The effect of porosity on the porous coated cylinder diameter

Cylinders placed in uniform flow produce a vortex shedding tone that can be observed in many commercial and industrial applications, such as chimney stacks, high-speed train pantographs, power lines and aircraft landing gear. Porous coating treatments have been effective at weakening this vortex shedding tone. The true outer diameter of a porous coated cylinder is uncertain, as the outer surface area decreases with increasing porosity, thus making the Strouhal number estimation of the cylinder difficult. An experimental investigation is presented in this paper. The investigated cylinders are three polyurethane coated cylinders with outer diameters of 60 mm and varying porosity coating thicknesses of 10 mm, and two bare cylinders with outer diameters of 40 mm and 60 mm. Far-field acoustic measurements conducted in an anechoic wind tunnel were obtained at four flow speeds, between 20 m/s and 40 m/s. From these data, a relationship between an effective porous coated cylinder diameter and porosity is presented.