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Aerodynamics and Fluid Mechanics Commons™
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- Turbulence (6)
- Fluid mechanics (5)
- Fluid dynamics (4)
- Wind power (4)
- Wakes (Aerodynamics) -- Mathematical models (3)
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- Wind turbines (3)
- Capillarity (2)
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- Wakes (Fluid dynamics) (2)
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- Evaporation -- Measurement (1)
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- Green roofs (Gardening) (1)
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- Jets -- Fluid dynamics -- Mathematical models (1)
- Microfluidics (1)
- Orthogonal decompositions (1)
- Ozone-depleting substance mitigation -- Evaluation (1)
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Articles 1 - 18 of 18
Full-Text Articles in Aerodynamics and Fluid Mechanics
Turbulent Structures In Coupled Wind-Wave Flows, Cerrina Mouchref
Turbulent Structures In Coupled Wind-Wave Flows, Cerrina Mouchref
Dissertations and Theses
The interactions between wind and waves in offshore environments are complex and have yet to be fully understood. Analyzing these interactions is motivated by an increased interest in climate modeling and the deployment of offshore construction, such as offshore wind farms. In this study, experiments are performed in a wind tunnel using particle image velocimetry (PIV) to analyze wind-wave interactions over various wave and wind speeds. The addition of the wave, a moving boundary, leads to the use of Reynolds triple decomposition in order to separate the turbulent and wave-phase coherent fluctuations. A curvilinear coordinate system was used to analyze …
Review: Dielectric Barrier Discharge Plasma Actuators For In-Flight Applications, Sabeel Saleem Mohammed
Review: Dielectric Barrier Discharge Plasma Actuators For In-Flight Applications, Sabeel Saleem Mohammed
Anthós
Dielectric barrier discharge (DBD) is a phenomenon observed when high voltage is passed through a dielectric barrier at high frequencies. Current DBD plasma actuators (PAs) excel at laminar fluid boundary layer control but suffer from limited momentum flux and fluid mechanic inefficiencies. In this article, Mohammed analyzes previous discourse on DBD PAs and offers directions for future research and potential DBD PA applications. Previous work on DBD PAs documented thrust generation at high voltages and frequencies, thrust in varying fluid compositions, and vortex generation. However, certain arrangements hinder flow magnitudes, limiting the use of multiple DBD PAs in close proximity. …
Consequences Of Spatial Heterogeneity For Turbulent Wake Development, Ryan Scott
Consequences Of Spatial Heterogeneity For Turbulent Wake Development, Ryan Scott
Dissertations and Theses
Spatial heterogeneity is an fundamental property of natural systems. In fluid dynamics subtle variations in fluid motion give rise to chaotic turbulent flows. When a fluid passes an object it retains an imprint of the object as a momentum deficit known as a wake. The resulting spatial structure of the wake is intrinsically linked to the object responsible for its creation. The coupling between geometric complexity in wake producing entities and turbulent wake evolution is considered in terms of spatial heterogeneity from individual wakes through turbulent canopy flows. First a novel Lacunarity-based method is developed for quantifying spatial heterogeneity in …
Proper Orthogonal Decomposition Of Reynolds And Dispersive Stresses In Turbulent Boundary Layers Over Multi-Scale Rough Patches, Catherine Virginia Spivey
Proper Orthogonal Decomposition Of Reynolds And Dispersive Stresses In Turbulent Boundary Layers Over Multi-Scale Rough Patches, Catherine Virginia Spivey
Dissertations and Theses
Multi-scale rough patches are present in topologies such as urban canopies (cities) and natural landscapes (forests, ocean floors). The flow over such canopies is three-dimensional, with turbulent structures known as secondary flows present in the boundary layer due to the difference in rough surface heterogeneities. Three dimensional instantaneous velocities are analyzed within the roughness sublayer over three generations of multi-scale rough patches at nine vertical planes using particle image velocimetry obtained experimentally. The secondary structures present in the flow are identified in the form of Reynolds and dispersive fluctuations. Proper orthogonal decomposition is employed to characterize the imprint of the …
Effectiveness Of Air Pollution Mitigation Systems: Transport, Transformation, And Control Of Ozone In The Indoor Environment, Pradeep Ramasubramanian
Effectiveness Of Air Pollution Mitigation Systems: Transport, Transformation, And Control Of Ozone In The Indoor Environment, Pradeep Ramasubramanian
Dissertations and Theses
Buildings are critical environments governing our collective exposure to air pollution and energy consumption. While there exist concerns regarding increases in building energy consumption due to indoor air interventions, improvements to the quality of air indoors can improve health, comfort, and productivity. Air cleaning technologies that can improve indoor air quality with minimal energy consumption have become ever more important. These technologies are utilized at various scales; from passive removal of pollutants in the air entering the indoor environment to active cleaning of air within the breathing zone. To better understand the effectiveness of active and passive ozone mitigation technologies …
A Three-Dimensional, Analytical Wind Turbine Wake Model: Flow Acceleration, Empirical Correlations, And Continuity, Zein Ahmad Sadek
A Three-Dimensional, Analytical Wind Turbine Wake Model: Flow Acceleration, Empirical Correlations, And Continuity, Zein Ahmad Sadek
Dissertations and Theses
A new, three-dimensional, analytical, steady state wake model is presented which includes local flow acceleration near the rotor improving wake description compared to existing models. Wake structures such as the momentum deficit and regions of accelerated flow are concisely described with compound and normal Gaussian functions. Large-eddy simulations (LES) are used as training data to develop the model using two, inline turbines under various inflow conditions parameterized by hub height wind speed and turbulence intensity. Mass conservation is considered by fixing two components of the wake velocity model and optimizing the third to best satisfy continuity; after which, the model …
The Return To Anisotropy Across A Jet In Crossflow, Gregory P. Sakradse
The Return To Anisotropy Across A Jet In Crossflow, Gregory P. Sakradse
Dissertations and Theses
With data from experiments on a jet of air emitting from an orifice flush with the floor of a wind tunnel providing a transverse flow, analysis is conducted to extract information about the state of anisotropy in the Reynolds stress tensor. Inflow velocities are modulated across two distinct turbulence intensity regimes while holding jet exit conditions constant, providing an opportunity to isolate effects of both jet to crossflow velocity ratio, r and the effects of the turbulence carried by the crossflow. Anisotropy in the Reynolds stress tensor is examined through anisotropy invariant maps and evolution of the function F, …
An Analysis Of Capillary Flow In Finite Length Interior Corners, Samuel Shaw Mohler
An Analysis Of Capillary Flow In Finite Length Interior Corners, Samuel Shaw Mohler
Dissertations and Theses
We analyze the mathematical robustness of slow massively parallel interior corner flows in low gravity environments. An interior corner provides a preferential orientation in low gravity environments. This is a luxury usually only found on earth. It also provides a passive pumping mechanism due to geometry of a conduit. The driving force for this flow is a pressure difference due to local surface curvature gradients. An alternative reasoning is that due to the geometrical constraints the interior corner surface energy is unbounded below. This results in the liquid wicking into corners indefinitely. Interior corner flow's main quantity of interest is …
Fixed Bottom Wind Turbine Wave-Wake Interaction, Ondrej Fercak
Fixed Bottom Wind Turbine Wave-Wake Interaction, Ondrej Fercak
Dissertations and Theses
The interest and benefits of offshore wind energy has also brought along legitimate design challenges for engineers. Most notably, the complex interaction between wind and turbine is further complicated by the addition of dynamic ocean waves. This dynamic coupling between wind, wave, and turbine is not fully understood. Even small improvements in wind turbine performance are welcome, so characterizing a fundamental dynamic in offshore energy is necessary to optimize design. Experimentation and simulation have been used to characterize inflow and turbine wakes and separately, wind-wave interactions. But only simulations have just begun to look at the wind, wave, and turbine …
Entrainment Processes For A Jet In Cross-Flow: The Quantification Of Turbulent Contributions And Their Importance On Accurate Modeling, Graham Asher Freedland
Entrainment Processes For A Jet In Cross-Flow: The Quantification Of Turbulent Contributions And Their Importance On Accurate Modeling, Graham Asher Freedland
Dissertations and Theses
A jet in cross flow (JICF) is examined experimentally by injecting a stream of air into crossing fluid with an aim into quantifying entrainment process and downstream evolution. The behavior of JICF is important to fields ranging from turbine-blade cooling to smokestack pollution and volcanic eruption dynamics. Existing simplified volcanic plume models are tested; most importantly, the near-field contributions of complex interconnected vortex systems, which present significant uncertainties because they assume negligible turbulence. While jets in irrotational cross-flow have been investigated, this analysis has focused on the interaction between a turbulent jet in low and highly turbulent cross-flow created by …
Dynamic Effects Of Inertial Particles On The Wake Recovery Of A Model Wind Turbine, Sarah E. Smith
Dynamic Effects Of Inertial Particles On The Wake Recovery Of A Model Wind Turbine, Sarah E. Smith
Dissertations and Theses
Impacting particles such as rain, dust, and other debris can have devastating structural effects on wind turbines, but little is known about the interaction of such debris within turbine wakes. This study aims to characterize behavior of inertial particles within the turbulent wake of a wind turbine and relative effects on wake recovery. Here a model wind turbine is subjected to varied two-phase inflow conditions, with wind as the carrier fluid (Reλ = 49 - 88) and polydisperse water droplets (26 to 45µm in diameter) at varied concentrations (Φv=0.24 x 10-5 - 1.3 …
Droplet Ejections During Wet Lab Operations Aboard Spacecraft, Caleb Cushman Turner
Droplet Ejections During Wet Lab Operations Aboard Spacecraft, Caleb Cushman Turner
Dissertations and Theses
The breakup and rupture of liquid bridges, thin films, bubbles, droplets, rivulets, and jets can produce satellite droplets that are subsequently ejected into their surrounding environment. For example, when any solid object is withdrawn from a liquid bath, the formation of an ever-thinning columnar liquid bridge eventually ruptures along the axis of the bridge. When rupture occurs under typical pipetting conditions the dynamics governing the rupture almost always produce at a minimum a satellite droplet. When these droplets occur they are often too small and too fast to be observed by the human eye. In a terrestrial environment they are …
A Numerical Investigation Of Microgravity Evaporation, Daniel Peter Ringle
A Numerical Investigation Of Microgravity Evaporation, Daniel Peter Ringle
Dissertations and Theses
Evaporation is important to myriad engineering processes such as cooling, distillation, thin film deposition, and others. In fact, NASA has renewed interest in using cabin air pressure evaporation as a means to recycle waste water in space. As one example, NASA recently conducted experiments aboard the International Space Station (ISS) to measure evaporation rates in microgravity and to determine the impacts of porous structure on the process. It has long been assumed that differences in evaporation rates between 1-g0 and microgravity are small. However, discrepancies by as much as 40% have been observed in practice. The assumption now …
Characterization Of Inertial Particles In The Turbulent Wake Of A Porous Disk, Kristin Nichole Travis
Characterization Of Inertial Particles In The Turbulent Wake Of A Porous Disk, Kristin Nichole Travis
Dissertations and Theses
This study presents the findings of a wind tunnel experiment investigating the behaviour of micrometric inertial particles in the turbulent wake of a stationary porous disk. Various concentrations [Φv ∈ (2.95 x 10-6 - 1.22 x 10-5)] of polydisperse water droplets (diameter 13-41 µm) are compared to sub-inertial tracer particles. Hot-wire anemometry, phase Doppler interferometry and particle image velocimetry were implemented in the near and far wake regions to study the complex dynamics of the particles. Turbulence statistics and particle size distributions are presented and used to explore the particle wake interaction.
Electro-Drop Bouncing In Low-Gravity, Erin Stivers Schmidt
Electro-Drop Bouncing In Low-Gravity, Erin Stivers Schmidt
Dissertations and Theses
We investigate the dynamics of spontaneous jumps of water drops from electrically charged superhydrophobic dielectric substrates during a sudden step reduction in gravity level. In the brief free-fall environment of a drop tower, with a non-homogeneous external electric field arising due to dielectric surface charges (with surface potentials 0.4-1.8 kV), body forces acting on the jumped drops are primarily supplied by polarization stress and Coulombic attraction instead of gravity. This electric body force leads to a drop bouncing behavior similar to well-known phenomena in 1-g0, though occurring for much larger drops (~0.5 mL). We show a simple …
Mechanisms And Identification Of Unsteady Separation Development And Remediation, Matthew Scott Melius
Mechanisms And Identification Of Unsteady Separation Development And Remediation, Matthew Scott Melius
Dissertations and Theses
Unsteady flow separation represents a highly complex and important area of study within fluid mechanics. The extent of separation and specific time scales over which it occurs are not fully understood and has significant consequences in numerous industrial applications such as helicopters, jet engines, hydroelectric turbines and wind turbines. A direct consequence of unsteady separation is the erratic movement of the separation point which causes highly dynamic and unpredictable loads on an airfoil. Current computational models underestimate the aerodynamic loads due to the inaccurate prediction of the emergence and severity of unsteady flow separation especially in response to a sudden …
Experimental Study On Influence Of Pitch Motion On The Wake Of A Floating Wind Turbine Model, Stanislav Rockel, Elizabeth Camp, Jonas Schmidt, Joachim Peinke, Raúl Bayoán Cal, Michael Höllimg
Experimental Study On Influence Of Pitch Motion On The Wake Of A Floating Wind Turbine Model, Stanislav Rockel, Elizabeth Camp, Jonas Schmidt, Joachim Peinke, Raúl Bayoán Cal, Michael Höllimg
Mechanical and Materials Engineering Faculty Publications and Presentations
Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind …
Capillary-Driven Flows Along Rounded Interior Corners, Yongkang Chen, Mark M. Weislogel, Cory L. Nardin
Capillary-Driven Flows Along Rounded Interior Corners, Yongkang Chen, Mark M. Weislogel, Cory L. Nardin
Mechanical and Materials Engineering Faculty Publications and Presentations
The problem of low-gravity isothermal capillary flow along interior corners that are rounded is revisited analytically in this work. By careful selection of geometric length scales and through the introduction of a new geometric scaling parameter Tc, the Navier–Stokes equation is reduced to a convenient∼O(1) form for both analytic and numeric solutions for all values of corner half-angle α and corner roundedness ratio λ for perfectly wetting fluids. The scaling and analysis of the problem captures much of the intricate geometric dependence of the viscous resistance and significantly reduces the reliance on numerical data compared with several previous solution methods …