Structured Porous Coated Cylinder Modifications Based on Internal Flow Field Data

Abstract

Porous coated cylinders have been proven to reduce vortex shedding tones relative to a bare cylinder. However, many porous treatments are based on the use of very complex, open-cell structures to manipulate turbulent flow. Due to complex geometries the physical mechanisms which can be drawn are problematic to investigate due to a typically randomised porous structure. The novel 3D printed Structured Porous Coated Cylinder (SPCC), which mimics the acoustics of open-cell foam's noise closely, absolves this issue thereby allowing improved observability and modifications. This study aims to draw from previous works and to investigate modified SPCCs to further understand the internal flows which attenuate fundamental vortex shedding tones. The initial study highlighted presented a preliminary analysis on the acoustic far-field of cylindrical structures and the validation against prior works. Following on from this, this paper highlights the modifications to the existing SPCC structure to affect the regions of stagnated flow within the porous layers, to investigate how these internal flows have impacted the vortex shedding attenuating capacity of the SPCC. Conducted at Brunel University London, the acoustic data shown confirms the ability of the SPCC to significantly reduce turbulent shedding noise over its bare cylinder counterparts and the three modified SPCCs proved the importance of the streamwise communication in the internal structure of the SPCC and that the stagnation regions as stipulated by earlier studies can be filled which retains the acoustic performance and most likely reduces the drag. Lastly, the removal of the ability for the flow to travel in the spanwise direction within the SPCC has been shown to improve the acoustic far field radiation over the original SPCC.