Square-section prism with rounded edges in a uniform cross-flow: Effect of incidence angle and Reynolds number on the (un)steady aerodynamics and proneness to galloping

Abstract

The steady and unsteady aerodynamics of a slightly rough square-section prism with rounded edges of $r/D$ = 0.16 is studied experimentally for a wide range of Reynolds numbers and incidence angles. Surface pressures, time-averaged and fluctuating lift, drag, and pitch moment coefficients, as well as eddy shedding frequencies are measured simultaneously for Reynolds numbers between 100,000 and 8 million. Analysis of the data reveals drastic changes in the cross-sectional surface pressure distribution with increasing Reynolds number for all incidence angles between −45° and 3.25°, caused by the promotion of the separated-shear-layer reattachment on the side faces owing to the rounded edges. At $\alpha$ = 0°, an unbounded supercritical flow regime exists, while at larger absolute incidence angles the upper transition and transcritical flow regimes appear and gradually spread over an increasing range of Reynolds numbers. The transitions from the critical to the supercritical flow regime and further to the upper transition are accompanied by sign reversals of the lift and pitch moment. Thereupon, the classical quasi-steady galloping models are applied to determine the stability boundaries of transverse and torsional galloping depending on the incidence angle and Reynolds number. Moreover, at specific combinations of both governing parameters the eddy shedding is fully suppressed.