Dept of Mechanical & Aerospace Engineering Seminar

Category: Seminar

For: Academic staff, Researchers staff

On the Non-local Geometry of Turbulence

Professor Dale I. Pullin
Theodore von Kármán Professor of Aeronautics at the Graduate Aeronautical Laboratories
California Institute of Technology, CA, USA

A multi-scale methodology for the study of the non-local geometry of structures in turbulence will be described. Starting from a given three-dimensional field, this consists of three main steps: extraction, characterization and classification of isosurfaces. Extraction is done using the curvelet transform, which produces a multi-scale decomposition. Characterization and classification are defined using differential-geometry properties of scale-dependent isosurfaces and their representation in a ``feature-space'' of reduced geometrical parameters. Application to fields of enstropy, dissipation and a passive scalar obtained from direct-numerical simulation of homogeneous turbulence will be described. These show a transition, with decreasing scale, from blob-like shapes at forced scales, to tube-like and sheet-like structures in the inertial range and finally pancake/sheet geometry at dissipation scales. The geometrical evolution of Lagrangian structures and ``vortex surfaces'' in turbulence will also be discussed. The general aim of the present work was to develop diagnostic tools suitable for studying the statistical geometry embedded within three-dimensional scalar fields. While the applications presented in the talk are from databases obtained from fluid-dynamical turbulence, the methodology developed can, in principle, be applied to any three-dimensional, volume-rendered data set for which the fast Fourier transform can be utilized.

Attachment:  dale-pullin (pdf, 140kb)

Enquiry:   Adrian Neild | 54655