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 Title
 Rapid distortion theory for rotor inflows.
 Creator
 Kawashima, Emilia, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

For aerospace and naval applications where low radiated noise levels are a requirement, rotor noise generated by inflow turbulence is of great interest. Inflow turbulence is stretched and distorted as it is ingested into a thrusting rotor which can have a significant impact on the noise source levels. This thesis studies the distortion of subsonic, high Reynolds number turbulent flow, with viscous effects ignored, that occur when a rotor is embedded in a turbulent boundary layer. The analysis...
Show moreFor aerospace and naval applications where low radiated noise levels are a requirement, rotor noise generated by inflow turbulence is of great interest. Inflow turbulence is stretched and distorted as it is ingested into a thrusting rotor which can have a significant impact on the noise source levels. This thesis studies the distortion of subsonic, high Reynolds number turbulent flow, with viscous effects ignored, that occur when a rotor is embedded in a turbulent boundary layer. The analysis is based on Rapid Distortion Theory (RDT), which describes the linear evolution of turbulent eddies as they are stretched by a mean flow distortion. Providing that the gust does not distort the mean flow streamlines the solution for a mean flow with shear is found to be the same as the solution for a mean potential flow with the addition of a potential flow gust. By investigating the inflow distortion of smallscale turbulence for various simple flows and rotor inflows with weak shear, it is shown that RDT can be applied to incompressible shear flows to determine the flow distortion. It is also shown that RDT can be applied to more complex flows modeled by the Reynolds Averaged Navier Stokes (RANS) equations.
Show less  Date Issued
 2013
 PURL
 http://purl.flvc.org/fau/fd/FA0004030
 Subject Headings
 Computational fluid dynamics, Fluid dynamic measurements, Fluid mechanics  Mathematical models, Turbulence  Computer simulation, Turbulence  Mathematical models
 Format
 Document (PDF)
 Title
 Predicting the flow & noise of a rotor in a turbulent boundary layer using an actuator disk – Rans approach.
 Creator
 Buono, Armand C., Glegg, Stewart A. L., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

The numerical method presented in this study attempts to predict the mean, nonuniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent...
Show moreThe numerical method presented in this study attempts to predict the mean, nonuniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent boundary layer (Configuration 3), were analyzed for a variety of advance ratios ranging from J = 0.48 to J =1.44. CFD results are shown to be in agreement with previous works and validated with experimental data of reverse flow occurring within the boundary layer above the flat plate upstream of a rotor in the Virginia Tech’s Stability Wind Tunnel facility. Results from Configuration 3 will be used in future aeroacoustic computations.
Show less  Date Issued
 2014
 PURL
 http://purl.flvc.org/fau/fd/FA00004269, http://purl.flvc.org/fau/fd/FA00004269
 Subject Headings
 Aeroelasticity, Computational fluid dynamics, Fluid dynamic measurements, Fluid mechanics  Mathematical models, Turbomachines  Fluid dynamics, Turbulence  Mathematical models
 Format
 Document (PDF)
 Title
 The acoustic far field of a turbulent boundary layer flow calculated from RANS simulations of the flow.
 Creator
 Blanc, JeanBaptiste., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

Boundary layers are regions where turbulence develops easily. In the case where the flow occurs on a surface showing a certain degree of roughness, turbulence eddies will interact with the roughness elements and will produce an acoustic field. This thesis aims at predicting this type of noise with the help of the Computational Fluid Dynamics (CFD) simulation of a wall jet using the Reynolds Average NavierStokes (RANS) equations. A frequency spectrum is reconstructed using a representation of...
Show moreBoundary layers are regions where turbulence develops easily. In the case where the flow occurs on a surface showing a certain degree of roughness, turbulence eddies will interact with the roughness elements and will produce an acoustic field. This thesis aims at predicting this type of noise with the help of the Computational Fluid Dynamics (CFD) simulation of a wall jet using the Reynolds Average NavierStokes (RANS) equations. A frequency spectrum is reconstructed using a representation of the turbulence with uncorrelated sheets of vorticity. Both aerodynamic and acoustic results are compared to experimental measurements of the flow. The CFD simulation of the flow returns consistent results but would benefit from a refinement of the grid. The surface pressure spectrum presents a slope in the high frequencies close to the experimental spectrum. The far field noise spectrum has a 5dB difference to the experiments.
Show less  Date Issued
 2009
 PURL
 http://purl.flvc.org/FAU/368611
 Subject Headings
 Computational fluid dynamics, Turbulence, Mathematical models, Fluid mechanics, Mathematical models, Acoustical engineering
 Format
 Document (PDF)
 Title
 Aerodynamic analysis of a propeller in a turbulent boundary layer flow.
 Creator
 Lachowski, Felipe Ferreira., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

Simulating the exact chaotic turbulent flow field about any geometry is a dilemma between accuracy and computational resources, which has been continuously studied for just over a hundred years. This thesis is a complete walkthrough of the entire process utilized to approximate the flow ingested by a Seviktype rotor based on solutions to the Reynolds Averaged NavierStokes equations (RANS). The Multiple Reference Frame fluid model is utilized by the code of ANSYSFLUENT and results are...
Show moreSimulating the exact chaotic turbulent flow field about any geometry is a dilemma between accuracy and computational resources, which has been continuously studied for just over a hundred years. This thesis is a complete walkthrough of the entire process utilized to approximate the flow ingested by a Seviktype rotor based on solutions to the Reynolds Averaged NavierStokes equations (RANS). The Multiple Reference Frame fluid model is utilized by the code of ANSYSFLUENT and results are validated by experimental wake data. Three open rotor configurations are studied including a uniform inflow and the rotor near a plate with and without a thick boundary layer. Furthermore, observations are made to determine the variation in velocity profiles of the ingested turbulent flow due to varying flow conditions.
Show less  Date Issued
 2013
 PURL
 http://purl.flvc.org/fcla/dt/3360798
 Subject Headings
 Acoustical engineering, Boundary layer control, Multiphase flow, Mathematical models, Fluid mechanics, Mathematical models, Turbulence, Mathematical models, Computatioinal fluid dynamics
 Format
 Document (PDF)
 Title
 FarField Noise From a Rotor in a Wind Tunnel.
 Creator
 Grant, Justin Alexander, Glegg, Stewart A. L., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

This project is intended to demonstrate the current state of knowledge in the prediction of the tonal and broadband noise radiation from a Sevik rotor. The rotor measurements were made at the Virginia Tech Stability Wind Tunnel. Details of the rotor noise and flow measurements were presented by Wisda et al(2014) and Murray et al(2015) respectively. This study presents predictions based on an approach detailed by Glegg et al(2015) for the broadband noise generated by a rotor in an...
Show moreThis project is intended to demonstrate the current state of knowledge in the prediction of the tonal and broadband noise radiation from a Sevik rotor. The rotor measurements were made at the Virginia Tech Stability Wind Tunnel. Details of the rotor noise and flow measurements were presented by Wisda et al(2014) and Murray et al(2015) respectively. This study presents predictions based on an approach detailed by Glegg et al(2015) for the broadband noise generated by a rotor in an inhomogeneous flow, and compares them to measured noise radiated from the rotor at prescribed observer locations. Discrepancies between the measurements and predictions led to comprehensive study of the flow in the wind tunnel and the discovery of a vortex upstream of the rotor at low advance ratios. The study presents results of RANS simulations. The static pressure and velocity profile in the domain near the rotor's tip gap region were compared to measurements obtained from a pressure port array and a PIV visualization of the rotor in the wind tunnel.
Show less  Date Issued
 2015
 PURL
 http://purl.flvc.org/fau/fd/FA00004501, http://purl.flvc.org/fau/fd/FA00004501
 Subject Headings
 Aerodynamic noise, Computational fluid dynamics, Fluid dynamic measurement, Fluid mechanics  Mathematical models, Fluid structure interactioin, Turbomachines  Fluid dynamics, Turbulence  Mathematical models, Unsteady flow (Fluid dynamics)
 Format
 Document (PDF)
 Title
 Evaluation of motion compensated ADV measurements for quantifying velocity fluctuations.
 Creator
 Lovenbury, James William., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

This study assesses the viability of using a towfish mounted ADV for quantifying water velocity fluctuations in the Florida Current relevant to ocean current turbine performance. For this study a motion compensated ADV is operated in a test flume. Water velocity fluctuations are generated by a 1.3 cm pipe suspended in front of the ADV at relative current speeds of 0.9 m/s and 0.15 m/s, giving Reynolds numbers on the order of 1000. ADV pitching motion of +/ 2.5 [degree] at 0.3 Hz and a heave...
Show moreThis study assesses the viability of using a towfish mounted ADV for quantifying water velocity fluctuations in the Florida Current relevant to ocean current turbine performance. For this study a motion compensated ADV is operated in a test flume. Water velocity fluctuations are generated by a 1.3 cm pipe suspended in front of the ADV at relative current speeds of 0.9 m/s and 0.15 m/s, giving Reynolds numbers on the order of 1000. ADV pitching motion of +/ 2.5 [degree] at 0.3 Hz and a heave motion of 0.3 m amplitude at 0.2 Hz are utilized to evaluate the motion compensation approach. The results show correction for motion provides up to an order of magnitude reduction in turbulent kinetic energy at frequencies of motion while the IMU is found to generate 2% error at 1/30 Hz and 9% error at 1/60 Hz in turbulence intensity.
Show less  Date Issued
 2013
 PURL
 http://purl.flvc.org/fcla/dt/3362482
 Subject Headings
 Motion control systems, Fluid dynamic measurements, Fluid mechanics, Mathematical models, Analysis of covariance
 Format
 Document (PDF)
 Title
 Hydrodynamics of mangrove roottype models.
 Creator
 Kazemi, Amirkhosro, Curet, Oscar M., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

Mangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitat for many organisms and protecting shorelines against storm surges, high winds, erosion, and tsunamis. The motivation of this proposal is to understand the complex interaction of mangrove roots during tidal flow conditions using simplified physical models. In this dissertation, the mangrove roots were modeled with a circular array of cylinders with different porosities and spacing ratios. In...
Show moreMangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitat for many organisms and protecting shorelines against storm surges, high winds, erosion, and tsunamis. The motivation of this proposal is to understand the complex interaction of mangrove roots during tidal flow conditions using simplified physical models. In this dissertation, the mangrove roots were modeled with a circular array of cylinders with different porosities and spacing ratios. In addition, we modeled the flexibility of the roots by attaching rigid cylinders to hinge connectors. The models were tested in a water tunnel for a range of Reynolds number from 2200 to 11000. Additionally, we performed 2D flow visualization for different root models in a flowing soap film setup. We measured drag force and the instantanous streamwise velocity downstream of the models. Furthermore, we investigated the fluid dynamics downstream of the models using a 2D timeresolved particle image velocimetry (PIV), and flow visualization. The result was analyzed to present timeaveraged and timeresolved flow parameters including the velocity distribution, vorticity, streamline, Reynolds shear stress and turbulent kinetic energy. We found that the frequency of the vortex shedding increases as the diameter of the small cylinders decreases while the patch diameter is constant, therefore increasing the Strouhal number, St=fD/U By comparing the change of Strouhal numbers with a single solid cylinder, we introduced a new length scale, the “effective diameter”. In addition, the effective diameter of the patch decreases as the porosity increases. In addition, patch drag decreases linearly as the spacing ratio increases. For flexible cylinders, we found that a decrease in stiffness increases both patch drag and the wake deficit behind the patch in a similar fashion as increasing the blockage of the patch. The average drag coefficient decreased with increasing Reynolds number and with increasing porosity. We found that the Reynolds stress (−u′v′) peak is not only shifted in the vortex structure because of shear layer interference, but also the intensity was weakened by increasing the porosity, which causes a weakening of the buckling of vorticity layers leading to a decline in vortex strength as well as increase in wake elongation.
Show less  Date Issued
 2017
 PURL
 http://purl.flvc.org/fau/fd/FA00004948, http://purl.flvc.org/fau/fd/FA00004948
 Subject Headings
 Fluid mechanics., Atmospheric models., Ocean currentsMathematical models., Sediment transport., Estuarine oceanography.
 Format
 Document (PDF)
 Title
 Internal waves on a continental shelf.
 Creator
 Jagannathan, Arjun., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

In this thesis, a 2D CHebyshev spectral domain decomposition method is developed for simulating the generation and propagation of internal waves over a topography. While the problem of stratified flow over topography is by no means a new one, many aspects of internal wave generation and breaking are still poorly understood. This thesis aims to reproduce certain observed features of internal waves by using a Chebyshev collation method in both spatial directions. The numerical model solves the...
Show moreIn this thesis, a 2D CHebyshev spectral domain decomposition method is developed for simulating the generation and propagation of internal waves over a topography. While the problem of stratified flow over topography is by no means a new one, many aspects of internal wave generation and breaking are still poorly understood. This thesis aims to reproduce certain observed features of internal waves by using a Chebyshev collation method in both spatial directions. The numerical model solves the inviscid, incomprehensible, fully nonlinear, nonhydrostatic Boussinesq equations in the vorticitystreamfunction formulation. A number of important features of internal waves over topography are captured with the present model, including the onset of wavebreaking at subcritical Froude numbers, up to the point of overturning of the pycnoclines. Density contours and wave spectra are presented for different combinations of Froude numbers, stratifications and topographic slope.
Show less  Date Issued
 2012
 PURL
 http://purl.flvc.org/FAU/3358549
 Subject Headings
 Engineering geology, Mathematical models, Chebyshev polynomials, Fluid dynamics, Continuum mechanics, Spectral theory (Mathematics)
 Format
 Document (PDF)
 Title
 Spectral evaluation of motion compensated adv systems for ocean turbulence measurements.
 Creator
 Egeland, Matthew Nicklas, von Ellenrieder, Karl, VanZwieten, James H., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

A motion compensated ADV system was evaluated to determine its ability to make measurements necessary for characterizing the variability of the ambient current in the Gulf Stream. The impact of IMU error relative to predicted turbulence spectra was quantified, as well as and the ability of the motion compensation approach to remove sensor motion from the ADV measurements. The presented data processing techniques are shown to allow the evaluated ADV to be effectively utilized for quantifying...
Show moreA motion compensated ADV system was evaluated to determine its ability to make measurements necessary for characterizing the variability of the ambient current in the Gulf Stream. The impact of IMU error relative to predicted turbulence spectra was quantified, as well as and the ability of the motion compensation approach to remove sensor motion from the ADV measurements. The presented data processing techniques are shown to allow the evaluated ADV to be effectively utilized for quantifying ambient current fluctuations from 0.02 to 1 Hz (50 to 1 seconds) for dissipation rates as low as 3x107. This measurement range is limited on the low frequency end by IMU error, primarily by the calculated transformation matrix, and on the high end by Doppler noise. Inshore testing has revealed a 0.37 Hz oscillation inherent in the towfish designed and manufactured as part of this project, which can nearly be removed using the IMU.
Show less  Date Issued
 2014
 PURL
 http://purl.flvc.org/fau/fd/FA00004191, http://purl.flvc.org/fau/fd/FA00004191
 Subject Headings
 Fluid dynamic measurements, Fluid mechanics  Mathematical models, Motion control systems, Ocean atmosphere interaction, Ocean circulation, Turbulence, Wave motion, Theory of
 Format
 Document (PDF)
 Title
 caHydrodynamic analysis of flapping foils for the propulsion of near surface under water vehicles using the panel method.
 Creator
 Bustos, Julia, Ananthakrishnan, Palaniswamy, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
 Abstract/Description

This thesis presents twodimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a sourcevortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is twodimensional, incompressible and inviscid. The analysis is first considered for the...
Show moreThis thesis presents twodimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a sourcevortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is twodimensional, incompressible and inviscid. The analysis is first considered for the case of a deeply submerged hydrofoil followed by the case where it is located in shallow water depth or near the free surface. In the second case, the presence of the free surface and wave effects are taken into account, specifically at high and low frequencies and small and large amplitudes of flapping. The objective is to determine the thrust and efficiency of the flapping –foils under the influence of added effects of the free surface. Results show that the freesurface can significantly affect the foil performance by increasing the efficiency particularly at high Frequencies.
Show less  Date Issued
 2015
 PURL
 http://purl.flvc.org/fau/fd/FA00004351, http://purl.flvc.org/fau/fd/FA00004351
 Subject Headings
 Aerodynamics  Mathematical models, Fluid mechanics, Naval architecture, Ships  Aerodynamics, Steering gear
 Format
 Document (PDF)