Report - Matthew Callesen Daniel Roberts MAE 3183 Wednesday...

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Matthew Callesen Daniel Roberts MAE 3183 Wednesday Section Experiment #5 Air Drag Force Date Performed: 9/20/06 Date Due: 9/27/06
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Abstract The purpose of this laboratory experiment was to determine the contributing factors to the drag coefficient of a fluid moving over a different rigid body, and compare them to published data. This was accomplished by placing four objects of known geometry in a wind tunnel: an airfoil, cylinder, sphere and square. The air velocity was incrementally increased, while the pressure drop, and air temperature and strain measurements was recorded in a DAQ. It was found that the main contributing factors to drag force were the objects geometry, the velocity of the fluid, the fluid characteristics, and the surface of the object. It was also found that square had the highest drag coefficient, followed by the cylinder and then the airfoil. The sphere had a drag coefficient of almost zero. The first three geometries behaved similar to published data, but the sphere data was found to be erroneous. This was caused by an inaccurate strain recording throughout the sphere tests. In the future the experiment could be improved by better strain recording data which started at a zero level instead of the varying initial point. It was also found that the experiment could be improved fan speed adjustment dial which had a higher level of precision instead of the free spinning analog dial utilized. Finally, the wind tunnel table should be reinforced to minimize apparatus vibrations. Introduction When a force balance is conducted on a moving body, there are many factors that must be considered. The friction of the propelling medium, the mass of the object, and the opposition by mechanical means are just a few common factors that need are typically accounted for. One additional force that must also be considered, particularly at higher velocities is the drag force that the body encounters. The effects of the immersed fluid on the rigid body can be considerable, and whether it is a person walking briskly down the street, or a rocket propelled car at challenging he land speed record, drag force is evident. The understanding of drag force has become an area of great interest recently because reducing the drag on an object reduces the power required to maintain constant velocity or accelerate. The energy consumed to overcome drag forces is essentially wasted. One example is the typical automobile. Reducing the drag of the car allows for
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increased gas mileage. Therefore engineers attempt to minimize drag by good design practices and extensive laboratory testing prior to manufacturing. Another example of the importance of understanding drag is in hydroelectric power generation. In this case it is beneficial to use blades with a high drag coefficient to utilize the available air. The purpose of this experiment is introducing engineering students to process
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Report - Matthew Callesen Daniel Roberts MAE 3183 Wednesday...

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