Shear Waves and Unsteady Selective Withdrawal

An experimental study examining the generation of internal waves by unsteady inertial outflows from a stratified reservoir is presented. The experiments show that shear waves generated when the outflow is begun are identical to those generated when the outflow is stopped. The amplitudes of the lowest mode shear waves can be calculated by assuming that they combine to form the steady withdrawal‐layer velocity profile at the wall. As R, the parameter governing steady withdrawal behavior, is increased, the observed shear‐wave amplitudes decrease relative to their theoretical values, with, the discrepancy increasing with increasing mode number. When the outflow is repeatedly pulsed, the strength of the average flow towards the sink indicates the existance of a withdrawal layer thicker than that which would have been formed given either the average flow rate or the maximum instantaneous flow rate. This observation suggests that one effect of unsteady withdrawals may be to create thicker withdrawal layers than are found for similar steady withdrawals.