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Title: ROBUSTNESS ANALYSIS FOR TURBOMACHINERY STALL FLUTTER.
Creator: Forhad, Md, Xu, Yunjun, University of Central Florida
Abstract / Description: Flutter is an aeroelastic instability phenomenon that can result either in serious damage or complete destruction of a gas turbine blade structure due to high cycle fatigue. Although 90% of potential high cycle fatigue occurrences are uncovered during engine development, the remaining 10% stand for one third of the total engine development costs. Field experience has shown that during the last decades as much as 46% of fighter aircrafts were not mission-capable in certain periods due to high...
Show moreFlutter is an aeroelastic instability phenomenon that can result either in serious damage or complete destruction of a gas turbine blade structure due to high cycle fatigue. Although 90% of potential high cycle fatigue occurrences are uncovered during engine development, the remaining 10% stand for one third of the total engine development costs. Field experience has shown that during the last decades as much as 46% of fighter aircrafts were not mission-capable in certain periods due to high cycle fatigue related mishaps. To assure a reliable and safe operation, potential for blade flutter must be eliminated from the turbomachinery stages. However, even the most computationally intensive higher order models of today are not able to predict flutter accurately. Moreover, there are uncertainties in the operational environment, and gas turbine parts degrade over time due to fouling, erosion and corrosion resulting in parametric uncertainties. Therefore, it is essential to design engines that are robust with respect to the possible uncertainties. In this thesis, the robustness of an axial compressor blade design is studied with respect to parametric uncertainties through the Mu analysis. The nominal flutter model is adopted from . This model was derived by matching a two dimensional incompressible flow field across the flexible rotor and the rigid stator. The aerodynamic load on the blade is derived via the control volume analysis. For use in the Mu analysis, first the model originally described by a set of partial differential equations is reduced to ordinary differential equations by the Fourier series based collocation method. After that, the nominal model is obtained by linearizing the achieved non-linear ordinary differential equations. The uncertainties coming from the modeling assumptions and imperfectly known parameters and coefficients are all modeled as parametric uncertainties through the Monte Carlo simulation. As compared with other robustness analysis tools, such as Hinf, the Mu analysis is less conservative and can handle both structured and unstructured perturbations. Finally, Genetic Algorithm is used as an optimization tool to find ideal parameters that will ensure best performance in terms of damping out flutter. Simulation results show that the procedure described in this thesis can be effective in studying the flutter stability margin and can be used to guide the gas turbine blade design.
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Date Issued: 2011
Identifier: CFE0003999, ucf:48666
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003999

Title: CHARACTERIZATION OF AN INLINE ROW IMPINGEMENT CHANNEL FOR TURBINE BLADE COOLING APPLICATIONS.
Creator: Ricklick, Mark, Kapat, Jayanta, University of Central Florida
Abstract / Description: Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient...
Show moreGas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel height effects on the performance of the channel side walls, effects of bulk temperature increase on heat transfer coefficients, circumferential heat variation effects, and effects on the uniformity of the heat transfer distribution. The main objectives of this dissertation are to explore the various previously unstudied characteristics of impingement channels, in order to sufficiently predict their performance in a wide range of applications. The potential exists, therefore, for a designer to develop a blade with cooling characteristics specifically tailored to the expected component thermal loads. Temperature sensitive paint (TSP) is one of several non-intrusive optical temperature measurements techniques that have gained a significant amount of popularity in the last decade. By employing the use of TSP, we have the ability to provide very accurate (less than 1 degree Celsius uncertainty), high resolution full-field temperature measurements. This has allowed us to investigate the local heat transfer characteristics of the various channel surfaces under a variety of steady state testing conditions. The comparison of thermal performance and uniformity for each impingement channel configuration then highlights the benefits and disadvantages of various configurations. Through these investigations, it has been shown that the channel side walls provide heat transfer coefficients comparable to those found on the target surface, especially at small impingement heights. Although the side walls suffer from highly non-uniform performance near the start of the channel, the profiles become very uniform as the cross flow develops and becomes a dominating contributor to the heat transfer coefficient. Increases in channel height result in increased non-uniformity in the streamwise direction and decreased heat transfer levels. Bulk temperature increases have also been shown to be an important consideration when investigating surfaces dominated by cross flow heat transfer effects, as enhancements up to 80% in some areas may be computed. Considerations of these bulk temperature changes also allow the determination of the point at which the flow transitions from an impingement dominated regime to one that is dominated by cross flow effects. Finally, circumferential heat variations have proven to have negligible effects on the calculated heat transfer coefficient, with the observed differences in heat transfer coefficient being contributed to the unaccounted variations in channel bulk temperature.
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Date Issued: 2009
Identifier: CFE0002955, ucf:47948
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002955

Title: Characterization of SLM-Manufactured Turbine Blade Microfeatures from Superalloy Powders.
Creator: Ealy, Brandon, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
Abstract / Description: The limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Inconel remains the material of choice for most hot gas path (HGP) components in gas turbines, however recent increases in turbine inlet temperature (TIT) are associated with the development of advanced convective cooling methods and ceramic thermal barrier coatings. Increasing cycle efficiency and cycle specific work are the primary drivers for increasing TIT. Lately, incremental...
Show moreThe limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Inconel remains the material of choice for most hot gas path (HGP) components in gas turbines, however recent increases in turbine inlet temperature (TIT) are associated with the development of advanced convective cooling methods and ceramic thermal barrier coatings. Increasing cycle efficiency and cycle specific work are the primary drivers for increasing TIT. Lately, incremental performance gains responsible for increasing the allowable TIT have been made mainly through innovations in cooling technology, specifically convective cooling schemes. An emerging manufacturing technology may further facilitate the increase of allowable maximum TIT, thereby impacting cycle efficiencies. Laser Additive Manufacturing (LAM) is a promising manufacturing technology that uses lasers to selectively melt powders of metal in a layer-by-layer process to directly manufacture components, paving the way to produce designs that are not possible with conventional casting methods. This study investigates manufacturing qualities seen in LAM methods and its ability to successfully produce complex microfeatures in a mock turbine blade leading edge. Various cooling features are incorporated in design, consisting of internal impingement cooling, internal lattice structures, and external showerhead cooling. The internal structure is designed as a lattice of intersecting cylinders in order to mimic that of a porous material. Through a non-destructive approach, the presented design is analyzed against the departure of the design by utilizing X-ray computed tomography (CT). Employing this non-destructive testing (NDT) method, a more thorough analysis of the quality of manufacture is established by revealing the internal structures of the porous region and internal impingement array. Variance distribution between the design and manufactured test article are carried out for both internal impingement and external transpiration hole diameters from CT data. Flow testing is performed to characterize the uniformity of porous regions and flow behavior across the entire article for various pressure ratios. Discharge coefficients of internal impingement arrays and porous structures are quantified. A numerical model of fluid flow through the exact CAD geometry is analyzed over the range of experimental flowrates. By comparison of experimental and numerical data, performance discrepancies associated with manufacturing quality are observed. Simplifying assumptions to the domain are evaluated to compare predictions of CFD using the exact geometry. This study yields quantitative data on the build quality of the LAM process, providing more insight as to whether it is a viable option for manufacture of micro-features in current turbine blade production.
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Date Issued: 2016
Identifier: CFE0006452, ucf:51428
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006452

Title: Academic Blade Geometries for Baseline Comparisons of Forced Vibration Response Predictions.
Creator: Little, James, Kauffman, Jeffrey, Gordon, Ali, Bai, Yuanli, University of Central Florida
Abstract / Description: Predicting the damping associated with underplatform dampers remains a challenge in turbomachineryblade and friction damper design. Turbomachinery blade forced response analysismethods usually rely on nonlinear codes and reduced order models to predict vibration characteristicsof blades. Two academic blade geometries coupled with underplatform dampers are presentedhere for comparison of these model reduction and forced response simulation techniques. The twoblades are representative of free...
Show morePredicting the damping associated with underplatform dampers remains a challenge in turbomachineryblade and friction damper design. Turbomachinery blade forced response analysismethods usually rely on nonlinear codes and reduced order models to predict vibration characteristicsof blades. Two academic blade geometries coupled with underplatform dampers are presentedhere for comparison of these model reduction and forced response simulation techniques. The twoblades are representative of free-standing turbine blades and exhibit qualitatively similar behavioras highly-complex industrial blades. This thesis fully describes the proposed academic bladegeometries and models; it further analyzes and predicts the blades forced response characteristicsusing the same procedure as industry blades. This analysis classifies the results in terms of resonancefrequency, vibration amplitude, and damping over a range of aerodynamic excitation toexamine the vibration behavior of the blade/damper system. Additionally, the analysis investigatesthe effect variations of the contact parameters (friction coefficient, damper / platform roughnessand damper mass) have on the predicted blade vibration characteristics, with sensitivities to each parameter. Finally, an investigation of the number of modes retained in the reduced order modelshows convergence behavior as well as providing additional data for comparison with alternativemodel reduction and forced response prediction methods. The academic blade models are shownto behave qualitatively similar to high fidelity industry blade models when the number of retained modes in a modal analysis are varied and behave qualitatively similar under sensitives to designparameters.
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Date Issued: 2017
Identifier: CFE0006616, ucf:51281
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006616

Title: EVOLUTION OF MICROSTRUCTURE AND RESIDUAL STRESS IN DISC-SHAPE EB-PVD THERMAL BARRIER COATINGS AND TEMPERATURE PROFILE OF HIGH PRESSURE TURBINE BLADE.
Creator: Mukherjee, Sriparna, Sohn, Yongho, University of Central Florida
Abstract / Description: A detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of...
Show moreA detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of TBCs that consisted of EB-PVD coated ZrO2-7wt.%Y2O3, (Pt,Ni)Al bond coat, and CMSX-4 Ni-based superalloy. At specific fraction of lifetime,TBCs were examined by electron microscopy and photostimulated luminescence (PL). Changes in the average compressive residual stress of the TGO determined by PL and the magnitude of rumpling, determined by tortuosity from quantitative microstructural analyses, were examined with respect to the furnace thermal cyclic lifetime and microstructural evolution of TBCs. The combination of elastic strain energy within the TGO and interfacial energy at the interface between the TGO and the bond coat was defined as the TGO energy, and its variation with cyclic oxidation time was found to remain approximately constant ~135J/m2 during thermal cycling from 10% to 80% thermal cyclic lifetime. Parametric study at ~135J/m2 was performed and variation in residual stress with rumpling for different oxide scale thicknesses was examined. This study showed that the contribution of rumpling in residual stress relaxation decreased with an increase in TGO thickness. High pressure turbine blades serviced for 2843 hours and in the as coated form were also examined using electron microscopy and photostimulated luminescence. The difference in residual stress values obtained using PL on the suction and pressure sides of as-coated turbine blade were discussed. The presence of a thick layer of deposit on the serviced blade gave signals from stress free alpha-Al2O3 in the deposit, not from the TGO. The TGO growth constant data from the disc-shape TBCs, thermally cycled at 1100[degrees]C, and studies by other authors at different temperatures but on similar EB-PVD coated TBCs with (Pt, Ni)Al bond coat and CMSX-4 Ni- based superalloy were used to determine the temperature profile at the YSZ/bond coat interface. The interfacial temperature profiles of the serviced blade and the YSZ thickness profile were compared to document the variable temperature exposure at the leading edge, trailing edge, suction and the pressure side.
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Date Issued: 2011
Identifier: CFE0003927, ucf:48700
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003927

Title: INVESTIGATION OF PS-PVD AND EB-PVD THERMAL BARRIER COATINGS OVER LIFETIME USING SYNCHROTRON X-RAY DIFFRACTION.
Creator: Northam, Matthew, Raghavan, Seetha, Ghosh, Ranajay, Vaidyanathan, Raj, University of Central Florida
Abstract / Description: Extreme operating temperatures within the turbine section of jet engines require sophisticated methods of cooling and material protection. Thermal barrier coatings (TBCs) achieve this through a ceramic coating applied to a substrate material (nickel-based superalloy). Electron-beam physical vapor deposition (EB-PVD) is the industry standard coating used on jet engines. By tailoring the microstructure of an emerging deposition method, Plasma-spray physical vapor deposition (PS-PVD), similar...
Show moreExtreme operating temperatures within the turbine section of jet engines require sophisticated methods of cooling and material protection. Thermal barrier coatings (TBCs) achieve this through a ceramic coating applied to a substrate material (nickel-based superalloy). Electron-beam physical vapor deposition (EB-PVD) is the industry standard coating used on jet engines. By tailoring the microstructure of an emerging deposition method, Plasma-spray physical vapor deposition (PS-PVD), similar microstructures to that of EB-PVD coatings can be fabricated, allowing the benefits of strain tolerance to be obtained while improving coating deposition times. This work investigates the strain through depth of uncycled and cycled samples using these coating techniques with synchrotron X-ray diffraction (XRD). In the TGO, room temperature XRD measurements indicated samples of both deposition methods showed similar in-plane compressive stresses after 300 and 600 thermal cycles. In-situ XRD measurements indicated similar high-temperature in-plane and out-of-plane stress in the TGO and no spallation after 600 thermal cycles for both coatings. Tensile in-plane residual stresses were found in the YSZ uncycled PS-PVD samples, similar to APS coatings. PS-PVD samples showed in most cases, higher compressive residual in-plane stress at the YSZ/TGO interface. These results provide valuable insight for optimizing the PS-PVD processing parameters to obtain strain compliance similar to that of EB-PVD. Additionally, external cooling methods used for thermal management in jet engine turbines were investigated. In this work, an additively manufactured lattice structure providing transpiration cooling holes is designed and residual strains are measured within an AM transpiration cooling sample using XRD. Strains within the lattice structure were found to have greater variation than that of the AM solid wall. These results provide valuable insight into the viability of implementing an AM lattice structure in turbine blades for the use of transpiration cooling.
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Date Issued: 2019
Identifier: CFE0007844, ucf:52830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007844

Title: DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS.
Creator: RATHOD, CHANDRASEN, Vaidyanathan, Raj, University of Central Florida
Abstract / Description: Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and...
Show moreDeformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.
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Date Issued: 2005
Identifier: CFE0000723, ucf:46608
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000723

synchrotron (2)	+ -
(Pt (1)	+ -
AM (1)	+ -
CATER (1)	+ -
EB-PVD TBCs (1)	+ -

Exposure temperature (1)	+ -
Flutter (1)	+ -
Friction damping (1)	+ -
Gas Turbine Blade (1)	+ -
Impingement Cooling (1)	+ -
Inconel 718 (1)	+ -
Laser Additive Manufacturing (1)	+ -
Mark Ricklick (1)	+ -
Mu Analysis (1)	+ -
Ni)Al bond coat (1)	+ -
NiTi (1)	+ -
Non-Destructive Testing (1)	+ -
Photostimulated Luminescence Spectroscopy. (1)	+ -
Power Generation (1)	+ -
Residual stress (1)	+ -
Robustness (1)	+ -
Rumpling (1)	+ -
Selective Laser Melting (1)	+ -
TBC (1)	+ -
Thermal Barrier Coatings (1)	+ -
Ti-6Al-4V turbine blade (1)	+ -
Turbine Blade (1)	+ -
Turbine Blade Cooling (1)	+ -
Turbine Blade Microfeatures (1)	+ -
Turbine Cooling (1)	+ -

University of Central Florida (7)	+ -
Kapat, Jayanta (2)	+ -
Vaidyanathan, Raj (2)	+ -
Ahmed, Kareem (1)	+ -
Bai, Yuanli (1)	+ -

Ealy, Brandon (1)	+ -
Forhad, Md (1)	+ -
Ghosh, Ranajay (1)	+ -
Gordon, Ali (1)	+ -
Kauffman, Jeffrey (1)	+ -
Little, James (1)	+ -
Mukherjee, Sriparna (1)	+ -
Northam, Matthew (1)	+ -
RATHOD, CHANDRASEN (1)	+ -
Raghavan, Seetha (1)	+ -
Ricklick, Mark (1)	+ -
Sohn, Yongho (1)	+ -
Vasu Sumathi, Subith (1)	+ -
Xu, Yunjun (1)	+ -

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