Dynamic behavior of an unsteady turbulent boundary layer
Abstract
Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70 percent greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle. Previously announced in STAR as N8128392
 Publication:

Unsteady Turbulent Shear Flows
 Pub Date:
 1981
 Bibcode:
 1981utsf.proc...35P
 Keywords:

 Boundary Layer Flow;
 Dynamic Characteristics;
 Turbulent Boundary Layer;
 Unsteady Flow;
 Flow Velocity;
 Free Flow;
 Oscillating Flow;
 Pressure Gradients;
 Reynolds Number;
 Stress Distribution;
 Fluid Mechanics and Heat Transfer