Use of electrochemical sensors for the determination of wall turbulence characteristics in annular swirling decaying flows

The wall shear stress and turbulence features in swirling decaying flow were analyzed near the inner cylinder of a cylindrical annulus fitted with a tangential inlet. The experimental method was based on the determination of the limiting diffusional current on electrochemical sensors mounted flush to the surface of the inner cylinder. The mean value of the diffusional current leads to the mean wall velocity gradient, and the power spectral density of the current fluctuations is linked to that of the velocity gradient fluctuations through a transfer function. The analysis of the mean wall velocity gradient allowed the three-dimensionality of the swirl flow and the swirl decay along the flow path to be studied. Just downstream of the tangential inlet, a recirculation zone is set up near the inner cylinder, followed by a nonmonotonic decay of the swirl motion. These two zones define the three-dimensional flow region. The wall turbulence was characterized by both the turbulence intensity and the cutoff frequency, defined by the transition between the low-frequency plateau and the inertial subrange of the power spectral density. The turbulence intensity, which is quasi-independent of the Reynolds number, decreases with axial distance from the inlet section and has a more complex evolution with the circumferential position with respect to the axis of the tangential inlet. (C) Elsevier Science Inc., 1997.