The effect of suction boundary condition on the local and average nusselt numbers for a free convection flow regime

This paper studies the effect of suction on local and average Nusselt number around a cylinder surface subjected to natural convection. The complete Navier-Stokes and energy equations are formulated in terms of stream function and vorticity. They are solved using the finite difference technique. The Rayleigh number is ranged between 1 x 10³ to 1 x 10⁵ in the current simulations. An increase in the overall Nusselt number with an increase in the suction flow rate for the three simulated Rayleigh numbers is reported. For the lowest simulated flow rate, i.e. Q = 5, the average Nusslet number difference between the three Ralyeigh number modeled cases is relatively signficant. However for the maximum simulated suction flow rate, i.e. Q = 40, the difference is relatively small. It is found that the location of the sharp drop of the Nusslet number is moved to a higher value of θ by increasing the suction flow rate. Also, the plume region size diminishes by increasing the value of Q. This behavior extends to a point, Q = 40, where the plume area disappears completely for the cases Ra = 1x10³ and Ra = 1x10⁴. Finally, the results designate a variation between the uniforn and non uniform suction on the cylinder surface.