Spatiotemporal distributions of sweeping jet film cooling with a compact geometry

The spatiotemporal distributions of the coolant coverage behind the 777-shaped hole, sweeping jet (SJ), and compact SJ were quantified comprehensively. Nitrogen gas was selected as the coolant, and its blowing ratio (M) was set from M = 1.0 to 3.0. The fast pressure-sensitive paint technique was applied to measure the instantaneous, mean, and unsteady film cooling effectiveness of the three configurations, and these data are compared side-by-side with the 777-shaped hole. The measured velocity spectra demonstrated a close level of Strouhal number for the SJ (St = 1.6–1.7) and compact SJ (St = 1.5–1.6). Due to the dynamic nature, both the SJ and compact SJ exhibited a highly unstable cooling effectiveness over the surface. Their effectiveness values were found to be lower than the 777 hole at relatively low M, but the compact SJ surpassed it and showed the highest effectiveness (i.e., the best cooling performance) as M ≥ 2.0 due to the widest coolant spreading. Compared with the SJ, the effectiveness of the compact SJ was consistently higher, but its coherence of flow structure was reduced, as revealed by a proper orthogonal decomposition analysis. Further simulations vividly describe the flow structures and oscillating processes inside the sweeping actuators. The SJ with compact geometry exhibited a lower exit momentum and more uniform coolant coverage than the SJ, leading to augmented adiabatic effectiveness.