Interaction of Vortex Breakdown with an Oscillating Plate
Submitted by mhr214 on Thu, 2013-10-03 17:13
Interaction of vortex breakdown with an oscillating plate. The impingement of vortex breakdown to the tail or other aerodynamic appendage of an aircraft can give rise to elastic oscillations of a surface. It is expected that these surface oscillations will have an upstream influence that, in turn, alters the onset and structure of vortex breakdown. The generic features of this interaction are simulated by the interaction indicated in the schematic. The plate is subjected to controlled oscillations at period Te relative to the period To of the inherent instability of the vortex breakdown mode. For the reference case of the stationary edge, represented by the top row of images, alternating patterns of azimuthal vorticity due to the spiral breakdown mode interact with the edge and are distorted as indicated. The corresponding velocity field shows a region of low velocity in the wake-like region of the breakdown bubble. When the edge is oscillated at a period Te = 2 sec, approximately corresponding to the inherent To of the spiral mode, the onset of breakdown is substantially retarded, as indicated by the patterns of vorticity and velocity in the middle row of images. Finally, at a smaller value of Te = 1 sec, as represented by the bottom row of images, the onset of vortex breakdown is actually advanced upstream and takes on a highly distorted form; the patterns of interaction in the leading-edge region are complex and involve secondary concentrations of vorticity from the edge . Instantaneous angle-of-attack of plate αp(t) = αp + (αp)o sinωet ; αp(t) = 0° ; αo= 2.5°.
Abstract:
A technique of high-image-density particle image velocimetry is employed to determine the instantaneous and averaged features of distortion of vortex breakdown incident upon a stationary and an oscillating leading-edge. It is demonstrated that the onset of vortex breakdown can be advanced or retarded substantially, depending upon the period of the edge oscillation relative to the inherent frequency of vortex breakdown. These features are interpreted with the aid of global representations of averaged and rms distributions of velocity, vorticity and Reynolds stress, as well as a cinema sequence of instantaneous patterns of velocity and vorticity. Moreover, instantaneous, wholefield images in a cinema sequence allow evaluation of global representations of spectra and cross-spectra, providing further insight into the central mechanisms that dictate the surface loading of the edge.
Album:
Vortex Impingement on Wings, Tails and Blades
