Steady RANS were performed to examine the ability of four turbulence models — realizable k-ε (k-ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSAM (RSM-τω) — to predict the turbulent flow and heat transfer in a U-duct with a trapezoidal cross section and with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimentally measured values.

For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k-ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, that maximum is 14.5% for RSM-τω, 29% for SST, and 50% for k-ε and RSM-LPS. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the secondary flow in the turn region and the separated flow downstream of the turn dominated in how well the models predict the HTC.

For the U-duct with pin fins, k-ε predicted the lowest and the least accurate HTCs, and SST and RSM-τω predicted the best. For k-ε, the maximum relative error in the averaged HTC is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

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