The Reynolds-Number Effect on the Steady and Unsteady Aerodynamic Loading on Smooth and Slightly-Rough Square-Section Cylinders with Rounded Corners

Abstract

The aerodynamics of smooth and slightly rough cylinders with square cross section and rounded corners is investigated experimentally. The aerodynamic forces on the cylinders, the Strouhal number, the base pressure and the wake profile were measured for two corner radii (r/D = 0.16 and 0.29) and three angles of incidence (α =0°, 22.5° and 45°) at Reynolds numbers up to ReD=107. It is shown that by increasing the corner roundness towards the circular cylinder case lower drag force coefficients and higher vortex shedding frequencies, but with lower intensities, are induced. A shift of the critical flow state towards lower Reynolds numbers and a decrease in its length were introduced, as well as a reduction of the supercritical flow state towards one single point. An increase of the surface roughness led to a weaker Reynolds-number dependency and a shift towards lower Reynolds numbers for all flow states.