Non-local dispersion and the reassessment of Richardson's t³-scaling law

The Richardson-scaling law states that the mean square separation of a fluid particle pair grows according to twithin the inertial range and at intermediate times. The theories predicting this scaling regime assume that the pair separation is within the inertial range and that the dispersion is local, which means that only eddies at the scale...

Do coherent structures organize scalar mixing in a turbulent boundary layer?

A scalar emanating from a point source in a turbulent boundary layer does not mix homogeneously, but is organized in large regions with little variation of the concentration: uniform concentration zones. We measure scalar concentration using laser-induced fluorescence and, simultaneously, the three-dimensional velocity field using tomographic...

Turbulence modulation in thermally expanding and contracting flows

We present direct numerical simulations of developing turbulent channel flows subjected to thermal expansion or contraction downstream of a heated or cooled wall. Using different constitutive relations for viscosity we analyse the response of variable property flows to streamwise acceleration/deceleration by separating the effect of...

Turbulent flow through a high aspect ratio cooling duct with asymmetric wall heating

We present well-resolved large-eddy simulations of turbulent flow through a straight, high aspect ratio cooling duct operated with water at a bulk Reynolds number of Re_b = 110 × 10³ and an average Nusselt number of Nuxz = 371. The geometry and boundary conditions follow an experimental reference case and good agreement...

How the turbulent/non-turbulent interface is different from internal turbulence

The average patterns of the velocity and scalar fields near turbulent/non-turbulent interfaces (TNTI), obtained from direct numerical simulations (DNS) of planar turbulent jets and shear free turbulence, are assessed in the strain eigenframe. These flow patterns help to clarify many aspects of the flow dynamics, including a passive scalar,...

Tracer particle dispersion around elementary flow patterns

The motion of tracer particles is kinematically simulated around three elementary flow patterns; a Burgers vortex, a shear-layer structure with coincident vortices and a node-saddle topology. These patterns are representative for their broader class of coherent structures in turbulence. Therefore, examining the dispersion in these elementary...

ILES of shock waves and turbulent mixing using high-resolution Riemann solvers and TVD methods

This paper derives the implicit model for high-resolution MUSCL reconstruction-based upwind Godunov schemes for turbulent flows. A Mach number expansion of the numerical scheme allows analysis of the theoretical behaviour of the implicit subgrid model as the Mach number becomes small. This shows that different limiting methods within the same...

Turbulent mixing layers in shallow water

This investigation on shallow mixing layers has two main objectives: - To gain insight in the influence of the depth on the evolution of large, horizontal eddies in a lateral mixing layer in a shallow free-surface flow. - To gain insight in the contribution of these eddies to the entrainment into the layer and to the mixing and to the transport...

Computations of a freshwater disposal into the Eastern Scheldt estuary