A Rayleigh-scatter lidar operated from Utah State University (41.7°N, 111.8°W) for a period spanning 11 years ― 1993 through 2004. Of the 900 nights observed, data on 150 extended to 90 km or above. They were the ones used in these studies related to atmospheric gravity waves (AGWs) between 45 and 90 km. This is the first study of AGWs with an extensive data set that spans the whole mesosphere. Using the temperature and temperature gradient profiles, we produced a climatology of the Brunt-Väisälä (buoyancy) angular frequency squared, N2 (rad/s)2. The minimum and maximum values of N2 vary between 2.2×10-4 (rad/s)2 and 9.0×10-4 (rad/s)2. The corresponding buoyancy periods vary between 7.0 and 3.5 minutes. While for long averages the atmosphere above Logan, Utah, is convectively stable, all-night and hourly profiles showed periods of convective instability (i.e., negative N2). The N2 values were often significantly different from values derived from the NRL-MSISe00 model atmosphere because of the effects of inversion layers and semiannual variability in the lidar data. Relative density fluctuation profiles with 3-km altitude resolution and 1-hour temporal resolution showed the presence of monochromatic gravity waves on almost every night throughout the mesosphere. The prevalent values of vertical wavelength and vertical phase velocity were 12-16 km and 0.5-0.6 m/s, respectively. However, the latter has the significant seasonal variation. Using these two observed parameters, buoyancy periods, and the AGW dispersion relation, we derived the ranges of horizontal wavelength, phase velocity, and source distance. The prevalent values were 550-950 km, 32-35 m/s, and 2500-3500 km, respectively. The potential energy per unit mass Ep showed great night-to-night variability, up to a factor of 20, at all heights. Ep grew at approximately the adiabatic rate below 55-65 km and above 75-80 km. Step function decreases in Ep imply that the AGWs in between gave up considerable energy to the background atmosphere. In addition, Ep varies seasonally. Below 70 km, it has a semiannual variation with a maximum in winter and minima in the equinoxes. At the highest altitudes it has an annual variation with a maximum in winter and a minimum in summer.

A digital learning-teaching environment is introduced in which undergraduate students are challenged to connect the basic physical concepts of oscillation, buoyancy and data analysis via an authentic experiment. The damped oscillation of a cylindrical body swimming upright in water is measured via the MEMS acceleration sensor of a wireless MCU SensorTag. The data are recorded with the app phyphox on a smartphone or tablet. The theoretical oscillation period and the experimentally determined periods obtained via different data analysis roots are found to agree showing an excellent theory-experiment interplay. The proposed experiment is suited for the physics home lab e.g. under the current pandemic situation or for open university courses as well as for physics lab courses.

Experimental measurements of the lift-off velocity and lift-off height, and numerical simulations were conducted on the liftoff and stabilization phenomena of laminar jet diffusion flames of inert-diluted C3H8 and CH4 fuels. Both non-reacting and reacting jets were investigated, including effects of multi-component diffusivities and heat release (buoyancy and gas expansion). The role of Schmidt number for non-reacting jets was investigated, with no conclusive Schmidt number criterion for liftoff previously known in similarity solutions. The cold-flow simulation for He-diluted CH4 fuel does not predict flame liftoff; however, adding heat release reaction leads to the prediction of liftoff, which is consistent with experimental observations. Including reaction was also found to improve liftoff height prediction for C3H8 flames, with the flame base location differing from that in the similarity solution - the intersection of the stoichiometric and iso-velocity contours is not necessary for flame stabilization (and thus lift-off). Possible mechanisms other than that proposed for similarity solution may better help to explain the stabilization and liftoff phenomena. The stretch rate at a wide range of isotherms near the base of the lifted tribrachial flame were also quantitatively plotted and analyzed.

No description available.

Detached Eddy Simulations (DES) is a hybrid URANS-LES technique that was proposed to obtain computationally feasible solutions of high Reynolds number flows undergoing massive separation with reliable accuracy. Since its inception, DES has been applied to a wide variety of flow fields, but mostly limited to unbounded external aerodynamic flows. This is the first study to apply and validate DES to predict the internal flow and heat transfer in non-canonical flows of industrial relevance. The prediction capabilities of DES in capturing the effects of Coriolis forces, which are induced by rotation, and centrifugal buoyancy forces, which are induced by thermal gradients, are also authenticated. The accurate prediction of turbulent flows is sensitive to the level of turbulence predicted by the turbulence scheme. By treating the regions of interest in LES mode, DES allows the unsteadiness in these regions to develop and hence predicts the turbulence levels accurately. Additionally, this permits DES to capture the effects of system rotation and buoyancy. Computations on a rotating system (a sudden expansion duct) and a system subjected to thermal gradients (cavity with a heated wall) validate the prediction capability of DES. The application of DES is further extended to a non-canonical, internal flow which is of relevance in internal cooling of gas turbine blades. Computations of the fully developed flow and heat transfer shows that DES surpasses several shortcomings of the RANS model on which it is based. DES accurately predicts the primary and secondary flow features, the turbulence characteristics and the heat transfer in stationary ducts and in rotating ducts, where the effects of Coriolis forces and centrifugal buoyancy forces are dominant. DES computations are carried out at a computational cost that is almost an order of magnitude less than the LES with little compromise on the accuracy. However, the capabilities of DES in predicting the transition to turbulence are inadequate, as highlighted by the flow features and the heat transfer in the developing region of the duct. But once the flow becomes fully turbulent, DES predicts the flow physics and shows good quantitative agreement with the experiments and LES. / Ph. D.

Increasing the turbine inlet temperature of gas turbine engines significantly increases their power output and efficiency, but it also increases the likelihood of thermal failure. Internal passages with tiny ribs are typically cast into turbine blades to cool them, and the ability to accurately predict the flow and heat transfer within these channels leads to higher design reliability and prevention of blade failure resulting from local thermal loading. Prediction of the flow through these channels is challenging, however, because the flow is highly turbulent and anisotropic, and the presence of rotational body forces further complicates the flow. Large Eddy Simulations are used to study these flows because of their ability to predict the unsteady flow effects and anisotropic turbulence more reliably than traditional RANS closure models. Calculations in a stationary duct are validated with experiments in the developing flow, fully developed, and 180° bend regions to establish the accuracy and prediction capability of the LES calculations and to aid in understanding the major flow structures encountered in a ribbed duct. It is found that most flow and heat transfer calculations come to within 10-15% of the measurements, typically showing excellent agreement in all comparisons. In the developing flow region, Coriolis effects are found to destabilize turbulence and increase heat transfer along the trailing wall (pressure side), while decreasing leading wall heat transfer by stabilizing turbulence. Coriolis forces improve flow turning in the 180° bend by shifting the shape of the separated recirculation zone at the tip of the dividing wall and increasing the mainstream flow area. In addition, turbulence is attenuated near the leading wall throughout the bend, while Coriolis forces have little effect on trailing wall turbulence in the bend. Introducing and increasing centrifugal buoyancy in the developing flow region increases trailing wall heat transfer monotonically. Along the leading wall, buoyancy increases the size of the recirculation zones, shifting the peak heat transfer to a region upstream of the rib, which decreases heat transfer at low buoyancy parameters but increases it as the buoyancy parameter is increased beyond a value of 0.3. Centrifugal buoyancy in the 180° bend initially decreases the size of the recirculation zone at the tip of the dividing wall, increasing flow area and decreasing flow impingement. At high buoyancy, however, the recirculation zone shifts to the middle of the bend, increasing flow resistance and causing strong flow impingement on the back wall. The Boussinesq approximation is used in the buoyancy calculations, but the accuracy of the approximation comes into question in the presence of large temperature differences. A variable property algorithm is developed to calculate unsteady low speed flows with large density variations resulting from large temperature differences. The algorithm is validated against two test cases: Rayleigh-Bénard convection and Poiseuille-Bénard flow. Finally, design issues in rotating ribbed ducts are considered. The fully developed assumption is discussed with regard to the developing flow region, and controlling the recirculation zone in the 180° bend is considered as a way to determine the blade tip heat transfer and pressure drop across the bend. / Ph. D.

This thesis describes the preliminary design of a system for remote terrain exploration and environmental sampling on worlds with dense atmospheres. The motivation for the system is to provide a platform for long-term scientific studies of these celestial bodies. The proposed system consists of three main components: a buoyancy-driven glider, designed to operate at low altitude; a tethered energy harvester, extracting wind energy at high altitudes; and a base station to recharge the gliders. This system is self-sustaining, extracting energy from the planetary boundary layer. A nine degree of freedom vehicle dynamic model has been developed for the buoyancydriven glider. This model was used to illustrate anecdotal evidence of the stability and controllability of the system. A representative system was simulated to examine the energy harvesting concept. / Master of Science

The primary objective of ventilation in a building is to ensure that the Indoor Air Quality (IAQ), together with the heating system, keep the thermal climate at an acceptable level. Meaning the deployment of ventilation air at the appropriate temperature rate supplied to meet the thermal climate into the parts of the building where residents reside. In Sweden, the two most commonly used ventilation strategies are stack ventilation and forced extract ventilation. Both methods utilize exhaust openings in kitchens and sanitary areas, while fresh air is drawn from either permeable external walls or through inlets located near windows and as distant as possible from the exhaust openings (Manz & Huber, 2000). Stack-effect ventilation, also known as buoyancy ventilation, utilizes convective forces. Thus, vertical interior openings such as stairways or atriums play an essential role in the distribution of air and its suitability. Utilizing additional building elements such as a chimney enhances the stack-effect ventilation by elevating the height of the “vertical core” of warm air within the structure. The disparity in density (the difference in temperature between hot and cold) increases as a result of the amplification of pressure disparities (Liu et al., 2010). Hence, larger differences in pressure between the inside and outside will result in an increased driving force for the stack effect by enhancing the convective currents. The principle operates by drawing cooler air from the exterior,generally from the bottom or sides of the building, into the building. The air is then gradually heated and ascends through the vertical core due to convective forces, before being ultimately discharged through the chimney (Savin & Jardinier, 2009). The architectural proposal seeks to adhere to sustainable building development by employing deliberate steps that incorporate a combination of principles and strategies based on the theory of convection. In order to acquire knowledge and validation, an extensive investigation of case studies was carried out, with the works of Philippe Rahm serving as the fundamental basis for further development. Furthermore, a laboratory environment was established to conduct physical tests as well as virtual simulations (CFD) in order to gain deeper understanding and accuracy regarding the relationship between convective forces and geometry. The thesis set out to place a bet based on the notion of consciousness, in terms of implementation of chosen principles, using materials with low embodied carbon, and employing a strategic geometric relationship. This approach enabled the design of an architectural proposal that is both responsive and educative, while also addressing the existing knowledge gap between different professions.

Computational fluid dynamics was used to simulate solar chimney power plants and investigate modeling techniques and expected energy output from the system. The solar chimney consists of three primary parts: a collector made of a transparent material such as glass, a tower made of concrete located at the center of the collector, and a turbine that is typically placed at the bottom of the tower. The collector absorbs solar radiation and heats the air below, whereby air flows inward towards the tower. As air exits at the top of the tower, more air is drawn below the collector repeating the process. The turbine converts pressure within the flow into power. The study investigated three validation cases to numerically model the system properly. Modeling the turbine as a pressure drop allows for the turbine power output to be calculated while not physically modeling the turbine. The numerical model was used to investigate air properties, such as velocity, temperature, and pressure. The results supported the claim that increasing the energy into the system increased both the velocities and temperatures. Also, increasing the turbine pressure drop decreases the velocities and increases the temperatures within the system. In addition to the numerical model, analytical models representing the vertical velocity without the turbine and the maximum power output from a specific chimney were used to investigate the effects on the flow when varying the geometry. Increasing the height of the tower increased the vertical velocity and power output, and increasing the diameter increased the power output. Dimensionless variables were used in a regression analysis to develop a predictive equation for power output. The predictive equation was tested with new simulations and was shown to be in very good agreement. / Master of Science

<p dir="ltr">The research study of Design and Modeling of a Balloon Robot with Wheel Paddles for Agricultural Use (Huang, et al. 2023) presented the design, analysis, and simulation of an innovative agricultural robot that integrated a buoyancy system with a helium balloon and wheeled paddles for navigation, aiming to optimize crop health monitoring. The thesis research initiated with a comprehensive examination of the conceptual design, focusing on the robot's buoyancy mechanism and propulsion system. Detailed motion analysis and kinematic studies underpinned the development of a dynamic model, which was rigorously tested through MATLAB simulations. The MATLAB simulations assessed the unmanned vehicle's operational efficiency, maneuverability, and energy consumption in the environment setting of agricultural. The findings of the new design highlighted the robot's potential to surpass traditional agricultural robots in precision and adaptability, mitigating the limitations of ground and aerial alternatives. The thesis study of the balloon robot concluded with strategic recommendations for future enhancements, emphasizing scalability, payload capacity, and environmental adaptability, thus paving the way for advanced agricultural robotics.</p>