Optical and acoustic observations of stratified flow behind a cylinder

Abstract

eter), an output amplifier, an electronic pulse shaper, an echo signal preamplifier, a stroboscopic transformer, and a recorder. The stroboscopic transformer was required to scale the time in order to make the "fast" echo signals compatible with the inertial characteristics of the recorder. At the same time, shadow photographs were made of the flow field. The trigger signal for the camera was connected to the reference input of the recorder output. The (salt concentration) was linearly stratified in a tank by a continuous extraction method. In these experiments, the buoyant frequency was N = 0.6 sec -I IN 2 = (g/p)dp/dz, where p is the density, g is the acceleration due to gravity, and z is the vertical axis.] The cylinder diameter was d = 5 cm, the towing velocity varied from u = 0.36 cm/sec to 2.4 cm/sec, which corresponded to Froude numbers Fr = u/Nd from 0.12 to 0.8 and Reynolds numbers Re = ud/v from 180 to 1200 (v = 0.01 cm2/sec). Ultrasounding was done along the vertical with a repetition period of I0 msec of pulses