User menu


Main menu

Bio-Inspired Flight


Simultaneous Pitch-Up and Rotation Maneuvers Effect of Pitch Rate Variation:  The present investigation focusses on the detailed flow structure along a low aspect ratio wing undergoing combined pitch-up and rotation for a range of extreme values of reduced pitch-rate.  Quantitative imaging is employed to characterize the detailed three-dimensional flow structure.

Principal Investigators: M. Bross

Simultaneous Pitch-Up and Rotation Maneuvers:  The present investigation focusses on the detailed flow structure along a low aspect ratio wing undergoing a prevalent combination of motions, i.e., combined pitch-up and rotation, in comparison with simple pitch-up and pure rotation.  Of particular interest is the effect of rotation on the evolution of the flow structure induced by pitch-up motion. Quantitative imaging is employed to characterize the detailed three-dimensional flow structure.

The pitch-up motion of a wing is a classic maneuver that gives rise to a large-scale leading-edge vortex, which moves away from the wing and in the downstream direction with increasing time. If the wing has a small aspect ratio, formation of the leading-edge vortex takes the form of an arch vortex, and at the plane of symmetry of the wing, the large-scale vortex rapidly departs from the leading-edge. It is demonstrated herein that the nature of the pitch-induced vortex at the leading-edge is fundamentally altered in presence of wing rotation. That is, the leading-edge vortex remains at, and close to, the surface of the leading-edge of the wing with the addition of rotation.

Principal Investigators: M. Bross and D.R.T. Smith


Flow Structure on a Rotationg Wing: Effect of Steady Incident Flow: The flow structure along a rotating wing in steady incident flow is compared to the structure on a rotating wing in quiescent fluid, in order to clarify the effect of advance ratio J (ratio of free-stream velocity to tip velocity of wing). Stereoscopic particle image velocimetry leads to patterns of vorticity, velocity, and Q-criterion (constant values of the second invariant of the velocity gradient tensor), as well as streamlines, which allow identification of critical points of the flow. The effective angle of attack is held constant over the range of J, and the wing rotates from rest to a large angle that corresponds to attainment of the asymptotic state of the flow structure. Prior to the onset of motion, the wing is at high angle of attack and the steady incident flow yields a fully stalled state along the wing. After the onset of rotation, the stalled region quickly gives rise to a stable leading edge vortex. Throughout the rotation maneuver, the development of the flow structure in the leading edge region is relatively insensitive to the value of J. In the trailing-edge region, however, the structure of the shed vorticity layer is strongly dependent on the value of J. Further insight into the effects of J is provided by three-dimensional patterns of spanwise-oriented vorticity, spanwise velocity, and Q-criterion.

Principal Investigators: M. Bross and C. Ozen

Effect of Radius of Gyration: The flow structure on a rotating wing is determined via stereoscopic particle image velocimetry. Sectional and three-dimensional, volumetric reconstructions define the flow patterns as a function of Radius of gyration Ro = rg/C. Aspect ratio AR = 1 and AR = 2 rectangular, flat plates are rotated at a geometric angle of attack α= 45. The flow structure is determined at various angles of rotation, in order to characterize both the initial development and the fully evolved state of the flow structure. The radius of gyration rg/C is varied via alteration of the radius of gyration rg of the wing, to give values from rg/C = 1.2 to rg/C = 5.1 for the AR = 1 wing, and values from rg/C = 1.7 to rg/C = 4.7 for the AR = 2 wing. Large changes of the flow structure are represented by images of of spanwise vorticity; Q-criterion, spanwise velocity, downwash velocity, tangential velocity, and helical density h. At small radius of gyration, a vortex is attached to the leading edge of the wing; it is present along most of the span. At larger radii of gyration, this leading-edge vortex becomes less organized and deflects away from the surface of the wing. At the largest radius of gyration investigated for each wing, the structure of the flow in the vicinity of the leading edge is most disorganized and resembles a separated shear layer. The nature of other elements of the three-dimensional flow, such as the root and tip vortices and the downwash velocity, are closely related to the degree of coherence of the leading-edge vortex.

Principal Investigators: M. Wolfinger