Investigation of flow characteristics in a rotor-stator cavity under crossflow using wall-modelled large-eddy simulation

Abstract

Rotor-stator cavities are frequently encountered in engineering applications such as gas turbine engines. They are usually subject to an external hot mainstream crossflow which in general is highly swirled under the effect of the nozzle guide vanes. To avoid hot mainstream gas ingress, the cavity is usually purged by a stream of sealing flow. The interactions between the external crossflow, cavity flow, and sealing flow are complicated and involve all scales of turbulent unsteadiness and flow instability which are beyond the resolution of the Reynolds-average approach. To cope with such a complex issue, a wall-modeled large-eddy simulation (WMLES) approach is adopted in this study. In the simulation, a 20° sector model is used and subjected to a uniform pre-swirled external crossflow and a stream of radial sealing flow. It is triggered by a convergent Reynolds-averaged Navier-Stokes (RANS) result in which the shear stress transport (SST) turbulent model is used. In the WMLES simulation, the Smagoringsky sub-grid scale (SGS) model is applied. A scalar transportation equation is solved to simulate the blending and transportation process in the cavity. The overall flow field characteristics and deviation between RANS and WMLES results are discussed first. Both RANS and WMLES results show a Batchelor flow mode, while distinct deviation is also observed. Deviations in the small-radius region are caused by the insufficiency of the RANS approach in capturing the small-scale vortex structures in the boundary layer while deviations in the large-radius region are caused by the insufficiency of the RANS approach in predicting the external crossflow ingestion. The boundary layer vortex and external ingestion are then discussed in detail, highlighting the related flow instabilities. Finally, the large-flow structures induced by external flow ingress are analyzed using unsteady pressure oscillation signals.

目的

目的

本文旨在探究带有均匀预旋速度的外部横流对转静系盘腔流动特性的影响, 从而指导对真实发动机条件下涡轮盘腔流动特性的研究。

创新点

1. 采用壁面函数大涡模拟(WMLES)方法, 获得了带有横流通道的转静系盘腔更为精细的流场结构;2. 识别了盘腔轮缘处的开尔文-赫姆霍茨(K-H)不稳定性, 并探究了K-H剪切涡结构对轮缘处流动特性的影响。

方法

1. 通过高精度大涡模拟方法, 捕捉流场中的精细化流场结构。2. 结合理论推导, 通过对于流动结构的机理和动力学分析, 探究外部横流和盘腔耦合流动特性。

结论

1. 由于雷诺平均(RANS)模拟对壁面小尺度涡结构和输运方程的解析能力不足, 所以RANS模拟流场与WMLES模拟流场出现了明显偏差。2. 在横流和盘腔流动的耦合作用下, 由于轮缘处的速度剪切诱导产生K-H涡结构, 所以这些涡结构将会加强轮缘处的外部入侵和盘腔出流流动。3. 在外部入侵和盘腔出流的影响下, 盘腔端区发现了大尺度流动结构;这些大尺度流动结构以一定的转速旋转, 且其转速和数量可以通过快速傅里叶变换以及相关性分析确定。