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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]

Mist-assisted film cooling has exhibited great potential for efficient cooling of a turbine vane due to the vaporization of water droplets flowing with the air. To further improve the film coverage and cooling effectiveness, it is necessary to find a structure that allows the coolant flow to expand laterally and inhibits the separation of the coolant jet from the wall. Therefore, we propose in this work to study the influence of serrate structure on the cooling performance of trenched holes by examining the flow and heat transfer characteristics of the mist/air mixture. As water evaporation is involved in this process, the dry-bulb temperature may not be suitable for evaluating the film cooling performance. Therefore, a wet-bulb-temperature-based film cooling effectiveness (WFCE) is proposed. The results show that the included angle of serrate plays a significant role in WFCE. In addition, the area-average WFCE of the trenched holes increases first and then decreases as the blowing ratio increases. The concentration of mist and the diameter of droplets are found to be crucial for significantly affecting the WFCE. The relationship between the film cooling effectiveness and the contribution of mist is explicated by empirical correlation with the mist concentration and droplet diameter. The empirical correlation, especially the exponential increasing trend with the square root of mist concentration at a constant droplet diameter, provides the basis for further theoretical analysis of the mechanism of cooling effectiveness improvement. Under the practical condition, it is also proved that the serrated transverse trench structure and the addition of mist to the coolant air can improve significantly the film cooling performance for the turbine vane. • Influence of serrate structure on mist/air film cooling performance of trenched holes is studied. • Wet-bulb-temperature-based film cooling effectiveness (WFCE) is proposed and evaluated. • WFCE increases linearly with droplet diameter when mist concentration is given. • WFCE increases exponentially with square root of mist concentration at constant droplet diameter. • The cooling strategy is proved for turbine vane under practical condition. [ABSTRACT FROM AUTHOR]

In this work, the influence of several lip structures on the effectiveness of film cooling and the flow fields of transverse trenched holes at different blowing ratios (BRs) ranging from 0.5 to 2.0 is numerically investigated, using the Reynolds averaged Navier Stokes method with the realizable k - ε turbulence model. The trenches include the traditional transverse trench, the bevel trenches, and the fillet trenches. It shows that the trenched holes produce weaker counter-rotating vortex pairs, which can enhance the effectiveness of film cooling compared with the standard cylindrical film hole. It demonstrates that the lip structures can improve the effectiveness of film cooling of the trenches at low BRs, but it has a negative effect at high BRs. It is found that the lower lip structures have less influence on the effectiveness of film cooling at different BRs than the upper lip structures. It is also found that the upper part of the fillet structure employs the Coanda effect to make the coolant flow close to the wall, thereby improving the effectiveness of film cooling; while the lower part of the fillet structure is conducive to converting the coolant flow into a vertical jet, thereby improving the effectiveness of film cooling at low BRs. [ABSTRACT FROM AUTHOR]

• A new method of defining the velocity field in the coolant inlet is used to quantitatively investigate the effects of the coolant swirl intensity on the film cooling performance in the operating conditions of h series turbine vanes. • The critical value of the coolant vorticity to the transformation of film coverage is 20,000 /s. • When the coolant vorticity is 40,000 /s, the area-averaged film cooling effectiveness at the near field downstream of the film hole is 54 % higher than the non-swirling case. • With high blowing ratios and large vorticities, a stable flow field is formed, where the additional coolant vortex and induced vortex appear. • For high blowing ratios, with the increase of the vorticity, the momentum advantage of the coolant gradually transforms into the effectiveness advantage. Advanced H/J series heavy-duty gas turbines are widely equipped with film cooling to protect turbine blades. Previous studies have shown that coolant swirl has an important influence on film cooling performance. However, there are few studies on the quantitative analysis of the coolant swirl intensity because of the swirl generated by the specific structure, and most of the research was carried out at relatively low temperatures. In this paper, a new method of defining the velocity field in the coolant inlet is used to quantitatively investigate the coolant swirl intensity. A numerical study of the film cooling performance for the coolant jet with various swirl intensities is conducted in the operating conditions of H series turbine vanes. The effects of the blowing ratio and coolant vorticity on the vortex structure and mixing process of the flow field are investigated emphatically, and the mechanisms for the variation of the film cooling effectiveness are analyzed. The results show that the film cooling effectiveness is greatly improved with the swirling coolant jet at high blowing ratios. When Ω n =40,000 /s, the area-averaged (L = 5 D) film cooling effectiveness is 54 % higher than the non-swirling case. Ω n =20,000 /s is a critical value of the coolant vorticity. When Ω n >20,000 /s, the film coverage transforms significantly. Furthermore, the main vortical structures in a typical SJICF flow field with high blowing ratios and large vorticities are proposed. Compared with the non-swirling JICF, the additional coolant vortex and induced vortex appear in the SJICF. Under the influence of the two vortices, the coolant momentum is sacrificed for enhanced attachment to the wall resulting in the momentum advantage gradually transforming into the effectiveness advantage with the increase of the vorticity. [ABSTRACT FROM AUTHOR]