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Fluid and Thermal Sciences

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Lordi, J.
Van Slooten, R.

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Research summaries

HIGH FIDELITY NUMERICAL MODELING AND SIMULATION OF FIRE SUPPRESSION -- The objective of this research is to develop an advanced modeling and simulation framework for predicting the suppression of large scale fires using water mists and sprays. The modeling is based on Large Eddy Simulation (LES) techniques using probabilistic based subgrid scale (SGS) models to account for multiphase coupling of buoyantly driven turbulence, combustion, suppression thermo-chemistry, droplet transport and thermal radiation heat transfer. The main challenge in controlling large fires is predicting the performance of the delivery system that depends on the understanding of dynamics of flame suppression processes in highly turbulent, strongly radiating, multiphase, combusting flows. One of the goals of this research is to provide a high fidelity predicative tool to simulate these processes. Such a tool will allow fire protection engineers to design better fire suppression systems to insure fire safety for our nations' critical infrastructures. -- P.E. DESJARDIN. Sponsor: National Science Foundation
FLUID STRUCTURE MODELING FOR COMPOSITE MATERIALS IN FIRES -- Up to 60% of the total heat transfer in a hydrocarbon fire comes from thermal radiation. The radiation heat transfer can cause significant degradation of structural integrity and ultimately material failure. The focus of this research is to model the response of composite structures from a pool fire. The activities include development of a thermo-mechanical damage model for composite materials and numerical algorithms to couple CFD and FEM based solid mechanics codes together using level set methodologies. The ultimate goal of this effort is to predict flame spread and failure of a composite structure from a fire. -- P.E. DESJARDIN. Sponsor: Office of Naval Research.
NUMERICAL MODELING AND SIMULATION OF METALIZED TWO-PHASE COMBUSTION SYSTEMS -- This effort is to examine the ignition and combustion of fine aluminum particles dispersed in a carrier gas containing multiple oxidizing agents. The focus of the research is to develop models for ignition and burning processes of aluminum particles. These particles are often employed for use in the design of explosives and are also used as an additive in propellants to enhance specific thrust. The goal of this effort is to use the aluminum particle models to simulate and understand the flow dynamics of highly energetic shock induced dispersal events. -- P.E. DESJARDIN. Sponsor: Sandia National Laboratories
ANOMALOUS TRANSPORT PHENOMENA -- Anomalous thermal behavior has been observed in which 'heating by cooling' (or 'cooling by heating') appears to occur. Our measurements show that by starting with a rod at a uniform high temperature, when one end is cooled the temperature of the other end first rises before it falls. This has been observed in each of the metal and dielectric samples we have investigated. The objective this study is to explain why this happens by performing additional thermal measurements to guide the analysis of the fundamental thermoelectric phenomena which underlies the observed behavior. -- J.D. FELSKE
ANALYTICAL STUDIES IN RADIATIVE AND MICROSCALE CONDUCTIVE HEAT TRANSFER -- The heat transfer processes being considered are: conduction transport at short time and length scales where multiple time scales are significant and non-continuum electron/phonon/boundary interactions are important. Radiative transport phenomena of interest are: data inversion schemes for analyzing laser light scattering measurements; modeling of the optical properties of nonhomogeneous particles and composite media; analytical and numerical solution of the radiative transport equation; modeling radiative heat transfer in combustion systems; computation of the scattering and absorption characteristics of combustion generated particulates -- J.D. FELSKE.
MICROSCALE HEATING OF FLOWING LIQUIDS -- Analytical and numerical studies are being pursued concerning the pulsed electrical resistance heating of fluids flowing in passages whose scale is of biofluidic interest (~ 25 microns). Being simulated is the transient, conjugated, solid-liquid phase transport plus in conjunction with the RTD detection of the fluid temperature downstream of the heater. -- J.D. FELSKE
BOUNDARY LAYER SEPARATION -- Solutions of the Prandtl's boundary layer equations near the point of separation are studied. The question of existence and uniqueness are investigated. Simple models will be constructed to exhibit the separation phenomena. Numerical methods will be established to solve the boundary layer continuation problem including the point of separation. -- C.S. LIU.
STABILITY OF HYPERSONIC BOUNDARY LAYER -- An analytic approach to the stability analysis is developed based on the WKB method. It is applicable to both insulated walls or walls with heat transfer. Using this model, it is also possible to extend the analysis to include the effects of pressure changes, such as in a corner. -- C.S. LIU, D.R. Bower. Sponsor: Calspan UB Research Center.
NONLINEAR RESPONSE OF HYSTERICALLY DAMPED SYSTEMS -- DAMPERS are known to be very effective devices in earthquake engineering. By using nonlinear dynamic system methods such as the averaging method, the response of hysterically damped systems is analyzed with emphasis on base isolation systems, and will render a more effective nonlinear model for practical engineers. -- C.S. LIU.
TURBULENCE-CHEMISTRY INTERACTIONS IN REACTIVE COMPRESSIBLE TURBULENCE -- Turbulent combustion is a complex physico-chemical phenomenon that is spatially three-dimensional and is of transient nature. This phenomenon has been the subject of intense research within the past sixty years and continues to be of high priority in view of the worldwide concern about energy and pollution control. Since the mean shear is present in most of the turbulent flows, the study of homogeneous shear flows can reveal many features of compressibility in practical turbulent flows. The influence of chemical reaction on the development of compressible turbulent shear flows is being studied by solving the Navier-Stokes equations, the energy equation, and the transport equations for the reactive scalars. -- C.K. MADNIA.
STOCHASTIC LARGE EDDY SIMULATIONS OF TURBULENT COMBUSTION -- Work in underway in assessing the validity of recently developed stochastic models for large eddy simulation (LES) of turbulent combustion. The assessment is via the use of DNS and is being applied to several reacting flow configuration. The stochastic model is based on the use of the probability density function (PDF) methodology for the unresolved subgrid scale quantities. The DNS data are used in both a priori and a posteriori manners to measure the PDFs of the statistical variables within the subgrid. The consistency, convergence, and accuracy of the LES/PDF equation and the Monte Carlo solution of its equivalent stochastic differential equations are assessed. The model predictions are further appraised by comparisons with data generated by DNS and with experimental measurements. In the absence of a closure for the SGS scalar correlations, the results based on the conventional LES are significantly different from those obtained by DNS. The LES/PDF results show a closer agreement with DNS. These results also agree favorably with laboratory data of exothermic reacting turbulent shear flows, and portray several of the features observed experimentally. -- C.K. MADNIA.
NANOSCALE HEAT TRANSFER IN THERMOELECTRIC MATERIALS -- Heat transfer in nanostructures may differ significantly from that in the bulk materials since the characteristic length scales associated with heat carriers, i.e., the mean free path and the wavelength, are comparable to the characteristic length of the nanostructures. Nanostructured materials hold the promise of novel phenomena, properties, and functions, which were not possible before. Thermoelectric properties are among the properties that may drastically change at nanoscale. The efficiency of thermoelectric energy conversion in a material is measured by a non-dimensional figure of merit (ZT). During the last decade, advances have been made in increasing ZT using nanostructures. The main thrust of this research is to model the thermal transport in nanocomposites. The Boltzmann Transport Equation (BTE) for the phonon intensity is solved in conjunction with suitable boundary and interface treatment. The treatment of interfaces between the two materials significantly affects the thermal characteristics of the nanocomposites. Unlike in bulk composites, the results show a strong dependence of thermal conductivity, temperature, and heat flux on the wire size, wire atomic ratio, and interface specularity parameter. -- C.K. MADNIA.
SIMULATION OF ENERGY TRANSPORT IN SILICON ON INSULATOR -- Silicon on Insulator (SOI) technology refers to the use of a layered silicon-insulator-silicon substrate in place of conventional silicon substrates in semiconductor manufacturing, especially microelectronics. Modeling heat transfer in SOI is of great interest and relevant to the heating and reliability of nanoscale transistors. As silicon transistor channel lengths decrease below 100nm, the dimensions become comparable to the phonon mean free path and hence the thermal simulations must consider the impact of phonon scattering on material boundaries and the small dimensions of the heated region. The thermal distribution cannot be accurately modeled using the heat diffusion equation based on the Fourier law. Nanoscale heat sources or 'hotspots', with sizes of the order of 10nm and power density reaching 1018 W / m3, are expected to form in the drain of the SOI. In these hotspots, the increased populations of slow optical phonons are expected to decay to acoustic modes and exhibit ballistic transport. The Boltzmann Transport Equation (BTE) is used to study heat transport in SOI devices. -- C.K. MADNIA.
COMPRESSIBILITY EFFECTS IN TURBULENT SHEAR FLOWS -- The development of the dilatational field is studied by considering the influence of the initial values of the turbulent and gradient Mach numbers. In nonreacting flows, for large values of the gradient Mach number the RDT limit for homogeneous shear flow is recovered. The RDT equations are examined and analytical solutions are found for the long time behavior of the pressure and dilatational velocity modes. The main contributions to the integral of their spectrum functions come from different regions of the wavenumber space than those mostly contributing to the one-point statistics in RDT limit of incompressible turbulent shear flow. This difference accounts for important physics of the dilatational field, and in particular explains the amplification of the dilatational effects in the direction of the mean velocity gradient found in the DNS results. -- C.K. MADNIA.
MODELING AND DNS OF HYDROCARBON FLAME-VORTEX INTERACTIONS -- The laminar diffusion flame-vortex ring configuration is a simple configuration that contains some of the key physical characteristics of turbulent diffusion flames. The ongoing investigation can help us extricate some of the fundamental questions that are central to the turbulent diffusion flame processes. The main objective of this study is to gain fundamental understanding of the physicochemical processes that occur during the combustion of non-premixed laminar hydrocarbon fuels. The main thrust of this research is to conduct direct numerical simulations (DNS) of non-premixed flame-vortex interactions with inclusion of "realistic" chemistry models. The DNS generated results will then be used to develop kinetic mechanisms for unsteady combustion systems. -- C.K. MADNIA.
RELIABLE CHEMISTRY MODELS FOR ANALYTICAL MODELING OF TURBULENT COMBUSTION -- A stumbling block in mathematical modeling of turbulent reacting flows is the mechanism of turbulence-chemistry interactions. The emphasis in almost all previous analytical studies of these flows has been on the turbulence phenomena, not the chemistry. For example, unrealistic one-step reaction schemes have been widely used within the past 15 years. Despite its simplicity and computational convenience, one-step chemistry models are unable to capture many important phenomena such as flame ignition, extinction, propagation, intermediate radical species concentration and soot formation. The objective of this work is to develop and implement more reliable chemistry schemes in theoretical-computational investigations of turbulent combustion phenomena. The implementation of ``full kinetics schemes�� for computations of hydrocarbon combustion is impossible; but it is possible to implement ``reduced kinetics schemes��. Reduced schemes imply simplified chemistry mechanisms deduced from the full chemistry. Several of available reduced kinetic schemes are being utilized in mathematical-computational modeling of hydrocarbon diffusion flames in various turbulent flow configurations -- C.K. MADNIA.
INTRACRANIAL ANEURYSMS -- At the Hemodynamics Lab at the Toshiba Stroke Research Center, we aim at understanding pathophysiology of intracranial aneurysms and improving their diagnosis and treatment, by combining computational fluid dynamics (CFD) and engineering design with medical imaging and molecular biology techniques. We analyze aneurysm rupture risk, evaluate endovascular device for stroke intervention, and develop patient-specific image-based computational fluid dynamics analysis to provide input for treatment. We also employ in vivo and in vitro models to study flow-mediated vascular responses and aneurysm pathogenesis. -- H. MENG. Sponsors: NIH, NSF, IRDF (UB).
DESIGN AND TESTING OF A TOTAL DIVER THERMAL PROTECTION GARMENT -- The aim of this program is to develop a proof-of-concept diving suit that combines passive and active technologies to protect divers in warm and cold water while wearing thermal protective gear or Chemical Warfare Gear. This garment has seven principal components that will be integrated: super insulation, a zoned total body liquid cooling and heating suit, heat storage capacity, active heating or cooling, a heat exchanger to dump excess heat, rechargeable power supply, and a physiological monitoring system. These elements would be combined into a diver thermal protection suit that will have durability and protective characteristics to meet the needs of Navy divers -- J.C.MOLLENDORF, CO-Pl, Dr. David Pendergast, Pl. Sponsor: Office of Naval Research.
MODELLING OF TURBULENT FLOWS -- in attempting to find a universal theory to predict various turbulent flows, researchers are utilizing equations involving higher order correlations in fluctuating velocities and pressure. Hence, dynamic equations for the Reynolds stresses are solved in addition to the mean momentum equations. Improvements are sought for the closure relations for the unknown correlations in the dynamic equations. Numerical solutions are carried out for shear flows (jets, wakes, plumes, etc.) and comparisons are made between calculated and experimental results to verify the closure hypothesis. -- D. TAULBEE.

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