Experimental study of entrainment and interface dynamics in a gravity current

D. Krug*, M. Holzner, B. Lüthi, M. Wolf, W. Kinzelbach, A. Tsinober

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)

Abstract

The special case of entrainment in a stratified flow, relevant to many geophysical flows such as oceanic overflows, so far has not been studied experimentally in terms of small-scale aspects around the turbulent/non-turbulent interface. In view of the fact that existing engineering concepts perform unsatisfactorily in practice, a new gravity current facility was designed with the goal to gain understanding of how stratification affects interfacial physics. Here, we present the design of the new setup and give details on the turbulence enhancement in the inflow and the refractive index matching technique used. Validation measurements ensure that there is negligible backflow and an essentially irrotational flow outside the current. Measurements via particle image velocimetry of a flow with inflow Reynolds and Richardson numbers of Re0≈4,000 and Ri 0 = 0.22 are reported. An analysis in a laboratory frame agrees well with flow features reported in the literature, i.e., a streamwise invariant top-hat velocity scale and a Reynolds stress distribution are matched closely by a mixing length model. In a second step, the instantaneous interface position is determined based on a threshold on the normal enstrophy component. An investigation in a frame of reference conditioned on the interface position reveals a strong interfacial shear layer that is much more pronounced than the one observed in jet flows. Its thickness is about two times the Taylor microscale. The data moreover suggest the existence of a fairly strong interfacial density jump across the shear layer. The entrainment parameter is estimated at E≈0.04 congruently from the evaluations in laboratory and conditioned frame, respectively.
Original languageEnglish
Article number1530
JournalExperiments in fluids
Volume54
DOIs
Publication statusPublished - 8 May 2013
Externally publishedYes

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