The leading-edge vortex (LEV) is known to produce transient high lift in a wide variety of circumstances. The underlying physics of LEV formation, growth, and shedding are explored for a set of canonical wing motions including wing translation, rotation, and pitching. A review of the literature reveals that, while there are many similarities in the LEV physics of these motions, the resulting force histories can be dramatically different. In two-dimensional motions (translation and pitch), the LEV sheds soon after its formation; lift drops as the LEV moves away from the wing. Wing rotation, in contrast, incites a spanwise flow that, through Coriolis tilting, balances the streamwise vorticity fluxes to produce an LEV that remains attached to much of the wing and thus sustains high lift. The state of the art of vortex-based modeling to capture both the flow field and corresponding forces of these motions is reviewed, including closure conditions at the leading edge and approaches for data-driven strategies.

The noise goal of the Silent Aircraft Initiative, a collaborative effort between the University of Cambridge and Massachusetts Institute of Technology, demanded an airframe design with noise as a prime design variable and a design philosophy that cut across multiple disciplines. This paper discusses a novel design methodology synthesizing first-principles analysis and high-fidelity simulations, and it presents the conceptual design of an aircraft with a calculated noise level of 62 dBA at the airport perimeter. This is near the background noise in a well-populated area, making the aircraft imperceptible to the human ear on takeoff and landing. The all-lifting airframe of the conceptual aircraft design also has the potential for improved fuel efficiency, as compared with existing commercial aircraft. A key enabling technology in this conceptual design is the aerodynamic shaping of the airframe centerbody. Design requirements and challenges are identified, and the resulting aerodynamic design is discussed in depth. The paper concludes with suggestions for continued research on enabling technologies for quiet commercial aircraft.

No abstract

The rotating wing experiment is a fully three-dimensional simplification of the flapping-wing motion observed in nature. The spanwise velocity gradient and the wing starting and stopping acceleration that exist on an insectlike flapping wing are generated by the rotational motion of a finite-span wing. The flow development around a rotating wing at Re 60; 000 has been studied using high-speed particle image velocimetry to capture the unsteady velocity field. Lift and drag forces have been measured for several different sets of wing kinematics and angles of attack. The lift curve shape was similar in all cases. A transient high lift peak, approximately 1.5 times the quasi-steady value, occurred in the first chord length of travel, and it was caused by the formation of a strong attached leading-edge vortex. This vortex then separated from the leading edge, resulting in a sharp drop in lift. As weaker leading-edge vortices continued to form and shed, lift values recovered to an intermediate value. The circulation of the leadingedge vortex has been measured and agrees well with the force data. Wing kinematics had only a small effect on the aerodynamic forces produced by the waving wing. In the early stages of the wing stroke, the velocity profiles with low accelerations affected the timing and the magnitude of the lift peak, but at higher accelerations, the velocity profile was insignificant.

No abstract