Aerodynamic impact of finned heat exchangers on transonic flows

Ongoing engine developments require advanced thermal management technologies to handle the increasing demand of refrigeration and lubrication. As the thermal capacity of the oil lubricant and coolant circuits becomes saturated, conventional fuel-based oil cooling systems need to be supplemented with additional cooling sources. Finned heat exchangers integrated in the core/bypass-flow splitter surface of a turbofan provide enhanced oil heat removal capabilities. For a positive impact in the overall engine efficiency, the surface heat exchangers need to be designed to maximize heat transfer while minimizing the impact in the propulsive efficiency. This work focuses on the sensitivity of the complex transonic and three-dimensional turbofan bypass-flow to arrays of fins embedded on the splitter, which determines the aerodynamic penalty that can be incurred at the benefit of increased oil heat capacity. We present an experimental study of a turbofan bypass-flow and asses the flow modifications introduced by two different fin heat exchanger designs, with “continuous” and “interrupted” fins, both aligned with the mean flow direction. Experiments were performed in a ground test facility that reproduces the flow in the bypass duct of turbofan at the design point characterized by cruise velocities and take-off atmospheric conditions. Different measurement techniques were adapted to the flow and wind tunnel requirements to provide an accurate characterization of the flow developing over the splitter surface. Results are reported in terms of flow velocity and orientation, turbulence intensity and temperature with and without the arrays if fins present in the flow. This work demonstrates the importance of aerodynamically optimized designs to minimize detrimental effects on propulsive efficiencies, and provides estimate values of flow disturbances in realistic engine conditions that can be incorporated into simplified engine performance models.