Accurate prediction of ribbed duct flow and heat transfer is of importance to the gas turbine industry. Detailed heat transfer in a two pass stationary square duct with rib turbulators is studied using wall modeled Large Eddy Simulations (WMLES). Each pass has ribs on two opposite walls and aligned normal to the main flow direction. The rib pitch to rib height (P/e) is 9.28, the rib height to channel hydraulic diameter (e/Dh) is 0.0625 and calculations have been carried out for a bulk Reynolds number of 25,000. The present study validates the use of WMLES for predicting flow and heat transfer with published data on similar geometries. The calculations predict the major flow features with reasonable accuracy especially distribution of mean and turbulent quantities in the developing, fully developed and 180° bend region. It is found that the mean flow and turbulent quantities do not become fully developed until the flow passes the fifth rib of the duct. Results show that the heat transfer augmentation is higher in the second pass after the 180° turn compared to the first pass. Local heat transfer comparisons show that the heat transfer augmentation shifts towards the outside smooth wall in the second pass after the 180° turn. In addition to primary flow effects, secondary flow impingement on the smooth walls is found to develop by the fifth rib, while it continues to evolve downstream of the sixth rib. Results show the local and average distribution of Nusselt numbers normalized with classical Dittus and Boelter correlation.

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