A computer model of a blow-down free-jet hypersonic propulsion test facility exists to validate facility control systems as well as predict problems with facility operation. One weakness in this computer model is the modeling of an air ejector diffuser system. Two examples of facilities that could use this ejector diffuser model are NASA Langley Research Center's 8-ft High Temp. Tunnel (HTT) and the Aero-Propulsion Test Unit (APTU) located at Arnold Engineering Development Center. Modeling an air ejector diffuser system for a hypersonic propulsion test facility includes modeling three coupled systems. These are the ejector system, the primary free-jet nozzle that entrains secondary airflow from the test cell, and the test article. Both of these facilities are capable of testing scramjets/ramjets at high Mach numbers. Compared with computer simulation data, experimental test cell pressure data do not agree due to the current modeling technique used. An improved computer model was derived that incorporates new techniques for modeling the ejector diffuser. This includes real gas effects at the ejector nozzles, flow constriction due to free-jet nozzle and ejector plumes, test article effects, and a correction factor of the normal shock pressure ratio in a supersonic diffuser. A method was developed to account for the drag and thrust terms of the test article by assuming a blockage factor and using a drag coefficient*Area term for both the test article and thrust stand derived from experimental data. An ideal ramjet model was also incorporated to account for the gross thrust of the test article on the system. The new ejector diffuser model developed improved the accuracy and fidelity of the facility model as compared with experimental test data while only negligibly affecting computational speed. Comparisons of the model data with experimental test data showed a close match for test cell pressure (within 1 percent for final test cell pressure). The model accurately simulated both the unstarted and started modes of ejector flow, in which test cell pressure increases with nozzle total pressure once in started mode.

A computer model of a blow-down free-jet hypersonic propulsion test facility exists to validate facility control systems as well as predict problems with facility operation. One weakness in this computer model is the modeling of an air ejector diffuser system. Two examples of facilities that could use this ejector diffuser model are NASA Langley Research Center's 8-ft High Temp. Tunnel (HTT) and the Aero-Propulsion Test Unit (APTU) located at Arnold Engineering Development Center. Modeling an air ejector diffuser system for a hypersonic propulsion test facility includes modeling three coupled systems. These are the ejector system, the primary free-jet nozzle that entrains secondary airflow from the test cell, and the test article. Both of these facilities are capable of testing scramjets/ramjets at high Mach numbers. Compared with computer simulation data, experimental test cell pressure data do not agree due to the current modeling technique used.An improved computer model was derived that incorporates new techniques for modeling the ejector diffuser. This includes real gas effects at the ejector nozzles, flow constriction due to free-jet nozzle and ejector plumes, test article effects, and a correction factor of the normal shock pressure ratio in a supersonic diffuser. A method was developed to account for the drag and thrust terms of the test article by assuming a blockage factor and using a drag coefficient*Area term for both the test article and thrust stand derived from experimental data. An ideal ramjet model was also incorporated to account for the gross thrust of the test article on the system.The new ejector diffuser model developed improved the accuracy and fidelity of the facility model as compared with experimental test data while only negligibly affecting computational speed. Comparisons of the model data with experimental test data showed a close match for test cell pressure (within 1 percent for final test cell pressure). The model accurately simulated both the unstarted and started modes of ejector flow, in which test cell pressure increases with nozzle total pressure once in started mode.

Convection at the interior surface of a building represents a significant portion of the heat transfer in office buildings with large glazing areas. While a large number of these office buildings utilize ceiling slot diffusers at the glazed building perimeter, convection correlations specific to these diffusers have not yet been investigated. This paper describes convection correlations developed for ceiling slot diffusers and examines the effect of temperature, various window geometries, and diffuser jet momentum on these correlations. The paper also examines the effect of venetian blinds on the overall correlations at various blind angle configurations: open, partially open, and closed. The results of the examined phenomena are validated in both heating and cooling conditions. All together, this paper represents the effort of over 100 individual experiments. The results show that forced convection is dominant at all air flow rates, and correlations are developed as a function of air volumetric flow rate with supply air temperature utilized as the reference. The correlations are found to rely only on window position, and are independent of temperature difference between surface and supply, diffuser position, and diffuser jet momentum. With respect to the blinds, the only relevant parameter is the angle of the blinds except when the blinds are open. When the blinds are open and at 45º, convective heat transfer is enhanced. Conversely, convection is decreased when the blinds are closed and at -45º. There is also a decrease in the convective heat transfer with a full window in contrast to a half window when the blinds are open. Finally, there is little difference between the convection correlations developed for heated and cooled environments. / text

Indoor jets considerably dominate air movement and distribution of temperature and velocity, as well as transport of particles and other pollutants. Indoor air temperature and velocity distribution substantially impact occupants’ thermal comfort and productivity, heat and mass transfer on indoor surfaces. In addition, jets produced by human respiratory activities, such as coughing and sneezing, enhance the spread of particles that might carry bacteria or viruses. Understanding and characterizing indoor jets and their impacts on air distribution, temperature and velocity fields, and particle transport are crucial for advancing heating, ventilation, and air conditioning (HVAC) systems when considering thermal comfort and developing strategies for exposure mitigation. This dissertation contributes to the scientific understanding regarding to indoor air distribution and particle transport associated with indoor air jets. Current HVAC system design defines indoor air distribution related to the selection of diffusers/ grilles that distribute supply air jets, according to the specifics of the space and internal heating and cooling loads. However, current design guidance was developed over 40 years ago. It requires expansion of diffuser/ grille types and the update for air distribution by diffuser/ grille air jets supplying warm air at heating mode. Unlike jets from diffusers/ grilles, jets created by human activities are inherently transient in nature and might perform quite differently from steady-state ones. Understanding the dynamics of unsteady-state jets, such as coughs, enhances the current state of understanding of the mechanisms of respiratory disease transmission, which enables development of exposure reduction measures. The investigations presented in this dissertation extend the state-of-the-art knowledge on indoor jets and analyze the effect of steady-state and unsteady-state jets on particle transport in indoor environments. Figure 1 illustrates the two objectives and six investigations conducted in this dissertation. The first objective includes four investigations that address air distribution and particle transport associated with steady-state jets created by diffusers/ grilles, and the remaining two investigations relate to the second objective on unsteady-state cough jets. The first objective of this dissertation characterizes air distribution and particle transport in a space with steady-state jets created by diffusers/ grilles. One of the major contributions of this objective to the-state-of-the-art knowledge on indoor air distribution is the newly developed method for diffuser performance assessment and design when considering heating mode. It advances the current diffuser/ grille selection guide that was outdated decades ago. Furthermore, based on 650 experimental set-ups this objective provides a systematic analysis of indoor air velocity that can be further used in indoor heat transfer and pollutant emission and transport. The second objective investigates velocity fields in unsteady-state cough jets and transport of coughed particles. This objective provides a theoretical analysis of the dynamics of cough jets and examines how human thermal plume affects the exposure to coughed particles when considering different particle sizes. Ultimately, these investigations fill the knowledge gaps in indoor air distribution and particle transport associated with steady-state and unsteady-state jets in spaces using all-air HVAC systems. The newly developed diffuser guideline will improve HVAC design for both heating and cooling conditions when considering thermal discomfort or air stagnant zones caused by a wrong diffuser selection. In addition, the systematic analysis of indoor air velocity will improve the prediction of indoor heat transfer, mass transfer, particle resuspension rate, pollutant emission rate from the floor and other indoor surfaces. Finally, the theoretical analysis of unsteady-state jets contributes the knowledge for fluid dynamics of unobstructed human coughs and also transport of coughed particles, including the distribution in the vicinity of an exposed person. / text

The first part of the thesis is research, which deals with electric luminaires and especially their light-active parts. Subsequently is described the problem of a specific luminaire, which is used during the control of the surface structure of materials. The next part of the thesis deals with the simulation of the current luminaire and the simulations of the proposed solutions that eliminate the shortcomings of the luminaire. The conclusion of this thesis is the evaluation of the originally used luminaire and the benefits of the proposed solution, which showed the best results in the simulation.

Hypolimnetic oxygenation systems, such as linear bubble-plume diffusers, are used to improve raw water quality. Linear bubble-plume diffusers were installed in Spring Hollow Reservoir (SHR) and Carvins Cove Reservoir (CCR). Diffusers induce mixing that aids distribution of oxygen throughout the hypolimnion. The induced mixing also creates an undesirable effect by increasing hypolimnetic oxygen demand (HOD). Nevertheless, oxygenation systems are commonly used and long-term oxygenation is hypothesized to actually decrease HOD. Increased oxygen concentrations in combination with the induced mixing affect the location of the oxic/anoxic boundary relative to the sediment water interface. If the oxic/anoxic boundary is pushed beneath the sediment/water interface, the concentrations of soluble iron and manganese in the bulk water are reduced. This work was performed to further validate a recently published bubble-plume model that predicts oxygen addition rates and the elevation in the reservoir where the majority of the oxygen is added. Also, the first field observations of a theoretically expected secondary plume are presented. Model predicted addition rates were compared to observed accumulation rates to evaluate HOD over a wide range of applied gas flow rates. Observations in both reservoirs showed evidence of horizontal spreading that correlated well with plume-model predictions and of vertical spreading below diffuser elevations, showing oxygen penetration into the sediment. Experimental observations of a theoretically expected secondary plume structure also correlated well with model predictions. Plume-induced mixing was shown to be a function of applied gas flow rates, and was observed to increase HOD. HOD was also observed to be independent of bulk hypolimnion oxygen concentration, indicating that the increase in oxygen concentration is not the cause of the increased HOD. Long-term oxygenation resulted in an overall decrease in background HOD as well as a decrease in induced HOD during diffuser operation. Elevated oxygen concentrations and mixing, which occur naturally during destratification and artificially during oxygenation, were observed to coincide with low dissolved metal concentrations in CCR. Movement of the oxic/anoxic boundary out of the sediment, which is also common during stratified periods, appears to facilitate transport of reduced Mn to the overlying waters. Hypolimnetic oxygenation increased oxygen concentrations throughout the hypolimnion, including down to the SWI, and induced mixing, although not to the extent observed during destratification. Subsequently, elevated Mn concentrations were observed to be restricted to the benthic waters located immediately over the sediments, while bulk (hypolimnion) water Mn concentrations remained low. The good agreement between the model and the experimental data show that the model can be used as a predictive tool when designing and operating bubble-plume diffusers. Linear bubble-plume diffusers provide sufficient horizontal and vertical spreading to enable oxygen to reach the sediments. Hypolimnetic oxygenation, despite the increased HOD, is a viable method to manage the negative consequences of hypolimnetic anoxia in water-supply reservoirs. / Ph. D.

As wind turbines are increasingly being adopted for meeting growing energy needs, their implementation for personal home use in the near future is imminent. There are very few studies conducted on small-scale turbines in the one to two meter diameter range because the power generated at this scale is currently not sufficient to justify the cost of installation and maintenance. The problem is further complicated by the fact that these turbines are normally mounted at low altitudes and thus there is necessity to have the optimum operating regime in the wind speed range of 3-10 mph (1.34 -- 4.47 m/s). This thesis discusses two methods for increasing the efficiency of horizontal axis small-scale wind energy conversion systems, 1) adding a diffuser to increase the wind speed at the rotor and 2) designing tubercles to enhance the flow characteristics over blades. Further, it was identified during the course of thesis that for simple installation and maintenance in the residential areas vertical axis turbines are advantageous. Thus, the second chapter of this thesis addresses the design of vertical axis turbines with power generation capability suitable for that of a typical US household. The study of the diffuser augmented wind turbine provides optimum dimensions for achieving high power density that can address the challenges associated with small scale wind energy systems; these challenges are to achieve a lower start-up speed and low wind speed operation. The diffuser design was modeled using commercial computational fluid dynamics code. Two-dimensional modeling using actuator disk theory was used to optimize the diffuser design. A statistical study was then conducted to reduce the computational time by selecting a descriptive set of models to simulate and characterize relevant parameters' effects instead of checking all the possible combinations of input parameters. Individual dimensions were incorporated into JMP® software and randomized to design the experiment. The results of the JMP® analysis are discussed in this paper. Consistent with the literature, a long outlet section with length one to three times the diameter coupled with a sharp angled inlet was found to provide the highest amplification for a wind turbine diffuser. The second study consisted of analyzing the capabilities of a small-scale vertical axis wind turbine. The turbine consisted of six blades of extruded aluminum NACA 0018 airfoils of 0.08732 m (3.44 in) in chord length. Small-scale wind turbines often operate at Reynolds numbers less than 200,000, and issues in modeling their flow characteristics are discussed throughout this thesis. After finding an appropriate modeling technique, it was found that the vertical axis wind turbine requires more accurate turbulence models to appropriately discover its performance capabilities. The use of tubercles on aerodynamic blades has been found to delay stall angle and increase the aerodynamic efficiency. Models of 440 mm (17.33 in) blades with and without tubercles were fabricated in Virginia Tech's Center for Energy Harvesting Materials and Systems (CEHMS) laboratory. Comparative analysis using three dimensional models of the blades with and without the tubercles will be required to determine whether the tubercle technology does, in fact, delays the stall. Further computational and experimental testing is necessary, but preliminary results indicate a 2% increase in power coefficient when tubercles are present on the blades. / Master of Science

A subsonic wind tunnel facility was designed and built to test and optimize various diffuser-collector box geometries at the one-twelfth scale.  The facility was designed to run continuously at an inlet Mach number of 0.42 and an inlet hydraulic diameter Reynolds number of 340,000. Different combinations of diffusers, hubs, and exhaust collector boxes were designed and evaluated for overall optimum performance. Both 3-hole and 5-hole probes were traversed into the flow to generate multiple diffuser inlet and collector exit performance profile plots. Surface oil flow visualization was performed to gain an understanding of the complex 3D flow structures inside the diffuser-collector subsystem. The cutback radial hardware was found to increase the subsystem pressure recovery by over 10% from baseline resulting in an approximate 1% increase in gas turbine power output. / Master of Science

Neste trabalho apresenta-se o estudo da transferência de massa (oxigênio) de bolhas de ar para a água, geradas por um difusor de ar, confeccionado com plástico microporoso e de fabricação nacional, em uma coluna de aeração. O processo de aeração conduziu à determinação do coeficiente volumétrico de transferência de massa, coeficiente volumétrico de transferência de massa global, e foi executado na coluna mencionada, construída em material transparente. Utilizou-se água de fonte, existente no abastecimento do Laboratório de Hidráulica Ambiental (SHS/CRHEA). Variou-se a vazão do ar no processo de aeração de 400 l/h a 2.000 l/h e o nível de água dentro da coluna de 0,50 m a 1,80 m. Optou-se pelo método químico para deaerar a água, utilizando sulfito de sódio anidro antes do início de cada ensaio. O aparelho WTW-323, um medidor de oxigênio do tipo membrana permeável, foi usado para determinar a evolução da concentração de oxigênio dissolvido na água durante todo o processo de aeração. Características hidrodinâmicas foram quantificadas, como os campos de velocidade ascensional das bolhas de ar, o diâmetro equivalente das bolhas e sua freqüência de ocorrência. Para essas quantificações utilizou-se equipamento Laser para velocimetria não-intrusiva. As características mencionadas são fundamentais para verificar as previsões para o coeficiente de transferência de massa encontradas na literatura. A coluna usada tem seção transversal quadrada de 0,19 m x 0,19 m, constante em toda sua extensão, e altura de 2,00 m. Através da determinação da eficiência de transferência de massa de oxigênio na água, variando a vazão de aeração e o nível de água na coluna, concluiu-se que a vazão entre 600 l/h e 800 l/h e nível de água de 1.80 m é que apresentou maior eficiência de transferência de massa. / The present work is a study of the oxygen mass transfer from air bubbles into water, generated by a diffuser of air, in a column of aeration. This diffuser was made of microporous plastic and produced in Brazil. The process of aeration in the column built with transparent material determined the volumetric coeficient of the mass transfer Kla. Water from the well located in the Environmental Hydraulic Laboratory (SHS/CRHEA) was used. The air flow in the process of aeration was changed from 400 l/h to 2000 l/h and the level of water, from 0,50 m to 1,80 m. The chemical method was chosen to deoxygenate water and sulfite of anhydrous sodium was used before starting each experiment. The equipment WTW-323, an oxygen gauge with permeable membrane, was used to determine the development of the oxygen concentration dissolved in water during the process of aeration. Several hydrodinamic characteristics were measured, such as the velocity range of the air bubbles, their diameter and their frequency, by using a laser equipment for non-intrusive velocimetry. These characteristics are fundamental to check the mass transfer coeficient that are in literature. The column used for the experiment had a square cross section of 0,19 m x 0,19 m in alI extension and height of 2 meters. After determination of the efficiency of the mass transfer of oxygen into water, changing the air flow rate and the level of water in the column, it was concluded that the air flow between 600 l/h and 800 l/h and the level of water of 1,80 m were the most efficient.

Specific power output from a Low Pressure (LP) steam turbine can be enhanced by increasing the stage efficiency or raising its pressure ratio; both methods are interlinked and must be dealt with together. The latter is achieved by connecting to the exhaust diffuser; space and cost constraints often insist the use of an axial-radial diffuser with high levels of diffusion. The present study aims to investigate the interaction between the last-stage blade and the axial-radial diffuser, which can influence the diffuser performance and thus the total work output from the stage. This work is carried out using CFD simulations of a generic last stage low pressure (LP) turbine and axial-radial exhaust diffuser attached to it. In order to determine the validity of the computational method, the CFD predictions are first compared with data obtained from an experimental test facility. A computational study is then performed for different design configurations of the diffuser and rotor casing shapes. The study focuses on typical flow features such as effects of rotor tip leakage flows and subsequent changes in the rotor-diffuser interactions. The results suggest that the rotor casing shape and diffuser configurations influences the rotor work extraction capability and yields significant improvements in the static pressure recovery.