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Cylindrical pin fins with tip clearances are investigated in the low Reynolds number range 5<ReD<400 in a plane minichannel. Five tip gaps are investigated ranging from a full pin fin (t*=0.0) to a clearance of t*=0.4D*, where D* is the pin diameter. It is established that unlike high Reynolds number flows, the flow and heat transfer are quite sensitive to tip clearance. A number of unique flow effects, which increase the heat transfer performance, are identified. The tip gap affects the heat transfer coefficient by eliminating viscosity dominated end wall effects on the pin, by eliminating the pin wake shadow on the end walls, by inducing accelerated flow in the clearance, by reducing or impeding the development of recirculating wakes, and by redistributing the flow along the height of the channel. In addition, tip gaps also reduce form losses and friction factor. A clearance of t*=0.3D* was found to provide the best performance at ReD<100; however, for ReD>100, both t*=0.2D* and 0.3D* were comparable in performance.

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Detailed investigation of film cooling for a cylindrical leading edge is carried out using Large Eddy Simulation (LES). Part-II of the paper focuses on the effect of coolant to mainstream blowing ratio on flow features and consequently on the adiabatic effectiveness and heat transfer ratio. With the advantage of obtaining unique, accurate and dynamic results from LES, the influential coherent structures in the flow are identified. Describing the mechanism of jet – mainstream interaction, it is shown that as the blowing ratio increases, a more turbulent shear layer and stronger mainstream entrainment occur. The combined effect, leads to a lower adiabatic effectiveness and higher heat transfer coefficient. Surface distribution and span-averaged profiles are shown for both adiabatic effectiveness and heat transfer (presented by Frossling number). Results are in good agreement with the experimental data of Ekkad et al. [12].