Effusion Cooling: Influence of Pressure Drop

Abstract

Combustor liners are exposed to significant thermal gradients with hot combustion gases on one side and compressor directed cooling air on the other side. To maintain effective life of the liners, development of effective methods to cool gas turbine combustor liners are a necessity. Effusion cooling uses uniformly spaced holes distributed throughout the surface of the combustor liner to introduce convective and film cooling to form a protective layer of coolant along the liner wall and hence reduce the impact of the combustion gases. This experimental study investigates the overall cooling effectiveness of effusion cooling under realistic crossflow coolant operating conditions. The primary factors influencing the coolant mass flow that passed through the liner into the hot main flow was hole geometry, coolant and main flow speed, and pressure drop. For this study, 4 different effusion cooling liners with increasing levels of hole density were studied. Each hole had a length to diameter ratio (L/D) of 5.8. Non-dimensionalized hole to hole spacing in the streamwise (x/D) and spanwise (y/D) direction was equal and included spacings 7.9, 11.2, 15.8, and 22.5. These configurations were tested at uniform hot side and cold side flow speeds of 7 m/s and 15 m/s with both co-flow and counter-flow coolant directions. Pressure drop through the plate was set to 2% and 4% for 7 m/s flow speed and 4% for the 15 m/s condition. Infrared Thermography (IRT) was utilized to capture hot side and cold side liner steady state temperatures. Overall, co-flow conditions resulted in higher coolant mass flow passing through the liner while counter-flow conditions increased performance. The highest hole density configuration had a 20.3% average increase in performance over the next best performing liner geometry. In addition, the highest percentage of air passed through the effusion plate liners at the lower flow rate conditions with a 4% pressure drop. Based upon the experiments done, it was clear that while multiple factors influenced the overall cooling performance of combustor liners, a higher pressure drop consistently resulted in increased performance while higher flow speed resulted in reduced overall cooling performance.