Primary and secondary vortices in oscillating fluids: their connection with skin friction

Abstract

The first three instantaneous photographs (figs. 1, a and b , and fig. 2) relate to the pressure conditions existing at the end of a tank in which water is caused to oscillate by moving the tank to and fro horizontally on rollers ; the tank was provided with an artificial end having a cavity in free communication with the water in the tank through a horizontal slot near the upper end of the cavity. Figs. 3 to 8 are instantaneous photographs of jets and vortices formed in oscillating water under various conditions ; figs. 4 a , 5, 6 and 8 were obtained by mixing aluminium powder with the water and allowing all but the finest particles to settle. For figs. 3 and 4 b water-colour paint was smeared on the end of the tank just above the mean water-level, whilst for fig. 7 such paint was squirted on the bottom of the trough after the clear water had been poured in and come to rest.