The Effect of Land Diffuser Angles on Film Cooling Effectiveness of Blade Trailing Edge Cutback

For the purpose of increasing the efficiency and power of gas turbines, turbine inlet temperature (TIT) has been increasing. Higher TIT induces higher thermal load on modern gas turbines, so the life of the components which are exposed to hot gas has decreased. Therefore, cooling techniques are required to reduce thermal load. The cooling techniques applied on blade trailing edge cutback are limited on account of structural features; for example, a relatively small and thin space of airfoils. Film cooling is one of the techniques that is currently applied for cutback cooling and it is a way to protect blade surface from hot mainstream by covering the surfaces with coolant coming out from the blade. However, because of the lip, vortex shedding occurs and induces the mixing of hot mainstream and coolant flow, which diminishes adiabatic film cooling effectiveness. In this study, the distributions of adiabatic film cooling effectiveness on the blade trailing edge cutback and land surfaces up to 15-slot-height-downstream from the slot were measured at the blowing ratio of 1 and three land diffuser angles: 0˚, 5˚ and 10˚. The pressure sensitive paint (PSP) technique was used to measure adiabatic film cooling effectiveness distributions. The test specimens were designed in two parts, one is pin-fin internal cooling and the other is cutback film cooling. The pitch to slot height ratio (P/H) of two row pin-fin arrays were 5. The lip thickness to slot height ratio (t/H) and the land width to slot height (Lb/H) are 1.5 and 2.67, respectively. The results indicate, among three cases, the case with the smallest land diffuser angle had the best laterally averaged effectiveness on the cutback surfaces. Furthermore, laterally averaged effectiveness decreased faster through streamwise direction as a diffuser angle gets larger. On the land surfaces, which is the top surfaces of the lands, the highest value of laterally averaged effectiveness of each case gets larger as a diffuser angle gets larger. Lastly, due to the area of cutback and land surfaces, following results were observed in terms of laterally averaged effectiveness for total surfaces including cutback and land surfaces: at the upstream, from slots to 9-slot-height-downstream, the case with the largest diffuser angle had the highest film cooling effectiveness, and moderate diffuser angle case had the highest film cooling effectiveness at further downstream.

(Acknowledgement: This work was supported by the Human Resources Development program (No.20174030201720) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy. This work is also supported by Doosan Heavy Industries & Construction.)