The turbulent/non-turbulent interface of a self-similar jet
Abstract
Conditionally sampled PIV measurements of a turbulent round submerged liquid jet in a laboratory have been taken at Re = 2000 in order to investigate the dynamics and transport processes at the continuous, and well-defined bounding interface between the turbulent and non-turbulent regions of flow. The jet carries a fluorescent dye measured with LIF. The distance of the fluctuating interface from the jet axis is identified as the surface discontinuity in the scalar concentration. Profiles of the conditional mean velocity, mean scalar, momentum and scalar fluxes show that at the interface there are clear discontinuities in the mean scalar and the scalar flux, and a tendency towards a singularity in mean vorticity with discontinuities in the mean velocity. These actual or asymptotic discontinuities are consistent with the conditional mean momentum and scalar transport equations integrated across the interface. Measurements of the flux of enstrophy are consistent with earlier computations in showing unambiguously that for a jet flow the entrainment process is dominated by small scale eddying at the highly sheared interface (``nibbling''), with large scale engulfing making a small (less than 10%) contribution. Theoretical arguments are proposed for how the internal structure of the interface layer relates to the rotational and irrotational motions on each side, which leads to the estimate that its thickness is of order of the Taylor micro scale. This is consistent with the experimental data.
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 2004
- Bibcode:
- 2004APS..DFD.NJ001W