Influence on tip leakage flow in a compressor cascade with plasma actuation
Abstract: As one of the key components of aero engines, compressor is required to endure higher pressure, possess higher efficiency and wider operating range. Intensive studies have been made on tip leakage flow and researchers find that by reasonably organizing tip leakage flow, aero engines are more likely to achieve better performance and reliability. Conventional flow controlling methods like casing treatment and micro jet could substantially modify tip leakage flow, unfortunately with a price of additional loss, not to mention the difficulty in manufacturing such structure. Whereas plasma actuation flow control method uses plasma actuators, such equipment is easy to build, responses fast and has a wide excitation bandwidth. This method has become a new trend in internal flow active control field. In this research, a phenomenological model is adopted to simulate DBD plasma actuation in the flow field inside a compressor cascade. The aim is to find out how plasma actuation will influence tip leakage flow. Meanwhile possible means to improve plasma actuation performance are discussed. First of all, numerical simulation of flow inside a compressor cascade without plasma actuation is conducted to validate accuracy of the numerical methodology adopted and then determine one numerical approach that satisfies specific needs sufficiently. Meanwhile, influence of casing movement on tip leakage flow as well as possible mechanism of tip leakage vortex core generation is investigated in detail. The results indicate: 1. Generating position of tip leakage vortex moves towards leading edge with increasing moving speed of shroud. 2. As shroud moving speed increases, trajectory of tip leakage vortex moves away from suction side of blade and closely towards shroud. 3. Casing movement tends to transform tip leakage vortex from circular to oval shape due to circumferential shearing. 4. Casing movement has little influence on total pressure field concerning absolute pressure value. While total pressure loss does reduce slightly with increasing moving speed of shroud. 5.Vorticity transport from tip clearance into passage may be contributing significantly to generation of tip leakage vortex inner core. Secondly, a simplified model of DBD plasma actuation based on literature [1] is derived and applied through UDF function of commercial software Fluent into the flow field. Different actuation positions, voltages and frequencies are applied in simulation and compared. After that casing movement is included. Main conclusions are as follow: 6. Plasma actuation shows significant suppressing effect on tip leakage vortex on both size, trajectory and strength. 7. The suppressing effect on tip leakage vortex grows stronger as actuator moves towards leading edge. 8. Increasing actuation voltage results in stronger suppressing effect on tip leakage vortex. 9. Plasma actuation can effectively improve total pressure loss situation near shroud region with increasing actuation power. 10. Increasing actuation frequency results in stronger suppressing effect on tip leakage vortex as well. Additionally, frequency performs slightly better than voltage. 11. Casing movement tends to weaken suppressing effect of tip leakage vortex by plasma actuation. More actuation power is needed to achieve sufficient suppressing effect in real compressors.
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