Effect of Grazing Flow on Grooved Over-the-Rotor Acoustic Casing Treatments

Bozak, Richard F ; Jones, Michael G ; Howerton, Brian M ; Brown, Martha C

关键词: ACOUSTIC ATTENUATION;    FREQUENCIES;    GRAZING FLOW;    GROOVES;    LININGS;    MACH NUMBER;    NOISE GENERATORS;    RESONANCE;    ROTORS;    SOUND PRESSURE;    TURBOFANS;   

RP-ID  :  GRC-E-DAA-TN67974

学科分类：航空航天科学

美国|英语

来源: NASA Technical Reports Server

【 摘 要 】

After testing grooved over-the-rotor acoustic casing treatments on a turbofan rotor, a follow-on study was performed to investigate the effect of flow on grooved acoustic liners. The experiment was performed to understand the scaling of acoustic liner absorption with grazing flow and investigate a potential noise source from grooved acoustic liners. Acoustic liner absorption and reflection characteristics were quantified by examining the reduction in amplitude of a plane wave traveling over 2 inch liners with grazing flow. For all liners tested, as the grazing flow Mach number is increased, the absorption curves broadened and the frequency of peak absorption decreased. Grazing flow over a series of grooves was found to generate resonances up to 152 dB sound pressure level. Adding acoustic treatment to the bottom of these grooves was found to reduce the magnitude of this resonance by up to 10 dB sound pressure level and increase its frequency by up to 10%. The quantification of the grazing flow effect and identification of a mechanism behind the noise penalty from the prior turbofan rotor experiment will aid in the design of future over-the-rotor treatments.