Experimental study on aerodynamic noise characteristics and control of non-fully open low-speed cavities

In this paper, the aerodynamic noise characteristics and control of a non-fully open rectangular cavity have been studied experimentally in a small-scale acoustic wind tunnel. The cavity opening ratio Lo/L (L is the cavity length) varies with changing the trailing edge(TE) length. Reynolds number set in the experiment was between 3.3 × 105 and 8.3 × 105, based on the cavity length L. Two control strategies, perforated TE and flat/serrated leading edge(LE), were applied to control the noise of the reference cavity with an opening ratio of 0.4. The aerodynamic noise results using near- and far-field microphones show that multi-significant tones exist at certain given flow conditions, closely related to the flow velocity and cavity opening ratio. However, the tone modes are not consistent with the empirical Rossiter modes. The two control measures have shown an excellent suppression effect on the noise of the non-fully open cavity, with a maximum noise reduction of up to 25 dB under the control of perforated TE at the perforation rate between 20%∼40%. The vortex shedding frequency measured by a hot wire is consistent with the dominant frequency of the non-fully open cavity noise.