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In film cooling for thermal protection of turbine airfoils, the interaction of the cooling jet with the mainstream creates a counter-rotating vortex pair, causing the coolant to detach from the wall, particularly at high blowing ratios (BRs). Eight bionic composite cooling structures inspired by the shark skin structure are proposed to improve the film cooling effectiveness (FCE). The flow characteristics, adiabatic FCE and flow loss are numerically analyzed in detail by using RANS method and Realizable k-ε model, emphasizing the flow loss in the BRs range of 0.5–1.5. Because the cooling jets are separated towards both sides, the coolant near the centerline of the sine-wave and V-shaped trenches is relatively reduced, but the CRVP formed on both sides pushes the cooling fluid back to the cooled wall surface. The mechanism of improved FCE is revealed by the gas convergence to the centerline of the V-shaped, fan-shaped, and wave-shaped surface structures. The variation of blow ratio has a slight influence on the FCE of different cooling configurations. At 25 < X/D < 30, the spanwise-averaged FCE of the VT-WaveS increases significantly, (11.66 %–12.20 % when the BR is 1.0 and by 10.74 %–12.42 % when the BR is 1.5) compared to the sine-wave trench with V-shaped surface. The blade-shaped surface forms more uniform temperature distribution on the flat plate. The discharge coefficient of the VT-BladeS performs best at the BRs of 1.0 and 1.5. The total pressure loss coefficients of the cases are very close. This study revealed the mechanism of the composite structure to improve the FCE of the blade, and the proposed surface structure laid a foundation for the application of shark-skin-inspired surfaces in blade cooling. [ABSTRACT FROM AUTHOR]

Film cooling is a commonly used thermal protection technology for turbine airfoils. However, due to the counter-rotating vortex pair (CVP) generated by the interaction between the cooling jet and the mainstream, the coolant gradually breaks away from the wall, which is particularly evident at high blowing ratios. For the sake of improving the film cooling effectiveness (FCE) under high inlet temperature conditions, a novel film cooling structure (SerrTrench-VSS) that combines serrated trench film holes with shark skin-inspired V-shaped surface (VSS) is proposed. The RANS method and realizable k - ε model are used for the simulations. The flow characteristics, adiabatic FCE, and resistance loss are analyzed in detail when the blowing ratio (BR) is 0.5–1.5 and then compared with the traditional cylindrical film hole and transverse trench film hole. In addition, the impact of VSS height on the cooling performance is investigated and the best height of the structure is determined. The results show that the SerrTrench-VSS has better FCE. The serrated trench can destroy the CVP and improve the spanwise spreading ability of the coolant. Also, the VSS can converge the cooling jet downstream of the film hole toward the centerline, thereby improving its extension ability along the flow direction. In the studied range of blowing ratio, the SerrTrench-VSS has the best FCE, and the spanwise-averaged FCE increases by up to 10.50% when BR = 0.5. The empirical correlations between the globally-averaged FCE and the height ratio within the range of the present study are also given. For the serrated trench, the cooling jet has the best spanwise spreading and flow extension ability when the VSS height is 0.5 D. The proposed novel film cooling structure (SerrTrench-VSS) can effectively improve the FCE and provide feasible means for the efficient cooling of a turbine blade under practical conditions. [Display omitted] • A V-shaped surface structure inspired by shark skin was proposed for film hole cooling. • It can concentrate the downstream cooling jet and inhibit the counter-rotating vortex pairs. • The best height of the V-shaped surface structure was determined. • The best cooling effectiveness can be obtained by combining a serrated trench with this structure. • The globally-averaged film cooling effectiveness and the height ratio were empirically correlated. [ABSTRACT FROM AUTHOR]