The present study aimed at studying the transition of annular lift fan aircraft through\ncomputational fluid dynamics (CFD) simulations. The oscillations of lift and drag, the optimization\nfor the figure of merit, and the characteristics of drag, yawing, rolling and pitching moments in\ntransition are studied. The results show that a two-stage upper and lower fan lift system can generate\noscillations of lift and drag in transition, while a single-stage inner and outer fan lift system can\neliminate the oscillations. The characteristics of momentum drag of the single-stage fans in transition\nare similar to that of the two-stage fans, but with the peak of drag lowered from 0.63 to 0.4 of\nthe aircraft weight. The strategy to start transition from a negative angle of attack âË?â??21ââ??¦ further\nreduces the peak of drag to 0.29 of the weight. The strategy also reduces the peak of pitching torque,\nwhich needs upward extra thrusts of 0.39 of the weight to eliminate. The peak of rolling moment in\ntransition needs differential upward thrusts of 0.04 of the weight to eliminate. The requirements for\nextra thrusts in transition lead to a total thrustââ?¬â??weight ratio of 0.7, which makes the aircraft more\nefficient for high speed cruise flight (higher than 0.7 Ma).
Loading....