Current Search: Turbulent boundary layer (x)
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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.
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 wavenumber-frequency 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
- 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
- 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
- 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
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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.
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
- 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.
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
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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.
Show less - 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
- The Effect of Shear Sheltering on Trailing Edge Noise: A Theoretical Study.
- Creator
- Jimenez, Ignacio, Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
Shear sheltering is defined as the effect of the mean flow velocity profile in a boundary layer on the turbulence caused by an imposed gust. In aeroacoustic applications turbulent boundary layers interacting with blade trailing edges or roughness elements are an important source of sound, and the effect of shear sheltering on these noise sources has not been studied in detail. Since the surface pressure spectrum below the boundary layer is the primary driver of trailing edge and roughness...
Show moreShear sheltering is defined as the effect of the mean flow velocity profile in a boundary layer on the turbulence caused by an imposed gust. In aeroacoustic applications turbulent boundary layers interacting with blade trailing edges or roughness elements are an important source of sound, and the effect of shear sheltering on these noise sources has not been studied in detail. Since the surface pressure spectrum below the boundary layer is the primary driver of trailing edge and roughness noise, this thesis considers the effect that shear sheltering has on the surface pressure spectrum below a boundary layer. This study presents a model of the incoming turbulence as a vortex sheet at a specified height above the surface and shows, using canonical boundary layers and approximations to numerical results, how the mean flow velocity profile can be manipulated to alter the surface pressure spectrum and hence the associated trailing edge noise. The results from this model demonstrate that different mean velocity profiles drive significant changes in the unsteady characteristics of the flow. The surface pressure fluctuations results also suggest that boundary layers where the shear in the mean velocity profile is significant can be beneficial for the reduction of trailing edge noise at particular frequencies.
Show less - Date Issued
- 2020
- PURL
- http://purl.flvc.org/fau/fd/FA00013535
- Subject Headings
- Turbulent boundary layer, Trailing edges (Aerodynamics), Aeroacoustics, Boundary layer noise, Shear sheltering
- Format
- Document (PDF)
- Title
- Bio-Inspired Modified Turbulent Boundary Layers.
- Creator
- French, Stone A., Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The reduction of drag and sound pressure levels (SPL) are desirable traits in many fluidics’ applications ranging from high-speed transportation to energy generation. Inspiration has been found in some species of owls that possess boundary layer control surface treatments on their wings that appear to reduce SPL while in flight. This modification of the flow over the wings is known as the development of a modified boundary layer (MBL). Virginia Tech is working in collaboration with Florida...
Show moreThe reduction of drag and sound pressure levels (SPL) are desirable traits in many fluidics’ applications ranging from high-speed transportation to energy generation. Inspiration has been found in some species of owls that possess boundary layer control surface treatments on their wings that appear to reduce SPL while in flight. This modification of the flow over the wings is known as the development of a modified boundary layer (MBL). Virginia Tech is working in collaboration with Florida Atlantic University to investigate this reduction in SPL experimentally but requires the assistance of RANS simulation to obtain drag results. This thesis investigates the drag effects of the rod style geometries being evaluated at VT to mimic the MBL of an owl. In doing this it was found that the height of the rods has a direct correlation with the amount of drag induced by the presence of the rods in the flow field.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013826
- Subject Headings
- Turbulent boundary layer, Sound pressure, Biomimicry, Drag (Aerodynamics)
- Format
- Document (PDF)
- Title
- Effect of applied periodic strain on coherent structures in a turbulent boundary layer.
- Creator
- Neravetla, Bharath Reddy, Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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The effect of applied periodic straining field on the behavior of coherent vortical structures in the turbulent boundary layer is studied. In particular, the coherent vortical longitudinal structures in the turbulent boundary layer in the form of isolated vortices or in the form of pairs of counter-rotating vortices is considered. The effect on the pressure fluctuations on the wall due to the applied periodic strain is studied. A numerical method using Contour Dynamics technique and...
Show moreThe effect of applied periodic straining field on the behavior of coherent vortical structures in the turbulent boundary layer is studied. In particular, the coherent vortical longitudinal structures in the turbulent boundary layer in the form of isolated vortices or in the form of pairs of counter-rotating vortices is considered. The effect on the pressure fluctuations on the wall due to the applied periodic strain is studied. A numerical method using Contour Dynamics technique and incompressible, inviscid equations of motion is developed to determine the evolution of these structures in time. The pressure fluctuations on the wall are calculated making use of the unsteady Bernoulli's equation. The various parameters associated with the coherent structures in the turbulent boundary layer such as the strength of the vortices, their distance from the wall, separation distance between counter-rotating vortices, the frequency of the applied straining field, the magnitude of the straining field and the stretching rate are varied to study the resultant pressure fluctuations. It is observed that at low applied frequencies, there are high modulations in the surface pressure fluctuations, and at higher applied frequencies of straining field there is reduction in surface pressure fluctuations in the boundary layer.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/15020
- Subject Headings
- Vortex-motion, Turbulent boundary layer, Pressure--Measurement
- Format
- Document (PDF)
- Title
- Numerical simulation of wave energy dissipation in turbulent boundary layers.
- Creator
- Moneris, Stephanie Sylvie., Florida Atlantic University, Slinn, D. N., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Shoaling surface waves create turbulent shear flows at the sea-bed and thereby contribute to wave energy dissipation in the bottom boundary layer. Turbulent boundary layers are examined using a high-resolution time-dependent three-dimensional numerical model. Simulations estimate the wave energy dissipation in the boundary layer. Results indicate that turbulence levels are coupled to the wave cycle; accelerating flow organizes the boundary layer structure, decelerating flow destabilizes it...
Show moreShoaling surface waves create turbulent shear flows at the sea-bed and thereby contribute to wave energy dissipation in the bottom boundary layer. Turbulent boundary layers are examined using a high-resolution time-dependent three-dimensional numerical model. Simulations estimate the wave energy dissipation in the boundary layer. Results indicate that turbulence levels are coupled to the wave cycle; accelerating flow organizes the boundary layer structure, decelerating flow destabilizes it and flow reversal induces the strongest turbulent bursts. Details of the flow are functions of the Reynolds number, wave frequency, wave complexity, presence of a mean current, and the flow history of the preceding wave period. Mean flow properties are compared between the three-dimensional model and one-dimensional eddy-viscosity based models. Generally, features of the boundary layer are satisfactorily approximated by the eddy-viscosity models, with accuracy depending on the wave amplitude, period, phase, and other forcing conditions.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/12692
- Subject Headings
- Waves--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., 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 walk-through of the entire process utilized to approximate the flow ingested by a Sevik-type rotor based on solutions to the Reynolds Averaged Navier-Stokes equations (RANS). The Multiple Reference Frame fluid model is utilized by the code of ANSYS-FLUENT 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 walk-through of the entire process utilized to approximate the flow ingested by a Sevik-type rotor based on solutions to the Reynolds Averaged Navier-Stokes equations (RANS). The Multiple Reference Frame fluid model is utilized by the code of ANSYS-FLUENT 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)