Application of Phased Array in the Study of Linear Cascade Noise Reduction on the Indoor Test Bed

A measurement technique with microphone array conventional beamforming for indoor linear cascade noise test is developing in NPU (Northwestern Polytechnical University of China) to quantify differences of sound source levels of linear cascade as a result of blade trailing edge modifications. The useful practical experience has been gained during this test. The special indoor microphones placement to avoid introducing ambiguities into sound source localization measurements in the hard-walled room test is firstly described in the paper. The reverberation time of test room is measured and is used to determine the range of direct-field of noise source acoustic radiation. A special microphones indoor placement method is used in the study to reduce the reflection from wall and to increase signal-to-noise ratio of the microphone array. The noise reduction potential of trailing edge serrations in NPU turbine linear cascade with 6 highloaded LPT turbine blades is investigated experimentally with low cascade outlet Mach number. It is shown that turbulent boundary layer trailing edge noise is reduced in the lowto midfrequency range and the largest noise reduction is about ~2 dB. This magnitude of cascade blade trailing edge noise reduction is obviously smaller than that of the isolated airfoil with using of serrated trailing edge.  Project 51276149 supported by National Natural Science Foundation of China. 1 Professor, Northwestern Polytechnical University, Xi’an, 710072, China, [email protected]. 2 PhD Student, Northwestern Polytechnical University, Xi’an, 710072, China, [email protected]. 3 PhD Student, Northwestern Polytechnical University, Xi’an, 710072, China, [email protected] 4 PhD Student, Northwestern Polytechnical University, Xi’an, 710072, China, [email protected]. 5 PhD Student, Northwestern Polytechnical University, Xi’an, 710072, China, [email protected]. 5 Berlin Beamforming Conference 2014 Qiao and Ji,et al