MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

This thesis follows and outlines experiments conducted from 2017 to 2019 related to the gaseous jet in a gaseous crossflow. The experiments examined and analyzed the steady jet in crossflow and the ventured into the steady jet in an oscillating crossflow. As will be explained in the introduction of this thesis, many works have been conducted on the steady jet in crossflow. Likewise, many works are also available for the modulated jet in a steady crossflow. This series of experiments differs in two ways: First, fuel is injected into the crossflow at very high velocities and across highly variant velocities. Second, the crossflow is modulated up to 450 Hz while the jet is kept steady. Analysis of the steady jet in a steady crossflow confirmed conclusions from previous studies while offering additional insights for consideration. First, when dealing highly variant input jet velocities, the effects of that velocity cannot be ignored when estimating jet centerline trajectory. It will be shown that increasing the Jet Reynolds Number yields an increased jet penetration. Second, a two-piece correlation equation determining jet trajectory is more accurate than a single equation. This allows for increased accuracy of the jet potential core, where mixing of the jet and crossflow is most prominent and dictates where the jet will propagate in the far field. Third, the end of the jet potential core, or breakup point, is a function of the momentum flux ratio and the jet Reynolds number. As these values vary, the jet potential core will cease at different x and y locations. Analysis of the steady jet in an oscillating crossflow allowed for further exploration of the JICF. First, it will be shown that under the effects of an oscillating crossflow, the jet will have a suppressed penetration. Second, on a time-averaged basis, a modulated jet plume will be wider and occupy a larger portion of the combustion chamber. Last, the modulation level, or percentage of ve (open full item for complete abstract)

Committee: Jongguen Lee Ph.D. (Committee Chair); Daniel Cuppoletti Ph.D. (Committee Member); Paul Orkwis Ph.D. (Committee Member) Subjects: Aerospace Materials

PhD, University of Cincinnati, 2010, Engineering : Aerospace Engineering

An experimental study has been conducted with liquid jets injected transversely into a crossflow to study the effect of non-uniformities in the crossflow velocity distribution to the jet behavior. Two different non-uniform crossflows were created during this work, a shear-laden crossflow and a swirling crossflow. The shear-laden crossflow was generated by merging two independent, co-directional, parallel airstreams creating a shear mixing layer at the interface between them. The crossflow exhibited a quasi-linear velocity gradient across the height of the test chamber. By varying the velocities of the two airstreams, the sense and the slope of the crossflow velocity gradient could be changed. Particle Image Velocimetry (PIV) studies were conducted to characterize the crossflow. The parameter, UR, is defined as the ratio of the velocities of the two streams and governs the velocity gradient. A positive velocity gradient was observed for UR > 1 and a negative velocity gradient for UR < 1. PIV and Phase Doppler Particle Anemometry (PDPA) studies were conducted to study the penetration and atomization of 0.5 mm diameter water jets injected into this crossflow. The crossflow velocity gradient was observed to have a significant effect on jet penetration as well as the post breakup spray. For high UR (> 1), jet penetration increased and the Sauter Mean Diameter (SMD) distribution became more uniform. For low UR (< 1), low penetration, higher droplet velocities and better atomization were observed. The second crossflow tested was a swirling flow generated using in-house designed axial swirlers. Three swirlers were used, with vane exit angles of 30°, 45° and 60°. Laser Doppler Velocimetry (LDV) was used to study the crossflow velocities. The axial and the tangential components of the crossflow velocity were observed to decrease with increasing radial distance away from the centerbody. The flow angle of the crossflow was smaller than the vane exit angle, with the difference (open full item for complete abstract)

Committee: San-Mou Jeng PhD (Committee Chair); Milind Jog PhD (Committee Member); Shaaban Abdallah PhD (Committee Member); George Hsiao PhD (Committee Member) Subjects: Aerospace Materials

MS, University of Cincinnati, 2022, Engineering and Applied Science: Aerospace Engineering

This research focuses on the atomization behaviors of perturbed liquid jets injected in oscillating crossflows. Liquid jet in crossflow is a configuration that is extensively used for primary atomization in gas turbine and ramjet engines. It is well known in the literature that acoustic fluctuations in a combustor can perturb the incoming airflow, which then interacts with the liquid fuel. If the conditions are appropriate, this can lead to combustion instabilities. Thus, understanding the interactions between oscillating crossflow and liquid jets is paramount to understanding combustion dynamics. One of the potential ways to mitigate combustion dynamics is by perturbing the liquid jet with appropriate frequency. While extensive research has been conducted on both these configurations separately, LJOCF (Liquid Jet Oscillating Crossflow) and PLJI (Pulsating Liquid Jet Injection) in a quiescent environment, there are significant research gaps when both the crossflow and the liquid jet are perturbed. Therefore, in this research effort, the jet and crossflow were manipulated by imposing sinusoidal disturbance to evaluate spray characteristics, such as jet column breakup, droplet formation, and atomization efficiency across the domain. The theoretical and mathematical formulation to investigate this two-phase problem is based on the three-dimensional incompressible Navier-Stokes equations with surface tension. A critical issue is the treatment of multi-scale liquid-liquid and gas-liquid interfaces; therefore, a state-of-the-art, high-resolution, volume-of-fluid (VOF) interface capturing method is adopted to resolve the interfacial evolution. Surface tension is accommodated as a Dirac delta distribution function on the interface. The theoretical formulation outlined above is solved numerically using a finite volume method augmented by an adaptive mesh refinement (AMR) technique based on an octree spatial discretization to improve the solution's accuracy and effici (open full item for complete abstract)

Committee: Prashant Khare Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Engineering

Master of Science (MS), Ohio University, 2016, Mechanical Engineering (Engineering and Technology)

Effect of transmembrane pressure and crossflow velocity on crossflow filtration of microalgae and performance of polypropylene and polyester felt material was studied. A crossflow filtration cell and a test system with the capability of varying transmembrane pressure and crossflow velocity was developed. In the first group of experiments 20 kPa, 40 kPa, and 60 kPa transmembrane pressures were tested at 0.5 m/s crossflow velocity for both the materials. In the second group of experiments 0.5 m/s and 1 m/s crossflow velocities were tested at the transmembrane pressure of 20 kPa. Permeate flux, filtration efficiency, cake resistance, and fouling resistance of filter materials was calculated from the data collected. Graphical and statistical analyses were performed on permeate flux and filtration efficiency values. Increase in transmembrane pressure increased permeate flux and filtration efficiency of both polypropylene and polyester material. Similarly, increase in crossflow velocity increased permeate flux and filtration efficiency of polypropylene and polyester felt materials.

Committee: David Bayless (Advisor) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering

An experimental investigation of response characteristics of a liquid jet in oscillating crossflow is undertaken to understand the behavior of a liquid fuel spray in the presence of combustion instabilities. The effect of crossflow oscillations on the liquid jet is studied in the near-field (within x/d˜8) and the far-field (x/d˜50) spray region. Experiments are conducted in bag breakup, multimode and shear breakup regimes by varying crossflow Weber number from 18 to 250, while momentum flux ratio is varied between 10 and 30. The crossflow is modulated in the frequency range of 90 Hz to 450 Hz, with modulation level varying between 5% and 20%, using a mechanical modulating device. High speed shadowgraph is employed to study the near-field and far-field spray movement while intensified high-speed camera images of laser Mie-scattering intensity are utilized in studying the spray cross-section in the far-field. A technique to extract time-varying momentum flux ratio from the windward trajectory of liquid jet in the near-field is developed. The response of near-field spray is quantified in terms of a ratio of the observed momentum flux ratio extracted from a correlation of upper penetration to the expected momentum flux ratio corresponding to the instantaneous crossflow velocity. The liquid jet penetration is found to respond to oscillations in the crossflow at all oscillation frequencies in the near-field. The strength of the response is found to be mainly dependent on the crossflow oscillation frequency, with the strength of response decreasing with increase in frequency. The momentum flux ratio and the modulation level are found to have relatively negligible effects on the level of normalized spray response. The spray response in the far-field is studied by observing the high-speed shadowgraphs and Mie-scattering intensity images at an axial distance of x/d=50. The spray field in the axial location is divided into ten bins and the intensity change in each bin is analy (open full item for complete abstract)

Committee: Jongguen Lee Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy (Ph.D.), University of Dayton, 2022, Aerospace Engineering

Combinations of various trends in global weather point towards an increased severity and frequency of wildfires. A handful of attempts have been made in the past that try to determine retardant ground deposits and their spatial distribution resulting from aerial drops in an effort to curtail fire growth. This study takes a multipronged approach at determining retardant ground deposits and spatial distribution at various coverage levels to better achieve fire control and extinguishment. The first approach fuses the dependent parameters, (line length, width, area, and ground distribution of the retardant), with the independent parameters using statistical regression in hopes to identify the probable parameters that are complicit in affecting the ground contours and their prediction the most. While the coverage prediction for the lower coverage levels (up to 3 GPC – Gallons per 100 ft.2) is accurate to 85% for area prediction with a variability of ±15% from actual while the length prediction is only accurate 58% of the time. This value was obtained using volume bounds on the input conditions. The estimate at higher coverage levels was poor along with the retardant's spatial distribution. An alternate approach was to model the drop phenomena in a relatively controlled, scaled down environment which was performed in the University of Dayton's Low Speed Wind Tunnel (UD – LSWT) facility. A 1 mm circular jet of water emanating from the underbelly of a model fuselage was placed in varying velocity crossflow (0 < Weber number < 101) of air. Shadowgraphs were initially performed, and the jet breakup was captured at 2000 frames per second which aided in discovery of breakup location with respect to surface waves. Experiments with Background Oriented Schlieren and Particle Image Velocimetry were also planned, however, they ultimately were not successful. Historical data points to two instabilities that govern the breakup process in jets, either in crossflow or quiescent a (open full item for complete abstract)

Committee: Aaron Altman (Advisor); Markus Rumpfkeil (Committee Member); Wiebke Diestelkamp (Committee Member); Sidaard Gunasekaran (Committee Member) Subjects: Aerospace Engineering

PhD, University of Cincinnati, 2022, Engineering and Applied Science: Aerospace Engineering

The injection of a liquid jet into a subsonic crossflow (LJCF) is a common strategy for atomizing liquid fuels in a wide variety of propulsion system applications. This has led to significant research interest in characterizing the complex multiphase and unsteady flowfield of the LJCF. The majority of previous research has focused on the injection of various liquids into ambient temperature and pressure air crossflows. However, modern high performance propulsion systems operate at increasingly elevated temperatures and pressures which can have unique implications for LJCF behavior. Additionally, if liquid fuel is circulated to cool propulsion system components prior to injection, the impact of elevated fuel temperatures on LJCF atomization and evaporation becomes important. The few studies that have investigated the LJCF at elevated jet and crossflow temperatures have avoided conditions where droplet evaporation becomes an important factor while also using test liquids that are not relevant to propulsion systems, such as water. The current work seeks to fill this void in the available literature by experimentally investigating the impact of elevated liquid jet and crossflow temperatures on the features of the LJCF in a well characterized test environment. Significant effort was put forth to characterize both the state of crossflow upstream of the injector, and the flow leaving the injector at different test conditions. Emphasis was placed on extracting quantitative data and developing empirical correlations that describe both the near- and far-field characteristics of the LJCF. This was done with the intent to provide validation data for numerical simulations of the LJCF. Characterization of the crossflow upstream of injector included measurements of the inlet gas temperature and Mach number profiles, the injection wall boundary layer, preburner emissions, and local test section acoustics. Injector evaluation consisted of internal injector visualizatio (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Member); Rodrigo Villalva Gomez Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Materials

MS, University of Cincinnati, 2021, Engineering and Applied Science: Aerospace Engineering

Scramjets are a class of air breathing propulsion systems which operate at very high Mach numbers. Efficient mixing and combustion of fuel has been a concern in the field of scramjet propulsion for the last five decades. The residence time for mixing of fuel and air has been low due to the inherent design of the propulsion system. Therefore, it is very important to create scenarios for the efficient mixing of fuel and air in the combustor. Pulsation of jets has shown to improve penetration, mixing and entrainment. To do this requires the complex understanding of jets in supersonic crossflows. Previous research has shown the effect of forcing/exciting flows using novel techniques in a subsonic crossflow, thoroughly. But there is limited research on the pulsation of jets in supersonic crossflows. A novel technique to force or excite jets in a crossflow was suggested by Murugappan and Gutmark. This technique employed the Hartmann Sprenger tube in a device called the High Frequency Actuator. This device showed an improvement in the penetration of jets in supersonic crossflow but failed to explain the dynamic structures which created situations that helped improve mixing. Hence, CFD tools such as ANSYS Fluent were suggested to bridge this gap. An axisymmetric WALE LES model and a three dimensional Smagorinsky-Lilly model was constructed for the operation of the High Frequency Actuator in quiescent flow and supersonic crossflow, respectively. Two cases with frequencies 2400 Hz (St# 0.09) and 2933 Hz (St# 0.12) were studied in quiescent flow. Quiescent flow was used to understand the underlying physics associated with the creation of strong pulses inside the Hartmann Sprenger tube based on the quarter wave resonance tone and other harmonics. Spectral Proper Orthogonal Decomposition (SPOD) was used to identify the fundamental tones and strong coherent structures were observed in the flow field. Following that, forcing of jets in a supersonic Mach 2 cold flow was conduc (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Rodrigo Villalva Gomez (Committee Member); Paul Orkwis Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy (PhD), Ohio University, 2019, Mechanical and Systems Engineering (Engineering and Technology)

Electrostatic precipitators (ESP) are used extensively for removing particulates from a gas flow by charging the particles and then removing them in the presence of an electric field. Traditional ESP designs use the walls of the flow channel as the grounded collection surface. The objective of this present study is to evaluate an ESP configuration in which an array of cylinders in a crossflow configuration is used as grounded collection surfaces. A numerical approach using ANSYS Fluent computational fluid dynamics (CFD) software was used to build a two-dimensional model for the gas flow and particulate capture. The model uses governing equations of fluid mechanics and electric fields to determine the fluid flow profiles, the charging of the particles, and the transport of the charged particles to the surfaces of grounded collection cylinders. The results of this study show that the particle collection is strongly influenced by two opposing phenomena, both of which are determined by the geometrical arrangement of the array of cylinders. The first phenomenon is the generation of turbulence regions behind the collector rows due to the cylinders obstructing the flow, which can enhance particulate capture downstream. The second is the shielding of the electric field by the cylinders which reduces the particulate transport to the grounded cylinder surfaces in the region separating the collector rows.

Committee: Muhammad Ali PhD (Advisor); Khairul Alam PhD (Committee Member); Alireza Sarvestani PhD (Committee Member); Sergio Ulloa PhD (Committee Member); Vic Matta PhD (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2007, Engineering : Aerospace Engineering

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

Committee: Dr. San-Mou Jeng (Advisor) Subjects: Engineering, Aerospace

MS, University of Cincinnati, 2004, Engineering : Aerospace Engineering

An experimental study has been conducted to study the behavior of liquid jets injected transversely into a subsonic crossflow of air. Liquid jet operating conditions are represented by the aerodynamic Weber number (We) and the liquid-air momentum ratio (q). Three injection liquids, water, Jet-A and N-Heptane, and two injection diameters (D), 0.381 and 0.762 mm, have been used to increase the range of operating conditions for the current experiments. q was restricted to 0.7-10.2 to ensure applicability to premix ducts of LPP combustors. Pulsed shadowgraphy and Phase Doppler Particle Analyzer (PDPA) techniques were used to take measurements for these experiments. Jet breakups and penetrations, and the structures of the sprays produced after breakup have been studied. Two breakup modes have been observed, column and surface breakup. The streamwise location of breakup is constant while the transverse location increases with q. Jet penetrations have been correlated with q, D and the streamwise distance (z). The volume flux of the spray exhibits a maximum in the spray core. Droplet axial velocities (Ud) exhibit a minimum below the spray core and increase with increasing transverse distance. The transverse location of the maximum in the droplet sizes occurs in the spray core for low q. Its location increases with an increase in q. Droplet sizes decrease with an increase in the crossflow velocity (U∞) while penetration increases with an increase in D or q. This property has been found to be very significant.

Committee: Dr. San-Mou Jeng (Advisor) Subjects: Engineering, Aerospace

Master of Science, University of Toledo, 2011, Civil Engineering

Membrane filtration is an effective technique used in water treatment to remove particles, organic pollutants, inorganic compounds, and microorganisms to accomplish a biologically safe and consistently high quality drinking water. One significant challenge to membrane separation technologies is membrane fouling causing pressure drop, flux decline and eventually significant cost of membrane replacement. Specifically, membrane biofouling is considered a major problem due to the capabilities of microorganisms to adapt their growth rate, multiply, and relocate even if they were 99.99% removed from the feed stream. The objective of this research was to determine the impact of metabolic activity of the pure culture of biofoulants on the membrane biofilm metabolic activity, biofilm formation rate, and operational flux decline. In this study, the metabolic activity of Pseudomonas fluorescens in active, inactive, and different growth phases were investigated during cross-flow filtration using a cellulose acetate ultrafiltration (UF) membrane at different sampling times (4, 11, and 24 hours) of filtration. In accordance with previous biofilm studies, ATP was used to determine the metabolical activity of the biomass. Dehydrogenase activity assessment of the membrane biofilm using CTC was also carried out on intact biofilms. Our results showed that after 10-12 hours of filtration, the biofilm ATP levels reach an equilibrium concentration (avg. 8 amol/cell) and do not appear to be related to biofoulant ATP levels from cells harvested in the late exponential growth phase regardless of initial ATP level. However, the bacterial growth phase affected the ATP activity of cells. Membrane biofilms formed from biofoulants in the lag and stationary phase of growth contained similar levels of ATP (avg. 1.8 amol/cell), and the exponential phase cells resulted in significant higher activity. Flux decline does not appear to be related to metabolic activity of the biofoulant or biofilm fol (open full item for complete abstract)

Committee: Cyndee L. Gruden PhD (Advisor); Youngwoo Seo PhD (Committee Member); Defne Apul PhD (Committee Member) Subjects: Civil Engineering; Environmental Engineering

Doctor of Philosophy in Engineering, University of Toledo, 2011, College of Engineering

To address drinking water quality concerns, membrane separation technologies have been developed, resulting in the continuous reduction of their cost and rapid extension of their application possibilities. Despite the remarkable advantages of membrane separation technologies, the drastic reduction of water flow due to membrane fouling and the high cost of membrane replacement pose a significant problem in water separation applications. This research investigated the impact of feed water characteristics (i.e., conductivity and pH), conditioning layer formed on biofilms, and presence and activity level of a biofoulant on the membrane-solute interaction forces (i.e. hydrophobic attraction) and membrane morphology. Experiments were performed on cellulose acetate ultrafiltration (CAUF) membranes (MWCO 20,000 D) in crossflow filtration for up to 53 hours. Fouled membrane characterization from the macro- to nano-scale was effectively carried out using existing and emerging techniques including fluorescence microscopy for cell activity, image analysis for biofilm surface coverage and intensity, ATR-FTIR for biofilm chemical composition, AFM for fouled membrane surface roughness and skewness, and CFM for its relationship to adhesion forces. As the feed water conductivity increased and the membrane surface roughness increased, the magnitude and range of the adhesion force increased and, subsequently, the permeate flux decline increased suggesting that feed water chemistry impacted membrane potential for fouling. Comprehensive biofilm characterization, specifically AFM, revealed that bacterial cells deposited, and then formed a consolidated biofilm, on the low shear rate areas of the membrane surface. And, as expected, the rate of biofilm formation was higher in the presence of a carbon source and active cells. Additional experiments were carried out to determine the contribution of abiotic fouling (conditioning layer) to cell activity and built up resistance on CAUF memb (open full item for complete abstract)

Committee: Cyndee Gruden (Committee Chair); Isabel Escobar (Committee Member); Ashok Kumar (Committee Member); Defne Apul (Committee Member); Youngwoo Seo (Committee Member) Subjects: Civil Engineering; Environmental Engineering