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Williams, Charles PLow Pressure Turbine Flow Control with Vortex Generator Jets
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
In an aircraft engine at high altitude, the low-pressure turbine (LPT) section can experience low-Reynolds number (Re) flows making the turbine blades susceptible to large separation losses. These losses are detrimental to the performance of the turbine and lead to a roadblock for “higher-lift” blade designs. Accurate prediction of the separation characteristics and an understanding of mitigation techniques are of the utmost importance. The current study conducts simulations of flow control techniques for the Air Force Research Laboratory (AFRL) L2A turbine blade at low-Re of 10,000 based on inlet velocity and blade axial chord. This blade was selected for its “high-lift” characteristics coupled with massive separation on the blade at low-Re which provides an excellent test blade for flow control techniques. Flow control techniques involved various configurations of vortex generator jets (VGJs) using momentum injection (i.e. jet blowing). All computations were executed on dual-topology, multi-block, structured meshes and incorporated the use of a parallel computing platform using the message passing interface (MPI) communications. A high-order implicit large eddy simulation (ILES) approach was used in the simulations allowing for a seamless transition between laminar, transitional, and turbulent flow without changing flow solver parameters. A validation study was conducted involving an AFRL L1A turbine blade which showed good agreement with experimental trends for cases which controlled separation in the experiments. The same cases showed good agreement between different grid sizes. The differences between experimental and numerical results are largely attributed to differences in the setup. That is, the simulation did not include freestream turbulence or wind-tunnel wall effects. The flow control study conducted for the L2A blade showed a small degree of separation control for jets placed just downstream (DS) of the separation point. A limited study was conducted with jets moved upstream (US) of the natural separation point which showed an increase in effectiveness for one of the VGJs. This indicates a sensitivity of VGJ location relative to the point of separation. For the DS VGJs, separation control, increased as blowing ratio (BR) was increased and jet blowing frequency (F+) decreased. The increase in jet efficacy with decreasing F+ was unexpected and is mostly attributed to the jets being downstream of the separation location and having a low duty cycle (10%). Turbulent kinetic energy frequency spectra also show the presence of jet harmonics in the flow downstream of the best performing VGJs which dramatically increased in power when the VGJ was moved upstream. The most effective jet found in this study had BR=3.0, F+=3.02, and was located at x/Cx=0.53. This VGJ provided a 42.1% reduction in normalized integrated wake loss. One follow-on simulation was conducted taking the most effective VGJ and increasing the blowing ratio from BR=3.0 to 8.0. This provided a decrease in the amount of separation, nearly eliminating separation with only a small separation bubble remaining. This VGJ was able to provide a 42.8% reduction in normalized integrated wake loss. This work was conducted in coordination with the AFRL and has been approved for public release, case number: 88ABW-2016-1657.

Committee:

Kirti Ghia, Ph.D. (Committee Chair); Rolf Sondergaard, Ph.D. (Committee Member); Shaaban Abdallah, Ph.D. (Committee Member); Urmila Ghia, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Low Pressure Turbine;Vortex Generator Jet;Active Flow Control;Implicit Large Eddy Simulation;L2A;Low Reynolds Number Flow

Ma, ZhengImpeller Power Draw Across the Full Reynolds Number Spectrum
Master of Science (M.S.), University of Dayton, 2014, Chemical Engineering
The objective of this work is to gain information that could be used to design full scale mixing systems, and also could develop a design guide that can provide a reliable prediction of the power draw of different types of impellers. To achieve this goal, the power number behavior, including three operation regimes, the limits of the operation regimes, and the effect of baffling on power number, was compared across the full Reynolds number spectrum for Newtonian fluids in a laboratory-scale agitator. Six industrially significant impellers were tested, including three radial flow impellers: D-6, CD-6, and S-4, and also three axial flow impellers: P-4, SC-3, and HE-3. Results in laminar regime indicate that baffling has no effect on power number in this operation regime. There is an inversely proportional relationship between power number and Reynolds number. The upper limit for this operation regime should be lower than 10, the limit commonly noted in the literature. The product of power number and Reynolds number in this particular regime is approximately proportional to the number of blades for these six impellers; however, other shape factors that were not included in this study also contribute to it. In turbulent operation, baffling has a significant effect on power number: the power number for most impellers remains relatively constant in the baffled configuration while that for unbaffled configuration decreases with increasing Reynolds number. The impeller blade number is not the dominant factor that affects power number in this regime. Two hydrofoil impellers, SC-3 and HE-3, exhibit much lower power numbers when compared with the other impellers. Additionally, the impellers with higher power numbers in baffled tank tend to have lower ratios between unbaffled power number and average baffled power number when comparing at same Reynolds number. No difference between two configurations, baffled and unbaffled, exists at low Reynolds number end of transitional regime, and the difference starts at intermediate Reynolds number and increases with an increase of Reynolds number. In the baffled configuration, four out of six impellers exhibit a minimum power number. In the unbaffled configuration, power numbers drop with increasing Reynolds number throughout the entire transitional regime for all impellers. The ratio of unbaffled to turbulent average power number for the six impellers retains a consistent order through the entire Reynolds number range with two high efficiency impellers having the highest ratio, then pitched blade impeller, and three radial flow impellers having the lowest ratios.

Committee:

Kevin Myers (Committee Chair); Eric Janz (Committee Member); Robert Wilkens (Committee Member)

Subjects:

Chemical Engineering

Keywords:

Power draw on different impellers; Newtonian Fluid; the Reynolds number limits for operation regimes; the effect of baffling on power number; minimum baffled power number; average baffled turbulent power number

Thake, Michael PatrickInvestigation of a Laminar Airfoil with Flow Control and the Effect of Reynolds Number
Master of Science, The Ohio State University, 2011, Aero/Astro Engineering
Wind tunnel tests are performed on a NACA 643-618 airfoil at Reynolds numbers of 6.4x104, 1.8x105, 1.0x106, and 4.0x106 in order study several aspects of a laminar airfoil. Studies of flow control, separation bubbles and the effect of Reynolds number are the major topics of this effort. The tools used for investigation are surface pressure measurements, wake surveys, particle image velocimetry, hot-film anemometry, surface-oil flow visualization, and infrared imaging in order to view the problem from many angles. Preliminary testing at a Reynolds number of 64,000 determined that four distinct flow regimes exist with respect to angle of attack: weak laminar separation, moderate laminar separation, laminar separation bubble, and strong leading edge laminar separation. A portion of the study investigates the cause of such dynamic flow physics. Attempts are then made to employ flow control to induce or imitate the laminar separation bubble. By creating the laminar separation bubbles, significant lift increase and drag reduction are realized over a broader range of angles of attack. Normal blowing, suction, and zigzag tape are used, which are all well-characterized devices and have the potential to enhance lift and reduce drag. Lift is increased significantly and separation is delayed in three of the four regions as a result of control, where the region of no change is when the laminar separation bubble is already in effect. It is observed that the optimal flow control device changes between regimes because different flow physics are required to induce a change. Studies of Reynolds number scaling found that the lift increased and drag decreased as Reynolds number increased. It is important to note that the laminar separation bubble becomes naturally effective at most angles of attack by a Reynolds number of 180,000. Therefore, the value of flow control diminishes except in regions where strong leading edge separation is the limiting element of the airfoil. This research suggests that the laminar airfoil can be controlled in an energy efficient manner such that high performance is gained across all flight regimes with straightforward actuation.

Committee:

Jeffrey Bons, PhD (Advisor); James Gregory, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering

Keywords:

laminar airfoil; aerodynamics; flow control; Reynolds number; separation

Stanley, Daniel C.Experiments in Vortex Formation of Plunging & Flapping Flat Plates
Master of Science (M.S.), University of Dayton, 2008, Aerospace Engineering

Reynolds number, Strouhal number, and formation number are insufficient to quantify the flow properties of a flapping wing system. These parameters do not take enough information from the input variables into account. As part of the current study, the velocity profile and angle of attack were varied during a single pure plunge flapping stroke using an infinite aspect ratio flat plate. Although the velocity profile was either a constant velocity or quarter-sine velocity, the average Reynolds number was held constant at 3000. Strong differences in the flow structure, both qualitatively and quantitatively, were obtained. A new metric is proposed that is able to take these differences in the input variables into account. This metric utilizes the theory of maximum work potential and statistical regressions of the experimental data in order to obtain a model of the experimental parameter space. With this model, estimates of the desired outputs can be made given values for the inputs.

The main portion of this study focuses on the differences in flow structure, using qualitative and quantitative techniques, due to finite aspect ratio and flapping about a hinge point. Data at various spanwise and chordwise locations were taken in order to analyze the leading edge, trailing edge, and tip vortices. A small study was also conducted on the effects of changing Reynolds number.

It was found that for the infinite aspect ratio plate, using a quarter-sine velocity profile, instead of a constant velocity profile, enhances the production of circulation. Operating at a slight angle of attack (85° instead of 90°) also enhances circulation production; however, operating at a large angle of attack (60° instead of 90°) has the opposite effect due to pinch-off of both the leading and trailing edge vortices. Hinging the wing at the root and using a finite aspect ratio causes the constant velocity profile to produce higher values of circulation than the quarter-sine velocity profile. This trend is the opposite of that seen for the infinite aspect ratio cases. It was also found that flapping in this highly three-dimensional manner greatly hinders the production of circulation as compared to the infinite aspect ratio, pure plunge experiments.

Committee:

Aaron Altman, PhD (Advisor); Michael Ol, PhD (Committee Member); Raymond Kolonay, PhD (Committee Member)

Subjects:

Fluid Dynamics

Keywords:

vortex formation; low Reynolds number fluid dynamics; formation parameter; formation time; formation number;

Haugen, Christina G. M.Numerical Investigation of Thermal Performance for Rotating High Aspect Ratio Serpentine Passages
Doctor of Philosophy, The Ohio State University, 2014, Mechanical Engineering
Three-passage serpentines with aspect ratios of 1:1, 1:2, and 1:6 were numerically studied using computational fluid dynamics and heat transfer. A CFD modeling methodology was systematically developed that balanced accurately resolving the flow physics with minimizing the computational cost, targeting industrial preliminary design requirements. The method was benchmarked against two published data sets consisting of turbulators on the leading and trailing walls in skewed 45 deg; to the flow offset parallel configuration with a fixed rib pitch to height ratio of 10 and a rib height to hydraulic diameter of 0.1 to 0.058, utilizing Reynolds numbers of 25,000 and 50,000 and rotation number ranging from 0 and 0.25. Predictions were completed to study the effects of changing aspect ratio between 1:1, 1:2, and 1:6 and changing rotation numbers from 0 to 0.3. The 1:6 aspect ratio predictions varied from the lower aspect ratios. Differences included flow recirculation along the leading wall of the first passage for rotation numbers greater than or equal to 0.2 and high Nusselt numbers immediately downstream of the turn for the wall opposite the Coriolis force direction. Overall enhancement values for the test section showed the aspect ratio has a greater influence on Nusselt numbers than rotation.

Committee:

Michael Dunn, Ph.D (Advisor); Jen-Ping Chen, Ph.D (Committee Member); Randall Mathison, Ph.D (Committee Member); Mohammad Samimy, Ph.D (Committee Member); Jeffrey Rambo, Ph.D (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

aspect ratio; serpentine; heat transfer; Nusselt number; rotation number; Reynolds number; Dean vortices; coriolis force; buoyancy force; turbulator; computational fluid dynamics; CFD; blade; internal passages; turbine; mid-circuit; pumping; HOST; OSU

Brezina, Aron JonMeasurement of Static and Dynamic Performance Characteristics of Electric Propulsion Systems
Master of Science in Engineering (MSEgr), Wright State University, 2012, Mechanical Engineering
Today's unmanned aerial vehicles are being utilized by numerous groups around the world for various missions. Most of the smaller vehicles that have been developed use commercially-off-the-shelf parts, and little information about the performance characteristics of the propulsion systems is available in the archival literature. In light of this, the aim of the present research was to determine the performance of various small-scale propellers in the 4.0 to 6.0 inch diameter range driven by an electric motor. An experimental test stand was designed and constructed in which the propeller/electric motor was mounted in a wind tunnel for both static and dynamic testing. Both static and dynamic results from the present experiment were compared to those from previous studies. For static testing, the coefficient of thrust, the coefficient of propeller power, and the overall efficiency, defined as the ratio of the propeller output power to the electrical input power, were plotted versus the propeller rotational speed. For dynamic testing, the rotational speed of the propeller was held constant at regular intervals while the freestream airspeed was increased from zero to the windmill state. The coefficient of thrust, the coefficient of power, the propeller efficiency and the overall efficiency were plotted versus the advance ratio for various rotational speeds. The thrust and torque were found to increase with rotational speed, propeller pitch and diameter, and decrease with airspeed. Using the present data and data from the archival and non-archival sources, it was found that the coefficient of thrust increases with propeller diameter for square propellers where D = P. The coefficient of thrust for a family of propellers (same manufacturer and application) was found to have a good correlation from static conditions to the windmill state. While the propeller efficiency was well correlated for this family of propellers, the goodness of fit parameter was improved by modifying the propeller efficiency with D/P.  

Committee:

Scott K. Thomas, PhD (Committee Chair); Haibo Dong, PhD (Committee Member); Zifeng Yang, PhD (Committee Member); Mitch Wolff, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Mechanical Engineering

Keywords:

Propeller; Small Unmanned Aerial Vehicle; UAV; Electric Propulsion System; Advance Ratio; Low Reynolds Number; Wind Tunnel Testing

Liang, ZongxianComputational Analysis of Vortex Structures in Flapping Flight
Doctor of Philosophy (PhD), Wright State University, 2013, Engineering PhD
Vortex structures and vortical formation in flapping flight are directly related to the force production. To analyze the connection between vortex structures and aerodynamic performance of flapping flight, we have developed highly efficient algorithms for large-scale flow simulations with moving and deforming bodies. To further understand the underlying mechanisms of force generation caused by the coherent structures of the vortex formation, a new analysis method has been developed to measure the influence of Proper Orthogonal Decomposition (POD) modes on aerodynamic forces. It is challenging to finish three-dimensional Direct Numerical Simulations (DNS) of insect flight in a limited amount of time. In the current work, the Modified Strongly Implicit Procedure (MSIP) has been implemented into an existing Computational Fluid Dynamics (CFD) solver, as a smoother for the multigrid method to solve the pressure equation and an iterative method to solve the momentum equation. The new solver is capable of performing a 17-million-mesh simulation within 10 days on a single core of an Intel i5-3570 chip at 3.4GHz, nearly 10 times faster than the traditional Line-SOR solver. Based on this numerical tool, the free flight of a dragonfly for eight-and-a-half wing beats is studied in detail. The results show that the dragonfly has experienced two flight stages during the flight. In a maneuver stage, wing-wake interaction generated by the fore- and hindwings attenuates the total force by 8% (peak value). In contrast, in an escape stage, the fore- and hindwings collaborate to generate force which is 8% larger than when they flap separately. Especially, the peak force on the forewing is significantly increased by 42% in a downstroke and this enhancement is known to associate with a distorted trailing edge vortex, as demonstrated by a theoretical model based on wake survey methods. The movement of the trailing edge vortex is a response to the motion of the hindwing. When the fore- and hingwings flap closely with only a short distance existing between them, the hindwing exerts a wall effect to the trailing edge vortex. Vortex formation of flapping flight and force generation are considered to be closely linked; however, it is difficult to accurately determine the influence of an individual vortex on the overall aerodynamic performance. Here, as an alternative, we examine the influence of coherent structures, which are thought as special types of vortices in terms of kinetic energy. First, wake structures are decomposed by the POD method and the most energetic vortices are extracted. Then, a pressure corrected POD Reduced-Order Models (ROM) method is used to verify that the POD modes can capture the dynamics of the flows. Finally, the force of POD modes is quantified by a new method, termed the POD mode Force Survey Method (POD-FSM). The process is applied to investigate the flow field generated by a two- or three-dimensional plate undergoing a pitching-plunging motion. Superposition of force of the POD modes shows a good agreement with the DNS result. In addition, it is found that some POD modes have zero lift, and some have zero thrust. These force behaviors are related to symmetry of POD mode. According to the symmetry or antisymmetry about the streamwise line (or the crossflow plane in three-dimension), the POD modes can be qualitatively grouped into two sets. Combining POD modes in the same set can help to decompose the flow into thrust- and lift-producing flows. It is found that the force acting on the plate is a linear combination of the force of the thrust- and lift-producing flows and their interactions. Because two flows have different frequency spectrum, it is possible to perform flow control with respect to frequency to achieve the desired aerodynamic performance.

Committee:

Haibo Dong, Ph.D. (Advisor); George Huang, Ph.D. (Committee Member); Joseph Shang, Ph.D. (Committee Member); Keke Chen, Ph.D. (Committee Member); Aaron Altman, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics

Keywords:

Low Reynolds Number Flow; Vortex Structure; CFD; Dragonfly; Free Flight; Proper Orthogonal Decomposition; POD; Reduced-Order Models; ROM; Force; POD Mode Force Survey Method; Symmetry

Jenson, RichardNumerical solution of weakly separated supersonic flows at high Reynolds number /
Doctor of Philosophy, The Ohio State University, 1977, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Reynolds number;Boundary layer

Oberly, Charles EvanThe effect of heat current modulation on the velocity fields and the critical Reynolds number in helium II /
Doctor of Philosophy, The Ohio State University, 1971, Graduate School

Committee:

Not Provided (Other)

Subjects:

Physics

Keywords:

Helium;Reynolds number

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

Kerze, David JamesPerformance Characteristics of an Innovative Wind Power System
Master of Science in Mechanical Engineering, Cleveland State University, 2007, Fenn College of Engineering
This project entails a study of a wind energy recovery system that utilizes a unique three-dimensional spiral structure to amplify wind speed and direct it toward pluralities of turbines. The system is comprised of an outer spiral shell, internal support structure, turbines, and mechanisms for positioning the turbines to face the prevailing wind. Computational Fluid Dynamics (CFD) analyses were conducted to determine the wind speed amplification factors as a result of a simulated wind flow around the spiral structure. To ensure accuracy of the results, state of the art CFD techniques were applied using Gambit 2.2.30 and Fluent 6.2.16. Specifically, wind speed amplification factors were determined for 25ft and 30ft radius spiral shells. The velocity profiles of the wind flow around both spiral structures were obtained under a postulated 10mph wind speed. This resulted in a turbulent flow with a Reynolds number of 5,596,819. All analyses were run using “standard k-ε” turbulence model with the “near wall treatment” option “standard wall function”. A “y+” value of 50 was held constant in all vi simulations. The affect of the grid size on the accuracy of the results was examined. Convergence criterion was satisfied in each case. The 25ft radius spiral structure yielded an average velocity amplification factor of 1.524; while the 30ft radius resulted in an average amplification factor of 1.539. This particular information can help the designer of the system to select an appropriate overall shell size based not only on the mechanical efficiency, but also considering the cost and economical factors.

Committee:

Majid Rashidi (Advisor)

Keywords:

Wind; Turbines; Energy; Clean Energy; Green Energy; Wind Amplification; Fluent; Gambit; Wind Recovery; Reynolds Number; Mach Number; Velocity Magnitude; Velocity Contours; Spiral Structure; Numerical Methods

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

Committee:

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

Subjects:

Mechanical Engineering

Keywords:

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

da Cunha, Daise Nunes QueirozProperties of Flow Through the Ascending Aorta in Boxer Dogs with Mild Aortic Stenosis: Momentum, Energy, Reynolds Number, Womersley’s, Unsteadiness Parameter, Vortex Shedding, and Transfer Function of Oscillations from Aorta to Thoracic Wall
Doctor of Philosophy, The Ohio State University, 2009, Veterinary Biosciences

Ejection murmurs of subaortic and aortic stenosis occur commonly in the mammalian population. Boxer-dogs have a high prevalence of systolic ejection murmurs (50 to 80%). The origin of these murmurs is a subject of discussion, especially in those cases that anatomical lesions are not evident, as with many cases of mild aortic stenosis. It has been speculated that turbulence is one of the most likely genesis of these ejection murmurs. Boxer-dogs with soft murmurs provide useful model to evaluate physical factors of aortic flow that may produce murmur.

A total of 15 Boxer-dogs were evaluated with physical examination, electrocardiography, and a complete echocardiographic exam. For studies conducted in both the catheterization and NMR laboratories, 7 Boxers were induced to anesthesia for evaluation of the fluid mechanical parameters. Sounds were recorded from the ascending aorta and the torso surface in the cath-lab. S2 was used to calculate transfer function between oscillations in the heart and oscillations on the body surface.

The images to study aortic blood flow were acquired on a 1.5T Siemens MRI system for 5 locations of the ascending aorta, 3 physiological states, and 7 dogs.

Mean and peak velocity, area, Reynolds number, Womersly parameter, energy, flow, momentum, and vorticity were calculated from the velocity-encoded images using MRI. Reynolds numbers were above the critical values indicated in the literature. Re’s correlated well with momentum (r2 =0.54) and flow (r2 =0.86). Rotational velocity in CCW direction were greatest at the arch (p<0.05), clockwise vortices were greater at the root and Valsalva-sinus (p<0.05). Ten variables indicated that turbulence may have occurred at the proximal regions of the aorta. The murmur of mild aortic stenosis was originated in the proximal regions of the ascending aorta, demonstrated by the most “violent” fluid-mechanical activities in these regions. There was a mathematical relationship between intensity of oscillations within the heart generating sound and the intensity of oscillation detected on the thoracic wall as heart sound.

Committee:

Robert Hamlin (Advisor); Lawrence Feth (Committee Member); Karsten Schober (Committee Member); Orlando Simonetti (Committee Member)

Subjects:

Acoustics; Anatomy and Physiology; Animals; Fluid Dynamics; Radiology

Keywords:

Boxer dogs; systolic ejection murmur; mild aortic stenois; fluid mechanics; Reynolds number; Womersley parameter; Vorticies; Kinetic energy; momentum; Dobutamine; aucultation; catheterization; acoustics;Transfer function; heart sounds frequency and amplit

Marks, Christopher R.Surface Stress Sensors for Closed Loop Low Reynolds Number Separation Control
Doctor of Philosophy (PhD), Wright State University, 2011, Engineering PhD
Low Reynolds number boundary layer separation causes reduced aerodynamic performance in a variety of applications such as MAVs, UAVs, and turbomachinery. The inclusion of a boundary layer separation control system offers a way to improve efficiency in conditions that would otherwise result in poor performance. Many effective passive and active boundary layer control methods exist. Active methods offer the ability to turn on, off, or adjust parameters of the flow control system with either an open loop or closed loop control strategy using sensors. This research investigates the use of a unique sensor called Surface Stress Sensitive Film (S3F) in a closed loop, low Reynolds number separation control system. S3F is an elastic film that responds to flow pressure gradients and shear stress along its wetted surface, allowing optical measurement of wall pressure and skin friction. A new method for installing the S3F sensor to assure a smooth interface between the wall and wetted S3F surface was investigated using Particle Image Velocimetry techniques (PIV). A Dielectric Barrier Discharge (DBD) plasma actuator is used to control laminar boundary layer separation on an Eppler 387 airfoil over a range of low Reynolds numbers. Several different DBD plasma actuator electrode configurations were fabricated and characterized in an open loop configuration to verify separation control of the Eppler 387 boundary layer. The open loop study led to the choice of a spanwise array of steady linear vertical jets generated by DBD plasma as the control system flow effecter. Operation of the plasma actuator resulted in a 33% reduction in section drag coefficient and reattachment of an otherwise separated boundary layer. The dissertation culminates with an experimental demonstration of S3F technology integrated with a control system and flow effecter for closed loop, low Reynolds number separation control. A simple On/Off controller and Proportional Integral (PI) controller were used to close the control loop.

Committee:

Mitch Wolff, PhD (Advisor); Rolf Sondergaard, PhD (Committee Member); James Menart, PhD (Committee Member); Mark Reeder, PhD (Committee Member); Joseph Shang, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

low Reynolds number; fluid dynamics; surface stress sensitive film; flow control; separation control; S3F; plasma actuator; dielectric barrier discharge;