Turbulence & mixing

Fundamental turbulent flows — entrainment, jets, plumes, gravity currents, and the way energy moves between scales.

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DNSLESRANSEntrainmentJetsPlumesGravity CurrentsMixingTNTIRayleigh–TaylorMass TransferConvectionStratificationIntegralMultiscaleExperiments

This is the methodological backbone — the canonical flows that give every other area its closures. Jets, plumes, fountains, gravity currents, and the way momentum, buoyancy, and scalars cross turbulent / non-turbulent interfaces (TNTI). Get this physics right and the rest of the lab’s work — urban microclimates, cloud edges, ventilation — has solid ground to stand on.

Entrainment — how a turbulent flow recruits ambient fluid — is a recurring obsession. The lab has produced energy-consistent entrainment relations for jets and plumes (van Reeuwijk & Craske, J. Fluid Mech. 2015), DNS of turbulent transport and entrainment (van Reeuwijk et al., Phys. Rev. Fluids 2016), and a unified description of turbulent entrainment (van Reeuwijk, Vassilicos & Craske, J. Fluid Mech. 2021) that ties the threads together.

The turbulent / non-turbulent interface itself is a research target in its own right — the place where engulfment, nibbling, and mixing actually happen. The turbulence boundary of a temporal jet (van Reeuwijk & Holzner, J. Fluid Mech. 2014) and fractal scaling and conditional statistics across interfaces (Krug et al., J. Fluid Mech. 2017; Mollicone et al., Phys. Rev. Fluids 2025) trace its structure across very different flow regimes.

Gravity currents bring the same questions into geophysics. Internal structure of inclined currents (Cui et al., J. Fluid Mech. 2025), entrainment suppression in stratified environments (van Reeuwijk et al., J. Fluid Mech. 2019), and small-scale entrainment in inclined currents (van Reeuwijk et al., Env. Fluid Mech. 2017).

Reduced-order theory is where the simulations pay off. Generalised plume theory for unsteady jets and plumes (Craske & van Reeuwijk, J. Fluid Mech. 2016); shear-flow dispersion in turbulent jets (Craske et al., J. Fluid Mech. 2015); energy dispersion in unsteady jets (Craske & van Reeuwijk, J. Fluid Mech. 2014 part 1 & part 2).

These closures — entrainment laws, TNTI structure, plume models — flow directly into the urban fluid mechanics and multiphase flows work, and provide the theoretical scaffolding for the simulation tools the group builds.

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