The Control Strategies Of The Tip Leakage Flow And The Mechanism Of Improving The Compressor Stability

The phenomenon of flow instability in the axial and centrifugal turbomachinery, including rotating stall and surge, has been a long-standing problem for the turbomachinery design and stable operation. To improve the performance and reliability of compressors, as well as the gas turbines, it is of great importance that the mechanism of unstable flow occurrence is well understood, and furthermore, this aerodynamic instability is successfully controlled. Based on a low-speed axial compressor at Institute of Engineering Thermophysics, variations of tip leakage flow and internal flow within blade passage under using of two passive control methods, circumferential grooves casing treatment and micro injection are discussed in details with the help of numerical simulation results. Mechanism of stall margin improvement with the above-mentioned passive control strategy is realized in this paper.Steady and unsteady numerical simulations are employed to investigate the character of the tip leakage flow and the change of loss and storage in different flow conditions. Then, the physical processes occurring when approaching stall have been assessed and, the influences of complex tip flow on flow instability has been analyzed.The flow field through the axial compressor rotor with circumferential groove casing has been simulated to investigate the effects of the number of grooves and the location of the grooves on the performance and stability of the compressor. Numerous studies were focused on the interaction between the complex tip flow and circumferential groove casing treatment. Detailed analyses of the flow visualization at the rotor tip have exposed the different tip flow topologies between the cases with treatment casing and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by circumferential groove casing treatment should be a result of the tip flow manipulation.Based on the result of micro injection experiment, the coupled flow through the axial compressor rotor and the injector is simulated with a state-of-the-art multi-block flow solver. The performance and the primary stall margin improvement are investigated in the case with tip injection. The relationships between the unsteady tip leakage vortex and the rotating stall for smooth wall and micro tip injection have been researched. It is the key to clarify the developing process of such unsteadiness through numerical simulations and to explore its effects on the stall inception. It should be helpful to utilize the above-mentioned computation results for designing the effective passive control method in industry.