Experimental investigation on the combined effects of surface roughness and corner radius for square cylinders at high Reynolds numbers up to 10^7

Kurzfassung

In this study, the aerodynamics of 2D, slightly rough, square-section cylinders with rounded corners is experimentally investigated for Reynolds numbers up to about 12 × 10^6. The cylinders have a mean relative surface roughness of k/D = 1 × 10^−3, a corner radius of either r/D = 0.16 or 0.29 and are positioned at an angle of incidence of 0° or −45° in cross-flow direction. The results show that a larger corner radius induces lower drag coefficients and higher vortex shedding frequencies for all flow regimes, but at lower shedding intensities. Changing the angle of incidence from 0° to −45° results in all coefficients and the wake profile to become nearly independent of the Reynolds number. The critical flow state furthermore shifts to higher Reynolds numbers and decreases in length, whereas the supercritical flow state reduces to a single point. An increase of the surface roughness height from k/D = 5 × 10^−6 to k/D = 1 × 10^−3 induces a shift of the flow regimes towards significantly lower Reynolds numbers. The values of the coefficients show a lower dependency on the Reynolds number in all flow regimes, whereas in the upper transition a strong recovery of all coefficients towards subcritical values takes place.