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Mandour Eldeeb, Mohamed FDevelopment and Assessment of Altitude Adjustable Convergent Divergent Nozzles Using Passive Flow Control
PhD, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering
The backward facing steps nozzle (BFSN) is a new developed flow adjustable exit area nozzle. It consists of two parts, the first is a base nozzle with small area ratio and the second part is a nozzle extension with surface consists of backward facing steps. The steps number and heights are carefully chosen to produce controlled flow separation at steps edges that adjust the nozzle exit area at all altitudes (pressure ratios). The BFSN performance parameters are assessed numerically in terms of thrust and side loads against the dual-bell nozzle with the same pressure ratios and cross sectional areas. Cold flow inside the planar BFSN and planar DBN are simulated using three-dimensional turbulent Navier-Stoke equations solver at different pressure ratios. The pressure distribution over the upper and the lower nozzles walls show symmetrical flow separation location inside the BFSN and an asymmetrical flow separation location inside the DBN at same vertical plane. The side loads are calculated by integrate the pressure over the nozzles walls at different pressure ratios for both nozzles. Time dependent solution for the DBN and the BFSN are obtained by solving two-dimensional turbulent flow. The side loads over the upper and lower nozzles walls are plotted against the flow time. The BFSN side loads history shows a small values of fluctuated side loads compared with the DBN which shows a high values with high fluctuations. Hot flow 3-D numerical solutions inside the axi-symmetric BFSN and DBN are obtained at different pressure ratios and compared to assess the BFSN performance against the DBN. Pressure distributions over the nozzles walls at different circumferential angels are plotted for both nozzles. The results show that the flow separation location is axi-symmetric inside the BFSN with symmetrical pressure distributions over the nozzle circumference at different pressure ratios. While the DBN results show an asymmetrical flow separation locations over the nozzle circumference at all pressure ratios.The results show that the side loads in the BFSN is 2.5% of its value in the DBN for same pressure ratio. For further confirmation of the axi-symmetric nature of the flow in the BFSN, 2-D axi-symmetric solutions are obtained at same pressure ratios and boundary conditions. The flow parameters at the nozzle exit are calculated the 3-D and the 2-D solutions and compared to each other. The maximum difference between the 3-D and the 2-D solutions is less than 1%. Parametric studies are carried out with number of the backward facing steps varied from two to forty. The results show that as the number of backward facing steps increase, the nozzle performance in terms of thrust approach the DBN performance. The BFSN with two and six steps are simulated for pressure ratios range from 148 to 1500 and compared with the DBN and a conventional bell nozzle. Expandable BFSN study is carried out on the BFSN with two steps where the nozzle operation is divided into three modes related to the operating altitude (PR). Backward facing steps concept is applied to a full scale conventional bell nozzle by adding two backward facing steps at the end of the nozzle increasing its expansion area results in 1.8% increasing in its performance in terms of thrust coefficient at high altitudes.

Committee:

Shaaban Abdallah, Ph.D. (Committee Chair); Milind Jog, Ph.D. (Committee Member); Jongguen Lee, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Backward facing steps nozzle;Altitude adaptive nozzle;Passive flow separation control;Nozzle side load reduction

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

Lakhamraju, Raghava RajuCharacterization of the jet emanating from a self-exciting flexible membrane nozzle
PhD, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering
The present research investigates the development and characterization of a novel self-exciting flexible membrane nozzle. Upon excitation (oscillations that are produced by exerting tension at the nozzle exit and passing air through it), the flexible nozzle is capable of producing time-dependent flow that is fairly consistent at a flow condition (a particular tension and volume flow rate of air). The fluidic device is a passive means of enhancing mixing as there is no external excitation mechanism. The resultant flow is self-excited over a range of conditions and produces pulsatile flow that is excited by the motion of the flexible membrane. The baseline configuration of the flexible membrane nozzle involves symmetrical placement of the edges at the nozzle exit. The exit of the nozzle offers variable area geometry, with the shape approximately resembling a variable aspect ratio ellipse. Particle Image Velocimetry (PIV) is employed to illustrate and characterize the large-scale flow structures of the jet motion and the eduction of coherent structures was performed using Proper Orthogonal Decomposition (POD). For a particular nozzle diameter, the flow conditions are controlled by the tension applied to the flexible nozzle and volume flowrate of air through it. PIV measurements have been conducted mainly along the mid-minor axis plane since the crucial flow structure interactions occur in this plane due to the nozzle operation. Based on a set of experiments conducted within the physical limitations of the nozzle, the near field of the nozzle exit was found to be governed by the interactions of two sets of large-scale vortical structures - starting vortices and entrainment vortices (features of pulsatile flows) and the exact nature of their evolution is dependent on the operating conditions. As in elliptic jets, the near field of the nozzle is found to be extremely sensitive to the initial conditions (nozzle configuration). A cross-spectral analysis is also performed in the near field of the jet using two hot-wire anemometers to characterize the evolution of large-scale flow structures for the various flow conditions. For a baseline nozzle in fully closed configuration, for a given tension at the nozzle exit, increase in volume flow tends to produce higher jet spread (more prominent at lower tensions) and increased range of turbulence production. For a particular flow rate, increase in tension results in a more symmetric jet along the centerline and high turbulence production in the near field. Under certain flow conditions, the dynamic flapping of the jet generated half-width spreading rates that exceeded that of slot nozzles. The flow characteristics are compared to that of existing nozzles that generate high mixing rates at the exit. The application of POD on the PIV information shows that the reconstructed images from few modes provide decent illustrations of the flow structures with filtered effect on the turbulent flow field. In essence, this analysis separates the oscillation of the jet from the velocity fluctuations due to the turbulent flow behavior. In the current study, with certain operating conditions, increased half-width spreading rates and enhanced centerline velocity decay can be generated. A predominant flapping jet or highly turbulent jet at the nozzle exit can be achieved by modifying the flow conditions.

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:

flow control;flexible nozzle;self-excitation;pulsatile jet;noncircular jet;starting and entrainment vortices;

Dolan, BrianFlame Interactions and Thermoacoustics in Multiple-Nozzle Combustors
PhD, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
The first major chapter of original research (Chapter 3) examines thermoacoustic oscillations in a low-emission staged multiple-nozzle lean direct injection (MLDI) combustor. This experimental program investigated a relatively practical combustor sector that was designed and built as part of a commercial development program. The research questions are both practical, such as under what conditions the combustor can be safely operated, and fundamental, including what is most significant to driving the combustion oscillations in this system. A comprehensive survey of operating conditions finds that the low-emission (and low-stability) intermediate and outer stages are necessary to drive significant thermoacoustics. Phase-averaged and time-resolved OH* imaging show that dramatic periodic strengthening and weakening of the reaction zone downstream of the low-emission combustion stages. An acoustic modal analysis shows the pressure wave shapes and identifies the dominant thermoacoustic behavior as the first longitudinal mode for this combustor geometry. Finally, a discussion of the likely significant coupling mechanisms is given. Periodic reaction zone behavior in the low-emission fuel stages is the primary contributor to unsteady heat release. Differences between the fuel stages in the air swirler design, the fuel number of the injectors, the lean blowout point, and the nominal operating conditions all likely contribute to the limit cycle behavior of the low-emission stages. Chapter 4 investigates the effects of interaction between two adjacent swirl-stabilized nozzles using experimental and numerical tools. These studies are more fundamental; while the nozzle hardware is the same as the lean direct injection nozzles used in the MLDI combustion concept, the findings are generally applicable to other swirl-stabilized combustion systems as well. Much of the work utilizes a new experiment where the distance between nozzles was varied to change the level of interaction between the two nozzles. A decrease in inter-nozzle spacing resulted in a penalty to the lean blowout point and NO\subscript{X} emissions. Particle image velocimetry shows that the nozzle spacing also has an important effect on the flowfield of the nozzles including the shape of the recirculation region and the quantitative flow velocities. In particular, interaction in the tangential velocity between the two nozzles has large effects on the swirl number and the recirculation zone. Numerical simulations of the isothermal airflows of two pilot nozzles are validated using experimental measurements and used to provide flowfield information outside of the measurement domain. At wider inter-nozzle spacings under certain reacting conditions, an alternating flow pattern develops in the combustion chamber. The shear layers of one nozzle extent into the combustion chamber whereas the inlet reactants from the other nozzle attach near the dome wall to create a very wide recirculation region. Combustion properties, including the fuel type, are shown experimentally to affect whether or not a system will develop an alternating pattern. Simplified computational models of two interacting swirling flows are used to parametrically study the effects of nozzle exit geometry and swirl number on an alternating pattern. Both parameters are shown to be potential drivers of an alternating pattern under some conditions. A hypothesis that proposes a physical mechanism explaining the alternating flow pattern, consistent with the work in this proposal and the research of other groups, is presented. When the nozzle design, flow, or combustion characteristics cause the shear layers of the adjacent nozzles to become sufficiently opposite in direction, the two flows can no longer mix. Instead, one shear layer goes underneath the other which results in the differing flow features of the adjacent nozzles.

Committee:

Ephraim Gutmark, Ph.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Milind Jog, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Gas Turbines;Combustors;Lean Direct Injection;Thermoacoustics;Nozzle Interaction;Alternating Flow Pattern

Sengupta, SoumyoInvestigation of Flow Dynamics of a Subsonic Circular to Rectangular Jet
Master of Science, The Ohio State University, 2016, Mechanical Engineering
Large Eddy Simulation based investigation is performed on a circular to rectangular Mach 0.226 jet to understand the effect of the non-axisymmetric geometry on the jet flow dynamics. The nozzle has a circular cross-section at the inlet and a 2:1 aspect ratio rectangular cross-section at the exit. The Reynolds number of the flow is 73,242 and the nozzle has an equivalent diameter of 0.054 meters. Comparison with experiments, indicate a good match of the normalized mean and rms velocities along the jet centerline. Q-criterion iso-levels confirm the existence of large hairpin like vortices, which initially are dominant along the major axis but further downstream appear along the minor axis as well. To highlight the influence of different frequency ranges, the velocity field at the core collapse location is first decomposed using Empirical Mode Decomposition (EMD). The spectrum in these different ranges is then correlated with observations along representative lip-line at the major and minor axes and the corner. The presence of the large scale structures corresponding to low frequency ranges is predominant along the corner compared to major and minor axes. The correlations provide information on the ffect of specific scales at the end of potential core along the streamwise direction. The major components of low frequency structures in the propagated signal occur between St = 0.05 and St = 0.3. The correlation analysis shows that structures formed along the corners and minor axis dominate the large scale dynamics of the flow. The Joint Probability Density Function (JPDF) analysis is used to study flow along major and minor axis of the rectangular jet as well as an equivalent circular nozzle. Variations in entrainment and ejection-like patterns along the minor and major axes of the rectangular jet are quantified. Results with an equivalent circular nozzle are compared which indicate enhanced ejection and entrainment like motions for the rectangular nozzle compared to the equivalent circular nozzle.

Committee:

Datta Gaitonde, Dr. (Advisor); Seung Hyun Kim, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Rectangular Nozzle, Subsonic, LES, Jet Flow, entrainment

Mustafa, MansoorInvestigation into Offset Streams for Jet Noise Reduction
Master of Science, The Ohio State University, 2015, Aero/Astro Engineering
This effort investigates the near field behavior of two ideally-expanded subsonic dual-stream jets. One case implements a traditional symmetric, concentric dual-stream nozzle configuration while the other imposes an asymmetric, eccentric layout to model the behavior of an offset stream. The essence of an offset stream is to force an uneven azimuthal distribution of the secondary coflow and create an outside stream that varies in thickness. Past studies have shown a benefit in acoustic propagation in the direction of the thickest coflow and the present work further analyzes this phenomenon. A LES (Large Eddy Simulation) approach is implemented to run the simulations for both cases and a number of qualitative and quantitative analyses tools are used for post-processing. A reduction in the noise levels for the lower, thicker side of the eccentric nozzle is observed in comparison to the baseline concentric case. Examination of the mean flow behavior shows a shorter, thinner primary potential core for the offset case and a faster axial velocity decay rate. The asymmetric distribution of the coflow causes varying velocity profiles in the radial direction for the top and bottom regions and consequently produces unique flow features on either side. Lower levels of shear stress and slower decay rates lead to less turbulence production on the lower side of the eccentric nozzle. An investigation into the flow structures reveals lower vorticity and weaker convective structures on the bottom which influences propagation in that direction. Two-point correlation analysis reveals the presence of smaller turbulence scales in the lower, thicker portion of the eccentric case. This is further confirmed by an Empirical Mode Decomposition (EMD) study that shows lower frequency ranges dominate the concentric near field in comparison to the eccentric. The combination of these unique features demonstrate the principles behind the acoustic benefit of implementing offset stream flows in dual-stream nozzle configurations.

Committee:

Datta Gaitonde (Advisor); Mei Zhuang (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

offset; noise reduction; jets; aerospace; aerodynamics; LES; computational simulation; jet noise; eccentric; concentric; dual-stream; nozzle

Ramasubramanian, ChandrasekarCharacterization of Near Field Spray for Impinging Doublets in Air Under High Pressure
MS, University of Cincinnati, 2014, Engineering and Applied Science: Mechanical Engineering
Atomization mechanism of gelled propellants in an impinging jet flow field is significantly different from that of non-gelled liquid propellants and is not clearly understood. In this study, rheologically matched non-Newtonian fluids which are non-reactive and non-toxic have been used as a simulant for the gelled hypergolic propellants. This study explores the effect of liquid fluid properties such as viscosity and surface tension on the liquid sheet breakup with a special emphasis on the effect of ambient pressure. Near field spray characteristics such as the sheet formation and breakup length of the liquid sheet are investigated using shadowgraph. The liquid breakup regimes have been quantitatively characterized for both non-gelled and gelled simulants over a range of flow conditions. For all fluid, the breakup length is found to decrease as the ambient pressure increases. Near-field imaging and its analysis show that the ambient pressure affects jet surface dynamics before impingement by increasing the jet surface disturbance length scale and sheet dynamics after impingement by shortening the surface wavelength, resulting in shorter breakup length with the increase of ambient pressure.

Committee:

Milind Jog, Ph.D. (Committee Chair); San-Mou Jeng, Ph.D. (Committee Member); Jongguen Lee, Ph.D. (Committee Member)

Subjects:

Engineering

Keywords:

impingment;sprays;gelled hypergolics;high pressure;regime map;doublet nozzle

Sasson, JonathanSmall Scale Mass Flow Plug Calibration
Master of Sciences, Case Western Reserve University, 2015, EMC - Aerospace Engineering
A simple control volume model has been developed to calculate the discharge coefficient through a mass flow plug (MFP) and validated with a calibration experiment. The maximum error of the model in the operating region of the MFP is 0.54%. The model uses the MFP geometry and operating pressure and temperature to couple continuity, momentum, energy, an equation of state, and wall shear. Eff ects of boundary layer growth and the reduction in cross-sectional flow area are calculated using an integral method. A CFD calibration is shown to be of lower accuracy with a maximum error of 1.35%, and slower by a factor of 100. Eff ects of total pressure distortion are taken into account in the experiment. Distortion creates a loss in flow rate and can be characterized by two di fferent distortion descriptors.

Committee:

Paul Barnhart (Advisor); Joseph Prahl (Committee Member); Kamotani Yasuhiro (Committee Member); David Davis (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

mass flow plug; control volume analysis; calibration; distortion; total pressure distortion; discharge coefficient; ASME nozzle

MOHAMED, ASHRAF ELSAIDAn Experimental Investigation of Supersonic Rectangular Over-Expanded Nozzle of Single and Two-Phase Flows
PhD, University of Cincinnati, 2008, Engineering : Aerospace Engineering
This dissertation presents the results of an experimental investigation and analysis of the supersonic rectangular over-expanded flow of single and two-phase flows. Recent interest in rectangular supersonic jets is motivated by the need to reduce plume length and acoustically excited structural loads in the exhaust system of high performance aircrafts. Semi-periodic shock structures form in the jet plumes of these vehicles during low speed flight at off design conditions. These shock cells affect the jet velocity and temperature decay as well as the jet spread rate and its acoustic field. The flow regimes and shock structure in the plume was characterized for jets in quiescent atmosphere at over-expanded conditions. Instantaneous and phase average schlieren/shadowgraph images of the internal flow and the jets are presented to show the over-expanded shock structure and jet spread rate at different nozzle pressure ratios ranged from 1.6 to 9.5. A high-pressure particle feeders have been constructed to steady feed the dispersed large particles and the seeding particle for LDA measurements at different particle loading rates. Schlieren pictures of the jets are presented to show the shock structure and jet spread rate. LDV measurements are presented for the jet flow field and the centerline velocity decay. The results indicate that the rectangular supersonic jet spread rate is greater along the minor axis and increases with the nozzle pressure ratio. The individual shock cell length, as well as, the total number of shock cells within the jet plume were found to increase with nozzle pressure ratio. In two-phase rectangular jets of gas and dispersed solid particles the shock strength was found to attenuate with increased particle loading. The design, construction and initial shakedown of the facility has been accomplished. The effort required to reach this stage has been greater than initially expected. Further more detailed data acquisitions and measurements will be accomplished in future studies.

Committee:

Awatef Hamed, Dr. (Committee Chair); Widen Tabakoff, Dr. (Committee Member); San-Mou Jeng, Dr. (Committee Member)

Subjects:

Aerospace Materials; Engineering

Keywords:

Over-Expanded; Rectangular Nozzle; Shock Train

Xiao, RuiyangThe Freezing of Highly Sub-cooled H2O/D2O Droplets
Master of Science, The Ohio State University, 2008, Environmental Science
The condensation of H2O and D2O in a supersonic Laval nozzle was investigated at different stagnation condition by using Pressure Trace Measurements (PTM) and Fourier Transformation Infrared (FTIR) spectroscopy. PTM determined several key properties highly related to nucleation such as the temperature and pressure corresponding to the onset of condensation, Ton, pon as well as the temperature and pressure corresponding to the maximum nucleation rate TJmax and Jmax. Moreover, the results from PTM provide important information for the FTIR study. The FTIR spectra of D2O and H2O nanodroplets in N2 carrier gas were measured in our nozzle. The observed spectra of D2O droplets had some clear peaks, and the shapes of the spectra changed as a function of flow rates and position in the nozzle. The broad peak of D2O between 2400 cm-1 and 2600 cm-1 was due to ν1, ν3, and overtone of ν2 in the liquid phase, and its peak area was correlated to the product of the weight fraction of condensate (g) and the density of the flowing mixture (ρ), values derived from PTM. There is good correlation between the peak area and g*ρ (p<0.001). From our FTIR H2O nanodroplets study, the same trends regarding spectral changes and flow rate were observed. Moreover, the first observation of cubic ice in our supersonic nozzle was made by FTIR spectroscopy at a location x =6 cm from the throat. The peak in the spectra was located at a frequency of 3250 cm-1. This result is consistent with previous FTIR and electron diffraction scattering studies of H2O nanodroplets done by Buch (Buch V., Bauerecker S., Devlin J. P., Buck U., and Kazimirski J. K. 2004. Int. Rev. Phys. Chem. 23. 375-433) and Huang (Huang J. F. and Bartell L. S. 1995, J. Phys. Chem. 99. 3924-3931), respectively. To determine the freezing rate from liquid phase to cubic ice, however, requires further optimization of the experimental setup and more quantitative study

Committee:

Barbara Wyslouzil, PhD (Advisor); Heather Allen, PhD (Advisor); Linda Weavers, PhD (Committee Member)

Subjects:

Chemistry

Keywords:

sub-cooled droplets; FTIR; supersonic nozzle

Seidu, IddrisuAnalytical and Numerical Validation of Nozzle Spray Measurement Data Obtained from a Newly Developed Production System
Master of Science in Mechanical Engineering, Cleveland State University, 2015, Washkewicz College of Engineering
A newly developed production test stand for measuring the spray angle of a pressure swirl atomizer was constructed and used to measure a product line of these pressure swirl atomizers – the macrospray atomizer. This new test stand, utilizing constant temperature hot wire anemometers, captures the spray angle data based on the voltage drop the hot wire probes see as they traverse the spray cone of the atomizer and as fluid droplets impinge upon the wire. Datasets acquired from the experiments are compared and correlated with computational fluid dynamics (CFD) simulation data. In addition, angles obtained from another type of spray characterization technique, the spray angle device, are also compared to see how closely CFD can predict the angle as captured by this new stand and how reliable and independent of human error it is. Another nozzle with a pressure swirl atomizer, the conventional atomizer, is also simulated to compare its agreement with experimental values obtained from the spray angle device. Finally, the datasets are compared to understand if the CFD results, when compared to the two spray characterization techniques used in this thesis for both the nozzle and atomizer can be utilized to assist in future atomizer designs. For the macrospray atomizer, it was found through the experiments that the hot wire stand predicts the spray angle more accurately within 10% error. The spray angle device measured the spray angles within an error of 29% while the CFD introduced more error into the spray angle measurement obtained, within 7% to 93%. The conventional atomizer was found to have an error up to 18% with CFD results and up to 28% with the manual spray angle device.

Committee:

Mounir Ibrahim, Ph.D. (Committee Chair); Vikram Shyam, Ph.D. (Committee Member); Ralph Volino, Ph.D. (Committee Member)

Subjects:

Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

atomization; spray; angles; hot wire anemometry; CFD; simulation; computational fluid dynamics; atomizers; atomizer; pressure swirl atomizer; spray cone; spray; nozzle; nozzles; sprays; measurement; spray angle; cone; air core; hot wire anemometers;

Maxted, Katsuo J.Experimental Investigation on Acoustic Characteristics of Convergent Orifices in Bias Flow
MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering
Oscillatory combustion dynamics in a lean, premixed, prevaporized (LPP) combustor has been a major problem in the last two decades. Within this field of study, recent work centers on thermoacoustic modeling of combustion dynamics, which requires acoustic characterization of combustor components. Acoustic characteristics of convergent orifices are experimentally investigated in a square duct to establish a reliable experimental method to determine relevant acoustic characteristics of combustor components and to better understand sound wave propagation in a combustor setting. Measurement error standards are determined by defining a maximum tolerance from acoustic pressure measurement-prediction agreements at certain locations in the duct. For variances in incident amplitude and differential pressure, nonlinear changes in absorption, transmission, and differential impedance trends are observed for all orifice geometries. These acoustic behaviors are found to be sensitive to geometry and steady flow speed.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Asif Syed, Ph.D. (Committee Member); J. Kim, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Acoustic;Impedance;Nozzle;Convergent;Orifice;Duct

Bonilla, Carlos HumbertoThe Effect of Film Cooling on Nozzle Guide Vane Ash Deposition
Master of Science, The Ohio State University, 2012, Aero/Astro Engineering
An accelerated deposition test facility was used to study the relationship between film cooling, surface temperature, and particle temperature at impact on deposit formation. Tests were run at gas turbine representative inlet Mach numbers (0.1) and temperatures (1090°C). Deposits were created from lignite coal fly ash with median diameters of 1.3 and 8.8µm. Two CFM56-5B nozzle guide vane doublets, comprising three full passages and two half passages of flow, were utilized as the test articles. Tests were run with different levels of film cooling back flow margin and coolant temperature. Particle temperature upon impact with the vane surface was shown to be the leading factor in deposition. Since the particle must traverse the boundary layer of the cooled vane before impact, deposition is directly affected by the film and metal surface temperature as well. Film coolant jet strength showed only minor effect on deposit patterns on the leading edge. However, larger Stokes number (resulting in higher particle impact temperature) corresponded with increased deposit coverage area on the shower head region. Additionally, infrared measurements showed a strong correlation between regions of greater deposits and elevated surface temperature on the pressure surface. Thickness distribution measurements also highlighted the effect of film cooling by showing reduced deposition immediately downstream of cooling holes. A set of secondary tests were also conducted to briefly study the effect of Stokes number on leading edge deposition with no cooling, in order to support conclusions from the primary tests. It was found that larger Stokes number led to an increase in rate of deposition due to a greater number of particles being able to follow their inertial trajectories and impact the vane. Implications for engine operation in particulate-laden environments are discussed.

Committee:

Jeffrey Bons, PhD (Advisor); Micheal Dunn, PhD (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Engineering

Keywords:

Deposition;film cooling;ash deposition;nozzle guide vane;deposit;heat transfer;turbine deposition;engine deposition

Murad, Mark RichardRadiation View Factors Between A Disk And The Interior Of A Class Of Axisymmetric Bodies Including Converging Diverging Rocket Nozzles
Master of Science in Mechanical Engineering, Cleveland State University, 2008, Fenn College of Engineering

A general symbolic exact analytic solution is developed for the radiation view factors including shadowing by the throat between a divergence thin gas disk between the combustion chamber and the beginning of the rocket nozzle radiating energy to the interior downstream of the nozzle contour for a class of coaxial axisymmetric converging diverging rocket nozzles. The radiation view factors presented in this thesis for the projection which are blocked or shadowed through the throat radiating downstream to the contour have never been presented before in the literature.

It was found that the curvature of the function of the contour of the nozzle being either concave up or down and the slope of the first derivative being either positive or negative determined the values used for the transformation of the Stokes Theorem into terms of x, r (radius) and f(x) for the evaluation of the line integral.

The analytical solutions from the view factors of, for example, the interior of a combustion chamber, or any radiating heat source to a disk may then be applied to the solution of the view factor of the disk to the interior of the rocket nozzle contour presented here. This modular building block type approach is what the author desires to allow the development of an interstellar matter antimatter rocket engine. The gases of this type of reaction shall approach those towards the speed of light, which shall involve a transport phenomena, which the author is looking forward to researching the solution.

Committee:

Asuquo Ebiana, PhD (Advisor); Majid Rashidi, PhD (Committee Member); John Frater, PhD (Committee Member); John Oprea, PhD (Committee Member)

Subjects:

Aerospace Materials; Astrophysics; Chemical Engineering; Computer Science; Electromagnetism; Engineering; Gases; Materials Science; Mathematics; Mechanical Engineering; Nuclear Chemistry; Nuclear Physics; Radiation; Radiology; Scientific Imaging; Transportation

Keywords:

shadowing; radiation view factor; rocket nozzle: cooling; radiation heat transfer; differential geometry; configuration factor

Soliman, Salah M.Micro-Particles and Gas Dynamics in an Axi-Symmetric Supersonic Nozzle
PhD, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
A new biolistic gene gun for micromolecular drug delivery to human skin has been developed and numerically tested. The device generates supersonic flow to accelerate the mediated microparticles to sufficient speeds to breach the outer human skin layer. The device is referred to as CDN-WPI and consists of; a high pressure gas tank, a convergent-divergent nozzle (C-D), and a constant area mixing duct. The mediated microparticles are entrained from a parallel inlet after the exit of the C-D nozzle. The gas from the high pressure tank accelerates through the C-D nozzle to supersonic speeds which in turn accelerate the powder microparticles through the constant area mixing duct to high speeds. A validated numerical procedure is used to study the two-phase flow dynamics inside the biolistic gun using different geometrical configurations. Different driver gas pressures, gas type (helium and air), adding gas swirl, microparticles types and size are considered in this study. The dimensions of the device C-D nozzle, mixing duct length, and the number of particles inlets are the geometrical configurations studied. It is found that using the CDN-WPI device requires reduced driver gas pressure by 50 % compared to the existing devices. The reduction in the gas driver pressure is a result of the elimination of the losses due to boundary layer separation found in all previous devices. The entrainment of the solid microparticles and gas from the parallel inlets precludes flow separation by energizing the boundary layer over the constant area duct walls. As a result, the CDN-WPI is more efficient and safer to use. Further validation is done using semi-empirical particle penetration calculations and the computed flow field which compare very well with the available experimental data. The axi-symmetric model has been used exclusively in all previous numerical solutions of biolistic guns. To check the validity of this assumption, the axi-symmetric results are compared with the results of 3-D model solutions with continuous particles inlet along periphery. The results compare very well which justify the axi-symmetric assumption solutions. We investigated the 3-D two-phase flow field with one, two, and four particle inlets. The 3-D simulations show that for practical and efficient gene gun device, more than one particle inlet is required.

Committee:

Shaaban Abdallah, PhD (Committee Chair); Kelly Cohen, PhD (Committee Member); Milind Jog, PhD (Committee Member); Mark Turner, ScD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

CFD;Supersonic nozzle;3-D numerical study;Biolistic Gene gun;Particles-gas flows

Bhabhe, Ashutosh ShrikantExperimental Study of Condensation and Freezing in a Supersonic Nozzle
Doctor of Philosophy, The Ohio State University, 2012, Chemical and Biomolecular Engineering

Phase transitions like condensation, vaporization, melting and freezing are ubiquitous and important in a host of applications across science and technology. A phase transition is initiated by nucleation, the process where fragments of a new phase begin to form in a supersaturated mother phase. This is followed by the growth of these fragments after they reach a critical size, and, finally, the new stable phase is formed by ageing. Understanding phase transitions, especially the nucleation step, has been an active area of research for over a century with approaches ranging from the development of theory, the refinement of experiments and, more recently, direct in silico simulations. The lack of a robust unified theory that can quantify the process of nucleation for all substances, across a broad range of pressures and temperatures, underscores the challenges involved.

Experimental studies on vapor-liquid nucleation have primarily focused on substances like water, straight chain alcohols and long chain alkanes. Given the complexity of these substances, the uncertainties in key physical properties and a lack of knowledge regarding the intermolecular potentials, meaningful comparisons between theory, experiments and simulations is challenging. A primary goal of this research is, therefore, to experimentally investigate the nucleation behavior of “simple” molecules including argon and nitrogen. Following on the work of Sinha (Dissertation, Ohio State University, 2008), the current work extends the range of experimental argon condensation data in a cryogenic supersonic nozzle (SSN) to lower temperatures and higher supersaturations. Based on the experimental measurements and estimated nucleation rates of 1017±1 cm-3s-1 in our SSN, Classical Nucleation Theory (CNT) predicts nucleation rates that are lower by 11-13 orders of magnitude. In contrast, rates predicted by Mean Field Kinetic Nucleation Theory (MKNT), a recent theory developed within the construct of statistical mechanics, are within 1-2 orders of magnitude of the experimental estimates. The experimental approach used for argon is successfully extended to study the condensation of nitrogen, a challenge given that expansions start at ~85 K, about 15 - 20 K lower than the argon experiments. For nitrogen, MKNT rate predictions again agree better with experiments, by ~11 orders of magnitude, than the predictions of CNT. The possible reasons for the success of MKNT are explored by combining the high rate data measured here with the lower rate data measured by Iland et al. (J. Chem. Phys. 127, 154506, 2007; J. Chem Phys., 130, 114508, 2009) in order to estimate the critical cluster properties, including the cluster size, excess internal energy, and excess entropy, for both argon and nitrogen. Although both CNT and MKNT over-predict the critical cluster size, the predictions of the excess internal energy and entropy predicted by MKNT are in significantly better agreement with experimental estimates of these quantities. In this work, the freezing of supercooled heavy water (D2O) droplets in a supersonic nozzle is studied by applying three in situ position resolved experimental techniques including static pressure measurements, small angle X-ray scattering and Fourier transform infra-red spectroscopy. Combining the information from these three techniques yields the size, phase, composition and number density of the droplets, as well as the flow variables including temperature, density and velocity. Freezing of supercooled D2O droplets in the size range of 3 to 9 nm occurs at droplet temperatures ranging from 222 K to 226 K while the corresponding ice nucleation rates are ~1023 cm-3s-1 assuming the phase transition can occur throughout the volume of the droplet and ~1016 cm-3s-1 assuming nucleation is initiated at the surface. The current D2O ice nucleation data are more consistent with nucleation initiated at the surface of the droplet, but uncertainty in the experiments makes it difficult to definitively state which process dominates. Some of the difficultly may simply be that for the smallest drops the outer 1 nm of the droplet constitutes ~70% of the volume. Using current estimates of the thermophysical properties of the condensed phases of D2O, the theoretical ice nucleation rates reproduce the experimental data trends qualitatively but not quantitatively.

Finally, given the importance of understanding the kinetics of formation of clathrate hydrates, a “proof of concept” study shows that these complex structures form on a microsecond time scale in a supersonic nozzle, when tetrahydrofuran (THF) is the guest molecule.

Committee:

Barbara Wyslouzil, PhD (Advisor); Isamu Kusaka, PhD (Committee Member); James Rathman, PhD (Committee Member); Brian Focht (Other)

Subjects:

Chemical Engineering; Chemistry; Condensation

Keywords:

Nucleation; Condensation; Freezing; Supersonic nozzle; Argon; Nitrogen; Heavy water; Clathrate Hydrates

MASPOLI, ORSO JEANPressure Mapping Investigation of Innovative Nozzles For Oil Drill-Bit
MS, University of Cincinnati, 2002, Engineering : Aerospace Engineering
The aim of this project is to study the flow dynamics and impact pressure of nozzles used in the hydraulic system of oil drilling rigs. Development of drill bit technology has been closely related to the comprehension of the hydraulic phenomenon. Hydraulics is a main factor in the drilling process; a good understanding of these parameters could insure a successful drilling. To improve the rate of penetration it was decided to understand the main functions of this drilling fluid: Cutting removal from the drill bit and the well bottom .* Cooling the cutting tools * Lubrification * Relief of hydrostatic pressure Two years ago, a test rig was built in Louisiana State University in order to investigate the influence of nozzles geometry on the flow dynamics and pressure distribution. Experiments had been conducted to compare the effects of four non-cylindrical nozzles versus a regular one. These tests included the measurement of the discharge coefficient and the plotting of 3-dimensional impact pressure mappings. This particular test rig was moved to the Fluids Mechanic and Propulsion Laboratory of the University of Cincinnati and modified to provide a tool capable of testing nozzles used in roller cone bits.

Committee:

Dr. Ephrain Gutmark (Advisor)

Keywords:

Nozzle; jet; inpinging; water; pressure mapping

Shin, Yun KyungThe water-amorphous silica interface: electrokinetic phenomena in a complex geometry, and treatment of interactions with biomolecules
Doctor of Philosophy, The Ohio State University, 2011, Chemistry

Advances in the construction of nanoscale biomedical devices requires increasingly realistic descriptions of interactions with biomolecules, and with fluid flow within micro- and nanochannels. We have made progress in both areas for nanostructures fabricated from amorphous silica. Silica is a material commonly used to fabricate biomedical devices, and the interactions of silica with aqueous solutions and biomolecules are of great importance in many fields. We developed a tractable model for biomolecules at the water/amorphous silica interface. This interaction model is based on one previously developed for the amorphous silica/water interface. Quantum chemical calculations of a series of probe molecules that mimic the common functional groups found in biomolecules were performed near a characteristic silica fragment. Our interaction model was designed to best reproduce the quantum chemical results. Then we investigated binding of two tripeptides (lys-trp-lys and glu-trp-glu) at the amorphous silica/water interface using molecular dynamics simulations. The preliminary studies reveal the great variety of binding motifs possible when biomolecules interact with silica, and illustrate how a peptide with overall negative charge like glu-trp-glu might bind to silica by hydrophilic/hydrophobic interactions on the highly inhomogeneous silica surface.

Electroosmotic transport of electrolyte solution in a nozzle geometry induced by an applied electric field was investigated with atomic level detail using non-equilibrium molecular dynamics (NEMD) simulations. Both ends of the nozzle are connected to flat channels and the walls consist of realistically modeled amorphous silica. The research is motivated by interesting issues arising from electrokinetic transport through the micro/nano interface such as ion concentration polarization and achieving optimum transport of biomolecules, ions and fluid. We found that the concentration of both counterions and coions are depleted in the nozzle region and consequently, a concentration gradient was generated in the direction of the flow. In addition, the flow pattern is not uniform along the channel unlike the uniform pore. The local back flow was observed in flat channel connected to the nozzle due to the combined effects of induced adverse pressure and electroosmotic flow. To understand the underlying mechanism of this phenomena, we compared the results of non-equilibrium molecular dynamics simulations to the predictions of continuum hydrodynamics, using both exact solutions to the Stokes equation and testing the standard lubrication approximation. In addition, the water polarization charge that accumulates near a wall which is not parallel to the external electric field was investigated.

Committee:

Sherwin J. Singer, PhD (Advisor); A. T. Conlisk, PhD (Committee Member); James V. Coe, PhD (Committee Member)

Subjects:

Materials Science; Mechanical Engineering; Physical Chemistry

Keywords:

nozzle;electrokinetics;induced adverse pressure;anisotropy;amorphous silica;water polarization

Eberhard, Walter WayneA mathematical model of ram-charging intake manifolds for four stroke diesel engines
Master of Science, The Ohio State University, 1971, Mechanical Engineering

Committee:

Helmuth Engelman (Advisor)

Keywords:

MANIFOLDS; ENGINES; engine speed; pipe; inlet pipe; VOLUMETRIC EFFICIENCY; nozzle

Jiang, HuaEffect of Changes in Flow Geometry, Rotation and High Heat Flux on Fluid Dynamics, Heat Transfer and Oxidation/Deposition of Jet Fuels
Doctor of Philosophy (Ph.D.), University of Dayton, 2011, Mechanical Engineering

Jet fuel is used in high-performance military flight vehicles for cooling purposes before combustion. It is desirable to investigate the influence of the flow and heating conditions on fuel heat transfer and thermal stability to develop viable mitigation strategies. Computational fluid dynamics (CFD) simulations and experiments can provide the understanding of the fuel physical phenomena which involves the fluid dynamics, heat transfer and chemical reactions. Three distinct topics are studied: The first topic considers the effect of flow geometry on fuel oxidation and deposition. Experiments and CFD modeling were performed for fuels flowing through heated tubes which have either a sudden expansion or contraction. It was found that the peak deposition occurs near the maximum oxidation rate and excess deposition is formed near the step. This study provides information for the fuel system designer which can help minimize surface deposition due to fuel thermal oxidation.

In the second area of study, the fuel passed heated rotational test articles to investigate the effect of rotation on fuel heat transfer. The coupled effects of centrifugal forces and turbulent flow result in fuel temperatures that increase with rotational speed. This indicates that the convective heat transfer is enhanced as rotational speed increases. This work can assist the understanding of using jet fuel to cool the turbine engine.

In the third segment of research, the fuel was exposed to “rocket-like” conditions. This investigation is to explore the effect of high heat flux and high flow velocity on fuel heat transfer and oxidation/deposition. Simulations show a temperature difference over several hundred degrees in the radial direction within the very thin thermal boundary layer under rapid heating. The fuel contacting the interior wall is locally heated to a supercritical state. As a result, the heat transfer is deteriorated in the supercritical boundary layer. Both simulated and measured deposit profiles show a peak deposit near the end of the heated section. These observations may eventually have an application to the design of high speed supersonic vehicles with improved cooling capabilities.

Committee:

Jamie S. Ervin, PhD (Advisor); Steven Zabarnick, PhD (Committee Co-Chair); Timothy J. Edwards, PhD (Committee Member); Kevin P. Hallinan, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

jet fuel; heat transfer deterioration; high heat flux; temperature peak; supercritical; fuel properties; nozzle; sudden expansion/contraction in flow path; fuel deposition; turbulence models; rotation passage; recirculation flow; excess deposition

Perrino, MichaelAn Experimental Study into Pylon, Wing, and Flap Installation Effects on Jet Noise Generated by Commercial Aircraft
PhD, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering
A pylon bottom bifurcation and a wing with variable flaps were designed and built to attach to a scaled model of a coaxial exhaust nozzle system. The presence of the pylon bifurcation, wing, and flaps modify the characteristics of the exhaust flow forc- ing asymmetric flow and acoustics. A parametric study was carried out for assessing and relating the flow field characteristics to the near-field pressure and far-field acous- tic spectra. The flow field was investigated experimentally using both stream-wise and cross-stream PIV techniques where the near-field pressure and far-field acoustic spectra were measured using microphone arrays. Contour mapping of the flow field characteristics (e.g. mean velocity and turbulence kinetic energy levels) and near-field acoustics with and without installation effects were used to explain the changes in the far-field acoustics.

Committee:

Ephraim Gutmark, Ph.D. D.Sc. (Committee Chair); Asif Syed, Ph.D. (Committee Member); Jeffrey Kastner, Ph.D. (Committee Member); Paul Orkwis, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Aeroacoustics;Aircraft Engine;Pylon;Noise;Nozzle

Pathak, HarshadNucleation and Droplet Growth During Co-condensation of Nonane and D2O in a Supersonic Nozzle
Doctor of Philosophy, The Ohio State University, 2013, Chemical and Biomolecular Engineering
Raw natural gas consists mainly of methane and has impurities like water vapor, higher alkanes, H2S etc. Dehydration of natural gas is important to prevent hydrate formation in pipelines carrying natural gas over long distances. Traditionally, dehydration is done using chemical methods like pressure swing absorption and glycol dehydration. An alternate method of dehydration is by using a mechanical process of supersonic separation. In this method, raw natural gas is cooled down by adiabatic expansion resulting in condensation of water vapor and higher alkanes. The goal of this work is to understand the nucleation and droplet growth when droplet sizes are of the order of nm and timescales are of the order of microseconds when water and alkanes, two substances which are immiscible, condense together. We use supersonic nozzles in this work where cooling rates are of the order of 105-106 K/s. The supersonic velocities of the flow enable measurements on a resolution of the order of microseconds. Pressure trace measurement (PTM) is our basic experimental technique and it characterizes the flow by measuring the pressure profile inside the supersonic nozzle as the vapor-gas mixture expands and vapor condenses inside the nozzle. These experiments give the initial estimate of temperature, density, velocity and mass fraction of the condensate. We use Fourier transform infrared spectroscopy (FTIR) to get the composition of the condensed liquid/vapor. To determine the amount of nonane condensed, we fit the measured spectrum of nonane to a linear combination of a well-characterized vapor and liquid spectrum. For D2O analysis, we calculate D2O vapor concentration by analyzing the vibrational-rotational spectrum of O-D stretch region. The size and number of droplets is characterized using small angle x-ray scattering (SAXS) that are performed in Argonne National Laboratory. The nucleation rates for pure D2O and nonane agree with previous measurements done by other researchers. The subsequent process of growth of the droplets can be sensitive to droplet temperatures Td. For pure nonane droplets, we observe that Td is not important enough to alter the growth rates unlike pure D2O. The growth of D2O droplets is further affected by coagulation once condensation has slowed down. We also observe that when nonane and D2O both are condensing, the presence of nonane inhibits D2O condensation even when D2O dominates the nucleation process. Prediction of the droplet structure of composite nonane-D2O droplets is challenging because the SAXS spectra of these droplets does not fit to standard shapes like spheres or core-shell structures. The small size of these droplets makes it possible to study them through molecular dynamics simulations. Our collaborators conduct simulations of these droplets and calculate the scattering behavior for those shapes. The SAXS spectra are fit to scattering from shapes derived from both density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Although the lens-on-sphere structures derived from MD simulations fits the scattering spectra better than all other structures which we tested, the overall composition from this structure predicts that the amount of D2O condensed is 30-40% less than that measured from FTIR.

Committee:

Barbara Wyslouzil (Advisor); Isamu Kusaka (Committee Member); Bhavik Bakshi (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Energy; Engineering; Experiments; Physics

Keywords:

nonane; D2O; supersonic nozzle; condensation; droplet growth; FTIR; SAXS; non-equilibrium, nucleation, droplet structure, guinier analysis, aerosol spectroscopy, natural gas dehydration