Experimental validation of large eddy simulations of flow and heat transfer in a stationary ribbed duct

Accurate prediction of ribbed duct flow and heat transfer is of importance to the gas turbine industry. The present study comprehensively validates the use of large eddy simulations (LES) for predicting flow and heat transfer with measured flowfield data in a stationary duct with 90° ribs and elucidates on the detailed physics encountered in the developing flow region, the fully developed region, and the 180° bend region. Among the major flow features predicted with accuracy are flow transition at the entrance of the duct; the distribution of mean and turbulent quantities in the developing, fully developed, and 180° bend; the development of secondary flows in the duct cross-section and the 180° bend; and friction and heat transfer augmentation. At the duct inlet, both the computations and experiments show that the peak turbulence intensities reach values as high as 40% in the streamwise and spanwise directions and 32% in the vertical direction, and a comparison of values along the centerline of the developing flow region shows that the mean flow and turbulent quantities do not become fully developed until they reach beyond the seventh rib of the duct. Turbulence intensities in the 180° bend are found to reach values as high as 50%, and local heat transfer comparisons show that the heat transfer augmentation shifts towards the outside wall downstream of the bend with little or no shift upstream. In addition to primary flow effects, secondary flow impingement on the smooth walls is found to develop by the third rib, while it continues to evolve downstream of the sixth rib. In all different aspects, it is found that LES produces the correct physics both qualitatively and quantitatively to within 10-15% of experiments.