Fundamental Study of Modulated Transverse Jets from a Film-Cooling Perspective

1The effects of jet flow pulsation on a vertical jet in crossflow over a flat plate were investigated using Mie scattering visualizations, hot-wire anemometry, and large eddy simulations. An unforced-jet study was conducted over a wide range of blowing ratios to provide a baseline comparison with pulsed results and exhibited two distinct transverse jet regimes with characteristic vortical-structure dynamics, separated by a transitional region responsible for a significant drop in film-cooling performance. The influence of the forcing parameters such as blowing ratio, forcing frequency, and duty cycle on pulsed jets was investigated in terms of the vortical structures generated during the transient parts of the forcing cycle, as well as their impact on wall coverage and adiabatic effectiveness. Although jet forcing led to a global decrease in film-cooling performance when compared with relevant unforced results in most cases, instantaneous quantifications revealed improvements associated with the jet-pulse onset that, if correctly exploited by proper alteration of the forcing signal, could lead to overall improved pulsed-jet film-cooling metrics.