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Fluid Mechanics: Drag and Friction

Drag and Friction

The frictional effects due the wall shear stress as the fluid passes over an object can cause drag on an object. The orientation of the surface has a large impact on how much drag will act on the object moving through the fluid. For example if the surface is perpendicular to the upstream velocity than the shear stresses will have no influence on the drag. Also, when dealing with large Reynolds numbers the effects of friction drag could be very small in comparison to other types of drag. However, for low Reynolds number, or for shapes that are highly stream line, the main source of drag could be due to friction drag. To calculate friction drag equation 2 would be use. To use equation 1 you will need to know a friction drag coefficient.

Drag equation due to fluid friction (1)

Df = Frictional Drag Force

ρ = Fluid Density

U = Fluid Velocity

b = Objects Width

L = Objects Length

Cdf = Drag Coefficient

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