CN113609599B - Wall surface distance effective unit calculation method for aircraft turbulence flow-around simulation - Google Patents

Wall surface distance effective unit calculation method for aircraft turbulence flow-around simulation Download PDF

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CN113609599B
CN113609599B CN202111173754.3A CN202111173754A CN113609599B CN 113609599 B CN113609599 B CN 113609599B CN 202111173754 A CN202111173754 A CN 202111173754A CN 113609599 B CN113609599 B CN 113609599B
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wall
unit
grid
wall surface
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CN113609599A (en
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蒋崇文
胡姝瑶
高振勋
许晨豪
李椿萱
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Beihang University
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Abstract

The invention discloses a method for calculating an effective wall space unit for turbulent flow and streaming simulation of an aircraft, which comprises the following steps of: reading and storing grid point coordinates and boundary conditions of the computational grid cells; preprocessing a wall surface unit; calculating the wall surface distance; and outputting the result. By the technical scheme, the calculation efficiency of the wall surface distance in large-scale dynamic grid turbulence simulation of the aircraft can be remarkably improved, so that the acceleration of the prediction of the unsteady aerodynamic characteristics of the aircraft is realized; the method has better applicability to complex shapes, the results are calculated based on geometric analysis relations, and numerical errors are not introduced; the wall surface units are stored in a more efficient and reasonable coding mode, and effective units are defined from two aspects of grid units to be calculated and wall surface units to be searched, so that the total calculation amount is obviously reduced.

Description

Wall surface distance effective unit calculation method for aircraft turbulence flow-around simulation
Technical Field
The invention belongs to the technical field of computational fluid mechanics, and particularly relates to a wall surface distance effective unit calculation method for aircraft turbulence flow-around simulation.
Background
Turbulence is the most common flow in aircraft bypass. The movement of the vortex generator is random and irregular, and the vortex generator has the characteristics of instability, nonlinearity, rich vortex structure, strong dissipation and the like. The main approaches of simulating the turbulent flow and the streaming flow field of an aircraft by using a computational fluid dynamics numerical value are a Reynolds average method (RANS) or a despun vortex simulation method (DES) at present and for decades in the future, which are limited by computer hardware technology. In both types of turbulence simulation methods, a parameter which is crucial to the simulation accuracy, namely the wall surface distance, exists, namely the minimum distance from the grid cell center to the surface of the aircraft is calculated.
Currently, the method for determining the wall distance mainly includes two categories, namely a search method and a differential equation solving method. Solving the differential equation method requires iterative solution of Eikonal equation or Hamilton-Jacobi equation, and the algorithm is complex to realize; for complex shapes, the solving efficiency and precision are difficult to guarantee. The simplest method in the search method is an exhaustive search method, namely, the distance of each flow field unit to all wall units is calculated, and the minimum value is taken as the distance from the unit to the wall. However, the exhaustive search method is inefficient, and is difficult to be applied to the large-scale dynamic grid numerical simulation which requires repeated calculation of wall surface distances, cannot be stored in advance, and requires computational efficiency.
For improving the efficiency of the search method, the search amount is mainly reduced by introducing an efficient search data structure and a wall surface element group. For example, the prior art proposes a wall distance calculation method called "circular box method" in which wall points are sorted by coordinates using an octree data structure, and grouping of wall elements is achieved by circularly bisecting circumscribed cuboids of the wall points. However, existing improvement methods are primarily from a geometric or computer perspective. From the viewpoint of computational fluid dynamics, the wall distance is only important in the near-wall turbulent flow region, and the variable does not influence the calculation at all in other regions. Obviously, if the method of calculating the wall-to-surface distances of all grid cells is still adopted at every physical moment in the large-scale dynamic grid numerical simulation, even if the most efficient search data structure and the point-to-surface distance calculation method are adopted, a large amount of invalid calculations still exist, and the calculation efficiency of the numerical simulation is seriously influenced.
Disclosure of Invention
In order to solve the problem of insufficient calculation efficiency of the wall space of the key parameter in the turbulence flow-around simulation of the aircraft, the invention provides a wall space effective unit calculation method for the turbulence flow-around simulation of the aircraft, and the specific technical scheme of the invention is as follows:
a wall-to-wall effective unit calculation method for aircraft turbulence bypass simulation comprises the following steps:
s1: reading and storing grid point coordinates and boundary conditions of the computational grid cells;
s2: preprocessing a wall surface unit;
s2-1: a collecting wall surface unit;
s2-2: determining the number of the external cuboids of the wall surface units: determining the number of wall surface units externally connected with cuboids used in the circulating box method according to the number of the calculated grid wall surface units, wherein the externally connected cuboids refer to the smallest cuboids containing the inner wall surface units;
s2-3: an initial external cuboid is established according to all the wall surface units, and information required to be recorded by the external cuboid comprises: the external rectangular body is connected with the Cartesian coordinate range, the number of the contained wall units and the serial numbers of the contained wall units;
s2-4: the external cuboid with the largest bisection wall surface point;
halving the external cuboid containing the most wall surface units into two external cuboids along the longest edge of the external cuboid, updating the information required to be recorded by the two external cuboids, and repeating the step S2-4 until the total number of the external cuboids reaches the number determined in the step S2-3;
s3: calculating the wall surface distance;
s4: and outputting the result.
Further, the step S2-1 includes the steps of:
s2-1-1: determining wall surface cells in the computational grid cells according to the boundary conditions read in the step S1;
s2-1-2: numbering the wall units and the wall points, and ensuring that the numbers of the wall units are consistent with the number of a certain vertex so as to search;
s2-1-3: respectively storing wall point coordinates according to the wall point number, storing the corresponding relation between a wall unit and the vertex thereof according to the wall unit number, and storing the number of the adjacent unit according to the wall unit number;
s2-1-4: traversing the wall units, and calculating and storing the unit normal of each wall unit.
Further, the step S3 includes the following steps:
s3-1: the wall surface distance returns to zero: distributing all spaces for calculating the storage wall-surface distances of the grid units, and assigning initial values of the spaces as 0; traversing all the calculation grid cells, and executing the step S3-2 on any cell;
s3-2: determining a wall surface distance calculation mode;
if the wall distances of the adjacent cells of the grid cells are smaller than the set threshold, accurately calculating the wall distances, and continuing to step S3-3;
if the wall space of the adjacent cell of the computational grid cell is larger than the set threshold, when the computational grid cell is positioned in the direction of reducing the wall space of the adjacent cell, accurately calculating the wall space, and continuing to step S3-3;
when the calculation grid cell is located in the increasing direction of the wall space of the adjacent cell, roughly estimating the wall space, and jumping to the step S3-5;
s3-3: searching 2 external cuboids with the nearest distance;
order tox i,cTo calculate the grid center coordinates of the grid cell,x i,min、x i,maxrespectively show an external rectangular parallelepipedx i The minimum value and the maximum value of the direction are calculated, and the distance from the grid unit to the external cuboid is calculatedd 0 Comprises the following steps:
Figure 872076DEST_PATH_IMAGE001
（1）
traversing all the external cuboids, screening out 2 external cuboids with the minimum distance according to the formula (1), and executing the step S3-4 on the 2 external cuboids;
s3-4: accurately calculating the wall surface distance;
s3-5: estimating wall face distance according to gradient: and calculating the gradient of the wall distance of the assigned adjacent unit by utilizing the unilateral difference, and estimating the wall distance of the current grid unit according to the gradient, the coordinate information of the current grid unit and the adjacent unit thereof.
Further, the step S3-4 includes the steps of:
according to the position information of the grid unit and the external cuboid, the method is divided into two conditions: when all grid points of the grid cells are positioned in the external rectangular parallelepiped, executing step S3-4-1; when the grid points which are not positioned in the circumscribed cuboid exist in the grid cell, executing step S3-4-2;
s3-4-1: traversing all wall surface units in the external cuboid, calculating the distance from the grid points of the current grid unit to the wall surface units one by one, and storing the minimum value;
s3-4-2: jump-accessing an external cuboid inner wall surface unit based on a vector method, optionally selecting a wall surface unit in the external cuboid, and calculating and storing the distance from the current grid unit to the external grid unit; calculating the projection direction of the vector of the face center of the wall unit pointing to the cell center of the current grid cell on the wall unit, wherein the next wall unit pointed by the projection direction is the next calculated wall unit; and jumping to access the current external cuboid inner wall surface unit until the projection direction points to the boundary of the current external cuboid.
The invention has the beneficial effects that:
1. the method for calculating the effective wall distance unit for the turbulent flow streaming simulation of the aircraft can obviously improve the calculation efficiency of the wall distance in the large-scale dynamic grid turbulent flow simulation of the aircraft, thereby realizing the acceleration of the prediction of the unsteady aerodynamic characteristics of the aircraft.
2. Compared with the existing wall space calculation method based on solving differential equations, the method has better applicability to complex shapes, the result is calculated based on the geometric analytic relationship, and numerical errors are not introduced.
3. Compared with the circulating box method in the existing search method, the invention adopts a more efficient and reasonable coding mode to store the wall surface units, and defines effective units from two aspects of the grid unit to be calculated and the wall surface unit to be searched, thereby obviously reducing the total calculation amount.
4. Compared with the prior art, the method can obviously reduce the total calculated amount of the wall-surface distance while ensuring the same accuracy of numerical simulation, thereby being beneficial to the improvement of the efficiency of predicting the unsteady aerodynamic characteristics of the complex aircraft;
in step S2-1, the invention is characterized in that the wall unit shares a number with a vertex thereof, and numbers the wall unit and the wall point, thereby ensuring high efficiency of accessing the wall unit according to the wall point;
in step S3-1, the invention discriminates the effective cells of the computational grid cells that need to compute the wall-to-surface distance accurately according to the influence of the wall-to-surface distance on the accuracy of the turbulence model equation: for the effective units, the wall surface distance is accurately solved by using a geometric relation; for the non-effective units, the wall surface distance is estimated by using the gradient;
in step S3-3, the present invention establishes a vector-based jump-type wall cell access method for the case where the computational mesh cells are not located in the circumscribed cuboid, thereby further reducing the number of wall cells accessed when accurately computing the wall distance.
Drawings
In order to illustrate embodiments of the present invention or technical solutions in the prior art more clearly, the drawings which are needed in the embodiments will be briefly described below, so that the features and advantages of the present invention can be understood more clearly by referring to the drawings, which are schematic and should not be construed as limiting the present invention in any way, and for a person skilled in the art, other drawings can be obtained on the basis of these drawings without any inventive effort. Wherein:
FIG. 1 is a flow chart of a wall-to-wall distance effective cell calculation method of the present invention;
FIG. 2 is a schematic diagram of the external cuboid generated when the RAE2822 airfoil wall pitch is calculated according to the invention;
FIG. 3 is a comparison of the results of the present invention and an exhaustive search method to calculate the M6 wing wall separation.
Detailed Description
In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. It should be noted that the embodiments of the present invention and features of the embodiments may be combined with each other without conflict.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and therefore the scope of the present invention is not limited by the specific embodiments disclosed below.
As shown in FIG. 1, the invention provides a wall-to-wall effective unit calculation method for aircraft turbulence bypass simulation, and the effective unit of the invention has two meanings: firstly, effective units in the wall units to be searched, namely the wall units of which the wall distances can be determined or determined in an auxiliary manner aiming at a certain computational grid unit; secondly, effective units in the grid units to be calculated are units with non-negligible influence on calculation accuracy by wall distance in numerical simulation. For the first type of effective units, the wall units are roughly screened by adopting a circulating box method, and then the wall units after rough screening are accessed in a jumping mode according to the close proximity relation of the wall units by establishing a vector method, so that the times of accessing the wall units are reduced. For the second type of effective units, by analyzing the influence range of the wall distance in the turbulence model equation, the wall distance calculation strategy of accurate calculation of the search method in the influence domain and gradient estimation outside the influence domain is realized.
Specifically, the method for calculating the effective wall-to-wall unit for the turbulence flow-around simulation of the aircraft comprises the following steps:
s1: reading and storing grid point coordinates and boundary conditions of the computational grid cells;
s2: preprocessing a wall surface unit;
s2-1: a collecting wall surface unit;
s2-1-1: determining wall surface cells in the computational grid cells according to the boundary conditions read in the step S1;
s2-1-2: the wall surface units and the wall surface points are numbered, so that the wall surface units and a top point which is not numbered are numbered by using the same number for convenience of searching, and the specific mode of selecting the top point is not limited;
s2-1-3: respectively storing wall point coordinates according to the wall point number, storing the corresponding relation between a wall unit and the vertex thereof according to the wall unit number, and storing the number of the adjacent unit according to the wall unit number;
s2-1-4: traversing the wall units, and calculating and storing the unit normal of each wall unit;
for the case of a two-dimensional situation,is provided with (x 1,y 1)、(x 2,y 2) Is 2 vertices of a wall cell, the unit normal of the wall cell is:
Figure 607951DEST_PATH_IMAGE002
（1）
for the three-dimensional case, let (x 1,y 1,z 1)、(x 2,y 2,z 2)、(x 3,y 3,z 3)、(x 4,y 4,z 4) The wall surface units are sequentially arranged with 4 vertexes, and the unit normal direction of the wall surface units is as follows:
q 1=(x 3-x 1 y 3-y 1 z 3-z 1)，q 2=(x 4-x 2 y 4-y 2 z 4-z 2)
Figure 134747DEST_PATH_IMAGE003
（2）
s2-2: determining the number of the cuboid externally connected with the wall surface unitN: determining the number of wall surface units externally connected with cuboids used in the circulating box method according to the number of the calculated grid wall surface units, wherein the externally connected cuboids refer to the smallest cuboids containing the inner wall surface units;
in some embodiments, grouped by 30 wall units, the computational efficiency is best. Therefore, the number of the external rectangular solids can be selectedN= wall unit total number/30]Wherein [.]Represents rounding to the whole.
S2-3: an initial external cuboid is established according to all the wall surface units, and information required to be recorded by the external cuboid comprises: the external rectangular body is connected with the Cartesian coordinate range, the number of the contained wall units and the serial number of the contained wall units.
S2-4: the external cuboid with the largest bisection wall surface point;
and halving the external cuboid containing the most wall surface units into two external cuboids along the longest edge of the external cuboid, updating the information required to be recorded by the two external cuboids, and repeating the step S2-4 until the total number of the external cuboids reaches the number determined in the step S2-3. Specifically, the method comprises the following steps:
firstly, traversing the existing external cuboid, and determining the external cuboid containing the most wall units according to the number of the wall units contained in the external cuboid;
secondly, determining the longest edge of the external cuboid according to the Cartesian coordinate range of the external cuboid; the direction of the longest side is the direction of dividing the external cuboid, and the midpoint of the direction coordinate range is the dividing coordinate;
and finally, grouping the wall surface units in the original external cuboid according to the segmentation direction and the coordinates thereof, and updating the information required to be stored by the two newly generated external cuboids.
Repeating the step S2-4 until the total number of the circumscribed cuboids reaches the number determined in the step S2-2N。
S3: calculating the wall surface distance;
s3-1: the wall surface distance returns to zero: distributing all spaces for calculating the storage wall-surface distances of the grid units, and assigning initial values of the spaces as 0; traversing all the calculation grid cells, and executing the step S3-2 on any cell;
s3-2: determining a wall surface distance calculation mode;
if the wall distances of the adjacent cells of the grid cells are smaller than the set threshold, accurately calculating the wall distances, and continuing to step S3-3;
if the wall space of the adjacent cell of the computational grid cell is larger than the set threshold, when the computational grid cell is positioned in the direction of reducing the wall space of the adjacent cell, accurately calculating the wall space, and continuing to step S3-3;
when the calculation grid cell is located in the increasing direction of the wall space of the adjacent cell, roughly estimating the wall space, and jumping to the step S3-5;
for example: analyzing the magnitude of the wall-to-surface distance term contained in the dimensionless S-A turbulence model shows that the influence of the wall-to-surface distance on the accuracy of the turbulence model equation is negligible when the dimensionless wall-to-surface distance is two magnitudes greater than the dimensionless voro mutex viscosity coefficient. Since the eddy viscosity coefficient takes 0.1 at the far field, the wall separation threshold may take 10.
And if the wall distances of the adjacent cells of the grid cells are all calculated to be less than 10, accurately calculating the wall distances, and continuing to the step S3-3. If the wall space of the adjacent cell of the computational grid cell is larger than 10, when the wall space of the adjacent cell of the computational grid cell is in the decreasing direction, the wall space is accurately computed, and the step S3-3 is continued; when the calculation grid cell is located in the increasing direction of the wall pitch of its immediate neighboring cell, the wall pitch is roughly estimated, and the process proceeds to step S3-5.
S3-3: searching 2 external cuboids with the nearest distance;
order tox i,cTo calculate the grid center coordinates of the grid cell,x i,min、x i,maxrespectively show an external rectangular parallelepipedx i The minimum value and the maximum value of the direction are calculated, and the distance from the grid unit to the external cuboid is calculatedd 0 Comprises the following steps:
Figure 69205DEST_PATH_IMAGE001
（3）
traversing all the external cuboids, screening out 2 external cuboids with the minimum distance according to the formula (1), and executing the step S3-4 on the 2 external cuboids;
s3-4: accurately calculating the wall surface distance;
according to the position information of the grid unit and the external cuboid, the method is divided into two conditions: when all grid points of the grid cells are positioned in the external rectangular parallelepiped, executing step S3-4-1; when the grid points not located within the circumscribed rectangular parallelepiped exist in the calculation grid cell, step S3-4-2 is performed.
S3-4-1: traversing all wall surface units in the external cuboid, calculating the distance from the grid points of the current grid unit to the wall surface units one by one, and storing the minimum value;
for the two-dimensional case: let the wall unit normal be: (n 1, n 2)，(x c, y c) Is the face center of the wall unit, and the coordinate of one point on the wall is (x 1, y 1) Then the straight line where the wall surface is located is:
n 1(x-x 1)+n 2(y-y 1)=0 （4）
the straight line passing through the center of the wall unit and perpendicular to the wall surface is as follows:
-n 2(x-x c)+n 1(y-y c)=0（5）
then, the projection points of the cell centers on the plane where the wall surface units are located are calculated as follows:
x 0= n 1 2 x 1 +n 2 2 x c+n 1 n 2 (y 1-y c)
y 0= n 1 2 y c +n 2 2 y 1+n 1 n 2 (x 1-x c) （6）
according to projection points (x 0, y 0) Vectors pointing to two wall points of the wall unit can judge whether the projection point is in the wall unit; if the cell is in the wall surface unit, the inner product of the two vectors is negative, and the distance between the wall surface and the cell center of the calculation cell to the wall surface unit is the distance; if not, the inner product of the two vectors is positive, and the wall distance is the distance from the center of the calculation cell to the top of the wall cell.
Calculating the distance from the cell center of the grid cell to the wall cell as
d w=|n 1(x c-x 1)+n 2(y c-y 1)|（7）
Calculating the distance from the center of the grid cell to the wall surface point as
Figure 531410DEST_PATH_IMAGE004
（8）
For the three-dimensional case: let the grid center coordinate of the cell to be solved be (x c,y c,z c) The unit normal direction of the wall surface unit is (n 1,n 2,n 3) The coordinates of a point on the wall are (x 1,y 1,z 1) Then, the plane of the wall unit is:
n 1 x+n 2 y+n 3z=D
D=n 1 x 1 +n 2 y 1 +n 3z1（9）
let the projection of the grid center coordinates on the plane where the wall surface unit is located be (x 0, y 0, z 0) Then the projection point satisfies the plane equation:
n 1 x 0 +n 2 y 0 +n 3z0= D（10）
the direction of the projection point pointing to the center of the calculation cell is the normal direction of the wall surface cell, then
Figure 128483DEST_PATH_IMAGE005
（11）
The proxel coordinates are then:
x 0= x c+n 1[D–(n 1 x c +n 2 y c +n 3zc)]（12）
y 0= y c+n 2[D–(n 1 x c +n 2 y c +n 3zc)]
z 0= z c+n 3[D-(n 1 x c +n 2 y c +n 3zc)]
if the cross product of the vectors of the vertex pointing to the projection point and the next wall surface point of all the wall surface units is the same as the sign, the projection point is in the wall surface unit, and the wall surface distance is the distance from the cell center of the calculation unit to the wall surface unit; if not, the wall distance is the distance from the center of the calculation cell to the cell vertex of the wall.
S3-4-2: jump-accessing an external cuboid inner wall surface unit based on a vector method, optionally selecting a wall surface unit in the external cuboid, and calculating and storing the distance from the current grid unit to the external grid unit; calculating the projection direction of the vector of the face center of the wall unit pointing to the cell center of the current grid cell on the wall unit, wherein the next wall unit pointed by the projection direction is the next calculated wall unit; and jumping to access the current external cuboid inner wall surface unit until the projection direction points to the boundary of the current external cuboid.
S3-5: estimating wall face distance according to gradient: and calculating the gradient of the wall distance of the assigned adjacent unit by utilizing the unilateral difference, and estimating the wall distance of the current grid unit according to the gradient, the coordinate information of the current grid unit and the adjacent unit thereof.
S4: and outputting the result.
For the convenience of understanding the above technical aspects of the present invention, the following detailed description will be given of the above technical aspects of the present invention by way of specific examples.
Example 1
In the embodiment, an RAE2822 airfoil is calculated, wherein FIG. 2 illustrates a generation process of a circumscribed cuboid when calculating a wall surface distance of a RAE2822 airfoil problem; in the figure, "■" marks the wall element, the numberThe number of wall surface units contained in the circumscribed cuboid. The rectangle in the upper left drawing, i.e. the undivided drawing, is the initial circumscribed cuboid, and comprises 304 wall units. According to the step S2-2,N10 times of cutting are needed. The finally generated 10 circumscribed cuboids are shown in the lowest diagram of fig. 2.
Example 2
In this embodiment, an M6 wing is calculated, fig. 3 compares the wall distance of the M6 wing determined by the present invention and an exhaustive search method, wherein a cloud chart is the result of the present invention, and a contour line is the result of the exhaustive search method. In fig. 3, the cloud images of different sections are completely overlapped with the contour line, so that the wall distance result calculated by the method is correct and reliable. For the calculation efficiency, 215.2s is consumed for calculating the wall space of 29.5 ten thousand grid units by an exhaustive search method, only 3.7s is required for calculating the same grid, and the consumed time is shortened by 98.3%.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (3)

1. A wall-to-effective unit calculation method for aircraft turbulence bypass simulation is characterized by comprising the following steps:
s1: reading and storing grid point coordinates and boundary conditions of the computational grid cells;
s2: preprocessing a wall surface unit;
s2-1: a collecting wall surface unit;
s2-2: determining the number of the external cuboids of the wall surface units: determining the number of wall surface units externally connected with cuboids used in the circulating box method according to the number of the calculated grid wall surface units, wherein the externally connected cuboids refer to the smallest cuboids containing the inner wall surface units;
s2-3: an initial external cuboid is established according to all the wall surface units, and information required to be recorded by the external cuboid comprises: the external rectangular body is connected with the Cartesian coordinate range, the number of the contained wall units and the serial numbers of the contained wall units;
s2-4: the external cuboid with the largest bisection wall surface point;
halving the external cuboid containing the most wall surface units into two external cuboids along the longest edge of the external cuboid, updating the information required to be recorded by the two external cuboids, and repeating the step S2-4 until the total number of the external cuboids reaches the number determined in the step S2-3;
s3: calculating the wall surface distance;
s3-1: the wall surface distance returns to zero: distributing all spaces for calculating the storage wall-surface distances of the grid units, and assigning initial values of the spaces as 0; traversing all the calculation grid cells, and executing the step S3-2 on any cell;
s3-2: determining a wall surface distance calculation mode;
if the wall distances of the adjacent cells of the grid cells are smaller than the set threshold, accurately calculating the wall distances, and continuing to step S3-3;
if the wall space of the adjacent cell of the computational grid cell is larger than the set threshold, when the computational grid cell is positioned in the direction of reducing the wall space of the adjacent cell, accurately calculating the wall space, and continuing to step S3-3;
when the calculation grid cell is located in the increasing direction of the wall space of the adjacent cell, roughly estimating the wall space, and jumping to the step S3-5;
s3-3: searching 2 external cuboids with the nearest distance;
order tox i,cTo calculate the grid center coordinates of the grid cell,x i,min、x i,maxrespectively show an external rectangular parallelepipedx i The minimum value and the maximum value of the direction are calculated, and the distance from the grid unit to the external cuboid is calculatedd 0 Comprises the following steps:
Figure 921704DEST_PATH_IMAGE001
（1）
traversing all the external cuboids, screening out 2 external cuboids with the minimum distance according to the formula (1), and executing the step S3-4 on the 2 external cuboids;
s3-4: accurately calculating the wall surface distance;
s3-5: estimating wall face distance according to gradient: calculating the gradient of the wall distance of the assigned adjacent unit by utilizing the unilateral difference, and estimating the wall distance of the current grid unit according to the gradient, the coordinate information of the current grid unit and the adjacent unit thereof;
s4: and outputting the result.
2. The method for calculating the wall-to-active cell of the aircraft turbulent flow bypass simulation according to claim 1, wherein the step S2-1 comprises the following steps:
s2-1-1: determining wall surface cells in the computational grid cells according to the boundary conditions read in the step S1;
s2-1-2: numbering the wall units and the wall points, and ensuring that the number of the wall unit and a vertex which is not numbered use the same number for searching;
s2-1-3: respectively storing wall point coordinates according to the wall point number, storing the corresponding relation between a wall unit and the vertex thereof according to the wall unit number, and storing the number of the adjacent unit according to the wall unit number;
s2-1-4: traversing the wall units, and calculating and storing the unit normal of each wall unit.
3. The method for calculating the wall-to-active cell of the aircraft turbulent flow bypass simulation according to claim 1, wherein the step S3-4 comprises the following steps:
according to the position information of the grid unit and the external cuboid, the method is divided into two conditions: when all grid points of the grid cells are positioned in the external rectangular parallelepiped, executing step S3-4-1; when the grid points which are not positioned in the circumscribed cuboid exist in the grid cell, executing step S3-4-2;
s3-4-1: traversing all wall surface units in the external cuboid, calculating the distance from the grid points of the current grid unit to the wall surface units one by one, and storing the minimum value;
s3-4-2: jump-accessing an external cuboid inner wall surface unit based on a vector method, optionally selecting a wall surface unit in the external cuboid, and calculating and storing the distance from the current grid unit to the external grid unit; calculating the projection direction of the vector of the face center of the wall unit pointing to the cell center of the current grid cell on the wall unit, wherein the next wall unit pointed by the projection direction is the next calculated wall unit; and jumping to access the current external cuboid inner wall surface unit until the projection direction points to the boundary of the current external cuboid.
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