Particle image velocimetry measurements of a steam-driven confined turbulent water jet

In this paper experiments are reported on a condensing steam jet. Superheated steam is injected at the bottom centre of a cylindrical water vessel, resulting in a turbulent jet with Reynolds numbers varying between 7.9 x 10(4) and 18.1 x 10.4, depending on the bulk temperature of the water. Near the steam inlet, the flow is two-phase with rapidly condensing steam. Downstream of a development region the jet is essentially single-phase. Using particle image velocimetry in a vertical plane through the central axis, instantaneous velocity fields of the single-phase region have been measured at a rate of 15 Hz. The velocity field in this region is found to be self-similar, i.e. the width of the jet, r(1/2), increases linearly with increasing distance to the virtual origin, and a Gaussian profile prevails if velocities and distances are properly scaled. The spreading rate is equal to the one usually found in single-phase jets, and temperature independent. The virtual origin of the jet is positioned at a temperature-dependent distance (3-7 nozzle diameters) upstream of the steam inlet, and this distance is shown to correlate with the length of the condensation region. The turbulence intensity is found to be similar to the intensities usually reported for single-phase jets, although full isotropy is only reached at a distance of 15 nozzle diameters from the nozzle. The jet exhibits a slow wobbling motion, which can be attributed to instability of the backflow resulting from the confinement. When the measurements are compensated for this wobble, a slightly smaller spreading rate is obtained, which indicates that unconditional averaging may conceal significant flow structuring.