Active control of transition to turbulence in the wake of a cylinder

Abstract

This paper presents experimental observations of two-dimensional air flows with a Reynolds number of 170 passing a stationary circular cylinder and its active control of transition to turbulence. One of the potentials of this research application is in aircraft design.

A hot-wire sensor was located in the upper shear layer of the cylinder at about 0.9d streamwise and about 0.8d above the cylinder axis. After the phase of the feedback signal shifted 180°±2° and the amplifier gain was adjusted, perturbations were imposed at vortex-shedding frequency on the wake of the cylinder on both sides of the wind tunnel. The induced perturbations were significant and the Karman vortex street responded vigorously to the feedback of the signal from the hot-wire sensor in the wake of the cylinder at vortex-shedding frequency. Thereafter, the amplitudes of velocity fluctuations were significantly reduced in the Karman vortex street. The Karman vortex street was studied at various locations spanwise to examine the extent of the response of the longitudinal components of velocity fluctuations in the wake. The amplitude of velocity fluctuations was measured with the hot-wire probe positioned at x/d=2 off the center about 1/2 diameter spanwise in the wake of the cylinder. Finally, the vortex street was studied at various locations to examine variability of the longitudinal components of the velocity fluctuations. The free stream velocity of the wind tunnel maintained uniformly at U_∞=80.4 cm/s during the experiment.