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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]

Modern gas turbines use high-performance ribs to improve internal cooling performance. In this study, the aerothermal performance of a bio-inspired truncated rib arrangement with stepped length and height variations, proposed in our previous work, is systematically studied using the numerical simulation method and the rib structures are optimized using the response surface methodology. A square channel model is employed to simulate the flow of actual turbine blade, and the rhombus-patterned ribs are placed on the two channel sidewalls. The studied structural parameters include the length variation rate, height variation rate, and pitch distance. It is found that as the rib height decreases, heat transfer is enhanced while the pressure drop is decreased. In general, however, as the variation rates of height and length increase, both the heat transfer coefficient and flow loss increase. The correlations between the thermal performance factor and the three structural parameters are obtained from thirteen cases of aerothermal performance analysis, and the optimal structure of rhombus-patterned ribs is further obtained: Δ l / l 1 = 0.333, Δ e / e 1 = 0.167, and p / e 1 = 2.000. The geometric layout optimization of the novel ribs is important for providing higher thermal performance of the internal channel and hence efficient cooling of the turbine blades. • Rhombus-patterned rib structures are optimized to enhance turbine blade aerothermal performance. • The response surface methodology is used for optimizing the structural parameters. • The optimized parameters include length variation rate, height variation rate, and pitch distance. • The relationship between the thermal performance factor and these parameters are correlated. • The rhombus-patterned ribs are also suitable for application in many heat exchange devices. [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]