Numerical predictions on fluid flow and heat transfer in U-shaped channel with the combination of ribs, dimples and protrusions under rotational effects

Recently, dimple and protrusion structure has been proved as an effective heat transfer augmentation approach on coolant channel due to its advantage on pressure penalty. A compound heat transfer enhancement technique, the combination of ribs, dimples or protrusions, is applied to a U-shaped square channel similar with the gas turbine blade internal passage. Considering the rotational condition of gas turbine blade on operation, the effect of rotation is also investigated for the coolant channel in order to approximate more to the real operation condition. Thus, the objective of this study is to discuss the effect of rotation on fluid flow and heat transfer performance of turbine blade similar U-shaped channel with the combination structure of ribs, dimples or protrusions. The investigated Reynolds number is 1.25 million and considered rotational number includes 0, 0.4 and 0.6. From the results, the fluid patterns of two-pass channel with compound heat transfer enhancement structure are presented for none-rotating and rotating cases. Meanwhile, spatially Nusselt distributions of roughened walls are obtained to reveal the heat transfer rates. Finally, the area averaged Nusselt number ratio and channel friction penalty are evaluated. The results indicate that rib-protrusion structure seems to be the most effective structure while rib-dimple structure has only slight advantage than ribbed channel. Furthermore, the additional friction penalty by dimple and protrusion structure is tiny. It can also be expected that, the thermal performance of this compound structure can be even improved after a denser arrangement of dimple/protrusion structure and optimal shape design.