Direct numerical simulation of the 7-7-7 film cooling at a range of compound angles

Film cooling is essential for protecting substrate materials from the hot gases in turbomachines. Recent experiments have explored the effects of compound angles for the 7-7-7 film cooling hole, a baseline shaped film cooling hole developed at the START lab. However, differences in facility conditions, manufacturing process uncertainties, uncertainties in flow conditions, and the absence of internal cooling hole measurements necessitate further investigation to fully understand the impact of compound angles and the associated flow physics. This study presents direct numerical simulations (DNS) for the baseline 7-7-7 shaped film cooling hole, examining a range of compound angles and flow conditions paralleling those in prior lab experiments. The data gleaned offers insights into the flow dynamics within and in the vicinity of the cooling hole, particularly in areas proximate to the wall. Our findings indicate that increasing the compound angle adversely affects adiabatic cooling efficiency. A detailed analysis reveals that this decline in efficiency is primarily due to hot gas intrusion into the cooling hole, the elevation of the cooling jet from the wall, and intensified secondary flows at higher compound angles. Additionally, the DNS data reveals a logarithmic scaling in the laterally averaged mean velocity profile and a self-similarity in temperature profiles beyond a certain distance from the cooling hole.