基于Turbulence的非线性URANS模型预测厚翼型分离诱导转捩
Prediction of Separation Induced Transition on Thick Airfoil Using Nonlinear URANS Based Turbulence Model
摘要：
实践中的大多数湍流模型都是基于雷诺应力和平均流动应变率之间的线性关系的假设，这通常在附着和完全湍流的情况下提供了良好的近似。本文采用k-ω SST模型，在Re = 120，000时，对NACA 0021在不同攻角下层流分离泡的形成过程进行了二维数值研究。LSB的正确预测需要雷诺应力的各向异性的准确分辨率。为了与其它线性模型进行比较，还用k-kl-ω、k-ω SST和SpalartAllmaras模型进行了模拟。这些模型的性能通过气动升力、阻力、压力和摩擦系数进行评估。发现非线性k-ω SST和k-kl-ω转变模型在升力和阻力系数方面提供了相当的预测质量（尽管非线性k-ω SST涉及求解比过渡模型更少数量的输运方程的事实），如实验中所观察到的，而k-ω SST涉及求解比过渡模型更少数量的输运方程的事实。由于不能捕捉分离诱导转捩，ω SST和SA模型在低迎角时低估了阻力系数值。还观察到，当使用非线性或过渡模型时，准确地捕获层流分离气泡的位置，而不是SA或线性SST模型，其缺乏预测相同的能力。
英文摘要：
Most of the turbulence models in practice are based on the assumption of a linear relation between Reynolds stresses and mean flow strain rates which generally provides a good approximation in case of attached and fully turbulent flows. A two dimensional numerical study has been carried out over NACA 0021 with k-ωSST model with non-linear correction at Re = 120,000 for various angles of attack which experiences the formation of a laminar separation bubble (LSB). A correct prediction of LSB requires an accurate resolution of anisotropy in Reynolds stresses. For comparison with other linear models, the simulations are also performed with k-kl-ω, k-ωSST and Spalart Allmaras. The performance of these models is assessed through aerodynamic lift, drag, pressure and friction coefficients. It is found that the non-linear k-ωSST and k-kl-ωtransition model provide comparable quality of prediction in lift and drag coefficients (in spite of the fact that non-linear k-ωSST involves solving less number of transport equation than the transition model) as observed in the experiments whereas k-ωSST and SA models under predict the drag coefficient value at low angle of attack due to inability to capture the separation induced transition. It is also observed that the location of laminar separation bubble is captured accurately when nonlinear or transition model is used as opposed to the SA or linear SST models, which lack in the ability to predict the same.
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