The design and noise characteristics of a structured porous coated cylinder in uniform flow

An experimental acoustic investigation of a novel 3-D printed structured porous coated cylinder conducted in an anechoic facility is presented. This design has significant flexibility, in that the porosity and pores-per-inch of the porous coating can be modified independently. A structured porous design introduced here is compared against well-known published materials, being polyurethane and metal foam with the same coating thickness and bare cylinder diameter. Acoustic tests conducted over a range of Reynolds numbers from Re = 0.8 × 10 to 2 × 10 reveal that all of the porous coating types cause significant reduction in vortex shedding noise with little dependence on the material type and the porosity. The similarities of the results using different types of materials indicates that a structured porous geometry, using both numerical methods and experimental fluid mechanics, can be used to understand the flow behaviour within the porous medium that reduces the cylinder vortex shedding tone, that is otherwise impossible with typical randomised porous structures. A preliminary CFD result is also presented that illustrates the similarities of the wake structure of the 3-D printed porous coated cylinder to that of an equivalent Darcy-Forchheimer model simulation.