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Semi-trucks: what a drag! (Senior Division).

Semi--trucks consume an enormous amount of fuel in overcoming aerodynamic drag on the rear end of its trailer. The drag on a semi-truck's trailer accounts for about one-half of the total drag force at 55-65 mph. With the increase in fuel cost, the reduction of drag has become a key factor in keeping semi-trucks profitable. Previous aerodynamic changes on semi-trucks have primarily involved improvements to the front profile. Shear stress is dependent on the length of an object, so if an object is really short then the shear stress is low. The second is pressure drag, which is the part due directly to the shape of an object. Pressure drag consists of the direction, magnitude, and orientation of an object. The philosophy behind reducing drag is to make an object long enough to reduce the pressure drag, but not so long that a great deal of shear stress is created. The experiment utilizes a wind tunnel by taking various pressure readings and condensing the data into a readable graph by measuring the total, static, and dynamic pressure upstream and downstream of the object. While the amount of drag shown is not the actual amount of drag due to the Reylond number, the graphs are comparable to the baseline graph, which shows the difference in drag from each object.

Robert Kamber, Laramie High School, Wyoming
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Author:Kamber, Robert
Publication:Journal of the Colorado-Wyoming Academy of Science
Article Type:Brief Article
Geographic Code:1USA
Date:Apr 1, 2002
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