An investigation of fixed separation in quasi-periodic and aperiodic, unsteady, two-dimensional flows

Abstract

This study asses the kinematic theory of fixed separation in unsteady, two-dimensional flows that has been proposed by Haller (2004). Experimental investigations were conducted that utilized the rotor-oscillator flow to drive low Reynolds number quasi-periodic and aperiodic flows. Flow separation was observed using flow visualization techniques that employed fluorescent dye. These experimental investigations show the existence of fixed separation in both quasi-periodic and aperiodic flows. The experimental results also suggest that the location of fixed separation is immune to relatively quick variations in the flow. Thus, the 'typical' behavior of a quasi-periodic or aperiodic flow dictates the location of fixed separation in addition to the amplitude of oscillation of the flow. Both of these findings imply that the time averaged zero skin friction point is a stronger predictor of separation, which supports the Haller (2004) criteria. Furthermore, while still premature, the experimental results have so far been corroborated by early numerical simulations of the Haller (2004) criteria in the quasi-periodic flows investigated in this study.