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 Title
 An Analysis of the Surface Pressure Spectra in a Fluid Flow with a ZeroPressure 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 wallpressure 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 wallpressure spectrum under a zeropressure 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.
Show less  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 wavenumberfrequency domains and estimated regions of convergence between the analytical models and the DNS data.
Show less  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 twodimensional 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 twodimensional 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 windinduced mixing processes in elongated lakes or reservoirs.
Show less  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, EricOlivier., 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 smallscale 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 smallscale 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.
Show less  Date Issued
 2001
 PURL
 http://purl.flvc.org/fcla/dt/12781
 Subject Headings
 Oceanographic submersibles, Turbulence, Oceanography
 Format
 Document (PDF)
 Title
 Frequencytime 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 bladefixed turbulence. It can qualitatively differ from the conventional bodyfixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,elocity, which causes foreandaft motions of the blade station through the turbulence waves. A closedform solution of a frequencytime 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 bladefixed turbulence. It can qualitatively differ from the conventional bodyfixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,elocity, which causes foreandaft motions of the blade station through the turbulence waves. A closedform solution of a frequencytime 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 lowfrequency region (< 1P or 1/ rcv.) to the highfrequency(> 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 bodyfixed turbulence is also presented over a comprehensive range of turbulcuce scale length and advance ratio; the comparison covers frequencytime spectra, correlations including standard deviations, and average thresholdcrossing rates of a flapping blade. A major contribution is to formulate both the cyclostationary turbulence and blade response by the frequencytime spectra, which predict simultaneously the time ancl frequencydependent characteristics such as the energy culltained in the frequency and time intervals. For lowaltitude and lowadvanceratio flights, such as napofthe earth or NOE flights, rotational velocity effects on turbulence modeling qualitatively affect the prediction of turbulence ancl response statistics.
Show less  Date Issued
 1991
 PURL
 http://purl.flvc.org/fcla/dt/14683
 Subject Headings
 Turbulence, Rotors (Helicopters)
 Format
 Document (PDF)
 Title
 A Computational Analysis of BioInspired 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. Nondimensional parameters which define the MBL’s geometry and flow environment were found to have a key role in optimizing the acoustic performance.
Show less  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 twodimensional incompressible turbulent flows. The methodology used in the present study is a unilateralstatisticalaverage 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 unilateralstatisticalaverage scheme, compared to Reynolds averaging, is that the firstorder information of the fluctuating velocity...
Show moreA new turbulence model is proposed in this dissertation for twodimensional incompressible turbulent flows. The methodology used in the present study is a unilateralstatisticalaverage 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 unilateralstatisticalaverage scheme, compared to Reynolds averaging, is that the firstorder 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 nonzero quantity, together with a specified length vector, is used to define a 3 x 3 matrix of orthotropic eddy viscosity. In an offstreamline coordinate system, the eddyviscosity 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 boundarylayer flow, turbulent freeshear jet flow, and turbulent wallbounded separation flow without using empirical constants or wallfunctions. Good agreements between the numerical results and experimental data or empirical predictions demonstrate that the unilateralstatisticalaverage scheme and the orthotropic nonlinear eddyviscosity 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.
Show less  Date Issued
 1999
 PURL
 http://purl.flvc.org/fcla/dt/12610
 Subject Headings
 TurbulenceMathematical models, Turbulent boundary layerMathematical 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
 20130412
 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 (FREQUENCYWAVENUMBER 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 frequencywavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequencywavenumber 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 frequencywavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequencywavenumber 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 frequencywavenumber spectrum and represent this data in a clear form. Frequencywavenumber 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.
Show less  Date Issued
 1986
 PURL
 http://purl.flvc.org/fcla/dt/14330
 Subject Headings
 TurbulenceMeasurement, 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 microstructure velocity. Attention is focused on ensuring that the platform is sufficiently quiet since smallscale, low level measurements are easily contaminated by the measurement process, structural vibrations, rigidbody motions and electrical interference; particularly so with the requisite machinery of a selfpropelled 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 wellknown 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).
Show less  Date Issued
 1997
 PURL
 http://purl.flvc.org/fcla/dt/12532
 Subject Headings
 Oceanographic submersibles, TurbulenceMeasurement
 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.
Show less  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 longspan 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 longspan 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 meansquare 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 longspan 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 meansquare 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 selfexcited loads. Only the selfexcited 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 complexconjugate eigenvalues of the combined structuralfluid 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 longtime 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 bandwidth of the turbulence spectrum.
Show less  Date Issued
 1993
 PURL
 http://purl.flvc.org/fcla/dt/12324
 Subject Headings
 Bridges, Longspan, 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 subtropical water column during the passage of cold lowpressure atmospheric front is characterized through synoptic and insitu 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), shipbased instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the...
Show moreThe developing subsurface structure of a shallow subtropical water column during the passage of cold lowpressure atmospheric front is characterized through synoptic and insitu 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), shipbased 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 smallscale turbulence in the water column and to estimate the insitu dissipation rate of turbulent kinetic energy. Prevailing meteorological conditions were determined from two NOAA CMAN 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 preprogrammed surveys over a 6day period. A turbulent kinetic energy dissipation rates of O(106W/kg) were observed in the water column during the passage of the front. Fetchlimited, offshore, windinduced 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 bottommounted ADCP and an AUVmounted 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 windgenerated currents, was observed. A third lowpressure 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 24hour 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 windinduced 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.
Show less  Date Issued
 2002
 PURL
 http://purl.flvc.org/fau/fd/FADT12001
 Subject Headings
 TurbulenceMeasurement, Oceanographic submersibles
 Format
 Document (PDF)
 Title
 Design and testing of an untethered vertically ascending profiler for use in measuring nearsurface turbulence.
 Creator
 Bogin, Jeffrey Isaac., Florida Atlantic University, Dhanak, Manhar R.
 Abstract/Description

The Vertically Ascending Microscale 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 Microscale 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.
Show less  Date Issued
 2003
 PURL
 http://purl.flvc.org/fcla/dt/13020
 Subject Headings
 TurbulenceMeasurement, 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 5075% 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).
Show less  Date Issued
 1978
 PURL
 http://purl.flvc.org/fcla/dt/13943
 Subject Headings
 TurbulenceMeasurement, 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.
Show less  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.
Show less  Date Issued
 1994
 PURL
 http://purl.flvc.org/fcla/dt/15048
 Subject Headings
 Turbulence, Whirlwinds, Vortexmotion, 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 allweather 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 turbulenceinduced rotor oscillations. This thesis addresses three fundamental aspects of the problem: (1) modeling and simulation of turbulence including crosscorrelation; (2) threedimensional...
Show moreFuture helicopters will require allweather 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 turbulenceinduced rotor oscillations. This thesis addresses three fundamental aspects of the problem: (1) modeling and simulation of turbulence including crosscorrelation; (2) threedimensional dynamicwake 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 frozenfield approximation. Quasisteady airfoil aerodynamics and a threedimensional 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 crosscorrelation are negligible when two stations lie on the same blade and appreciable when two stations lie on different blades. (ii) In modeling the threedimensional wake, 3 harmonics are required and dynamic wake has dominant influence on response statistics. (iii) With increasing comprehensiveness of helicopterturbulence modeling, the sequential execution times increase dramatically; by comparison, the parallel execution times are far lower and, more significantly, remain nearly constant.
Show less  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 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
 DATADRIVEN 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

Wallbounded 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 longpursued endeavor yielding plentiful scientific and engineering discoveries, but there is much that remains unexplained from a...
Show moreWallbounded 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 longpursued 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 nearwall 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 wallbounded 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 Gradientbased 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 threedimensional data in any scientific domain where the underlying physics may be unknown.
Show less  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)