Flow Structure and Loading due to Instabilities from AN Oscillating-Edge of Finite Thickness.
This investigation addresses the unsteady wake from a blunt trailing-edge subjected to controlled perturbations. Flow visualization, velocity measurements in the near-wake region, and pressure measurements along the surface of the edge reveal several new aspects of this class of flows. The response of the near-wake to perturbations of the trailing-edge can be classified into two general categories: a modulated wake, characterized by ordered and repetitive variations in the near-wake flow structure over a number of cycles of oscillation of the trailing -edge: and a phase-locked wake, whereby the near-wake structure does not change from cycle to cycle of the edge oscillation. For the modulated wake, a simple model allows prediction of the number of edge oscillation cycles that make up a modulation cycle of the vortex shedding process. For the phase-locked wake, this model gives the phase shift between the process of vortex shedding and the edge motion, which is shown to be highly sensitive to small variations in oscillation frequency of the edge. Irrespective of whether the boundary layer at separation is fully turbulent or laminar, highly organized oscillations occur; this observation suggests the existence of a powerful mechanism of absolute instability in the near-wake region.
- Pub Date:
- December 1988
- Engineering: Mechanical; Physics: Fluid and Plasma