CN112016165A - Method and device for processing helicopter flow field data - Google Patents

Method and device for processing helicopter flow field data Download PDF

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CN112016165A
CN112016165A CN202010946331.XA CN202010946331A CN112016165A CN 112016165 A CN112016165 A CN 112016165A CN 202010946331 A CN202010946331 A CN 202010946331A CN 112016165 A CN112016165 A CN 112016165A
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张居晖
陈仁良
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Nanjing University of Aeronautics and Astronautics
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Abstract

The embodiment of the invention discloses a method and a device for processing helicopter flow field data, relates to the technical field of design of a rotor craft, and can reduce numerical dissipation in a transportation process of rotor tip vortex caused by a traditional second-order JST format and achieve higher capturing precision of flow details such as tip vortex. The invention comprises the following steps: generating a Cartesian background grid and a skin non-structural grid, and acquiring grid data information; by utilizing the grid data information, searching the serial number of the unit where the fictitious node required for constructing the seven-order WENO format corresponding to each interface is located in advance on a Cartesian background grid and storing the serial number; acquiring left and right state values on unit interfaces, solving a circulation value to generate a Cartesian background grid and a skin non-structural grid, acquiring grid data information, searching unit serial numbers of fictional nodes required for constructing a seven-order WENO format corresponding to each interface in advance and storing the unit serial numbers by utilizing the grid data information on the Cartesian background grid, acquiring left and right state values on the unit interfaces and solving the circulation value; carrying out iterative processing on the flux in the flow field by using the acquired convection flux on the cell interface, and converging the processing result; and outputting the processing result to display equipment. The method is suitable for processing the flow field data such as the blade tip vortex and the like.

Description

Method and device for processing helicopter flow field data
Technical Field
The invention relates to a design technology of a rotor craft, in particular to a method and a device for processing flow field data of a helicopter.
Background
A helicopter is an aviation aircraft with a rotor as a main lift source, and is widely applied to various fields of military use and civil use. The development of the new era requires helicopters to have high speed, long range, low noise and low vibration characteristics, which the aerodynamic characteristics of the rotor have a minor effect on. Therefore, the study of the aerodynamic characteristics of the rotor is very important for the development of helicopters.
As computer performance has improved, rotor flow fields and aerodynamic characteristics can be analyzed using Computational Fluid Dynamics (CFD) methods. The rotor CFD technology has the advantages of low cost and less time consumption, and can effectively reduce the research and development cost and shorten the research and development period. The second-order Jameson central difference scheme (JST) is a common space discrete method at present, has the advantages of simple programming, high calculation efficiency, good format robustness and the like in practical application, and is widely applied to various domestic laboratories at present.
However, JST requires the addition of artificial dissipation terms in the application, which requires additional computation and has low precision at discontinuities and boundaries. And the flow details such as the blade tip vortex and the like are poor in capturing capability due to the severe numerical dissipation of the blade tip vortex in the transportation process, so that the capturing capability of the flow details is poor when the JST scheme is adopted to process the flow field data such as the blade tip vortex and the like. This problem severely affects the efficiency and difficulty of research and development of rotorcraft.
Disclosure of Invention
The embodiment of the invention provides a method and a device for processing helicopter flow field data, which can reduce numerical value dissipation in the transportation process of rotor blade tip vortex caused by the traditional second-order JST format and have higher capturing precision on flow details such as blade tip vortex and the like.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a method, including:
s1, generating a Cartesian background grid and a skin non-structural grid, and acquiring grid data information;
s2, using grid data information to search and store the serial number of the unit where the fictitious node corresponding to each interface and required for constructing the seven-order WENO format is located on the Cartesian background grid in advance;
s3, acquiring left and right state values on a cell interface by using the searched cell serial number and solving a convection current value;
s4, carrying out iterative processing on the flux in the flow field by using the acquired flux on the cell interface, and converging the processing result;
and S5, outputting the processing result to a display device.
Obtaining a convective flux at the cell interface, comprising: performing piecewise linear reconstruction on the skin non-structural grid, and then acquiring flow variable values on the left side and the right side of a cell interface; and acquiring the convection flux on the unit interface according to the left and right state values on the unit interface.
In a second aspect, an embodiment of the present invention provides an apparatus, including:
the preprocessing module is used for generating a Cartesian background grid and a skin non-structural grid and acquiring grid data information;
the processing module is used for searching and storing the serial number of the unit where the fictitious node required for constructing the seven-order WENO format corresponding to each interface is located in advance on the Cartesian background grid by utilizing grid data information; then, acquiring left and right state values on a cell interface by using the searched cell serial number, and solving a convection current value;
the iterative convergence module is used for carrying out iterative processing on the flux in the flow field by using the acquired convection flux on the cell interface and converging a processing result;
and the output module is used for outputting the processing result to the display equipment.
The processing module is specifically used for performing piecewise linear reconstruction on the skin non-structural grid and then acquiring flow variable values on the left side and the right side of a unit interface; and acquiring the convection flux on the unit interface according to the left and right state values on the unit interface.
The method and the device for processing the flow field data of the helicopter provided by the embodiment of the invention adopt the non-structural motion nested grid technology to generate a grid system surrounding a rotor wing, a fuselage and the like of the helicopter; calculating the convection flux by adopting WENO-piecewise linear format through space dispersion, wherein the seven-order Roe-WENO format is adopted on a Cartesian background grid, and the Roe-piecewise linear format is adopted on a skin unstructured grid; and time dispersion adopts an efficient double-time implicit LU-SGS method to carry out time advancing. The invention designs a high-precision CFD method suitable for helicopter flow field simulation by combining the characteristics of a helicopter, can effectively reduce numerical value dissipation in the transportation process of rotor tip vortex caused by the traditional second-order JST format, has higher capturing precision of the flow details such as the tip vortex and the like, and can be used for calculating the rotor flow field and the whole-aircraft flow field of the helicopter.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of interpolation of left state values of a seven-order WENO format interface according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a piecewise linear reconstruction provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram comparing the capturing effect of the vortex amount of the rotor provided by the embodiment of the present invention, mainly illustrating the length of the tip vortex of the rotor;
FIGS. 4 and 5 are graphs comparing the vorticity contour lines with the vorticity strength values of 300 and 600 for the sections with the azimuth angles of 0 ° and 90 ° under the same grid and calculation conditions, mainly illustrating the length of the blade tip vortex;
FIG. 6 is a schematic diagram illustrating a comparison of the cross-sectional pressure coefficient distribution of a C-T rotor with experimental values provided by an embodiment of the present invention;
fig. 7 is a schematic diagram illustrating a comparison between a cross-sectional pressure coefficient distribution and an experimental value of a heliscape 7A rotor according to an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating a comparison between the distribution of the coefficient of fuselage skin pressure and experimental values provided by an embodiment of the present invention;
fig. 9 is a schematic diagram of a method flow provided by the embodiment of the invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As computer performance has improved, rotor flow fields and aerodynamic characteristics can be analyzed using Computational Fluid Dynamics (CFD) methods. The rotor CFD technology has the advantages of low cost and less time consumption, and can effectively reduce the research and development cost and shorten the research and development period. The second-order Jameson central difference scheme (JST) is a common space discrete method at present, has the advantages of simple programming, high calculation efficiency, good format robustness and the like in practical application, and is widely applied to various domestic laboratories at present. Jameson center format (JST) has second-order precision, but because the center format does not contain dissipation terms, numerical errors cannot be attenuated, in order to avoid numerical value oscillation possibly existing in the final solution and ensure the convergence of the format, artificial dissipation terms need to be added into the format, extra calculation amount needs to be added, and the precision of the Jameson center format at the discontinuity and the boundary is low. Just because the Jameson central format is added with an artificial dissipation item, when numerical simulation is carried out on a rotor vortex field, a rotor blade tip vortex can generate serious numerical dissipation in the transportation process, and the simulation is not accurate enough when shock waves and other contact discontinuity phenomena on blades are simulated, so that the numerical simulation and aerodynamic performance calculation of the rotor vortex field are greatly influenced. The numerical simulation of the Caradona-Tung rotor hovering flow field is carried out by using JST (Java Server transform) format based on the unstructured grid, the calculation result is well matched with the experimental data, but the severe numerical dissipation of the rotor blade tip vortex in the transportation process can occur under the condition that the Cartesian background grid is not subjected to self-adaptive encryption, and the capturing capability of the flow details such as the blade tip vortex is poor.
The design of the embodiment aims to alleviate the problem of numerical dissipation caused by the conventional second-order JST format, and specifically provides a helicopter flow field high-precision numerical simulation method based on the WENO-piecewise linear format, so that the capturing capability of flow details such as vortexes can be effectively improved.
The method for processing helicopter flow field data, as shown in fig. 9, provided by the embodiment includes:
and S1, generating a Cartesian background grid and a skin non-structural grid, and acquiring grid data information.
The "mesh" described in this embodiment is specifically divided into a structural mesh and an unstructured mesh, where the skin unstructured mesh refers to an unstructured mesh including an object plane.
And S2, searching and storing the serial numbers of the cells where the fictitious nodes required by the seven-order WENO format are located on the Cartesian background grid in advance by utilizing the grid data information.
Wherein, the background grid refers to a grid containing the entire calculation area without an object plane. The cell number refers to the number corresponding to the cell, and the unstructured mesh traverses all the mesh cells with the cell number.
And S3, acquiring left and right state values on the cell interface by using the searched cell serial number, and solving the convection current value.
And S4, utilizing the acquired convection flux on the unit interface to carry out iterative processing on the flux in the flow field, and converging the processing result.
And S5, outputting the processing result to a display device.
In order to reduce the numerical dissipation caused by the conventional second-order JST format, the embodiment provides a helicopter flow field high-precision numerical simulation method based on the WENO-piecewise linear format, which can effectively improve the capturing capability of flow details such as vortexes. Specifically, the Roe format can be used to solve the convection flux on the interface. Calculating the convection flux at the cell interface using the Roe format requires the use of flow variable values to the left and right of the interface. The simplest method is to replace the flow variable values on the left and right sides with the flow variable values at the cell centers on both sides of the interface, but this is only a first order of accuracy. To further improve the calculation accuracy of the flow field, a high-accuracy interpolation format is usually employed to reconstruct the flow variable values on both sides of the interface. In this embodiment, a seven-order WENO format is adopted on a cartesian background grid, and the flow variable values on the left and right sides of the interface are calculated on a skin unstructured grid by using a piecewise linear reconstruction method. The constructed WENO-piecewise linear format can effectively reduce numerical dissipation in the transportation process of rotor blade tip vortexes, and has strong capturing capability on flow details such as vortexes.
The high-precision CFD method based on WENO-piecewise linear format and suitable for helicopter flow field simulation is provided by the embodiment and aims at the unstructured grid center format. Generating a grid system surrounding a rotor wing, a fuselage and the like of the helicopter by adopting a non-structural motion nested grid technology; selecting a Navier-Stokes equation from the master control equation; calculating the convection flux by adopting WENO-piecewise linear format in space dispersion, wherein the seven-order Roe-WENO format is adopted on a Cartesian background grid, and the Roe-piecewise linear format is adopted on a skin unstructured grid; and time dispersion adopts an efficient double-time implicit LU-SGS method to carry out time advancing. The invention designs a high-precision CFD method suitable for helicopter flow field simulation by combining the characteristics of a helicopter, can effectively reduce numerical value dissipation in the transportation process of rotor tip vortex caused by the traditional second-order JST format, has higher capturing precision of the flow details such as the tip vortex and the like, and can be used for calculating the rotor flow field and the whole-aircraft flow field of the helicopter.
Specifically, the acquiring the convection flux on the interface of the unit includes: and performing piecewise linear reconstruction on the skin non-structural grid, and then acquiring the flow variable values of the left side and the right side of the cell interface. And acquiring the convection flux on the unit interface according to the left and right state values on the unit interface. For example: and (4) interpolating the flow variable values at the left and right cell centers of the interface to obtain left and right state values at the face center of the interface. After the gradients of the original variables at the centers of all the cells are calculated by utilizing a Green-Gaussian method, the left and right state values of each interface can be obtained through interpolation. In general, the Roe format can be used to obtain the convective flux at the cell interface and record the values of flow variables on the left and right sides of the cell interface. The simplest method is to replace the flow variable values on the left and right sides with the flow variable values at the cell centers on both sides of the interface, but this is only a first order of accuracy. To further improve the calculation accuracy of the flow field, a high-accuracy interpolation format is usually employed to reconstruct the flow variable values on both sides of the interface. In this embodiment, a seven-order WENO format is adopted on the cartesian background grid, and the flow variable values on the left and right sides of the interface are calculated on the skin unstructured grid by using a piecewise linear reconstruction method.
Further, in the piecewise linear reconstruction of this embodiment, the left and right state values are solved by the piecewise linear reconstruction on the surface-mounted unstructured grid, and the left and right state values at the interface surface center are obtained by interpolating the flow variable values at the left and right cell centers of the interface. After the gradients of the original variables at the centers of all the cells are calculated by utilizing a Green-Gaussian method, the left and right state values of each interface can be obtained through interpolation. The schematic diagram of piecewise linear reconstruction interpolation is shown in fig. 2, where points I, J are cell I, J grid centers.
The performing piecewise linear reconstruction on the skin unstructured grid comprises: the piecewise linear reconstruction of the skin unstructured grid is as follows:
Figure BDA0002675403730000081
Figure BDA0002675403730000082
wherein, ULAnd URRespectively representing the values of flow variables on the left and right sides of the cell interface, I, J being the reference numerals of the cell and being positive integers, UI,UJThe values of the flow variables for units I, J,
Figure BDA0002675403730000083
gradient of flow variable, Ψ, for units I, J, respectivelyI,ΨJIs a limiter used to avoid oscillations in large gradient regions, rL，rRCalculation parameters respectively representing the left and right sides of the cell interface for participating in ULAnd URWherein the limiter may be a computing process implemented by a computer program, such as a script running a limiting function.
Specifically, the restriction function in the limiter includes:
Figure BDA0002675403730000084
wherein, the points I, J are the cell centers of the units I, J,
Figure BDA0002675403730000085
respectively, the vector, U, pointing from the center of the unit I, J grid to the center of the interfacemaxRepresents the maximum value, U, of the values of the flow variables in unit I and all the adjacent units of unit IminRepresents the minimum value, Δ, of the flow variable values in unit I and all the adjacent units of unit I2Representing the difference between the value of the flow variable at the interface and the value of the flow variable at the cell center, a parameter2Is a small quantity related to the grid scale, which here is understood to be a value in the order of 10e-6, for controlling the size of the limiter, the convection flux calculated in this way having a second order accuracy.
Δ1,max＝Umax-Ui,Δ1,min＝Umin-Ui. To ΨJExpression of (c) and ΨISimilarly. Wherein, Deltal，minAnd Δl，maxTwo intermediate variables are respectively, and Ui refers to the variable value of the flow field of the unit serial number i.
In this embodiment, the values of the flow variables on the left and right sides of the interface of the obtaining unit are: and acquiring the flow variable values of the left side and the right side of the interface of the unit through a seven-order WENO format. Specifically, the seventh-order WENO format of the present embodiment can be understood as: the left and right state values on the interface are calculated in a seven-order WENO format on a Cartesian background grid. The interpolation diagram of the seven-order WENO format is shown in FIG. 1, and a point I and a point J are the grid centers of a left unit I and a right unit J of an interface to be interpolated respectively.
Firstly, obtaining the reconstruction templates of the unit interface, four reconstruction templates m1,m2,m3,m4The expression of (a) is as follows:
Figure BDA0002675403730000091
i ', i ", i '", j ', j ", j '" are imaginary nodes which are all on the extension line of the points i and j and satisfy that the direct distances between two adjacent points are equal, i ' "i" j "m1,m2,m3,m4The four reconstruction templates respectively represent left state values on the cell interface, and the weighted reconstruction formula of the left state values is as follows:
Figure BDA0002675403730000092
wherein the nonlinear weighting coefficient w1To w4All are weight coefficients, and the solving method is as follows:
Figure BDA0002675403730000093
Figure BDA0002675403730000094
represents the left state value of the interface of cell I and J.
The weight coefficients adopted are respectively
Figure BDA0002675403730000095
The small amount introduced for preventing the denominator from being 0 can be 1.0-6,ISkThe smoothness metric coefficient of the kth template is specifically expressed as:
IS1＝Ui”'(547Ui”'-3882Ui”+462Ui'-1854Ui)+Ui”(7043Ui”+17246Ui'+7042Ui)+Ui'(11003Ui'-9402Ui)+2107Ui 2
Figure BDA0002675403730000096
Figure BDA0002675403730000097
Figure BDA0002675403730000098
Figure BDA0002675403730000101
Figure BDA0002675403730000102
Figure BDA0002675403730000103
Figure BDA0002675403730000104
wherein the parameter U with lower right corner mark represents the value of the flow variable on each imaginary node, and the parameters in the corner marks i, i ', j' etc. represent the specific number of the imaginary node in the interface IJ, such as UiRepresenting the value of the flow variable at imaginary node i. And the expression of these numbers is not limited in this embodiment.
Further, the method for obtaining the right state value of the interface IJ is the same as the above, and can be calculated according to the symmetry.
The flow field control model in this embodiment may adopt Navier-Stokes as follows:
Figure BDA0002675403730000105
where t is time, Ω represents the volume of the control unit, W is a conservative variable, FcFor convection flux, FvFor the sticky term, Q is the source term, here taken to be 0. W, Fc，FvAre respectively represented as
Figure BDA0002675403730000106
Wherein rho, E and H are density, total energy per unit mass and total enthalpy per unit mass respectively; u, v, w are the velocity components in x, y, z, respectively; vrIs the normal velocity of the fluid relative to the interface; n isx，ny，nzThe components of unit normal vectors of the interface in the x, y and z directions respectively; vtThe inversion speed is adopted; τ represents the viscous tensor component; Θ represents the combined term of viscous stress work and fluid thermal conduction.
The Roe format on the motion grid is used in this embodiment to calculate the convection flux. The solution to the N-S equation is based on a lattice-centered format, and the flux values at the interface of cell I and cell J are given by
Figure BDA0002675403730000111
Wherein:
Figure BDA0002675403730000112
Figure BDA0002675403730000113
subscript IJ denotes the interface of cell I and cell J. L and R are respectively the left side and the right side of the unit interface. Further, the mean value of Roe is defined as follows
Figure BDA0002675403730000114
Figure BDA0002675403730000115
Figure BDA0002675403730000116
Figure BDA0002675403730000117
Figure BDA0002675403730000118
Figure BDA0002675403730000119
Figure BDA00026754037300001110
Figure BDA00026754037300001111
Defining: Δ (·) ═ (·)R-(·)L. In the formula (I), the compound is shown in the specification,
Figure BDA00026754037300001112
the average value of the density Roe is,
Figure BDA00026754037300001113
are the Roe averages of the velocity components in the x, y, z directions, respectively,
Figure BDA00026754037300001114
is the Roe average of the local speed of sound,
Figure BDA00026754037300001115
the average value of the speed Roe is,
Figure BDA0002675403730000121
is the mean value of the velocity squared Roe
Figure BDA0002675403730000122
Figure BDA0002675403730000123
Figure BDA0002675403730000124
Figure BDA0002675403730000125
Since the sound velocity point cannot be identified in the original format, in order to solve this problem, the eigenvalue | Λ is modified in this embodimentcThe | is modified to the following model:
Figure BDA0002675403730000126
taken as 1/10 at the local speed of sound.
The time dispersion in this embodiment is performed by three-point backward difference:
Figure BDA0002675403730000127
where Δ t represents the real time step and R represents the sum of the fluxes on the surface of the control unit; l is the number of time steps.
The time discrete iteration method adopts a double-time implicit LU-SGS method to realize time advance. The implicit LU-SGS method is widely applied to time-marching iterations due to low numerical complexity and appropriate computational resource requirements. Two sweeps forward and backward are required to be implemented in the LU-SGS iterative method.
Figure BDA0002675403730000131
Figure BDA0002675403730000132
Wherein U (i), L (i) respectively represent the upper of the unit i, the adjacent unit in the lower matrix, Delta SijIndicating the area of the interface of cell i and cell j,
Figure BDA0002675403730000133
is an identity matrix, and Δ τ is a pseudo time step
Figure BDA0002675403730000134
Figure BDA0002675403730000135
Figure BDA0002675403730000136
Figure BDA0002675403730000137
The following can be verified by calculation: two rotors with different shapes are selected as examples to verify the effectiveness of the calculation method on the rotor flow field. Example calculation states are shown in table 1, both examples being hover states.
TABLE 1 rotor hover State example calculation of State parameters
Figure BDA0002675403730000138
Specifically, fig. 6 shows the comparison between the calculation results of example 1 and the experimental data, and fig. 7 shows the comparison between the calculation results of example 2 and the experimental data. The abscissa x/c represents the ratio of the distance to the blade leading edge to the chord length and the ordinate Cp represents the pressure coefficient. It can be seen from the comparison of fig. 6 and 7 that both the calculated results and the experimental values are well matched.
A Robin rotor/airframe combined model example is selected to verify the effectiveness of the method in calculating the aerodynamic interference of the helicopter rotor/airframe. The Robin rotor/fuselage combination model comprises four blades and a fuselage, wherein the length of the fuselage is 3.148M, the radius of the rotor is 1.574M, the chord length is 0.108M, the airfoil is NASA RC-10- (B) M002, the aircraft has no tip, the negative torque is 8 degrees, the forward inclination angle of a rotor shaft is 2 degrees, the rotating speed of the rotor is 1200r/min, the rotor rotates rightly, and the rotating center of the rotor is 0.431276M away from a fuselage reference line. Rotor calculated state parameters are shown in table 2.
TABLE 2 Robin rotor/fuselage combination model rotor calculation state parameters
Fig. 8 shows the comparison of the calculated fuselage surface pressure coefficient distribution with the experimental values, and it can be seen from the comparison that the present invention can effectively calculate the rotor/fuselage aerodynamic interference. The abscissa y/R represents the ratio of the y-direction coordinate to the rotor radius R and the ordinate Cp represents the pressure coefficient.
The following experimental tests show the advantages of the embodiment: the exemplary rotor was a Caradonna & Tung rotor, with a calculated state tip mach number of 0.877, a pitch of 8 °, and a background grid number of about 70 ten thousand. Fig. 3 shows the vorticity capture contrast at isocontour intensity values (300) under the same grid and computational conditions, with the WENO-piecewise linear format capable of capturing about 500 ° tip vortices, whereas the JST format is only capable of capturing about 240 ° tip vortices. From this result, it can be seen that the WENO-piecewise linear format has higher accuracy of blade tip vortex capture than the JST format.
FIGS. 4 and 5 show the same grid and calculated vorticity contour comparisons for vortex intensity values of 300-600 for 0 and 90 azimuthal sections. As can be seen from the figure, under the 0-degree azimuth section, the JST format can only capture 1 vortex with stronger intensity, and the WENO-piecewise linear format can capture 2 vortexes with stronger intensity; under the 90-degree azimuth section, only 1 strong vortex is captured by the JST format, and 2 strong vortices and 1 weak vortex can be captured by the WENO-piecewise linear format. From the above results, it can be seen that the WENO-piecewise linear format is more computationally efficient in capturing and vortex intensity of the blade tip vortex than the JST format.
In this embodiment, a device for processing helicopter flow field data is further provided, including:
and the preprocessing module is used for generating a Cartesian background grid and a skin non-structural grid and acquiring grid data information.
And the processing module is used for searching and storing the serial number of the unit where the fictitious node required for constructing the seven-order WENO format corresponding to each interface is located in advance on the Cartesian background grid by utilizing the grid data information. And then, acquiring left and right state values on a unit interface by using the unit serial number obtained by searching, and solving the convection current value.
And the iterative convergence module is used for performing iterative processing on the flux in the flow field by using the acquired flux on the cell interface and converging the processing result.
And the output module is used for outputting the processing result to the display equipment.
Specifically, the processing module is specifically configured to perform piecewise linear reconstruction on the skin unstructured grid, and then obtain values of flow variables on left and right sides of the cell interface. And acquiring the convection flux on the unit interface according to the left and right state values on the unit interface.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the apparatus embodiment, since it is substantially similar to the method embodiment, it is relatively simple to describe, and reference may be made to some descriptions of the method embodiment for relevant points. The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. A method of processing helicopter flow field data, comprising:
s1, generating a Cartesian background grid and a skin non-structural grid, and acquiring grid data information;
s2, using grid data information to search and store the serial number of the unit where the fictitious node corresponding to each interface and required for constructing the seven-order WENO format is located on the Cartesian background grid in advance;
s3, acquiring left and right state values on a cell interface by using the searched cell serial number and solving a convection current value;
s4, carrying out iterative processing on the flux in the flow field by using the acquired flux on the cell interface, and converging the processing result;
and S5, outputting the processing result to a display device.
2. The method of claim 1, wherein said obtaining a convective flux at a cell interface comprises:
performing piecewise linear reconstruction on the skin non-structural grid, and then acquiring flow variable values on the left side and the right side of a cell interface;
and acquiring the convection flux on the unit interface according to the left and right state values on the unit interface.
3. The method according to claim 1 or 2, wherein said piecewise linear reconstruction on said skin unstructured grid comprises:
the piecewise linear reconstruction of the skin unstructured grid is as follows:
Figure FDA0002675403720000011
Figure FDA0002675403720000012
wherein, ULAnd URRespectively representing the values of flow variables on the left and right sides of the cell interface, I, J being the reference numerals of the cell and being positive integers, UI,UJThe values of the flow variables for units I, J,
Figure FDA0002675403720000013
gradient of flow variable, Ψ, for units I, J, respectivelyI,ΨJIs a limiter used to avoid oscillations in large gradient regions, rL，rRRespectively representing the calculation parameters of the left and right sides of the cell interface.
4. A method according to claim 3, wherein the limiter employed comprises:
Figure FDA0002675403720000021
wherein, the points I, J are the cell centers of the units I, J,
Figure FDA0002675403720000022
respectively, the vector, U, pointing from the center of the unit I, J grid to the center of the interfacemaxRepresents the maximum value, U, of the values of the flow variables in unit I and all the adjacent units of unit IminRepresents the minimum value, Δ, of the flow variable values in unit I and all the adjacent units of unit I2Representing the difference between the value of the flow variable at the interface and the value of the flow variable at the cell center, a parameter2Is a small quantity related to the grid dimension for controlling the size of the limiter, Δ1,max＝Umax-Ui,Δ1,min＝Umin-UiWherein, is1，minAnd Δ1，maxTwo intermediate variables are respectively, and Ui refers to the variable value of the flow field of the unit serial number i.
5. The method of claim 3, wherein the values of the left and right flow variables of the interface of the acquisition unit are: acquiring flow variable values of the left side and the right side of a unit interface through a seven-order WENO format;
firstly, acquiring a reconstruction template of a unit interface:
Figure FDA0002675403720000023
a parameter symbol U with a lower right corner mark represents the value of the flow variable on each imaginary node and is distinguished by the symbol of the lower right corner mark, wherein i ', i ", i'", j ', j ", j'" are imaginary nodes which are all on the extension line of the points i and j and satisfy the direct distance equality between two adjacent points, i '"i" ═ i' ═ ij ═ j '═ j "j" ("j'", m "")1,m2,m3,m4The four reconstruction templates respectively represent left state values on the cell interface, and the weighted reconstruction formula of the left state values is as follows:
Figure FDA0002675403720000024
wherein the nonlinear weighting coefficient w1To w4All are weight coefficients, and the solving method is as follows:
Figure FDA0002675403720000031
Figure FDA0002675403720000032
represents the left state value of the interface of cell I and J.
6. The method according to claim 5, characterized in that the weight coefficients used are respectively
Figure FDA0002675403720000033
To prevent a small amount of 0 denominator, 1.0 is taken-6,ISkThe smoothness metric coefficient of the kth template is specifically expressed as:
IS1＝Ui”'(547Ui”'-3882Ui”+462Ui'-1854Ui)+Ui”(7043Ui”+17246Ui'+7042Ui)+Ui'(11003Ui'-9402Ui)+2107Ui 2
Figure FDA0002675403720000034
Figure FDA0002675403720000035
Figure FDA0002675403720000036
7. an apparatus for processing helicopter flow field data, comprising:
the preprocessing module is used for generating a Cartesian background grid and a skin non-structural grid and acquiring grid data information;
the processing module is used for searching and storing the serial number of the unit where the fictitious node required for constructing the seven-order WENO format corresponding to each interface is located in advance on the Cartesian background grid by utilizing grid data information; then, acquiring left and right state values on a cell interface by using the searched cell serial number, and solving a convection current value;
the iterative convergence module is used for carrying out iterative processing on the flux in the flow field by using the acquired convection flux on the cell interface and converging a processing result;
and the output module is used for outputting the processing result to the display equipment.
8. The apparatus according to claim 1, wherein the processing module is specifically configured to perform piecewise linear reconstruction on the skin unstructured mesh, and then obtain values of flow variables on left and right sides of a cell interface; and acquiring the convection flux on the unit interface according to the left and right state values on the unit interface.
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