Fig 23.5 Flow Around Thin Aerofoil
A vortical motion of strength at x= develops a velocity at the point p which may be expressed as
The total induced velocity in the upward direction at point p due to the entire vortex distribution along the camber line is
(23.14)
For a small camber (having small α), this expression is identically valid for the induced velocity at point p' due to the vortex sheet of variable strength on the camber line. The resultant velocity due to and v(x) must be tangential to the camber line so that the slope of a camber line may be expressed as
From Eqs (23.14) and (23.15) we can write
Consider an element ds on the camber line. Consider a small rectangle (drawn with dotted line) around ds. The upper and lower sides of the rectangle are very close to each other and these are parallel to the camber line. The other two sides are normal to the camber line. The circulation along the rectangle is measured in clockwise direction as
If the mean velocity in the tangential direction at the camber line is given by it can be rewritten as
if v is very small becomes equal to . The difference in velocity across the camber line brought about by the vortex sheet of variable strength causes pressure difference and generates lift force.
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Flow Around a Thin Aerofoil
12:53 PM
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