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Henning, James CMEASUREMENT OF AIR FLOW VELOCITIES IN MICROSIZED IONIC WIND PUMPS USING PARTICLE IMAGE VELOCEMITRY
Master of Sciences (Engineering), Case Western Reserve University, 2013, EMC - Aerospace Engineering
The knowledge of the flow fields inside of microsized ionic wind pumps has become more important as the need for smaller and more efficient heat removal devices has increased. Understanding these flow fields will help optimize the ionic wind pumps. Non-intrusive microscale particle image velocemity (PIV) utilizing a microscopic objective lens is used to obtain the flow field inside of the ionic wind pump. Voltages ranging from 1700 to 2000 V are used, as well as seeded flow rates of 1.5 and 1.84 L/min. Computational models are used to qualitatively verify the flow fields. The effects of voltage and seed flow rate are also compared. The computational and PIV flow fields are shown to be very similar. It is shown that as the voltage applied to the ionic wind pump increased, the maximum velocity inside of the ionic wind pump increased, ranging from 1.71 m/s to 3.19 m/s. The average mass flow rate inside of the device also increased as the voltage increased, ranging from .0009 g/s to .0019 g/s. It is also shown that the seed flow rate has little effect on the PIV flow field obtained.

Committee:

Jaikrishnan Kadambi, Dr. (Advisor); Alexis Abramson, Dr. (Committee Member); Yasuhiro Kamotani, Dr. (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

PIV; Microchannels; Ionic Wind; Ionic Wind Pump; Micro-PIV; Heat Removal

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

Renjie, KeExperimental and CFD investigations of the fluid flow inside a hydrocyclone separator with an air core
Master of Sciences (Engineering), Case Western Reserve University, 2015, EMC - Mechanical Engineering
Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions, which are considered to be multi-phase systems. Numerous valuable studies have been conducted in recent years to investigate the flow fields inside hydrocyclones. However, much of the information regarding the performance of cyclones in the literature has limitations, based on in some part on the respectively current-available theoretical models, and much of it cannot be considered as completely applicable to most real-world applications; many of the studies investigated the flow fields within extremely simplified hydraulic designs that are not representative of the complex geometries or large sizes which are typical in industry. Therefore, in this study, the two phase flow system inside the actual hydraulic geometry of a milling circuit hydrocyclone was explored with the aid of both computational and experimental techniques (Particle Image Velocimetry). In this study, the flow field with an air core has been investigated; in essence, the research was a two-phase problem, which caused some challenges on both the computational and experimental sides. The computational modelling was conducted using Star CCM+, a commercial Computational Fluid Dynamics (CFD) software package. Within its built-in mesh generator, a mesh domain containing more than 700,000 unstructured cells was created in a Cartesian coordinate system. In order to improve the numerical calculation accuracy and provide a logical and meaningful comparison with the experimental results, different numerical models were used: the Reynolds Stress Turbulence Model (RSM), Large Eddy Turbulence Model (LES), and the Volume of Fluid multiphase model to handle the air core. The second order discretization scheme was used for both turbulence models. The velocity and pressure contours belonging to various plane sections will be presented and discussed. Additionally, the computational studies also focused on the prediction of the dimensions and shape of the air core. Particle Image Velocimetry (PIV) was used for the experimental measurements. The model hydrocyclone was made of optically clear acrylic. Refractive index matching was achieved using sodium iodide aqueous solution (63.3% NAI by weight) to facilitate PIV measurements. 10 µm silver coated hollow glass spheres were introduced into the flow as tracing particles. Different section planes of hydrocyclone were selected as planes of interest and then were divided into several fields of view (FOV). Two dimensional experimental velocity vector maps were obtained in each of the fields of view. Numerical results are compared to the experimental data. A more physically accurate air volume fraction contour was obtained when the Large Eddy Turbulence model was applied with the Volume of Fluid Multi-phase model, as compared to the RSM model. The shape and diameter of the air core were in good agreement with the experimental results, and the physical time of the air core generation calculated from the simulation approximated to the time scale observed in the experiments.

Committee:

Jaikrishnan Kadambi, Dr. (Committee Chair); Bo Li, Dr. (Committee Member); Vikas Prakash, Dr. (Committee Member); John Furlan, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Hydroyclone separator; PIV; CFD

Woods, Nathan MichaelPHASE-LOCKED PIV INVESTIGATION OF THE EFFECTS OF THE BLOWING RATIO OF A PULSED VORTEX GENERATOR JET IN A LOW-PRESSURE TURBINE
Master of Science in Engineering (MSEgr), Wright State University, 2007, Mechanical Engineering
At very high altitudes the Reynolds number flow through the low pressure turbine section of the gas turbine engine can drop below 25,000. At these low Reynolds numbers the flow is laminar and extremely susceptible to separation which can lead to increased losses and reduced lift. Small jets of air injected through the suction surface of the airfoil, called Vortex Generator Jets (VGJs), have been shown successful in suppressing separation and maintaining attached flow. Pulsing of these jets has been shown to be as effective as steady jets while reducing the amount of mass flow needed. An experiment using Particle Image Velocimetry (PIV) was set up to study the interaction of the VGJ flow with the main flow. A cascade of Pratt and Whitney Pack-B turbine blades were mounted in the test section of a low speed wind tunnel at Wright Patterson Air Force Base. On the middle six blades were rows of 1mm VGJ holes. The VGJ holes were oriented with a 30o pitch angle and 90o skew angle. The pitch angle is the angle the jet makes with the surface of the turbine blade while the skew angle is the angle the jet makes with the cross-flow. Blowing ratios, a ratio of the jet velocity to the cross-flow velocity, of 0.5, 1, and 2 were examined. These three blowing ratios were selected because they represent when the cross-flow momentum dominates the fluid interaction (B=0.5); when the momentums of the jet flow and cross-flow are equal (B=1); and when the momentum of the jet flow dominates the interaction. Blowing ratios of 0.5 and 1 were studied for pulsing frequencies of 10Hz and 0.4Hz while the blow ratio of 2 was studied only with 10Hz pulsing. A duty cycle of 50% was used for both pulsing frequencies. The two pulsing frequencies allowed data to be taken to show how the pulsed VGJ maintains attached flow (10Hz) and how the pulsed VGJ suppresses the separation bubble (0.4Hz). Results show that jets interacting with separated flow are able to suppress the separation bubble almost immediately for a blowing ratio of 1 and 0.5. The results for suppression and separation growth show the response of the crossflow is very similar in magnitude and timing between the two blowing ratios. The results for the 10Hz pulsing frequency show blowing ratios of 0.5, 1, and 2 are effective. A blowing ratio of 2 is undesirable because it carries more momentum than is needed and would therefore use more massflow than the B=1 or 0.5 case. Results from the B=0.5 case suggest that a blowing ratio of 0.5 is near the minimum effective blowing ratio.

Committee:

Mitch Wolff (Advisor)

Keywords:

Turbine; Pack-B; Pak-B; separation; Low Pressure Turbine; Vortex Generator Jets; PIV

Webb, CharlesSeparation and Vorticity Transport in Massively-Unsteady Low Reynolds Number Flows
Master of Science in Engineering (MSEgr), Wright State University, 2009, Mechanical Engineering

There is no doubt that nature has existed as the very inspiration for many of technological achievements of today. Flight is no exception though our conventional methods of flight seem to be completely devoid of any flapping modes commonly seen in insects and birds. This is because the unsteady characteristics of natures keen flight capabilities is very difficult to study. However, as our computational and experimental methods of investigation have improved, our imagination again begins to turn to this one aspect of flight that has eluded man thus far. Birds and more specifically insects are capable of flying at such slow speeds and on such small scales that man’s understanding of aerodynamics begins to breakdown and fails to account for the force necessary for insects to fly. This has led to serious complications in the design of a small semi-autonomous flying robot or Micro Air Vehicle (MAV) that the military as well as a few civilian organizations have high interest in for multiple purposes.

This thesis uses a user-defined computational Navier Stokes solver, called Vicar3d for reasons discussed within this thesis, as well as information from an experimental facility to test some basic concepts inherent to flapping foils such as the ability of the angle of attack to predict either interaction with the airfoil and the wake and/or the loads history. Also, whether the selection of the airfoils has any effect on the wake or loads history as well, mainstream flapping foil literature has mainly concentrated on using conventional airfoils commonly employed in fixed wing aircraft. It was the intention of the author of this thesis to test airfoils that were shaped from actual cross-sections of actual insect species as these foils have shown greater performance in static testing. Additionally, some interesting phenomena was discovered along the course of these studies and an unconventional type of flapping motion resulted that was studied to determine possible applications to MAVs with the motions’ higher performance capabilities.

It was found that the existing definition of the effective angle of attack for a flapping foil is either erroneous or simply insufficient information to predict either wake interaction or loads history with no obvious relationship between the angle of attack and loads time traces. Finally, the proper selection of airfoil, most notably those inspired by wing cross sections from specific insect species has very little effect on the wake interaction, but oddly enough seems to have an impact on the lift generated. Comparing performance from these cross-sections to the performance of more conventional cross-sections showed considerable increases making them excellent candidates for future MAVs. Also the unconventional “limp wrist” motion that was discovered by doubling the frequency of the pitch over the plunge displayed favorable performance characteristics give an intelligent selection of the pivot point. Pivot points closer to the leading edge of the airfoil showed remarkable averaged thrust and lift coefficients and pivot points closer to the trailing edge of the airfoil showed very high values of lift, unfortunately also showed high values of drag as well. All conclusions seem to point to the fact that there is still much to be learned in this area of unsteady aeronautics as there seems to be hundreds of parameters and options to exercise.

Committee:

Haibo Dong, PhD (Committee Chair); Michael Ol, PhD (Committee Member); James Menart, PhD (Committee Member); Yanhua (Felix) Wu, PhD (Committee Member); George P.G. Huang, PhD (Other); Joseph F. Thomas, Jr., PhD (Other)

Keywords:

airfoil; plunge; angle of attack; motion; PIV; REYNOLDS NUMBER; wing

AlAdawy, Ahmed SEffects of Turbulence on NOx Emissions from Lean Perfectly-Premixed Combustion
PhD, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering
Effect of turbulence on NOx emissions is studied for a perfectly-premixed combustor running on methane/air at the mixture inlet temperature of 495 K and the combustor pressure of 5 atm over a range of equivalence ratios (0.54 - 0.85). Turbulence level is varied by a factor of 2-3 by changing the length of a portion of channels in a perforated plate on which the flame is stabilized. Simultaneous PIV and OH-PLIF measurements are used to calculate the relevant turbulence parameters such as turbulence intensity and turbulence mixing time scales, and define the flame structure such as average flame height and hence flame zone residence time scales, respectively. Effect of turbulence level is found to have negligible effect on NOx emissions level. NOx emissions are predicted by using a partially-stirred reactor (PaSR) model in CHEMKIN-PRO package with the measured turbulence parameters as the input. The modeling results agree very well with the measured NOx emission level but show that it slightly increases with the increase of turbulence level.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Ahmed M ElKady, Ph.D. (Committee Member); Bassam Sabry Mohammad Abdelnabi, Ph.D. (Committee Member); Shaaban Abdallah, Ph.D. (Committee Member); San-Mou Jeng, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

turbulence;NOx;premixed combustion;Partially-Stirred Reactor;PIV;PLIF

Moore, Kenneth JayLarge Scale Visualization of Pulsed Vortex Generator Jets
Master of Science in Engineering (MSEgr), Wright State University, 2005, Mechanical Engineering
Moore, Kenneth Jay. M.S., Department of Mechanical and Materials Engineering, Wright State University, 2005. Large Scale Visualization of Pulsed Vortex Generator Jets. The use of small jets of air has proven to be an effective means of flow control on low Reynolds number turbine blades. Pulsing of these jets has also shown benefits in reducing the amount of air needed to achieve the same level of flow control. An experiment using Hot Wire Anemometry and Particle Image Velocimetry (PIV) has been used to investigate how these pulsed jets interact with the boundary layer to help keep the flow attached. A 25x scaled jet in a flat plate has been utilized. The 25.4 mm diameter jet has a pitch angle of 30° and a skew angle of 90°. Pitch angle is defined as the angle the jet makes with the surface of the plate, and the skew angle is the angle that the projection of the jet on the surface makes with the crossflow. The jet was pulsed at both 0.5 Hz and 4 Hz with varying pulse durations (duty cycles), as well as various blowing ratios (ratio of the jet velocity to the freestream velocity). Duty cycles of 10, 25, 50, and100 percent were implemented at a blowing ratio of unity. Blowing ratios of 0.5, 1, 2, and 4 were implemented at a 50% duty cycle and at 0.5 Hz. Velocity and vorticity planes were obtained at various spanwise locations and used in the characterization of the jetflow. Both the free jet as well as the jet in crossflow were studied. A calibration experiment was also performed using PIV on a rotating disk. The calibration experiment was successful and the PIV results averaged a 1.56% error. The hot wire experiment with the free jet showed that the starting vortex is a key event at the beginning of each cycle, and the end of each cycle included a “kick-back” and a suction effect that could also have an influence on the boundary layer. The PIV experiment was performed first on the free jet, and results were comparable to the hot wire results. When the PIV experiment was performed on the jet in crossflow, it was clear that both the beginning and ending events of the jet cycle were keys to eliminating or delaying flow separation.The effect of the beginning and ending events can be used to keep the flow attached for longer periods of time by increasing the frequency of the jet pulse. Due to limitations of the setup, higher frequency cases could not be studied. However, the experiment was successful in controlling a separated crossflow for blowing ratios greater than unity. The larger blowing ratios resulted in larger attachment size, and were able to sustain attachment for longer time periods.

Committee:

Mitch Wolff (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

PIV; Flow Control; Separation Control; VGJ; Pulsed Jets

MA, ZHANHUAINVESTIGATION ON THE INTERNAL FLOW CHARACTERISTICS OF PRESSURE-SWIRL ATOMIZERS
PhD, University of Cincinnati, 2002, Engineering : Aerospace Engineering
The performance of liquid fuel atomizer in gas turbine combustor has direct effects on flame stability, combustion efficiency, and pollutant emissions. Therefore, further understanding of the underlying physics of these atomizers is one of the primary requirements for advanced gas turbine combustor design. Simplex atomizers are commonly used in air-breathing gas turbine engines because they produce good atomization characteristics and are relatively simple and inexpensive to manufacture. Internal flow characteristics of simplex nozzles play a very important role on the atomizer performance. So it is of great practical interest to examine the relationships between internal flow characteristics, nozzle design variables, and important spray features. Part I of this dissertation revealed the detailed flow structure inside simplex atomizers through the DPIV and LDV study. The internal flow field is generally symmetric except very near the inlet slot plane. The velocity profiles are very similar at different axial locations within the swirl chamber. The discharge parameters were measured and used to examine the correlations from previous researchers. Detailed flow field information was linked with the discharge parameters to obtain more insight into the nozzle performance. The relationship between the internal flow characteristics and discharge parameters confirmed that the internal flow structure plays a very important role on the atomizer performance. Part II presents the internal flow structure of large-scale simplex nozzles at two different working-fluid/ambient-fluid density ratios. The effects of density ratio, Reynolds number and orifice geometry on the internal flow field were examined by using a 2-D LDV probe. At the higher density ratio, Reynolds number and orifice geometry has little impact on the internal flow field. At the lower density ratio, the orifice contraction angle has little effect on the internal flow field, whereas the expansion angle can significantly affect the internal flow structure. A dominant frequency was found from the velocity frequency analysis, which indicates that the internal flow is controlled by certain dominant frequency. A dimensionless dominant frequency, similar to the Strouhal number in the flow past a cylinder, was defined using the orifice diameter and mean axial velocity in the orifice. In the part III of this dissertation, the internal flow field of the simplex atomizer with macrolaminated geometry was measured by using the refractive index matching fluid method and DPIV system. In the swirl chamber, the liquid flow is unsteady and exhibits 3-D features, which is more evident as the flow rate increases. In the orifice, the liquid flow is more uniform and axisymmetrical. The discharge parameters were measured and compared with the correlations from previous researchers.

Committee:

Dr. San-Mou Jeng (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

simplex nozzle; pressure-swirl atomizer; internal flow; index matching fluid method; PIV; LDU

Rejent, AndrewExperimental Study of the Flow and Acoustic Characteristics of a High-Bypass Coaxial Nozzle with Pylon Bifurcations
MS, University of Cincinnati, 2009, Engineering : Aerospace Engineering

The thrust of this thesis is to initiate an investigation into the acoustic effects related to the presence of a pylon installed on a high bypass ratio turbofan engine. It is well known that the presence of a pylon bifurcation generates an asymmetric sound field and modifies the characteristics of the exhaust flow. This study was designed to gain an understanding between these two results of the pylon’s presence. To accomplish this, a pylon was designed and built to modify the existing bypass ratio 5 nozzle in the Aeroacoustic Test Facility at the University of Cincinnati’s Gas Dynamics and Propulsions Laboratory. This pylon and bottom bifurcation modifies the baseline nozzle in a manner geometrically similar to that of a real engine configuration.

Experiments were carried out to measure the acoustic properties of the pylon configuration and understand their connection to the observed flow field. Both near and far field recordings were made of the baseline nozzle and the pylon nozzle at several azimuthal positions. Velocimetry measurements were also taken for these configurations.

It was seen that the classic pylon effects were present on the tested configuration; the core flow was turned towards the pylon, the fan stream was directed away from the pylon. The resulting far field and near field signatures were asymmetric. In the far-field, the presence of the pylon at the highest bypass cycle condition exhibited a maximum increase in noise production of 2.2 EPNL dB, at the sideline angle, and a minimum increase of 1.1 EPNL dB directly under the pylon. Increasing the shear velocity lowered the increase in sound production due to the pylon, but the azimuthal variation was largely unaffected.

A chevron nozzle, an existing noise reduction technology, was tested on the pylon nozzle configuration to study how the pylon affects the acoustic benefits of this technology across a range of cycle conditions. Also, a new technology known as an internal chevron nozzle was designed and tested with the baseline and pylon configurations. This internal chevron nozzle was designed as an alternative to the existing chevron technology; intended to reduce the sensitivity to shear velocities exhibited by traditional chevron nozzles.

The 8LP core chevron reduced the EPNL of the baseline nozzle by up to 1.6 dB, and the internal chevron nozzle provided up to a 0.8 EPNL dB reduction. However, the presence of the pylon modified the effectiveness of these nozzles. The chevron nozzle increased sound production at high shear velocity, but reduced noise up to 2.0dB for lower shear cases. The effectiveness of the internal chevron nozzle grew at both the medium and low shear conditions for all azimuthal positions, up to a 1.3 EPNL dB reduction. However, reductions seen at high shear velocity were reduced by the presence of the pylon. The noise reduction of the internal chevron nozzle was less than the chevron nozzle, but its design was successful in being less dependent on the cycle condition.

Committee:

Dr. Ephraim Gutmark (Committee Chair); Dr. Shaaban Abdallah (Committee Member); Dr. Mark Turner (Committee Member); Dr. John Wojno (Committee Member)

Subjects:

Acoustics; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

jet noise; acoustics; aeroacoustics; pylon; far-field; near-field; piv; jet-pylon interaction; EPNL

Zhou, XinquanMeasurement and Modeling of the Liquid-phase Turbulence in Adiabatic Air-water Two-phase Flows with a Wide Range of Void Fractions
Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering
The current work focuses on the measurement and modeling of liquid-phase turbulence in adiabatic air-water two-phase flow with a relatively wide range of void fractions. The purpose of this research work is to understand and accurately predict two-phase flow behavior. Emphasis is placed on the liquid-phase turbulence characteristics for different flow regimes. A state-of-the-art particle image velocimetry (PIV) was used to perform liquid-phase turbulence measurements on two flow channels, a circular pipe with an inner diameter (ID) of 50 mm at OSU and a rectangular channel with a cross section dimension of 30 mm x 10 mm at Virginia Tech, respectively. Three local measurement ports were used to study the flow development along the test section. An advanced optical phase separation method, namely planar laser-induced fluorescence (PLIF), was applied to separate the liquid-phase particles from bubbles in the flow. An image pre-processing scheme was developed and imposed on the two-phase flow PIV images to remove remaining noise and therefore improve phase separation. The combination of the optical phase separation method and image pre-processing scheme proved capable of effectively reducing the noise in the two-phase flow PIV images and therefore increasing the measurement accuracy. The PIV measurement uncertainty analysis, as an integral part of the measurements, was conducted to assess the confidence in the measurement results. Different approaches were adopted to address different important uncertainty sources in the measurements. In addition, multiple benchmark tests were performed to assess the measurements and to explore the feasibility of the PIV measurements in high void fraction flow conditions. The measured liquid-phase velocity associated with the void fraction distribution measured by a four-sensor conductivity was used to calculate the superficial liquid velocity, which was benchmarked by the flow rate reading from a magnetic flow meter. The results obtained by using the PIV system were quantitatively and qualitatively compared with those obtained in the literature which used different instruments at similar flow conditions. Reasonable agreement was found between the present data and those found in the literature. Extensive data of the liquid-phase turbulence in air-water two-phase flow was acquired using the PIV-PLIF system. The void fraction of the flow conditions varied from 0 to 40% for the circular pipe at OSU and approximately to 60% for the rectangular channel at VT. The flow regimes studied include single-phase, bubbly, cap-bubbly, slug, and churn-turbulent flows with the superficial liquid velocity ranging from 0.5 to 3.4 m/s. The turbulence characteristics include the axial mean velocity, turbulence intensity, axial and radial velocity fluctuation, Reynolds stress, and relative velocity. A liquid-phase turbulence model for two-phase bubbly flows was developed based on the two-phase extension of the single-phase k-e model. Similar to the single-phase k-e model, the two-phase k-e model has all the counterparts except an extra interfacial transfer term, which indicates additional turbulence generated due to the interaction between the two phases. To assess the liquid-phase turbulence model, numerical simulations were performed using Fluent 14.0 and the results were compared against the experimental data. A reasonable agreement of the kinetic energy prediction was found in several bubbly flow runs.

Committee:

Xiaodong Sun, Dr. (Committee Chair); Marcello Canova, Dr. (Committee Member); Richard Christensen, Dr. (Committee Member); Jeffrey Sutton, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Two-phase flow; PIV; Turbulence; Void fraction; Measurement; Modeling; Nuclear Engineering

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;

Bunjevac, Joseph AntunPIV Analysis of Wake Structure of Real Elephant Seal Whiskers
Master of Science in Mechanical Engineering, Cleveland State University, 2017, Washkewicz College of Engineering
Seals are able to accurately detect minute disturbances in the ambient flow environment using their whiskers, which is attributed to the exceptional capability of their whiskers to suppress vortex-induced vibrations in the wake. To explore potential applications for designing smart flow devices, such as high-sensitivity underwater flow sensors and drag reduction components, researchers have studied how the role of some key parameters of whisker-like morphology affect the wake structure. Due to the naturally presented variation in size and curvature along the length of whiskers, it is not well understood how a real whisker changes the surrounding flow and the vortex shedding behavior. This study aims to detail the flow statistics around a real Elephant Seal whisker at low Reynolds numbers (i.e. one hundred) using particle image velocimetry in a water channel. Wake flow structures are inspected and compared between two Elephant Seal whiskers (undulating) and a California Sea Lion whisker (smooth), along with idealized whisker-like models. Undulating whiskers significantly change the mean flow properties and suppress turbulence intensities in the wake region as compared to the smooth whisker at the tested Re. The undulating whiskers are able to create a low turbulence intensity area directly behind the whiskers trailing, vproviding these whiskers with their Vortex Induced Vibration reduction properties.

Committee:

Wei Zhang, Ph.D. (Advisor); Mounir Ibrahim, Ph.D. (Committee Member); Thijs Heus, Ph.D. (Committee Member)

Subjects:

Biomechanics; Fluid Dynamics

Keywords:

Undulating whiskers, vortex dynamics, seal whiskers, elephant seal, harbor seal, PIV, water channel, flow, vortex induced vibration, VIV, turbulence, vortex supression, undulations

Geyman, Matthew KennethWing/Wall Aerodynamic Interactions in Free Flying, Maneuvering MAVs
Master of Science (M.S.), University of Dayton, 2012, Aerospace Engineering
Micro Air Vehicles (MAVs) are small remotely piloted air vehicles that can be flown between or inside of buildings for military or surveillance purposes. This type of flight in the urban environment involves many aerodynamic hazards. The research in this thesis investigates how the aerodynamic interactions between a maneuvering MAV’s wingtip vortex and its distance away from a building wall could affect the MAV’s flight controls. Free flight particle image velocimetry (PIV) testing and wind tunnel testing are used to investigate the aerodynamic interactions between a MAV wingtip vortex and a wall. Elliptical instabilities and a vortex rebound off of the wall are discovered in the PIV testing while the wind tunnel results show a higher aircraft coefficient of lift near the wall. All of these results force the aircraft to experience a rolling motion while flying along a wall. It is imperative that a MAV anticipate this motion and adjust its flight controls in order to accurately fly along a wall and successfully complete its mission in an urban environment.

Committee:

Aaron Altman, PhD (Committee Chair); Gregory Parker, PhD (Committee Member); Markus Rumpfkeil, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

MAV; UAV; aerodynamics; wall effect; wingtip vortex; PIV; wind tunnel; micro air vehicle; vicon

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

Gancedo, MatthieuEffect of Self Recirculation Casing Treatment on the Performance of a Turbocharger Centrifugal Compressor
PhD, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering
Increase in emission regulations in the transport industry brings the need to have more efficient engines. A path followed by the automobile industry is to downsize the size of the internal combustion engine and increase the air density at the intake to keep the engine power when needed. Typically a centrifugal compressor is used to force the air into the engine, it can be powered from the engine shaft (superchargers) or extracting energy contained into the hot exhaust gases with a turbine (turbochargers). The flow range of the compressor needs to match the one of the engine. However compressors mass flow operating range is limited by choke on the high end and surge on the low end. In order to extend the operation at low mass flow rates, the use of passive devices for turbocharger centrifugal compressors was explored since the late 80's. Hence, casing treatments including flow recirculation from the inducer part of the compressor have been shown to move the surge limit to lower flows. Yet, the working mechanisms are still not well understood and thus, to optimize the design of this by-pass system, it is necessary to determine the nature of the changes induced by the device both on the dynamic stability of the pressure delivery and on the flow at the inlet. The compressor studied here features a self-recirculating casing treatment at the inlet. The recirculation passage could be blocked to carry a direct comparison between the cases with and without the flow feature. To grasp the effect on compressor stability, pressure measurements were taken in the different constituting elements of the compressor. The study of the mean pressure variations across the operating map showed that the tongue region is a limiting element. Dynamic pressure measurements revealed that the instabilities generated near the inducer when the recirculation is blocked increase the overall instability levels at the compressor outlet and propagating pressure waves starting at the tongue occurred, different in nature from rotating stall. The flow velocity was also measured at the inlet of the compressor by means of planar PIV measurements. The case without recirculation showed strong back flow occurrence at low MFR on the shroud of the inlet passage due to tip recirculation. With recirculation, this back flow was significantly reduced improving the overall stability. However, with the current recirculation channels design, there is an efficiency penalty and the recirculated flow introduces non-homogeneities in the mixing region. Finally, to explore experimentally the effect of variations of the casing treatment, several different designs were tested. It was seen that modifications of the supporting rib shape impacted the efficiency. Also, improvements on the surge line were obtained with flow reinjection near the inducer in the direction of the main flow at low speeds and with induced counter swirl for all speeds.

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:

Turbocharger;Surge;Centrifugal compressor;PIV;Pressure measurements;Experimental

Smith, Todd J.Development, Design, Manufacture and Test of Flapping Wing Micro Aerial Vehicles
Doctor of Philosophy (PhD), Wright State University, 2016, Engineering PhD
The field of FlappingWing Micro Air Vehicles (FWMAV) has been of interest in recent years and as shown to have many aerodynamic principles unconventional to traditional aviation aerodynamics. In addition to traditional manufacturing techniques, MAVs have utilized techniques and machines that have gained significant interest and investment over the past decade, namely in additive manufacturing. This dissertation discusses the techniques used to manufacture and build a 30 gram-force (gf) model which approaches the lower limit allowed by current commercial off-the-shelf items. The vehicle utilizes a novel mechanism that minimizes traditional kinematic issues associated with four bar mechanisms for flapping wing vehicles. A kinematic reasoning for large amplitude flapping is demonstrated namely, by lowering the cycle averaged angular acceleration of the wings. The vehicle is tested for control authority and lift of the mechanism using three servo drives for wing manipulation. The study then discusses the wing design, manufacturing techniques and limitations involved with the wings for a FWMAV. A set of 17 different wings are tested for lift reaching lifts of 38 gf using the aforementioned vehicle design. The variation in wings spurs the investigation of the flow patterns generated by the flexible wings and its interactions for multiple flapping amplitudes. Phase-lock particle image velocimetry (PIV) is used to investigate the unsteady flows generated by the vehicle. A novel flow pattern is experimentally found, namely “trailing edge vortex capture” upon wing reversal for all three flapping amplitudes, alluding to a newly discovered addition to the lift enhancing effect of wake capture. This effect is believed to be a result of flexible wings and may provide lift enhancing characteristics to wake capture.

Committee:

George Huang, Ph.D. (Advisor); James Menart, Ph.D. (Committee Member); Zifeng Yang, Ph.D. (Committee Member); Richard Cobb, Ph.D. (Committee Member); Michael Oppenheimer, Ph.D. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

FWMAV; MAV; flapping wings; vortex capture; Phase-Lock; PIV; trailing edge vortex capture; vortex capture; flexible wings

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

Grage, Danielle L.Study of jet exhaust noise sources and their mitigation through lobed mixers and chevrons
MS, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
As regulations to reduce noise pollution become more stringent, understanding the noise sources within jet exhaust and how they can be mitigated is important as jet noise is one of the dominant contributors to the overall acoustic signature of an engine. The objective of this study is to understand the effects two exhaust mixing devises, lobed mixers and chevrons. To this end, three basic configurations were studied: a confluent mixer and nozzle (Confluent), a buried lobed mixer with a circular nozzle (MixerA), and a buried lobed mixer with a chevron nozzle (Chevron+MixerB). The hardware was tested at GE Aviation’s Cell-41 – Anechoic free jet facility. Acoustic data was acquired, as well as flowfield data using Particle Image Velocimetry (PIV). RANS-based (Reynolds Averaged Navier-Stokes) Computational Fluid Dynamics (CFD) analyses were also conducted to complement the test data. Three operating conditions were considered, defined by their shear level, which is a function of the average mixed velocity of the core flow: low shear (80%), nominal shear (100%), and high shear (112%). The results from the PIV and CFD were used for mutual validation and very good correlation was observed for the MixerA configuration with good correlation overall. The acoustic results were consistent with the flowfield analysis, as well as previous studies, and showed that the presence of mixing devices can provide a low frequency acoustic benefit with some modest increase in high frequency noise, due to increasing mixing near the nozzle and reduced turbulence downstream. An additional high frequency noise source was also identified for MixerA at the high shear condition, which was not present for other configurations. This source showed similar features to the High Mach Lift (HML) previously reported by Tester et al and Garrison et al in 2005. It is thought to be the result of shear layer interaction with a normal shock, resulting from localized pockets of supersonic flow that form near the nozzle exit plane. This source was absent for the Chevron+MixerB configuration and more work must be done to better understand the phenomenon.

Committee:

Ephraim Gutmark, PhDDSc (Committee Chair); Shaaban Abdallah, PhD (Committee Member); Jeffrey Kastner, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

jet exhaust;lobed mixer;acoustic;chevron;PIV;CFD

ELSHAMY, OMAR MEXPERIMENTAL INVESTIGATIONS OF STEADY AND DYNAMIC BEHAVIOR OF TRANSVERSE LIQUID JETS
PhD, University of Cincinnati, 2007, Engineering : Aerospace Engineering
The injection of a liquid jet into a crossflow of air provides a means of higher penetration and rapidly mixing liquid fuel and air for combustion applications. The structure of the spray, formed is investigated. To attain this goal, the problem is divided into the following tasks which involve: (1) characterize the penetration, breakup, atomization, mixing, and breakup of liquid jet injected into crossflow at conditions relevant to real engine conditions, (2) establish an understanding of the structure of that transverse jet near the injection point, and (3) study the dynamics behavior of the transverse jet and propose new method to control the transverse liquid jet in crossflow. Two breakup modes have been observed, column and surface breakup. The agreement between the breakup map developed in the present study with the existing ones is quite good. The agreement between the PIV and LDV measurements was good and within 10% accuracy. PIV probe has been proven as a good tool to capture the aero-structure of spray generated by liquid jet in cross flows by comparing its results with the corresponding LDV results. Droplet velocity exhibits a minimum in the spray core. As the momentum ratio increases, the transverse location as well as the droplet velocity of the spray core increase, while the droplet velocity at the outer periphery decreases. Elevating the ambient pressure slightly decreases the penetration and decreases the spray spread. At higher ambient pressure, shorter axial distance is required for the droplet to follow the air flow. Mechanically exciting the transverse liquid jet can have a significant effect on the mixing, spreading, and penetration of the liquid jet in crossflow. The penetration of the jet may increase by more than 40 % while the spread of the jet by 100 % at an axial location of about ten diameters downstream of the injection point. The optimum excitation Strouhal number is about 0.0047, at which homogenous droplet average velocity distribution and maximum interaction between the liquid jet and the crossflow are observed. Novel correlations that describe the outer and inner boundaries of the dynamic jet are developed.

Committee:

Dr. San-Mou Jeng (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Dynamic Jet; PIV; LDV; Crossflow; Atomozation; LPP; Excitation; Modulation

Huang, Shih kangAn Experimental Investigation on the Micro Air Vehicle
Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering
An experimental investigation was conducted to study the flow characteristics of the flow around the flapping wings of a four-wing flapper as well as the lift and thrust coefficient of a four-wing flapper. In the present study, a clap-and-fling type of four-wing flapper was designed and manufactured by using several flexible materials, such as PET film, latex, and aluminized Mylar. Different cross-strut patterns and dimensions of wings were manufactured and tested to optimize the wing designs. In addition to taking the lift and thrust measurements using a highly sensitive force moment sensor unit, a high-resolution Particle Image Velocimetry (PIV) system was employed to achieve detailed flow field measurements to quantify the evolution of the unsteady vortex flow structure around the wings and in the downstream of the flapper. The force measurements were analyzed in correlation with the detailed flow measurements to elucidate the underlying physics to improve our understanding for an optimized flexible wing design and to achieve better performance for flapping wing micro air vehicles. A woofer loudspeaker was employed at the test section where the four-wing flapper was placed to generate sound distances. The effect of different frequencies and amplitudes of sound waves on the aerodynamic performance was investigated. A sensitive force moment sensor unit and PIV system were utilized to measure the lift and thrust and to take detailed flow field measurements to quantify the effect of sound waves on the flow and wing deformation. The force measurements were analyzed in correlation with the detailed flow measurements and qualitative wing deformation data to elucidate underlying the physics in to improve our understanding of the effect of acoustic disturbances on flexible wings and the overall aerodynamic performance of MAVs.

Committee:

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

Subjects:

Engineering; Mechanical Engineering; Technology

Keywords:

Micro Air Vehicle PIV

HARIHARAN, PRASANNAFree field characterization of High Intensity Focused Ultrasound (HIFU) transducers using acoustic streaming
PhD, University of Cincinnati, 2008, Engineering : Mechanical Engineering

This work described in this dissertation addresses the problem of characterizing HIFU fields at clinically relevant power levels. Two new techniques are presented for determining the intensity distributions of HIFU transducers in liquid media. The new techniques are based upon the acoustic streaming field generated by absorption of the HIFU beam in the liquid. The streaming field is quantified using a flow visualization technique called Digital Particle Image Velocimetry (DPIV). From the experimental streaming field, acoustic intensity and power are calculated using two different approaches: i) Iterative method and ii) Direct method. In the iterative approach, an optimization algorithm is developed to compute the acoustic intensity field by iteratively minimizing the difference between a theoretical estimate of the streaming velocity and the one measured experimentally. In the direct streaming method, the differential operations of the Navier-Stokes equations are performed directly upon the experimentally measured streaming velocity to get the acoustic field.

The acoustic fields estimated using the streaming techniques were validated with the standard measurement techniques such as hydrophone scans and radiation force balance (RFB) at low power levels. Intensity fields and acoustic powers predicted using the streaming methods were found to agree within 20% with measurements obtained using hydrophones and RFB. Comparisons performed in the range 100 to 1000 W/cm2 focal intensity showed differences between the direct methods and the iterative streaming technique to be less than 20%. Besides acoustic intensity fields, the streaming technique may be used to determine other important HIFU parameters, such as beam tilt angle or absorption of the propagation medium.

Finally, the effect of acoustic non-linearities on the accuracy of the streaming techniques was studied. Results suggest that the methods as presented here are accurate in the moderate intensity regime - intensities that are high enough to potentially damage to conventional hydrophones, but below the levels where nonlinear propagation effects are appreciable. The upper range of this moderate intensity regime is approximately 1000 W/cm2. Consequently, to measure intensities beyond about a thousand W/cm2, modifications have to be made in the technique to account for nonlinear effects emerging during sound propagation.

Committee:

Rupak K. Banerjee, Dr. (Committee Chair); Matthew R. Myers, Dr. (Committee Member); Neville G. Pinto, Dr. (Committee Member); Jay Kim, Dr. (Committee Member); Michael Kazmierczak, Dr. (Committee Member)

Subjects:

Acoustics; Biomedical Research; Mechanical Engineering

Keywords:

HIFU; Acoustic Streaming; Transducer characterization; PIV