Date of Award

Summer 2003

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Colin P. Britcher

Committee Member

Oktay Baysal

Committee Member

Drew Landman

Abstract

A key to better performance and fuel economy for both road vehicles and aerospace vehicles is better understanding of the drag and lift mechanisms. Drag and lift can be evaluated computationally or experimentally by using various methods, such as wake surveys. Wake surveys with total pressure rakes, 5-hole rakes, and Particle Image Velocimetry techniques are routinely conducted in wind tunnels to provide insight into the flow field and hence to improve the design of the road vehicles or aircraft. However, systematic decomposition of the wake into components such as profile, induced, or wave drag appears to be further advanced in the case of aircrafts.

This thesis presents an experimental study of the wake behind a scaled racecar in a wind tunnel. It has been suggested that profile and induced drag can be evaluated if the distributions of total pressure and crossflow velocity are known in the wake. A generic 1/10th scale American LeMans Series style car model was tested in the Old Dominion University low speed wind tunnel. Wake surveys are performed at a free stream velocity of 40 mis giving a Reynolds number of 1.36x 106based on the model length. Quantitative total pressure measurements in the wake were obtained by using a pitot rake mounted on a traverse mechanism. Crossflow velocity values were obtained by use of a two-dimensional Particle Image Velocimetry system. These wake surveys allow us in principle to separate drag components, such as profile drag and induced drag, by evaluating the change in streamwise momentum of the air passing the body and the generation of wake kinetic energy. It also provides some lift information without the use of a balance. The issue of ground effect on negative vehicle lift ( down force) is a key difference between the application of these approaches to aircraft or automotive models and is examined in more detail. It is observed that the wake of a bluff body is highly unsteady, also that the vortices generated in the wake do not have to be symmetric nor counter-rotating. The drag coefficient of the model is found to be around 0.56 for standard conditions.

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DOI

10.25777/gjac-nd97

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