Unstructured Adaptive Mesh Refinement Method Based Investigation Of The Multi-scale Mechanisms In Compressor

Constructing high efficient and high accurate simulation system is crucial to investi-gate and model the complex mechanisms of multi-scale flow in compressor,and explore the advanced control method.It is an important part to develop the modern advanced gas turbine and high performance aero-engine.Complex small-scale key features exist in the compressor,and they directly influence the compressor performance.Accurately predicting these key features is important for mechanism investigation.On the other hand,the compressor contains multi-scale turbulent flows,and the traditional RANS method can not fully satisfy the accuracy requirement of these flows.It is imperative to employee the accurate Large Eddy Simulation method(LES)for compressor simulation,but the large computational cost restricts the abroad application of LES for the high-Reynolds number flow in compressor.Considering the complex geometry in compressor which is difficult to generate high-quality structured grid,a high efficient and high accurate simulation system is developed based on the unstructured Adaptive Mesh Refinement method(AMR).A novel high order element based unstructured AMR method is proposed in this work.The existing unstructured AMR method in the literature is not robust enough to handle the complex geometry with hybrid grid.Our method introduces high order element to con-struct the high order mapping between the computational space and parametric space,and this enhances the robustness of our AMR strategy with complex geometry.The developed unstructured AMR method preserves good accuracy and robustness.Three-dimensional hybrid unstructured mesh of huge size and complex geometry can be automatically refined by the developed method.With several two-dimensional/three-dimensional test cases,the current AMR method proves to be reliable to handle complex geometry and can be used to accurately capture the small-scale key features with automation.The AMR based LES method is further developed in this work.Based on the estimation of the ratio of modeled turbulent kinetic energy,the local grid resolution is automatically adjusted with AMR method,and this achieves high accurate and high resolution LES results with grid number as small as possible.The current LES method proves to be efficient according to test case of flow over circular cylinder at Re_D=3900.The developed AMR method is implemented to investigate the interaction of shock wave,boundary layer and tip leakage vortex in transonic compressor.The results of compressor Rotor37 reveal the complex flow structures of shock wave/boundary layer and in the tip region,the tip unstable sources and their effects on the vortex structure.The importance of the local refined mesh for the accurately prediction of small-scale key features like shock wave and tip leakage vortex is also investigated.Current work high-lights the importance of a carefully checking about the accurate prediction of key features within mesh convergence analysis,if these small-scale features are the primary concern.The DDES results of compressor cascade reveal that periodic shock wave oscillation with low frequency arises on some operation point.The unsteady characteristics of shock wave/boundary layer interaction are further investigated in this work.In summary,a novel high order element unstructured AMR method is proposed and the AMR based LES method is developed.The interaction of the shock wave,boundary layer and tip leakage flow is investigated with our developed numerical methods.This high efficient and high accurate simulation system provides a tool for further mechanism investigation of multi-scale flows in compressor.