Laser-Doppler measurements on a round turbulent jet in dilute polymer solutions

Abstract

A laser-Doppler velocimeter suitable for the measurement of mean and fluctuating flow velocities in water is described. Results of a study using this system in an axisymmetric turbulent jet of water and dilute polymer solutions are given. The laser-Doppler technique is better suited for such measurements than either Pitot tubes or heat-transfer gauges because the Doppler velocity measurements are independent of the physical properties of the fluid. Previous velocity measurements in polymer jets have suffered from the effects of the additives upon the sensors.Turbulent round jets with Reynolds numbers between 5000 and 50000 were studied. Por a jet issuing from a convergent nozzle the additives were found to have no effect upon the mean axial velocity or turbulence intensity at any point in the jet. However, for a jet issuing from a long length of circular pipe, the additives reduced the centre-line velocity and increased the turbulence level in the early part of the jet. Thus the principal effect of a polymer additive upon tlie jet appears to result from its effect upon the initial conditions.

Polymer-induced turbulence modifications in an impinging jet

“…These two concentrations were selected based on the results of Koziol and Glowacki (1989) and Glowacki (1989), as it was observed that radial profiles of shear stress on the wall and the turbulent intensity decreased monotonically with polymer concentration until attaining a minimum at 50 ppm, followed by enhancement for increasing concentration. Based on the detailed preparation recommendations in Barker (1973) to ensure repeatability, the polymer was aged in water for approximately 24 hours, mixed gently in the master tank and then allowed to stabilize for roughly 2 additional hours prior to running an experiment. Before stabilization of the polymer solution, hollow glass spheres (Sphericel TM 110P8; specific weight of 1.1) of mean diameter 11 µm were added.…”

“…Barker (1973) observed that polymer additives (50 and 100 ppm) in a free jet issuing from a converging nozzle with no upstream development length had little influence on the mean axial velocity and turbulence intensity. In contrast, Barker observed jets issuing from pipes with long development lengths to have larger axial turbulence intensities and faster spreading rates.…”

“…In consequence, for a given axial position within the interacting region, the radial distribution of turbulence intensity peaks at the center of the mixing layer, exhibiting an annular maximum at r/D ≈ 0.5 (Corrsin, 1943;Corrsin and Kistler, 1955;Angioletti et al, 2003;Gardon and Cobonpue, 1962;Gardon and Akfirat, 1965;Fitzgerald and Garimella, 1998). At the same time, the turbulence intensity increases monotonically along the axial coordinate in the interacting region as the jet broadens radially (Barker, 1973;Vlasov et al, 1973). Another interesting point to note is that, keeping other exit conditions of the jet fixed, the length of the potential core appears to be independent of Re D .…”

“…The developing region occurs typically in the interval 8.0 < x/D < 30.0. The radial profile of turbulence intensity becomes bell-shaped in the interval 10.0 < x/D < 20.0, but one must approach x/D ≈ 30.0 before a self-similar state is reached (Corrsin, 1943;Corrsin and Kistler, 1955;Barker, 1973;Vlasov et al, 1973). Beyond this distance, the jet is in a self-similar state wherein both the turbulence intensity and mean velocity profiles decay in a self-similar manner (i.e., their decay can be reconciled with the growth of the jet cross-section with increasing x).…”

Evaluation of scaling correlations for mobilization of double-shell tank waste

“…A summary of some of the work in this area is given in McComb (1990). Barker (1973) performed measurements in jets consisting of dilute polymer suspensions and reported no effect on the mean velocity or turbulent intensity. In a study on a yield pseudoplastic jet, using a quantitative flow visualization technique, Shekarriz et al (1995a) observed a macroscopic jet…”