CFD analysis of the heat transfer from a self-launch sailplane radiator

Abstract

A self-launch sailplane is an aircraft equipped with a retractable engine/propeller combination which can take-off on its own power. The engine can also be used to extend flights if necessary. The engine-driven propeller is mounted on a pylon and can be deployed from the engine bay as needed. A new self-launch system is being developed to be incorporated into a high performance sailplane. The radiator plays an integral role to ensure that the engine is adequately cooled. Due to limited space in high performance sailplanes, the components of the self-launch system are located in close proximity to one another. The influence of the different components on the heat transfer capabilities of the radiator needed to be determined. Experimental tests, as well as CFD (Computational Fluid Dynamics) heat transfer and airflow analyses were required to understand how these components influence the heat transfer of the radiator. Experimental tests were completed on a grounded test bench to characterise the radiator of the self-launch system, and to determine if the engine could be sufficiently cooled by the radiator. The experiments confirmed that the radiator could not deliver satisfactorily cooling to the engine. Propeller static thrust, and radiator pressure drop experiments were also performed to acquire the necessary data for validation and setup of the simplified CFD simulation. A CFD analysis was performed to investigate the various phenomena of the self-launch system and to acquire a better comprehension of the system. A computationally efficient CFD simulation of the self-launch system was created to assist in making improving alterations to the heat transfer capabilities of the system. The radiator was simulated as a porous medium, and the propeller as a blade element momentum virtual disk. These simplified methods helped to reduce the computational power needed for the CFD simulation. The CFD simulation revealed that the pylon directed airflow away from the radiator, reducing the airflow travelling through the radiator. A radiator scoop and a pylon fairing were added to the CFD simulation, in an attempt to increase the airflow through the radiator. Both the radiator scoop and the pylon fairing increased the airflow through the radiator by an impressive 25% and 19% respectively. Additionally, the radiator scoop was designed to be uncomplicated, quick and economical to manufacture. It was therefore chosen as the superior concept to be used to reduce the engine temperatures in the final experiments. The experiments were repeated with the radiator scoop installed in order to determine the improvements made in the heat exchanged by the radiator. It was found that the engine could reach its maximum speed of 6000 rpm without overheating. Without the scoop installed, the system overheated at 5100 rpm. The scoop forced enough air through the radiator to ensure that the engine was adequately cooled when run at full throttle. All the study's objectives were met and it proved that CFD can be an effective tool to analyse the airflow and heat transfer of a sailplane self-launch system. The study also showed that the CFD simulation can be used to improve systems with complex flow phenomena.