Relationship between vortex shedding noise and remotely-sensed surface pressure fluctuations of a structured porous-coated cylinder

Tonal noise suppression of a cylinder placed in uniform flow has been achieved, to some extent, by coating it with a structured porous material as a form of passive flow and noise control. A structured porous-coated cylinder (SPCC) was investigated in an anechoic wind tunnel to determine the relationship between the far-field vortex shedding noise and the pressure recorded on the outer porous surface. To date, no experimental studies have been conducted on the surface pressure of any type of porous-coated cylinder. Acoustic measurements were carried out using a far-field microphone and simultaneously unsteady surface pressure fluctuations were obtained around the cylinder mid-span circumference using remote-sensing techniques. By obtaining simultaneous timedependent signals, more light is shed on the underlying noise-reduction mechanism of the structured porous-coated cylinder. The pressure distribution results demonstrated a delay in the boundary layer separation in the case of the SPCC compared to the bare cylinder. The far-field noise measurement results showed that significant noise reduction can be achieved by the use of an SPCC. The surface pressure results and directivity pattern of the tonal noise level have also shown that substantial noise reduction can be achieved with the applications of the SPCC. In this paper, strong relationships between surface pressures and acoustic signals were revealed at the vortex shedding frequency in the case of the bare cylinder, while it was insignificant for the SPCC, signifying the strong role of the structured porous media in suppression of the surface pressure energy content.