Title:

Stochastic Lagrangian Models for Turbulent Flows

Speaker:

Dr. Stephen Pope

Affiliation:

Cornell University

When:

Thursday, October 21, 2010 at 3:30:00 PM   Add to Calendar

Where:

Guggenheim Building, Room 442

Host:

Mitchell Walker
mitchell.walker AT aerospace.gatech.edu

Abstract

The objectives of this talk are to explain and to demonstrate the success of a particular modeling approach to turbulent flows, namely, stochastic Lagrangian models. In this approach, stochastic models are constructed for physical properties following fluid particles. This leads to a turbulence closure based on a probability density function (PDF). We focus on the modeling of two turbulent flows: dispersion from a line source in grid turbulence; and, a lifted non-premixed turbulent jet flame. Stochastic Lagrangian models and the related PDF methods are described, and are shown to model these flows satisfactorily.

For the line source, the Langevin equation is introduced to model the velocity following a fluid particle, and a simple relaxation model is used for the particle temperature. Comparison with experimental data shows that the resulting model describes accurately the dispersion from single and multiple line sources. These simple stochastic Lagrangian models are then applied to the much more challenging case of a lifted non-premixed jet flame. the stochastic Lagrangian models form the basis for a particle/mesh numerical method for solving a modeled transport equation for the Eulerian joint probability density function (PDF) of velocity and composition. The PDF calculations are in excellent agreement with the experimental data, and exhibit the observed extreme sensitivity of the flame to the temperature of the co-flow. The PDF model calculations presented clearly demonstrate that simple models can be very useful, even though aspects of their behavior may be inaccurate or incomplete. The shortcomings of the Langevin equation are examined, and more advanced models (designed to overcome some of these shortcomings) are described.

Biography

Stephen Pope is the Sibley College Professor of the Sibley School of Mechanical and Aerospace Engineering at Cornell University. He received his undergraduate and graduate education in the Mechanical Engineering Department of Imperial College, London. Following post-doctoral positions at Imperial College and in Applied Mathematics at the California Institute of Technology, he joined the Mechanical Engineering faculty at the Massachusetts Institute of Technology, and then moved to Cornell in 1982. Stephen Pope's research is in the areas of modeling and simulation of turbulent flows and turbulent combustion. He pioneered the use of probability density function (PDF) models for turbulent reactive flows, and has contributed to the statistical modeling of turbulent flows, and to their study via direct numerical simulations.

Notes

Refreshments will be served.