A new unsteady casing treatment for micro centrifugal compressors to enlarge stall margin

Abstract

Tip clearance flow, particularly tip leakage vortex, is an important source of losses in centrifugal compressor rotors, which limits the stall margin and even causes compressor surge. To address this issue, a passive unsteady flow control method is proposed with equal-circumferential-spacing through-holes on the casing of a micro centrifugal compressor. The numerical simulation shows that the unsteady excitation near the generating position of the leakage vortex can weaken the fluctuation caused by the leakage vortex. The stall margin increases by 19.3% and the efficiency decreases by 0.8% when the mass flow rate of the excitation flow is only 0.12% of the main flow. Furthermore, a proof experiment on a micro centrifugal compressor shows that the stall margin increases by 13.3% considering a 100% design rotation speed and 15.4% considering an 80% design rotation speed, while the efficiency and pressure ratio decrease slightly. Therefore, both the simulation and experiment prove that the flow control method is effective and can easily be used in practice.