Abstract
High thrust and low specific fuel consumption (SFC) are important for vertical takeoff and landing (VTOL) vehicles. An effective way to decrease the SFC is to increase the bypass ratio (BPR) of the propulsion system. The air-driven fan (or fan-in-wing) has a very high bypass ratio and has proved to be successful in VTOL aircrafts. However, the tip turbine that extracts energy for the air-driven fan faces the low-solidity problem and performs inadequately. In this study, we developed a high-reaction method for the aerodynamic design of a tip turbine to solve the low-solidity problem. A typical tip turbine was selected and designed by both conventional and high-reaction methods. Three-dimensional flow fields were numerically simulated through a Reynolds-averaged Navier-Stokes (RANS)-based computational fluid dynamics (CFD) method. The energy extraction rate was proposed to evaluate and display the energy extraction capability of the turbine. The results showed that the high-reaction turbine could solve the low-solidity problem and significantly increase the isentropic efficiency from approximately 80.0% to 85.6% and improve the isentropic work by 71.9% compared with the conventional method (from 10.28 kW/kg to 17.67 kW/kg).
Highlights
The aircraft vertical takeoff and landing (VTOL) capability has become an important field in current aviation technology research
For VTOL aircraft, Zimbrich concluded in reference [5] that the bypass ratio (BPR) of its engine must be high under takeoff conditions to ensure the thrust against its weight
We developed the high-reaction method for the aerodynamic design of a tip turbine to achieve high efficiency with a limited blade number, and summarized the mechanism of this method to improve the flow field, which is a continuation of the research done on ADFTTs
Summary
The aircraft vertical takeoff and landing (VTOL) capability has become an important field in current aviation technology research. The propulsion systems for VTOL vehicles have two requirements: low specific fuel consumption (SFC) during takeoff and landing procedures and a multipoint distributed arrangement. The air-driven fan (as well as the lift fan) has proved to be very effective at achieving vertical takeoff and landing. Przedpelski [3] studied the XV-5 using lift fan in the early. 1960s, and Hunziker [4] summarized the research work of X-32 of the Boeing Company, which applied a lift fan in the 2000s. For VTOL aircraft, Zimbrich concluded in reference [5] that the bypass ratio (BPR) of its engine must be high under takeoff conditions to ensure the thrust against its weight
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