The Effect of variation Longitudinal Ribs Height in Spanwise Direction on Flow and Heat Transfer Characteristics in a Rectangular Duct

Abstract

The present work has investigated numerically and experimentally the effect of a streamwise riblet on the flow and heat transfer characteristics for fully developed turbulent flow in a rectangular duct heated with constant heat flux for Reynolds number based on hydraulic diameter range of (1.5×〖10〗^4-6×〖10〗^4). Numerical simulations have been done by solving thegoverning equations (Continuity, Reynolds. Averaging Navier-stokes and Energy) in turbulent regime with appropriate turbulence model Shear-Stress Transport (k-ω) in three dimensions by using the FLUENT version (12.1.2). The variation of peak to peak height of riblet in spanwise direction ratio with 〖(h〗_s⁄h_L =0.5)was simulated. The flow structure and heat transfer characteristics (the velocity contours, vorticity contours, secondary flow contours, temperature contours, the distribution of local wall shear stress and heat transfer coefficient in spanwise direction at ribs)were presented as results. Also the effects of ribs on the flow and heat transfer characteristic at duct were presented, as the percentage of average skin friction, Stanton number and the heat transfer efficiency relative to a smooth surface. Experiments were conducted for rectangular duct of aspect ratio =10. Experimental results indicated an increase in the thickness of hydraulic and thermal sub-layer and shifted up the velocity profile, reducing the skin friction coefficient and Stanton number by about (6 %) and (23%) respectively. The experimental results gave a good agreement with the numerical simulation and previous works.

Keywords

• turbulent flow
• drag reduction by riblet
• heat transfer for ribbed surface