# Measurements in Boundary Layer Flows

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Abstract: In this experiment, the velocity profile for a flat plate at zero pressure gradient of a boundary layer at two different stream wise points were acquired. The investigation was also based on and how changes in Reynolds number affect the velocity distribution within boundary layers. Parameters such as the Momentum Thickness, Displacement Thickness, Shape Factor, shear stress and coefficient of friction was also calculated to gain a better understand of boundary layers. The experimental values calculated were compared to the theoretical Blasius for laminar flow and Power Law Solutions for turbulent flow to see how they varied. It was found out the higher the Reynolds number the greater the boundary layer thickness. As the…show more content…
 The boundary layer can also be measured by other factors. One factor is the Displacement Thickness, δ*. It is defined as the distance by which the free streamlines are displaced in the y-direction due to the formation of the boundary layer. The formation of the boundary layer reduces the mass flow rate per unit area. This is because near the surface the molecules are travelling slower, meaning less flow rate per unit area is going out compared to coming in. In order to compensate for this loss in mass flow rate, the external streamlines (free streamlines) will be displaced. The distance it displaced is the δ*.  When deriving this equation it is assumed the flow is incompressible and steady. Another factor is the Momentum Thickness, ϴ. It is defined as the thickness of a layer of freestream fluid carrying a momentum flow rate equal to the reduction in momentum flow rate caused by the formation of the boundary layer. Closer to the surface of the object, the flow is slower. This means that the momentum is also slower. ϴ is a measurement of the compensation that makes us the momentum flow rate that was lost due to the formation of the boundary layer. The momentum thickness is useful in determining the skin friction drag on a surface.  When deriving this equation it is assumed the flow is incompressible and steady. Momentum Thickness is an indication of Drag. Two parameters that