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Engineering

Research project: Scalar mixing and turbulent intermittency

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The inherent statistical inhomogeneity of free shear flow manifested as intermittent behaviour provides challenges to accurately predicting the mixing process using fully developed turbulence models. The physical interpretation of intermittency can be divided into two parts – internal and external intermittency. The interfacial distinction between turbulent-bearing fluid (e.g. the jet or the boundary layer) and non-turbulent fluid (free stream) is referred as the external intermittency. Internal intermittency refers to local fluctuations of turbulence intensity (the intermittency in an inertial range of a turbulent flow). Both external and internal intermittency can be seen as multiscale spatiotemporal random processes. The intermittent behaviour of turbulent jets is of particular interest since it is influential in many processes of practical relevance, including mixing, combustion, emissions and aero-acoustics.

The importance of intermittency in many processes of practical relevance means that there is a clear need for the reliable prediction of turbulent intermittent flows using statistical engineering models. Direct numerical simulation (DNS) is possible, but only below the high Reynolds numbers of engineering importance, and whilst large eddy simulation (LES) can be performed at such Reynolds numbers, computer run times restrict its use in simulating many practical engineering systems. Direct numerical and large eddy simulation are of significant benefit to the development of improved understanding of intermittency, and the derivation of more fundamentally based turbulence models, particularly in the absence of detailed experimental data on the simultaneous influence of intermittency on both the velocity and scalar fields in a jet. In this work, we investigate the scalar intermittency of turbulent jets, or, more precisely, to investigate probability density function distributions and radial variation of external intermittency profiles using DNS and LES, and to check the possibility of better understanding the intermittency phenomena for turbulent free shear flows. The long term objective is the development of more generic turbulence models able to tackle intermittency in more effective way.

Modelling of coaxial jet efflux mixing using LES
Modelling of coaxial jet efflux
Modelling of coaxial jet efflux mixing using LES
Modelling of coaxial jet efflux
Passive scalar probability density function distributions and intermittency profiles
Passive scalar probability density
Passive scalar probability density function distributions and intermittency profiles
Passive scalar probability density

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