A Study on the Interaction between a Grid-Generated Turbulence and a Circular Cylinder. Phase Average Estimation of the Wake Induced Velocity in the Upstream Region of the Cylinder.

Abstract

The interaction between the grid-generated turbulent flow and a 2-dimensional circular cylinder is investigated experimentally. Particular attention has been devoted to the effect of the velocity fluctuations induced by the cylinder wake vortices on the upstream turbulent field. The simultaneous velocity measurements at three different points around the cylinder (one in the upstream region and two in the near wake) have been performed by the I-type hot-wire probes. The velocity signals are analyzed by the phase average technique on the basis of the reference velocity signals in the near wake. It is found that the phase averaged velocity in the upstream region of the cylinder shows the large value when the vortices are growing up behind the cylinder. The fluctuation of the phase averaged velocity increases as the cylinder surface is approached and the largest value appears along the line of θ=90° near the cylinder surface. Some kinematic vortex-shedding model is suggested to estimate the intensity of the wake-induced velocity fluctuation. The spatial distribution of the calculated velocity r.m.s. fluctuation shows qualitatively good agreements with the experimental results.