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(1 - 8 of 8)
- Title
- FLOW CONTROL OF TANDEM CYLINDERS USING PLASMA ACTUATORS.
- Creator
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Larsen, Jonah, Bhattacharya, Samik, University of Central Florida
- Abstract / Description
-
The flow over a set of tandem cylinders at a moderate Reynolds numbers (Re), and with different separation lengths has been studied. Two dimensional (2D) and three-dimensional (3D) plasma actuators were used to control the flow over the leading cylinder to change the vortex shedding, and subsequently the flow on the second cylinder. The 3D plasma actuator was segmented along the length of the cylinder with a spacing of ? = 4 while the 2D actuator simply ran straight down the span of the...
Show moreThe flow over a set of tandem cylinders at a moderate Reynolds numbers (Re), and with different separation lengths has been studied. Two dimensional (2D) and three-dimensional (3D) plasma actuators were used to control the flow over the leading cylinder to change the vortex shedding, and subsequently the flow on the second cylinder. The 3D plasma actuator was segmented along the length of the cylinder with a spacing of ? = 4 while the 2D actuator simply ran straight down the span of the cylinder. Particle image velocimetry (PIV) measurements were used to investigate the flow along the central plane in the wake of the cylinders. The image pairs were processed into velocity grids which were then averaged. Plots of the shear, vorticity, and turbulent kinetic energy were created. These plots are used to understand how the character of vortex shedding from the upstream cylinder changes the same from the downstream one.
Show less - Date Issued
- 2018
- Identifier
- CFH2000425, ucf:45872
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000425
- Title
- CRYOGENIC SHAPE MEMORY ALLOY ACTUATORS FOR SPACEPORT TECHNOLOGIES: MATERIALS CHARACTERIZATION AND PROTOTYPE TESTING.
- Creator
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Lemanski, Jennifer, Vaidyanathan, Rajan, University of Central Florida
- Abstract / Description
-
Shape memory alloys (SMAs) possess the unique ability to change their shape by undergoing a solid-state phase transformation at a particular temperature. The shape change is associated with a large strain recovery as the material returns to its "remembered" shape. Their ability to act as both sensor and actuator has made them an attractive subject of study for numerous applications. SMAs have many characteristics which are advantageous in space-related applications, including generation of...
Show moreShape memory alloys (SMAs) possess the unique ability to change their shape by undergoing a solid-state phase transformation at a particular temperature. The shape change is associated with a large strain recovery as the material returns to its "remembered" shape. Their ability to act as both sensor and actuator has made them an attractive subject of study for numerous applications. SMAs have many characteristics which are advantageous in space-related applications, including generation of large forces associated with the strain recovery, smooth and controlled movements, large movement to weight ratio, high reliability, and spark-free operation. The objective of this work is the further development and testing of a cryogenic thermal conduction switch as part of NASA funded projects. The switch was developed to provide a variable conductive pathway between liquid methane and liquid oxygen dewars in order to passively regulate the methane temperature. Development of the switch concept has been continued in this work by utilizing Ni-Ti-Fe as the active SMA element. Ni-Ti-Fe exhibits the shape memory effect at cryogenic temperatures, which makes it well suited for low temperature applications. This alloy is also distinguished by an intermediate phase change known as the rhombohedral or R-phase, which is characterized by a small hysteresis (typically 1-2 deg C) and offers the advantage of precise control over a set temperature range. For the Ni-Ti-Fe alloy used, its thermomechanical processing, subsequent characterization using dilatometry and differential scanning calorimetry and implementation in the conduction switch configuration are addressed. This work was funded by grants from NASA KSC (NAG10-323) and NASA GRC (NAG3-2751).
Show less - Date Issued
- 2005
- Identifier
- CFE0000501, ucf:46448
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000501
- Title
- DESIGN, FABRICATION AND TESTING OF A LOW TEMPERATURE HEAT PIPE THERMAL SWITCH WITH SHAPE MEMORY HELICAL ACTUATORS.
- Creator
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Benafan, Othmane, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states are actuated by shape memory alloy elements while heat is transferred by a heat-pipe. The motivation for such a switch comes from NASA's need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. For example, as the temperature can approximately vary between 40 K to 400 K during lunar day/night cycles, such a switch can reject...
Show moreThis work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states are actuated by shape memory alloy elements while heat is transferred by a heat-pipe. The motivation for such a switch comes from NASA's need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. For example, as the temperature can approximately vary between 40 K to 400 K during lunar day/night cycles, such a switch can reject heat from a cryogen tank in to space during the night cycle while providing thermal isolation during the day cycle. By utilizing shape memory alloy elements in the thermal switch, the need for complicated sensors and active control systems are eliminated while offering superior thermal isolation in the open state. Nickel-Titanium-Iron (Ni-Ti-Fe) shape memory springs are used as the sensing and actuating elements. Iron (Fe) lowers the phase transformation temperatures to cryogenic regimes of operation while introducing an intermediate, low hysteretic, trigonal R-phase in addition to the usual cubic and monoclinic phases typically observed in binary NiTi. The R-phase to cubic phase transformation is used in this application. The methodology of shape memory spring design and fabrication from wire including shape setting is described. Heat transfer is accomplished via heat acquisition, transport and rejection in a variable length heat pipe with pentane and R-134a as working fluids. The approach used to design the shape memory elements, quantify the heat transfer at both ends of the heat pipe and the pressures and stresses associated with the actuation are outlined. Testing of the switch is accomplished in a vacuum bell jar with instrumentation feedthroughs using valves to control the flow of liquid nitrogen and heaters to simulate the temperature changes. Various performance parameters are measured and reported under both transient and steady-state conditions. Funding from NASA Kennedy Space Center for this work is gratefully acknowledged.
Show less - Date Issued
- 2009
- Identifier
- CFE0002810, ucf:48142
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002810
- Title
- LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS: ACTUATOR ENGINEERING AND INVESTIGATION OF DEFORMATION MECHANISMS USING IN SITU NEUTRON DIFFRACTION AT LOS ALAMOS NATIONAL LABORATORY.
- Creator
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Krishnan, Vinu, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
Shape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable...
Show moreShape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable fatigue response. Overall, this work is an investigation of selected science and engineering aspects of low temperature NiTiFe shape memory alloys. The scientific study was performed using in situ neutron diffraction measurements at the newly developed low temperature loading capability on the Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory and encompasses three aspects of the behavior of Ni46.8Ti50Fe3.2 at 92 K (the lowest steady state temperature attainable with the capability). First, in order to study deformation mechanisms in the R-phase in NiTiFe, measurements were performed at a constant temperature of 92 K under external loading. Second, with the objective of examining NiTiFe in one-time, high-stroke, actuator applications (such as in safety valves), a NiTiFe sample was strained to approximately 5% (the R-phase was transformed to B19' phase in the process) at 92 K and subsequently heated to full strain recovery under a load. Third, with the objective of examining NiTiFe in cyclic, low-stroke, actuator applications (such as in cryogenic thermal switches), a NiTiFe sample was strained to 1% at 92 K and subsequently heated to full strain recovery under load. Neutron diffraction spectra were recorded at selected time and stress intervals during these experiments. The spectra were subsequently used to obtain quantitative information related to the phase-specific strain, texture and phase fraction evolution using the Rietveld technique. The mechanical characterization of NiTiFe alloys using the cryogenic capability at SMARTS provided considerable insight into the mechanisms of phase transformation and twinning at cryogenic temperatures. Both mechanisms contribute to shape memory and pseudoelasticity phenomena. Three phases (R, B19' and B33 phases) were found to coexist at 92 K in the unloaded condition (nominal holding stress of 8 MPa). For the first time the elastic modulus of R-phase was reported from neutron diffraction experiments. Furthermore, for the first time a base-centered orthorhombic (B33) martensitic phase was identified experimentally in a NiTi-based shape memory alloy. The orthorhombic B33 phase has been theoretically predicted in NiTi from density function theory (DFT) calculations but hitherto has never been observed experimentally. The orthorhombic B33 phase was observed while observing shifting of a peak (identified to be B33) between the R and B19' peaks in the diffraction spectra collected during loading. Given the existing ambiguity in the published literature as to whether the trigonal R-phase belongs to the P3 or P space groups, Rietveld analyses were separately carried out incorporating the symmetries associated with both space groups and the impact of this choice evaluated. The constrained recovery of the B19' phase to the R-phase recorded approximately 4% strain recovery between 150 K and 170 K, with half of that recovery occurring between 160 K and 162 K. Additionally, the aforementioned research methodology developed for Ni46.8Ti50Fe3.2 shape memory alloys was applied to experiments performed on a new high temperature Ni29.5Ti50.5Pd20 shape memory alloys. The engineering aspect focused on the development of (i) a NiTiFe based thermal conduction switch that minimized the heat gradient across the shape memory actuator element, (ii) a NiTiFe based thermal conduction switch that incorporated the actuator element in the form of helical springs, and (iii) a NiTi based release mechanism. Patents are being filed for all the three shape memory actuators developed as a part of this work. This work was supported by grants from SRI, NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF. Additionally, this work benefited from the use of the Lujan Center at the Los Alamos Neutron Science Center, funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36.
Show less - Date Issued
- 2007
- Identifier
- CFE0001934, ucf:47437
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001934
- Title
- ON THE NATURE OF THE FLOW IN A SEPARATED ANNULAR DIFFUSER.
- Creator
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Dunn, Jason, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
The combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are...
Show moreThe combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are two diffusion processes in the combustor-diffuser system: The flow first exits the compressor into a pre-diffuser, or compressor discharge diffuser. This diffuser is responsible for a majority of the pressure recovery. The flow then exits the pre-diffuser by a sudden expansion into the dump diffuser. The dump diffuser comprises the majority of the losses, but is necessary to reduce the fluid velocity within acceptable limits for combustion. The topic of active flow control is gaining interest in the industry because such a technique may be able to alleviate some of the requirements of the dump diffuser. If a wider angle pre-diffuser with separation control were used the fluid velocity would be slowed more within that region without significant losses. Experiments were performed on two annular diffusers to characterize the flow separation to create a foundation for future active flow control techniques. Both diffusers had the same fully developed inlet flow condition, however, the expansion of the two diffusers differed such that one diffuser replicated a typical compressor discharge diffuser found in a real machine while the other would create a naturally separated flow along the outer wall. Both diffusers were tested at two Reynolds numbers, 5x104 and 1x105, with and without a vertical wall downstream of the exit to replicate the dump diffuser that re-directs the flow from the pre-diffuser outlet to the combustor. Static pressure measurements were obtained along the OD and ID wall of the diffusers to determine the recovered pressure throughout the diffuser. In addition to these measurements, tufts were used to visualize the flow. A turbulent CFD model was also created to compare against experimental results. In the end, the results were validated against empirical data as well as the CFD model. It was shown that the location of the vertical wall was directly related to the amount of separation as well as the separation characteristics. These findings support previous work and help guide future work for active flow control in a separated annular diffuser both computationally and experimentally.
Show less - Date Issued
- 2009
- Identifier
- CFE0002953, ucf:47944
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002953
- Title
- Thermomechanical Behavior of High-Temperature Shape Memory Alloy NiTiPdPt Actuators.
- Creator
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Nicholson, Douglas, Vaidyanathan, Rajan, Kumar, Ranganathan, Chen, Ruey-Hung, University of Central Florida
- Abstract / Description
-
To date the commercial use of shape memory alloys (SMAs) has been mostly limited to binary NiTi alloys with transformation temperatures approximately in the -100 to 100 (&)#186;C range. In an ongoing effort to develop high-temperature shape memory alloys (HTSMAs), ternary and quaternary additions are being made to binary NiTi to form NiTi-X (e.g., X: Pd, Pt, Au and Hf) alloys. Stability and repeatability can be further increased at these higher temperatures by limiting the stress, but the...
Show moreTo date the commercial use of shape memory alloys (SMAs) has been mostly limited to binary NiTi alloys with transformation temperatures approximately in the -100 to 100 (&)#186;C range. In an ongoing effort to develop high-temperature shape memory alloys (HTSMAs), ternary and quaternary additions are being made to binary NiTi to form NiTi-X (e.g., X: Pd, Pt, Au and Hf) alloys. Stability and repeatability can be further increased at these higher temperatures by limiting the stress, but the tradeoff is reduced work output and stroke. However, HTSMAs operating at decreased stresses can still be used effectively in actuator applications that require large strokes when used in the form of springs. The overall objective of this work is to facilitate the development of HTSMAs for use as high-force actuators in active/adaptive aerospace structures.A modular test setup was assembled with the objective of acquiring stroke, stress, temperature and moment data in real time during joule heating and forced convective cooling of Ni19.5Ti50.5Pd25Pt5 HTSMA springs. The spring actuators were evaluated under both monotonic axial loading and thermomechanical cycling. The role of rotational constraints (i.e., by restricting rotation or allowing for free rotation at the ends of the springs) on stroke performance was also assessed. Recognizing that evolution in the material microstructure results in changes in geometry and vice versa in HTSMA springs, the objective of the present study also included assessing the contributions from the material microstructural evolution, by eliminating contributions from changes in geometry, to overall HTSMA spring performance. The finite element method (FEM) was used to support the analytical analyses and provided further insight into the behavior and heterogeneous stress states that exist in these spring actuators.Furthermore, with the goal of improving dimensional stability there is a need to better understand the microstructural evolution in HTSMAs that contributes to irrecoverable strains. Towards this goal, available Ni29.5Ti50.5Pd20 neutron diffraction data (from a comparable HTMSA alloy without the solid solution strengthening offered by the Pt addition) were analyzed. The data was obtained from in situ neutron diffraction experiments performed on Ni29.5Ti50.5Pd20 during compressive loading while heating/cooling, using the Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory. Specifically, in this work emphasis was placed on neutron diffraction data analysis via Rietveld refinement and capturing the texture evolution through inverse pole figures. Such analyses provided quantitative information on the evolution of lattice strain, phase volume fraction (including retained martensite that exists above the austenite finish temperature) and texture (martensite variant reorientation and detwinning) under temperature and stress. Financial support for this work from NASA's Fundamental Aeronautics Program Supersonics Project (NNX08AB51A), Subsonic Fixed Wing Program (NNX11AI57A) and the Florida Center for Advanced Aero-Propulsion (FCAAP) is gratefully acknowledged. It benefited additionally from the use of the Lujan Neutron Scattering Center at Los Alamos National Laboratory, which is funded by the Office of Basic Energy Sciences (Department of Energy) and is operated by Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396.
Show less - Date Issued
- 2011
- Identifier
- CFE0004147, ucf:49059
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004147
- Title
- DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH.
- Creator
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Krishnan, Vinu Bala, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of...
Show moreShape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.
Show less - Date Issued
- 2004
- Identifier
- CFE0000038, ucf:46136
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000038
- Title
- INVESTIGATION OF THERMAL, ELASTIC AND LOAD-BIASED TRANSFORMATION STRAINS IN NITI SHAPE MEMORY ALLOYS.
- Creator
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Qiu, Shipeng, Vaidyanathan, Raj, University of Central Florida
- Abstract / Description
-
Polycrystalline NiTi shape memory alloys have the ability to recover their original, pre-deformed shape in the presence of external loads when heated through a solid-solid phase transformation from a lower-symmetry B19' martensite phase to a higher-symmetry B2 austenite phase. The strain associated with a shape memory alloy in an actuator application typically has thermal, elastic and inelastic contributions. The objective of this work was to investigate the aforementioned strains by...
Show morePolycrystalline NiTi shape memory alloys have the ability to recover their original, pre-deformed shape in the presence of external loads when heated through a solid-solid phase transformation from a lower-symmetry B19' martensite phase to a higher-symmetry B2 austenite phase. The strain associated with a shape memory alloy in an actuator application typically has thermal, elastic and inelastic contributions. The objective of this work was to investigate the aforementioned strains by recourse to in situ neutron diffraction experiments during selected combinations of heating, cooling and/or mechanical loading. The primary studies were conducted on polycrystalline Ni49.9Ti50.1 specimens on the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory. Quantitative information on the phase-specific strain, texture and phase fraction evolution was obtained from the neutron data using Rietveld refinement and single-peak analyses, and compared with macroscopic data from extensometry. First, the lattice strain evolution during heating and cooling in an unloaded sample (i.e., free-recovery experiment) was studied. The lattice strain evolution remained linear with temperature and was not influenced by intergranular stresses, enabling the determination of a thermal expansion tensor that quantified the associated anisotropy due to the symmetry of B19' NiTi. The tensor thus determined was subsequently used to obtain an average coefficient of thermal expansion that was consistent with macroscopic dilatometric measurements and a 30,000 grain polycrystalline self-consistent model. The accommodative nature of B19' NiTi was found to account for macroscopic shape changes lagging (with temperature) the start and finish of the transformation. Second, the elastic response of B19' martensitic NiTi variants during monotonic loading was studied. Emphasis was placed on capturing and quantifying the strain anisotropy which arises from the symmetry of monoclinic martensite and internal stresses resulting from intergranular constraints between individual variants and load re-distribution among variants as the texture evolved during variant reorientation and detwinning. The methodology adopted took into account both tensile and compressive loading given the asymmetric response in the texture evolution. Plane specific elastic moduli were determined from neutron measurements and compared with those determined using a self-consistent polycrystalline deformation model and from recently reported elastic stiffness constants determined via ab initio calculations. The comparison among the three approaches further helped understand the influence of elastic anisotropy, intergranular constraint, and texture evolution on the deformation behavior of polycrystalline B19' NiTi. Connections were additionally made between the assessed elastic properties of martensitic NiTi single crystals (i.e., the single crystal stiffness tensor) and the overall macroscopic response in bulk polycrystalline form. Lastly, the role of upper-cycle temperature, i.e., the maximum temperature reached during thermal cycling, was investigated during load-biased thermal cycling of NiTi shape memory alloys at selected combinations of stress and temperature. Results showed that the upper-cycle temperature, under isobaric conditions, significantly affected the amount of transformation strain and thus the work output available for actuation. With the objective of investigating the underlying microstructural and micromechanical changes due to the influence of the upper-cycle temperature, the texture evolution was systematically analyzed. While the changes in transformation strain were closely related to the evolution in texture of the room temperature martensite, retained martensite in the austenite state could additionally affect the transformation strain. Additionally, multiple thermal cycles were performed under load-biased conditions in both NiTi and NiTiPd alloys, to further assess and understand the role of retained martensite. Dimensional and thermal stabilities of these alloys were correlated with the volume fraction and texture of retained martensite, and the internal strain evolution in these alloys. The role of symmetry, i.e., B19' monoclinic martensite vs. B19 orthorhombic martensite in these alloys was also assessed. This work not only established a methodology to study the thermal and elastic properties of the low symmetry B19' monoclinic martensite, but also provided valuable insight into quantitative micromechanical and microstructural changes responsible for the thermomechanical response of NiTi shape memory alloys. It has immediate implications for optimizing shape memory behavior in the alloys investigated, with extension to high temperature shape memory alloys with ternary and quaternary elemental additions, such as Pd, Pt and Hf. This work was supported by funding from NASAÂÂ's Fundamental Aeronautics Program, Supersonics Project (NNX08AB51A) and NSF (CAREER DMR-0239512). It benefited additionally from the use of the Lujan Neutron Scattering Center at Los Alamos National Laboratory, which is funded by the Office of Basic Energy Sciences (Department of Energy) and is operated by Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396.
Show less - Date Issued
- 2010
- Identifier
- CFE0003362, ucf:48440
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003362
