Directional Effects of Effusion Cooling on the Cooling Film Effectiveness

Effusion cooling in gas turbine combustors is complicated by swirling flows for anchoring flame, whereas miniature effusion cooling jets are highly directional. This work aims at understanding the directional effects of effusion cooling by studying the effectiveness of cooling film as a function of the offset flow angle beta between the main flow and effusion cooling jets. The directional effects of effusion cooling on the cooling film effectiveness are investigated at offset angles of 0, 30, 60, and 90 deg. The cooling film effectiveness is determined by invoking the heat/mass transfer analogy using pressure-sensitive paint that is sensitive to the oxygen partial pressure at the paint surface. Experimental results indicate that offset angles beta have a strong effect on the cooling film effectiveness. At lower coolant mass flow rates, an offset angle increases the uniformness of the cooling film because the flows from each individual hole coalesce together to form the protective film. At higher coolant mass flow rates, the cooling film effectiveness is less sensitive to the offset angles beta. This is believed to be caused by the coolant flow lifting off the surface and dissipating more easily in the mainstream flow.