THE IMPULSIVELY STARTED ELLIPTIC CYLINDER -- ORIGIN OF LIFT.
MASSACHUSETTS INST OF TECH CAMBRIDGE FLUID DYNAMICS RESEARCH LAB
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A theoretical investigation was made of the subsequent transient motion of the flow field due to an impulsively started elliptic cylinder in an infinite fluid. The fluid is assumed to be slightly viscous such that the Reynolds number is large. The Navier-Stokes equations then pose a singular perturbation problem. The behavior at small times is investigated through the method of matched asymptotic expansions. The non-linear transport of momentum from the boundary layer and the induced flow is responsible for the pressure lift. Preliminary results show that the lift behaves as t to the 32 power. The phenomenon of stall is also discussed. The flow field induced by an impulsively started circular cylinder is investigated in detail. The induced exterior flow by the boundary layer behaves like a doublet whose strength increases as t to the 12 power. The apparent radius of the cylinder increases as more fluid is retarded. The asymmetric part is like a quadrapole increasing as t to the 32, which gives a pair of growing eddies behind the cylinder. The results are confirmed by qualitative experiments and existing photographs of the starting process. Author
- Fluid Mechanics