Numerical Analysis Seminars: Scalar decay in smooth random flows
11 February 2005 14:00 in CM105
"The concentration of a passive scalar released in a smooth random flow decays exponentially. We examine the factors that control the corresponding decay rate in the limit of small diffusivity. For certain classes of flows, a closed evolution equation can be derived for the concentration variance, and its decay rate is found as the eigenvalue of a linear operator. By analysing this eigenvalue problem asymptotically, we establish that the variance decay rate is either controlled (i) locally, by the stretching characteristics of the flow, or (ii) globally, by the large-scale transport properties of the flow and by the domain geometry. The two types of controls are distinguished by the limiting behaviour of the eigenvalue as the diffusivity tends to zero: in the local case (i) it coincides with the lower limit of a continuous spectrum, whilst in the global case (ii) it is an isolated discrete eigenvalue. (Joint work with P H Haynes, Cambridge). "
Contact David.Bourne@durham.ac.uk for more information