Development of Three-Dimensional Turbulent Wall Jets

Abstract

<p>Detailed flow field measurements were performed to investigate the development of the three-dimensional wall jet, the effect of initial conditions on the development of wall jets and the evolution of the large-scale vortex structures that causes the large lateral growth rate in the flow. Single-point measurements in the wall jet exiting a contoured nozzle indicated that there were two regions in the intermediate field 10 ≤ x/D ≤ 40. The flow underwent a significant change in the region 10 ≤ x/D ≤ 20 as it adjusted to the wall. The changes of the profiles of the moments and the reorientation of the regions of the mean streamwise vorticity slowed down in the region beyond x/D=20 and were not apparent by x/D=40. The comparison of measurements of wall jets exiting the contoured nozzle and the fully developed long pipe indicated that changes in intial conditions do affect the jet half-widths and the decay of the maximum streamwise velocity through near and intermediate fields. The differences in growth rates of wall jets, profiles of moments and contours of the mean streamwise vorticity in the two jets were reduced in the region after x/D=10 and were not apparent in the region beyond x/D=20 - 30. Measurements of two-point, two-time correlation of the streamwise fluctuating velocity indicated that the large-scale vortex structures that consist two pair of horseshoe vortices in the flow continued to develop throughout the intermediate field. In particular, the inner vortex structures were induced towards the wall by the outer structures and the legs of the outer structures inclines relative to the streamwise direction as the flow evolved downstream. Measurements also indicated that the flow below the outer region of the streamwise vorticity was laterally convected faster than the outer vortex structures.</p>