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How many times is the angular velocity of flow behind airscrew compared to that of angular velocity in plane of airscrew?(a) Same(b) Twice(c) Thrice(d) Four timesThis question was posed to me during a job interview.My query is from Blade Element Theory topic in chapter Helicopter Dynamics of Aerodynamics

Answer»

Right answer is (b) Twice

The best I can explain: If we consider the ANGULAR VELOCITY of FLOW in plane of the airscrew blade as bΩ, and the angular velocity behind the blade as indicated by the BOUND vortices as +βΩ, then the angular velocity of the flow behind the airscrew is given by:

ω=(b+β)Ω=2bΩ

This value is twice that of the angular velocity in plane of the airscrew.



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