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Dubief Receives NSF Award

Release Date: 06-24-2010

Author: Dawn Densmore
Email: Dawn.Densmore@uvm.edu

Dr. Yves Dubief Thanks to a $400,000 award from the National Science Foundation (NSF), Yves Dubief, Assistant Professor in mechanical engineering in the School of Engineering within UVM's College of Engineering and Mathematical Sciences, will lead a collaborative effort with Christopher White from the Mechanical Engineering Department of the University of New Hampshire (UNH). White will conduct an experimental investigation of turbulent ablation of low-melting point temperature materials. Dubief and his students will perform massively parallel simulations of similar flows using the Vermont Advanced Computing Center (VACC) and NSF Teragrids. (Abstract below)

Using software developed by Dubief's group, hundreds to thousands of processors will generate the many Terabytes of data necessary to reproduce temporal and spatial features of turbulent ablation processes in simulations. Combining high quality measurements from UNH and high-fidelity simulations from UVM is anticipated to advance the understanding of the processes of turbulent erosion and ablation towards the development of theory and predictive model.
"Turbulence is a fairly old research field which attracts an interesting mix of engineers, physicists and mathematicians," says Dubief. "After over half a century of intense research, uncharted territories are very rare and rapid erosion is one of them. I am very grateful for the initial support of National Aeronautics Science Administration (NASA) Experimental Program to Stimulate Competitive Research (EPSCOR) which enabled us to develop the proof of concept of our algorithm and, ultimately, to be competitive the National Science Foundation level. This project will showcase UVM's expertise in high fidelity, massively parallel numerical simulations and UNH's expertise in experimental fluid dynamics."

The general objective is to develop predictive numerical models of the rapid erosion process of a surface caused by a flow. Erosion comes in many forms, including river flows or sea currents transporting sediments, abrasion generated by the impact of particles moving with a flow, cavitation in high speed water flows around blades of a propeller or turbine, ablation by phase change and chemical reactions occurring on the heat shield of space vehicles during reentry. Understanding and predicting the evolution of rapid erosion processes is critical to the assessment and mitigation of risks of catastrophic failure whenever erosion may cause significant structural damage.

Some examples are the erosion of the foundation of a levee or bridge pillar caused by a flood or storm currents, or the rapid ablation of a damaged heat shield which could lead to the loss of a space vehicle as in the Columbia space shuttle incident. The difficulty in predicting rapid erosion processes is in the complex interplay between the flow and the evolution of the eroded surface, where the energy of the flow, and therefore the erosion rate, often increase as the surface recedes. The underlying non-linear, out-of-equilibrium physics is not captured by existing models, leaving engineers and scientists unable to reliably predict and avoid catastrophic failures of erodible surfaces.

This project has also led to the invitation of Dubief and his PhD student, Ryan Crocker to the 2010 Center for Turbulence Research Summer Program (June 27 to July 23), at Stanford University in California -- a biennial, month-long event that gathers about 50 researchers on a series of research projects that are the most relevant to current challenges in turbulence understanding and modeling. For more information on this program visit: Summer Program

For more information: Yves Dubief, Ph.D. Or visit: http://www.uvm.edu/~ydubief/

Abstract
This research will aid development of the fundamental understanding necessary to determine how a turbulent flow interacts with an eroding or ablating surface. Specifically, the coherent structures within a turbulent boundary layer, for example, trigger and drive the growth of non-uniform surface topography. In turn, the evolving topography influences the coherent structures within the turbulent flow. The coupling between the flow and solid structures can exist under either isothermal or non-isothermal conditions involving heat transfer.

Intellectual Merit: The research team includes investigators at the University of Vermont and the University of New Hampshire. The computational component of the research is aimed at developing a generalized algorithm to simulate the spatially-varying ablation of an initially-smooth surface under heated conditions. Corresponding experimentation will involve acquisition of detailed data to validate the computational model. The model will be based upon the direct numerical simulation methodology which is capable of predicting the fine detail of the flow field as well as the potentially complex surface shape evolution. Correspondingly, the experimental program will utilize, for example, particle image velocimetry to measure the detail of the flow structure, as well as optical methods to capture the surface shape evolution. Both isothermal and non-isothermal conditions will be considered.

Broader Impacts: The coupled dynamics of turbulent flow and surface erosion or ablation is important in applications ranging from high speed flight to latent energy storage. Additional applications include erosion and movement of sand or soil around bridge pilings, and beach erosion. The research will involve a diverse cadre of undergraduate students while a special topics graduate course will address the integration of experiment and computation.