Cooled Vortex Street with Large Vortex Spirals Generated by Cooling a Circular Cylinder at Low Reynolds Number: Effects of Fluid Kinds on Wake Patterns

Abstract

Cooled wakes of mercury and water are numerically simulated, and computed results are shown and discussed. As a result, effects of fluid kinds on wake patterns, i.e., the streaklines, streamlines, equi-vorticity lines, and isothermal lines, are elucidated as follows. 1) The results are validated in mercury and air by comparing the mean Nusselt number in the isothermal wake with the previous result, and are supposed to be valid in water because the resolution in the isothermal lines is sufficient. 2) Effects of fluid kinds on the cooled wake and the cooled vortex street are extremely strong, because the dominant action is the temperature diffusion in mercury, and the temperature advection in water. 3) The temperature distribution is extremely different between mercury and water. In mercury, the temperature varies in the whole wake, and the isothermal lines draw almost concentric circles. In water, a number of the temperature islands are generated, and transport heat to the downstream. 4) The cooled vortex street is generated in both mercury and water. The shape of the vortex spiral is vague and is not circular in water, but rotates as a vortex with smooth and clear streaklines in mercury. 5) The motion of two separated shear layers of vorticity is extremely different between mercury and water. 6) The critical Richardson numbers for onsets of the cooled vortex street and symmetric wake in water are much larger than those in mercury.