CN113420379A

CN113420379A - Method for extracting surface-average pressure distribution from CFL3D calculation result

Info

Publication number: CN113420379A
Application number: CN202110724489.7A
Authority: CN
Inventors: 赵帅; 李�杰; 杨钊
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2021-09-21

Abstract

The invention relates to a method for extracting surface-time average pressure distribution from a CFL3D calculation result, and belongs to the field of computational fluid mechanics. By utilizing the time-averaged flow field file output by the CFL3D, according to the object plane fragment information extracted from the input file of the CFL3D, Tecplot software is adopted to solve the pressure coefficient of the flow field and extract the time-averaged object plane in the calculation domain, thereby realizing interception and derivation of the time-averaged pressure distribution of the object plane. The method can be used for processing pressure-equalizing force distribution in complex configuration object surfaces, and has good adaptability and operability.

Description

Method for extracting surface-average pressure distribution from CFL3D calculation result

Technical Field

The invention belongs to the field of computational fluid mechanics, and particularly relates to a method for extracting surface-average pressure distribution from a CFL3D calculation result.

Background

CFL3D is an open source multi-block structured grid CFD solver developed by the NASA Lanley research center, USA. The software has extremely high calculation efficiency, can perform steady and unsteady numerical simulation, is suitable for low-speed and transonic flow, and is widely applied to the field of aerospace.

Object plane pressure distribution, i.e. pressure coefficient (usually C)_pRepresenting) distribution along a certain direction is an important parameter required in aircraft design and flow field analysis. For high angles of attack, high sideslip conditions, or unsteady flow related to component motion, the object plane pressure distribution is constantly changing over time, thus requiring averaging of the object plane pressure distribution over time.

The CFL3D only has the function of outputting a transient object plane flow field information file and a time-averaged spatial flow field information file, but cannot output the time-averaged object plane flow field information file, and the time-averaged spatial flow field information output by the software does not include a pressure coefficient item.

At present, the published documents and patents do not disclose the method of pressure-equalizing distribution at the time of extracting the surface from the calculation result of CFL3D.

Disclosure of Invention

Technical problem to be solved

To avoid the disadvantages of the prior art, the present invention proposes a method for extracting the level-averaged pressure distribution from the results of CFL3D calculation.

Technical scheme

A method for extracting an areal mean pressure distribution from CFL3D calculations, characterized by the steps of:

step 1: selecting output time-averaged flow field data when CFL3D is adopted for calculation;

step 2: collecting object plane fragment information from the input file of CFL 3D;

and step 3: reading and recording the position of each object surface fragment in the corresponding grid block from the object surface fragment information extracted in the step 2;

and 4, step 4: opening a time flow field file output by CFL3D in Tecplot software, and editing a formula to solve the pressure coefficient of the whole flow field;

and 5: closing the grid blocks which do not contain the object plane in Tecplot, and displaying the grids at the corresponding positions in the grid blocks according to the object plane position information which is arranged in the step 3 for the grid blocks containing the object plane;

step 6: the flow field data at the target position is intercepted in the Tecplot, and then the coordinates and the pressure coefficient are output so as to obtain the pressure distribution of the section.

The formula in the step 4 is specifically as follows: { Cp } - (V8/V4-1/1.4)/(0.5V 4 Ma 2), wherein V8 represents a dimensionless static pressure value of a conservative form, V4 represents a density, and Ma is a free incoming flow mach number; v8 and V4 are fixed inputs, and Ma is adjusted according to the calculated incoming flow conditions.

In the step 5, the object plane segment is displayed manually or in a programming mode.

The position information in the step 3 includes an object plane direction and a layer number.

Advantageous effects

The invention provides a method for extracting time-average pressure distribution from CFL3D calculation results, which utilizes a time-average flow field file output by CFL3D, solves the pressure coefficient of a flow field by adopting Tecplot software according to object plane fragment information extracted from an input file of CFL3D, extracts a time-average object plane in a calculation domain, and further realizes interception and derivation of the time-average pressure distribution of the object plane. The method can be used for processing pressure-equalizing force distribution in complex configuration object surfaces, and has good adaptability and operability.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a background aircraft profile view of an embodiment;

FIG. 2 is a basic flow diagram of the present invention;

FIG. 3 is a schematic diagram of an input control command ipertavg 1;

FIG. 4 is a diagram illustrating the setting of the Zone Style/Surfaces To Plot option of the grid block numbered 860 in the embodiment;

FIG. 5 is a diagram illustrating the setting of the Zone Style/Surfaces/Range For K-planes option of the lattice block numbered 860 in the embodiment;

FIG. 6 is an extracted background aircraft mean object plane;

fig. 7 is a pressure distribution comparison result.

Wherein:

exp is the experimental result;

cal _ avg is a time average calculation result;

cal _ Ψ -0 degree is a calculation result when the propeller rotates to a phase angle of 0 degree;

and Cal _ Ψ is a calculation result when the propeller rotates to a phase angle of 30 degrees by 30 degrees.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in FIG. 2, the present invention provides a method for extracting the time-averaged pressure distribution from the CFL3D calculation result, comprising the following steps:

step 1: as shown in fig. 3, the control command iptavg 1 is written in the cfl3d.inp file before calculation.

Step 2: the CFD numerical simulation was started.

And step 3: and extracting object-plane fragment information with the boundary condition of 2004 from the cfl3d. inp file, and integrating the object-plane fragment information of the same grid block.

Table 1 shows the object plane fragment information contained in the extracted, integrated grid block No. 860. It can be determined from the table that the object plane segment is located in the first layer grid cell in the K direction of the grid block with the number 860;

and 4, step 4: opening Tecplot software and respectively importing a flow field grid and a flow field to obtain a cfl3d _ avgg _ ruvwp.p3d file and a cfl3d _ avg _ ruvwp.p3d file;

and 5: the pressure coefficient was calculated by inputting the formula "{ Cp } - (V8/V4-1/1.4)/(0.5 × V4 × 0.2 × 2)" to Tecplot, where 0.2 is the free stream mach number in the CFD calculation, V8 is the dimensionless static pressure value in the conservative form, and V4 is the density.

Step 6: according to the information integrated in the step 3, closing all the zones which do not contain the object plane in Tecplot;

and 7: and for the Zone containing the object plane, judging whether the object plane is in the I direction, the J direction or the K direction according To the information integrated in the step 3, and correspondingly activating I-Planes, J-Planes or Z-Planes in a Zone Style/Surfaces To Plot option.

As shown in FIG. 4, for the mesh block numbered 860, K-planes is selected in the Zone Style/Surfaces To Plot option.

And 8: and (3) judging which layer of the object plane is in the I direction, the J direction and the K direction according to the integrated information in the step 3, and correspondingly inputting specific numerical values in the Zone Style/Surfaces/Range For I-planes, Range For J-planes and Range For K-planes.

As shown in FIG. 5, For the mesh block numbered 860, in the Zone Style/Surfaces/Range For K-planes option, Begin, End, Skip are all set to 1.

As shown in fig. 6, in this embodiment, in order to obtain the pressure distribution of the station Section a, the whole machine plane after the time averaging is extracted.

And step 9: intercepting the pressure coefficient of the target position by using a DATA/Extract/Slice from plane command;

step 10: the cross-sectional pressure profile was derived using the File/Write Data File command.

The flow field of the propeller-driven airplane in a power state has typical unsteady characteristics, and the object plane pressure distribution is different when propeller blades are positioned at different phases. Fig. 7 shows the comparison of the time-averaged calculation result of the station Section a pressure distribution with the experimental result and the calculation result at the phase angle of 0 ° and the calculation result at the phase angle of 30 °. It can be seen from the figure that the pressure distribution extracted by the method of the present invention is very close to the experimental results, indicating that the method of the present invention is very reasonable. It can be seen from the figure that the time-averaged calculation result is obviously different from the negative pressure peak value predicted by the transient result, which also reflects the necessity of adopting the time-averaged pressure distribution result.

Table 1 object plane information contained in mesh block No. 860

Grid Block numbering	Direction of object plane	Number of layers
			860	In the K direction	First layer

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications or substitutions can be easily made by those skilled in the art within the technical scope of the present disclosure.

Claims

1. A method for extracting an areal mean pressure distribution from CFL3D calculations, characterized by the steps of:

2. The method of claim 1, wherein the formula in step 4 is specifically as follows: { Cp } - (V8/V4-1/1.4)/(0.5V 4 Ma 2), wherein V8 represents a dimensionless static pressure value of a conservative form, V4 represents a density, and Ma is a free incoming flow mach number; v8 and V4 are fixed inputs, and Ma is adjusted according to the calculated incoming flow conditions.

3. The method of claim 1, wherein the object-plane segment is manually or programmatically displayed in step 5.

4. The method as claimed in claim 1, wherein the position information in step 3 includes 2 object plane direction and number of layers.