Effect of Fixed Separation Points on Wake Oscillation and Surface Character in Suppression of the Karman Vortex Street due to Positive Buoyancy from a Cylinder

To elucidate an effect of fixed separation points on the wake oscillation and surface character in the suppression of the Karman vortex street due to positive buoyancy, a wake with positive buoyancy from a heated elliptic cylinder submerged in an upward air mainstream is calculated by numerical analysis. Numerical results agree well with the previous result for the isothermal wake, and show that separation points are exactly fixed with time and do not move by buoyancy. The critical Richardson number Ric is much larger than that in a circular cylinder wake. This means that the wake vorticity is larger and harder to disappear than that in the circular cylinder wake. With an increase of the Richardson number, the local Nusselt number and wall shear stress vary with time between separation points, and the mean Nusselt number decreases near Ric, which dose not occur in a circular cylinder wake.