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Title: An Analysis of the Surface Pressure Spectra in a Fluid Flow with a Zero-Pressure Gradient Turbulent Boundary Layer.
Creator: Balestrieri, Frank, Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: The objective of this thesis is to review recently developed empirical and analytical models for the surface pressure and wavenumber spectra for fully developed boundary layers to highlight the effect of assumptions about the turbulence length scales and show how the effects of mean flow Reynolds number has on the spectra shape. The Goody model is used as a reference model to compare the spectra shape as it characterizes the basic physical features of the wall-pressure spectrum under a zero...
Show moreThe objective of this thesis is to review recently developed empirical and analytical models for the surface pressure and wavenumber spectra for fully developed boundary layers to highlight the effect of assumptions about the turbulence length scales and show how the effects of mean flow Reynolds number has on the spectra shape. The Goody model is used as a reference model to compare the spectra shape as it characterizes the basic physical features of the wall-pressure spectrum under a zero-pressure gradient turbulent boundary layer and scales as a function of Reynolds number. The turbulence length scales of the comparison models are modified to observe the effects on the shape of the spectra. A new model is also considered that also scales as a function of Reynolds number and is compared to the Goody model.
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Date Issued: 2021
PURL: http://purl.flvc.org/fau/fd/FA00013816
Subject Headings: Turbulent boundary layer, Turbulence
Format: Document (PDF)

Title: Wall Pressure Fluctuation in a Turbulent Channel Flow.
Creator: Denissova, Lyubov, Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: Turbulent flow is a complex three dimensional system of velocity and pressure fluctuations in a fluid that creates vorticity, eddies and other flow structures. In this study we are specifically concerned with the surface pressure fluctuations below a turbulent boundary layer which is one of the primary sources of panel vibration on aircraft fuselages and ship hulls as well a major issue in ship hydrodynamics. The most accepted analytical approaches to describe the surface pressure...
Show moreTurbulent flow is a complex three dimensional system of velocity and pressure fluctuations in a fluid that creates vorticity, eddies and other flow structures. In this study we are specifically concerned with the surface pressure fluctuations below a turbulent boundary layer which is one of the primary sources of panel vibration on aircraft fuselages and ship hulls as well a major issue in ship hydrodynamics. The most accepted analytical approaches to describe the surface pressure fluctuations are the Chase model [1] for the surface pressure wavenumber spectrum and Goody’s model [2] for the pressure spectrum at a point. The most accurate numerical approach to use is Direct Numerical Simulations (DNS) [3]. In this study we compared Chase and Goody’s models against DNS of a turbulent channel flow in the space–time and wavenumber-frequency domains and estimated regions of convergence between the analytical models and the DNS data.
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Date Issued: 2022
PURL: http://purl.flvc.org/fau/fd/FA00014034
Subject Headings: Turbulence, Turbulent boundary layer, Pressure
Format: Document (PDF)

Title: Dynamic modeling of two layered stratification.
Creator: Zhang, Yaodong., Florida Atlantic University, Scarlatos, Panagiotis (Pete) D., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: In this thesis, a two-dimensional in the vertical plane numerical model has been developed for simulation of the free surface and density interface profiles due to a wind shear stress applied on a stratified water body, such as lake or reservoir. The results agreed qualitatively and quantitatively with our experimental results, as well as with the work of other researchers. A computer algorithm is established that can be used to estimate the shear stress along the interface and the velocity...
Show moreIn this thesis, a two-dimensional in the vertical plane numerical model has been developed for simulation of the free surface and density interface profiles due to a wind shear stress applied on a stratified water body, such as lake or reservoir. The results agreed qualitatively and quantitatively with our experimental results, as well as with the work of other researchers. A computer algorithm is established that can be used to estimate the shear stress along the interface and the velocity field throughout the water body. The model can be applied for prediction of wind-induced mixing processes in elongated lakes or reservoirs.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/14809
Subject Headings: Upwelling, Turbulence, Density currents
Format: Document (PDF)

Title: Oceanic turbulence measurement using an AUV platform and development of graphical interfaces for data acquisition and analysis.
Creator: Leindecker, Eric-Olivier., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Application of a small autonomous underwater vehicle (AUV) is described as a platform for measurement of oceanic turbulence in coastal waters during cold atmospheric fronts. The turbulence package, mounted on the AUV, allows horizontal profiling and measurement of small-scale fluctuations of velocity and temperature and other characteristics of the flow in the ocean mixed layer. The turbulence measurements were made in conjunction with current profile measurements, conductivity, temperature,...
Show moreApplication of a small autonomous underwater vehicle (AUV) is described as a platform for measurement of oceanic turbulence in coastal waters during cold atmospheric fronts. The turbulence package, mounted on the AUV, allows horizontal profiling and measurement of small-scale fluctuations of velocity and temperature and other characteristics of the flow in the ocean mixed layer. The turbulence measurements were made in conjunction with current profile measurements, conductivity, temperature, and depth measurements, providing the background conditions. The navigation and tracking data from the ship and the underwater vehicle are also presented. The primary focus of this research was to collect and analyze data from the ocean in order to resolve the turbulent velocity fluctuations and the dissipation rates of turbulent kinetic energy. The aim of this thesis is to explain the approach for measurement and analysis of ocean data. It includes the manufacture of the measurement probes, the preparation of the electronic system, the coding of the acquisition software and use of several algorithms for detecting the presence of turbulence and mixing. Two observational oceanographic experiments are described as a basis for illustrating the techniques and methods in data acquisition and analysis of the oceanographic and turbulent quantities.
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Date Issued: 2001
PURL: http://purl.flvc.org/fcla/dt/12781
Subject Headings: Oceanographic submersibles, Turbulence, Oceanography
Format: Document (PDF)

Title: Frequency-time spectral analysis of helicopter turbulence and response in forward flight.
Creator: Vellathottam, George V., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The atmospheric turbulence that a blade station experiences is called blade-fixed turbulence. It can qualitatively differ from the conventional body-fixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,-elocity, which causes fore-and-aft motions of the blade station through the turbulence waves. A closed-form solution of a frequency-time spectrum for the dominant vertical turbulence velocity at an arbitrary blade station is dc,...
Show moreThe atmospheric turbulence that a blade station experiences is called blade-fixed turbulence. It can qualitatively differ from the conventional body-fixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,-elocity, which causes fore-and-aft motions of the blade station through the turbulence waves. A closed-form solution of a frequency-time spectrum for the dominant vertical turbulence velocity at an arbitrary blade station is dc,·eloped. This solution makes it possible to explain qualitatively the turbulence cllcrgy transfer due to rotational velocity from the low-frequency region (< 1P or 1/ rcv.) to the high-frequency(> 1P) region with the occurrence of spectral peaks and split peaks at 1P /2, 1P, 3P /2, 2P etc. Comparison of blade responses to bladeand body-fixed turbulence is also presented over a comprehensive range of turbulcuce scale length and advance ratio; the comparison covers frequency-time spectra, correlations including standard deviations, and average threshold-crossing rates of a flapping blade. A major contribution is to formulate both the cyclostationary turbulence and blade response by the frequency-time spectra, which predict simultaneously the time- ancl frequency-dependent characteristics such as the energy culltained in the frequency and time intervals. For low-altitude and low-advanceratio flights, such as nap-of-the earth or NOE flights, rotational velocity effects on turbulence modeling qualitatively affect the prediction of turbulence ancl response statistics.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/14683
Subject Headings: Turbulence, Rotors (Helicopters)
Format: Document (PDF)

Title: A Computational Analysis of Bio-Inspired Modified Boundary Layers for Acoustic Pressure Shielding in A Turbulent Wall Jet.
Creator: Gonzalez, Alexander J., Glegg, Stewart, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Surface pressure fluctuations developed by turbulent flow within a boundary layer is a major cause of flow noise from a body and an issue which reveals itself over a wide range of engineering applications. Modified boundary layers (MBLs) inspired by the down coat of an owl’s wing has shown to reduce the acoustic effects caused by flow noise. This thesis investigates the mechanisms that modified boundary layers can provide for reducing the surface pressure fluctuations in a boundary layer....
Show moreSurface pressure fluctuations developed by turbulent flow within a boundary layer is a major cause of flow noise from a body and an issue which reveals itself over a wide range of engineering applications. Modified boundary layers (MBLs) inspired by the down coat of an owl’s wing has shown to reduce the acoustic effects caused by flow noise. This thesis investigates the mechanisms that modified boundary layers can provide for reducing the surface pressure fluctuations in a boundary layer. This study analyzes various types of MBLs in a wall jet wind tunnel through computational fluid dynamics and numerical surface pressure spectrum predictions. A novel surface pressure fluctuation spectrum model is developed for use in a wall jet boundary layer and demonstrates high accuracy over a range of Reynolds numbers. Non-dimensional parameters which define the MBL’s geometry and flow environment were found to have a key role in optimizing the acoustic performance.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013209
Subject Headings: Turbulent flow, Turbulent boundary layer, Computational fluid dynamics, Wall jets
Format: Document (PDF)

Title: Rational study of incompressible turbulent flows.
Creator: Pu, Xiaoyan., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A new turbulence model is proposed in this dissertation for two-dimensional incompressible turbulent flows. The methodology used in the present study is a unilateral-statistical-average scheme with the concept of orthotropic eddy viscosity. This methodology has never been explored before in any research work of this nature. The distinguished feature of the unilateral-statistical-average scheme, compared to Reynolds averaging, is that the first-order information of the fluctuating velocity...
Show moreA new turbulence model is proposed in this dissertation for two-dimensional incompressible turbulent flows. The methodology used in the present study is a unilateral-statistical-average scheme with the concept of orthotropic eddy viscosity. This methodology has never been explored before in any research work of this nature. The distinguished feature of the unilateral-statistical-average scheme, compared to Reynolds averaging, is that the first-order information of the fluctuating velocity field is retained. This is achieved by dividing the fluctuating velocities into two groups and applying the average only to a single group. It is proved that the mean value of the fluctuating velocities of the first group solutions is not equal to zero. This non-zero quantity, together with a specified length vector, is used to define a 3 x 3 matrix of orthotropic eddy viscosity. In an off-streamline coordinate system, the eddy-viscosity matrix exhibits anisotropy characteristic, where each component of the turbulent stresses is related to all the components of the rate of strains of the mean fluid flow. The present model has been successfully applied to turbulent boundary-layer flow, turbulent free-shear jet flow, and turbulent wall-bounded separation flow without using empirical constants or wall-functions. Good agreements between the numerical results and experimental data or empirical predictions demonstrate that the unilateral-statistical-average scheme and the orthotropic non-linear eddy-viscosity formulation are robust and efficient in modeling basic turbulent flows. Applicability and predictability of the model to more complex engineering turbulence problems are worthy of further investigation in the future research.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/12610
Subject Headings: Turbulence--Mathematical models, Turbulent boundary layer--Mathematical models
Format: Document (PDF)

Title: Aerodynamic analysis of a propeller in a turbulent boundary layer flow.
Creator: Lachowski, Felipe Ferreira., Glegg, Stewart A. L., Graduate College
Date Issued: 2013-04-12
PURL: http://purl.flvc.org/fcla/dt/3361938
Subject Headings: Turbulent boundary layer, Propellers, Aerodynamics
Format: Document (PDF)

Title: PRESSURE FLUCTUATION MEASUREMENT TECHNIQUES IN A CIRCULAR DUCT WITH INCOMPRESSIBLE TURBULENT FLOW (FREQUENCY-WAVENUMBER SPECTRA).
Creator: DAVIS, HARRY LEE., Florida Atlantic University, Cuschieri, Joseph M.
Abstract/Description: Turbulent pressure fluctuations and acoustical shock waves formed at pipe discontinuities are the primary source of flow noise. fhe pipe response is excited by the fluctuating forces associated with the turbulent pressure fluctuations. The forcing functions can be determined from the frequency-wavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequency-wavenumber spectrum due to fully developed turbulent flow. The data analysis procedures developed...
Show moreTurbulent pressure fluctuations and acoustical shock waves formed at pipe discontinuities are the primary source of flow noise. fhe pipe response is excited by the fluctuating forces associated with the turbulent pressure fluctuations. The forcing functions can be determined from the frequency-wavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequency-wavenumber spectrum due to fully developed turbulent flow. The data analysis procedures developed in this study to analyze the pressure fluctuations provide a good means to determine the frequency-wavenumber spectrum and represent this data in a clear form. Frequency-wavenumber spectra have been obtained for simulated pressure data. In the experimental system designed to collect turbulent pressure data, it was determined that a recessed transducer configuration cannot be used in water pipe flow turbulent pressure fluctuation studies because of the enhanced turbulence created by the upstream holes. Therefore, flush mounted transducers are required.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14330
Subject Headings: Turbulence--Measurement, Fluid dynamics
Format: Document (PDF)

Title: Ocean turbulence measurement using an autonomous underwater vehicle.
Creator: Holappa, Kenneth Walter., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The complex dynamics of the oceans are only beginning to be understood. There is a wide range of dynamic scales in the ocean from the Gulf Stream, with scales as large as the ocean itself, to the microstructure scales of turbulent dissipation. The program of work presented in this dissertation involves the implementation of a turbulence measurement package on board a recently developed small autonomous underwater vehicle (AUV), as well as the design of an optimized AUV platform and the...
Show moreThe complex dynamics of the oceans are only beginning to be understood. There is a wide range of dynamic scales in the ocean from the Gulf Stream, with scales as large as the ocean itself, to the microstructure scales of turbulent dissipation. The program of work presented in this dissertation involves the implementation of a turbulence measurement package on board a recently developed small autonomous underwater vehicle (AUV), as well as the design of an optimized AUV platform and the development of new oceanographic sensors for measurement of micro-structure velocity. Attention is focused on ensuring that the platform is sufficiently quiet since small-scale, low level measurements are easily contaminated by the measurement process, structural vibrations, rigid-body motions and electrical interference; particularly so with the requisite machinery of a self-propelled AUV. Successful measurement entails making suitable modification to the AUV and its mode of operation. In addition to optimization of the measurement platform, consideration is given here to the optimization of the sensors for flow measurement using an AUV. Included in the research are laboratory tests of the new probes and a successful mission in making high quality measurements of ocean turbulence. Modern adaptation of the well-known Pitot tube shows promise in being less sensitive to vehicle self motion as well as yielding a greater spectral range, thereby facilitating more accurate measurement. Comparisons with shear probes and hot film probes, conducted in an axisymmetric water jet and in a wind tunnel, suggest that the pressure probe, developed as part of the work presented here, resolves the dissipation scales more fully than the shear probe. Additionally, the pressure probe does not suffer from the spectral distortion of the signal observed in measurements using a shear probe. In addition to measurement of velocity microstructure, consideration is given to the implementation of modern signal processing hardware in designing a method for the direct measurement of density microstructure. This basic property of the ocean has never before been measured directly. Results, obtained off the Florida coast in 18 meter deep water with the Ocean Explorer AUV; Cook, reveal a complex mixing event. Simultaneous measurement of two components of the velocity microstructure and measurements with a CTD package are analyzed and the instantaneous rates of viscous dissipation of turbulent energy are calculated. The dissipation rate was not stationary and showed a gradient vertically with depth as well as horizontally. The AUV platform, modified for low vibration noise, allowed measurement of dissipation rates of O(10^-8 W/kg).
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Date Issued: 1997
PURL: http://purl.flvc.org/fcla/dt/12532
Subject Headings: Oceanographic submersibles, Turbulence--Measurement
Format: Document (PDF)

Title: Response of a cascade of blades to an incoming turbulent flow.
Creator: Bocquillion, Olivier Christophe., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description: The purpose of this research is to study the modification of a turbulent flow as it passes through a cascade of flat plates. The results will then be compared with experimental results obtained in a companion experimental study being conducted at Virginia Tech. In a typical marine propulsor turbulent flow passes through a set of inlet guide vanes (IGVs) and then interacts with the propeller blades: this process creates unwanted vibration and sound. The purpose of this research is to determine...
Show moreThe purpose of this research is to study the modification of a turbulent flow as it passes through a cascade of flat plates. The results will then be compared with experimental results obtained in a companion experimental study being conducted at Virginia Tech. In a typical marine propulsor turbulent flow passes through a set of inlet guide vanes (IGVs) and then interacts with the propeller blades: this process creates unwanted vibration and sound. The purpose of this research is to determine if the arrangement of the IGVs can be used to reduce the propulsor noise generation. In this study the incoming flow to the propeller is modeled as homogeneous turbulence and the IGVs are represented by a cascade of flat plates. We will consider the equations, which describe the blade response to an incoming harmonic gust, and we will represent the turbulent flow using a modal description.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/12971
Subject Headings: Blades, Turbulence, Cascades (Fluid dynamics)
Format: Document (PDF)

Title: Theoretical and experimental investigations of motion stability of long-span bridges in turbulent flow.
Creator: Li, Qiang, Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The motion stability of long-span bridges under turbulent wind is studied. A new stochastic theory, developed on the basis of a new wind turbulence model, is applied to experimentally measured bridge deck models to determine the stochastic stability boundaries. The new turbulence model has a finite mean-square value and a versatile spectral shape, and is capable of closely matching a target spectrum, such as the Dryden or the von Karman spectrum, by changing the parameters of the model. The...
Show moreThe motion stability of long-span bridges under turbulent wind is studied. A new stochastic theory, developed on the basis of a new wind turbulence model, is applied to experimentally measured bridge deck models to determine the stochastic stability boundaries. The new turbulence model has a finite mean-square value and a versatile spectral shape, and is capable of closely matching a target spectrum, such as the Dryden or the von Karman spectrum, by changing the parameters of the model. The bridge motion is represented as a linear system of single degree of freedom in torsion. A bridge is generally subject to two types of wind loads: the buffeting loads and the self-excited loads. Only the self-excited loads are considered in the investigation, since the buffeting loads, which appear as inhomogeneous terms in the differential equation of motion, do not affect the motion stability of a linear system. In the absence of turbulence, the onset of flutter instability occurs at a critical wind velocity at which a pair of complex-conjugate eigenvalues of the combined structural-fluid system becomes purely imaginary. The corresponding eigenvectors describe the interaction between the structure and the surrounding fluid. Upon the introduction of turbulence, the composition of the structural and fluid components is changed. Since the turbulence portion of the flow fluctuates randomly in time, a new state of balance between the energy inflow from fluid to structure, and the energy outflow from structure to fluid, can only be reached in the statistical sense, or equivalently, in the sense of long-time average under the ergodicity assumption. It is the random deviation from the deterministic flutter mode that renders either the stabilizing or destabilizing effect possible. The asymptotic sample stability boundary of the motion is obtained. The aerodynamic constants for the theoretical analysis are measured experimentally in a forced vibration test conducted in a water channel, with water substituting for air as the working fluid. For a particular bridge deck model, the computed stability boundary shows that the presence of turbulence in the wind flow can be either stabilizing or destabilizing depending on the peak frequency and band-width of the turbulence spectrum.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12324
Subject Headings: Bridges, Long-span, Turbulence
Format: Document (PDF)

Title: Subsurface structure of an atmospherically forced water column in littoral waters.
Creator: Chernys, Michael., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the...
Show moreThe developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the fronts passed through the region. Airfoil shear probes mounted in a package on the nose of the AUV were used to measure the level and distribution of small-scale turbulence in the water column and to estimate the in-situ dissipation rate of turbulent kinetic energy. Prevailing meteorological conditions were determined from two NOAA C-MAN stations and, for two of the experiments, from a local Air Sea Interaction Spar buoy (ASIS). The first atmospheric front examined was in December 1998. A significant 10°C drop in air temperature was recorded. The AUV carried out several pre-programmed surveys over a 6-day period. A turbulent kinetic energy dissipation rates of O(10-6W/kg) were observed in the water column during the passage of the front. Fetch-limited, offshore, wind-induced surface and subsurface currents were identified during the passage of the front on April 9, 2000. As the winds increased in magnitude and shifted direction, a change in surface current was apparent in the OSCR observations. A bottom-mounted ADCP and an AUV-mounted ADCP both recorded distinct corresponding contributions to the subsurface current due to the winds. Clockwise rotation of the current profile in the water column, consistent with wind-generated currents, was observed. A third low-pressure cold front passed through the region on April 18 an 19, 2000. AUV surveys were carried out as the front passed over the region for 19 hours within a 24-hour period. Dissipation rates reached O(10 -6W/kg) during the period of the survey and decreased to O(10 -8W/kg) subsequently. The distribution of dissipation rate appeared to agree with the characteristic log law for wind-induced turbulence at the start of the passage of the front, but was significantly higher subsequently and more dependent on the combination of convective fluxes and wind stress.
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Date Issued: 2002
PURL: http://purl.flvc.org/fau/fd/FADT12001
Subject Headings: Turbulence--Measurement, Oceanographic submersibles
Format: Document (PDF)

Title: Design and testing of an untethered vertically ascending profiler for use in measuring near-surface turbulence.
Creator: Bogin, Jeffrey Isaac., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: The Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum...
Show moreThe Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum. Data processing techniques made it possible to filter out motion generated by surface wave action, which allowed VAMP to collect data at depths as shallow as the troughs of the surface waves. VAMP can be launched, deployed several times, and recovered all within a thirty minute time frame by a crew of four.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/13020
Subject Headings: Turbulence--Measurement, Surface waves (Oceanography)
Format: Document (PDF)

Title: A TURBULENCE CURRENT METER DESIGN, CONSTRUCTION AND USE.
Creator: KIDERA, EDWARD HENRY, IV., Florida Atlantic University, Tennant, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The...
Show moreThe objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The instrument's usefulness was illustrated in the open channel flow of a tidal estuary by its ability to detect the horizontal velocity field. The data obtained for the turbulence shows large variation in velocity of the lateral component on the order of 50-75% of the "mean" current speed. Digital filtering of the data reveals distinct structures of high energy, intermittent in their nature and analogous to "bursting". The energy spectrum of the longitudinal component follows the predicted slope of -1 for over two decades (.01 to 1.3 + Hz).
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Date Issued: 1978
PURL: http://purl.flvc.org/fcla/dt/13943
Subject Headings: Turbulence--Measurement, Water current meters
Format: Document (PDF)

Title: Trailing edge noise propagation through a cascade of blades.
Creator: Roy, Charlie Desire., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Aircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It...
Show moreAircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It completely blocks the sound and limits the study to entirely subsonic flow. In this type of flow, a sound propagation simulator has been implemented. The linearized form of Howe's equation is solved by a high frequency method. The ray caustic problem which causes regular ray tracing failure is fixed by interpolating the field on a preset grid. Results are compared with the analytical solution in uniform flow and computations in realistic flow are presented.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/12990
Subject Headings: Trailing edges (Aerodynamics), Blades, Turbulent boundary layer
Format: Document (PDF)

Title: Interaction of vortex sheet with a finite vortex.
Creator: Viswanathan, K. S., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is...
Show moreThe rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is shown to substantially affect the development of the vortex sheet rollup. The vortex sheet undergoes significant deformation at the rolling up tip region due to its devouring the vortex patch as well as due to the formation of secondary rollup features on the sheet. These features are believed to be important in inhibiting rollup considerably. The interaction is quantified by using a criterion developed to measure the extent of the tip vortex rollup and its characteristics are studied for a range of flow parameters. The strength of the rolling up tip region of the vortex sheet is found to be highly dependent on the location and the vorticity in the finite vortex.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15048
Subject Headings: Turbulence, Whirlwinds, Vortex-motion, Wakes (Aerodynamics)
Format: Document (PDF)

Title: Turbulence modeling and simulation and related effects on helicopter response with wake dynamics using finite elements and parallelism.
Creator: Dang, Ying Yi., Florida Atlantic University, Gaonkar, Gopal H.
Abstract/Description: Future helicopters will require all-weather capability for stabilized flight through severe atmospheric turbulence. This requirement has brought into focus the effect of turbulence on handling qualities. Accordingly, there is renewed interest in modeling and simulating turbulence and predicting turbulence-induced rotor oscillations. This thesis addresses three fundamental aspects of the problem: (1) modeling and simulation of turbulence including cross-correlation; (2) three-dimensional...
Show moreFuture helicopters will require all-weather capability for stabilized flight through severe atmospheric turbulence. This requirement has brought into focus the effect of turbulence on handling qualities. Accordingly, there is renewed interest in modeling and simulating turbulence and predicting turbulence-induced rotor oscillations. This thesis addresses three fundamental aspects of the problem: (1) modeling and simulation of turbulence including cross-correlation; (2) three-dimensional dynamic-wake effects on rotor response to turbulence and (3) prediction of turbulence and response statistics. The analysis is based on the theory of isotropic and homogeneous turbulence and Taylor's frozen-field approximation. Quasisteady airfoil aerodynamics and a three-dimensional wake are used. Both the isolated blades and isolated rotors are treated. The parallelization is carried out on a massively parallel MasPar SIMD computer. Major conclusions include: (i) The effects of cross-correlation are negligible when two stations lie on the same blade and appreciable when two stations lie on different blades. (ii) In modeling the three-dimensional wake, 3 harmonics are required and dynamic wake has dominant influence on response statistics. (iii) With increasing comprehensiveness of helicopter-turbulence modeling, the sequential execution times increase dramatically; by comparison, the parallel execution times are far lower and, more significantly, remain nearly constant.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/15117
Subject Headings: Helicopters, Turbulence, Rotors (Helicopters), Boundary layer noise
Format: Document (PDF)

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 small-scale 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.
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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: DATA-DRIVEN IDENTIFICATION AND CONTROL OF TURBULENT STRUCTURES USING DEEP NEURAL NETWORKS.
Creator: Jagodinski, Eric, Verma, Siddhartha, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: Wall-bounded turbulent flows are pervasive in numerous physics and engineering applications. Such flows tend to have a strong impact on the design of ships, airplanes and rockets, industrial chemical mixing, wind and hydrokinetic energy, utility infrastructure and innumerable other fields. Understanding and controlling wall bounded turbulence has been a long-pursued endeavor yielding plentiful scientific and engineering discoveries, but there is much that remains unexplained from a...
Show moreWall-bounded turbulent flows are pervasive in numerous physics and engineering applications. Such flows tend to have a strong impact on the design of ships, airplanes and rockets, industrial chemical mixing, wind and hydrokinetic energy, utility infrastructure and innumerable other fields. Understanding and controlling wall bounded turbulence has been a long-pursued endeavor yielding plentiful scientific and engineering discoveries, but there is much that remains unexplained from a fundamental viewpoint. One unexplained phenomenon is the formation and impact of coherent structures like the ejections of slow near-wall fluid into faster moving ow which have been shown to correlate with increases in friction drag. This thesis focuses on recognizing and regulating organized structures within wall-bounded turbulent flows using a variety of machine learning techniques to overcome the nonlinear nature of this phenomenon. Deep Learning has provided new avenues of analyzing large amounts of data by applying techniques modeled after biological neurons. These techniques allow for the discovery of nonlinear relationships in massive, complex systems like the data found frequently in fluid dynamics simulation. Using a neural network architecture called Convolutional Neural Networks that specializes in uncovering spatial relationships, a network was trained to estimate the relative intensity of ejection structures within turbulent flow simulation without any a priori knowledge of the underlying flow dynamics. To explore the underlying physics that the trained network might reveal, an interpretation technique called Gradient-based Class Activation Mapping was modified to identify salient regions in the flow field which most influenced the trained network to make an accurate estimation of these organized structures. Using various statistical techniques, these salient regions were found to have a high correlation to ejection structures, and to high positive kinetic energy production, low negative production, and low energy dissipation regions within the flow. Additionally, these techniques present a general framework for identifying nonlinear causal structures in general three-dimensional data in any scientific domain where the underlying physics may be unknown.
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Date Issued: 2022
PURL: http://purl.flvc.org/fau/fd/FA00014119
Subject Headings: Turbulent flow, Turbulence, Neural networks (Computer science), Deep learning (Machine learning)
Format: Document (PDF)

FAU Theses and Dissertations (39)	+ -
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