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Submitted by mab509 on Thu, 2014-01-09 15:19

**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

Several representations of three-dimensional flow strucutre on wings undergoing unsteady manuevers are displayed below.

Images of three-dimensional helical density on iso-*Q* surfaces for a wing undergoing pure pitch-up, combined pitch-up and rotation, and pure rotation are displayed above. The helical density, *h,* or helicity per unit volume, is calculated by taking the scalar product of the three-dimensional velocity field **V** and the three-dimensional vorticity field **ω**, i.e. *h* = *(V*** ∙ω). **Helical density indicates to what degree a flow structure is three dimensional and serves as an indicator of vorticity flux on the primary axis of the vortex. Values of

Images of Pitch-Up and Rotation apparatus are shown below.

Fluids Research Laboratory

Lehigh University

Bethlehem, PA 18015

27 Memorial Drive West, Bethlehem, PA 18015