Investigation of Passive Flow Modulation for Full-Scale Air-Oil Coolers for Turbofan Engine Applications

Commercial aircraft are used every day to transport people and goods around the world. For this reason, a need has been created to improve the thrust specific fuel consumption and improve the fuel efficiency of the engines used for these aircraft. To further improve the efficiency of the turbofan engine research has been focused on the cooling and lubricating system. The thrust specific fuel consumption can be increased if the thrust produced by the bypass is increased with keeping all other variables constant. The thrust can be improved within the bypass if the total pressure drop through the bypass is minimized. One of the biggest pressure drops currently in the bypass are the surface aircooled oil-coolers. Previous experimental research has been done focusing on a single heat-exchanger with a trailing flap concept to passively modulate the amount of air flow that can flow through the heat-exchanger. The previous research has focused on fix flap positions and Computational models to support that experimental rig and test section. The current research builds upon the knowledge learned from both the previous experimental and computational models. The current work, building upon previous knowledge and information gained, investigates the full-scale applications of a novel airoil cooler concept. Within this air-oil cooler configuration 3 heat exchanger assemblies have been placed in series, with water acting in place of the oil for experimental purposes. The focus of the current research is to see how the heat-exchangers and flaps would work together to passively modulate the airflow going through heat-exchangers and control the temperature of the water returning the reservoir. To accomplish this both computational models and experimental pretest predictions were done to see how the full-scale concept is going to operate. Within the computational domain several different initial Mach numbers ranging from 0.1 to 0.45 were tested both at steady-state and as a transient solution. To ensure that the experimental test rig will not fail during testing at the Embry-Riddle low-speed recirculating wind tunnel, a structural analysis was performed assuming worst case scenarios at 20% over the desired maximum test Mach number within the wind tunnel. All components designed were designed around a freestream Mach number of 0.4, and achieve a factor of safety of at least 5. Having previously tested a heat-exchanger concept model at Mach 0.45 at NASA Langley’s Curve Duct Test Rig. The Full-Scale test article was designed to the same standards that the previous model was subject to at NASA Langley. Before testing the experimental model, a series of pretest predictions were performed and showed that all 3 flaps can be at different flap angles and regulate the temperature returning to the reservoir