On the multiscale oscillations of a hinged plate under stratified coherent motions

Wind tunnel experiments are conducted to characterize and quantify the unsteady motions of a rigid plate under stratified turbulence containing spatially-varied, energetic vortices. The structure was able to oscillate around a vertical axis located at a quarter chord length from the leading edge. Vertically-oriented, von-Kármán vortices that varied in frequency and strength along the vertical span of the plate were imposed on the incoming flow using a variety of tapered cylinders. Telemetry and hotwire anemometry were used to characterize the motions of the plate, and wake at selected locations. Results show that the plate oscillations is dominated by two distinct modes. One of them, f_p, corresponds to the mean flow-induced oscillation frequency; whereas the other, f_v, is determined by the distribution of the vortex shedding cells from the non-uniform cylinders. These frequencies exhibited distinct trends with the distance from the cylinders, and the distribution of the incoming coherent motions, which were determined by the tapered ratio of the cylinders, R_t. In particular, f_v increased proportionally with R_t, whereas f_p was inversely proportional with R_t in the near wake. These characteristic frequencies were constant in the far field with values dependent on R_t.