Numerical Investigation Of The Stall Mechanism And Casing Treatment Of Transonic Compressor

Compressor is one of the core components of aero-engine. Its performance has a decisive influence to the overall performance of an aero-engine. Modern development of aero-engine requires a compressor with higher and higher total pressure ratio per stage. It challenges our understanding on the phenomena like rotating stall et al, which restrict the performance of compressor and threaten the safety of aero-engine. Casing treatment as a simple but effective passive flow control method has been widely used to extend the compressor stall margin. But the lack of good knowledge on the mechanism of casing treatment makes the design largely depend on ad hoc experiments and usually be accompanied with efficiency penalty.The flow structures in the transonic compressor and casing treatment are investigated in detail via an advanced numerical simulation. Based on the discussion on the change and development of the critical flow structures at tip region at different operation points, the blade trailing edge separation and the breakdown of the leading edge tip leakage vortex is considered to be the direct reason for the triggering of stall respectively for configurations with small and large tip clearance width. These two phenomena are both related to the second leakage of the leading edge tip leakage flow which is greatly influenced by the trajectory of the leading edge tip leakage vortex. The results reveal the physical mechanism behind the widely accepted stall criteria.On the basis of the discussion on the stall process, a numerical investigation on the application of Circumferential Groove Casing Treatment (CGCT) on the transonic axial compressor is performed. The influence of the axial location and depth of the grooves is studied. The mechanism of CGCT is also discussed via an analysis on the mass and momentum transport across the blade tip. The result is accordance with the stall process of the compressor. Some design suggestions are presented, and validated by the application in ND-TAC test compressor.Besides, the application of a self recirculation casing treatment on the transonic centrifugal compressor is numerically studied. The mechanisms for the stall margin improvement and efficiency loss are analyzed. Designing the casing treatment channel like a diffuser is suggested as a design rule. Following this rule, the influence of the location, width and diffusion level is investigated. A new casing treatment configuration which leads to significantly improved compressor efficiency (compare with datum casing treatment design) is achieved. The result is supported by experiments.