Thermo-Fluidic characterization of different protuberance shapes upstream of transverse trench on the film cooling performance

Abstract

The efficiency of turbomachines is limited by the maximum temperature that can be supported by the blades without failure and strategy. The combined impact of transverse trenches and divided step for improving the efficiency of film cooling has been numerically investigated. The synergistic effect on working fluid and coolant flows changing position and shape of divided steps upstream of transverse trenches has been studied that can help in better coolant dispersion in the boundary-layer flow. The impact of six different configurations was analyzed with four different spacing arrangements for divided steps i.e., 2.5 mm, 5 mm, 10 mm, and 15 mm gap in the middle, one arrangement with 2.5 mm gap on both sides of the step and one full step. The effectiveness of film cooling was evaluated for blowing ratio, M = 1.0, 1.5, and 2.0 while keeping a constant density ratio of 0.97. The complex flow dynamics are simulated using the classic k-ε model in combination with 3-dimensional average Navier-Stokes equations. The results highlight the significant impact on the film cooling performance downstream of the film holes due to combined impact of trench and divided step at different blowing ratios. A 2.5 mm center dividing gap upstream of the coolant hole, in particular, show encouraging outcomes at M = 2.0. These arrangements show promise for greatly increasing the efficiency of lateral adiabatic cooling while reducing the corresponding penalty for total pressure loss. The analysis of the results shows that Case 4 with a gap size of 10 mm and at M = 2.0, exhibited the highest overall effectiveness rendering this arrangement the best for film cooling design in the gas turbines. These revelations provide significant contributions to the engineering field, where film cooling optimization, with minimum impact on mainstream flow, is crucial for overall performance, increased efficiency, and reliability.