基于混合RANS/LES的跨音速叶栅流动机理与损失分析

随着透平负荷的不断提高,跨音速叶栅通道中的激波/边界层干涉、非定常尾迹等复杂流动现象成为损失的主要来源。目前常用的RANS方法难以准确预测这些非定常多尺度湍流流动,亟待基于高精度湍流模拟方法研究其精细流动结构及损失机理。基于自主开发的混合RANS/LES方法对某跨音速叶型进行了研究,并利用本征正交分解方法(Proper Orthogonal Decomposition,POD)获得了关键流场结构特征,最后利用基于热力学第二定律的熵生成率分析方法进行了损失机理研究。结果表明:基于混合RANS/LES方法在跨音速叶栅通道内的求解具有可靠性和精确性,尤其对尾迹流场细节的捕捉,该方法更具有优势;在跨音速叶栅流场中,尾迹区的非定常涡脱落和激波间断是流场中非定常效应的主要来源;黏性耗散引起的熵生成率在时均和瞬时熵生成率中占主要作用,是流场损失的主要的来源。

Unsteady Flow Mechanism and Loss Analysis of Transonic Cascade Based on Hybrid RANS/LES

As the turbine load continues to increase, complex flow phenomena such as shock/boundary layer interaction and unsteady wakes in the transonic blade channel becomes the main source of loss. At present, the commonly used RANS method is difficult to accurately predict these unsteady multi-scale turbulence flow, and it is urgent to study its finer flow structure and loss mechanism based on high-precision turbulence simulation method. In this paper, based on the self- developed hybrid RANS/LES method, a transonic blade is studied, and the characteristics of the key flow field are obtained by using the Proper Orthogonal Decomposition (POD). Finally, the loss mechanism is studied by using the entropy generation rate analysis method based on the second law of thermodynamics. The results show that the solution based on the hybrid RANS/LES method in the transonic cascade channel is reliable and accurate. Especially for the capture of the wake flow field details, this method is more advantageous. In the transonic cascade flow field, the unsteady vortex shedding and shock discontinuity in the wake region are the main sources of unsteady effects. The entropy generation rate caused by viscous dissipation plays a major role in the time-averaged and instantaneous entropy generation rate, and is the main source of flow field loss.