A wall shear stress parallel acquisition method based on arbitrary position flow field information

Abstract

The application provides a wall shear stress parallel acquisition method based on flow field information at an arbitrary position, comprising the following steps: (1) reading a parameter setting file; (2) determining the wall grid corresponding unit position, and counting the same process and cross-process unit numbers; (3) collecting the variable information of the group same process and Q2 group cross-process face-body relationship; (4) calculating the variables of the group same process and Q2 group cross-process face-body relationship and performing communication; (5) updating the velocity at the grid unit center in the face-body relationship; (6) acquiring the wall shear stress; (7) performing flow numerical simulation until the wall shear stress at all calculation time points is completely acquired. The application adopts the process communication of the height function and parallel calculation, acquires the wall shear stress based on the flow field information at an arbitrary position, solves the problem that the prediction result is low when the wall shear stress is acquired by using the flow field information of the first layer grid, supports the parallel calculation of the whole calculation process, and improves the calculation precision and the problem solving scale.

Description

Technical Field

[0001] The present invention relates to the technical field of computational fluid dynamics, and in particular to a method for parallel acquisition of wall shear stress based on flow field information at arbitrary positions. Background Art

[0002] In flow problems in fields such as aerospace, naval architecture, and marine engineering, the interaction between fluids and structures significantly affects aerodynamic and hydrodynamic properties, such as drag and lift. Currently, numerical simulation methods are commonly used to solve these flow problems, with large eddy simulation (LES) being considered a core flow-solving method for next-generation engineering software. However, because the scale of near-wall flows is proportional to the distance from the wall, LES requires a large number of meshes near the wall to resolve the near-wall flow. This significantly limits LES's application to high-Reynolds-number wall turbulence problems. For example, for a boundary layer flow with a Reynolds number of 6, 99% of the mesh is used to resolve the flow within 10% of the boundary layer thickness. To reduce the mesh resolution requirement for LES, the flow near the wall can be assumed to have a known velocity profile. The wall shear stress can be calculated from any point on the velocity profile, thereby modifying the momentum transport process near the wall in the momentum equation and avoiding the need for an extremely dense mesh to accurately resolve the near-wall flow and obtain the wall shear stress.

[0003] In classical numerical methods of computational fluid dynamics, such as the finite volume method, since the topological connection between the wall grid and the grid to which it belongs (i.e., the first layer of grid near the wall) is known, the velocity at the center of the first layer of grid near the wall is usually used directly to calculate the wall shear stress at the wall. However, since the first layer of grid near the wall cannot fully resolve the flow within this grid scale, and the correlation between the velocity pulsation at the center of the first layer of grid near the wall and the wall shear stress pulsation is non-physical, the predicted wall shear stress will be too low. This problem can be solved by using flow field information at different locations to obtain the wall shear stress, but there is currently no universal, highly robust method for parallel acquisition of wall shear stress based on flow field information at arbitrary locations. Summary of the Invention

[0004] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a parallel acquisition method for wall shear stress based on flow field information at any position. The method has a reasonable concept, adopts process communication of height function and parallel computing, and obtains wall shear stress based on flow field information at any position, thereby solving the problem of low prediction results when obtaining wall shear stress using the first-layer grid flow field information. The method supports parallel computing of the entire calculation process, thereby improving computing efficiency and the scale of problem solving.

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

[0006] (1) Read parameter setting file;

[0007] (2) Determine the corresponding unit position of the wall grid and count the number of units in the same process and across processes;

[0008] (3) Collection variables for group intra-process and Q2 group inter-process face-body relationships;

[0009] (4) Calculation Group variables of the same process and Q2 group cross-process face-body relationships and communicate;

[0010] (5) Update the velocity at the center of the mesh cell in the surface-body relationship;

[0011] (6) Obtaining wall shear stress;

[0012] (7) Perform numerical flow simulation and repeat (5) to (7) until the wall shear stress at all calculation moments is fully obtained.

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

[0014] 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; v is the fluid kinematic viscosity coefficient; is the unit vector in the x direction.

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

[0016] First get the height function formula Corresponding position:

[0017]

[0018] 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;

[0019] Redefine R F and R C are the numbers of the processes to which the Fth grid surface and the Cth grid cell 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 counting the total number of units in the current process When R F ≠R C When counting the total number of units that are not in the current process, that is, the R C The number of cross-process units for a process is

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

[0021]

[0022] The method for parallel acquisition 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, 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 grid surface in the current process; C is the number of the grid cell in the current process;

[0024] (3.2) Allocate memory to store variables for the Q2 group's cross-process face-body relationships: F, R F 、 C.R. C d F,C and

[0025] The method for parallel acquisition 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 R F In a 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;

[0027] The distance d between the wall corresponding to the Fth grid surface and the Cth grid unit F,C for:

[0028]

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

[0030] (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:

[0031] Coordinates of the center of the Fth mesh face

[0032]

[0033] 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 F-th mesh face, and are the unit vectors in the x, y and z directions respectively;

[0034] point means point is the center coordinate of the Fth mesh face and height function The vector sum of

[0035] Process communication is accomplished using the MPI_Gather and MPI_Scatter functions of the internationally accepted MPI communication protocol.

[0036] (4.3) Calculate the grid cell C of the cross-process face-body 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 in the process (1,2,3,…,N)

[0037] Traverse, when the space formed by the i-th unit contains the point When, let C = i;

[0038] (4.4) in R C In each process, calculate the variable d of the Q2 group's cross-process face-body relationship F,C , pass this information to the Rth through process communication F The specific process is:

[0039] The distance d between the wall corresponding to the Fth grid surface and the Cth grid unit F,C :

[0040]

[0041] In the above formula, x F 、y F and z F are the coordinates of the center of the Fth mesh face respectively The x-, y-, and z-coordinates of C 、y C and z C are the x-coordinate, y-coordinate, and z-coordinate of the center of the C-th grid cell.

[0042] The method for parallel acquisition of wall shear stress based on flow field information at any position, wherein the specific process of step (5) is as follows: for the grid surface number F, when R F =R C When Determine the corresponding grid cell C in the surface-body relationship of the group and obtain the wall distance d of the point F,C and speed When R F ≠R C When the corresponding grid cell C is determined in the Q2 group cross-process surface-body relationship, the wall distance d of the point is obtained. F, , and update the velocity at the center of the mesh cell in the surface-body relationship

[0043] The method for parallel acquisition of wall shear stress based on flow field information at any position, wherein: 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 :

[0044]

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

[0046]

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

[0048] The parallel acquisition method of wall shear stress based on flow field information at any position, wherein: 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 , advance the time and enter step (5) until the simulation is completed, and obtain the wall shear stress at all calculation moments.

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

[0050] The parallel acquisition method of wall shear stress based on flow field information at any position of the present invention is rationally conceived. The height function is used to obtain wall shear stress based on flow field information at any position, thereby solving the problem of low prediction results when obtaining wall shear stress using the first layer of grid flow field information. The correct simulation process of momentum transport in the near-wall area is realized, thereby 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. Message passing between different processes is implemented based on MPI (Message Passing Interface), which solves the problem of low computational efficiency of existing serial methods and improves the scale of problem solving.

[0052] The present invention realizes message transmission between different processes based on MPI (Message Passing Interface), and combines OpenFOAM software to realize parallel computing of the entire computing flow, thereby improving the computing 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 briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0054] Figure 1 Schematic diagram of the wall grid and corresponding grid units involved in the method for parallel acquisition of wall shear stress based on flow field information at any position of the present invention;

[0055] Figure 2 This is a flow chart of the method for parallel acquisition of wall shear stress based on flow field information at any position according to 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 of the present invention;

[0057] Figure 4 It is an instantaneous flow velocity distribution diagram of the channel flow calculation results involved in the parallel acquisition method of wall shear stress based on flow field information at any position of the present invention;

[0058] Figure 5 It is a velocity diagram of the channel flow calculation results involved in the parallel acquisition method of wall shear stress based on flow field information at any position of the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0060] The present invention will be further explained below with reference to specific embodiments.

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

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

[0063]

[0064] 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, and U ∞ is the incoming flow velocity, v is the fluid kinematic viscosity coefficient, is the unit vector in the x direction.

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

[0066]

[0067] In the above formula, is the center coordinate of the Fth mesh surface, F is the number of the mesh surface in the current process; then define R F and R C are the numbers of the processes to which the Fth grid surface and the Cth grid cell 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 CWhen counting the total number of units in the current process When R F ≠R C When counting the total number of units that are not in the current process, that is, the R C The number of cross-process units per process The total number of cross-process units solved for all processes is Q2:

[0068]

[0069] S3. Allocating computer memory, specifically including the following steps:

[0070] S31, dynamically allocate memory for storage Variables for group process face-body relationships: F, C, d F,C and Among them, F is the number of the grid surface in the current process; C is the number of the grid cell in the current process; d F,C The distance between the wall surface corresponding to the Fth grid surface and the Cth grid unit, is the velocity at the center of the Cth grid cell.

[0071] S32. Allocate memory to store variables for the Q2 group's cross-process face-body relationships: F, R F 、 C.R. C d F,C and

[0072] S4. Calculation The variables of the same process and Q2 group cross-process face-body relationships are communicated, including the following steps:

[0073] S41, in R F In a process, calculation Variables C and d of the face-body relationship of the same process F,C ;

[0074] C is the number of the grid cell in the current process. The calculation process is: traverse all grid cells (1, 2, 3, ..., N) in the current process. When the space formed by the i-th cell contains the point When, let C = i;

[0075] d F, is the distance between the wall surface corresponding to the Fth grid surface and the Cth grid unit, and its calculation formula is:

[0076]

[0077] In the above formula, x F 、yF 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 C-th grid cell, respectively. The above coordinates are the information possessed by the international general computing grid.

[0078] S42, in R F In each process, calculate the variables of the Q2 group of cross-process face-body relationships: This information is passed to all processes via process communication;

[0079] Coordinates of the center of the Fth mesh 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 center of the F-th mesh face, and are the unit vectors in the x, y, and z directions respectively. The above coordinates are the information possessed by the international general computing grid;

[0082] point means point is the center coordinate of the Fth mesh face and height function The vector sum of

[0083] The process communication is implemented using the international general communication protocol MPI (Message Passing Interface)'s collection function MPI_Gather and distribution function MPI_Scatter.

[0084] S43. Calculate variables C and R of the cross-process face-body relationship of group Q2 C The specific process is:

[0085] 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) are traversed in the process. When the space formed by the i-th cell contains the point When , let C = i.

[0086] S44, in the R CIn each process, calculate the variable d of the Q2 group's cross-process face-body relationship F,C , pass this information to the Rth through process communication F The specific process is:

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

[0088]

[0089] In the above formula, x F 、y F and z F are the coordinates of the center of the Fth mesh face respectively The x-coordinate, y-coordinate and z-coordinate of x C 、y C and z C are the x-coordinate, y-coordinate, and z-coordinate of the center of the C-th grid cell, respectively. The above coordinates are the information possessed by the international general computing grid.

[0090] S5. For the mesh face number F, when R F =R C When Determine the corresponding grid cell C in the surface-body relationship of the group and obtain the wall distance d of the point F,C and speed (speed The velocity field in the computational fluid dynamics open source program OpenFOAM can be obtained by indexing the grid cell C number. F ≠R C When the corresponding grid cell C is determined in the Q2 group cross-process surface-body relationship, the wall distance d of the point is obtained. F, , and update the velocity at the center of the mesh cell in the surface-body relationship (In R C In-process, speed The velocity field in the computational fluid dynamics open source program OpenFOAM can be obtained by indexing the grid cell C number, and the international general communication protocol MPI's collection MPI_Gather and distribution MPI_Scatter are used to complete process communication and propagate information to all processes).

[0091] S6, wall distance d corresponding to the grid surface number F F, and speed Get the wall shear stress τ w :

[0092]

[0093] In the above formula, μ and μ tare the fluid dynamic viscosity coefficient and turbulent dynamic viscosity coefficient respectively;

[0094]

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

[0096] S7. Use the computational fluid dynamics open source program OpenFOAM to perform flow numerical 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 , advance the time 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 relying on specific solutions for the momentum equation, pressure Poisson equation and turbulence model in computational fluid dynamics programs;

[0098] Typically, a computational fluid dynamics program solves the following three equations (sets) in sequence: 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, which is the product of the velocity gradient and the viscosity coefficient. Usually, the momentum equation can be solved using the preconditioned bi-conjugate gradient method.

[0101] The Poisson equation for pressure is:

[0102]

[0103] In the above formula, is the contribution of the diagonal elements of the discrete matrix of the momentum equation, Contributes to the non-diagonal elements of the discrete matrix of the momentum equation; usually, the pressure Poisson equation can be solved using the multi-grid method;

[0104] There are many types of turbulence models, and they need to be selected based on the characteristics of the problem and actual needs. Commonly used large eddy simulation turbulence models include the Smagorinsky model and the WALE (Wall Adapting Local Eddy-viscosity) model. Specifically, the most commonly used Smagorinsky model is as follows:

[0105]

[0106] In the above formula, C S is the model coefficient, usually 0.094, Δ is the length scale, S ij is the strain rate tensor. Usually, the turbulence model equations can be solved using the preconditioned bi-conjugate gradient method.

[0107] For three-dimensional channel turbulence, the present invention is used to simulate the flow, and the calculation domain is as follows: Figure 3 As shown in Figure 1, the x-direction (stream direction) and z-direction (span direction) are periodic boundary conditions, and the upper and lower walls are no-slip boundary conditions. The calculation parameters are shown in Table 1.

[0108] Table 1 Parameters of three-dimensional channel turbulence example

[0109]

[0110]

[0111] The results obtained by the present invention are shown in Figure 4 、 Figure 5 and Table 2. Figure 4 The instantaneous flow velocity distribution in the XY plane is given. The result is dimensionless based on the incoming flow velocity. The red area is the high-speed area in the center of the channel, and the blue area is the low-speed area near the wall. Figure 5 The velocity distribution results are given in the normal direction of the wall, and the horizontal axis is the dimensionless wall distance y based on the viscosity length. + , the vertical axis is the dimensionless velocity u based on the friction velocity + The gray dashed line is the zero-pressure gradient plate velocity type, the black solid line is the velocity type given by direct numerical simulation, and the red solid line with a circle is the velocity type obtained by the traditional method using the first layer of grid center velocity (i.e. Figure 3 The velocity type corresponding to the wall shear stress is calculated at point C1 in the figure. The blue solid line with square marks is the velocity type used in this invention. The velocity of the center of the nearby grid (i.e. Figure 3 C in h The velocity pattern corresponding to the wall shear stress is calculated.

[0112] Table 2 shows the results of the conventional method and the proposed method. The values ​​in the table are dimensionless values ​​based on the incoming flow density and velocity. Compared with the direct numerical simulation results, the conventional method underestimates the wall shear stress by 11%, while the proposed method has an error of less than 1%. These results demonstrate that the proposed method, which uses a height function to obtain wall shear stress based on flow field information at any position, can address the problem of underestimation when using the flow field information of the first layer of mesh.

[0113] Table 2 Wall friction results

[0114] method value Results of traditional methods 0.00162 Results of the method of the present invention 0.00183 Direct numerical simulation 0.00182

[0115] The present invention adopts process communication of height function and parallel computing, and can obtain wall shear stress based on flow field information at any position, solving the problem of low prediction results when obtaining wall shear stress using the first layer of grid flow field information, supporting parallel computing of the entire calculation process, and improving calculation accuracy and problem solving scale.

[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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parallel acquisition method for wall shear stress based on flow field information at any position, characterized in that: The following steps are involved: (1) Read parameter setting file Read the height function formula from the parameter setting file through the C++ language program : ； In the above formula, and To set parameters; the positive direction of the x-axis of the coordinate system points to the flow direction; x is the spatial coordinate; is the incoming flow velocity; is the fluid kinematic viscosity coefficient; is the unit vector in the x direction; (2) Determine the cell positions corresponding to the wall grid and count the number of cells in the same process and across processes; (3) Collection Group process and Variable information of group cross-process face-body relationships; (4) Calculation Group process and Group variables of cross-process face-body relationships and communicate; the specific process is: (4.1) In a process, calculation Variables for grouping process face-body relationships: 、 The specific process is: for all grid cells in the current process ( ) to traverse, when the space formed by the i-th unit contains the point season ; The wall distance between the Fth grid surface and the Cth grid unit for: ； In the above formula, 、 and are the x-coordinate, y-coordinate, and z-coordinate of the center of the F-th mesh face respectively; 、 and are the x-coordinate, y-coordinate, and z-coordinate of the center of the C-th grid cell; (4.2) In a process, calculation Variables for grouping 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, 、 and are the x-coordinate, y-coordinate and z-coordinate of the center of the F-th mesh face, 、 and are the unit vectors in the x, y and z directions respectively; point , meaning point is the center coordinate of the Fth mesh face and height function The vector sum of Process communication is accomplished using the MPI_Gather and MPI_Scatter functions of the internationally accepted MPI communication protocol. (4.3) Calculation Grouping mesh cells with cross-process face-volume relationships and the current process , the specific process is: for all processes ( ) is traversed, when the space composed of all grid cells of the jth process contains the point season ;right All grid cells in the process ( ) to traverse, when the space formed by the i-th unit contains the point season ; (4.4) In a process, calculation Variables for group cross-process face-body relationships , pass this information to the first The specific process is: The wall distance between the Fth grid surface and the Cth grid unit : ； In the above formula, 、 and are the coordinates of the center of the Fth mesh face respectively The x-, y-, and z-coordinates of 、 and are the x-coordinate, y-coordinate, and z-coordinate of the center of the C-th grid cell; (5) Update the velocity at the center of the mesh cell in the surface-body relationship; (6) Obtaining wall shear stress Based on mesh face numbering Corresponding wall distance and speed , to obtain the wall shear stress : ； In the above formula, and are the fluid dynamic viscosity coefficient and turbulent dynamic viscosity coefficient respectively; ； In the above formula, 、 and are vectors The x-, y-, and z-direction components of (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 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 and are the numbers of the processes to which the Fth grid surface and the Cth grid cell belong, respectively, and C is the number of the process containing the point The number of the grid cell in the current process; when When counting the total number of units in the current process ;when When counting the total number of units that are not in the current process, that is, The number of cross-process units for a process is ; Finally, the total number of cross-process units solved for all processes is : 。 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 (3) is as follows: (3.1) First define is the wall distance between the Fth grid surface and the Cth grid unit, is the velocity at the center of the Cth grid cell; Reallocate computer memory to store Variables for grouping process face-body relationships: 、 、 and ; F is the number of the grid surface in the current process; C is the number of the grid cell in the current process; (3.2) Allocate memory for storage Variables for grouping cross-process face-body relationships: 、 、 、 、 、 、 and .

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 (5) is as follows: ,when When Determine the corresponding grid cells in the surface-body relationship of the group , get the wall distance of the point and speed ;when When Determine the corresponding grid cells in the cross-process surface-body relationship , get the wall distance of the point , and update the velocity at the center of the mesh cell in the surface-body relationship .

5. 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 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 , advance the time and enter the step (5) until the simulation ends, and obtain the wall shear stress at all calculation moments.

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