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Memory, Curtis L.Turbulent Transition Behavior in a Low Pressure Turbine Subjected to Separated and Attached-Flow Conditions
Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering
Various time accurate numerical simulations were conducted on the aft-loaded L1A low pressure turbine airfoil operating at Reynolds numbers presenting with fully-stalled, non-reattaching laminar separation. The numerical solver TURBO was modified from its annular gas turbine simulation configuration to conduct simulations based on a linear cascade wind tunnel facility. Simulation results for the fully separated flow fields revealed various turbulent decay mechanisms. Separated shear layer decay, in the form of vortices forming between the shear layer and the blade wall, was shown to agree with experimental particle image velocimetry (PIV) data in terms of decay vortex size and core vorticity levels. These vortical structures eventually mix into a large recirculation zone which dominates the blade wake. Turbulent wake extent and time-averaged velocity distributions agreed with PIV data. Steady-blowing vortex generating jet (VGJ) flow control was then applied to the flow fields. VGJ-induced streamwise vorticity was only present at blowing ratios above 1.5. VGJs actuated at the point of flow separation on the blade wall were more effective than those actuated downstream, within the separation zone. Pulsed-blowing VGJs at the upstream blade wall position were then actuated at various pulsing frequencies, duty cycles, and blowing ratios. These condition variations yielded differing levels of separation zone mitigation. Pulsed VGJs were shown to be more effective than steady blowing VGJs at conditions of high blowing ratio, high frequency, or high duty cycle, where blowing ratio had the highest level of influence on pulsed jet efficacy. The characteristic "calm zone" following the end of a given VGJ pulse was observed in simulations exhibiting high levels of separation zone mitigation. Numerical velocity fields near the blade wall during this calm zone was shown to be similar to velocity fields observed in PIV data. Instantaneous numerical vorticity fields indicated that the elimination of the separation zone directly downstream of the VGJ hole is a primary indicator of pulsed VGJ efficacy. This indicator was confirmed by numerical time-averaged velocity magnitude rms data in the same region.

Committee:

JenPing Chen, PhD (Advisor); Jeffrey P. Bons, PhD (Committee Member); James W. Gregory, PhD (Committee Member); Mei Zhuang, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

vortex generating jet; low pressure turbine; direct numeric simulation; steady blowing; pulsed blowing; particle image velocimetry; vortex

Bani Younes, Ahmad HaniInvestigation of the Flowfield Surrounding Small Photodriven Flapping Wings
Master of Science (M.S.), University of Dayton, 2009, Aerospace Engineering

The flowfield surrounding wings with a pure flapping motion was studied in quiescent air at a Reynolds number of approximately 200 using particle image velocimetry (PIV) in unusually thin illuminated planes (~0.3 mm). Typical wing semi-spans were on the order of a few millimeters. The polymer cantilever wings consisting of monodomain liquid crystal polymers made from azobenzene (azo-LCN) were flapped at 30 Hz at a large amplitude (>170°). Chordwise and spanwise planar slices of the flow across the wings were obtained and used to estimate the unsteady aerodynamic forces generated by the flapping wings.

This study focuses on the flapping flight of small-scale wings in order to visualize the flowfield characteristics. The small-scale wings were, indeed, able to induce the surrounding flowfield and generate aerodynamic contribution, which was clearly observed in spanwise plane. Images at various spanwise and chordwise locations were acquired and processed. In terms of results, the spanwise flow was the dominant. The chordwise results were not conclusive useful due to the poor light filtering. The PIV displacement and velocity uncertainties were small quantitatives compared to the vorticity and circulation uncertainties.

Committee:

Aaron Altman (Advisor); Altman Aaron (Committee Chair); Anwar Ahmed (Committee Member); Dong Haibo (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Particle Image velocimetry (PIV); Flapping Wing; Photodriven flapper; Liquid Crystal Polymer; Flow visualization; Spanwise Flow; Vortex Flow

Perelstein, YuriInvestigation of Erosive Flow Injected Through Apertures into a Narrow Annulus
PhD, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
It is common to convey solid particulates using liquids, forming a slurry. Those slurries conveyed in conduits generate erosion caused by particulate impingements on the walls. The erosive action of slurry may significantly reduce the service life of processing equipment, even at slow transport velocities. The particulates are subjected to the forces exerted by the carrying liquid. Therefore, continuous phase flow field strongly influences erosion by slurry. The erosive action and relevant flow features are investigated herein for a case of dilute slurry passing from the inner to the outer annulus through four equally spaced rectangular apertures on the periphery of a tube dividing these two conduits. This study consists of numerical and experimental investigations. The velocity and the Reynolds stresses were measured using Stereoscopic Particle Image Velocimetry. The erosive flow features of the continuous phase flow were identified and explored in detail. The measurements show that the flow develops high velocity near aperture edges directed towards the outermost wall. These measurements allowed validating the numerical solution of the continuous phase. The flow of dilute slurry was solved numerically. A consideration was given to the effects of particle size on erosion rate and statistical distribution of impact velocity, angle, and total erodent mass generating adverse wear rates. A confined trailing vortex forms at the longitudinal edge of the aperture, amplifying the erosive wear on the outer wall of the annulus. Also, large amount of particulates passes near the aperture horizontal downstream edge at high velocity and intensifies the erosion rate above it. The effect of these flow features becomes more pronounced for larger particulates. The statistical analysis of impact velocity, angle, and mass showed that the mean velocity in the channel dominates erosion caused by impacts of large particulates. On the other hand, the near-wall turbulence mainly affects the erosion resulting from impacts by small particulates. Note:

Committee:

Ephraim Gutmark, Ph.D. D.Sc. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Solid particle erosion;Slurry erosion;Vortex-induced wear;Flow through aperture;Impaction statistics;Particle Image Velocimetry

Gunasekaran, SidaardRelationship Between the Free Shear Layer, the Wingtip Vortex and Aerodynamic Efficiency
Doctor of Philosophy (Ph.D.), University of Dayton, 2016, Aerospace Engineering
The overarching objective of this experimental investigation is to explore the relationship between the aerodynamic efficiency of the wing and its turbulent wake (both the free shear layer and the wingtip vortex). Recent evidence of unique turbulent signatures in the free shear layer of a turbulent generator provided the motivation behind this research. The balance of induced drag and the parasite drag was hypothesized to be mirrored in the properties of the wingtip vortex and the free shear layer respectively expanding from classical theoretical descriptions. Experimental investigations were focused on the wake of wings to understand this balance in the parasite and the induced drag and to explore the use of the properties in the turbulent wake to increase the aerodynamic efficiency of the wing. Because of the highly complex nature of the wake, the research is broken down into several individual sub-studies which explore a) the relationship between the aerodynamic efficiency and the free shear layer, b) the relationship between the aerodynamic efficiency and the wingtip vortex, and c) the relationship between the free shear layer and the wingtip vortex and their correlation to the aerodynamic efficiency. Particle Image Velocimetry (PIV) was used to measure the velocity in the wake of an SD 7003 wall-to-wall model and an AR 4 flat plate with and without a spanwise boundary layer trip in the Horizontal Free Surface Water Tunnel (HFWT) at the Air Force Research Labs (AFRL) and in the Low Speed Wind Tunnel at the University of Dayton (UD-LSWT). The results from experimental investigations were Reynolds decomposed to study the mean and fluctuating quantities in the wake of the wing. The initial prediction of these quantities in the wake of SD 7003 wall-to-wall model and AR 4 flat plate were made using the existing momentum deficit and Reynolds stress models (which are derived from simplified Navier-Stokes equations). Even though the momentum deficit model yielded a good match with the experimental data, the Reynolds stress model was not able to predict the experimental data because of the asymmetry in the distribution. The eddy viscosity parameter in the algebraic models was then identified and incorporated in the algebraic models. The variation in the surrogate eddy viscosity parameter when compared to the experimental data showed direct correlation with the variation in the aerodynamic efficiency of the wing. In order to fortify the relationship between the turbulent properties in the free shear layer and the aerodynamic efficiency, the energy loss in the wake of the SD7003 wall-to-wall model was quantified by determining the viscous dissipation (Exergy) as a function of initial conditions upstream. The changes in Exergy mirrored the aerodynamic efficiency of the SD 7003 wall-to-wall model. But in the AR 4 wing wake, there existed a net spanwise momentum due to the formation of the wingtip vortices. Using orthogonal PIV planes of interrogation in the wingtip vortex station across several distances downstream, the evolution of the wingtip vortex and its relationship with aerodynamic efficiency of the wing were investigated. The wake-like to jet-like transition in the core of the wingtip vortex was not observed at the angle of attack of maximum aerodynamic efficiency. However the maximum viscous dissipation and the Reynolds stress in the wingtip vortex shows changes in the slope at the maximum (L/D) location. In the presence of a spanwise boundary layer trip, the location of the change of slope in the viscous dissipation and Reynolds stress was changed indicating a direct correlation to the properties in the wingtip vortex and the aerodynamic efficiency of the wing. Significant changes in the boundary layer of the flat plate with the boundary layer trip were observed at lower angles of attack. The resulting changes in the turbulence character of the wingtip vortex and the free shear layer were investigated for evidence of an interaction between the free shear layer and the evolution of the wingtip vortex. The streamwise, cross-stream and spanwise oriented PIV of the wingtip vortex shows definitive evidence of the free shear layer interaction with the wingtip vortex at angles of attack lower than maximum (L/D). This interaction was reflected in the normalized azimuthal velocity profile of the wingtip vortex as well. The composite of the velocity profiles from the multiple different planes showed a transfer of momentum from the free shear layer to the wingtip vortex in the vicinity of maximum (L/D) angle of attack. This suggests that by manipulating the cross-stream flow in the wake of the wing from the wing root to the wingtip, the balance of induced drag and parasite drag can be altered given initial conditions and the aerodynamic efficiency can be improved in off-design conditions.

Committee:

Aaron Altman (Advisor); Markus Rumpfkeil (Committee Member); Jose Camberos (Committee Member); Ryan Schmit (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

Wingtip Vortex; Free Shear Layer; Turbulence; Exergy; Wingtip Vortex Shear Layer Interaction; Aerodynamics; Fluid Dynamics; Boundary Layer Trip; Serrated Leading Edge; Streamwise Wingtip Vortex Particle Image Velocimetry; Momentum Transfer;

Disotell, Kevin JamesLow-Frequency Flow Oscillations on Stalled Wings Exhibiting Cellular Separation Topology
Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering
One of the most pervasive threats to aircraft controllability is wing stall, a condition associated with loss of lift due to separation of air flow from the wing surface at high angles of attack. A recognized need for improved upset recovery training in extended-envelope flight simulators is a physical understanding of the post-stall aerodynamic environment, particularly key flow phenomena which influence the vehicle trajectory. Large-scale flow structures known as stall cells, which scale with the wing chord and are spatially-periodic along the span, have been previously observed on post-stall airfoils with trailing-edge separation present. Despite extensive documentation of stall cells in the literature, the physical mechanisms behind their formation and evolution have proven to be elusive. The undertaken study has sought to characterize the inherently turbulent separated flow existing above the wing surface with cell formation present. In particular, the question of how the unsteady separated flow may interact with the wing to produce time-averaged cellular surface patterns is considered. Time-resolved, two-component particle image velocimetry measurements were acquired at the plane of symmetry of a single stall cell formed on an extruded NACA 0015 airfoil model at chord Reynolds number of 560,000 to obtain insight into the time-dependent flow structure. The evolution of flow unsteadiness was analyzed over a static angle-of-attack range covering the narrow post-stall regime in which stall cells have been observed. Spectral analysis of velocity fields acquired near the stall angle confirmed a low-frequency flow oscillation previously detected in pointwise surface measurements by Yon and Katz (1998), corresponding to a Strouhal number of 0.042 based on frontal projected chord height. Probability density functions of the streamwise velocity component were used to estimate the convective speed of this mode at approximately half the free-stream velocity, in agreement with Yon and Katz. Large-amplitude streamwise Reynolds stresses in the separated shear layer were found to be manifested by the low-frequency oscillation through inspection of the spectral energy distribution. Using the method of Proper Orthogonal Decomposition to construct reduced-order models of the acquired time sequences, the low-frequency unsteadiness appeared to be linked to an interaction between the separated and trailing-edge shear layers, in contrast to a bubble-bursting mechanism which has been observed for different stall behaviors. As the static angle of attack was increased further, the separated flow structure was seen to transition to a faster eddy motion expected for bluff-body wakes. A novel scaling study was conducted to evaluate the potential role of low-frequency unsteadiness in producing the spanwise wavelengths associated with cell formation, which was found to be in favorable agreement with scaling trends in the literature. Finally, instantaneous pressure-sensitive paint measurements were demonstrated on a DU 97-W-300 wind turbine airfoil at chord Reynolds number of 225,000 with leading-edge trip applied, in which the development of spiral node structures associated with cell formation were captured in the trailing-edge separation. The contributed work suggests that further study into the influence of large-scale unsteadiness on the three-dimensional organization of stall cells is merited.

Committee:

James Gregory, Ph.D. (Advisor); Jeffrey Bons, Ph.D. (Committee Member); Mo Samimy, Ph.D. (Committee Member); Jen-Ping Chen, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

wing aerodynamics; stall cells; high-angle-of-attack airfoil aerodynamics; turbulent separated flows; three-dimensional separation; large-scale unsteadiness; vortical wakes; low-frequency flow oscillations; time-resolved particle image velocimetry

Elder, John PriceThe Sensory Basis of Rheotaxis in Turbulent Flow
Master of Science (MS), Bowling Green State University, 2014, Biological Sciences
Rheotaxis is a robust, multisensory behavior with many potential benefits for fish and other aquatic animals, yet the influence of different fluvial conditions on rheotactic performance and its sensory basis is still poorly understood. Here, we examine the role that vision and the lateral line play in the rheotactic behavior of a stream-dwelling species (Mexican tetra, Astyanax mexicanus) under both rectilinear and turbulent flow conditions. Turbulence enhanced overall rheotactic strength and lowered the flow speed at which rheotaxis was initiated; this effect did not depend on the availability of either visual or lateral line information. Compared to fish without access to visual information, fish with access to visual information exhibited increased levels of positional stability and as a result, increased levels of rheotactic accuracy. No disruption in rheotactic performance was found when the lateral line was disabled, suggesting that this sensory system is not necessary for either rheotaxis or turbulence detection under the conditions of this study.

Committee:

Sheryl Coombs, PhD (Advisor); Paul Moore, PhD (Committee Member); Moira van Staaden, PhD (Committee Member)

Subjects:

Animals; Behavioral Sciences; Biology; Experiments; Neurosciences; Organismal Biology; Zoology

Keywords:

Biology; rheotaxis; fish swimming behavior; lateral line; vision; turbulence; station holding; particle image velocimetry; optic flow

Kucukal, ErdemEXPERIMENTAL AND CFD INVESTIGATIONS OF THE FLUID FLOW INSIDE A HYDROCYCLONE SEPARATOR WITHOUT AN AIR CORE
Master of Sciences, Case Western Reserve University, 2015, EMC - Mechanical Engineering
Hydrocyclone separators are used in various industrial applications such as mineral processing in order to separate solid particles or liquid droplets from multiphase systems. A large number of studies have been conducted in recent years for understanding the flow characteristics within a cyclone. The currently available theoretical models only provide a limited amount of information regarding the cyclone performance and not applicable to most real-life applications. In this thesis, the single-phase fluid flow through a hydrocyclone was investigated by means of both computational and experimental techniques (Particle Image Velocimetry). The computational modelling was carried out using a commercial Computational Fluid Dynamics (CFD) code, Star CCM+. A mesh domain with more than 700k unstructured cells was created in a Cartesian coordinate system. Two turbulence models were used during the numerical calculations: The k-w model (with the curvature xvi correction) and the Reynolds Stress Model. In both cases, the first order discretization scheme was unable to resolve the flow field accurately due to the high levels of numerical dissipation. The velocity and pressure contours on various planes were drawn for both turbulence models, which showed the superiority of the RSM over the k-w model in the computational simulation of highly swirling flows. Particle Image Velocimetry (PIV) was used for the experimental investigations of the flow inside an optically clear hydrocyclone. The refractive index of the working fluid was matched to that of the model cyclone material, which was acrylic plastic, in order to prevent any optical distortions in the test setup. The refractive index matching was accomplished by using a sodium iodide solution (63.3 % NAI by weight). 10 µm silver coated hollow glass spheres were injected into the system as tracing particles. Investigations of the flow field were performed on two different regions of interest, and the first region was divided into seven fields of view (FOV). The results show that the radial-tangential velocities tend to increase from the cyclone wall to the vortex finder and reach a maximum value before they began to decline rapidly and eventually become zero on the wall. The experimental data were used to validate the numerical results both on a global level and based upon local velocity profiles. The comparisons showed that the two models were in good agreement particularly in the near-wall regions.

Committee:

Jaikrishnan Kadambi (Advisor)

Subjects:

Mechanical Engineering

Keywords:

Hydrocyclone, Particle Image Velocimetry, computational fluid dynamics, turbulence, swirling flows

Guillou, ErwannFlow Characterization and Dynamic Analysis of a Radial Compressor with Passive Method of Surge Control
PhD, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering

Due to recent emission regulations, the use of turbochargers for force induction of internal combustion engines has increased. Actually, the trend in diesel engines is to downsize the engine by use of turbochargers that operate at higher pressure ratio. Unfortunately, increasing the rotational speed tends to reduce the turbocharger radial compressor range of operation which is limited at low mass flow rate by the occurrence of surge.

In order to extent the operability of turbochargers, compressor housings can be equipped with a passive surge control device also known as ported shroud. This specific casing treatment has been demonstrated to enhance surge margin with minor negative impact on the compressor efficiency. However, the actual working mechanisms of the bypass system remain not well understood. In order to optimize the design of the ported shroud, it is then crucial to identify the dynamic flow changes induced by the implementation of the device to control instabilities.

Experimental methods were used to assess the development of instabilities from stable, stall and eventually surge regimes of a ported shroud centrifugal compressor. Systematic comparison was conducted with the same compressor design without ported shroud. Hence, the full pressure dynamic survey of both compressors’ performance characteristics converged toward two different and probably interrelated driving mechanisms to the development and/or propagation of unsteadiness within each compressor. One related the pressure disturbances at the compressor inlet, and notably the more apparent development of perturbations in the non-ported compressor impeller, whereas the other was attributed to the pressure distortions induced by the presence of the tongue in the asymmetric design of the compressor volute.

Specific points of operation were selected to carry out planar flow measurements. At normal working, both standard and stereoscopic particle imaging velocimetry (PIV) measurements were performed to calculate the instantaneous and mean velocity fields at the inlet of the compressor. At incipient and full surge, phase-locked PIV measurements were added. In this work, satisfying characterization of the compressor inlet flow instabilities was obtained at different operational speeds. Combining transient pressure data and PIV measurements, the time evolution of the complex flow patterns occurring at surge was reconstructed and a better insight into the bypass mechanisms was achieved.

Committee:

Ephraim Gutmark, PhD,DSc (Committee Chair); Shaaban Abdallah, PhD (Committee Member); Jeffrey Kastner, PhD (Committee Member); Paul Orkwis, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Radial Compressor;Surge;Passive Control;Ported Shroud;Particle Image Velocimetry;PIV

Memon, Muhammad OmarWingtip Vortices and Free Shear Layer Interaction in the Vicinity of Maximum Lift to Drag Ratio Lift Condition
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Aerospace Engineering
Cost-effective air-travel is something everyone wishes for when it comes to booking flights. The continued and projected increase in commercial air travel advocates for energy efficient airplanes, reduced carbon footprint, and a strong need to accommodate more airplanes into airports. All of these needs are directly affected by the magnitudes of drag these aircraft experience and the nature of their wingtip vortex. A large portion of the aerodynamic drag results from the airflow rolling from the higher pressure side of the wing to the lower pressure side, causing the wingtip vortices. The generation of this particular drag is inevitable however, a more fundamental understanding of the phenomenon could result in applications whose benefits extend much beyond the relatively minuscule benefits of commonly-used winglets. Maximizing airport efficiency calls for shorter intervals between takeoffs and landings. Wingtip vortices can be hazardous for following aircraft that may fly directly through the high-velocity swirls causing upsets at vulnerably low speeds and altitudes. The vortex system in the near wake is typically more complex since strong vortices tend to continue developing throughout the near wake region. Several chord lengths distance downstream of a wing, the so-called fully rolled up wing wake evolves into a combination of a discrete wingtip vortex pair and a free shear layer. Lift induced drag is generated as a byproduct of downwash induced by the wingtip vortices. The parasite drag results from a combination of form/pressure drag and the upper and lower surface boundary layers. These parasite effects amalgamate to create the free shear layer in the wake. While the wingtip vortices embody a large portion of the total drag at lifting angles, flow properties in the free shear layer also reveal their contribution to the aerodynamic efficiency of the aircraft. Since aircraft rarely cruise at maximum aerodynamic efficiency, a better understanding of the balance between the lift induced drag (wingtip vortices) and parasite drag (free shear layer) can have a significant impact. Particle Image Velocimetry (PIV) experiments were performed at a) a water tunnel at ILR Aachen, Germany, and b) at the University of Dayton Low Speed Wind Tunnel in the near wake of an AR 6 wing with a Clark-Y airfoil to investigate the characteristics of the wingtip vortex and free shear layer at angles of attack in the vicinity of maximum aerodynamic efficiency for the wing. The data was taken 1.5 and 3 chord lengths downstream of the wing at varying free-stream velocities. A unique exergy-based technique was introduced to quantify distinct changes in the wingtip vortex axial core flow. The existence of wingtip vortex axial core flow transformation from wake-like (velocity less-than the freestream) to jet-like (velocity greater-than the freestream) behavior in the vicinity of the maximum (L/D) angles was observed. The exergy-based technique was able to identify the change in the out of plane profile and corresponding changes in the L/D performance. The resulting velocity components in and around the free shear layer in the wing wake showed counter flow in the cross-flow plane presumably corresponding to behavior associated with the flow over the upper and lower surfaces of the wing. Even though the velocity magnitudes in the free shear layer in cross-flow plane are a small fraction of the freestream velocity (~10%), significant directional flow was observed. An indication of the possibility of the transfer of momentum (from inboard to outboard of the wing) was identified through spanwise flow corresponding to the upper and lower surfaces through the free shear layer in the wake. A transition from minimal cross flow in the free shear layer to a well-established shear flow in the spanwise direction occurs in the vicinity of maximum lift-to-drag ratio (max L/D) angle of attack. A distinctive balance between the lift induced drag and parasite drag was identified. Improved understanding of this relationship could be extended not only to improve aircraft performance through the reduction of lift induced drag, but also to air vehicle performance in off-design cruise conditions.

Committee:

Aaron Altman (Advisor); Markus Rumpfkeil (Committee Member); Jose Camberos (Committee Member); Wiebke Diestelkamp (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

Wingtip Vortices, Free Shear Layer, Circulation, Vortex Identification, Exergy Destruction Rate, Particle Image Velocimetry, Momentum Transfer, University of Dayton Low Speed Wind Tunnel, Water Tunnel, Aerodynamic Efficiency

Landers, Brian DMixing Characteristics of Turbulent Twin Impinging Axisymmetric Jets at Various Impingement Angles
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
An experimental study is first presented on the comparison between two commonly used velocity measurement techniques applied in experimental fluid dynamics: Constant Temperature Anemometry (CTA) and Particle Image Velocimetry (PIV). The comparison is performed in the near-field region of an axisymmetric circular turbulent jet where the flow field contains large scale turbulent structures. The comparison was performed for five Reynolds numbers, based on diameter, between 5,000 and 25,000. The Reynolds numbers selected cover the critical Reynolds number range, 10,000 to 20,000 where the characteristics of the flow transition to a fully developed turbulent mixing layer. A comparison between these two measurement techniques was performed in order to determine the differences between an intrusive (CTA) and non-intrusive (PIV) method when applied to a practical application. The results and observations obtained from the comparison between the two techniques were applied to better characterize the time-averaged characteristics of a single axisymmetric turbulent jet with a Reynolds number of 7,500. The mean and fluctuating velocities, turbulent kinetic energy (TKE), and vorticity were measured as a baseline case. Additionally, smoke visualization was utilized to determine the mixing characteristics of the transient start of an axisymmetric turbulent jet. The shedding frequencies, also known as, the `preferred mode’ were investigated for a single jet. Particle Image Velocimetry (PIV) was also utilized to characterize the pre-and post-regions of the interaction region of two axisymmetric, incompressible turbulent jets at included angles: 30, 45, and 60 degrees. The Reynolds number selected (7,500) was within the range of critical Reynolds numbers and the geometrical distance to twin jet impingement, X0, remained constant at 10.33D for each impingement angle. The mean and fluctuating velocities, vorticity, and turbulent kinetic energy (TKE) were measured. Smoke Visualization was utilized to measure the mixing characteristics of impinging jets during the transient start as well as when the jets had reached a steady state condition.

Committee:

Peter Disimile, Ph.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Milind Jog, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Impinging Jets;Axisymmetric Turbulent Jet;Particle Image Velocimetry;Constant Temperature Anemometry;Hotwire Anemometry;Turbulent Flow

Gogar, Ravikumar LeelamchandFlow Investigation in Spacers of Membrane Modules.
Master of Science, University of Toledo, 2015, Chemical Engineering
Spacers are used in membrane modules to keep membrane leaves separated. Introduction of a spacer between membrane layers create a flow channel of definite height. Typically, conventional spacers are woven or layered filaments. The spacer also disrupts fluid flow and can thereby improve mixing. The improvement in mixing comes at the cost of an increase in pressure drop. Particle Image Velocimetry (PIV) and Computational Fluid dynamics (CFD) was used to investigate the flow of water in symmetric and asymmetric spacer channels. In PIV, motion of the tracer particles in the fluid is captured to obtain the spatial distribution of velocity. 2D-PIV provides details of two components of velocity in a planar layer while 2D-3C-PIV provides details of all three components of velocity. Velocity profiles obtained from the PIV and simulations of fluid flow in spacer-filled channels are compared in terms of flow direction and velocity magnitude for different positions within the channel. Analysis of the velocity profile from PIV validates the simulations conducted using COMSOL Multiphysics and the assumptions made therein.

Committee:

Glenn Lipscomb (Committee Chair); Dong-Shik Kim (Committee Member); Sridhar Viamajala (Committee Member)

Subjects:

Chemical Engineering

Keywords:

Spacers, CFD, Particle Image Velocimetry

Zerai, BiniamCO2 Sequestration in Saline Aquifer: Geochemical Modeling, Reactive Transport Simulation and Single-phase Flow Experiment
Doctor of Philosophy, Case Western Reserve University, 2006, Geological Sciences

Storage of CO2 in saline aquifers is one way to limit the buildup of greenhouse gases in the atmosphere. Large-scale injection of CO2 into saline aquifers will induce a variety of coupled physical and chemical processes including multiphase fluid flow, solute transport, and chemical reactions between fluids and formation minerals. These issues were addressed using CO2 solubility modeling, simulation using geochemical reaction, 1-D reactive transport and Particle Image Velocimetry (PIV).

Comparison of CO2 solubility model against experimental data suggest that Duan and Sun (2003) CO2 solubility model (DS-CSM) accurately modeled solubility of CO2 in brine for range of temperatures, pressures and salinities. Modeling under equilibrium, path-of-reaction and kinetic rate using a reactor type Geochemists Workbench demonstrate that dissolution of albite, K-feldspar, and glauconite, and the precipitation of dawsonite and siderite are very important for mineral trapping of CO2.

A 1-D reactive transport was developed based on CO2 solubility model that take in to account the high salinity of Rose Run brine and a module that calculates the equilibrium constants based on temperature and pressure. The results indicate that the extent of sequestration through solubility and mineral trapping is sensitive to the choice of CO2 solubility model and the fugacity of CO2. Reactive transport modeling underscores in the long-run siderite and dawsonite minerals are important sink in trapping CO2 in the Rose Run Sandstone but over a short time-scale the hydrodynamic trapping plays a crucial role. The calculated storage capacity using DS-CSM suggest that for the first 100 years, 90 percent of the injected CO2 trapped as free CO2 whereas 6 percent are trapped in dissolve form and the rest sequestered in minerals.

Micro-scale single-phase flow through a network model of porous rock was investigated using experimental and numerical analysis. PIV with refractive index matching was developed to map velocity of pore-scale fluid flow through acrylic two-dimensional network without chemical reaction. Experimentally determined velocity vectors for single-phase flow through pore bodies and adjoining throats as well as for the outlet of the flow cell were compared with numerical simulations of flow through the cell using FLUENT computer code.

Committee:

Beverly Saylor (Advisor)

Keywords:

CO2 sequestration; Reactive transport simulation; Rose Run Sandstone; Geochemical modeling; Particle Image Velocimetry

Rinehart, Aidan WalkerA Characterization of Seal Whisker Morphology and the Effects of Angle of Incidence on Wake Structure
Master of Science in Mechanical Engineering, Cleveland State University, 2016, Washkewicz College of Engineering
Seal whiskers have been found to produce unique wake flow structures that minimize self-induced vibration and reduce drag. The cause of these wake features are due to the peculiar three-dimensional morphology of the whisker surface. The whisker morphology can be described as an elliptical cross section with variation of diameter in the major and minor axis along the length and, angle of incidence, rotation of the elliptical plane with respect to the whisker axis, α at the peak and β at the trough. This research provided a more complete morphology characterization accomplished through CT scanning and analysis of 27 harbor and elephant seal whisker samples. The results of this study confirmed previously reported values and added a characterization of the angle of incidence finding that the majority of angles observed fall within ±5° and exhibit a random variation in magnitude and direction along the whisker length. While the wake effects of several parameters of the whisker morphology have been studied, the effect of the angle of incidence has not been well understood. This research examined the influence of the angle of incidence on the wake flow structure through series of water channel studies. Four models of whisker-like geometries based on the morphology study were tested which isolate the angle of incidence as the only variation between models. The model variations in angle of incidence selected provided a baseline case (α = β = 0°), captured the range of angles observed in nature (α = β = -5°, and α = β = -15°), and investigated the influence of direction of angle of incidence (α = -5°, β = -5°). The wake structure for each seal whisker model was measured through particle image velocimetry (PIV). Angle of incidence was found to influence the wake structure through reorganization of velocity field patterns, reduction of recovery length and modification of magnitude of Tu. The results of this research helped provide a more complete understanding of the seal whisker morphology relationship to wake structure and can provide insight into design practices for application of whisker-like geometry to various engineering problems.

Committee:

Wei Zhang, PhD (Advisor); Ibrahim Mounir, PhD (Committee Member); Shyam Vikram, PhD (Committee Member)

Subjects:

Aerospace Engineering; Aquatic Sciences; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

seal; whisker; PIV; biomimicry; fluid dynamics; particle image velocimetry; bio-engineering; engineering; mechanical engineering; aerospace engineering; experimental fluid dynamics;

Benton, Stuart IraCapitalizing on Convective Instabilities in a Streamwise Vortex-Wall Interaction
Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering
Secondary flows in turbomachinery and similar engineering applications are often dominated by a single streamwise vortex structure. Investigations into the control of these flows using periodic forcing have shown a discrete range of forcing frequency where the vortex is particularly receptive. Forcing in this frequency range results in increased movement of the vortex and decreased total pressure losses. Based on the hypothesis that this occurs due to a linear instability associated with the Crow instability, a fundamental study of instabilities in streamwise vortex-wall interactions is performed. In the first part of this study a three-dimensional vortex-wall interaction is computed and analyzed for the presence of convective instabilities. It is shown that the Crow instability and a range of elliptic instabilities exist in a similar form as to what has been studied in counter-rotating vortex pairs. The Crow instability is particularly affected by the presence of a solid no-slip wall. Differences in the amplification rate, oscillation angle, Reynolds number sensitivity, and transient growth are each discussed. The spatial development of the vortex-wall interaction is shown to have a further stabilizing effect on the Crow instability due to a “lift-off” behavior. Despite these discoveries, it is still shown that amplitude growth on the order of 20% is possible and transient growth mechanisms might result in an order-of-magnitude of further growth if properly initiated. With these results in mind, an experiment is developed to isolate the streamwise vortex-wall interaction. Through the use of a vortex generating wing section and a suspended splitter plate, a stable interaction is created that agrees favorably in structure to the three-dimensional computations. A small synthetic jet actuator is mounted on the splitter plate below the vortex. Phase-locked stereo-PIV velocity data and surface pressure taps both show spatial amplification of the disturbance in a frequency range which agrees well with the prediction for the Crow instability. An analysis of the vortex response shows a primarily horizontal oscillation of the vortex column which strongly interacts with the secondary vortex structure that develops in the boundary layer.

Committee:

Jeffrey Bons, Ph.D. (Advisor); Mohammad Samimy, Ph.D. (Committee Member); James Gregory, Ph.D. (Committee Member); Jen-Ping Chen, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

active flow control; vortex; linear stability; synthetic jet actuator; wind tunnel; particle image velocimetry; turbomachinery; low pressure turbine;

Tomac, Mehmet NazimInternal Fluid Dynamics and Frequency Characteristics of Feedback-Free Fluidic Oscillators
Doctor of Philosophy, The Ohio State University, 2013, Aero/Astro Engineering
In this work, the internal fluid dynamics and frequency characteristics of feedback-free fluidic oscillators are investigated experimentally and numerically. The internal flow field of various scale oscillators was extracted using a refractive index-matched Particle Image Velocimetry (PIV) technique with the help of a PIV phase averaging method and a new sensor setup for simultaneous frequency measurements in refractive index matching fluid. Three different operating regimes (low flow rate, transition and high flow rate regions) and the fluid dynamics of the oscillating behavior in these regimes are revealed with PIV measurements. Flow topologies extracted with PIV measurements differ in these three flow regimes and were found to exhibit various flow features. Frequency measurements were conducted with the use of various experimental techniques including a method that allows non-intrusive measurement. The frequency characteristics were varied depending on properties such as the working fluid, scale and cavity geometry of the fluidic oscillator. Non-dimensional parameters were defined by taking the effects of these variables into account to allow effective comparison of fluidic oscillator designs. Furthermore, 33 modified designs were also tested to provide support for future fluidic oscillator modifications.

Committee:

James W. Gregory, PhD (Advisor); Mohammad Samimy, PhD (Committee Member); Mei Zhuang, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

experimental fluid dynamics; refractive index matched particle image velocimetry; flow control; flow control actuators; fluidic oscillator; feedback-free fluidic oscillator; jet interactions; jet bifurcations

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

Cuppoletti, Daniel RSupersonic Jet Noise Reduction with Novel Fluidic Injection Techniques
PhD, University of Cincinnati, 2013, Engineering and Applied Science: Aerospace Engineering
Supersonic jets provide unique challenges in the aeroacoustic field due to very high jet velocities, shock associated noise components, flow dependence on jet expansion, and stringent performance requirements. Current noise suppression technology for commercial and military jet engines revolves around using chevrons or mechanical vortex generators to increase mixing near the nozzle exit, subsequently reducing peak turbulence levels in the mixing region. Passive noise control methods such as mechanical chevrons cause thrust loss throughout the flight envelope and performance can vary with the engine operating condition. Development of active noise control methods have the potential of improved performance throughout the flight envelope and the benefit of being deactivated when noise control is unnecessary. Fluidic injection of air into a supersonic jet is studied as an active control method with an emphasis on understanding the physics of the problem and identifying the controlling parameters. An experimental investigation with computational collaboration was conducted to understand the effect of nozzle design on supersonic jet noise and to develop various fluidic injection techniques to control noise from a supersonic jet with a design Mach number of 1.56. The jet was studied at overexpanded, ideally expanded, and underexpanded conditions to evaluate the effects throughout the operational envelope. As a passive noise control method, the internal contour of a realistic nozzle was modified to investigate the effect on acoustics and performance. Thrust was improved up to 10% with no acoustic penalties through nozzle design, however it was found that the shock noise components were highly sensitive to the shock structure in the jet. Steady fluidic injection was used to generate vorticity at the trailing edge of the nozzle showing that noise reduction is achieved through vorticity generation, modification of the shock structure, and interference with the screech feedback mechanism by decoupling the phase relationship between jet turbulence and shock spacing. Reduction of shock noise was found to be optimum at an intermediate injection pressure due to shock weakening from the fluidic injectors and injector interactions with the jet shock-expansion structure. Large-scale mixing noise reduction was shown to depend on the vorticity strength and circulation. Unprecedented reduction of OASPL up to -8.5 dB were achieved at the peak noise direction through strong jet mixing and rapid collapse of the potential core. Pulsed fluidic injection was investigated to understand the acoustic benefits and drawbacks of unsteady injection. Valve frequency response up to 500 Hz was achieved but noise reduction dropped off above 100 Hz due to poor flow response as verified by hot-wire and dynamic pressure measurements. At low pulse frequencies it was found that moderate noise reduction could be achieved with less flow than steady injection, but in general the mixing noise reduction scaled with the time integrated mass flow injection. It was discovered that the different components of supersonic jet noise had different characteristic response times to unsteady injection. Analysis of high speed shadowgraph images and acoustic spectra was used to identify time response of the jet during the unsteady injection cycle.

Committee:

Ephraim Gutmark, Ph.D., D.Sc. (Committee Chair); Steve Martens, Ph.D. (Committee Member); Awatef Hamed, Ph.D. (Committee Member); Jeffrey Kastner, Ph.D. (Committee Member); David Munday, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Jet Noise;Aeroacoustics;Fluid Dynamics;Particle Image Velocimetry;Acoustics;Supersonic

Doucet, Daniel JosephMeasurements of Air Flow Velocities in Microchannels Using Particle Image Velocimetry
Master of Sciences (Engineering), Case Western Reserve University, 2012, EMC - Aerospace Engineering
The knowledge of the flow field in microchannels is becoming increasingly important with the advent of the ionic wind pump and other microscale heat removal devices. The understanding of this flow field will lead to more effective and improved designs. Non-intrusive microscale particle image velocimetry (PIV) utilizing a microscopic objective lens is used to obtain the velocity field in microchannels. The scales of these channels are similar to those encountered in such devices as the ionic wind pump. Microchannels with dimensions ranging from 0.8 mm to 2 mm are used. Computational fluid dynamics (CFD) models are used to replicate each test, with varying inlet conditions and mesh densities. The CFD flow fields are compared to the PIV results for validation purposes, with relative errors between CFD and PIV typically between 2% and 10%. The agreement between the experimental data and computational results ranged from acceptable to excellent, validating this method. The channel with lowest aspect ratio consistently showed the largest agreement between experimental and numerical values.

Committee:

Jaikrishnan R. Kadambi, PhD (Advisor); J. Iwan D. Alexander, PhD (Committee Member); Vikas Prakash, PhD (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

particle image velocimetry; computational fluid dynamics; microchannel; experimental fluid mechanics

Nessler, Chase A.Characterization of Internal Wake Generator at Low Reynolds Number with a Linear Cascade of Low Pressure Turbine Blades
Master of Science in Engineering (MSEgr), Wright State University, 2010, Mechanical Engineering

Unsteady flow and its effects on the boundary layer of a low pressure turbine blade is complex in nature. The flow encountered in a low pressure turbine contains unstructured free-stream turbulence, as well as structured periodic perturbations caused by upstream vane row wake shedding. Researchers have shown that these conditions strongly influence turbine blade performance and boundary layer separation, especially at low Reynolds numbers. In order to simulate these realistic engine conditions and to study the effects of periodic unsteadiness, a moving bar wake generator has been designed and characterized for use in the Air Force Research Labs low speed wind tunnel. The layout is similar to other traditional squirrel cage designs, however, the entire wake generator is enclosed inside the wind tunnel, up-stream of a linear cascade. The wake shed from the wake generator was characterized by its momentum deficit, wake width, and peak velocity deficit. It is shown that the wakes produce a periodic unsteadiness that is consistent with other wake generator designs.

The effect of the periodic disturbances on turbine blade performance has been investigated at low Reynolds number using the highly loaded, AFRL designed L1A low pressure turbine profile. Wake loss measurements, pressure coefficient distribution, and particle image velocimetry was used to quantify the L1A blade performance with unsteady wakes at a Reynolds number of 25,000 with 0.5% and 3.4% free-stream turbulence. Wake loss data showed that the inclusion of periodic wakes reduced the profile losses by 56% compared to steady flow losses. Previous pressure coefficient distributions showed that the L1A blade profile, under steady flow conditions, has non-reattaching separated flow along the suction surface. With the inclusion of the periodic wakes, the pressure coefficient profile revealed that the flow separation had been dramatically reduced to a small separation bubble.

The wake passing event was split into six phases and captured using two-dimensional planer PIV. The interaction between the passing wakes and the separation bubble was noted. The bubble was observed to grow in size between passing wakes, but was only able to achieve a fraction of the original level of separation. The streamlines through the unrestricted blade passage were able to better follow the blade profile, indicating an improved exit flow angle with lower losses. The data shows that the wake generator was successfully implemented into the wind tunnel and is able to properly simulate blade row interactions.

Committee:

Mitch Wolff, PhD (Committee Chair); James Menart, PhD (Committee Member); Haibo Dong, PhD (Committee Member); Rolf Sondergaard, PhD (Committee Member); George Huang, PhD (Other); John Bantle, PhD (Other)

Subjects:

Engineering; Fluid Dynamics; Mechanical Engineering; Technology

Keywords:

low pressure turbine; unsteady flow; wake generator; unsteady wakes; particle image velocimetry; L1A;