Unsteady propeller/wing aerodynamic interactions
Abstract
The unsteady nature of the propeller slipstream interacting with a wing has been studied by flow visualization and unsteady wing surface pressure measurements. This work has yielded information on the motion of the propeller wake as it passes over the wing. The flow field encountered in a propeller swirl recovery vane combination was investigated using a stator mounted downstream of a propeller. Flow visualization was done on the motion of the propeller helical vortex as it passes over the center of a 9.0 aspect ratio wing. Viscous dissipation at the leading edge causes the vortex to be severed, with the filaments ending on the upper and lower wing surface. The propeller tip vortex was found to experience significant spanwise displacements when passing across a lifting wing. An image vortex effect which deformed the propeller tip vortex was observed at the wing leading edge. Unsteady wing surface pressures in the propeller wake were measured by traversing a pressure instrumented wing section in a spanwise direction through the propeller wake. Inexpensive microphones proved to be suitable for pressure measurements of this type and were successfully utilized in this experiment. The propeller tip vortex was identifiable as a small region of low pressure relative to the rest of the wake. Vortex position on the wing was evident from contour plots of the pressures. Spanwise motions of the tip vortex were plotted and found to support an image vortex model proposed after the flow visualization tests. Chordwise motion of the tip vortex showed that for a lifting wing condition the upper surface vortex had a higher velocity than the lower surface. This observation on the chordwise speed agrees with what is expected for flow over a lifting wing. Viscous action on the surface of the wing was attributed with decreasing the magnitude of the wing surface pressure fluctuations as the wake progressed along the wing surface. The vortex interaction encountered in the flow field of a propeller and a stator was investigated using smoke flow visualization. A stator at angle of attack was used to generate a line vortex which interacted with the helical vortex filaments generated by a propeller. Changes in the relative vortex strengths and vortex rotational directions yielded several distinct vortex structures. Axial flow in the vortex cores is determined to influence the development of the vortex interaction.
Degree
Ph.D.
Advisors
Sullivan, Purdue University.
Subject Area
Aerospace materials
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