Large Eddy Simulation of Flow and Heat Transfer in a 90° Ribbed Duct With Rotation: Effect of Coriolis and Centrifugal Buoyancy Forces

Abstract

Results from large eddy simulations (LES) of fully developed flow in a 90° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height-to-hydraulic-diameter ratio e/Dh = 0.1. Three rotation numbers Ro = 0.18, 0.36 and 0.68 are studied at a nominal Reynolds number based on bulk velocity of 20,000. Centrifugal buoyancy effects are included at two Richardson numbers of Ri = 12, 28 (Buoyancy number, Bo = 0.12 and 0.30) for each rotation case. Buoyancy strengthens the secondary flow cells in the duct cross-section which leads to an increase of 20% to 30% in heat transfer augmentation at the smooth walls over and above the effect of Coriolis forces. Buoyancy also accentuates the augmentation of turbulence near the trailing wall of the duct and increases the heat transfer augmentation ratio 10% to 20% over the action of Coriolis forces alone. However, it does not have any significant effect at the leading side of the duct. The overall effect of buoyancy on heat transfer augmentation for the ribbed duct is found to be less than 10% over the effect of Coriolis forces alone. Friction on the other hand is augmented 15% to 20% at the highest buoyancy number studied. Comparison with available experiments in the literature show excellent agreement.