An Experimental Investigation on the Noise Reduction of a Linear Cascade with Serrated Trailing-edge based on Linear Microphone Array Measurements

A Linear microphone array has been applied to experimentally investigate the effect of serrated trailing-edge on turbomachinery linear cascade broadband noise in an anechoic cascade wind tunnel. The linear cascade with three high-loaded LPT turbine blade profile (Zweifel lift coefficient is 1.4) with- and without- serrated trailing-edges was investigated for cascade outlet airflow velocity in the range of 30m/s to 80m/s and corresponding Reynolds number range of 2.2×105 to 5.5×105. Acoustic beamforming with phased microphone array is performed to identify and quantify the cascade blade trailing-edge noise source. The two different serration configurations, one of which is with a amplitude of 8 mm and wavelength of 8mm, and another is with a amplitude of 8 mm and wavelength of 4 mm, were tested in this study. It is found that the overall sound pressure level (OASPL) of the LPT cascade trailing-edge noise varies approximately as U6.102, which is some deviation from the classical aeroacoustic theory for the isolated airfoil trailing-edge noise at the attack angle of zero degree. The experimental results indicated that the turbulent boundary layer trailing-edge noise of the linear cascade with high load and large turning angle is considerably reduced in specific frequency range with the serrated trailing-edge which is similar as that for previous isolated airfoil investigations. The maximum noise reduction for the total sound pressure level in the frequency range of 1000Hz-10000Hz for the present LPT cascade is about 5.9dB. The higher the air speed is, the more obvious the noise reduction effect is, and the frequency range of effective noise reduction gradually moves to the high frequency region.