High Reynolds-Number Flows Over Two Equal In-Line Rounded Square-Section Prisms at Incidence

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 Reynolds number for all studied incidence angles between \({0^ \circ }\) and \({45^ \circ }\) 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 aerodynamic coefficients with incidence angle between the upstream and reference prism are obtained. Proximity effects are nevertheless clearly visible in the surface pressures, particularly at \(\alpha = 25.5{^ \circ} \). Contrarily, wake-interference effects lead to a much lower and even negative drag on the downstream prism. The impingement of the shear layers coming from the upstream prism or of the eddies, formed in the gap between both prisms, dominates the aerodynamics of the downstream prism. This leads not only to transitions between the adjacent separation and wedge flow regimes, as well as between the co-shedding and reattachment flow states, but also triggers the vortex shedding processes between both prisms.