VORTEX REYNOLDS-NUMBER IN TURBULENT BOUNDARY-LAYERS

The effects of vortex Reynolds number on the statistics of turbulence in a turbulent boundary layer have been investigated. Vortex Reynolds number is defined as the ratio of circulation around the vortex struct ure to the fluid viscosity. The vortex structure of the outer region w as modeled and a full numerical simulation was then conducted using a high-order spectral method. A unit domain of the outer region of a tur bulent boundary layer was assumed to be composed of essentially three elements: a wall, a Blasius mean shear, and an elliptic vortex incline d at 45 degrees to the flow direction. The laminar base-flow Reynolds number is roughly in the same range as that of a turbulent boundary la yer based on eddy viscosity, and the vortex-core diameter based on the boundary-layer thickness is nearly the same as the maximum mixing len gth in a turbulent boundary layer. The computational box size, namely, 500, 150, and 250 wall units in the streamwise, surface-normal, and s panwise directions, respectively, is approximately the same as the mea sured quasi-periodic spacings of the near-wall turbulence-producing ev ents in a turbulent boundary layer. The effects of vortex Reynolds num ber and the signs of the circulation on the moments of turbulence were examined. The signs mimic the ejection and sweep types of organized m otions of a turbulent boundary layer. A vortex Reynolds number of 200 describes the turbulence moments in the outer layer reasonably well.