Attenuation of acoustic resonances in an inclined open cavity using Micro Perforated Panels

Airframe noise is equal to or louder than engine noise during the landing approach of a commercial aircraft. Cavity noise is one of the most important airframe noises. When airflow passes over an open cavity, due to vortex shedding at the upstream edge of the cavity and the geometry of the cavity, high-level aero-acoustic noise may be generated. When the incident acoustic waves produced by the airflow couples with the acoustic cavity resonances intensive tones are generated in and around the cavity at resonant discrete frequencies. Sound radiation due to the acoustic cavity resonances in an open cavity could be achieved by passive means such as lining the walls with absorbent materials. Porous and fibrous materials are used where there is no airflow. However, in presence of airflow, Micro Perforated Panels (MPP) and Porous metals are employed instead. This paper presents experimental and simulated results of the attenuation of acoustic cavity resonance tones in and around of an open cavity without and with inclined walls with lined Micro Perforated Panels.