Heat convection from a sphere placed in a fluctuating free stream



The effect of sinusoidal fluctuations superimposed on the average free-stream velocity on mixed convection from a spherical particle is investigated. The parameters considered are the Reynolds number Re, Grashof number Gr, and the relative amplitude of fluctuations. The results indicate that due to the adverse pressure gradients created by the deceleration of the free-stream, separation may occur at a Reynolds number well below that at which it occurs in uniform flow. The rising buoyancy currents, however, weaken and possibly destroy the formation of vortices at the rear stagnation point. The average Nusselt number is found to increase with the increase of the amplitude of the free stream fluctuations and with the increase of Gr/Re2, as along as the flow does not reverse its direction. The time and space averaged Nusselt number increases with Gr/Re2, with the effect of the amplitude of the free-stream fluctuations becoming less pronounced at higher values of Gr/Re2. © 2007 American Institute of Chemical Engineers AIChE J, 2007