Date of Award

Summer 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Colin P. Britcher

Committee Member

Robert L. Ash

Committee Member

Richard W. Barnwell

Committee Member

Oktay Baysal

Committee Member

David A. Dress

Abstract

A study is reported on subsonic bluff body near-wake flows. It has been determined that one family of bluff bodies, namely slanted-base ogive cylinders, can experience either a closed recirculating near-wake, or a longitudinal vortex near-wake depending on the base slant-angle and the Reynolds number. This suggests a dependence of near-wake parameters on the state of the boundary layer ahead of separation. This report addresses the influence of the boundary layer on the near-wake of slanted-base bluff bodies. Experiments were conducted in two facilities, the 6-inch Magnetic Suspension and Balance System (MSBS) at NASA Langley Research Center and the Old Dominion University low-speed wind tunnel. Interference-free drag measurements in the 6-inch MSBS validated previous drag results. Measurements in the ODU facility were made to determine base pressures, wake stagnation point locations, and boundary layer velocity profiles. Furthermore, spectral and cross-spectral analyses of the fluctuating streamwise velocity in the near-wake were performed to determine frequencies and coherence of large-scale structures. It was determined that despite variations in the boundary layer state, base pressures and wake stagnation point locations correlate with the Reynolds number based on the boundary layer momentum thickness as the independent variable. Variations in the frequency and coherence of large-scale structures were shown to exist with fixed boundary layer transition. A two-dimensional representation of a slanted-base configuration was studied analytically using classical theories and computationally using an existing finite element package. This study confirmed that the sudden changeover in wake structure is a result of flow reattachment onto the slanted-base.

DOI

10.25777/05xq-r588

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