Group Summary: Experiments

Abstract

The experimental portion of the workshop consisted of two experiments on laminar flow instability and transition. Although they were conducted in widely differing flow regimes, they shared the common feature of utilizing facilities with very low background disturbances levels. The first experiment presented deals with laminar flow over a rotating disk in a quiescent ambient, i.e. a flow with an essentially non-existent “free-stream” disturbance input. Of particular interest is the generation, growth and interactions of primary and secondary cross-flow disturbance modes. An array of piezoelectric actuators was utilized to generate axially symmetric and azimuthally progressive waves which were tracked using smoke-wire and hot-wire diagnostic techniques. It was found that the installation roughness due to the actuators was excessive rendering the low amplitude input of the actuators ineffective against the stronger roughness-triggered stationary disturbance modes. Significantly, however, the existence of stationary modes with growth at Reynolds numbers below that predicted by linear-parallel theory was observed and documented with the implication that non-parallel effects may be important.