CN-122021446-A - Vortex numerical analysis method based on transport equation decomposition

CN122021446ACN 122021446 ACN122021446 ACN 122021446ACN-122021446-A

Abstract

The invention discloses a vortex numerical analysis method based on transportation equation decomposition, which comprises the steps of 1) constructing a three-dimensional geometric model, 2) leading out a calculation domain established by the model into an ICEM CFD to establish a model grid and simulate the generation condition of a vortex in simulation software, 3) extracting fluid data of each grid unit, 4) obtaining and representing Liutex vectors, namely, calculating Liutex vectors of each unit based on a given speed field, 5) selecting a proper vortex core threshold, 6) calculating Liutex transportation equation decomposition, 7) extracting the calculated result of each grid decomposition, 8) statistically displaying each decomposed item in post-processing software, and 9) analyzing mechanisms, namely, analyzing the effect of the vortex through the displayed post-processing result and data. According to the invention, by constructing a Liutex vector transportation equation, decomposition and quantification of different physical effects in the Liutex vector evolution process are completed, and mechanism analysis is realized.

Inventors

HUANG XIANBEI
ZHAO JINYING
GUO QIANG
LIU XIAODONG

Assignees

扬州大学

Dates

Publication Date: 20260512
Application Date: 20260206

Claims (3)

1. The swirl numerical analysis method based on the decomposition of the transport equation is characterized by comprising the following steps of: The method comprises the steps of 1) constructing a three-dimensional geometric model, namely, establishing a full-size three-dimensional model of an actual project through three-dimensional design software, wherein the model comprises key geometric features reflecting the actual project; step 2) exporting a calculation domain established by the model to an ICEM CFD for establishing a model grid and simulating the generation condition of a vortex in simulation software; step 3) extracting the grid data, and extracting the fluid data of each grid unit after the simulation calculation is completed; data format standardization, converting the extracted discrete data into CSV structured format, and establishing a corresponding table of grid number-space coordinate-speed component; step 4) Liutex, obtaining and representing vectors, namely, traversing all units in a fluid calculation domain by writing a post-processing program of CFD software based on a given speed field, and calculating Liutex vectors of the units; step 5) selecting a proper vortex core threshold, namely selecting Liutex threshold serving as a vortex core boundary according to actual conditions, and extracting the vortex core in post-processing software; Step 6) calculating Liutex transport equation decomposition, namely considering Liutex vectors as physical quantities evolving along with fluid movement and local deformation based on continuous medium mechanics and Liutex theory, traversing all units through a post-processing program of CFD software, and calculating convection, stretching and bending items of the vectors of each unit Liutex so as to realize the decomposition of Liutex vector transport equation; Step 7) extracting the result after decomposition calculation, namely integrating Liutex vector data in the step 4) and transportation equation subentry data in the step 6) with speed and coordinate data in the step 3), taking a grid number as a unique index, taking a vortex core threshold value as a selection standard, and outputting a full-quantity data set containing 'space position-Liutex vector-transportation equation subentry'; Step 8) counting and displaying the decomposed items in post-processing software, namely displaying the directions of the stretching and bending items obtained by calculation, and carrying out qualitative space feature analysis of vortexes; And 9) analyzing the mechanism, namely analyzing the vortex mechanism through the displayed post-processing result and data.
2. The method of claim 1, wherein the step 4) comprises recording, in the fluid calculation domain, a spatial rate of change of velocity at any point in the flow field based on a given velocity field, as Decomposed into symmetrical shear tensors And anti-symmetric rotation tensor : ; Wherein the shear tensor: the off-diagonal elements reflect the shearing action and the diagonal elements reflect the stretching action; Rotation tensor: describing only rigid rotation, and vorticity Satisfy the following requirements I.e. the vorticity is 2 times the rotation tensor; by writing the post-processing program of CFD software, in the fluid computing domain, all cells are traversed, and Liutex vectors for each cell are computed as follows The explicit formula is expressed as: ; Wherein: , Is a velocity gradient Is a real feature vector of (1): Flow field local vorticity ; The intensity of Liutex is expressed to characterize the rotation intensity of the fluid unit, and the vortex quantity is satisfied I.e. 。
3. The method for analyzing the vortex numerical value based on the decomposition of the transportation equation according to claim 1, wherein the step 6) specifically comprises: Based on continuous media mechanics and Liutex theory, the Liutex vector is regarded as a physical quantity evolving with fluid motion and local deformation, and the transport equation is expressed as: ; Wherein, the Is a fluid velocity vector; A convection term representing Liutex vectors; a representation Liutex stretch term; a representation Liutex of the curved term; Calculating a time variation term, namely expanding Liutex vectors according to a time gradient, wherein the time variation term is expressed as: Wherein, the method comprises the steps of, Representing Liutex changes in intensity over time; representing Liutex changes in direction over time; Calculating a convection item, namely expanding Liutex vectors according to intensity and direction, and expressing the convection item as: ; Wherein, the Representing Liutex intensity as a function of flow bulk convection; the change in Liutex direction with flow convection is shown; The tensile term is calculated to describe the effect of the fluid strain field on Liutex strength evolution along the vortex axis direction, expressed as: ; S is a strain rate tensor obtained by calculating a velocity gradient tensor; the bending term is calculated to describe the spatial deflection of the vortex axis direction due to the rotation field non-uniformity, and is expressed as: ; Wherein, the A rotation tensor calculated for the velocity gradient tensor; the direction derivative results are orthogonally projected, components along the Liutex direction are removed, and only components perpendicular to the vortex axis are retained.

Description

Vortex numerical analysis method based on transport equation decomposition Technical Field The invention relates to the field of computational fluid mechanics, in particular to a vortex numerical analysis method based on transport equation decomposition. Background In hydrodynamic studies, the vortex structure is considered to be a critical factor in determining flow morphology evolution, momentum and energy transport, and turbulence formation. How to accurately identify the vortex and analyze the evolution mechanism thereof has been an important research content in computational fluid mechanics and experimental fluid mechanics. Traditional vortex analysis is based on methods such as vorticity, Q criterion, lambda 2 criterion and the like. Although widely adopted in engineering application, the method is basically dependent on invariant or second derivative information of the velocity gradient, and the shearing effect is easily misjudged as a rotating structure in a strong shearing area, so that the identification and dynamics interpretation of the real vortex are affected. Liutex theory, by stripping the shear component from the velocity gradient tensor, only the portion representing the true rigid body rotation is retained, a rotation intensity vector with a definite physical meaning can be given. The Liutex vector not only characterizes the magnitude of the rotational strength, but also indicates the direction of the rotational axis of the local vortex, and therefore has become an important tool for vortex research in recent years. However, liutex is only used for identifying the vortex, and a corresponding method for analyzing the bending and deflection effects of the vortex is not available, so that the research on the vortex mechanism is limited. In addition, in the existing transportation equation research, partial scholars couple stretching and bending in the vortex effect into one item based on the vortex quantity transportation equation, and although the method has a good effect in high-Reynolds-number two-dimensional flow, the vortex mechanism is difficult to accurately describe in three-dimensional flow, and clear distinction of physical effects such as convection, stretching and bending of the vortex under the condition of three-dimensional full Reynolds number is difficult to realize. Disclosure of Invention Aiming at the defects existing in the prior art, the invention provides a swirl numerical analysis method based on the decomposition of a transport equation, and the analysis of contributions of different physical mechanisms in the Liutex vector evolution process is realized by constructing the transport equation of Liutex vectors and carrying out the decomposition of the right end terms with definite physical meaning. The invention aims to realize the vortex numerical analysis method based on the decomposition of the transportation equation, which comprises the following steps: The method comprises the steps of 1) constructing a three-dimensional geometric model, namely, establishing a full-size three-dimensional model of an actual project through three-dimensional design software, wherein the model comprises key geometric features reflecting the actual project; step 2) exporting a calculation domain established by the model to an ICEM CFD for establishing a model grid and simulating the generation condition of a vortex in simulation software; step 3) extracting the grid data, and extracting the fluid data of each grid unit after the simulation calculation is completed; data format standardization, converting the extracted discrete data into CSV structured format, and establishing a corresponding table of grid number-space coordinate-speed component; step 4) Liutex, obtaining and representing vectors, namely, traversing all units in a fluid calculation domain by writing a post-processing program of CFD software based on a given speed field, and calculating Liutex vectors of the units; step 5) selecting a proper vortex core threshold, namely selecting Liutex threshold serving as a vortex core boundary according to actual conditions, and extracting the vortex core in post-processing software; Step 6) calculating Liutex transport equation decomposition, namely considering Liutex vectors as physical quantities evolving along with fluid movement and local deformation based on continuous medium mechanics and Liutex theory, traversing all units through a post-processing program of CFD software, and calculating convection, stretching and bending items of the vectors of each unit Liutex so as to realize the decomposition of Liutex vector transport equation; Step 7) extracting the result after decomposition calculation, namely integrating Liutex vector data in the step 4) and transportation equation subentry data in the step 6) with speed and coordinate data in the step 3), taking a grid number as a unique index, taking a vortex core threshold value as a selection standard, and outputting a full-qu