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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 83 for “"Velocity fluctuations"”.
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Velocity fluctuations in slow flow through porous media
… flow also possesses long-tailed, non-Gaussian velocity probability density distributions. A main result of our simulations is that the statistics of the flow through a single channel captures the entire flow, insofar as the patterns and probability distributions are concerned. I have …
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Laser Doppler velocimetry measurements of particle velocity fluctuations in a concentrated suspension
… average kinetic energy contained in the particle velocity fluctuations. These models have not yet been compared systematically with experimental data. In addition, the "temperature" models assume isotropic particle velocity fluctuations, since the "suspension temperature" is given as a scalar, in …
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Analysis of surface pressure and velocity fluctuations in the flow over surface-mounted prisms
… complicated by the high levels of turbulence fluctuations associated with strong winds. On the other hand, numerical and wind tunnel simulations are usually carried out at smaller values of Re. Consequently, the validation of these simulations should only be based on physical phenomena derived …
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Comparing Turbulent Dispersion Models for RANS Simulations of Particle-Laden Flows
… from the fact that RANS simulations neglect velocity fluctuations and solve for the time averaged velocity field. This leads to non-physical results since these velocity fluctuations affect the particle trajectories. To improve the accuracy, the simula- tions of the particles are adapted with …
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Planar Velocity Measurements in an Incompressible and a Weakly Compressible Mixing Layer
For the weakly compressible mixing layer, the velocity ratio was 0.53, the density ratio was 0.67, and the convective Mach number was 0.38. At the location where the PIV images were obtained, Rex = 3.7 x 106 , Redw = 1.8 x 105, and Rx/lambda = 18. The planar velocity fields obtained in this study …
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Hot-Wire Anemometer for the Boundary Layer Data System
… with a sensor that could directly measure flow velocity fluctuations caused by turbulence. Hot-wires are commonly operated in constant-temperature mode for high frequency response, but require a carefully tuned bridge. The constant-voltage anemometer (CVA) uses a simple op-amp circuit to improve …
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Measurements in the bimodal region of a wing-body junction flow with a rapidly-scanning two-velocity-component laser-Doppler velocimeter
… x/t=-2.15, and δ/t=0.5. A rapidly-scanning two-velocity-component laser-Doppler anemometer system was developed for use in investigating this flow. U and V velocity components were measured simultaneously with surface pressure measurements at the location of the most bimodal pressure histogram …
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Particles and Bubbles Collisions Frequency in Homogeneous Turbulence and Applications to Minerals Flotation Machines
… simulations (LES) are conducted to determine velocity fluctuations of the carrier phase. The DNS results are used to validate existing theoretical models as well as the LES results. The dissertation also presents a CFD-based flotation model for predicting the pulp recovery rate in froth …
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Turbulence Spectra in a Well-Mixed Estuary
… are identified by the study of turbulent velocity fluctuations. These velocity records have been analyzed using standard digital methods to obtain spectral density, spectral energy, and cross-spectra of velocity. In order to study the generation and transfer of the turbulent moment and …
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Large-eddy simulation of turbulent wall-pressure fluctuations using the finite element method
… present dissertation, turbulent wall-pressure fluctuations are characterized. To capture the turbulent characteristics of the flow, large-eddy simulation is used to resolve the large scale motions of the flow directly. A wall-adapting local eddy-viscosity model is selected to account for the …
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Spectral estimates and flow characteristics from non-uniformly sampled LDV data in a turbulent junction vortex
… analysis and time resolved measurements of the velocity fluctuations to characterize the time variant flow on the plane of symmetry. All the measurements were performed with a two-color, two-component, frequency shifted laser Doppler velocimeter. Spectral analysis methods for randomly sampled …
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The effects of turbulence on the measurements of five-hole probes
… static pressure and the three components of velocity at a point in the flow. Previous research has demonstrated that the measurements of simple pressure probes such as Pitot probes are significantly influenced by the presence of turbulence. Turbulent velocity fluctuations contaminate the …
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Studies of the Interaction Between Drag-Reducing Polymers and a Turbulent Flow Field Using Pulsed Image Velocimetry and FENE Bead-Spring Model
… unraveling of polymer molecules by the turbulent velocity fluctuations causing an increase in the viscosity in the buffer zone but not in the viscous sublayer. This increase in the viscosity results in damping of small eddies and an increase in the thickness of the buffer layer and reducing the …
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A Study of Constant Voltage Anemometry Frequency Response
… need for the explicit autonomous measurement of velocity fluctuations in the boundary layer. The frequency response of a sensor operated by CVA has been studied analytically and experimentally. The thermal lag of the sensor is quantified by a time constant, <em>M<sub>CVA</sub></em>. When the time …
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The Spatial Structure of Turbulent Rayleigh-Benard Convection
… that the wind of turbulence (U) scales with the velocity fluctuations (ufluct), U ∼ u fluct. The visualizations indicate that the large-scale circulation engulfs the small-scale structures and advect them across the layer. The engulfment of small-scale buoyant elements may be the mechanism by …
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Control of Turbulent Flow Over an Articulating Turret for Reduction of Adverse Aero-Optic Effects
… objective of the controller was to drive the velocity fluctuations over the aperture of the turret to zero. The next set of experiments fixed the pitch angle and dynamically rotated the hemisphere in the azimuthal direction. Like the pitch tests, steady suction actuation applied over the top …
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On the interaction of ocean waves and turbulence
… were overcome. Observations of near-surface velocity fluctuations revealed that wave attenuation rates induced by the unexpectedly weak rainfall-triggered turbulence were greater than previously anticipated by Teixeira and Belcher (2002). Measured near-surface velocity fluctuations are also …
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Modification of Turbulent Channel Flow by Passive and Additive Devices
… study. The instantaneous streamwise and normal velocity fluctuations were measured using LDV for four different Reynolds numbers; $Re\sb{b}$ = 13300, 19100, 3200, and 49100. For a fixed volumetric flow the pressure drop is reduced by 62 to 76 per cent when compared to a Newtonian flow with an …
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Adaptive control of a four-bar linkage
… are developed and applied to Four-bar linkage velocity control to reduce the input link velocity fluctuations without compromising the control system velocity transient response. The successful control techniques use the known mechanism kinematics and the mechanism input link position to …
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Investigation Of Pressure Fluctuations In The Hyporheic Zone In Response To Flow Around A Hydraulic Structure
… interface. This study maps hyporheic pressure fluctuations as they are related to surface water velocity. The pressure map is used to evaluate lift enhancement and destabilization forces on the riverbed. High pressure events in the subsurface help generate a destabilizing force from within the …
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