Aerodynamic Analysis-Driven Design and Simulation of a Lift Fan System for Next Generation Fighter Aircraft

Abstract

The advancement in the aerospace industry has given much versatile technologies, but they all have their own complications and limitations. The history of Vertical Take-off and Landing (VTOL) aircrafts started with helicopters, then to tilt rotor aircrafts and then to turbo powered machines, but they all had their limitations when it came to their implementation in a fighter aircraft. The main purpose of this research is to design a contra-rotating ducted lift fan for VTOL application in the Next Generation Fighter Aircrafts (NGFA). CFD simulations of an NGFA are performed in ANSYS Fluent at various operating conditions in cruise and VTOL mode to identify lift fan design requirements. RANS with SST k-ω turbulence model was used to perform Cruise simulations at 0.7-0.9 Mach number at 0 to 5 degrees angle of attack. Similarly, for VTOL overset mesh technique of ANSYS Fluent was utilized. Based on CFD simulations, theoretical calculations were performed to obtain blade profile, number of blades, number of stages, and duct diameter etc. The analysis suggested a two stage contra-rotating ducted fan with 50inch diameter designed to achieve 80kN thrust. To achieve 80KN thrust, pressure ratio of 1.9 at 3000 RPM and 204 kg/s mass flow rate was proposed. To test the performance of the proposed lift fan, ANSYS CFX which specializes in CFD of turbomachinery was used. The simulation results showed an excellent agreement with the theoretical design calculations. The proposed two stage contra-rotating lift fan attained 71% efficiency to achieve the design requirements of 80KN thrust with 12% error. The pressure ratios, velocity differentials, swirling, isentropic efficiencies, temperature variations along with density changes were mainly observed for the thrust production of the lift fan unit.