Visualization and measurement of steady streaming induced in oscillating flow

Non-zero time averaged flows can be induced in fluctuating flows. Previous works have shown that such time-averaged streaming can occur in stratified fluids excited in a vertical, stationary cylinder at a frequency close to the natural frequency of the axisymmetric interface wave.Particle imaging velocimetry (PIV) measurements have revealed intermittent formation of a stagnation region close the fluid-fluid interface that enables a jet-like flow departing from the center of the interface to be sustained over cycles. The jet-like flow induces a recirculating streaming flow that extends several diameters away from the interface. Difficulty still remains in quantifying experimentally the detailed flow structure and defining the driving mechanisms, since the streaming is more than one order of magnitude smaller than the forced oscillating flow. The present paper presents PIV data that show temporal evolution of the flow in each cycle, the effect of fluid viscosities and the excitation frequency and amplitude. The results indicate the dependence of the resonance characteristics of interface wave in response to forced sinusoidal excitation on the kind of upper fluid and the wall material. Both viscosity of the upper fluid and the wettability of the wall material have an impact. The material dependence of the wave response to the forced excitation results in the dependence of the depth of the streaming region below the interface