As a propulsion system for vertical take-off and landing (VTOL) aircraft, the gas-driven fan propulsion system has received some attention in recent years due to its simple mechanical structure and good performance. During the operation of the propulsion system, the core turbofan exhaust is directed to the tip turbine to drive the ducted fan to obtain thrust, and the louvered vector exhaust device is used to achieve lift/thrust switching. However, due to the linkage characteristics of the guide vanes of the exhaust device, the exhaust area will gradually change with the deflection of the guide vanes. This may cause uncertain effects on the system. Besides, considering the development cost of the propulsion system, it is necessary to clarify whether the core turbofan needs to be redesigned based on the characteristics of the system. Further, the transitional performance (VTOL to flight) of the propulsion system also needs to be studied. To this end, this study established an overall model of the gas-driven fan propulsion system combined with the characteristics of the core turbofan to analyze these problems. The results indicate that the louvered vector exhaust device can well match the gas-driven fan propulsion system. And when the propulsion system is composed, the gas-driven fan will not significantly affect the operation characteristics of the core turbofan. Besides, the preliminary analysis shows that the gas-driven fan propulsion system can meet the power requirements of the transition state of the fixed-wing VTOL aircraft. And the characteristics of the propulsion system may make the take-off thrust-weight ratio requirement of the fixed-wing VTOL aircraft be as low as 1.1.
CFD Study of an Annular-Ducted Fan Lift System for VTOL Aircraft
