The University of Southampton
Engineering and the Environment

Research project: Dispersion of Small Inertial Particles in Characteristic Atmospheric Boundary Layer Flows

Currently Active: 
No

Prediction of Smoke and Hazardous Plumes in Complex Terrain.

Project Overview

DSTL currently make predictions of the dispersion of scalar pollutants and toxic agents using a variety of Gaussian Plume Model formulations, and use these predictions to estimate source origin, suggest sensor placement. These are applied to outdoor and also urban environments and to understand how small airborne particulates are transported and dispersed. There is a need to update the near field accuracy and/or the level of model used for these predictions, e.g. though an improved parameterisation scheme. The basic project plan is to analyse relatively small scale volumes, of order 1km using Large Eddy simulation (LES) to supply the flow and scalar fluctuation information. This aspect of the project is primarily covered by the companion project- Towards Airborne Hazard Emergency Management System for Local Environments, led by Dr. Xie.

The research interest for this project is to model the dispersion of the small particles within the Large Eddy Simulation, given that the unresolved scales, modelled by the LES are typically the scales that disperse the particles locally. The problem is compounded by the highly anisotropic turbulence in the near ground region, which, unfortunately, is of most interest to DSTL.

The project will compute a series of low speed flows using Direct Numerical Simulation (DNS), and then post process (filter) the DNS data to obtain filtered (large eddy) flow fields for a range of filter widths. Particles will then be dispersed in the DNS and also in the LES flow fields of increasing filter width to first understand the connection between the dispersion prediction error and the filter width. Several studies already exist in the literature for particle dispersion in large eddy simulations of isotropic turbulence, and these models will form a basis for the development for dispersion models in wall dominated flows of (relatively) very large filter width. One example is given here:

Shotorban, B., and Balachandar, S., ``Particle Concentration in Homogeneous Shear Turbulence Simulated via Lagrangian and Equilibrium Eulerian Approaches,'' Physics of Fluids, 18, 065105, 2006.

The final objective of the project will be to suggest appropriate dispersion coefficients to enable an Eulerian framework for the particle phase to be computed as part of the LES computation, obviating the need to compute particle trajectories in the Lagrangian sense. These models will be validated by extending an existing Fortran code for Eulerian particle dispersion and then implemented in OpenFOAM as a freely available toolkit for the prediction of small particle dispersion over large scales.

 

Again a useful starting point may be a monosize framework, for example :

Shotorban, B., and Balachandar, S., ``A Eulerian Model for Large-eddy Simulation of Concentration of Particles with Small Stokes Numbers,'' Physics of Fluids, 19, 118107, 2007.

Configurations include steady/puff point releases (dry powder and liquid). For the dry powder releases, the particle sizes ranges from 1 µm to 5 µm, and the puff release time ranges up to 30 s. For the liquid releases, the particle sizes ranges from 20 µm to 160 µm, and the puff release time ranges up to 5 mins. The liquid release type will include evaporation of droplets, coalescence etc. and pooling of liquid on the floor followed by subsequent evaporation.

These models will in turn, provide verification and extension of fast prediction methods currently deployed by DSTL.

 

Related research groups

Aerodynamics and Flight Mechanics

Staff

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