Michal Hradisky

Extending Applicability of Correlation Equations to Predict Colloidal Retention in Porous Media at Low Fluid Velocity

In this work, we analyzed causes for a recently noted shortcoming of filtration models, which is to predict collector efficiencies greater than unity under low fluid velocity conditions. For Eulerian flux approaches, both the underlying mechanistic model and the correlation equation used to export model results may contribute to this error. For particle trajectory approaches, the error results solely from the correlation equation, not from the underlying mechanistic model, making correction a relatively simple endeavor. Whereas a fitted saturation factor was recently used in a correlation equation to try to force collector efficiencies to remain below unity, we herein develop a different saturation factor based on classic mass transfer relationships to extend the applicability of our correlation equation to low fluid velocities.

A Validation of Flare Combustion Efficiency Predictions from Large Eddy Simulations

Societal concerns about the wide-spread use of flaring of waste gases have motivated methods for predicting combustion efficiency from industrial flare systems under high crosswind conditions. The objective of this paper is to demonstrate, with a quantified degree of accuracy, a prediction procedure for the combustion efficiency of industrial flares in crosswind by using large eddy simulations (LES). LES is shown to resolve the important mixing between fuel and entrained air governing the extent of reaction to within less than a percent of combustion efficiency. The experimental data from the 4-inch flare tests performed at the CanmetENERGY wind tunnel flare facility was used as experimentally measured metrics to validate the simulation with quantified uncertainty. The approach used prior information about the models and experimental data and the associated likelihood functions to determine informative posterior distributions. The model values were subjected to a consistency constraint, which requires that all experiments and simulations be bounded by their individual experimental uncertainty. The final result was a predictive capability (in the nearby regime) for flare combustion efficiency where no/sparse experimental data is available but where the validation process produces error bars for the predicted combustion efficiency.

Large eddy simulation of industrial flares

At the Institute for Clean and Secure Energy at the University of Utah we are focused on education through interdisciplinary research on high-temperature fuel-utilization processes for energy generation, and the associated health, environmental, policy and performance issues. We also work closely with the government agencies and private industry companies to promote rapid deployment of new technologies through the use of high performance computational tools. Industrial flare simulation can provide important information on combustion efficiency, pollutant emissions, and operational parameter sensitivities for design or operation that cannot be measured. These simulations provide information that may help design or operate flares so as to reduce or eliminate harmful pollutants and increase combustion efficiency. Fires and flares have been particularly difficult to simulate with traditional computational fluid dynamics (CFD) simulation tools that are based on Reynolds-Averaged Navier-Stokes (RANS) approaches. The large-scale mixing due to vortical coherent structures in these flames is not readily reduced to steady-state CFD calculations with RANS. Simulation of combustion using Large Eddy Simulations (LES) has made it possible to more accurately simulate the complex combustion seen in these flares. Resolution of all length and time scales is not possible even for the largest supercomputers. LES gives a numerical technique which resolves the large length and time scales while using models for more homogenous smaller scales. By using LES, the combustion dynamics capture the puffing created by buoyancy in industrial flare simulation. All of our simulations were performed using either the University of Utahs ARCHES simulation tool or the commercially available Star-CCM+ software. ARCHES is a finite-volume Large Eddy Simulation code built within the Uintah framework, which is a set of software components and libraries that facilitate the solution of partial differential equations on structured adaptive mesh refinement grids using thousands of processors. Uintah is the product of a ten-year partnership with the Department of Energys Advanced Simulation and Computing (ASC) program through the University of Utahs Center for Simulation of Accidental Fires and Explosions (C-SAFE). The ARCHES component was initially designed for predicting the heat-flux from large buoyant pool fires with potential hazards immersed in or near a pool fire of transportation fuel. Since then, this component has been extended to solve many industrially relevant problems such as industrial flares, oxy-coal combustion processes, and fuel gasification. In this report we showcase selected results that help us visualize and understand the physical processes occurring in the simulated systems. Most of the simulations were completed on the University of Utahs Updraft and Ember high performance computing clusters, which are managed by the Center for High Performance Computing. High performance computational tools are essential in our effort to successfully answer all aspects of our research areas and we promote the use of high performance computational tools beyond the research environment by directly working with our industry partners.

Large eddy simulation of a turbulent buoyant helium plume

At the Institute for Clean and Secure Energy at the University of Utah we are focused on education through interdisciplinary research on high-temperature fuel-utilization processes for energy generation, and the associated health, environmental, policy and performance issues. We also work closely with the government agencies and private industry companies to promote rapid deployment of new technologies through the use of high performance computational tools. Buoyant flows are encountered in many situations of engineering and environmental importance, including fires, subsea and atmospheric exhaust phenomena, gas releases and geothermal events. Buoyancy-driven flows also play a key role in such physical processes as the spread of smoke or toxic gases from fires. As such, buoyant flow experiments are an important step in developing and validating simulation tools for numerical techniques such as Large Eddy Simulation (LES) for predictive use of complex systems. Large Eddy Simulation is a turbulence model that provides a much greater degree of resolution of physical scales than the more common Reynolds-Averaged Navier Stokes models. The validation activity requires increasing levels of complexity to sequentially quantify the effects of coupling increased physics, and to explore the effects of scale on the objectives of the simulation. In this project we are using buoyant flows to examine the validity and accuracy of numerical techniques. By using the non-reacting buoyant helium plume flow we can study the generation of turbulence due to buoyancy, uncoupled from the complexities of combustion chemistry. We are performing Large Eddy Simulation of a one-meter diameter buoyancy-driven helium plume using two software simulation tools -- ARCHES and Star-CCM+. ARCHES is a finite-volume Large Eddy Simulation code built within the Uintah framework, which is a set of software components and libraries that facilitate the solution of partial differential equations on structured adaptive mesh refinement grids using thousands of processors. Uintah is the product of a ten-year partnership with the Department of Energys Advanced Simulation and Computing (ASC) program through the University of Utahs Center for Simulation of Accidental Fires and Explosions (C-SAFE). The ARCHES component was initially designed for predicting the heat-flux from large buoyant pool fires with potential hazards immersed in or near a pool fire of transportation fuel. Since then, this component has been extended to solve many industrially relevant problems such as industrial flares, oxy-coal combustion processes, and fuel gasification. The second simulation tool, Star-CCM+, is a commercial, integrated software environment developed by CD-adapco, that can be used to simulate the entire engineering simulation process. The engineering process can be started with CAD preparation, meshing, model setup, and continued with running simulations, post-processing, and visualizing the results. This allows for faster development and design turn-over time, especially for industry-type application. Star-CCM+ was build from ground up to provide scalable parallel performance. Furthermore, it is not only supported on the industry-standard Linux HPC platforms, but also on Windows HPC, allowing us to explore computational demands on both Linux as well as Windows-based HPC clusters.