Controlled Experiments on Resonant Cross-Flow Mode Interactions

Abstract

An experiment is outlined which utilizes the flow over the surface of a rotating disk to study primary and secondary instabilities of cross-flow modes. This considers both stationary and traveling cross-flow modes, and conditions that might lead to a resonant energy exchange between them, as well on modes of breakdown which ultimately lead to turbulence. For this, the emphasis will be on the effect of different initial disturbance conditions which are introduced by an array of surface mounted v-component producing elements. These are produced by a specially designed pattern of metalized electrodes which are vapor deposited onto a piezoelectrically active film bonded to the surface of the disk. The motion of these elements are individually controllable in frequency, amplitude and phase, to seed combinations of stationary and traveling (with respect to the disk rotation frame) disturbance inputs. This paper outlines the fabrication of this setup and initial results in the passively (naturally) excited boundary layer. The results document amplified stationary cross-flow modes which originate upstream of the critical Reynolds number predicted from linear theory for a parallel flow. For these, amplification rates and eigenfunction moduli are presented.