Control of aerodynamic noise with biased flow

Abstract

Aerodynamic noise radiated from flat plate cascades are known to generate a strong sound pressure by the coupling of the flow field and the sound field. Although a cascade plates noise is dependent on the ratio of the plate thickness b and the flat plate spacing s, unfortunately, the ratio of the front grille of the conventional vehicles are close to those in is a condition that resonance is increased. From the constraints on the design of conventional vehicles, the ratio, s/b cannot be significantly changed; therefore, we attempted to develop a method of inhibiting the resonance sound without changing s/b. When the distance between the plates of cascade become narrow, interfere with each plate wake occur and the width of each wake may become a flow called different biased flow. Vortex shedding frequency of the biased flow has different properties for each plate, and we tried to use these phenomena to suppress the resonance noise of the cascades. We introduced a cascade of changing the thickness of the blade alternately to generate biased flow. The wind tunnel result and numerical results showed that this method can be reduced resonance noise of flat plates cascade.