them, C l is the optimal lift coefficient, C d is the optimal drag coefficient, is the lift coefficient on the m-th blade micro-segment, is the drag coefficient on the m-th blade micro-segment, and m is the serial number corresponding to the minimum error value.

9. A system for extracting the lift and drag coefficients of a rotor profile, characterized in that The system for extracting the lift and drag coefficients of the rotor profile includes: A data acquisition unit for acquiring the central coordinates, unit area, unit surface normal vector, and absolute pressure of each grid cell in the grid model of the rotor; the grid model includes a plurality of grid cells; A position width determination unit connected to the data acquisition unit for determining the profile position and the initial micro-segment width in the grid model; A blade micro-segment determination unit connected to the position width determination unit for, for the n-th iteration, determining the n-th blade micro-segment in the grid model according to the profile position and the n-th micro-segment width, 1 ≤ n ≤ N, where N is the iteration number threshold; the width of the first micro-segment is the initial micro-segment width; A classification unit connected to the blade micro-segment determination unit and the data acquisition unit for classifying each grid cell according to the positional relationship between the central coordinates of each grid cell and the position of the n-th blade micro-segment; A pressure difference force determination unit connected to the classification unit and the data acquisition unit for, for any grid cell, determining the pressure difference force of the grid cell according to the category, unit area, and absolute pressure of the grid cell; A lift and drag determination unit connected to the pressure difference force determination unit and the data acquisition unit for determining the lift and drag of the n-th blade micro-segment according to the pressure difference forces of each grid cell and the unit surface normal vectors of each grid cell; A coefficient determination unit, connected to the lift and drag determination unit, is configured to determine the lift coefficient and drag coefficient on the nth blade micro-segment according to the lift of the nth blade micro-segment and the drag of the nth blade micro-segment; A first judgment unit, connected to the coefficient determination unit, is configured to judge whether n is equal to N; A first optimal coefficient determination unit, connected to the first judgment unit and the coefficient determination unit, is configured to determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficient and drag coefficient on the 1st blade micro-segment to the lift coefficient and drag coefficient on the Nth blade micro-segment when n is equal to N; A width increase unit, connected to the first judgment unit, is configured to increase the width of the nth micro-segment by a set increment to obtain the width of the (n + 1)th micro-segment when n is less than N; A second judgment unit, connected to the width increase unit, is configured to judge whether the width of the (n + 1)th micro-segment is greater than or equal to a set threshold; A second optimal coefficient determination unit, connected to the second judgment unit and the coefficient determination unit, is configured to determine the optimal lift coefficient and optimal drag coefficient according to the lift coefficient and drag coefficient on the 1st blade micro-segment to the lift coefficient and drag coefficient on the nth blade micro-segment when the width of the (n + 1)th micro-segment is greater than or equal to the set threshold; An iteration unit, connected to the second judgment unit and the blade micro-segment determination unit, is configured to perform the (n + 1)th iteration when the width of the (n + 1)th micro-segment is less than the set threshold.

10. The lift and drag coefficient extraction system for a rotor profile according to claim 9, characterized in that, the categories of grid cells include internal grids, first cross grids, second cross grids, and external grids; the classification unit includes: An internal grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the center coordinates of the grid cell are located inside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an internal grid; A first cross grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the center coordinates of the grid cell are located inside the blade micro-segment and a part of the area of the grid cell is outside the blade micro-segment, then the category of the grid cell is a first cross grid; A second cross grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the center coordinates of the grid cell are located outside the blade micro-segment and a part of the area of the grid cell is inside the blade micro-segment, then the category of the grid cell is a second cross grid; An external grid determination module, connected to the blade micro-segment determination unit and the data acquisition unit, is configured to, for any grid cell, if the center coordinates of the grid cell are located outside the blade micro-segment and the grid cell has no intersection with the boundary of the blade micro-segment, then the category of the grid cell is an external grid.

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