fluids 3

# fluids 3 - Date March 1st 2008 To Fred Thomas From John...

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Date: March 1 st , 2008 To: Fred Thomas From: John Fyffe Re: Boundary Layer Analysis in a Wind Tunnel Description of Experiment In this experiment we were trying to find the boundary layer thickness in a wind tunnel for different locations and speeds of air. To find the boundary layer thickness we measured the static and stagnation pressures at differing heights in the wind tunnel at two different locations and at two different speeds. The boundary layer thickness is defined as the region closest to the surface that has a velocity that is less than or equal to 99% of the free-stream velocity. The free-stream velocity is the velocity that is basically constant throughout the middle of a wind tunnel. As you approach a surface of the wind tunnel, the velocity will decrease when you get very close, finally reaching zero when you reach the surface. This distance, from surface to the 99% free-stream velocity point, is called the boundary layer. The boundary layer varies based on quite a few factors. The boundary layer thickness is a function of the distance you measure at from the beginning of the test section, the density of the fluid you are using, the viscosity of the fluid being used and the free-stream velocity. The distance from the point at which you are measuring the pressure to the beginning of the test section is referred to as x. The further from the beginning you measure (as x is increasing) the larger the boundary layer becomes. The density of the fluid has an inverse affect on the boundary layer, where as you use more dense fluids, the boundary layer decreases in size. The viscosity, however, has a direct relation to the boundary layer, which means that as the viscosity increases, so does the boundary layer thickness. Finally, the free-stream velocity has an indirect correlation which shows that as the free-stream velocity of the fluid is increased, the boundary layer thickness will decrease. To calculate the boundary layer thickness, since we already know the density, viscosity, and we can directly measure the distance from the start of the test section, all we needed to do was to find the point where the velocity was 99% that of the free-stream velocity. To do this, we measured the difference between the stagnation pressure and the static

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## This note was uploaded on 04/07/2008 for the course ME 330 taught by Professor All during the Spring '08 term at University of Texas.

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fluids 3 - Date March 1st 2008 To Fred Thomas From John...

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