湍流及气动噪声仿真培训.pdf

ANSYS CFD 湍流模型 及流动噪声高级应用培训 姓名 刘伟 公司 安世亚太 目录 • ANSYS CFD 湍流模型新发展 • ANSYS CFD 湍流模型使用技巧 • ANSYS CFD 湍流模型验证案例 • ANSYS CFD 流动噪声模型简介 • ANSYS CFD 噪声计算案例 主题 • ANSYS CFD 湍流模型新发展 • ANSYS CFD 湍流模型使用技巧 • ANSYS CFD 湍流模型验证案例 • ANSYS CFD 流动噪声模型简介 • ANSYS CFD 噪声计算案例 Turbulence Models in FLUENT Increase in computati onal cost One-Equation Model Spalart-Allmaras Two-Equation Models Standard k–ε RNG k–ε Realizable k–ε Standard k–ω SST k–ω k-kl-ω Transition Model (3 eq.) SST Transition Model (4 eq.) 4-Equation v2f Model Reynolds Stress Model Detached Eddy Simulation SAS Large Eddy Simulation RANS Models Menter’s SST k k- -ω ω Model •The two sets of equations and the model constants are blended in such a way that the resulting equation set transitions smoothly from one equation to another. ()   ∂∂ ∂∂=      ==−20 222 2*14 1110,12max4,500,maxminargargtanhjjkkxxkCDyCDk yykFω ωρσσρ ων ωβωωωω()()γσσβφφφφρρω,,,where112111outer1 inner1kFFDtDkFDtDkF=−+= ⋅ ⋅ ⋅+−+ ⋅ ⋅ ⋅+layer outler the inlayer inner the in0111 →=FFWilcox’ original k-ω model εε23k=Wall k-ω model transformed from std. k-ε model Modified Wilcox k-ω model Embedded LES • 嵌入式大涡模拟 – 也可以和DES/SAS模型联用 E-LES: Fully developed channel flow Viscosity ratio on iso-surfaces of q-criterion (-500) Mean velocity values inside LES zone. RANS LES Re=395 E-LES: Spatially decaying turbulence • A large number of turbulence models are available in CFX, some have very specific applications while others can be applied to a wider class of flows with a reasonable degree of confidence RANS Eddy-viscosity Models: 1)Zero Equation model. 2)SA model 3)Standard k-ε model. 4)RNG k-ε model. 5)Standard k-ω model. 6)Baseline (BSL) zonal k-ω based model. 7)SST zonal k-ω based model. 8)(k-ε)1E model. RANS Reynolds-Stress Models: 1) LRR Reynolds Stress 2) QI Reynolds Stress 3) Speziale, Sarkar and Gatski Reynolds Stress 4) SMC-ω model 5) Baseline (BSL) Reynolds' Stress model Eddy Simulation Models: 1) Large Eddy Simulation (LES) [transient] 2) Detached Eddy Simulation (DES)* [transient] 3) Scale Adaptive Simulation SST (SAS)* [transient] * Not available in the ANSYS CFD-Flo product Turbulence Models in CFX Transition Modelling in Industrial CFD • Re number effects • Heat transfer • Wall shear stress • Separation behaviour • Efficiency of many technical devices Effects Modelling • Numerous developments: – Correlation based models – Low-Re models – en linear stability – … – DNS Almost all industrial CFD simulations are calculated without a transition model Transition Modelling in Industrial CFD •Low-Re models (only bypass transition) –Based on transport equations for e.g. k and ε (compatible with modern CFD codes) –Cannot be calibrated independently of viscous sublayer model –Poor accuracy and robustness – not used in industry •eN method (only natural transition) –Very accurate predictions for 2D airfoils (low FSTI) –N-S codes are not accurate enough to evaluate stability equations –Extension to generic 3D flows very difficult (impossible?) –Cannot account of non-linear effects (e.g. high FSTI, roughness) •Correlation based model –Reasonably accurate –Correlations can be found for many different transition mechanisms (e.g. FSTI, dp/dx, Roughness) –Not compatible with 3D flows and unstructured/parallel CFD codes – non-local formulation Goal – correlation based model using transport equations Transition Model Formulation in CFX • 2 Transport Equations – Intermittency (γ) Equation • Fraction of turbulent vs laminar flow • Transition onset controlled by relation between vorticity Reynolds number and Reθt – Transition Onset Reynolds number Equation • Used to pass information about freestream conditions into b.l. e.g. impinging wakes Unsteady Models •URANS –URANS gives unphysical single mode unsteady behavior •LES (Large Eddy Simulation) –Too expensive for most industrial flows due to high resolution requirements in boundary layers •DES (Detached Eddy Simulation) –First industrial-strength model for high-Re with LES-content –Increased complexity (grid sensitivity) due to explicit mix of to modelling concepts •SAS (Scale-Adaptive Simulation) –Extends URANS to many technical flows –Provides “LES”-content in unsteady regions. URANS SAS-URANS Hybrid Models •Hybrid Model: – RANS equations in bl – LES „ detached “ regions •Switch of model – Based on ratio of turbulent length-scale to grid size – Different numerical treatment in RANS and LES regions RANS LES ? ∆≤ cLt∆≥ cLt•Overcomes threshold limit of LES •Strong grid sensitivity in RANS region •Open question concerning transition region between RANS and LES 主题 • ANSYS CFD 湍流模型新发展 • ANSYS CFD 湍流模型使用技巧 • ANSYS CFD 湍流模型验证案例 • ANSYS CFD 流动噪声模型简介 • ANSYS CFD 噪声计算案例 Industrial Turbulent Flows thin shear flows rotating Detry, Manera, Detandt, d’Udekem; SAE NVH 2009 ANSYS FLUENT Coupling with ACTRAN Example 集成于WorkBench下的Actran噪声模块 THANKS 。