Effect Of The Staggered Casing Treatment On The Rotor Stability Of The Transonic Compressor

The modern aviation compressor is mainly a multi-stage axial transonic compressor.The main features are high pressure ratio of each stage,high tip tangential speed and high aerodynamic load.The operating stability of the compressor has crucial effects for the normal operation of the whole engine.The internal flow of the compressor is complicated and the combination of the leakage vortex and the shock wave in the tip region causes the unstability of the compressor and the loss of the flow.As a passive stability enhancement technique with simple structure,obvious stability enhancement effect and high reliability,the circumferential groove casing treatment is widely used in modern aeroengines.Based on the transonic compressor of Rotor 37 rotor with smooth-wall casing and in terms of practical application,six different staggered circumferential groove casing treatment in the meridional section have been designed.Using the CFD(Computational Fluid Dynamic)simulation software,the operations of the compressor at various conditions have been predicted numerically.The flow field of tip clearance has been analyzed with the smooth wall and with casing treatment.The mechanism of the improvement of the stability margin of the compressor has been investigated.Finally,the influence of different tip clearances on the stability of the transonic compressor rotor with staggered casing treatment has been briefly analyzed by choosing the concave-shaped casing treatment.Numerical simulations indicate that six design schemes have significantly improved the stability margin of the compressor.Among them,the concave-shaped circumferential groove casing treatment has the most obvious effect of the stability enhancement and the smallest efficiency loss.The stall caused by the breaking of the tip leakage vortex and the separation of the boundary layer is the basic reason of compressor instability and the flow field blockage caused by the breaking of the tip leakage vortex is the main factor.The radial velocity at the interface between the circumferential groove and the main flow passage reflects not only the momentum and the flow rate exchange inside the groove but also the process of improvement of the blockage at the top of the compressor blade by the circumferential groove.The axial negative momentum at the tip region reflects the blockage degree of flow field of the compressor.Finally,further research show that the size of the tip clearance is also an important factor affecting the stability margin and efficiency.The concave-shaped casing treatment achieves the maximum stability margin under the middle tip clearance,but the efficiency decreases slightly.