Date of Award

Winter 2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Colin P. Britcher

Committee Member

Oktay Baysal

Committee Member

Drew Landman

Committee Member

Stephen P. Wilkinson

Abstract

Mean and fluctuating forces acting on a body are strongly related to vortex shedding generated behind it. Therefore, it is possible to obtain substantial reductions of at least the unsteady forces if vortex shedding is controlled or its regularity is reduced. While conventional active flow control methods are mainly concerned with direct interaction with, and alteration of, the mean flow about a body, modern techniques involve altering existing flow instabilities using relatively small inputs to obtain large-scale changes of mean flows. Aerodynamic flow control may be intended to delay or suppress boundary layer separation through creation of a boundary layer downstream from the control input that is able to withstand adverse pressure gradients imposed by the outer (global) flow.

In the present work, aerodynamic characteristics of a circular cylinder at Re=156,000 and an axisymmetric body (ogive cylinder) at Re=170,000 are first analyzed using a proposed phase averaging technique for the Particle Image Velocimetry (PIV) data. Later, the effect of plasma actuators on the aerodynamic characteristics of these bodies is investigated.

When plasma actuators were placed 10° upstream of the separation point on the circular cylinder, momentum addition, and maybe the effect of local heating, modified the streamwise pressure gradient, leading to the establishment of a thinner boundary layer downstream. Phase synchronization of vortex shedding was also obtained for Re=156,000 for a narrow frequency band of the carrier signal of the actuators when they operated with a 90° phase shift To the knowledge of the author no other method has been shown to achieve vortex shedding control up to this high a Reynolds number.

Effects of the different configurations of plasma actuators on the circumference, on the base, and in a streamwise direction were investigated for the ogive cylinder. It was observed that direct alteration of the mean flow about a body was not as effective as the boundary layer flow control where the flow instabilities are exploited. Also, the three dimensionalities in this flow made it significantly more complex to analyze.

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DOI

10.25777/6twc-p129

ISBN

9780549920861

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