Experiments on the Turbulent Boundary Layer on a Thin Cylinder Rotating in an Axial Flow : 2nd Report, Energy Budgets and Power Spectrum

Abstract

The budgets of mean flow and turbulent energy as well as the power spectra of u-and v-fluctuating velocities in a three-dimensional turbulent boundary layer on a thin cylinder rotating in a uniform stream are examined experimentally. Advection and diffusion of mean flow energy balance each other in the outer region of the boundary layer, and their absolute values normalized by the characteristic velocity decrease with increasing rotation speed of the cylinder. Over the entire region of the layer, the production and dissipation of turbulent energy are dominant and balance each other, indicating an equilibrium boundary layer. Although advection of turbulent energy is small across the layer, it slightly increases in the outer layer. The power spectra of u-and v-fluctuating velocities measured near the wall exhibit a small peak when the cylinder is rotating, which indicates the existence of an organized eddy structure. There is an increase in the relative population of small-size eddies.