Longitudinal Dispersion in Unsteady Pipe Flows

James Hart, Fred Sonnenwald, Virginia Stovin, Ian Guymer

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


Temporal concentration profiles resulting from an injected pulse of fluorescent tracer were recorded at multiple locations along a pipe during controlled unsteady flow conditions. A linear temporal change in discharge over durations of 5, 10, or 60 s for both accelerating and decelerating flow conditions was studied. Tests were performed for flows that changed within the turbulent range, between Reynolds numbers of 6,500 and 47,000, and for laminar to turbulent flows, between Reynolds numbers of 2,700 and 47,000. Analysis of the data shows the limitations of employing steady-state routing of temporal concentration profiles in unsteady flow. Employing a flow weighted time routing approach, using tracer mean velocity and dispersion coefficients, provides accurate predictions of mixing in unsteady flow. For decelerating flows, longitudinal dispersion coefficients were lower than for the equivalent mean steady discharge. Previously unreported disaggregation of the tracer cloud was observed during all experiments accelerating from laminar to turbulent conditions.

Original languageEnglish
Article number04021033
Journal Journal of Hydraulic Engineering, ASCE
Issue number9
Early online date8 Jul 2021
Publication statusPublished - Sept 2021


EPSRC Grant No. EP/P012027/1


  • Longitudinal dispersion
  • Mixing
  • Pipe
  • Solute routing
  • Tracing
  • Unsteady flow

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Water Science and Technology
  • Mechanical Engineering


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