Effect of pulsed coolant injection on unsteady film cooling characteristics with serrated trench design

Abstract

To increase cooling effectiveness, film-hole designs with serrated trenches have been widely reported in the gas turbine industry. However, the unsteadiness level of the film coverage and the inevitable environmental pulsation are always neglected, which may lead to an unexpected failure of hot components by the instantaneous exposure to a high-temperature environment. In this work, a series of large eddy simulations are conducted to comprehensively evaluate the transient film cooling performance with serrated trench designs, and the effect of pulsed cooling air injection is discussed. Time-averaged results reveal that: 1) under steady condition, serrated trench design exhibits a higher film effectiveness in most regions compared to the traditional transverse trench, which supports the previously reported advantage. 2) Pulsed cooling air injection would cause a significant reduction of film effectiveness for the serrated trenches. Under the pulsed condition, film effectiveness with a serrated angle of 100° can be over 20% lower than that with a traditional transverse trench. Moreover, transient results indicate that under both steady and pulsed conditions, the serrated trenches always exhibit a lower steadiness level of film cooling, relative to the traditional transverse trench. Therefore, it should be prudent to suggest film cooling with serrated trenches in practical designs.