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Full-Text Articles in Mechanical Engineering
Effect Of Processing Conditions On The Development Of Morphology In Clay Nanoparticle Filled Nylon 6 Fibers, Zeynep Ergungor, Mukerrem Cakmak, Celal Batur
Effect Of Processing Conditions On The Development Of Morphology In Clay Nanoparticle Filled Nylon 6 Fibers, Zeynep Ergungor, Mukerrem Cakmak, Celal Batur
Dr. Celal Batur
The effect of melt temperature on the phase behavior and preferential orientation development in Nylon 6/montmorillonite nanocomposites were investigated at melt spinning temperatures ranging from 230° to 250°C. The fibers were found to exhibit mostly γ crystalline form that is typical of Nylon 6 filled with montmorillonite nanoparticles. At higher take-up speeds α-crystals begin to appear in the crystalline phase. The presence of nanoparticles was found to impart substantial chain orientation levels even at low to moderate take up speeds reaching a plateau at moderate take up speeds. This was attributed to the increased spin line stress in the presence …
Non-Intrusive Laser-Based, Full-Field Quantitative Flow Measurements Aided By Digital Image Processing. Part 2: The Hydrostatic Journal Bearing, Minel Braun, Celal Batur
Non-Intrusive Laser-Based, Full-Field Quantitative Flow Measurements Aided By Digital Image Processing. Part 2: The Hydrostatic Journal Bearing, Minel Braun, Celal Batur
Dr. Celal Batur
The full field flow tracking technique based on computer-aided image processing in combination with the non-intrusive particle tracking procedure described in Part 1 of this paper is used for quantification of qualitative images of flow in a six-pocket hydrostatic journal bearing. The method uses long distance microscopy (LDM) to evaluate at the same station in time, trajectories, velocities and accelerations throughout the flow field. For accurate and detailed evaluation, a new windowing procedure (WP) and an associated windowing assembly procedure (WAP) are introduced. The combination of WP and WAP brings together the LDM high magnification individually indexed windows into a …
A Stability Model For Steam Generators, Ahmet Duyar, Richard Gross
A Stability Model For Steam Generators, Ahmet Duyar, Richard Gross
Dr. Richard J. Gross
A mathematical model to analyze the stability of the two-phase flow in a generalized steam generator is developed. A counter flow heat exchanger in which a high temperature primary fluid heats and vaporizes a lower temperature secondary fluid is considered as the system. The governing equations of this system is obtained by using the transient field equations, constitutive relations, boundary conditions and the initial conditions of both the primary and the secondary fluids. The governing equations of the secondary fluid are decoupled from the equations of the primary fluid by determining a heat flux profile and superimposing it on the …
Membrane Transport Characteristics Of Ultrafine Capillaries, Richard Gross, J. Osterle
Membrane Transport Characteristics Of Ultrafine Capillaries, Richard Gross, J. Osterle
Dr. Richard J. Gross
No abstract provided.
Natural Convection In A Shallow Cavity, Jerry Dummond
Natural Convection In A Shallow Cavity, Jerry Dummond
Dr. Jerry E. Drummond
We present numerical solutions of natural convection in a shallow enclosure heated from a side. As a result of hydrodynamic instability transverse cells appear in the flow if the Prandtl number is sufficiently small. Both conducting and insulated top and bottom boundaries were considered. For fluids of small Prandtl number the differences in the flow patterns in these two cases are slight, the strength of the circulation in the cells being somewhat weaker when the boundaries are insulated. This is a result of a more stable flow in this case, caused by the kinetic energy being more vigorously expended in …
Heat Transfer Through A Double Pane Window, S. Korpela, Yee Lee, Jerry Drummond
Heat Transfer Through A Double Pane Window, S. Korpela, Yee Lee, Jerry Drummond
Dr. Jerry E. Drummond
No abstract provided.
Why You Should Not Use 'Hybrid', 'Power-Law' Or Related Exponential Schemes For Convective Modelling—There Are Much Better Alternatives, Brian Leonard, Jerry Drummond
Why You Should Not Use 'Hybrid', 'Power-Law' Or Related Exponential Schemes For Convective Modelling—There Are Much Better Alternatives, Brian Leonard, Jerry Drummond
Dr. Jerry E. Drummond
In many areas of computational fluid dynamics, especially numerical convective heat and mass transfer, the ‘Hybrid’ and ‘Power-Law’ schemes have been widely used for many years. The popularity of these methods for steady-state computations is based on a combination of algorithmic simplicity, fast convergence, and plausible looking results. By contrast, classical (second-order central) methods often involve convergence problems and may lead to obviously unphysical solutions exhibiting spurious numerical oscillations. Hybrid, Power-Law, and the exponential-difference scheme on which they are based give reasonably accurate solutions for steady, quasi-one-dimensional flow (when the grid is aligned with the main flow direction). However, they …
Experimental Investigation Of Leak-Rate Performance Of A Subscale Composite Elastomer-Retainer Docking Seal, Nicholas Garafolo, Christopher Daniels
Experimental Investigation Of Leak-Rate Performance Of A Subscale Composite Elastomer-Retainer Docking Seal, Nicholas Garafolo, Christopher Daniels
Dr. Nicholas Garafolo
A novel docking seal was investigated for application to the main interface seal of NASA’s low-impact docking system. This interface seal was designed to maintain acceptable leak rates while being exposed to the harsh environmental conditions of outer space. In this experimental evaluation, the leak rate of a candidate docking-seal assembly was characterized and evaluated. The composite seal was manufactured from silicone elastomer S0383-70, vacuum molded into a metal retaining ring. Four seal designs were considered with unique characteristic heights. The leak-rate performance was characterized through a mass point leak-rate method by monitoring gas properties within an internal control volume. …
Effect Of System Variables On The Uncertainty Of The Mass Point Leak Rate Methodology Using First-Order Regression, Christopher Daniels, Nicholas Garafolo
Effect Of System Variables On The Uncertainty Of The Mass Point Leak Rate Methodology Using First-Order Regression, Christopher Daniels, Nicholas Garafolo
Dr. Nicholas Garafolo
Advances in nondestructive testing for leak rate characterisation are rare because procedures are well accepted; however, for many critical applications, an understanding of the accuracy and reliability of a reported leak rate is equally as important as the leak rate itself (e.g., manned spacecraft and nuclear power industry). Although it is known that the mass point leak rate method can achieve high accuracies, the measurement uncertainty and limitations of the method are less understood. Using a least-squares regression on a mass–time population and a statistical analysis of regression uncertainty, this study investigated the influence of (1) differential pressure, (2) steady-state …
A Compressible Permeation Approach To Elastomeric Space Seal Characterization, Nicholas Garafolo, Christopher Daniels
A Compressible Permeation Approach To Elastomeric Space Seal Characterization, Nicholas Garafolo, Christopher Daniels
Dr. Nicholas Garafolo
The development of elastomeric face seals is imperative for NASA’s manned space flight program. Lacking in the development of state-of-the-art space seals was a technique for predicting the performance of candidate designs prior to experimental characterization. To this end, a physics-based model for compressible permeation in elastomeric face seals was developed to provide a predictive methodology for designers and researchers. In this novel approach for seal research, compressibility effects and the dependence of permeability on pressure was retained. Two independent permeation parameters arose from an exact, analytical solution to the one-dimensional permeation transport equations. The application of the derived transport …
High-Accuracy Large-Step Explicit Runge–Kutta (Hale-Rk) Schemes For Computational Aeroacoustics, Vasanth Allampalli, Ray Hixon, Raj Nallasamy, Scott Sawyer
High-Accuracy Large-Step Explicit Runge–Kutta (Hale-Rk) Schemes For Computational Aeroacoustics, Vasanth Allampalli, Ray Hixon, Raj Nallasamy, Scott Sawyer
Dr. Scott Sawyer
In many realistic calculations, the computational grid spacing required to resolve the mean flow gradients is much smaller than the grid spacing required to resolve the unsteady propagating waves of interest. Because of this, the high temporal resolution provided by existing optimized time marching schemes can be excessive due to the small time step required for stability in regions of clustered grid. In this work, explicit fourth-order accurate Runge–Kutta time marching schemes are optimized to increase the inviscid stability limit rather than the accuracy at large time steps. Single and multiple-step optimized schemes are developed and analyzed. The resulting schemes …
A Laplace Transform/Potential-Theoretic Method For Acoustic Propagation In Subsonic Flows, S. Hariharan, Scott Sawyer, D, Quinn
A Laplace Transform/Potential-Theoretic Method For Acoustic Propagation In Subsonic Flows, S. Hariharan, Scott Sawyer, D, Quinn
Dr. Scott Sawyer
This paper introduces a competitive computational approach for determining time-dependent far-field sound generated by subsonic flows around lifting airfoils. The procedure assumes the linearity of the sound field away from a bounded region surrounding the airfoil. It is assumed that the sound pressure on the boundary of this enclosed region (referred to as the Kirchhoff surface) is specified, possibly by another procedure such as solving the full Euler equations. Away from the Kirchhoff surface, the Euler equations are linearized about a uniform mean flow. It is well known that linearized Euler equations can be uncoupled into a scalar convective wave …
Active Control Of Discrete-Frequency Noise Generated By Rotor-Stator Interactions, Scott Sawyer, Sanford Fleeter, John Simonich
Active Control Of Discrete-Frequency Noise Generated By Rotor-Stator Interactions, Scott Sawyer, Sanford Fleeter, John Simonich
Dr. Scott Sawyer
Discrete-frequency tones generated by unsteady blade row interactions are of particular concern in the design of advanced turbine engines...
Transform Potential-Theoretic Method For Acoustic Radiation From Structures, S. Hariharan, Scott Sawyer
Transform Potential-Theoretic Method For Acoustic Radiation From Structures, S. Hariharan, Scott Sawyer
Dr. Scott Sawyer
This paper presents further development in a new time-domain computational technique developed for the determination of far-field acoustic radiation. This method, referred to as the transform potential-theoretic (TPT) method, solves linear time-dependent wave propagation problems in an unbounded medium, combining techniques involving numerical transforms/inverse transforms and potential theory. The end result is a robust procedure that is accurate and computationally efficient. The TPT technique is meshless, yet it can handle arbitrary geometries for the acoustic source. The validity of the procedure is demonstrated for the case of an acoustic wave propagation from a two-dimensional bounded surface embedded in a uniform …
Validation Of A Computational Aeroacoustics Code For Nonlinear Flow About Complex Geometries Using Ringleb's Flow, Vinit Satav, Ray Hixon, M. Nallasamy, Scott Sawyer
Validation Of A Computational Aeroacoustics Code For Nonlinear Flow About Complex Geometries Using Ringleb's Flow, Vinit Satav, Ray Hixon, M. Nallasamy, Scott Sawyer
Dr. Scott Sawyer
This work is concerned with the validation of a high-accuracy Computational Aeroacoustics (CAA) code designed for use in the prediction of unsteady compressible flow about complex geometries, using Ringleb's analytic solution of the compressible steady Euler equations...
Flutter Stability Of A Detuned Cascade In Subsonic Compressible Flow, Scott Sawyer, Sanford Fleeter
Flutter Stability Of A Detuned Cascade In Subsonic Compressible Flow, Scott Sawyer, Sanford Fleeter
Dr. Scott Sawyer
A mathematical model is developed to predict the unsteady aerodynamics of a detuned two-dimensional flat plate cascade in subsonic compressible flow. Aerodynamic detuning is introduced by nonuniform circumferential spacing and chordwise offset. Combined aerodynamic-structural detuning is accomplished by replacing alternative airfoils with splitter blades...
Effect Of Grid Singularities On The Solution Accuracy Of A Caa Code, R. Hixon, M. Nallasamy, Scott Sawyer
Effect Of Grid Singularities On The Solution Accuracy Of A Caa Code, R. Hixon, M. Nallasamy, Scott Sawyer
Dr. Scott Sawyer
In this work, the effect of a grid singularities on the solution accuracy of a high-accuracy finite-difference Computational Aeroacoustics code is investigated by applying the NASA Glen Research Center ABS code to a simple benchmark flow.
Application Of A Nonlinear Computational Aeroacoustics Code To The Gust-Airfoil Problem, R. Hixon, V. Golubev, R. Mankbadi, J. Scott, Scott Sawyer, M. Nallasamy
Application Of A Nonlinear Computational Aeroacoustics Code To The Gust-Airfoil Problem, R. Hixon, V. Golubev, R. Mankbadi, J. Scott, Scott Sawyer, M. Nallasamy
Dr. Scott Sawyer
A time-domain solution of the gust-airfoil problem is obtained using a high-accuracy computational aeroacoustics code to solve the nonlinear Euler equations. For computational efficiency, the equations are cast in chain-rule curvilinear form, and a structured multiblock solver is used on a distributed-memory parallel computer cluster.
Bass Code Development, Scott Sawyer
Bass Code Development, Scott Sawyer
Dr. Scott Sawyer
The BASS computational aeroacoustic code solves the fully nonlinear Euler equations in the time domain in two-dimensions. The acoustic response of the stator is determined simultaneously for the first three harmonics of the convected vortical gust of the rotor. The spatial mode generation, propagation and decay characteristics are predicted by assuming the acoustic field away from the stator can be represented as a uniform flow with small harmonic perturbations superimposed. The computed field is then decomposed using a joint temporal-spatial transform to determine the wave amplitudes as a function of rotor harmonic and spatial mode order. This report details the …
A Computational Aeroacoustic Prediction Of Discrete-Frequency Rotor-Stator Interaction Noise - A Linear Theory Analysis, Scott Sawyer, M. Nallasamy, R. Hixon, R. Dyson
A Computational Aeroacoustic Prediction Of Discrete-Frequency Rotor-Stator Interaction Noise - A Linear Theory Analysis, Scott Sawyer, M. Nallasamy, R. Hixon, R. Dyson
Dr. Scott Sawyer
The discrete-frequency noise generated by a rotor-stator interaction is computed by solving the fully nonlinear Euler equations in the time domain in two-dimensions. The acoustic response of the stator is determined simultaneously for the first three harmonics of the convected vertical gust of the rotor. The spatial mode generation, propagation and decay characteristics are predicted by assuming the acoustic field away from the stator can be represented as a uniform flow with small harmonic perturbations superimposed...
Solution Of Unsteady Euler Equations: Gust–Cascade Interaction Tones, Raj Nallasamy, Ray Hixon, Scott Sawyer
Solution Of Unsteady Euler Equations: Gust–Cascade Interaction Tones, Raj Nallasamy, Ray Hixon, Scott Sawyer
Dr. Scott Sawyer
The problem of interaction of a vortical gust with a two-dimensional cascade is considered. Full nonlinear time dependent Euler equations governing the flow are solved employing a 6th-order accurate spatial differencing scheme and a 4th-order accurate time marching technique. The vortical gust is represented by a Fourier series which includes three harmonics. The acoustic response of the cascade for single and multi frequency (vortical) excitations are calculated. The solutions show the generation and propagation of modes that are expected from the theory. It is demonstrated that at low amplitudes of excitation, the time domain analysis produces characteristics of the propagating …
Comparison Of Numerical Schemes For A Realistic Computational Aeroacoustics Benchmark Problem, R. Hixon, M. Nallasamy, Scott Sawyer, R. Dyson
Comparison Of Numerical Schemes For A Realistic Computational Aeroacoustics Benchmark Problem, R. Hixon, M. Nallasamy, Scott Sawyer, R. Dyson
Dr. Scott Sawyer
In this work, a nonlinear block-structured CAA solver, the NASA Glenn Research Center BASS code, is tested on a realistic CAA benchmark problem in order to ascertain what effect the high-accuracy solution methods used in CAA have on a realistic test problem.
Simulating Nonlinear Stator Noise For Active Control, Rodgers Dyson, Ray Hixon, M. Nallasamy, Scott Sawyer
Simulating Nonlinear Stator Noise For Active Control, Rodgers Dyson, Ray Hixon, M. Nallasamy, Scott Sawyer
Dr. Scott Sawyer
No abstract provided.
Vortical Gust Boundary Condition For Realistic Rotor Wake/Stator Interaction Noise Prediction Using Computational Aeroacoustics, Ray Hixon, Adrian Sescu, Scott Sawyer
Vortical Gust Boundary Condition For Realistic Rotor Wake/Stator Interaction Noise Prediction Using Computational Aeroacoustics, Ray Hixon, Adrian Sescu, Scott Sawyer
Dr. Scott Sawyer
In this work, the NASA Glenn Research Center Broadband Aeroacoustic Stator Simulation (BASS) code is extended for use in the prediction of noise produced by realistic three-dimensional rotor wakes impinging on a downstream stator row. In order to accurately simulate such a flow using a nonlinear time-accurate solver, the inflow and outflow boundary conditions must simultaneously maintain the desired mean flow, allow outgoing vortical, entropic, and acoustic waves to cleanly exit the domain, and accurately impose the desired incoming flow disturbances. This work validates a new method for the acoustics-free imposition of three-dimensional vortical disturbances using benchmark test cases. Vortical …
Modal Decomposition Of Rotor Wake-Stator Interaction Noise In A Swirling Shear Flow, Scott Sawyer, M. Nallasamy, R. Hixon
Modal Decomposition Of Rotor Wake-Stator Interaction Noise In A Swirling Shear Flow, Scott Sawyer, M. Nallasamy, R. Hixon
Dr. Scott Sawyer
Accurate prediction of turbomachinery noise is a continuing concern for aircraft engine designers. Although significant reductions in the noise generation have been achieved, future noise reductions will rely on a fundamental understanding of the noise generation process...
Mean Stator Loading Effect On The Acoustic Response Of A Rotating Cascade, Scott Sawyer, Sanford Fleeter
Mean Stator Loading Effect On The Acoustic Response Of A Rotating Cascade, Scott Sawyer, Sanford Fleeter
Dr. Scott Sawyer
Discrete-frequency tones generated by unsteady blade row interactions are of particular concern in the design of advanced turbine engines.With a rotor-stator mounted in a duct, only certain specific spatial modes are generated by the rotor-stator interaction, where the generated modes are a function of the number of rotor blades and stator vanes.
Passive Control Of Discrete-Frequency Tones Generated By Coupled Detuned Cascades, Scott Sawyer, S. Fleeter
Passive Control Of Discrete-Frequency Tones Generated By Coupled Detuned Cascades, Scott Sawyer, S. Fleeter
Dr. Scott Sawyer
Discrete-frequency tones generated by rotor–stator interactions are of particular concern in the design of fans and compressors. Classical theory considers an isolated flat-plate cascade of identical uniformly spaced airfoils. The current analysis extends this tuned isolated cascade theory to consider coupled aerodynamically detuned cascades where aerodynamic detuning is accomplished by changing the chord of alternate rotor blades and stator vanes. In a coupled cascade analysis, the configuration of the rotor influences the downstream acoustic response of the stator, and the stator configuration influences the upstream acoustic response of the rotor. This coupled detuned cascade unsteady aerodynamic model is first applied …
Engineering A Dynamic Science Learning Environment For K-12 Teachers, Patricia Hardré, Mark Nanny, Hazem Refai, Chen Ling, Janis Slater
Engineering A Dynamic Science Learning Environment For K-12 Teachers, Patricia Hardré, Mark Nanny, Hazem Refai, Chen Ling, Janis Slater
Dr. Chen Ling
The present study follows a cohort of 17 K-12 teachers through a six-week resident learning experience in science and engineering, and on into the planning and implementation of applications for their classrooms. This Research Experiences for Teachers (RET) program was examined using the strategic approach of design-based research, with its fluid, adaptive management of the complexity of authentic learning "in situ" and its attentive documentation of expected and unexpected events, in process and products, to capture the richness of teachers' and mentors' experiences. Research on effective teacher professional development, adult learning, situated cognition, and learning transfer were utilized to inform …
Effect Of Plastic Prestrain On High Cycle Fatigue Of Ti–6al–4v, David Lanning, Theodore Nicholas, George Haritos
Effect Of Plastic Prestrain On High Cycle Fatigue Of Ti–6al–4v, David Lanning, Theodore Nicholas, George Haritos
Dr. George K. Haritos
The effect of initial plastic strain on the high cycle fatigue (HCF) lives of smooth cylindrical Ti–6Al–4V specimens is investigated. Specimens were monotonically, quasi-statically loaded under strain control in tension to produce plastic strains from 1% to 5% and under load control in compression to produce 9.5% plastic strain. A step-loading technique was then employed to establish the 106 or 107 cycle fatigue limit stress under load control conditions for stress ratios of R=0.1, 0.5 and 0.8 at frequencies of either f=50 or 400 Hz. Results are compared with baseline fatigue limit stresses for Ti–6Al–4V without prior plastic strain. Initial …
On The Use Of Critical Distance Theories For The Prediction Of The High Cycle Fatigue Limit Stress In Notched Ti–6al–4v ☆, David Lanning, Theodore Nicholas, George Haritos
On The Use Of Critical Distance Theories For The Prediction Of The High Cycle Fatigue Limit Stress In Notched Ti–6al–4v ☆, David Lanning, Theodore Nicholas, George Haritos
Dr. George K. Haritos
Methods are investigated for predicting the high cycle fatigue (HCF) lives of notched cylindrical Ti–6Al–4V specimens using critical distance concepts that employ the stress distribution in the vicinity of the notch. Cylindrical fatigue specimens had circumferential V-notches with a range of elastic stress concentration factors (kt=1.97–4.07). Notched and unnotched specimens were cycled to failure using a step-loading technique to generate points on a Haigh (Goodman) diagram for a constant fatigue life of 106 cycles. Finite element solutions were generated to provide stress distributions for the notched gage sections. The stress distributions were used in the search for a critical distance …