Abstract of talk by Tyler Fara:

We present a computational model for simulation of body temperature subject to the extreme cold (hypothermia) or extreme heat (hyperthermic treatment of tumors by ablation). The model approximates a parabolic PDE enhanced by the energy exchange terms associated with the blood perfusion through tissue, a multiscale phenomenon involving the flow through large vessels and an incalculably complex network of capillaries. As shown in literature, these terms are found by applying homogenization as well as the concept of overlapping continua. We apply the mixed finite element method on Cartesian grids and use an immersed boundary approach to handle complex shaped domains such as a human hand. In addition, we model the body's response to hypothermia by vasoconstriction, where the body aims to preserve the core body temperature even at the expense of sacrificing the hand.

Abstract of talk by Shashank Karra:

The interchange of mass and momentum between streamflow and groundwater occurs across the sediment-water interface (SWI) and into the porous bed underneath, termed as the hyporheic zone. Hyporheic transient storage or retention and transport of solutes such as chemicals and pollutants, dissolved oxygen, nutrients, and heat across the SWI is one of the most important concepts for stream ecology. Turbulent transport across the SWI has been hypothesized as a critical mechanism impacting transient storage, however, it is not well understood. Therefore, in this work, high Reynolds number turbulent flows over underlying porous sediment beds in rivers and streams are analyzed using high-fidelity, predictive simulations based on first principles, wherein all temporal and spatial scales relevant to the flow and geometry are fully resolved. Pore-resolved direction numerical simulations are performed using a fictitious domain method to investigate the interactions between streamflow turbulence and groundwater flow through a randomly packed porous sediment bed for three permeability Reynolds numbers, ReK, of 2.56, 5.17, and 8.94, representative of natural aquatic systems. It is found that the mean flow and shear penetration depths increase with ReK and are found to be nonlinear functions of non-dimensional permeability. Model fits for probability distribution functions based on higher-order statistics of bed shear stress fluctuations and pressure fluctuations at the SWI are developed, which can be used in providing better boundary conditions in modeling of incipient motion and reach-scale transport in the hyporheic zone. Next, a flow solver is developed for a continuum approach based on the upscaled, volume-averaged Navier-Stokes (VANS) equations. The results from this VANS-model are compared with the pore-resolved DNS for turbulent flow over a randomly packed sediment bed at ReK = 2.56. It is found that various primary and secondary statistics such as mean velocity, Reynolds stresses, total fluid stress, TKE budgets are well predicted by the VANS-model compared to the pore-resolved data. The VANS-model uses significantly fewer control volumes and computing resources, resulting in faster predictions. It can be easily extended to large eddy simulation or Reynolds-averaged Navier Stokes approaches, and effectively used to investigate mass and momentum exchange for flows over sediment beds over a wide range of parameter space for flat as well as complex bedforms.

BIO: Shashank Karra is an applications development manager at CPFD Software. He also has a Bachelors in Biomedical Engineering and a Masters in Engineering Science from the University of Tennessee and a PhD in Mechanical engineering from Oregon State University. His research work focused on using pore-resolved DNS simulations to study turbulent flows over sediment beds, and developing numerical methods for high-speed reacting compressible flows. His industrial experience involves applications related to thermal-fluid problems using multiphase Euler-Euler, Euler-Lagrangian, Discrete Particle Method (DPM), porous media, and phase-change models in pipes, wellbores, porous structures, and for heavy oil applications.