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The Boundary layer over a flat plate

Sanders, M.P.J. (2014) The Boundary layer over a flat plate.

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Abstract:The properties of the boundary-layer over a at plate have been investigated analytically, experi- mentally and numerically employing XFOIL. With the theory from Blasius and von K�arm�an, the boundary-layer properties over an in�nitesimally thin at plate have been investigated analytically. A �nite thickness plate, designed to behave aerodynamically as a at plate, with a Hermite polynomial leading edge and a trailing edge corresponding to the last 70% of a NACA 4-series airfoil section, has been analyzed with XFOIL and has been investigated mounted at zero angle of attack in the Silent Wind Tunnel of the University of Twente. Initial measurements have been performed to obtain the drag force and velocity pro�le. The drag force was measured with load cells and the velocity pro�le was determined with a Pitot tube and a single-wire Hot Wire probe (55P11) at various Reynolds numbers. The measurements indicate a delayed transition from laminar to turbulent ow at a Reynolds number around Recrit=3�106 instead of the expected Recrit=5�105. Leading-edge turbulence strips were also applied in order to investigate the drag force and the transitional boundary layer. The found delayed transition is unfavourable for further research on the in uence of the surface roughness on transition because of the maximum velocity achievable in the Silent Wind Tunnel. Since the turbulence level of the Silent Wind Tunnel is relatively low (approximately 0.25%), other possibil- ities have been investigated on the cause of the delayed transition. Results of numerical simulations using XFOIL indicated that a small change in the streamwise pressure gradient can delay transition substantially. Therefore, additional measurements have been performed on the streamwise pressure gradient in the Silent Wind Tunnel. These results indicate an existing streamwise pressure gradient in the test section of the Silent Wind Tunnel which is ampli�ed when the plate is installed in the wind tunnel and may have been the cause of the delayed transition.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering BSc (56966)
Link to this item:http://purl.utwente.nl/essays/65492
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