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• 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]

• A novel double-wall with composite swirl/film cooling structure was proposed. • The structure exhibited outstanding overall cooling effectiveness (OCE) in the simulated range. • The cooling performance at high blowing ratios were obtained and the OCE was sensitive to bi. • The empirical correlations obtained by nonlinear fitting were in good agreement with the simulations. • It provided a guidance for developing advanced gas turbine blades double-wall cooling structures. A novel double-wall with composite swirl/film cooling structure is proposed in this work to enhance the cooling effectiveness of contemporary gas turbine blades. The influence of different shaped chambers and Biot numbers on the overall cooling effectiveness (OCE) are investigated by Reynolds time-averaged Navier-Stokes simulations and conjugate heat transfer analysis. The results suggest that the proposed composite cooling configuration exhibits outstanding OCE in the simulated range. When the R m is 1.00 and the Biot number is 0.11, the OCE of the composite structure is improved by 8.92 % over the conventional double-wall structure, and the distribution is more uniform. In addition, the optimal flow and cooling performance of the composite swirl/film cooling structure at high R m conditions are obtained. The OCE is very sensitive to the variation of the Biot number. Finally, the empirical correlations obtained by the multivariate nonlinear regression fitting method are in good agreement with the simulations, with errors within 10 %. The results also provide important guidance for the development of advanced gas turbine blades double-wall cooling structures. [ABSTRACT FROM AUTHOR]

• Impact of double rows on air/mist film cooling is studied for the first time. • Sellers prediction model is appropriately modified for double rows. • Modified sellers method is proved to be more suitable for air/mist film cooling. • Air/mist film cooling effectiveness is accurately correlated by the modified model. Improving the multi-row film cooling effectiveness of turbine vanes and blades is becoming increasingly important, and the configuration design of the multi-row holes is becoming increasingly complex. This paper presents a simulation study of the air/mist film cooling characteristics on double-row-hole flat plates and makes predictions about spanwise-averaged cooling effectiveness using a modified Sellers superposition method. The effects of blowing ratio, row spacing, row arrangement, droplet diameter, and mist mass ratio on film cooling are systematically investigated. It is found that the injected mist improves the film cooling effectiveness under all operating conditions for the coolant air. The air/mist cooling is particularly effective at a blowing ratio of 1.25 or a row spacing of 5 D with the staggered two-row holes. The improvement in cooling effectiveness increases with increasing mass ratio or decreasing droplet diameter of the mist. Furthermore, the spanwise-averaged cooling effectiveness can be accurately predicted by modifying the classical Sellers superposition model. This study lays the foundation for accurately predicting the distribution of air/mist film cooling effectiveness of turbine vanes and blades, and helps to promote the development of practical air/mist film cooling technology. [ABSTRACT FROM AUTHOR]