Vorticity characteristics of the turbulent intermediate wake

Abstract

Measurements of the lateral components ω j (j=2 and 3) of the vorticity fluctuation vector have been made, using a vorticity probe consisting of two X-wires, in the intermediate wake of a circular cylinder. The effect of the spatial resolution of the probe on the measurement of ω j has been studied. As the spatial resolution impairs, the variance and flatness factor of ω j decrease whereas the skewness of ω j increases. Reasonably accurate values of ω j 2 can be obtained by applying spectral corrections for the spatial resolution effect. Near the beginning of the intermediate wake, the variance of ω 2 is larger than that of ω 3 due to the significant contribution from ribs which connect consecutive spanwise roll vortices. This difference decreases with downstream distance. Also, the presence of the rolls is reflected by a local extremum in the skewness of ω 3 on each side of the wake centerline. The magnitude of the extremum decreases with downstream distance.