﻿ SST-DES在小分离流动数值模拟中的改进
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SST-DES在小分离流动数值模拟中的改进

Improved SST-DES in numerical simulation of mild separation
Wang Xiangyu, Li Dong
National Key Laboratory of Science and Technology on Aerodynamic Design and Research, Northwestern Polytechnical University, Xi'an 710072, China
Abstract:In the numerical simulation of mild separation by detached eddy simulation (DES) based on shear stress transport (SST) turbulence model, too large turbulent viscosity may translate from the upstream Reynolds averaged navier stokes (RANS) zone to the downstream large eddy simulation (LES) zone by convection, which could restrain the development of resolved turbulence, delay the instability of shear layer and is known as the grey area. Starting from the standard k-equation sub-grid scale model, an improved SST-DES was put forward by preventing the influence of the mixed dependent variables to turbulent viscosity as a result of the original k-equation-like sub-grid model. The numerical study of flow over AS239 airfoil shows that the improved SST-DES keeps the characteristics of delayed detached eddy simulation (DDES) in the boundary layer and increases the accuracy of resolution in the regions far away from the wall at the same time and gets closer results to the experiment compared with SST-DES and SST-DDES.
Key words: detached eddy simulation (DES)     shear stress transport (SST) turbulence model     mild separation     grey area     sub-grid model
1 问题提出

 图 1 理想的DES模拟效果和实际的DES模拟效果[6]Fig. 1 Comparison between the ideal situation and actual situation in DES[6]

SST-DES可写作下面的形式[7]:

 图 2 DES,DDES和I-DES的湍流黏性系数和涡量对比 Fig. 2 Comparison between DES,DDES and I-DES in turbulent viscosity and vorticity magnitude

 图 3 摩擦阻力系数曲线 Fig. 3 Skin friction coefficient along the suction side
 图 4 翼型表面压力系数曲线 Fig. 4 Pressure coefficient along the aerofoil

 图 5 翼型尾迹区流向速度分布比较 Fig. 5 Comparison of streamwise velocity profiles in the wake region

1) 对小分离流动而言，漩涡传递湍动信息能力较弱，SST-DES中下游LES区域缺乏上游附体流区域解析湍流信息，受RANS区域较大湍流黏性干扰严重，在RANS/LES交界附近湍流发展受到抑制，即出现了所谓灰区效应；

2) 通过对原始SST-DES方程的分析，降低了其中类亚格子模式对湍流黏性的多参数影响，促进了自由剪切层湍流的发展，用标准k方程亚格子模式将SST-DES重新构造，得到了一种改进的SST-DES方法；

3) 通过对AS239翼型最大升力点小分离流动的数值模拟，改进后的SST-DES方法在翼型表面具有类似DDES延迟RANS的特性，避免出现DES中网格诱导分离现象，同时在尾迹区大大降低了湍流黏性，明显减轻了灰区的影响，验证了该改进方法的正确性.

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#### 文章信息

Wang Xiangyu, Li Dong
SST-DES在小分离流动数值模拟中的改进
Improved SST-DES in numerical simulation of mild separation

Journal of Beijing University of Aeronautics and Astronsutics, 2014, 40(9): 1245-1249.
http://dx.doi.org/10.13700/j.bh.1001-5965.2013.0587