Experimental and numerical investigation of the flow in a cylindrical cavity with an unsteady rotating lid

In this paper, we analyse the flowin a cylindrical cavity of aspect ratioH/R = 2, with a top lid rotating with a sinusoidal time-varying speed. The Reynolds numbers, based on the time-averaged rotating speed and the radius of the cavity (Re = Omega R-0(2)/nu) are 2800, 3500 and 4100. Particle Image velocimetry measurements and numerical simulations are performed to determine the effect on the flow of different imposed frequencies on the rotating lid. The acceleration and deceleration of the lid produce a marked pulsatile flow behaviour. It is found that at low Reynolds numbers the frequencies measured in the flow coincide with the frequency imposed on the rotating lid, while at the largest Re considered the flow frequencies are significantly lower, especially when the frequency of the disk is large. The fluctuations induced in the vertical velocity component are about 100% of the instantaneous values while for the angular component the fluctuations are of the same order as the instantaneous values.