The effect of the boundary layer present in wind tunnels on the aerodynamic drag of a model truck

This thesis deals with a system that reduces the oncoming boundary layer displacement thickness in a wind tunnel. The device is then used to examine the effect that this boundary layer has on the aerodynamic drag of a standard truck, which is classified as a bluff body with a high ground clearance and the same truck fitted with skirts all round, which is then classified as a bluff body with a low ground clearance. To gain insight into this field of industrial aerodynamics, an extensive literature survey was done in which all the relevant SAE papers onwards from the late sixties were studied and summarised in the first section of this report. The second section deals with a system that can limit the boundary layer displacement thickness in the test section of the 3/4 open jet wind tunnel. Through investigations and an extensive literature research a suction device was designed and built. This boundary layer removal system was then tested to ensure that the main flow indicators are not influenced by the suction and thus lie within internationally accepted limits. Included in this section are a description of the truck model and the other instruments or devices used to complete the testing. The third section deals with the aerodynamic drag experienced by the bluff body with a high ground clearance. Included in the third section is an investigation that deals with the aerodynamic drag of the same truck model, when skirting has been added which considerably lowers the ground clearance. The results obtained from the above investigations indicate that the drag of the Ground Simulation model without skirts is increased by about 3.8% with the removal of the boundary layer and up to 10% for the model with the skirts. It is thus shown that the farther the object protrudes into the boundary layer, the larger the increase in drag will be once this boundary layer has been removed. These figures were obtained from testing the model at 22.2m/s free stream velocity and a 6mm wheel-ground clearance, with the wheels rotating.

Grantor dc:publisher.institution

Department of Mechanical Engineering

Year dc:date.issued

1997

Author dc:creator

• Lutz, Thomas

Advisor dc:contributor.advisor

• Sayers, Anthony

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/17542

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/17542