Numerical Investigation of Effect of Parameters on Hovering Efficiency of an Annular Lift Fan Aircraft

Abstract

Abstract:The effects of various parameters on the hovering performance of an annular lift fan aircraft are investigated by using numerical scheme. The pitch angle, thickness, aspect ratio (chord length), number of blades, and radius of duct inlet lip are explored to optimize the figure of merit. The annular lift fan is also compared with a conventional circular lift fan of the same features with the same disc loading and similar geometry. The simulation results show that the pitch angle of 27 • , the thickness of 4% chord length, the aspect ratio of 3.5~4.0, 32 blades, and the radius of inlet lip of 4.7% generate the maximum figure of merit of 0.733. The optimized configuration can be used for further studies of the annular lift fan aircraft.

Numerical Study of Transition of an Annular Lift Fan Aircraft

“…Single-stage ducted fans were observed not to cause serious oscillations during transition. Although single-stage fans might have lower hovering efficiency due to the swirl loss, they save the space in the duct to realize larger radius of inlet lip and longer diffuser exit, which increase the figure of merit [7]. In fact, the optimized single-stage fans had the same figure of merit 0.733 as the two-stage fans [7].…”

“…Although single-stage fans might have lower hovering efficiency due to the swirl loss, they save the space in the duct to realize larger radius of inlet lip and longer diffuser exit, which increase the figure of merit [7]. In fact, the optimized single-stage fans had the same figure of merit 0.733 as the two-stage fans [7]. Single-stage fans also save duct space for stator and struts that connect the central fuselage and the outer wing.…”

“…The weight of the aircraft was 10.433 tons, the same as the maximum takeoff weight of the Apache helicopter. The geometry was optimized for hovering efficiency [7] and transition. The optimized aircraft has the figure of merit 0.733 with power loading 4.50 kg/kw.…”

“…The length of inner fan blades is 1.35 m (r = 6.35-5 m); the length of outer fan blades is 0.65 m (r = 7.1-6.45 m). The geometry was optimized for hovering efficiency [7] and transition. The optimized aircraft has the figure of merit 0.733 with power loading 4.50 kg/kw.…”

“…In the present work, the transition was studied in detail and in depth to eliminate the oscillations. Once the oscillations were improved, the configuration of the annular lift fan aircraft was optimized for hovering efficiency [7], and then the pitching, rolling, and yawing moments as well as the momentum drag during transition were further investigated with the optimized model. constrained by the sizes of fuselage or wing that the disk loading has to be high, thus leading to low lift efficiency (power loading).…”