A multidimensional finite element method for CFD

A finite element method is used to solve the equations of motion for 2- and 3-D fluid flow. The time-dependent equations are solved explicitly using quadrilateral (2-D) and hexahedral (3-D) elements, mass lumping, and reduced integration. A Petrov-Galerkin technique is applied to the advection terms. The method requires a minimum of computational storage, executes quickly, and is scalable for execution on computer systems ranging from PCs to supercomputers

Numerical simulation of heat, mass, and momentum transfer in an atmospheric boundary layer

Considerable interest has developed in recent years to understand transport phenomena in thermally stratified boundary layers. More complete knowledge in this field is needed to improve the prediction of the diffusion of air pollutants in the lower atmosphere as well as in forecasting air-water circulation for weather conditions. The atmospheric boundary layer is modeled using the equations of continuity, momentum, energy, and concentration. Closure of this set of partial differential equations is hindered by the turbulence terms. Using turbulence kinetic energy, the system of equations is closed by internally determining the exchange coefficients of heat, mass, and momentum along with other atmospheric parameters. This approach makes it possible for the history of turbulent motion to be taken into account. Verification of this model is made by systematically comparing the numerical results with available wind tunnel data for neutral, stable, and unstable conditions. Application of the model is made to study the formation of advection fogs occurring over cold sea surfaces. However, the predicted results of liquid water and water vapor contents have yet to be verified with actual data obtained from field measurements --Abstract, page ii

Turbulent structure in the wake of sphere

The study of turbulent wakes is considered necessary to understand the droplet behavior associated with the collision coalescence phenomena in atmospheric clouds. The Vertical Atmospheric Wind Tunnel enables experiments dealing with this droplet behavior to be analyzed. The experiments conducted in the UMR Vertical Atmospheric Wind Tunnel consist of two parts: one is the investigation of the flow field characteristics in the test section of the wind tunnel; the other is the measurement of the turbulent structure in the wake of a sphere. The test section is rectangular in design and has a cross-sectional area of 36 square inches (6 inches X 6 inches). Mean velocity profiles show the flow to be uniform but increasing in magnitude throughout the downstream portion of the test section. Boundary layer thickness becomes noticeable during the latter portion of the test section. Turbulence intensity, measured in the longitudinal direction of the test section at 10 different downstream positions by a DISA 55D01 hot-wire anemometer, show the background turbulence generated by the wind tunnel to be very small. Mean velocity profiles in the wake of a sphere indicate rapid wake dissipation and show wake interaction with the wall boundary layer of the test section. Axisymmetric turbulence intensities are measured using an X-probe and two DISA 55D01 CTA units in both the Near and Far wakes of the sphere. Reynolds shear stresses are likewise measured and the wake development analyzed through the turbulent energy equation --Abstract, pages ii-iii

Modeling Indoor Contaminant Dispersion

Extended Abstract The study of indoor air pollution requires understanding fundamental principles of fluid mechanics, species transport, heat transfer, and systems engineering. Buildings have become complex entities with considerable electronic control features embedded within the structures. Of particular concern are issues involving contaminants that routinely enter or lie dormant within building interiors, and their affects upon human health. Articles can be commonly found in newspapers printed throughout the world describing groups of people becoming sick while staying in a hotel, cruising on a ship, or travelling in planes or buses. Efforts to define and describe pollutant transport within buildings and interiors has become complex. Modeling pollutant transport within indoor environments now requires computational methods and techniques that were utilized only in research laboratories a few years ago. Knowledge of fundamental principles of ventilation and building systems, including HVAC, must now be coupled with computational fluid dynamics techniques in order to accurately assess human health and predicting contaminant transport. Toxic fumes and airborne diseases are known to produce undesirable odors, eye and nose irritations, sickness, and occasionally death. Other products such as tobacco smoke and carbon monoxide can also have serious health effects on people exposed to a poorly ventilated environment; studies indicate that indirect or passive smoking can also lead to lung cancer. Recommendations for outdoor airflow rates to dilute indoor polluted air vary considerably. In recent years there has been extensive activity in the development and use of CFD tools and special programs for room air movement and contaminant transport applications. These investigations range from the prediction of air jet diffusion, air velocity and temperature distribution in rooms, spread of contamination in enclosures, to fire and smoke spread inside buildings. In most cases the predicted results have been promising when compared to available experimental data. However, numerical modeling of ventilation and associated interior contaminant transport is still at an early stage of development. A considerable amount of research and development work is still needed, particularly in the areas of efficient computational schemes, irregular and adaptive grids, turbulence modeling and wall functions

Autoimmune and autoinflammatory mechanisms in uveitis

The eye, as currently viewed, is neither immunologically ignorant nor sequestered from the systemic environment. The eye utilises distinct immunoregulatory mechanisms to preserve tissue and cellular function in the face of immune-mediated insult; clinically, inflammation following such an insult is termed uveitis. The intra-ocular inflammation in uveitis may be clinically obvious as a result of infection (e.g. toxoplasma, herpes), but in the main infection, if any, remains covert. We now recognise that healthy tissues including the retina have regulatory mechanisms imparted by control of myeloid cells through receptors (e.g. CD200R) and soluble inhibitory factors (e.g. alpha-MSH), regulation of the blood retinal barrier, and active immune surveillance. Once homoeostasis has been disrupted and inflammation ensues, the mechanisms to regulate inflammation, including T cell apoptosis, generation of Treg cells, and myeloid cell suppression in situ, are less successful. Why inflammation becomes persistent remains unknown, but extrapolating from animal models, possibilities include differential trafficking of T cells from the retina, residency of CD8(+) T cells, and alterations of myeloid cell phenotype and function. Translating lessons learned from animal models to humans has been helped by system biology approaches and informatics, which suggest that diseased animals and people share similar changes in T cell phenotypes and monocyte function to date. Together the data infer a possible cryptic infectious drive in uveitis that unlocks and drives persistent autoimmune responses, or promotes further innate immune responses. Thus there may be many mechanisms in common with those observed in autoinflammatory disorders

Computational Heat Transfer using the Method of Second Moments

The Method of Second Moments is a unique numerical scheme developed in the early 1970s for species transport simulations. The ability of the quasi-Lagrangian method to exactly advect a quantity without numerical dispersion is one of its attractive features. The zeroth, first, and second moments correspond to the value of the quantity, the centroid, and the distribution spread within an elemental volume. Application of this method is particularly attractive for general heat transfer calculations, and provides sub-grid scale accuracy even when using coarse grids. The method is simple to employ, fast, accurate, and serves as an alternative to more robust and complex methods utilizing mesh refinement techniques

Cálculos de convección natural en una cavidad usando el método de segundos momentos

RESUMEN Un método numérico cuasi-Lagrangiano usado principalmente para problemas de transporte en el medio ambiente se utiliza aqui para resolver el conjunto de ecuaciones para transporte convectivo de calor en una cavidad calentada en forma diferencial. El método numérico calcula las distribuciones de los momentos cero, primero y segundo de la vorticidad y temperatura en una celda computacional. Un procedimiento Lagrangiano que utiliza las distribuciones de momentos es usado para resolver los términos de advección para poder eliminar los errores por dispersión numérica. Como el modelo mantiene una resolución a nivel sub-malla, distribuciones en una sola célula computacional y áreas de cambios violentos se pueden resolver sin introducir cantidades significativas de amortización computacional. El metodo de etapas fraccionadas se utiliza para calcular los términos de advección y difusión en forma separada. La tecnica es particularmente atractiva para cálculos de simulación de transmisión de calor hasta números de Rayleigh moderamente altos; sin embargo, se requieren límites pequeños en el número CFL para números de Rayleigh mayores que 10 4. SUMMARY A quasi-Lagrangian numerical method used primarily for environmental transport problems is used to solve the equation set for convective heat transfer within a differentially heated enclosure. The numerical method calculates the zeroth, first, and second moment distributions of vorticity and temperature within a cell. A Lagrangian procedure which uses the moment distributions is used to solve the advection terms in order to eliminate numerical dispersion errors. Since the method maintains subgrid scale resolution, single cell distributions and areas of steep gradients can be resolved without significant computational damping. The method of fractional steps is used to calculate the advection and diffusion terms separately. The technique is particularly attractive for heat transfer calculations and low to moderate Rayleigh number sirnulations; however, low CFL limits are required for Rayleigh numbers greater than 10 .Peer Reviewe

Cálculos de convección natural en una cavidad usando el método de segundos momentos

RESUMEN Un método numérico cuasi-Lagrangiano usado principalmente para problemas de transporte en el medio ambiente se utiliza aqui para resolver el conjunto de ecuaciones para transporte convectivo de calor en una cavidad calentada en forma diferencial. El método numérico calcula las distribuciones de los momentos cero, primero y segundo de la vorticidad y temperatura en una celda computacional. Un procedimiento Lagrangiano que utiliza las distribuciones de momentos es usado para resolver los términos de advección para poder eliminar los errores por dispersión numérica. Como el modelo mantiene una resolución a nivel sub-malla, distribuciones en una sola célula computacional y áreas de cambios violentos se pueden resolver sin introducir cantidades significativas de amortización computacional. El metodo de etapas fraccionadas se utiliza para calcular los términos de advección y difusión en forma separada. La tecnica es particularmente atractiva para cálculos de simulación de transmisión de calor hasta números de Rayleigh moderamente altos; sin embargo, se requieren límites pequeños en el número CFL para números de Rayleigh mayores que 10 4. SUMMARY A quasi-Lagrangian numerical method used primarily for environmental transport problems is used to solve the equation set for convective heat transfer within a differentially heated enclosure. The numerical method calculates the zeroth, first, and second moment distributions of vorticity and temperature within a cell. A Lagrangian procedure which uses the moment distributions is used to solve the advection terms in order to eliminate numerical dispersion errors. Since the method maintains subgrid scale resolution, single cell distributions and areas of steep gradients can be resolved without significant computational damping. The method of fractional steps is used to calculate the advection and diffusion terms separately. The technique is particularly attractive for heat transfer calculations and low to moderate Rayleigh number sirnulations; however, low CFL limits are required for Rayleigh numbers greater than 10 .Peer Reviewe