Unsteady Flow past a Flat Plate Normal to the Direction of Motion

The development of the separated flow past a flat plate which was started from rest either impulsively or with uniform acceleration was investigated experimentally by using flow-visualization techniques. The flow is irrotational initially. The onset of separation takes place at the two edges of the plate. The symmetrical twin-vortices are always formed at small times no matter how large the Reynolds number may be. The length of the wake bubble is nearly proportional to ( U t / d ) 2/3 or ( a t 2 / d ) 2/3 at small values of (ν t / d 2 ) (where U is the plate speed, t the time from the start, d the plate length, a the acceleration and ν the kinematic viscosity). The length of the symmetrical wake bubble exceeds 4.1 plate lengths at a d 3 /ν 2 =4.2×10 2 .