基于IDDES方法和γ-Reθ转捩模型的粗糙颗粒诱导高速边界层强制转捩模拟

Roughness Induced High Speed Boundary Layer ForcedTransition Simulation Using γ-Reθ Transition ModelBased on IDDES Method

关键词:  转捩模式  流场  激波  涡  边界层  转捩

Key words:  Transition model  Flow field  Shock wave  Vortex  Boundary layer  Transition

摘要:

采用γ-Re_θ转捩模型与IDDES（Improved Delayed Detached Eddy Simulation）相结合的方法对BAM6QT（Boeing/AFOSR Mach-6 Quiet Tunnel）中的马赫6来流条件下粗糙颗粒诱导转捩情况进行了数值模拟研究，通过与试验测量的压力脉动均方根值、脉动主频和边界层内的皮托压分布的定量对比及与文献中DNS（Direct Numerical Simulation）流场结构的定性对比，表明该方法可以捕捉粗糙单元诱导出的流向涡，能够模拟颗粒前缘分离激波和弓形激波之间的震荡现象，能够模拟流向涡向下游的发展失稳过程及其脉动发展过程。计算结果表明流向涡结构在粗糙颗粒下游40倍颗粒直径位置开始破碎，非定常扰动能也在该点附近增长达到最大值。粗糙单元诱导出了明显的条带涡结构，其中低速条带处于边界层上层,在向下游发展的过程中逐渐扩散至边界层外缘并耗散掉。高速条带位于边界层底部，在向下游发展的同时往展向两侧拓展，最终展向上多条高速条带接触并互相耦合，导致最后条带涡结构的破碎和尾迹区边界层的转捩。

Abstract:

The hypersonic boundary layer transition induced by roughness element in BAM6QT is simulated using γ-Re_θ transition model based on IDDES method. The root-mean-square of wall pressure fluctuations, the dominant frequency of the disturbance and the mean Pitot pressure distribution in the wake boundary layer are compared with the experiment results quantitatively. The flow field structures are compared with DNS results qualitatively. The results show that this new method has the ability to simulate the formation, development and break down process of the roughness element induced stream wise vortex and to capture the vibration between the separation shock and the bow shock in the upstream of the roughness element. The simulating results also show that the stream wise vortex structures begin to break down at around 40 times of the element diameter downstream. The unsteady disturbance energy achieves the maximum value around this point too. Obvious streak vortices are induced by the roughness elements. Among them, the low speed streaks are in the upper region of the boundary layer. They gradually move to the outside of the boundary layer and dissipate at last. While the high speed streaks, in the bottom region of the boundary layer, spread to both sizes while developing downstream. The contact and interaction of several high speed streaks leads the finally break down of the vortex structures and the transition of the boundary layer in the wake region.