壁面網(wǎng)格劃分規(guī)則

1、Guideli nes for Mesh Gen eratio n頁碼，2/3簡介：本節(jié)主要介紹如何確定第一層網(wǎng)格距壁面距離，計算邊界層厚度以及在邊界層內(nèi) ANSYS CFX-Solver Modeling Guide | Turbulence and Near-Wall Modeling | Modeling Flow Near the Wall |劃分多少層網(wǎng)格。Solver Yplus and YplusDoma in In terface Modeli ngUp / HomePrevUp / HomeNextGuideli nes for Mesh Gen erati onOne of

2、 the most esse ntial issues for the optimal performa nee of turbule nee models is the proper resolution of the boundary layer. In this seetion, two criteria are suggested for judging the quality of a mesh:對湍流模型來說，如果想得到理想的結(jié)果，邊界層網(wǎng)格的生成是最重要的 i Minimum spaeing between nodes in the boundary layer 因素之一。本節(jié)將

3、介紹兩種判斷邊界 i Mi nimum nu mber of no des in the boundary layer層網(wǎng)格質(zhì)量的準貝 U：1，邊界層內(nèi)節(jié)點最小間距；2邊界層內(nèi)節(jié)點These are simple guideli nes for the gen erati on of meshes which satisfy the minimal requireme nts for accurate boundary layer computati ons.最小數(shù)量。簡單介紹了生成滿足邊界層計算最低精度所需的網(wǎng)格生成方法。Mi nimum Node Spac ingThe goal is t

4、o determ ine the required n ear wall mesh spaci ng,' , in terms of Reyno Ids nu mber, 目的是由雷諾數(shù)、行程長度及y+目標值確定近壁 running |ength, and a .target vabe.網(wǎng)格所需間距 deta y。A >：' < 200 is acceptable if you are using the automatic wall treatment, if not, continue to read the advice below.如果使用了自動壁面處理，貝

5、y+<200即可，否則請繼續(xù)往下看After running a solution, the value of 一】 (in particular, the value given by the solver variableYplus , rePresenting the|/ va|ue for thefstnodefrgmthe wall)with:20 < Zky+ < 100 for wall function Ay+ 2 fcr low-Re model在運仃結(jié)束后，y+值應(yīng)滿足：對壁面方程對低雷諾模型Equation 2.NoteHere, y+ refers t

6、o the solver variable Yplus (not the solver variable Solver Yplus ), which isstored at each node on a wall boundary. For details, see Solver Yplus and Yplus. 注意此處 y+ 不是 solver y+ y+值儲存在壁面邊界層每個節(jié)點上NoteHere, low- Re model means using a fine mesh and one of the、models (which include the SSTmodel). The 人

7、 models do accept coarser meshes, due tothe automatic near-wall treatment for,”，these models.此處低雷諾模型的意思是，使用了較密的網(wǎng)格和k-omega模型中的一種。k-omega模型也允許較粗糙的模型，但需選中自動壁面處理”Formulation選項。The estimates will be based on correlati ons for a flat plate with a Reyno Ids nu mber of:,-r -此處以平板為例推導(dǎo)了計算第一層網(wǎng)格距離的公式，氏務(wù) = 具體過程不

8、解釋。Equatio n 14P-with characteristic velocity and length of the plate L .The correlati on for the wall shear stress coefficie nt, cf, is give n by: -1 /7Equati on 15.? = 0 025where is the distance along the plate from the leading edge.The definition of ® for this estimate is:mk:MSITStore:C:Prog

9、ram%20FilesANSYS%20l ncv110CFXhelpjarhelp.2011-3-22Guideli nes for Mesh Gen eratio n頁碼，3/3mk:MSITStore:C:Program%20FilesANSYS%20l ncv110CFXhelpjarhelp.2011-3-22Guideli nes for Mesh Gen eratio n頁碼，4/3Equati on 16.r being the mesh spaci ng betwee n the wall and the first node away from the wall.withUs

10、ing the definition2puT=2y = 2P%Equati on 17.乩丁can be elimi nated in Equati on 16 to yield:Equati on 18.勺 can be eliminated using Equation 15 to yield:Ay = £爐施賦小丄ReLEquati on 19.Further simplification can be made by assuming that:where 'T is some fraction.1/14Assu ming that -,the n, except f

11、or very small Rq, the result is:Ay = £Ay+-?8013/14Equati on 20.This equati on allows us to set the target 'value at a give n 二 locati on and obta in the meshspaci ng,for nodes in the boundary layer.通過公式20即可計算出所需y+對應(yīng)的第一層 網(wǎng)格避免距離deta y。Minimum Number of NodesGoalA good mesh should have a minim

12、um nu mber of mesh points in side the boun dary layer in order for the turbule nee model to work properly. As a gen eral guideli ne, a boun dary layer should be resolved with at least:一個好的網(wǎng)格在邊界層內(nèi)應(yīng)有足夠多數(shù)量的網(wǎng)格層數(shù)，以保證11 r !湍流模型計算準確。最低層數(shù)如下Wforwllfunctw 10,對壁面方程Equation 21亠二1：15，對低雷諾模型q.formal =where Nn orm

13、alis the nu mber of no des in the boun dary layer in the direct ion no rmal to the wall.上述為垂直壁面方向網(wǎng)格層數(shù)。F面為計算邊界層厚度公式推導(dǎo)：can the n be computed from the correlati on:Formulati onThe boun dary layer thick ness= 0A4R nEquati on 22.to be:Equati on 23.mk:MSITStore:C:Program%20FilesANSYS%20l ncv110CFXhelpjarh

14、elp.2011-3-22Guideli nes for Mesh Gen eratio n頁碼，5/35 = 0,141 J? n X ip >3丄 對鈍體”來說，Rex的邊界層并非從駐點處的零厚度The boundary layer for a blunt body does not start with zero thickness at the stagnation point for_. It is, therefore, safe to assume that is some fraction of f , say 25%. With thisassumption, you get:位置開始，因此，安全起見設(shè) Red為ReL的0.25倍，可得_1 nEquati on 24.6 = 0.035'因此，我們需要選擇一個點（對低雷諾模型是第十五個.， 然后保證其滿足左式。'You would, therefore, select a point, say the fifteenth off the surface (for a low-Re model, or 10th for a wall fun cti on model) and check to make sure that:n(15) -m(1) < 6Pr