Numerical study of fully developed unsteady flow and heat transfer in asymmetric wavy channels

The present study aims at the numerical investigation of fully developed flow and heat transfer through asymmetric wavy-walled geometry. The flow characteristics and thermal performance of wavy-walled configuration is assessed for three different geometries generated using three phase shift angles (φ) between the two opposite heated walls. The function y = 2a·sin2(πx/L) is used to describe the walls of the wavy channel. For the symmetric geometry (φ = 180°) considered in the present study, the ratios Hmin/Hmax and L/a are kept fixed to 0.4 and 8.0 respectively while the four asymmetric channels are created through a desired phase-shift of φ = 0°, 45°, 90° and 135° between the two opposite sine-wave walls. The finite volume method on collocated grid has been employed to solve the time dependent Navier-Stokes and energy equation. The fully developed flow and heat transfer has been modeled using periodic boundary conditions. The critical Reynolds number of unsteadiness is found to be the highest for the symmetric (φ = 180°) wavy-walled channel. The flow in all three geometries has been found to be equally complex but the asymmetric geometry with 0° phase-shift reveals maximum flow asymmetry about the flow centreline. It has also been observed that the most asymmetric geometry having 0° phase-shift encourages best heat transfer over symmetric configuration with 180° phase-shift, but is accompanied by the highest friction penalty.