Simulation and Modeling of the Decay of Anisotropic Turbulence

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

A very large number of industrial and environmental processes involve fluids whose motion is turbulent. This project involves the accurate statistical prediction and modeling of these chaotic, unsteady, and three-dimensional fluid motions. The focus is on simulating and then modeling the turbulent return-to-isotropy process which has resisted modeling efforts in the past. The return-to-isotropy process significantly influences near wall turbulence, duct flows, atmospheric and oceanic heat and mass transfer processes like CO2 absorption, heat exchanger performance, wing tip vortices, and a host of important and currently poorly modeled turbulent flow situations. Information about the structure (i.e. the shape of the underlying eddies) is hypothesized to control the return-to-isotropy process. In order to determine the contribution due to structure, large domain direct numerical simulations (DNS) of return-to-isotropy in homogeneous anisotropic turbulence are performed. Anisotropy is generated by five fundamentally different mean strains and by walls. Each produces very different turbulent structures. The influence on the return-to-isotropy process of the Reynolds number, initial length scale, and initial structure (parameterized by the two-point correlations) will be characterized and used to calibrate the oriented-eddy turbulence model. The oriented-eddy collision model is implemented in the open source CFD program, OpenFoam making it easily available to the scientific community. This open source implementation will allow others to rapidly test the accuracy of the model in any complex configuration of their choosing. Intellectual Merit: This work will significantly enhance our current understanding of how turbulence structure influences its nonlinear evolution. It is anticipated that the oriented-eddy collision model will be the first turbulence model capable of predicting the return-to-isotropy process accurately for a wide variety of different scenarios. In addition, this work will provide critical information for other turbulence models which incorporate turbulence structure. Broader Impacts: Turbulence models are a necessary component of most computational fluid dynamics (CFD) simulations. Models with quantitative predictive accuracy could radically transform the utility of CFD as a design and prediction tool. This project will provide researchers in this field with a high quality database consisting of canonical turbulent flows. Some of the supercomputing tasks in this project can, and will, be performed by undergraduate researchers during summer REU experiences that target women and minorities. This work will be disseminated to the general public via WFCR, our local public radio affiliate.