Due to the demand of unmanned helicopters for drag reduction and rain-proof, the helicopter nacelle must be sealed. It will lead to a decrease in the heat transfer efficiency of the radiator, and the output power of the engine will drop dramatically. The helicopter's flight safety will be seriously jeopardized, especially when the helicopter is hovering (maximum engine power is needed). Currently, active cooling by equipping the radiator with a fan is the only solution, and the heat transfer efficiency of the radiator could be controlled by fan. Therefore, the performance of the fan directly affects the flight safety of the whole system. In this study, the Airfoils 30, suitable for low Reynolds number flows, is adopted to design the fan blade considering the characteristics of helicopter heat sink miniaturization and high integration. Then, a three-dimensional CFD (computational fluid dynamics) k-omega SST model is developed to investigate the effects of fan blade torsion angle, chord length, mounting angle and the number of blades on the performance of the fan. Furthermore, the constraints of radiator dimension, air flow resistance on the performance of the fan are considered comprehensively to finalize the new fan configuration. The optimised parameters of fan suitable for high flow rate (above 1.17 kg/s) are chord length is 55 mm, torsion angle is 26°, mounting angle is 39° and the blade number is 7. The fan efficiency increases about 13.6%. The power consumption decreases about 9.5% (about 73 W). The fan rotational speed decreases 10.5%. The improvement of fan efficiency is a key measure for energy conservation and carbon reduction in unmanned helicopter systems. The 73 W power consumption of the fan decrease indicates that 1.2 kg green-house gas emission reduces per day. The lower power consumption will result in a 0.14% cruising endurance increase. The fan is then manufactured by additive manufacturing based on CFD optimization results. This deep integration between CFD and additive manufacturing reduces trial and error costs and energy consumption. It also shows the promising future of UAV components autonomous manufacturing. Finally, the experiment is conducted in lab under 40℃. The experimental results indicate that the maximum output power of the engine is over than 90 kW. Based on the helicopter main rotor performance curve, the helicopter could hover indefinitely with 500 kg loading under 40 °C. It is a criterion to identify the designing success.
Si et al. (Sat,) studied this question.