Journal of Fluid Mechanics

Papers

Turbulent characteristics of a shallow wall-bounded plane jet: experimental implications for river mouth hydrodynamics

JOEL C. ROWLANDa1 c1, MARK T. STACEYa2 and WILLIAM E. DIETRICHa3

a1 Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, USA

a2 Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA

a3 Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA

Abstract

Jets arising from rivers, streams and tidal flows entering still waters differ from most experimental studies of jets both in aspect ratio and in the presence of a solid bottom boundary and an upper free surface. Despite these differences, the applicability of experimental jet studies to these systems remains largely untested by either field or realistically scaled experimental studies. Here we present experimental results for a wall-bounded plane jet scaled to jets created by flow discharging into floodplain lakes. A characteristic feature of both our prototype and experimental jets is the presence of large-scale meandering turbulent structures that span the width of the jets. In our experimental jets, we observe self-similarity in the distribution of mean streamwise velocities by a distance of six channel widths downstream of the jet outlet. After a distance of nine channel widths the velocity decay and the spreading rates largely agree with prior experimental results for plane jets. The magnitudes and distributions of the cross-stream velocity and lateral shear stresses approach self-preserving conditions in the upper half of the flow, but decrease in magnitude, and deviate from self-preserving distributions with proximity to the bed. The presence of the meandering structure has little influence on the mean structure of the jet, but dominates the jet turbulence. A comparison of turbulence analysed at time scales both greater than and less than the period of the meandering structure indicates that these structures increase turbulence intensities by 3–5 times, and produce lateral shear stresses and momentum diffusivities that are one and two orders of magnitude greater, respectively, than turbulence generated by bed friction alone.

(Received March 25 2008)

(Revised January 13 2009)

Key Words

  • River dynamics;
  • Jets;
  • Turbulent mixing

Correspondence:

c1 Present address: Earth and Environmental Sciences Division, Los Alamos National Lab, Los Alamos, NM 87545, USA. Email address for correspondence: jrowland@lanl.gov

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