Wall surface shear stress parallel acquisition method based on flow field information at any position

Abstract

The invention provides a wall shear stress parallel acquisition method based on flow field information at any position. The method comprises the following steps: (1) reading a parameter setting file; (2) determining unit positions corresponding to the wall surface grids, and counting the number of units in the same process and the number of units in the cross-process; (3) collecting the variable information of the same process of the # imgabs0 # group and the variable information of the cross-process surface-volume relationship of the Q2 group; (4) calculating variables of the same-process surface-volume relationship of the # imgabs 1 # group and the cross-process surface-volume relationship of the Q2 group, and performing communication; (5) updating the speed at the center of the grid unit in the surface-body relation; (6) obtaining wall surface shear stress; and (7) carrying out flow numerical simulation until the wall surface shear stress at all calculation moments is completely obtained. According to the method, the wall surface shear stress is obtained based on flow field information of any position by adopting process communication of a height function and parallel computing, the problem that a prediction result is low when the wall surface shear stress is obtained by utilizing flow field information of a first layer of grids is solved, parallel computing of the whole computing process is supported, and the computing precision and the problem solving scale are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of computational fluid dynamics, and particularly relates to a parallel method for obtaining wall shear stress based on flow field information at any position. Background Art

[0002] In flow problems in fields such as aerospace, ship and ocean engineering, the interaction between fluid and structure will significantly affect the aerodynamic / hydrodynamic performance of the structure, such as drag and lift. At present, numerical simulation methods are often used to calculate flow problems. Among them, the large eddy simulation method is considered as the core flow solving method for the next generation of engineering software. However, since the scale of the near-wall flow structure of the structure is proportional to the distance from the wall, in order to resolve the near-wall flow, a large number of grids need to be arranged in the near-wall region in large eddy simulation, which greatly limits the application of large eddy simulation to high Reynolds number wall turbulence problems. For example, for the boundary layer flow with a Reynolds number of the sixth power, 99% of the grids are used to resolve the flow in the range of 10% of the boundary layer thickness. In order to reduce the requirement of large eddy simulation for grid resolution, it can be assumed that the near-wall flow satisfies a known velocity distribution form, and the wall shear stress can be calculated from any point on the velocity distribution, thereby correcting the momentum transport process near the wall in the momentum equation and avoiding the need for extremely dense grids to resolve the near-wall flow to accurately give the wall shear stress.

[0003] In classical numerical methods of computational fluid dynamics, such as the finite volume method, since the topological connection relationship between the wall grid and its affiliated grid (i.e., the first near-wall grid) is known, the velocity at the centroid of the first near-wall grid is usually directly used to calculate the wall shear stress at the wall. However, since the first near-wall grid cannot fully resolve the flow within the grid scale, and the correlation between the velocity fluctuation at the centroid of the first near-wall grid and the wall shear stress fluctuation is non-physical, it will lead to a low prediction of the wall shear stress. This problem can be solved by using flow field information at different positions to obtain the wall shear stress, but currently there is no general and strongly robust parallel method for obtaining wall shear stress based on flow field information at any position. Summary of the Invention

[0004] Aiming at the technical problems existing in the above background art, the present invention proposes a parallel method for obtaining wall shear stress based on flow field information at any position. Its concept is reasonable, and it uses a height function and process communication for parallel computing to obtain the wall shear stress based on flow field information at any position, solves the problem that the predicted result is low when obtaining the wall shear stress using the flow field information of the first layer of grids, supports parallel computing of the entire calculation process, and improves the calculation efficiency and the scale of problem solving.

[0005] To solve the above technical problems, a parallel method for obtaining wall shear stress based on flow field information at any position provided by the present invention is characterized by mainly including the following steps:

[0006] (1) Read the parameter setting file;

[0007] (2) Determine the positions of the cells corresponding to the wall grid, and count the number of cells within the same process and across processes;

[0008] (3) Collect variables of the face - volume relationship for Q1 groups within the same process and Q2 groups across processes;

[0009] (4) Calculate variables of the face - volume relationship for Q1 groups within the same process and Q2 groups across processes and perform communication;

[0010] (5) Update the velocity at the centroid of the grid cell in the face - volume relationship;

[0011] (6) Obtain the wall shear stress;

[0012] (7) Conduct a numerical simulation of the flow, and repeat steps (5) - (7) until the wall shear stress at all calculation times is fully obtained.

[0013] The method for parallel obtaining of wall shear stress based on flow field information at any position, wherein in step (1), the height function formula is read from the parameter setting file through a C++ language program

[0014] In the above formula, a 1 and a 2 are set parameters; the positive x - axis direction of the coordinate system points to the main flow direction; x is the spatial coordinate; U ∞ is the incoming flow velocity; v is the kinematic viscosity of the fluid; is the unit vector in the x - direction.

[0015] The method for parallel obtaining of wall shear stress based on flow field information at any position, wherein the specific process of step (2) is as follows:

[0016] First, obtain the position corresponding to the height function formula :

[0017]

[0018] In the above formula, is the centroid coordinate of the F - th grid face; F is the number of the grid face within the current process;

[0019] Then, define R F and R C as the numbers of the processes to which the F - th grid face and the C - th grid cell belong respectively, where C is the number of the grid cell containing the point within the current process; when R F = R CWhen, count the total number of units located in the current process When R F ≠R C When, count the total number of units not located in the current process, that is, the number of cross - process units of the R C th process is

[0020] Finally, the total number of cross - process units obtained by solving for all processes is Q2:

[0021]

[0022] The parallel acquisition method of wall shear stress based on flow field information at any position, wherein the specific process of step (3) is as follows:

[0023] (3.1) First, define d F, as the wall distance corresponding to the F - th grid face and the C - th grid unit, and as the velocity at the centroid of the C - th grid unit; then allocate computer memory to store groups of variables of the same - process face - body relationship: F, C, d F,C and F is the number of the grid face within the current process; C is the number of the grid unit within the current process;

[0024] (3.2) Allocate memory to store Q2 groups of variables of the cross - process face - body relationship: F, R F 、 C, R C 、d F,C and

[0025] The parallel acquisition method of wall shear stress based on flow field information at any position, wherein the specific process of step (4) is as follows:

[0026] (4.1) In the R F th process, calculate groups of variables of the same - process face - body relationship: C, d F,C , and the specific process is as follows: traverse all grid units (1, 2, 3,..., N) within the current process. When the space formed by the i - th unit contains the point , let C = i;

[0027] The wall distance d F,C corresponding to the F - th grid face and the C - th grid unit is:

[0028]

[0029] In the above formula, x F 、yF and z F are respectively the x - coordinate, y - coordinate and z - coordinate of the centroid of the F - th grid face; x C , y C and z C are respectively the x - coordinate, y - coordinate and z - coordinate of the centroid of the C - th grid cell;

[0030] (4.2) In the R F -th process, calculate the variables of the Q2 group of cross - process face - body relationships: Transfer this information to all processes through process communication; the specific calculation process is as follows:

[0031] The centroid coordinates of the F - th grid face

[0032]

[0033] In the above formula, x F , y F and z F are respectively the x - coordinate, y - coordinate and z - coordinate of the centroid of the F - th grid face, and are respectively the unit vectors in the x - direction, y - direction and z - direction;

[0034] The point means that the point is the vector sum of the centroid coordinates of the F - th grid face and the height function ;

[0035] Process communication is completed by using the gather function MPI_Gather and scatter function MPI_Scatter of the internationally - used communication protocol MPI;

[0036] (4.3) Calculate the grid cell C and the current process R C of the Q2 group of cross - process face - body relationships. The specific process is as follows: Traverse all processes (1, 2, 3, …, N). When the space formed by all grid cells of the j - th process contains the point , let R C = j; Traverse all grid cells (1, 2, 3, …, N) within the R C process. When the space formed by the i - th cell contains the point

[0037] , let C = i;

[0038] (4.4) In the R(4.4) In the R C -th process, calculate the variable d F,C of the Q2 group of cross - process face - body relationships and transfer this information to the RF A process, and the specific process is as follows:

[0039] The wall distance d between the F-th grid surface and the wall corresponding to the C-th grid cell F,C :

[0040]

[0041] In the above formula, x F , y F and z F are respectively the x-coordinate, y-coordinate and z-coordinate of the centroid of the F-th grid surface ; x C , y C and z C are respectively the x-coordinate, y-coordinate and z-coordinate of the center of volume of the C-th grid cell.

[0042] The parallel acquisition method of wall shear stress based on flow field information at any position, wherein the specific process of the step (5) is as follows: For the grid surface number F, when R F = R C , determine the corresponding grid cell C in the group of same-process face-volume relationships, and obtain the wall distance d at this point F,C and velocity When R F ≠ R C , determine the corresponding grid cell C in the Q2 group of cross-process face-volume relationships, obtain the wall distance d at this point F, , and update the velocity at the center of volume of the grid cell in the face-volume relationship

[0043] The parallel acquisition method of wall shear stress based on flow field information at any position, wherein: The step (6) is to obtain the wall shear stress τ F,C based on the wall distance d corresponding to the grid surface number F and the velocity w :

[0044]

[0045] In the above formula, μ and μ t are respectively the hydrodynamic viscosity coefficient and the turbulent dynamic viscosity coefficient;

[0046]

[0047] In the above formula, U Cx , U Cy and U Cz are respectively the x-direction, y-direction and z-direction components of the vector .

[0048] The method for parallel obtaining of wall shear stress based on flow field information at any position, wherein: step (7) is to perform flow simulation using the open-source computational fluid dynamics program OpenFOAM, including solving the momentum equation, solving the pressure Poisson equation, and solving the turbulence model equation to obtain the flow field velocity at the current moment pressure, and turbulent dynamic viscosity coefficient μ t , perform time advancement, and enter step (5) until the simulation ends to obtain the wall shear stress at all calculation moments.

[0049] Adopting the above technical solution, the present invention has the following beneficial effects:

[0050] The method for parallel obtaining of wall shear stress based on flow field information at any position of the present invention is reasonably conceived. By using the height function, the wall shear stress can be obtained based on the flow field information at any position, solving the problem that the prediction result is on the low side when obtaining the wall shear stress using the flow field information of the first layer of grids, realizing the correct simulation process of momentum transport in the near-wall region, and improving the simulation accuracy of the flow.

[0051] By specifying the height function, the wall shear stress can be obtained based on the flow field information at any position, and message passing between different processes is realized based on MPI (Message Passing Interface), solving the problem of low computational efficiency of the existing serial method and improving the scale of problem solving.

[0052] The present invention realizes message passing between different processes based on MPI (Message Passing Interface), combines with the OpenFOAM software to realize parallel computing of the entire calculation process, and improves the computational accuracy and the scale of problem solving. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are 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.

[0054] Figure 1 It is a schematic diagram of the wall grid and the corresponding grid unit involved in the method for parallel obtaining of wall shear stress based on flow field information at any position of the present invention;

[0055] Figure 2 It is a flowchart of the method for parallel obtaining of wall shear stress based on flow field information at any position of the present invention;

[0056] Figure 3Schematic diagram of channel flow involved in the method for parallel acquisition of wall shear stress based on flow field information at any position according to the present invention;

[0057] Figure 4 Instantaneous streamwise velocity distribution diagram of the calculation result of channel flow involved in the method for parallel acquisition of wall shear stress based on flow field information at any position according to the present invention;

[0058] Figure 5 Schematic diagram of velocity profile of the calculation result of channel flow involved in the method for parallel acquisition of wall shear stress based on flow field information at any position according to the present invention. Detailed implementation manners

[0059] The technical solutions of the present invention will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. 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.

[0060] The present invention will be further explained below in conjunction with specific implementation manners.

[0061] As Figure 1 shown, a method for parallel acquisition of wall shear stress based on flow field information at any position provided in this embodiment includes the following steps:

[0062] S1. Read the height function from the parameter setting file by a C++ language program

[0063]

[0064] In the above formula, a 1 and a 2 are set parameters. The positive direction of the x-axis of the coordinate system points to the main flow direction, x is the spatial coordinate, U ∞ is the incoming flow velocity, v is the kinematic viscosity of the fluid, is the unit vector in the x direction.

[0065] S2. First, obtain the position corresponding to the height function h:

[0066]

[0067] In the above formula, is the centroid coordinate of the F-th grid face, and F is the number of the grid face within the current process; then define R F and R C as the numbers of the processes to which the F-th grid face and the C-th grid cell belong respectively, and C is the number of the grid cell containing the point within the current process; when RF = R C When it is, count the total number of units in the current process When R F ≠ R C When it is, count the total number of units not in the current process, that is, the number of cross - process units of the R C th process The total number of cross - process units solved for all processes is Q2:

[0068]

[0069] S3. Allocate computer memory, which specifically includes the following steps:

[0070] S31. Dynamically allocate memory for storing variables of the same - process face - volume relationship: F, C, d F,C and where F is the number of the grid face within the current process; C is the number of the grid unit within the current process; d F,C is the wall distance corresponding to the F - th grid face and the C - th grid unit, and is the velocity at the centroid of the C - th grid unit body

[0071] S32. Allocate memory for storing variables of Q2 groups of cross - process face - volume relationships: F, R F , C, R C , d F,C and

[0072] S4. Calculate variables of the same - process and Q2 groups of cross - process face - volume relationships and perform communication, including the following steps:

[0073] S41. In the R F th process, calculate variables of the same - process face - volume relationship C and d F,C ;

[0074] C is the number of the grid unit within the current process, and its calculation process is: traverse all grid units (1, 2, 3,..., N) within the current process. When the space formed by the i - th unit contains the point then let C = i;

[0075] d F, is the wall distance corresponding to the F - th grid face and the C - th grid unit, and its calculation formula is:

[0076]

[0077] In the above formula, x F , y F and z F are the x - coordinate, y - coordinate, and z - coordinate of the centroid of the F - th grid face respectively, and x C , y C and z C are the x - coordinate, y - coordinate, and z - coordinate of the centroid of the C - th grid cell respectively. The above coordinates are the information possessed by the internationally - common computational grid.

[0078] S42. In the R F -th process, calculate the variables of the Q2 - group cross - process face - volume relationship: Transfer this information to all processes through process communication;

[0079] The centroid coordinates of the F - th grid face:

[0080]

[0081] In the above formula, x F , y F and z F are the x - coordinate, y - coordinate, and z - coordinate of the centroid of the F - th grid face respectively, and are the unit vectors in the x - direction, y - direction, and z - direction respectively. The above coordinates are the information possessed by the internationally - common computational grid;

[0082] The point means that the point is the vector sum of the centroid coordinates of the F - th grid face and the height function ;

[0083] Process communication is completed using the gather function MPI_Gather and scatter function MPI_Scatter of the internationally - common communication protocol MPI (Message Passing Interface).

[0084] S43. Calculate the variables C and R of the Q2 - group cross - process face - volume relationship C , and the specific process is as follows:

[0085] Traverse all processes (1, 2, 3, …, N). When the space formed by all grid cells of the j - th process contains the point , let R C = j; Traverse all grid cells (1, 2, 3, …, N) within the R C process. When the space formed by the i - th cell contains the point , let C = i.

[0086] S44. In the RC In a process, the variable d for calculating the cross-process surface-volume relationship of group Q2 F,C , and this information is transmitted to the Rth F process through process communication; the specific process is as follows:

[0087] The wall distance corresponding to the Fth grid surface and the Cth grid cell:

[0088]

[0089] In the above formula, x F , y F and z F are the x-coordinate, y-coordinate, and z-coordinate of the centroid of the Fth grid surface respectively , and x C , y C and z C are the x-coordinate, y-coordinate, and z-coordinate of the center of mass of the Cth grid cell respectively. The above coordinates are the information possessed by the internationally common computational grid.

[0090] S5. For the grid surface number F, when R F = R C , determine the corresponding grid cell C in the group of same-process surface-volume relationships, and obtain the wall distance d F,C and velocity (The velocity can be obtained by indexing the velocity field in the open-source computational fluid dynamics program OpenFOAM according to the grid cell C number). When R F ≠ R C , determine the corresponding grid cell C in the Q2 group of cross-process surface-volume relationships, obtain the wall distance d F, , and update the velocity at the center of mass of the grid cell in the surface-volume relationship (Within the Rth C process, the velocity can be obtained by indexing the velocity field in the open-source computational fluid dynamics program OpenFOAM according to the grid cell C number, and the process communication is completed by using the collective MPI_Gather and scatter MPI_Scatter of the internationally common communication protocol MPI to propagate the information to all processes).

[0091] S6. Based on the wall distance d F, and velocity corresponding to the grid surface number F, obtain the wall shear stress τ w :

[0092]

[0093] In the above formula, μ and μt are the hydrodynamic viscosity coefficient and the turbulent dynamic viscosity coefficient, respectively;

[0094]

[0095] In the above formula, U Cx , U Cy and U Cz are the x-direction, y-direction and z-direction components of the vector respectively.

[0096] S7. Use the open-source computational fluid dynamics program OpenFOAM to perform flow numerical simulation, including solving the momentum equation, solving the pressure Poisson equation, and solving the turbulent model equation, to obtain the flow field velocity , pressure and turbulent dynamic viscosity coefficient μ t at the current moment, perform time advancement, and enter the above step S5 until the simulation ends.

[0097] The present invention provides wall shear stress for the momentum equation in flow simulation, without depending on the specific solution methods for the momentum equation, pressure Poisson equation, and turbulent model in the computational fluid dynamics program;

[0098] Generally, the computational fluid dynamics program sequentially solves the following three equations (sets): First, the momentum equation is:

[0099]

[0100] In the above formula, is the transpose of the velocity gradient. The value of the wall shear stress is reflected in the second term on the right side of the equation, manifested as the product of the velocity gradient and the viscosity coefficient; generally, the momentum equation can be solved by the Preconditioned Bi-Conjugate Gradient Method;

[0101] The pressure Poisson equation is:

[0102]

[0103] In the above formula, is the contribution of the diagonal elements of the discrete matrix of the momentum equation, is the contribution of the non-diagonal elements of the discrete matrix of the momentum equation; generally, the pressure Poisson equation can be solved by the Multi-Grid Method;

[0104] There is a wide variety of turbulence models, which need to be selected according to the problem characteristics and actual requirements. Commonly used large-eddy simulation turbulence models include: the Smagorinsky model and the WALE (Wall Adapting Local Eddy-viscosity) model, etc.; specifically, the most commonly used Smagorinsky model is as follows:

[0105]

[0106] In the above formula, C S is the model coefficient, usually taken as 0.094, Δ is the length scale, and S ij is the strain rate tensor. Usually, the turbulence model equation can be solved by the Preconditioned Bi-Conjugate Gradient Method.

[0107] For three-dimensional channel turbulence, the present invention is used to simulate this flow, and the computational domain is as Figure 3 shown. The x-direction (flow direction) and z-direction (spanwise direction) are periodic boundary conditions, and the upper and lower wall surfaces are no-slip boundary conditions. The example parameters are shown in Table 1.

[0108] Table 1 Example parameters of three-dimensional channel turbulence

[0109]

[0110]

[0111] The results obtained by the present invention are shown in Figure 4 、 Figure 5 and Table 2. Figure 4 shows the instantaneous flow velocity distribution in the XY plane. The results are dimensionless based on the incoming flow velocity. The red color represents the high-speed area at the center of the channel, and the blue color represents the low-speed area near the wall. Figure 5 shows the velocity distribution result in the wall-normal direction. The abscissa is the dimensionless wall distance y + based on the viscous length, and the ordinate is the dimensionless velocity u + based on the friction velocity. The gray dashed line is the velocity profile of a zero-pressure-gradient flat plate, the black solid line is the velocity profile given by direct numerical simulation, and the red solid line with circular markers is the velocity profile corresponding to the wall shear stress calculated using the velocity at the center of the first-layer grid (i.e., the C Figure 3 point in 1 ) in the traditional method. The blue solid line with square markers is the velocity profile corresponding to the wall shear stress calculated using the velocity at the center of the grid near (i.e., the C Figure 3 point in h ) in the present invention.

[0112] Table 2 presents the results of the traditional method and the method of the present invention. The values in the table are dimensionless values based on the incoming flow density and the incoming flow velocity. Comparing with the direct numerical simulation results, the predicted wall shear stress by the traditional method is 11% lower, while the error of the result of the method of the present invention is less than 1%. The above results indicate that the method of the present invention uses a height function to obtain the wall shear stress based on the flow field information at any position, which can solve the problem of the low prediction result of obtaining the wall shear stress using the flow field information of the first layer of grid.

[0113] Table 2 Results of wall friction

[0114] Method Value Result of traditional method 0.00162 Result of the method of the present invention 0.00183 Direct numerical simulation 0.00182

[0115] The present invention uses a height function and process communication for parallel computing, which can obtain the wall shear stress based on the flow field information at any position, solve the problem of the low prediction result of obtaining the wall shear stress using the flow field information of the first layer of grid, support the parallel computing of the entire calculation process, and improve the calculation accuracy and the scale of problem solving.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parallel acquisition method of wall shear stress based on flow field information at any position, characterized in that: The main steps include: (1) Read parameter setting file; (2) Determine the corresponding unit position of the wall grid and count the number of units in the same process and across processes; (3) Collection Variable information of face-body relationships of the same process of group Q2 and cross-process of group Q2; (4) Calculation Group variables of the same process and Q2 group cross-process face-body relationships and communicate; (5) Update the velocity at the center of the mesh unit in the surface-body relationship; (6) Obtaining wall shear stress; (7) Perform numerical flow simulation and repeat (5) to (7) until the wall shear stress at all calculation moments is fully obtained.

2. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 1, characterized in that: The step (1) is to read the height function formula from the parameter setting file through a C++ language program. In the above formula, a1 and a2 are setting parameters; the positive direction of the x-axis of the coordinate system points to the main flow direction; x is the spatial coordinate; U ∞ is the incoming flow velocity; ν is the fluid kinematic viscosity coefficient; is the unit vector in the x direction.

3. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 2, characterized in that: The specific process of step (2) is as follows: First get the height function formula Corresponding position: In the above formula, is the center coordinate of the Fth mesh face; F is the number of the mesh face in the current process; Redefine R F and R C are the numbers of the processes to which the Fth grid surface and the Cth grid unit belong respectively, and C is the number of the process containing the point The number of the grid cell in the current process; when R F =R C When , count the total number of units in the current process When R F ≠R C When the total number of units not in the current process is counted, that is, the Rth C The number of cross-process units for a process is Finally, the total number of cross-process units solved for all processes is Q2:

4. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 3, characterized in that: The specific process of step (3) is as follows: (3.1) First define d F,C is the wall distance between the Fth grid surface and the Cth grid unit, is the velocity at the center of the Cth grid unit; reallocate computer memory to store Variables for group process face-body relationships: F, C, d F,C and F is the number of the mesh surface in the current process; C is the number of the mesh cell in the current process; (3.2) Allocate memory to store variables for the Q2 group of cross-process face-body relationships: F, R F , C. R C ,d F,C and 5. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 1, characterized in that: The specific process of step (4) is as follows: (4.1) In R F In the process, calculation Variables for group process face-body relationships: C, d F,C The specific process is: traverse all grid cells (1, 2, 3, ..., N) in the current process, and when the space formed by the i-th cell contains the point When, let C = i; The distance d between the wall corresponding to the Fth grid surface and the Cth grid unit F,C for: In the above formula, x F ,y F and z F are the x-coordinate, y-coordinate and z-coordinate of the center of the Fth mesh face respectively; C ,y C and z C are the x-coordinate, y-coordinate and z-coordinate of the center of the Cth grid cell respectively; (4.2) In R F In each process, calculate the variables of the Q2 group of cross-process face-body relationships: This information is transmitted to all processes through process communication; the specific calculation process is: Coordinates of the center of the Fth mesh face In the above formula, x F ,y F and z F are the x-coordinate, y-coordinate and z-coordinate of the center of the Fth mesh face, and are the unit vectors in the x, y and z directions respectively; point means point is the center coordinate of the Fth mesh face and height function The vector sum of The process communication is completed by using the collection function MPI_Gather and the distribution function MPI_Scatter of the international general communication protocol MPI; (4.3) Calculate the grid cell C of the cross-process face-volume relationship of group Q2 and the current process R C The specific process is: traverse all processes (1, 2, 3, ..., N), when the space composed of all grid cells of the jth process contains the point When R C =j; for R C All grid cells (1, 2, 3, ..., N) in the process are traversed. When the space formed by the i-th cell contains the point When, let C = i; (4.4) In R C In each process, calculate the variable d of the Q2 group of cross-process face-body relationships F,C , pass this information to the Rth F The specific process is: The distance d between the wall corresponding to the Fth grid surface and the Cth grid unit F,C : In the above formula, x F ,y F and z F are the center coordinates of the Fth mesh face respectively. The x-coordinate, y-coordinate, and z-coordinate of C ,y C and z C are the x-coordinate, y-coordinate, and z-coordinate of the center of the Cth grid cell.

6. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 4, characterized in that: The specific process of step (5) is as follows: for the mesh surface number F, when R F =R C When Determine the corresponding grid cell C in the surface-volume relationship of the same process, and obtain the wall distance d of the point F,C and speed When R F ≠R C When , determine the corresponding grid cell C in the cross-process surface-body relationship of group Q2, and obtain the wall distance d of the point F,C , and update the velocity at the center of the mesh unit in the surface-volume relationship 7. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 4, characterized in that: The step (6) is based on the wall distance d corresponding to the grid surface number F. F,C and speed Get the wall shear stress τ w : In the above formula, μ and μ t are the fluid dynamic viscosity coefficient and the turbulent dynamic viscosity coefficient respectively; In the above formula, U Cx , U Cy and U Cz Respectively vector The x-, y-, and z-direction components of .

8. The method for parallel acquisition of wall shear stress based on flow field information at any position according to claim 4, characterized in that: The step (7) is to use the computational fluid dynamics open source program OpenFOAM to perform flow simulation, including solving the momentum equation, solving the pressure Poisson equation and solving the turbulence model equation to obtain the flow field velocity at the current moment. Pressure and turbulent dynamic viscosity coefficient μ t , and proceed with time advancement to step (5) until the simulation is completed, and the wall shear stress at all calculation moments is obtained.

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