High Reynolds-number flows over two equal in-line rounded square-section prisms at incidence

Abstract

This paper investigates the time-averaged and fluctuating aerodynamics of two slightly rough square-section prisms with rounded lateral edges of r/D=0.16, positioned in-line at a centre-to-centre distance S/D=4.0. For that purpose, distributions of the time-dependent surface pressures along both prisms’ mid-span cross-sections, the derived mean sectional pressure drag, lift, and pitch moment coefficients, as well as spanwise-integrated fluctuating fluid loads on the downstream prism and the frequency of the eddy shedding in its wake were measured simultaneously for Reynolds numbers between 100,000 and 7 million. Evaluation of the data and comparison with the results of an identical single prism revealed substantial changes of the flow over both prisms with increasing Reynolds number for all studied incidence angles between 0deg and 45deg in the form of mutual aerodynamic influences due to proximity and wake-interference effects. For most studied flow parameters, a good agreement of the trends of the mean aerodynamic coefficients with incidence angle between the upstream and reference prism are obtained. Proximity effects are nevertheless clearly visible in the surface pressures, in particular at alpha1 > 25.5deg. Contrarily, wake-interference effects lead to a much lower and even negative drag on the downstream prism and opposite trends for lift and pitch moment compared to the upstream prism. The impingement of either one or both shear layer(s) coming from the upstream prism or of the eddies formed in the gap between both prisms not only influences the time-dependent surface pressures on the downstream prism, but also triggers and synchronises the eddy shedding between both prisms.