MEMS 411: Lift Demonstration

A portable lift demonstration was requested to get children interested and thinking about what happens with fluid movement. The demonstration had size and weight requirements, which were both met. Accuracy of lift force representation was not requested, but simple force and flow visualizations were required. The demonstration had variable wind speeds, and showed the change in force with change in angle of attack

Validation and Verification of the Wray-Agarwal Turbulence and Algebraic Transition Models for 2D External Airfoil Flows

Validation and verification benchmark test cases are employed in computational fluid dynamics (CFD) to determine the best practices in application of various CFD tools. These cases focus on the geometry modeling, mesh generation, numerical algorithms, and turbulence models to ensure consistent and accurate numerical simulation of physical phenomena. Assessing model accuracy is essential to identify areas of improvement in various turbulence models. Flow past several symmetric NACA airfoils, namely NACA 0012, NACA 0015 and NACA 0018 are standard test cases for validating and evaluating turbulence models’ accuracy since the experimental data is available for these airfoils. Available wind tunnel data allows for testing turbulence models’ capability to predict lift, drag, and pressure distributions for various angles of attack ranging at high Reynolds numbers. In this study, two turbulence models are compared to experimental data for the NACA 0012, 0015, and 0018 airfoils. The two turbulence models are the well-known one equation Spalart-Allmaras (SA) and the recently developed Wray-Agarwal (WA) model. Numerical results show that both turbulence models are capable of accurately predicting lift and pressure coefficients but generally over predict drag. However, the WA model exhibits higher accuracy in predicting lift at high angles of attack for two of the airfoils and peak pressure for NACA 0012 airfoil. The Wray-Agarwal Algebraic Transition (WA-AT) model is a recently proposed new transition model with the goal to obtain similar level or better accuracy with substantially less computational cost compared to existing three (k-kl-ω) or four ( ) equation transition models. The WA-AT model uses the wall distance free version of WA turbulence model (WA2018) in combination with an algebraic transition model. The model has been previously validated for various ERCOFTAC benchmark flat plate cases and for some aerodynamic bodies. To further validate this model, the transitional flows past NACA 0012, 0015, and 0018 airfoils are simulated for a range of Reynolds numbers, turbulence intensities, and angles of attack in ANSYS Fluent. The NACA airfoil cases are simulated at angles of attack from zero to ten degrees, and Reynolds numbers ranging from to , and turbulence intensities ranging from 0.07% to 0.3%. The validation studies show similar or improved predictions using the WA-AT model over the Langtry-Menter’s four equation transition-SST (k –ω – γ - Reθt) model for pressure, drag, lift, and transition location. Overall, the results demonstrate that the WA-AT model offers similar or better accuracy as the four-equation transition-SST model for simulation of transitional flow over NACA 0012, 0015, and 0018 airfoils at much less computational cost. In NASA’s High Fidelity CFD Workshop 2022, the Joukowski airfoil was identified as a benchmark verification case to test the convergence behavior of different turbulence models in different CFD solvers with particular emphasis on SA-neg-QCR 2000 turbulence model. This thesis also studies the accuracy and convergence behavior of Wray-Agarwal (WA) and Spalart-Allmaras (SA) one equation turbulence models by computing the flow past Joukowski airfoil on a sequence of seven workshop specified grids from coarse to fine. The benchmark case has free stream Mach number of 0.15, chord Reynolds number of 3x106 and angle of attack of 0 degree. The goal is to evaluate the convergence behavior of drag coefficient on a sequence of seven grids using WA and original version of SA model in ANSYS Fluent. Both models exhibit nearly first order convergence rates for first order solutions and second order convergence rates for second order solutions. There is no notable difference in the convergence rates between the two turbulence models for both first order and second order implementations

Optimization of staged rankine energy conversion cycles for high efficiency

Because of the fuel crisis and problems associated with thermal pollution there is new impetus and urgency for developing more efficient energy conversion systems for power generation. A preliminary analysis was undertaken to determine the potential of staged Rankine cycle systems for substantially higher efficiency. It was necessary to optimize the cycles to determine maximum potential efficiency, and the Sequential Unconstrained Minimization Technique of nonlinear programming was implemented on the Oregon State University CDC 3300 computer for this purpose. Binary, ternary, and quaternary Rankine cycle configurations were optimized for maximum efficiency under a set of realistic constraints. Liquid metal working fluids were used for the higher temperature stages with water for the low temperature stage fluid. Maximum efficiencies are presented for the best cycle configurations with peak temperatures from 900°F to 3000°F. Sensitivity of the results to certain critical assumptions is also included. The potential efficiency gains at current peak cycle temperatures are small, but, if high temperature expanders such as high temperature turbines, graphite helical rotor expanders, or MHD vapor expanders prove to be feasible, staged Rankine cycles can clearly provide high efficiencies with much lower temperature requirements than magnetohydrodynamic Brayton systems. In order to determine ultimate potential of the staged cycles, conventional Rankine cycle improvements were considered for each stage also. Only extraction/regeneration was found to give any significant improvement and results are presented for a binary configuration with one to five extractions on each stage. Organic working fluids were considered as a replacement for mercury, and ammonia was considered as a low temperature stage working fluid for a stage below the steam cycle. Neither organic fluids nor ammonia proved to have any outstanding advantages for use in staged cycles. Staged cycles with a metal working fluid topping a steam cycle are probably best overall

A Rod-Sparing Retinopathy in Bardet-Biedl Syndrome

Bardet-Biedl syndrome is a continuum of disorders characterized by systemic and ocular findings. Retinal abnormalities typically present as diffuse photoreceptor degeneration. Here, we report a novel case that suggests a rod-sparing variant of Bardet-Biedl syndrome

Slow nonequilibrium dynamics: parallels between classical and quantum glasses and gently driven systems

We review an scenario for the non-equilibrium dynamics of glassy systems that has been motivated by the exact solution of simple models. This approach allows one to set on firmer grounds well-known phenomenological theories. The old ideas of entropy crisis, fictive temperatures, free-volume... have clear definitions within these models. Aging effects in the glass phase are also captured. One of the salient features of the analytic solution, the breakdown of the fluctuation-dissipation relations, provides a definition of a bonafide {\it effective temperature} that is measurable by a thermometer, controls heat flows, partial equilibrations, and the reaction to the external injection of heat. The effective temperature is an extremely robust concept that appears in non-equilibrium systems in the limit of small entropy production as, for instance, sheared fluids, glasses at low temperatures when quantum fluctuations are relevant, tapped or vibrated granular matter, etc. The emerging scenario is one of partial equilibrations, in which glassy systems arrange their internal degrees of freedom so that the slow ones select their own effective temperatures. It has been proven to be consistent within any perturbative resummation scheme (mode coupling, etc) and it can be challenged by experimental and numerical tests, some of which it has already passed.Comment: 15 pages, 8 figure

A New High Channel-Count, High Scan-Rate, Data Acquisition System for the NASA Langley Transonic Dynamics Tunnel

A data acquisition system upgrade project, known as AB-DAS, is underway at the NASA Langley Transonic Dynamics Tunnel. AB-DAS will soon serve as the primary data system and will substantially increase the scan-rate capabilities and analog channel count while maintaining other unique aeroelastic and dynamic test capabilities required of the facility. AB-DAS is configurable, adaptable, and enables buffet and aeroacoustic tests by synchronously scanning all analog channels and recording the high scan-rate time history values for each data quantity. AB-DAS is currently available for use as a stand-alone data system with limited capabilities while development continues. This paper describes AB-DAS, the design methodology, and the current features and capabilities. It also outlines the future work and projected capabilities following completion of the data system upgrade project

Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics

The celebrated electronic properties of graphene have opened way for materials just one-atom-thick to be used in the post-silicon electronic era. An important milestone was the creation of heterostructures based on graphene and other two-dimensional (2D) crystals, which can be assembled in 3D stacks with atomic layer precision. These layered structures have already led to a range of fascinating physical phenomena, and also have been used in demonstrating a prototype field effect tunnelling transistor - a candidate for post-CMOS technology. The range of possible materials which could be incorporated into such stacks is very large. Indeed, there are many other materials where layers are linked by weak van der Waals forces, which can be exfoliated and combined together to create novel highly-tailored heterostructures. Here we describe a new generation of field effect vertical tunnelling transistors where 2D tungsten disulphide serves as an atomically thin barrier between two layers of either mechanically exfoliated or CVD-grown graphene. Our devices have unprecedented current modulation exceeding one million at room temperature and can also operate on transparent and flexible substrates

Atomically thin boron nitride: a tunnelling barrier for graphene devices

We investigate the electronic properties of heterostructures based on ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between two layers of graphene as well as other conducting materials (graphite, gold). The tunnel conductance depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Exponential behaviour of I-V characteristics for graphene/BN/graphene and graphite/BN/graphite devices is determined mainly by the changes in the density of states with bias voltage in the electrodes. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field; it offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.Comment: 7 pages, 5 figure

A Small-molecule Inhibitor Directed against the Chemokine Receptor CXCR4 Prevents its Use as an HIV-1 Coreceptor

The chemokine receptor CXCR4 is the major coreceptor used for cellular entry by T cell– tropic human immunodeficiency virus (HIV)-1 strains, whereas CCR5 is used by macrophage (M)-tropic strains. Here we show that a small-molecule inhibitor, ALX40-4C, inhibits HIV-1 envelope (Env)-mediated membrane fusion and viral entry directly at the level of coreceptor use. ALX40-4C inhibited HIV-1 use of the coreceptor CXCR4 by T- and dual-tropic HIV-1 strains, whereas use of CCR5 by M- and dual-tropic strains was not inhibited. Dual-tropic viruses capable of using both CXCR4 and CCR5 were inhibited by ALX40-4C only when cells expressed CXCR4 alone. ALX40-4C blocked stromal-derived factor (SDF)-1α–mediated activation of CXCR4 and binding of the monoclonal antibody 12G5 to cells expressing CXCR4. Overlap of the ALX40-4C binding site with that of 12G5 and SDF implicates direct blocking of Env interactions, rather than downregulation of receptor, as the mechanism of inhibition. Thus, ALX40-4C represents a small-molecule inhibitor of HIV-1 infection that acts directly against a chemokine receptor at the level of Env-mediated membrane fusion

Trouble at the top: The construction of a tenant identity in the governance of social housing organizations

The project of citizen governance has transformed the social housing sector in England where 20,000 tenants now sit as directors on the boards of housing associations, but the entrance of social housing tenants to the boardroom has aroused opposition from the chief executives of housing companies and triggered regulatory intervention from government inspectors. This paper investigates the cause of these tensions through a theoretical framework drawn from the work of feminist philosopher Judith Butler. It interprets housing governance as an identificatory project with the power to constitute tenant directors as regulated subjects, and presents evidence to suggest that this project of identity fails to completely enclose its subject, allowing tenant directors to engage in ‘identity work’ that threatens the supposed unity of the board. The paper charts the development of antagonism and political tension in the board rooms of housing companies to present an innovative account of the construction and contestation of identities in housing governance