Abstract
In a triple-hole system comprising a primary hole and two sister holes, when the sister holes are positioned slightly downstream of the main hole under steady flow conditions, their jets generate an anti-counter-rotating vortex pair. Vortex interactions between the jets increase the effectiveness of adiabatic film cooling. In this study, a series of large-eddy simulations were conducted to understand how pulsations in the main flow affect film cooling in a triple hole. To understand the effects of pulsations on film cooling performance is important for better cooling design of the gas turbine engines. The numerical simulations were carried out on a flat plate geometry with a triple cylindrical hole system at 35° injection angle. The pulsations were approximately sinusoidal, and their effect on film cooling was investigated at several frequencies (2, 16, and 32 Hz) and Strouhal numbers (Sr = 0.1005, 0.8043, and 1.6085) at an average blowing ratio of 0.5. The results for the triple-hole system were compared with those for a single hole for the same amount of cooling air and the same cross-sectional area of the holes. Increasing the Strouhal number of the main flow decreased η in both systems. However, at each Strouhal number, η was higher in the triple hole. Furthermore, the triple-hole system was found to be better for film cooling than a single-hole system for higher values of the pulsation Strouhal number. Contours of time-averaged film cooling effectiveness and dimensionless temperature, instantaneous film cooling effectiveness contours on a test plate, mean velocity magnitude contours in the hole, and Q-contours for the triple holes under the application of pulsations to the flow were investigated.
Highlights
The efficiency of the gas turbine can be improved by raising the inlet temperature [1]
By performing an large-eddy simulation (LES), the current study investigated the effect of oscillating the main flow at various Strouhal numbers on film cooling with cylindrical triple holes on a flat plate
The specific goal of the current study is to investigate the effects of the main flow pulsation on the film cooling performance for the triple holes system in order to help for making better cooling design of the gas turbine engines
Summary
The efficiency of the gas turbine can be improved by raising the inlet temperature [1]. Javadi et al [5] controlled the vortex interactions between injectant and main flow at the blowing ratio, M of 0.5 They numerically found that two sister holes reduced the mixing between the coolant injectant and the crossflow, thereby increasing η. Ely et al [6] numerically investigated the increase in η after forming two sister holes [3] They varied the blowing ratio among the values 0.2, 0.5, 1.0, and 1.5 and reported an obvious improvement in η at high M. Wu et al [8] determined the cooling performance of three types of sister hole configurations by using experimental and numerical methods They stated that the effectiveness of the film cooling was considerably higher for the triple-hole configurations compared with that for a single-hole configuration under steady flow conditions
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