On Vortex Formation in the Wake Flows of Transonic Turbine Blades and Oscillating Airfoils

This paper demonstrates similarities between the vortex shedding from blunt trailing-edged transonic turbine nozzle blades and from oscillating bluff bodies. Under subsonic conditions the turbine nozzle cascade shed wake vortices in a conventional von Ka´rma´n vortex-street. This was linked with a depressed base pressure and associated energy separation in the wake. Under transonic conditions a variety of different shedding configurations was observed with vortices shedding and pairing in several different ways. Similarities are addressed between the observed structures and those from vortex shedding in some other physical situations. The authors have investigated the similarity between the vortex wakes shed from cylinders and airfoils in sinusoidal heaving motion in low speed flow and the wakes shed from the turbine nozzle cascade in transonic flow. The established field of vortex-induced vibration has provided a developed classification scheme for the phenomena observed. The paper has brought together three previously unrelated fields of investigation and, by showing that the three are essentially related, has provided the basis for a new synthesis.