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Kudla, Thomas LucasImplementation and Validation of a Modified Non-Equilibrium Wilcox K Omega Turbulence Model in Subsonic and Transonic Flow Regimes
Master of Science (M.S.), University of Dayton, 2013, Aerospace Engineering
Large Eddy Simulations (LES) are beginning to emerge as the state-of-the art for turbulence modeling in Computational Fluid Dynamics (CFD), but due to current computational constraints, the need will continue to exist for a lower fidelity, yet robust set of Reynolds-Averaged Navier- Stokes (RANS) turbulence models. Many of these turbulence models are based off of the classic Boussinesq approximation which relates the mean flow stresses to the turbulent eddy viscosity. The traditional Boussinesq approximation relies upon the instantaneous strain rate which may produce large errors in solutions for flows with significant changes in strain (such as areas of massive separation and re-attachment). The unstructured Navier-Stokes solver AVUS is modified using a new method developed by Peter E. Hamlington and Werner J. A. Dahm which replaces the classic Boussinesq approximation with a new non-equilibrium closure technique. The new non-equilibrium k omega turbulence model modification takes into account the time history of the strain rate by modifying the eddy viscosity term found in the k omega Wilcox turbulence model. Computational results from this new model are compared to experimental data from numerous test cases which include a two-dimensional flat plate, NACA 0012 airfoil, RAE 2822 transonic airfoil, and a fully three-dimensional unmanned aerial vehicle. The results of the new model are encouraging since they are more closely correlating to experimental data.

Committee:

Markus Rumpfkeil (Advisor)

Subjects:

Aerospace Engineering

Keywords:

Hamlington and Dahm; turbulence; turbulence modeling; RANS; non-equilibrium turbulence modeling

Deng, DingfengA NUMERICAL AND EXPERIMENTAL INVESTIGATION OF TAYLOR FLOW INSTABILITIES IN NARROW GAPS AND THEIR RELATIONSHIP TO TURBULENT FLOW IN BEARINGS
Doctor of Philosophy, University of Akron, 2007, Mechanical Engineering
The relationship between the onset of Taylor instability and appearance of what is commonly known as “turbulence” in narrow gaps between two cylinders is investigated. A question open to debate is whether the flow formations observed during Taylor instability regimes are, or are related to the actual “turbulence” as it is presently modeled in micro-scale clearance flows. This question is approached by considering the viscous fluid flow in narrow gaps between two cylinders with various eccentricity ratios. The computational engine is provided by CFD-ACE+, a commercial multi-physics software. The flow patterns, velocity profiles and torques on the outer cylinder are determined when the speed of the inner cylinder, clearance and eccentricity ratio are changed on a parametric basis. Calculations show that during the Taylor and wavy vortex regime velocity profiles in the radial direction are sinusoidal with pressure variations in the axial direction even for the case of the “long journal bearing” (L/D>2). Based on these findings, a new model for predicting the flow behavior in long and short journal bearing films in the transition regime is proposed. Unlike the modified turbulent viscosity of the most accepted models (Constantinescu, Ng-Pan, Hirs and Gross et al.), the viscosity used in the new model is kept at its laminar value. Experimental torque measurements and flow visualization are performed for three kinds of oils with different viscosities. It is shown that in general there is a good agreement between the numerical and experimental torques except those in turbulent regime. Comparison between numerical and experimental flow patterns is also made and it shows that they match well in the Couette, Taylor and Wavy regimes. In general there is a good agreement between the numerical and experimental results including torque measurements and flow patterns. The new model for predicting the flow behavior in journal bearing films in the transition regime is justified.

Committee:

Minel Braun (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Taylor Instability; Flow Patterns; Velocity Profiles; New Model; Transition Flow; Narrow Gaps; Long Journal Bearings; Transition Reynolds Equation; Turbulence; Turbulence Models; Torque Measurements; Flow Visualizations

Reierson, Joseph L.Analysis of Atmospheric Turbulence Effects on Laser Beam Propagation Using Multi-Wavelength Laser Beacons
Master of Science (M.S.), University of Dayton, 2011, Electro-Optics
Atmospheric turbulence affects optical systems that operate in various atmospheric conditions. The characteristics of the optical wave transmitted through atmospheric turbulence can undergo dramatic changes resulting in potential system performance degradation. Knowledge of atmospheric turbulence effects would aid in the development of a wide class of atmospheric-optics systems including laser communication, directed energy, lidar, remote sensing, and active and passive imaging systems. In the classical atmospheric turbulence theory, the refractive index structure parameter is the key parameter known to describe the strength of the atmospheric turbulence and accurate measurement of this parameter represents an important task. The refractive index structure parameter can be difficult to measure, as it is influenced by many factors including path length, time of day, season, and microclimate conditions which cannot be applied universally and may change in a matter of minutes. To further complicate atmospheric turbulence characterization, the key assumptions of classical (Kolmogorov) turbulence theory, such as statistical homogeneity and isotropy of the refractive index random field, are not always satisfied. From this viewpoint, experimental analyses to determine the applicability of the Kolmogorov turbulence theory in different optical wave propagation conditions represent important tasks and can assist in the adequate evaluation of atmospheric turbulence effects on optical system performance and design. In this thesis, the applicability of the classical turbulence theory was verified through simultaneous intensity measurements (pupil- and focal-plane intensity distributions) from multi-wavelength laser beacons over a near-ground, near-horizontal, and seven-kilometer-long propagation path. These measurements allowed independent evaluation of the refractive index structure parameter for two different wavelengths (λ1 = 532 nm, λ2 = 1064 nm), and these results were compared to theoretical predictions. In addition, the turbulence-induced intensity scintillations were investigated across the projected laser beam footprint, and a numerical analysis of the propagation was compared to the experimental data. To obtain the intensity measurements, the optical setup included four sub-systems using fast-framing (~150 frames/second) cameras that were synchronized using previously developed control software; additional software was developed for data acquisition and processing. The conducted experiments in the turbulence conditions investigated here showed that the results of measurements and predictions based on the Kolmogorov turbulence theory are in reasonably good agreement but are particularly sensitive to the footprint position of the transmitted beacon. The atmospheric characterization technique using a multi-wavelength beacon provided a useful tool for examining the applicability of the Kolmogorov turbulence theory along this propagation path.

Committee:

Mikhail A. Vorontsov, PhD (Committee Chair); Joseph W. Haus, PhD (Committee Member); Edward A. Watson, PhD (Committee Member)

Subjects:

Engineering; Optics; Physics

Keywords:

atmospheric optical turbulence; scintillations; multi-wavelength sensing; optical sensing; remote sensing; imaging through turbulence; laser beam propagation

Power, Jonathan DavidModeling Anisoplanatic Effects from Atmospheric Turbulence across Slanted Optical Paths in Imagery
Master of Science (M.S.), University of Dayton, 2016, Electrical Engineering
When viewing objects over long distances, atmospheric turbulence introduces significant aberrations in imagery from optics with large apertures. We present a model for simulating turbulent effects in imagery using a technique similar to Bos and Roggemann's model [1]. This simulation will support efforts in developing innovative turbulence mitigation techniques and replacing expensive flight tests. The technique implements the commonly used split-step beam propagation method with phase screens optimally placed along the optical path. This method is used to supply a turbulence distorted point spread function (PSF) along the unique, optical path from the object to the camera aperture for each pixel of an image. The image is then distorted by scaling and summing each PSF with the appropriate surrounding area of the corresponding pixel for new pixel values. Very large phase screens have been integrated into the simulation to account for low spatial frequencies and wind speed in video. Additionally, a modified version of Schmidt's method [2] is implemented for estimating statistics for the individual phase screens in the model and for angle spectrum propagation through free space. The proposed model has the capability of simulating over horizontal or slanted paths using the Huffnagel Valley turbulence profile. For verification purposes, analysis of average simulated PSFs for short and long exposures and angle of arrival were compared to theoretical results. Further analysis of simulated error statistics were carried out against varying elevation in the atmosphere.

Committee:

Russell Hardie, Ph.D. (Advisor); Monish Chatterjee, Ph.D. (Committee Member); Barry Karch, Ph.D. (Committee Member)

Subjects:

Atmospheric Sciences; Computer Science; Electrical Engineering; Engineering; Optics

Keywords:

Atmospheric Turbulence; Numerical Simulation; Anisoplanatism; Turbulence in Imagery

YODER, DENNIS ALLENALGEBRAIC REYNOLDS STRESS MODELING OF PLANAR MIXING LAYER FLOWS
PhD, University of Cincinnati, 2005, Engineering : Aerospace Engineering
This work investigates the ability of algebraic Reynolds stress models to predict planar mixing layer flows, including effects caused by increasing compressibility such as the reduction in mixing layer growth rate and disproportionate reduction in individual turbulent stresses which causes an increase in turbulence anisotropy. To achieve these results a new algebraic Reynolds stress model is developed from first principles with careful consideration for incorporating additional correlation terms which arise in compressible flows. A new explicit solution procedure for the Reynolds stresses is also developed using an appropriate three-term tensor basis representation for compressible flows. This new solution procedure is moderately more complicated than existing explicit solution procedures for incompressible algebraic stress models since it requires the solution of a quartic, rather than cubic, equation for one of the tensor basis coefficients. Special consideration must also be given to the treatment of specific degenerate cases which are self-correcting in the incompressible formulation. For two-dimensional incompressible flow, the new solution procedure properly reduces to that used in existing explicit algebraic stress models. The new algebraic stress model has been calibrated against detailed experimental data for a benchmark incompressible mixing layer. To aid in this calibration an automated numerical optimization procedure was developed. This calibration yielded a new set of coefficients for the pressure-strain correlation tensor that improves the predicted incompressible mixing layer growth rate and turbulent stresses. Recent experimental data and direct numerical simulations of compressible mixing layers indicate that the observed changes in mixing layer growth rate and turbulence anisotropy are caused by reduced pressure fluctuations. This reduced communication results in changes to the turbulent length scale and pressure-strain correlation tensor. Compressibility corrections based upon these physical mechanisms as well as explicit dilatational corrections have been examined. None of these corrections adequately predicts all of the observed changes in compressible mixing layers. However, this work shows that by combining the turbulent length scale correction with a reformulated correction factor to the pressure-strain correlation tensor better agreement with the mixing layer growth rate is achieved and simultaneous changes in the Reynolds stresses are demonstrated.

Committee:

Dr. Paul Orkwis (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

turbulence; turbulence modeling; compressible flow; mixing layer; optimization

Lakshmanan, KrisQuantitative computer image processing of color particle markers in flow visualization /
Doctor of Philosophy, The Ohio State University, 1986, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Turbulence;Turbulence;Image processing;Flow visualization

Khosravi Rahmani, RaminTHREE-DIMENSIONAL NUMERICAL SIMULATION AND PERFORMANCE STUDY OF AN INDUSTRIAL HELICAL STATIC MIXER
Doctor of Philosophy in Engineering, University of Toledo, 2004, Engineering
In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality. Static mixers economically promote the mixing of flowing fluid streams. One typical static mixer, the helical static mixer, consists of left- and right-twisting helical elements placed at right angles to each other. The range of Reynolds numbers of practical flows for helical static mixers in industry is usually from very small values to not very large values (e.g., Re = 5,000). This thesis describes how static mixing processes of single-phase Newtonian and also non-Newtonian liquids can be simulated numerically and provides useful information that can be extracted from the simulation results. The Turbulent flow case is solved using the most common Reynolds Averaged Navier-Stocks (RANS) models as well as Large-Eddy Simulation (LES) turbulent flow model. The numerical simulation of the mixing in the helical static mixer has been performed via a two-step procedure. In the first step, the flow velocity (and the pressure) is computed. These values are then used as input to the next step. In the second step the particle trajectory in the flow field is calculated. At the entry of the pipe inlet, a large number of marker particles are uniformly distributed over half of the flow field. This represents a simplified model for diametrical feeding of the mixer with two liquids. Using different measurement tools, such as Residence Time Distribution (RTD) and Particles Distribution Uniformity (PDU), the performance of a six-element helical static mixer is studied. It is shown that the Reynolds number has a major impact on the performance of a static mixer. It is also shown that the performance of a helical static mixer is different for Newtonian and non-Newtonian fluids in non-creeping flows. Finally, heat transfer within a helical static mixer is investigated. The effects of different flow conditions on the performance of the mixer are studied. It is shown that the helical static mixer is more effective for low Reynolds number laminar flows.

Committee:

Theo Keith (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Static Mixer; Large-Eddy Simulation; RANS Turbulence Model; Non-Newtonian Fluid; Heat Transfer; LES Turbulence Model; Pseudo-plastic Fluid

Sefidbakht, SiavashTurbulence on Blunt Bodies at Reentry Speeds
Master of Science, The Ohio State University, 2011, Mechanical Engineering
Four new two-equation turbulence models are recently added to LAURA (NASA Langley’s aerothermodynamics CFD code). LAURA is usually used to calculate the aerodynamic heating for reentry vehicles. These new two-equation turbulence models are: Wilcox 2006 k-w, Wilcox 1998 k-w, Menter SST and Menter two-equation model. In this research these models are run for the first time on blunt bodies, which are cases with a stagnation point. It has been shown that for hypersonic flows with stagnation point, it is better to calculate the turbulence kinetic energy production term by the vorticity-based method, rather than the strain-based method that is in the original formulation of these models. The models are run on two test cases: an axisymmetric hemisphere and an 86 block full scale half-body MPCV. On the axisymmetric hemisphere, the models with strain-based production term, generate large amounts of extra k right after the shock, near the stagnation point. This extra k disrupts the flow field, and prevents the case from converging. With vorticity-based production term, all the models gave results close to the Cebeci-Smith algebraic model that has been present in the code for a long time and is trusted for these types of attached flows. On the half-body MPCV case, we run the Wilcox 2006 k-w model with the strain-based and vorticity-based production terms, and we got very close results by the two methods

Committee:

Michael Dunn, PhD (Advisor); Jen Ping Chen, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Reentry Problem; Turbulence; Aerodynamic Heating; Hypersonics

Papp, John LaszloSIMULATION OF TURBULENT SUPERSONIC SEPARATED BASE FLOWS USING ENHANCED TURBULENCE MODELING TECHNIQUES WITH APPLICATION TO AN X-33 AEROSPIKE ROCKET NOZZLE SYSTEM
PhD, University of Cincinnati, 2000, Engineering : Aerospace Engineering
The successful application of CFD and turbulence modeling methods to an aerospike nozzle system first involves the successful simulation of its key flow components. This report addresses the task using the Chien low-Re k-? and the Yakhot et al. high-Re RNG k-? turbulence models. An improved implicit axis of symmetry boundary condition is also developed to increase stability and lower artificial dissipation. Grid adaptation through the SAGE post-processing package is used throughout the study. The RNG model, after low-Re modifications, and the Chien low-Re k-? model are applied to the supersonic axisymmetric base flow problem. Both models predict a peak recirculation velocity almost twice as large as experiment. The RNG model predicts a flatter base pressure and lower recirculation velocity more consistent with experimental data using less grid points than a comparable Chien model solution. The turbulent quantities predicted by both models are typical of other numerical results and generally under predict peak values obtained in experiment suggesting that too little turbulent eddy viscosity is produced. After several test cases, the full 3-D aerospike nozzle is simulated using both the Chien and modified RNG low-Re models. The Chien model outperforms the RNG model in all circumstances. The surface pressure predicted by the Chien model along the nozzle center-plane is very near experiment while mid-plane results are not as close but useful for design purposes. The lack of a thick boundary layer along the nozzle surface in RNG simulations is the cause of poor surface pressure comparisons. Although initial base flow comparisons between the model predictions and experiment are poor, the profiles are relatively flat. To accelerate the progress to a steady-state solution, a process involving the artificial lowering of the base pressure and subsequent iteration to a new steady state is undertaken. After several of these steps, the resulting steady-state base pressure is very near experimental values. The effect of a slight geometry change on the flow characteristics is also examined through different thruster nozzle faceplate designs. The result of the slight modification is a tremendous reduction in surface pressure and temperature caused by recirculation at the thruster nozzle exit without adverse nozzle performance losses.

Committee:

Karman Ghia (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Turbulence Modeling; Renormalization Group Theory (RNG); Supersonic separated base flows; Numerical Methods; Numerical Simulation

Clark, Adam W.Characterization of Fluidic Instabilities in Vortex-Dominated Flows Using Time-Accurate Open Source CFD
MS, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering
The CFD software market of today has become saturated with two very different approaches; single purpose software codes written to model a specific type of flow, or jack-of-all-trades 'universal' commercial packages. Academics often argue that the commercial packages offer too little control over the details of the simulations, and companies frequently rail against the excessive cost and time commitments to develop their own specific-built CFD codes. The present study attempts to bridge this gap by examining the capabilities of OpenFOAM, an open source numerical solver, in a highly turbulent, vortex-dominated flow. The highly complex flowfield in the region immediately downstream of the backward facing step has provided a benchmark for numerical simulations since turbulence modeling began. A range of turbulence models within OpenFOAM are considered and compared against experimental data and literature. Two-equation models resulted in steady flow, albeit with reasonable average flowfield properties. The more advanced Reynolds Stress Transport Model resulted in an unsteady simulation with free shear layer properties in general agreement with both experimental and published data. This behavior mirrors other publications and codes, where it has been hypothesized that numerical perturbations caused by the discretization scheme excite the primary mode of instability of the free shear layer for the Reynolds Stress Models, but the overly dissipative nature of the two-equation models is sufficiently high to damp these stochastic fluctuations. With attention to the proper settings and turbulence model, OpenFOAM appears to perform relatively well in this complex and unsteady flowfield. The extreme level of control afforded by OpenFOAM would appear to meet the needs of academics and researchers while also satisfying corporate clients searching for a readily available package exhibiting a wide range of off-the-shelf capabilities.

Committee:

Shaaban Abdallah, PhD (Committee Chair); Grant Schaffner, PhD (Committee Member); Mark Turner, ScD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

OpenFOAM;open source;CFD;backstep;backward facing step;turbulence modeling;

Cheng, WenPropagation of Vortex Beams through a turbulent atmosphere
Master of Science (M.S.), University of Dayton, 2009, Electro-Optics

This thesis study and compare the propagation properties of both scalar and vector vortex beams through turbulent atmosphere. The irradiance pattern, degree ofpolarization, and scintillation index of radially polarized beam are computed for different propagation distance into an atmosphere with weak and strong turbulence. Corresponding properties of a fundamental Gaussian beam, a scalar vortex beam with topological charge of +1 propagating through an atmosphere under the same turbulence condition are calculated for comparison.

The results demonstrate that the existence of the vectorial vortex can be identified with longer propagation distance than the scalar vortex even with disappearing characteristic vortex structure in the irradiance images. This indicates the potential advantages of using vector vortex to mitigate atmospheric effects and enable a more robust free space communication channel with longer link distance.

Committee:

Qiwen Zhan, PhD (Advisor); Joseph Haus, PhD (Committee Member); Peter Powers, PhD (Committee Member)

Subjects:

Optics

Keywords:

Vortex Beam Propagation; Turbulence; Scintillation Index

Cui, ZheHydrodynamics in a bubble column at elevated pressures and turbulence energy distribution in bubbling gas-liquid and gas-liquid-solid flow systems
Doctor of Philosophy, The Ohio State University, 2005, Chemical Engineering
Bubble columns are widely used as multiphase reactors in chemical industries due to many advantages. The transport behavior in these systems is complex and a comprehensive knowledge of the transport phenomena, including hydrodynamics and turbulence properties are required. The hydrodynamics in a high pressure bubble column is experimentally investigated. The liquid velocities are measured using a LDV (Laser Doppler velocimetry). The Reynolds stresses are obtained. The effect of the pressure on the transition of the flow regime, flow field and the Reynolds stresses are studied. Furthermore, the effects of the liquid properties on the hydrodynamics of the bubble column are discussed. The turbulence energy distributions in the bubble columns are investigated using the LDV and PIV. The energy containing ranges for the bubble-induced and shear-induced turbulence are determined from the power spectra. Experimental results indicate that the bubble-induced turbulence dominates over the shear-induced turbulence under the operating conditions. The bubble-induced turbulence includes the turbulence in the bubble wake and that from the drift velocity change. The interaction between two turbulence field can only be observed when the turbulence in both fields is strong and the interaction tends to enhance the turbulence in both fields. The liquid phase turbulence is enhanced in the presence of particles at high superficial gas velocities while it is attenuated under low superficial gas velocity conditions. A criterion based on the variation of the ratio, Ug( r )/umf is proposed to account for the effect of the solids on the liquid phase turbulence. The prediction based on this criterion matches well with the experimental results. The behavior of a 6 mm mesobubble in an acoustic standing wave field is examined both experimentally and numerically. The acoustic standing waves at 16 kHz and 20 kHz are generated using two Nickel magnetostrictive transducers. The bubble rise velocity is significantly lower than that in the absence of an acoustic field. The behavior of bubble volume contraction and expansion can be accounted for by a 3-D direct numerical simulation of the bubble dynamics and flow field based on the compressible N-S equations coupled with the level-set method.

Committee:

LiangShih Fan (Advisor)

Subjects:

Engineering, Chemical

Keywords:

BUBBLE COLUMN; TURBULENCE; liquid phase; velocity; liquid; gas velocity

Schlawin, Everett A.Radiative Transfer Models of the Galactic Center
BA, Oberlin College, 2009, Physics and Astronomy

This thesis discusses research being done to understand the inner parts of the Milky Way Galaxy. We already know that there are dense star clouds, a supermassive black hole, and a large bar structure, but much of the inner galaxy is shrouded in mystery. Dust absorption, for one thing, prevents us from seeing the galactic center directly with our eyes.

To help understand the elusive inner Milky Way, we examine radio telescope data taken in Antarctica by Oberlin College Professor Chris Martin. His gigahertz radio observations were already analyzed to help understand how gas funnels into the Milky Way's supermassive black hole. We study this data further to characterize turbulence and predict how hot or cold the gas is.

The analysis of this data will also help prepare for the next thing: Herschel Space Observatory. This European telescope is scheduled to be launched in late April and will begin taking data in the fall of 2009. Chris Martin was granted 125 hours of observation time on the telescope to study the Inner Milky Way.

Committee:

Chris Martin, PhD (Advisor)

Subjects:

Astrophysics

Keywords:

Inner Galaxy; Astrophysics; Radiative Transfer; Turbulence; Milky Way Galaxy; Herschel; Velocity Centroids

Neal, Alexandra ElyseChanges in Behavior as A Result of Exposure to Naproxen: Mimicking Natural Systems
Master of Science (MS), Bowling Green State University, 2016, Biological Sciences
Animals living within aquatic habitats regularly encounter chemical pollution as a result of anthropogenic activities. Typically, the toxicity of a chemical pollutant or toxicant is determined by the median lethal concentration (LC50). However, LC50 values do not provide an accurate representation of exposure to a pollutant within natural systems. In their native habitats, animals experience exposure as a fluctuating concentration as a result of turbulent mixing. Edwards and Moore (2014) showed that more turbulent environments produce exposures with a high degree of fluctuation in frequency, duration, and intensity. In order to more effectively evaluate the effects of pollutants, we created a more ecologically relevant exposure paradigm, utilizing both flow and substrate within a small mesocosm. A commonly used pharmaceutical, naproxen, was used as the toxicant and female crayfish (Orconectes virilis) as the target organism to investigate changes in fighting behavior as a result of dynamic exposure. Crayfish underwent either a static or a dynamic exposure to naproxen in 23 hour long trials. Following exposure, the target crayfish and an unexposed size matched opponent underwent a 15 minute fight trial. These fight trials were recorded and later analyzed using a standard ethogram. Results indicate that exposure to sublethal concentrations of naproxen, in both static and flowing conditions, negatively impact aggressive behavior. Results also indicate that a dynamic exposure paradigm has a greater negative impact on behavior than a static exposure. Turbulence and habitat structure play important roles in shaping chemical exposure. Research in the future should incorporate features of chemical signals, such as intermittency and number of peaks above the mean concentration in order to form a more comprehensive image of chemical exposure and predict the resulting sublethal effects from exposure.

Committee:

Paul Moore (Advisor); Jeff Miner (Committee Member); Rachelle Belanger (Committee Member)

Subjects:

Biology; Ecology

Keywords:

ecotoxicology; exposure; naproxen; sublethal effects; turbulence

Stucky, Duane LarryThe effect of the exit velocity profile on the aerodynamic noise generation in a submerged turbulent subsonic jet /
Doctor of Philosophy, The Ohio State University, 1969, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Aerodynamic noise;Turbulence

Yieh, Heh-nienTurbulent mixing with chemical reaction.
Doctor of Philosophy, The Ohio State University, 1970, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Chemical kinetics;Turbulence

Craig, Roger RonaldTurbulence in free diffusion flames of hydrogen-nitrogen mixtures burning in still air /
Doctor of Philosophy, The Ohio State University, 1973, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Turbulence;Hydrogen;Nitrogen

Bear, Philip StevenOn the Experimental Evaluation of Loss Production and Reduction in a Highly Loaded Low Pressure Turbine Cascade
Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering
Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with and without blade profile contouring at the junction of the blade and endwall. The current work explores the loss production mechanisms inside the low pressure turbine cascade. Stereoscopic particle image velocimetry data, total pressure loss data and oil flow visualization are used to describe the secondary flow field. The flow is analyzed in terms of total pressure loss, vorticity, Q-Criterion, Reynolds’ stresses, turbulence intensity and turbulence production. The flow description is then expanded upon using an Implicit Large Eddy Simulation of the flow field. The RANS momentum equations contain terms with static pressure derivatives. With some manipulation these equations can be rearranged to form an equation for the change in total pressure along a streamline as a function of velocity only. After simplifying for the flow field in question the equation can be interpreted as the total pressure transport along a streamline. A comparison of the total pressure transport calculated from the velocity components and the total pressure loss is presented and discussed. Peak values of total pressure transport overlap peak values of total pressure loss through and downstream of the passage suggesting that total pressure transport is a useful tool for localizing and predicting loss origins and loss development using velocity data which can be obtained non-intrusively.

Committee:

Mitch Wolff, Ph.D. (Advisor); Rolf Sondergaard, Ph.D. (Committee Member); Rory Roberts, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Engineering

Keywords:

turbines; PIV; SPIV; particle image velocimetry; low pressure turbines; high lift turbines; total pressure loss; experimental measurements; aerodynamics; total pressure transport; turbulent flow; reynolds stress; turbulence production; deformation work

Theobold, David McCleadGain degradation and amplitude scintillation due to tropospheric turbulence /
Doctor of Philosophy, The Ohio State University, 1978, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Troposphere;Scintillators;Turbulence

Babajimopoulos, Christos SotirosThe preservation of the statistical structure in turbulent lake transport computations /
Doctor of Philosophy, The Ohio State University, 1978, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Quantum statistics;Turbulence

Bricker, David A.Analysis of Joint Effects of Refraction and Turbulence on Laser Beam Propagation in the Atmosphere
Master of Science (M.S.), University of Dayton, 2013, Electro-Optics
Experimental data obtained from recently conducted long-range laser beam propagation experiments has revealed inconsistencies with analytic and numeric simulations results based on classical Kolmogorov turbulence theory. This inconsistency may be related with not accounting for refraction effects caused by refractive index variation with elevation and presence of large-scale atmospheric structures which introduce refractive index gradients and can alter the trajectory of optical wave energy flux. In this thesis, atmospheric refraction effects are studied using a ray tracing technique. Due to refraction a ray propagating in the atmosphere doesn't follow a straight line and may not arrive to a desired location. In this thesis the ray tracing technique was applied for analysis of optical propagation over a 150 km propagation path. It was shown that due to refraction the ray trajectory may deviate from the geometric straight line by 60m in the middle of the path. We also considered the impact of refraction on atmospheric propagation of laser beams with different wavelengths (λ=0.532µm, λ=1.064µm, and λ=1.550µm) which were launched at the same angle. Due to the difference in refractive index of air for different wavelengths, the ray's paths follow different trajectories. It was shown that at the end of the propagation path, the distance between ray trajectories can be as long as ~4.1m for the 0.532µm and the 1.064µm rays, and ~4.3m for 0.532µm and 1.550µm rays. Besides traditional ray tracing technique we also introduced a new computational method that allows analysis of combined refraction and turbulence effects on laser beam propagation. In this method, traditional beam propagation using the well-known split step operator method is combined with ray tracing. In this technique the atmospheric volume is represented as a set of thin phase screens that obey Kolmogorov turbulence statistics. The ray tracing technique is applied to describe optical wave propagation between phase screens. At each screen, the turbulence-induced random tip and tilt wave-front phase component is added to the ray angle. In this way, the ray trajectory is no longer deterministic, but it has a turbulence induced uncertainty. It was shown that at the end of a 150km propagation path, the turbulence induced deviation on ray trajectory can be on the order of 5m. These results show that for correct analysis of laser beam propagation over long distances in the atmosphere, refraction and turbulence effects should be considered jointly. The proposed numerical simulation technique allows this joint analysis.

Committee:

Mikhail Vorontsov, Ph.D (Advisor); Partha Banerjee, Ph.D (Committee Member); Paul McManamon, Ph.D (Committee Member)

Subjects:

Optics

Keywords:

Atmospheric Turbulence, Ray Tracing, Numerical Simulation, Laser Beam Propagation

Alhassan, Saeed M.COLLOIDAL INTERACTIONS AND STABILITY IN PROCESSING, FORMATION AND PROPERTIES OF INORGANIC-ORGANIC NANOCOMPOSITES
Doctor of Philosophy, Case Western Reserve University, 2011, Chemical Engineering
Colloidal interactions are important in understanding and controlling the stability of colloids since these systems are usually far from thermodynamic equilibrium. Colloidal interactions in liquid based colloids are either attractive or repulsive. The Derjaguin and Landau, Verwey and Overbeek theory (DLVO) of colloidal stability assumes that the total potential interaction is a sum of attractive and repulsive forces. The additivity assumption does not hold for all colloidal systems, especially for colloids stabilized or flocculated by the presence of polymer in solution. However, the qualitative success of the theory is used to explain the observed phenomena herein. In the first part of the project, the effects of electrolyte and polymer addition on formation and mechanical properties of clay aerogels were explored. Incoherent aerogels were formed in samples with low polymer loading and low electrolyte concentration but all other loadings, coherent aerogels were produced. The mechanical properties of aerogels have a power law dependence on relative and bulk density with high exponent values. The high exponent values are attributed to the aerogel layered structure, anisotropy and enhanced exfoliation with polymer addition. In the second part of the project, the exfoliation of graphene in water was achieved using turbulent mixing at ambient conditions. Turbulent mixing was used as mean to overcome van der Waals forces between graphene layers in graphite and laponite was used to arrest exfoliated graphene from aggregation. The method can exfoliate graphite down to bilayer graphene as evident from Raman spectra, transmission electron microscopy (TEM) and x-ray diffraction. The laponite colloidal Wigner glass is a suitable medium for studying, not only graphene, but also other nanoparticles and biological macromolecules. In the third part of the study, main chain benzoxazine polymer was used to synthesize aerogels and nanocomposites. The aerogel was produced through thermally induced phase separation method. The mechanical properties of these aerogels have power law dependence on density with exponent values that are comparable to those reported for silica aerogels and clay aerogels. Graphene oxide polybenzoxazine nanocomposites were made via solution casting. Surprisingly, the thermal properties of these nanocomposties decrease due to reactivity of graphene oxide at the same processing window of polybenzoxazine.

Committee:

Syed Qutubuddin, PhD (Advisor); David Schiraldi, PhD (Advisor); J. Adin Mann Jr., PhD (Committee Member); R. Mohan Sankaran, PhD (Committee Member)

Subjects:

Chemical Engineering

Keywords:

clay; graphene; graphene oxide; aerogel; laponite; turbulence; exfoliation; colloidal interactions; DLVO theory; colloidal stability; nanocomposites

Yu, HongtaoA Validation Study of SC/Tetra CFD Code
Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering
The goal of this study is to validate the accuracy of the SC/Tetra CFD code by modeling four cases: a 2D zero pressure gradient flat plate, an axisymmetric separated boundary layer, flow over an NACA 0012 airfoil, and flow over an NACA 4412 airfoil trailing edge separation. The results will be compared to experimental data and CFL3D results. This study also investigates the sensitivity of SC/Tetra results to different set up details such as mesh resolution, turbulence model, and under-relaxation settings. Automation using the Visual Basic programming language was used to vary these set up details and efficiently process a large number of simulations for NACA 0012. The Flat plate case focuses on skin friction coefficient and velocity profiles. The axisymmetric separated boundary layer case concentrates on pressure coefficient and velocity profiles. For the NACA 0012 airfoil, evaluation focuses on Cp profiles. Cp and velocity profiles and streamlines are considered for the NACA 4412 airfoil. In general, coarser meshes are shown to be less accurate than finer meshes and the SST k-OMG is more accurate.

Committee:

George Huang, Ph.D. (Advisor); Zifeng Yang, Ph.D. (Committee Member); Joseph Shang, Ph.D (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Flat Plate; Axisymmetric Separated Boundary Layer; Turbulence Model; NACA 0012; NACA 4412

Casey, David MichaelCharacterization of Transition to Turbulence for Blood in an Eccentric Stenosis Under Steady Flow Conditions
Master of Science in Engineering, University of Akron, 2014, Mechanical Engineering
Blood is a complex fluid that consists of approximately 45% solid particulates by volume. These solid particulates, erythrocytes, cause the fluid to exhibit a non-Newtonian, shear thinning rheology under low shear rates (<200s-1) and Newtonian rheology otherwise. Many researchers employ Newtonian blood analogs to study the relationship between hemodynamics and morphogenesis when the predominant shear rates in the vessel are high. Non-biological, shear thinning fluids have been observed to transition from laminar to turbulent flow differently than Newtonian fluids. A discrepancy between the critical Reynolds number of blood and a Newtonian analog could result in erroneous predictions of hemodynamic forces. The goal of the present study was to compare velocity profiles near transition to turbulence of whole blood and a Newtonian blood analog downstream of a stenosis under steady flow conditions. Doppler ultrasound was used to measure velocity profiles of whole porcine blood and a Newtonian fluid in an in vitro experiment at 13 different Reynolds numbers ranging from 150 to 1200. Three samples of each fluid were examined and fluid rheology was measured before and after each experiment. Results show parabolic like velocity profiles for both whole blood and the Newtonian fluid at Reynolds numbers less than 250 (based on the viscosity at 400s-1). The Newtonian fluid had blunt velocity profiles with large velocity fluctuations (root mean square as high as 25%) starting at Reynolds numbers ~250 which indicated transition to turbulence. In contrast, whole blood did not transition to turbulence until a Reynolds number of ~300-600. All three blood samples were delayed compared to that of the Newtonian fluid, although there were variabilities between the critical Reynolds numbers. For Reynolds numbers larger than 700, the delay in transition resulted in differences in velocity profiles between the two fluids as high as 35%. A Newtonian assumption for blood at flow conditions near transition can lead to large errors in velocity prediction for steady flow in a poststenotic flow field. Since this study was limited to a single velocity profile, further studies are required to fully understand the post-stenotic flow field. Further research is necessary to understand the importance of pulsatile flow and compliance.

Committee:

Francis Loth, Dr. (Advisor); Yang Yun, Dr. (Committee Member); Abhilash Chandy, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

turbulence, blood, Doppler ultrasound, non-Newtonian, rheology, fluid dynamics, Reynolds number

Hoffmeister, Kathryn Nicole GabetDevelopment and Application of High-Speed Raman/Rayleigh Scattering in Turbulent Nonpremixed Flames
Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering
In this dissertation, a new, high-speed, combined 1D Raman-Rayleigh scattering imaging approach was developed for quantitative temporally-correlated (10-kHz) measurements of temperature, major combustion species (O2, N2, H2O, and H2), and mixture fraction in the turbulent DLR H3 nonpremixed jet flame. The new high-speed measurements presented here were facilitated through the development of a custom high-speed imaging spectrometer, implementation of a robust data reduction methodology, and the use of the High-Energy Pulse Burst Laser System (HEPBLS) at Ohio State, which produces ultra-high pulse energies at multi-kHz repetition rates. Detailed measurements in near-adiabatic, laminar calibration flames were used to assess the accuracy and precision of the kHz-rate measurements using the high-speed Raman/Rayleigh scattering imaging system. In general, good agreement was found as compared to adiabatic flame calculations over a broad range of temperature and equivalence ratios. Current 10-kHz measurements and derived statistics within the turbulent H3 flames were compared to previously-measured, low-repetition-rate scalar data available through the Turbulent Nonpremixed Flame (TNF) workshop database. In general, good agreement between the mean values and RMS fluctuations of the temperature and major species were found between the current and previous data, indicating sufficient accuracy in single-shot measurements in turbulent environments. Following technique development, a series of 10-kHz measurements were used to visualize the highly intermittent dynamics of the scalar fields. In addition to flow visualization, time-dependent measurements were used to deduce the temporal autocorrelation function and the associated integral time-scales of the major species, mixture fraction, and temperature in the DLR H3 flames. This research presents the first measurements of the integral timescales of the major combustion species and mixture fraction in turbulent flames as well as the first reporting of integral timescales of multiple scalars simultaneously. While the integral timescales of all scalars (O2, H2O, and H2, ξ, and T) generally increase with both axial and radial position, the individual integral timescales are significantly different, displaying a factor of three spread across all of the measured scalars. The integral timescales for temperature and water are highly correlated to one another at all spatial locations, while the integral timescale for mixture fraction closely tracks that of hydrogen between the jet centerline and the stoichiometric contour and tracks that of oxygen between the stoichiometric contour and the co-flowing oxidizer stream. Results indicate that in regions of high chemical activity and heat release, the use of single characteristic (integral) timescale to describe the large-scale behavior is not appropriate; that is, each scalar has its own unique spatially-dependent integral timescale. For spatial positions beyond the flame tip, the integral timescales for all scalars collapse upon one another meaning that the system can be described adequately as a pure mixing situation with a single characteristic timescale. Finally, new, temporal cross-correlations of various scalar pairs are presented along with a discussion of the derived scalar interaction times. In general, the scalar interaction times are bound by the individual scalar integral timescales, although unique characteristics are observed near the stoichiometric contour, which varies amongst the various scalar pairs. It is expected that the newly developed high-speed 1D Raman/Rayleigh imaging approach will provide new physical insight into the intermittent behavior of turbulent nonpremixed combustion and the subsequent turbulence-chemistry interaction, as well as providing new, time-resolved data for assessment and validation of time-dependent combustion models.

Committee:

Jeffrey Sutton (Advisor); Walter Lempert (Committee Member); Mohammad Samimy (Committee Member); Shaurya Prakash (Committee Member)

Subjects:

Aerospace Engineering; Chemistry; Experiments; Fluid Dynamics; Mechanical Engineering

Keywords:

Laser Diagnostics; High-Speed Laser Diagnostics; Combustion; Turbulent Combustion; Raman Scattering; Rayleigh Scattering; Turbulence-Chemistry Interaction; H3 Flame

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