15th European Turbulence Conference 2015
August 25-28th, 2015, Delft, The Netherlands
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Dispersion in unsteady jets and plumes


Go-down etc15 Tracking Number 495

Presentation:
Session: Jets and Wakes 2
Room: Room E
Session start: 15:00 Tue 25 Aug 2015

John Craske   john.craske07@imperial.ac.uk
Affifliation: Imperial College London

Maarten van Reeuwijk   m.vanreeuwijk@imperial.ac.uk
Affifliation: Imperial College London


Topics: - Transport and mixing, - Thermally driven turbulence, - Jets and wakes

Abstract:

We investigate the transport of both passive and active scalars in fully developed turbulent axisymmetric jets and plumes using data from direct numerical simulation. In both cases we simulate the response of the flow to an instantaneous increase in the scalar flux at the source and our focus is on the determination of the rate at which the resulting disturbance propagates and spreads in the longitudinal direction. We apply Taylor's theory of shear-flow dispersion to free-shear flows and therefore model the way in which departures from self-similarity result in the longitudinal mixing of integral quantities. The resulting integral models exhibit a good agreement with the simulation data and, in the case of passive scalar transport, admit an analytical similarity solution. For the case of active scalar transport we examine the buoyancy flux in an unsteady plume and show that the momentum-energy framework, rather than the classical volume-momentum framework, provides the natural setting from which to view the effects of dispersion. Consequently, we demonstrate the effect that dispersion has on turbulent entrainment and the way in which a plume responds to source perturbations in its buoyancy flux.