Systematic Numerical Investigations of Heat Exchangers Integrated Behind Propellers of Hybrid-Electric Propulsion Aircraft Configurations

Abstract

Hybrid-electric propulsion concepts have a great potential to reduce the overall emissions of aviation. For fuel cell applications heat exchangers are required to dissipate the waste heat produced by the fuel cell. The integration of heat exchangers has an impact on the aircraft aerodynamics which in turn is influencing the flow through the cooler duct. This paper applies a new method in the DLR TAU code to model a heat exchanger using the body force method in the Flowsimulator framework.

Integrating heat exchangers behind propellers generally has the benefit that heat can be dissipated even at low aircraft velocities due to the propeller slipstream. This paper analyzes integration effects of a cooler placed behind a propeller. The cooler position behind the propeller and the cooler duct shape are varied by adjusting the length and cross-sections of the diffuser, heat exchanger, and the nozzle.

The studies showed that the heat flux is mainly influenced by the outlet and inlet areas. The position of the components only has a minor impact on the heat flux but can be used to optimize the aerodynamic efficiency by avoiding flow separations and minimizing the drag. The results indicate that the slip stream can also have a negative effect on the cooler performance if the distance to the propeller is too low and local side slip angles get too high leading to flow separations.