CONVECTIVE TRANSPORT ENHANCEMENT DUE TO A ROTATING WAVY DISK

An enhancement in the turbulent convective transport in a rotating disk boundary layer is achieved by considering an isothermal axisymmetric wavy disk. The wavy surface texture does not alter the qualitative behavior of the turbulent rotating disk boundary layer but contributes nontrivially to increasing the production of shear stress and heat flux. Surface undulations are seen to manifest themselves in a variety of ways in the three-dimensional rotating disk turbulent boundary layer. They contribute to increasing the gradients in the circumferential and cross-flow velocity components, indicating an enhanced convective transport across the boundary layer. However, increased gradients in the cross-flow velocity profile, causing further skewing of the velocity vector, are usually believed to be responsible for producing less shear stress and heat flux by the turbulence structures in the near-wall region. This raises an interesting question of how the surface non-flatness executes the increasing shear stress and heat flux in the near-wall region despite an increase in the cross-flow velocity gradients. Interestingly, cross-flow velocity gradients are increased, and the polar plot shows further skewing of the velocity vector but a significant rise in momentum and thermal transport is still witnessed. This observation offers further investigations into the three-dimensional rotating disk turbulent boundary layer with regard to its inherited suppressed ability of convective transport. This seems primarily due to the reduced boundary layer thickness and reduced local flow swirl angle as the rise in the gradients of the circumferential velocity profile is quite larger than the rise in the gradients of the cross-flow velocity profile. That is why the peaks of the wavy disk polar plots are a little bit higher than those of the flat disk. This offers another way of understanding the transport process in a three-dimensional turbulent boundary layer (3DTBL). The increased surface area of the wavy disk is also an important feature in increasing the rate of momentum and heat transport. Consequently, a significant gain in the overall convective transport is achieved. As a by-product, the moment coefficient and the volumetric flow rate also increase significantly. Averaged radial and circumferential coefficients of skin friction, Nusselt number, moment coefficient, and mass flow rate are increased by 23%, 28%, 27%, 59%, and 99%, respectively at <i>a</i><sub>0</sub>/λ = 0.2, in comparison to a flat disk case. The famous Cebeci-Smith eddy-viscosity turbulence model is utilized in numerical computations, and an approximate solution is obtained due to an integral method. A comparison of the two is exceptionally good.