Research on Acoustic Noise Characteristic of a Three-Stage Axial-Flow Wind-Tunnel Compressor

Wind-tunnel dynamic flow quality plays a vital role in determining the accuracy of wind-tunnel testing results. Practices show that it impossible to evaluate the aerodynamic performance as well as aero-thermal performance of aero-vehicles with high accuracy in high background noise testing condition. The background noise level in normal continuous transonic wind tunnel test section is generally one order of magnitude higher than that under real flight condition and wind-tunnel compressor is the main test section background noise source. In order to suppress the wind-tunnel compressor emission noise level and thus the background noise level of a continuous transonic wind tunnel, the main driver of the wind-tunnel, which is a three-stage axial-flow compressor, is carefully designed with the properly chosen rotor blade/stator vane ratio and the rotor-stator spacing. Experimental results show that with proper rotor-stator spacing and rotor blade/stator vane ratio, the amplitude of the BPF tonal noise is suppressed. Heidmann method is applied to predict the aero-acoustic noise level of the compressor and it shows that the method can predict the noise level with acceptable accuracy around design operation condition. Under off-design operation condition, however, the prediction does not agree well with the experimental results. Spectrum analysis reveals that the existence of abnormal high amplitude tonal noise under low testing Mach number condition is the main reason for unsatisfactory prediction under off-design operation condition and the abnormal high tonal noise having greater influence on inlet acoustic noise level than that on outlet acoustic noise level. Both steady and unsteady numerical fluid simulation of the compressor is carried out and the numerical results show that specific unsteady fluid structures rather than structural vibration are the main reason for the existence of abnormal high amplitude tonal noise.