Investigaton Of Centrifugal Compressor Stall And Stability Enhancement By Inducer Shroud Casing Treatment

Casing treatment is a kind of efficient and economic ways for compressor stability enhancement. Although its application has a history of decades, people’s awareness about the mechanism of casing treatemetn is not perfect to this day. With the sustained growth of the load, the application of casing treatment on the centrifugal compressor is becoming more common. At present, experience is dominated in design process with the expense of the trial and error. Research on flow characteristics and mechanism of casing treatment stabilizing stall margin is helpful to change the current status and conducive to meet the urgent need for the high performance aircraft engine stabilizing stall margin in the future. In this paper, numerical simulation and experimental were carried out to study two kinds of casing treatment, self-recirculating casing treatment and inducer tip endwall bleeding, including the following aspects:1) Internal flow characteristics of flow instability in a single stage centrifugal compressor under different rotational speed. From the matching relationship between parts and pressure ratio – mass flow characteristics of the inducer and impeller, the trigger part of instability could be found. In addition, three types of stall model and the changing rule of the stalled part were analyzed under different rotating speed. The flow of the tip leakage flow structure, a kind of important secondary flow in tip clearance, and the trigger mechanism for compressor stall were also explored.2) Designed a kind of self-recirculating casing treatment with external cavity and two-way slotted ring according to the experience and general knowledge. Geometric parameters include axial length between the suction slots and the inducer, slot angle, slot number, slot width and ring cavity volume were researched. Through the solid wall casing and casing treatment contrast test, it has verified the stability enhancement effects of casing treatment. The test results showed the performance of casing treatment changed with rotating speed, which can help to select operating point for numerical simulation to avoid the blindness.3) Established a flow structure model for the centrifugal compressor with self-recirculating casing treatment. Through the model, the casing treatment on the influence of rim power, the law of prewhirl injection angle of backflow and the relationship between backflow rate and margine increase were analyzed.4) Unsteady flow dynamic of the whole stage compressor with the self-recirculating casing treatment was simulated using the nonlinear harmonic method. The unsteady flow characteristics in casing treatment and the rotor/stator interference effects between the impeller and casing treatment have been researched. These studies provide a reasonable basis for using steady simulation with frozen rotor method to further simplify the computation.5) Steady simulation was carried out for the centrifugal compressor with casing treatment at 50%, 80% and 100% design speed. By analysing the results of numerical simulation, we studied the mechanism of stability enhancement by inducer shroud casing treatment and the speed influence of the performance about stability and efficiency. Finally, the criterion for the application of self-recirculating casing treatment was summarized by combining different centrifugal compressor stall models.6) Inducer tip endwall bleeding effects on both single stage centrifugal compressor and mixed-centrifugal combined compressor were investigated by numerical metheod. The differences in stabilizing effect and efficiency between self-recirculating casing treatment and inducer tip endwall bleeding were compared. We also discussed about the advantages of inducer tip endwall bleeding relative to inter-stage bleeding.