VTechWorks Repository :: Browsing by Author "Battaglia, Francine"

Browsing by Author "Battaglia, Francine"

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3D Dynamic Stall Simulation of Flow over NACA0012 Airfoil at 10⁵ and 10⁶ Reynolds Numbers
Kasibhotla, Venkata ravishankar (Virginia Tech, 2014-04-03)
The work presented in this thesis attempts to provide an understanding of the physics behind the dynamic stall process by simulating the flow past pitching NACA-0012 airfoil at 100,000 and 1 million Reynolds number based on the chord length of the airfoil and at different reduced frequencies of 0.188 and 0.25 respectively in a three dimensional flow field. The mean angles of attack are 12 deg. and 15 deg. and the amplitudes of pitching are 6 deg. and 10 deg. respectively. The turbulence in the flow field is resolved using large eddy simulations with dynamic Smagorinsky model at the sub grid scale. The lift hysteresis plots of this simulation for both the configurations are compared with the corresponding experiments. The development of dynamic stall vortex, vortex shedding and reattachment as predicted by the present study are discussed in detail. There is a fairly good match between the predicted and experimentally measured lift coefficient during the upstroke for both cases. The net lift coefficient for the Re = 100,000 case during downstroke matches with the corresponding experimental data, the present study under-predicts the lift coefficient as compared to the experimental values at the start of downstroke and over-estimates for the remaining part of the downstroke. The trend of the lift coefficient hysteresis plot with the experimental data for the Re = 1 million case is also similar. This present simulations have shown that the downstroke phase of the pitching motion is strongly three dimensional and is highly complex, whereas the flow is practically two dimensional during the upstroke.
The Application of the Solar Chimney for Ventilating Buildings
Park, David (Virginia Tech, 2016-11-09)
This study sought to demonstrate the potential applications of the solar chimney for the naturally ventilating a building. Computational fluid dynamics (CFD) was used to model various room configurations to assess ventilation strategies. A parametric study of the solar chimney system was executed, and three-dimensional simulations were compared and validated with experiments. A new definition for the hydraulic diameter that incorporated the chimney geometry was developed to predict the flow regime in the solar chimney system. To mitigate the cost and effort to use experiments to analyze building energy, a mathematical approach was considered. A relationship between small- and full-scale models was investigated using non-dimensional analysis. Multiple parameters were involved in the mathematical model to predict the air velocity, where the predictions were in good agreement with experimental data as well as the numerical simulations from the present study. The second part of the study considered building design optimization to improve ventilation using air changes per hour (ACH) as a metric, and air circulation patterns within the building. An upper vent was introduced near the ceiling of the chimney system, which induced better air circulation by removing the warm air in the building. The study pursued to model a realistic scenario for the solar chimney system, where it investigated the effect of the vent sizes, insulation, and a reasonable solar chimney size. It was shown that it is critical to insulate the backside of the absorber and that the ratio of the conditioned area to chimney volume should be at least 10. Lastly, the application of the solar chimney system for basement ventilation was discussed. Appropriate vent locations in the basement were determined, where the best ventilation was achieved when the duct inlet was located near the ceiling and the exhaust vent was located near the floor of the chimney. Sufficient ventilation was also achieved even for scenarios of a congested building when modeling the presence of multiple people.
Bacteria-Enabled Autonomous Drug Delivery Systems: Development, Characterization of Intratumoral Transport and Modeling
Suh, SeungBeum (Virginia Tech, 2017-08-17)
Systemic chemotherapy is a major therapeutic approach for nearly all types and stages of cancer. Success of this treatment depends not only on the efficacy of the therapeutics but also on the transport of the drug to all tumor cells in sufficient concentrations. Intratumoral drug transport is limited by characteristics of the tumor microenvironment such as elevated interstitial pressure and sparse, irregular vascularization. Moreover, poor tumor selectivity, leads to systemic toxicity. Bacteria possess a host of characteristics that address the aforementioned challenges in conventional drug delivery approaches including tumor selectivity, preferential tumor colonization, effective tumor penetration, which can be augmented via genetic engineering. However, in clinical trials conducted to date, bacteria have rarely been able to inhibit tumor growth solely by their presence in the tumor. The overall goal of this doctoral dissertation is to develop a novel tumor treatment system based on Salmonella Typhimurium VNP20009 (genetically modified for preferential tumor colonization and attenuation) coupled with biodegradable copolymer, poly(lactic-co-glycolic acid) nanoparticles, hereafter referred to as NanoBEADS (Nanoscale Bacteria Enabled Autonomous Drug Delivery System). To this end, a NanoBEADS fabrication procedure that is robust and repeatable was established and a microfluidic chemotaxis-based sorting platform for the separation NanoBEADS from unattached nanoparticles was developed. The transport efficacy of NanoBEADS compared to the commonly used passively-diffusing nanoparticle was investigated in vitro and in vivo and the intratumoral penetration of the therapeutic vectors was quantified using a custom image processing algorithm. The mechanism of intratumoral penetration was elucidated through 2D and 3D invasion assays. Lastly, we developed a biophysical model of intratumoral transport of NanoBEADS based on the intratumoral penetration experimental results towards the theoretical evaluation of the drug transport profile following the administration of NanoBEADS.
CFD analysis of airflow patterns and heat transfer in small, medium, and large structures
Detaranto, Michael Francis (Virginia Tech, 2014-11-05)
Designing buildings to use energy more efficiently can lead to lower energy costs, while maintaining comfort for occupants. Computational fluid dynamics (CFD) can be utilized to visualize and simulate expected flows in buildings and structures. CFD gives architects and designers the ability to calculate the velocity, pressure, and heat transfer within a building. Previous research has not modeled natural ventilation situations that challenge common design rules of thumb used for cross-ventilation and single-sided ventilation. The current study uses a commercial code (FLUENT) to simulate cross-ventilation in simple structures and analyzes the flow patterns and heat transfer in the rooms. In the Casa Giuliana apartment and the Affleck house, this study simulates passive cooling in spaces well-designed for natural ventilation. Heat loads, human models, and electronics are included in the apartment to expand on prior research into natural ventilation in a full-scale building. Two different cases were simulated. The first had a volume flow rate similar to the ambient conditions, while the second had a much lower flow rate that had an ACH of 5, near the minimum recommended value Passive cooling in the Affleck house is simulated and has an unorthodox ventilation method; a window in the floor that opens to an exterior basement is opened along with windows and doors of the main floor to create a pressure difference. In the Affleck house, two different combinations of window and door openings are simulated to model different scenarios. Temperature contours, flow patterns, and the air changes per hour (ACH) are explored to analyze the ventilation of these structures.
Challege and Opportunities of Membrane Bioelctrochemical Reactors for Wastewater Treatment
Li, Jian (Virginia Tech, 2016-04-26)
Microbial fuel cells (MFCs) are potentially advantageous as an energy-efficient approach for wastewater treatment. Integrating membrane filtration with MFCs could be a viable option for advanced wastewater treatment with a low energy input. Such an integration is termed as membrane bioelectrochemical reactors (MBERs). Comparing to the conventional membrane bioreactors or anaerobic membrane bioreactors, MBER could be a competitive technology, due to the its advantages on energy consumption and nutrients removal. By installing the membrane in the cathodic compartment or applying granular activated carbon as fluidized bed materials, membrane fouling issue could be alleviated significantly. In order to drive MBER technology to become a more versatile platform, applying anion exchange membrane (AEM) could be an option for nutrients removal in MBERs. Wastewater can be reclaimed and reused for subsequent fermentation use after a series MFC-MBR treatment process. Such a synergistic configuration not only provide a solution for sustainable wastewater treatment, but also save water and chemical usage from other non-renewable resource. Integrating membrane process with microbial fuel cells through an external configuration provides another solution on sustainable wastewater treatment through a minimal maintenance requirement.
Characterization and Modeling of the Thermal Properties of Photopolymers for Material Jetting Processes
Mikkelson, Emily Cleary (Virginia Tech, 2014-03-25)
One emerging application of additive manufacturing is building parts with embedded electronics, but the thermal management of these assemblies is a potential issue. Electrical components have efficiency losses, and a significant portion of that lost energy is converted into heat. Embedding electronics in PolyJet parts is of particular interest since material jetting additive manufacturing has the ability to deposit multiple, functionally graded materials on a pixel by pixel basis. Although there is existing literature on other PolyJet material properties, there is limited research on their thermal characterization. The goal of this work is to determine the thermal conductivities of select PolyJet photopolymers (VeroWhitePlus, TangoBlackPlus, and Grey60) by using the heat flow meter method. The resulting thermal conductivities are then applied in finite element analysis (FEA) simulations to model the thermal distribution of heated PolyJet parts. Two FEA models of one-dimensional conduction in PolyJet parts are defined and compared to a corresponding physical model to verify the thermal conductivity measurements; one simulation expresses thermal conductivity as a function of temperature and the other uses an average value of thermal conductivity. The thermal conductivities were determined for a range of temperatures, and the average values were 0.2376 W/(m•K), 0.2307 W/(m•K), and 0.2272 W/(m•K) for VeroWhitePlus, TangoBlackPlus, and Grey60, respectively. When applying the thermal conductivity results to an FEA model, it was concluded that defining thermal conductivity as a function of temperature (as opposed to a constant value), reduced the average error in the predicted temperatures by less than 1%.
A Comprehensive Entry, Descent, Landing, and Locomotion (EDLL) Vehicle for Planetary Exploration
Schroeder, Kevin Kent (Virginia Tech, 2017-08-26)
The 2012 Decadal Survey has stated that there is a critical role for a Venus In-situ Explore (VISE) missions to a variety of important sites, specifically the Tessera terrain. This work aims to answer the Decadal Survey's call by developing a new comprehensive Entry, Descent, Landing, and Locomotion (EDLL) vehicle for in-situ exploration of Venus, especially in the Tessera regions. TANDEM, the Tension Adjustable Network for Deploying Entry Membrane, is a new planetary probe concept in which all of EDLL is achieved by a single multifunctional tensegrity structure. The concept uses same fundamental concept as the ADEPT (Adaptable Deployable Entry and Placement Technology) deployable heat shield but replaces the standard internal structure with the structure from the tensegrity-actuated rover to provide a combined aeroshell and rover design. The tensegrity system implemented by TANDEM reduces the mass of the overall system while enabling surface locomotion and mitigating risk associated with landing in the rough terrain of Venus's Tessera regions, which is otherwise nearly inaccessible to surface missions. TANDEM was compared to other state-of-the-art lander designs for an in-situ mission to Venus. It was shown that TANDEM provides the same scientific experimentation capabilities that were proposed for the VITaL mission, with a combined mass reduction for the aeroshell and lander of 52% (1445 kg), while eliminating the identified risks associated with entry loads and very rough terrain. Additionally, TANDEM provides locomotion when on the surface as well as a host of other maneuvers during entry and descent, which was not present in the VITaL design. Based on its unique multifunctional infrastructure and excellent crashworthiness for impact on rough surfaces, TANDEM presents a robust system to address some of the Decadal Survey's most pressing questions about Venus.
Comprehensive Multi-Scale Progressive Failure Analysis for Damage Arresting Advanced Aerospace Hybrid Structures
Horton, Brandon Alexander (Virginia Tech, 2017-08-31)
In recent years, the prevalence and application of composite materials has exploded. Due to the demands of commercial transportation, the aviation industry has taken a leading role in the integration of composite structures. Among the leading concepts to develop lighter, more fuel-efficient commercial transport is the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. The highly integrated structure of PRSEUS allows pressurized, non-circular fuselage designs to be implemented, enabling the feasibility of Hybrid Wing Body (HWB) aircraft. In addition to its unique fabrication process, the through-thickness stitching utilized by PRSEUS overcomes the low post-damage strength present in typical composites. Although many proof-of-concept tests have been performed that demonstrate the potential for PRSEUS, efficient computational tools must be developed before the concept can be commercially certified and implemented. In an attempt to address this need, a comprehensive modeling approach is developed that investigates PRSEUS at multiple scales. The majority of available experiments for comparison have been conducted at the coupon level. Therefore, a computational methodology is progressively developed based on physically realistic concepts without the use of tuning parameters. A thorough verification study is performed to identify the most effective approach to model PRSEUS, including the effect of element type, boundary conditions, bonding properties, and model fidelity. Using the results of this baseline study, a high fidelity stringer model is created at the component scale and validated against the existing experiments. Finally, the validated model is extended to larger scales to compare PRSEUS to the current state-of-the-art. Throughout the current work, the developed methodology is demonstrated to make accurate predictions that are well beyond the capability of existing predictive models. While using commercially available predictive tools, the methodology developed herein can accurately predict local behavior up to and beyond failure for stitched structures such as PRSEUS for the first time. Additionally, by extending the methodology to a large scale fuselage section drop scenario, the dynamic behavior of PRSEUS was investigated for the first time. With the predictive capabilities and unique insight provided, the work herein may serve to benefit future iteration of PRSEUS as well as certification by analysis efforts for future airframe development.
Computational Fluid Flow Analysis of the Enhanced-Once through Steam generator Auxiliary feedwater system
Sethapati, Vivek Venkata (Virginia Tech, 2011-05-02)
The once through steam generator (OTSG) is a single pass counter flow heat exchanger in which primary pressurized water from the core is circulated. Main Feedwater is injected in an annular gap on the outer periphery of the steam generator shroud such that it aspirates steam to preheat the feedwater to saturation temperature. An important component of the OTSG and enhanced once through steam generator (EOTSG) is the auxiliary feedwater system (AFW), which is used during accident/transient scenarios to remove residual heat by injecting water through jets along the outer periphery of the heat exchanger core directly on to the tubes at the top of the OTSG. The intention is for the injected water, which is subcooled, to spread into the tube nest and wet as many tubes as possible. In this project, the main objectives were to use first principles Computational Fluid Dynamics to predict the number of wetted tubes versus flow rate in the EOTSG at the AFW injection location above the top tube support plate. To perform the fluid analysis, the losses in the bypass leakage flow and broached hole leakage flow were first quantified and then used to model a 1/8th sector of the EOTSG. Using user defined functions (UDF), the loss coefficients of the leakage flows were implemented on the 1/8th sector of the EOTSG computational model to provide boundary conditions at the bypass flow and leakage flow locations With this method, the number of tubes wetted in the sector of EOTSG for various AFW flow rates was found. Results showed that the number of wetted tubes was in very close agreement to that predicted by experimental-analytical methods by the sponsor, AREVA. With the maximum flow rate of 65 l/s a total of 318 tubes were wetted and the percentage of tubes wetted with broached holes was 8.7%. The analysis on the bypass leakage flow showed that the loss coefficients was a function of the mass flow rate or the flow Reynolds number through the gap and it increased as the Reynolds number increased from 300 to 1600. The experimental and computational loss coefficients agree to within 15% of each other. In contrast, the constant loss coefficient of 1.3 used by AREVA was much higher than that obtained in this study, particularly in the low Reynolds number range. As the Reynolds number approached 3000, the loss coefficients from this study approached the value of 1.3. This value of the loss coefficient was implemented for the bypass flow leakage in the 1/8th sector of the EOTSG model. The analysis on the broached hole leakage flow was performed using a single hole, five holes, and one, two, four and eight rows of broached holes in order to characterize the loss coefficients. The one hole and five hole computational models were validated with experiments. The computational models showed the presence of voids in the leakage flow through the tube support plate (TSP), which were not observed (visually) in the experiments. The characterization of the broached hole leakage in the one, two and four rows showed that the loss coefficient of the control broached hole increased as the number of rows increased. These results indicated that for the same height of water on the TSP, the resistance to leakage flow increased as the number of tubes increased. They also indicated that leakage flow through the broached holes was not solely a function of the height of water above the TSP but also the surrounding geometrical topology and the flow characteristics. However, the analysis done for eight rows showed that the loss coefficient became constant after a certain number of rows as the loss coefficient differed by only 5% from the results of the four rows. From these results it was determined that the loss coefficient asymptotes to an estimated value of 4.0 which was implemented in the broached hole leakage flow in the 1/8th sector of the EOTSG. Computational models of the 1/8th sector of the EOTSG were implemented with the respective loss coefficients for the bypass and leakage flows. Results showed that as the AFW flow rate increased, the percentage wetted tubes increased. The data matched closely with AREVA's experimental-analytical model for flow rates of 14.5 l/s and higher. It was also deduced that complete wetting of the tubes is not possible at the maximum AFW flow rate of 65 l/s.
Computational investigation of the flow field contribution to improve electricity generation in granular activated carbon-assisted microbial fuel cells
Zhao, Lei; Li, Jian; Battaglia, Francine; He, Zhen (Elsevier, 2016-11-30)
Microbial fuel cells (MFCs) offer an alternative approach to treat wastewater with less energy input and direct electricity generation. To optimize MFC anodic performance, adding granular activated carbon (GAC) has been proved to be an effective way, most likely due to the enlarged electrode surface for biomass attachment and improved mixing of the flow field. The impact of a flow field on the current enhancement within a porous anode medium (e.g., GAC) has not been well understood before, and thus is investigated in this study by using mathematical modeling of the multi-order Butler-Volmer equation with computational fluid dynamics (CFD) techniques. By comparing three different CFD cases (without GAC, with GAC as a nonreactive porous medium, and with GAC as a reactive porous medium), it is demonstrated that adding GAC contributes to a uniform flow field and a total current enhancement of 17%, a factor that cannot be neglected in MFC design. However, in an actual MFC operation, this percentage could be even higher because of the microbial competition and energy loss issues within a porous medium. The results of the present study are expected to help with formulating strategies to optimize MFC with a better flow pattern design. (C) 2016 Elsevier B.V. All rights reserved.
Computational Modeling and Simulations of Hydrodynamics for Air-Water External Loop Airlift Reactors
Law, Deify (Virginia Tech, 2010-05-27)
External loop airlift reactors are widely used for biochemical applications such as syngas fermentation and wastewater treatment. To further understand the inherent gas-liquid flow physics within the reactors, computational modeling and simulations of hydrodynamics for air-water external loop airlift reactors were investigated. The gas-liquid flow dynamics in a bubble column were simulated using a FORTRAN code developed by Los Alamos National Laboratory, CFDLib, which employs an Eulerian-Eulerian ensemble averaged method. A two-dimensional Cartesian coordinate system was used to conduct an extensive grid resolution study; it was found that grid cells smaller than the bubble diameter produced unstable solutions. Next, closure models for drag force and turbulent viscosity were investigated for a simple bubble column geometry. The effects of using a bubble pressure model and two drag coefficient models, the White model and the Schiller-Naumann model, were investigated. The bubble pressure model performed best for homogeneous (low velocity) flows and the Schiller-Naumann model was best for all flow regimes. Based on the studies for bubble column flows, an external loop airlift reactor was simulated using both two- and three-dimensional coordinates and results for gas holdup and riser velocity agreed better with experimental data for the 3D simulations. It was concluded that when performing 2D and 3D simulations, care must be taken when specifying the effective bubble diameter size, especially at high flow rates. Population balance models (PBM) for bubble break-up and coalescence were implemented into CFDLib, validated with experiments, and simulated for the external loop airlift reactor at high inlet superficial gas velocities. The PBM predictions for multiple bubble sizes were comparable with the single bubble size simulations; however, the PBM simulations better predicted the formation of the gas bubble in the downcomer. The 3D PBM simulations also gave better predictions for the average bubble diameter size in the riser. It was concluded that a two-dimensional domain is adequate for gas-liquid flow simulations of a simple bubble column geometry, whereas three-dimensional simulations are required for the complex airlift reactor geometry. To conclude, a two-fluid Eulerian-Eulerian model coupled with a PBM is needed for quantitative as well as physical predictions of gas-liquid external loop airlift reactor flows at high inlet superficial gas velocities.
Computational Simulation of Coal Gasification in Fluidized Bed Reactors
Soncini, Ryan Michael (Virginia Tech, 2017-08-24)
The gasification of carbonaceous fuel materials offers significant potential for the production of both energy and chemical products. Advancement of gasification technologies may be expedited through the use of computational fluid dynamics, as virtual reactor design offers a low cost method for system prototyping. To that end, a series of numerical studies were conducted to identify a computational modeling strategy for the simulation of coal gasification in fluidized bed reactors. The efforts set forth by this work first involved the development of a validatable hydrodynamic modeling strategy for the simulation of sand and coal fluidization. Those fluidization models were then applied to systems at elevated temperatures and polydisperse systems that featured a complex material injection geometry, for which no experimental data exists. A method for establishing similitude between 2-D and 3-D multiphase systems that feature non-symmetric material injection were then delineated and numerically tested. Following the development of the hydrodynamic modeling strategy, simulations of coal gasification were conducted using three different chemistry models. Simulated results were compared to experimental outcomes in an effort to assess the validity of each gasification chemistry model. The chemistry model that exhibited the highest degree of agreement with the experimental findings was then further analyzed identify areas of potential improvement.
A Computational Study of the Hydrodynamics of Gas-Solid Fluidized Beds
Teaters, Lindsey Claire (Virginia Tech, 2012-05-31)
Computational fluid dynamics (CFD) modeling was used to predict the gas-solid hydrodynamics of fluidized beds. An Eulerian-Eulerian multi-fluid model and granular kinetic theory were used to simulate fluidization and to capture the complex physics associated therewith. The commercial code ANSYS FLUENT was used to study two-dimensional single solids phase glass bead and walnut shell fluidized beds. Current modeling codes only allow for modeling of spherical, uniform-density particles. Owing to the fact that biomass material, such as walnut shell, is abnormally shaped and has non-uniform density, a study was conducted to find the best modeling approach to accurately predict pressure drop, minimum fluidization velocity, and void fraction in the bed. Furthermore, experiments have revealed that all of the bed mass does not completely fluidize due to agglomeration of material between jets in the distributor plate. It was shown that the best modeling approach to capture the physics of the biomass bed was by correcting the amount of mass present in the bed in order to match how much material truly fluidizes experimentally, whereby the initial bed height of the system is altered. The approach was referred to as the SIM approach. A flow regime identification study was also performed on a glass bead fluidized bed to show the distinction between bubbling, slugging, and turbulent flow regimes by examining void fraction contours and bubble dynamics, as well as by comparison of simulated data with an established trend of standard deviation of pressure versus inlet gas velocity. Modeling was carried out with and without turbulence modeling (k-Ïµ), to show the effect of turbulence modeling on two-dimensional simulations.
Computational Study of Turbulent Combustion Systems and Global Reactor Networks
Chen, Lu (Virginia Tech, 2017-09-05)
A numerical study of turbulent combustion systems was pursued to examine different computational modeling techniques, namely computational fluid dynamics (CFD) and chemical reactor network (CRN) methods. Both methods have been studied and analyzed as individual techniques as well as a coupled approach to pursue better understandings of the mechanisms and interactions between turbulent flow and mixing, ignition behavior and pollutant formation. A thorough analysis and comparison of both turbulence models and chemistry representation methods was executed and simulations were compared and validated with experimental works. An extensive study of turbulence modeling methods, and the optimization of modeling techniques including turbulence intensity and computational domain size have been conducted. The final CFD model has demonstrated good predictive performance for different turbulent bluff-body flames. The NOx formation and the effects of fuel mixtures indicated that the addition of hydrogen to the fuel and non-flammable diluents like CO2 and H2O contribute to the reduction of NOx. The second part of the study focused on developing chemical models and methods that include the detailed gaseous reaction mechanism of GRI-Mech 3.0 but cost less computational time. A new chemical reactor network has been created based on the CFD results of combustion characteristics and flow fields. The proposed CRN has been validated with the temperature and species emission for different bluff-body flames and has shown the capability of being applied to general bluff-body systems. Specifically, the rate of production of NOx and the sensitivity analysis based on the CRN results helped to summarize the reduced reaction mechanism, which not only provided a promising method to generate representative reactions from hundreds of species and reactions in gaseous mechanism but also presented valuable information of the combustion mechanisms and NOx formation. Finally, the proposed reduced reaction mechanism from the sensitivity analysis was applied to the CFD simulations, which created a fully coupled process between CFD and CRN, and the results from the reduced reaction mechanism have shown good predictions compared with the probability density function method.
Conceptual Design and Instrumentation Study for a 2-D, Linear, Wet Steam Turbine Cascade Facility
McFarland, Jacob Andrew (Virginia Tech, 2008-12-04)
The design of last stage low pressure steam (LP) turbines has become increasingly complicated as turbine manufacturers have pushed for larger and more efficient turbines. The tip sections of these LP turbines encounter condensing wet steam at high velocities resulting in increased losses. These losses are difficult to predict with computational fluid dynamic models. To study these losses and improve the design of LP turbines a study was commissioned to determine the feasibility and cost of a steam cascade facility for measuring low pressure turbine blade tip section aerodynamic and thermodynamic performance. This study focused on two objectives: 1) design a steam production facility capable of simulating actual LP turbine operating conditions, and 2) design an instrumentation system to measure blade performance in wet steam. The steam production facility was designed to allow the test section size to be selected later. A computer code was developed to model the facility cycle and provide equipment requirements. Equipment to meet these requirements, vendors to provide it, and costs were found for a range of test section sizes. A method to control the test section conditions was also developed. To design the instrumentation system two methods of measuring blade losses through entropy generation were proposed. The first method uses existing total pressure probe techniques. The second method uses advanced particle imaging velocimetry techniques possibly for the first time in wet steam. A new method is then proposed to modify the two techniques to take measurements at non-equilibrium states. Finally accuracy issues are discussed and the challenges associated with achieving periodic flow in this facility are investigated.
Coupled Field Modeling of Gas Tungsten Arc Welding
Sen, Debamoy (Virginia Tech, 2012-07-03)
Welding is used extensively in aerospace, automotive, chemical, manufacturing, electronic and power-generation industries. Thermally-induced residual stresses due to welding can significantly impair the performance and reliability of welded structures. Numerical simulation of weld pool dynamics is important as experimental measurements of velocities and temperature profiles are difficult due to the small size of the weld pool and the presence of the arc. From a structural integrity perspective of welded structures, it is necessary to have an accurate spatial and temporal thermal distribution in the welded structure before stress analysis is performed. Existing research on weld pool dynamics simulation has ignored the effect of fluid flow in the weld pool on the temperature field of the welded joint. Previous research has established that the weld pool depth/width (D/W) ratio and Heat Affected Zone (HAZ) are significantly altered by the weld pool dynamics. Hence, for a more accurate estimation of the thermally-induced stresses it is desired to incorporate the weld pool dynamics into the analysis. Moreover, the effects of microstructure evolution in the HAZ on the mechanical behavior of the structure need to be included in the analysis for better mechanical response prediction. In this study, a three-dimensional model for the thermo-mechanical analysis of Gas Tungsten Arc (GTA) welding of thin stainless steel butt-joint plates has been developed. The model incorporates the effects of thermal energy redistribution through weld pool dynamics into the structural behavior calculations. Through material modeling the effects of microstructure change/phase transformation are indirectly included in the model. The developed weld pool dynamics model includes the effects of current, arc length, and electrode angle on the heat flux and current density distributions. All the major weld pool driving forces are included, namely surface tension gradient, plasma drag force, electromagnetic force, and buoyancy. The weld D/W predictions are validated with experimental results. They agree well. The effects of welding parameters (like welding speed, current, arc length, etc.) on the weld D/W ratio are documented. The workpiece deformation and stress distributions are also highlighted. The transverse and longitudinal residual stress distribution plots across the weld bead and their variations with welding speed and current are also provided. The mathematical framework developed here serves as a robust tool for better prediction of weld D/W ratio and thermally-induced stress evolution and distribution in a welded structure by coupling the different fields in a welding process.
Decentralized HVAC Operations: Novel Sensing Technologies and Control for Human-Aware HVAC Operations
Jung, Wooyoung (Virginia Tech, 2020-04-13)
Advances in Information and Communication Technology (ICT) paved the way for decentralized Heating, Ventilation, and Air-Conditioning (HVAC) HVAC operations. It has been envisioned that development of personal thermal comfort profiles leads to accurate predictions of each occupant's thermal comfort state and such information is employed in context-aware HVAC operations for energy efficiency. This dissertation has three key contributions in realizing this envisioned HVAC operation. First, it presents a systematic review of research trends and developments in context-aware HVAC operations. Second, it contributes to expanding the feasibility of the envisioned HVAC operation by introducing novel sensing technologies. Third, it contributes to shedding light on viability and potentials of comfort-aware operations (i.e., integrating personal thermal comfort models into HVAC control logic) through a comprehensive assessment of energy efficiency implications. In the first contribution, by developing a taxonomy, two major modalities – occupancy-driven and comfort-aware operations – in Human-In-The-Loop (HITL) HVAC operations were identified and reviewed quantitatively and qualitatively. The synthesis of previous studies has indicated that field evaluations of occupancy-driven operations showed lower potentials in energy saving, compared to the ones with comfort-aware operations. However, the results in comfort-aware operations could be biased given the small number of explorations. Moreover, required data representation schema have been presented to foster constructive performance assessments across different research efforts. In the end, the current state of research and future directions of HITL HVAC operations were discussed to shed light on future research need. As the second contribution, moving toward expanding the feasibility of comfort-aware operations, novel and smart sensing solutions have been introduced. It has been noted that, in order to have high accuracy in predicting individual's thermal comfort state (≥90%), user physiological response data play a key part. However, the limited number of applicable sensing technologies (e.g., infrared cameras) has impeded the potentials of implementation. After defining required characteristics in physiological sensing solutions in context of comfort-aware operations (applicability, sensitivity, ubiquity, and non-intrusiveness), the potentials of RGB cameras, Doppler radar sensors, and heat flux sensors were evaluated. RGB cameras, available in many smart computing devices, could be a ubiquitous solution in quantifying thermoregulation states. Leveraging the mechanism of skin blood perfusion, two thermoregulation state quantification methods have been developed. Then, applicability and sensitivity were checked with two experimental studies. In the first experimental study aiming to see applicability (distinguishing between 20 and 30C with fully acclimated human bodies), for 16 out of 18 human subjects, an increase in their blood perfusion was observed. In the second experimental study aiming to evaluate sensitivity (distinguishing responses to a continuous variation of air temperature from 20 to 30C), 10 out of 15 subjects showed a positive correlation between blood perfusion and thermal sensations. Also, the superiority of heat flux data, compared to skin temperature data, has been demonstrated in predicting personal thermal comfort states through the developments of machine-learning-based prediction models with feature engineering. Specifically, with random forest classifier, the median value of prediction accuracy was improved by 3.8%. Lastly, Doppler radar sensors were evaluated for their capability of quantifying user thermoregulation states leveraging the periodic movement of the chest/abdomen area induced by respiration. In an experimental study, the results showed that, with sufficient acclimation time, the DRS-based approach could show distinction between respiration states for two distinct air temperatures (20 and 30C). On the other hand, in a transient temperature without acclimation time, it was shown that, some of the human subjects (38.9%) used respiration as an active means of heat exchange for thermoregulation. Lastly, a comprehensive evaluation of comfort-aware operations' performance was carried out with a diverse set of contextual and operational factors. First, a novel comfort-aware operation strategy was introduced to leverage personal sensitivity to thermal comfort (i.e., different responses to temperature changes; e.g., sensitive to being cold) in optimization. By developing an agent-based simulation framework and thorough diverse scenarios with different numbers and combinations of occupants (i.e., human agents in the simulation), it was shown that this approach is superior in generating collectively satisfying environments against other approaches focusing on individual preferred temperatures in selection of optimized setpoints. The energy implications of comfort-aware operations were also evaluated to understand the impact from a wide range of factors (e.g., human and building factors) and their combinatorial effect given the uncertainty of multioccupancy scenarios. The results demonstrated that characteristics of occupants' thermal comfort profiles are dominant in impacting the energy use patterns, followed by the number of occupants, and the operational strategies. In addition, when it comes to energy efficiency, more occupants in a thermal zone/building result in reducing the efficacy of comfort-driven operation (i.e., the integration of personal thermal comfort profiles). Hence, this study provided a better understanding of true viability of comfort-driven HVAC operations and provided the probabilistic bounds of energy saving potentials. These series of studies have been presented as seven journal articles and they are included in this dissertation.
The development and analysis of a mobile explosive containment unit for on-board aircraft protection
Costain, Andrew J. (Virginia Tech, 2014-09-17)
This body of work examines the process involved in researching a mobile explosive containment unit for use on board a commercial aircraft. If a device with unknown origin were discovered on board a commercial aircraft an explosive containment unit could be used to dispose of it thereby preventing the passengers and the hardware from incurring any harm. A methodology was developed to help understand and effectively capture the properties of nominal explosives, the detonation pulse, ensuing shock and pressure waves. This methodology was developed with the purpose of mitigating these explosive effects. The information concerning the material properties, shape and sizes of an explosive containment unit were all analyzed to identify one optimal containment unit. This containment unit was utilized extensively in modeling to determine a range of possible materials and reinforcement methods, for reducing the total weight of the unit. Upon optimizing the containment unit numerical analysis was performed on a fuselage section of a narrow body commercial aircraft with the containment unit. The containment unit was successful in arresting the explosion before it was able to cause harm to its surroundings. The success of these containment units proves that the methodology discussed and developed here is capable of rabidly developing and analyzing explosive containment units to fit a wide variety of needs.
Development and Validation of Fluid-Structure Interaction in Aircraft Crashworthiness Studies
Satterwhite, Matthew Ryan (Virginia Tech, 2013-09-04)
Current Federal Aviation Regulations require costly and time consuming crashworthiness testing to certify aircraft. These tests are only capable of a limited assessment of progressive damage and all crash configurations and scenarios cannot be physically evaluated. Advancements in technology have led to accurate and effective developments in numerical modeling that have the possibility of replacing these rigorous physical experiments. Through finite element analysis, an in-depth investigation of an aircraft equipped with a fabricated composite undercarriage was evaluated during water ditching. The severe impact of aircraft ditching is dynamic and nonlinear in nature; the goal of this work to develop a methodology that not only captures the structural response of the aircraft, but also the fluidic behavior of the water. Fundamental studies were first conducted on a well-researched fluid-solid interaction problem, the water entry of a wedge. Typical modeling strategies did not capture the desired detail of the event. An advanced meshing scheme combining meshed and meshless Lagrangian techniques was developed and multiple wedge angles were tested and compared to analytic and qualitative results. The meshing technique proved valid, as the difficult to model phenomena of splashing was captured and the maximum impact force was within five percent of analytical calculations for the 20° and 30° deadrise wedge. Physical small scale aircraft ditching experiments were then performed with an innovative testing platform capable of producing varied aircraft approach configurations. The model was outfitted with an instrumented composite undercarriage to record data throughout the impact while a high-speed camera recorded the event. Numerical simulations of the model aircraft were then compared to experimental results with a strong correlation. This methodology was then ultimately tested on a deformable model of a fuselage section of a full-size aircraft.
Development of Comprehensive Dynamic Damage Assessment Methodology for High-Bypass Air Breathing Propulsion Subject to Foreign Object Ingestion
Song, Yangkun (Virginia Tech, 2016-11-10)
Foreign object ingestion (FOI) into jet engines is a recurring scenario during the operation life of aircraft. Objects can range from as small as a pebble on the tarmac to the size of a large bird. Among the potential ingestion scenarios, damage caused by smaller objects may be considered to be negligible. Alternatively, larger objects can initiate progressive damage, potentially leading to catastrophic failure, compromising the integrity of the structure, and endangering the safety of passengers. Considering the dramatic increase in air traffic, FOI represents a crucial safety hazard, and must be better understood to minimize possible damage and structural failure. The main purpose of this study is to develop a unique methodology to assess the response and dynamic damage progression of an advanced, high-bypass propulsion system in the event of an FOI during operation. Using a finite element framework, a unique modeling methodology has been proposed in order to characterize the FOI response of the system. In order to demonstrate versatility of the computational analysis, the impact characteristics of two most common foreign object materials, bird and ice, were investigated. These materials were then defined in finite element domain, verified computationally, and then validated against the existing physical experiments. In addition to the mechanics of the two FOI materials, other material definitions, used to characterize the structures of the high-bypass propulsion system, were also explored. Both composite materials and rate dependent definitions for metal alloys were investigated to represent the damage mechanics in the event of an FOI. Subsequently, damage sequence of high-bypass propulsion systems subject to FOI was developed and assessed, using a uniquely devised Fluid-Structure Interaction (FSI) technique. Using advanced finite element formulation, this approach enabled the accurate simulation of the comprehensive damage progression of the propulsion systems by including aerodynamic interaction. Through this strategy, fluid mechanics was combined with structural mechanics in order to simulate the mutual interaction between both continua, allowing the interpretation of both the additional damage caused by the fluid flow and disrupted aerodynamics induced by the dynamic deformation of the fan blade. Subsequently, this multidisciplinary-multiphysics computational approach, in the framework of the comprehensive analysis methodology introduced, enabled the effective determination of details on the overall progressive impact damage, not traditionally available to propulsion designers.

Browsing by Author "Battaglia, Francine"

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