Aerodynamic Performance and Aeroacoustic Characteristics of Model Rotor with Anhedral Blade Tip in Hover

Experimental investigation on the aerodynamic performance and aeroacoustic characteristics of model rotors with different tip anhedral angles in hover are conducted in the paper.Three sets of model rotors with blade-tip anhedral angle 0°(reference rotor),20°and 45°respectively are designed to analyze the influence of the anhedral angle on the hovering performance and aeroacoustics of rotor.In the environment of anechoic chamber,the hover experiments under the different collective pitch and blade numbers,are carried out to measure the figure of merit(FM),time history of sound pressure and sound pressure level(SPL)of the three rotor models.Based on test results,the comparison and analysis of hovering performance and aeroacoustic characteristics among the three rotor models have been done.Meanwhile,for the sake of analysis,the rotor wake and blade pressure distribution are simulated by means of computational fluid method(CFD).At last,some conclusions about the effects of blade-tip anhedral angle on the aerodynamic performance and aeroacoustic characteristics in hover are obtained.An anhedral blade tip can enhance the FM of the rotor,and decrease the rotor loads noise to some extent.

Aerodynamics of non-slender delta and reverse delta wings:Wing thickness,anhedral angle and cropping ratio

The effects of thickness-to-chord(t=c)ratio,anhedral angle(d),and cropping ratio from trailing-edge(Cr%)on the aerodynamics of non-slender reverse delta wings in comparison to non-slender delta wings with sweep angle of 45°were characterized in a low-speed wind tunnel using force and pressure measurements.The measurements were conducted for total of 8 different delta and reverse delta wings.Two different t/c ratios of 5.9%and 1.1%,and two different anhedral angles ofd=15°and 30°for non-cropped and cropped at Cr=30%conditions were tested.The results indicate that the reverse delta wings generate higher lift-to-drag ratio and have better longitudinal static stability characteristics compared to the delta wings.The wing thickness has favorable effect on longitudinal static stability for the reverse delta wing whereas longitudinal static stability is not influenced by wing thickness for the delta wing.For reverse delta wings,the anhe-draled wing without cropping has adverse effect on aerodynamic performance and decreases the lift-to-drag ratio.Cropping in anhedraled wing causes significant improvement in lift-to-drag ratio,shift in aerodynamic and pressure centers towards the trailing-edge,and enhancement in longitudi-nal static stability.