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The Mass Transfer of Single, Solid Uranium Spheres to Flowing Molten Cadmium in Laminar and Turbulent Flow

Description: From Summary and Abstract: "In this study, a 1/2-inch diameter uranium sphere was used and molten cadmium was pumped past the test spheres at different flow rates. Mass transfer coefficients were determined from weight losses of the test spheres."
Date: September 1965
Creator: Traylor, E. Dean
Partner: UNT Libraries Government Documents Department

Apparatus for measurements of time and space correlation

Description: The report describes a brief review is made of improvements to an experimental apparatus for time and space correlation designed for study of turbulence. Included is a description of the control of the measurements and a few particular applications.
Date: April 1955
Creator: Favre, Alexandre; Gaviglio, J & Dumas, R
Partner: UNT Libraries Government Documents Department

Airspeed fluctuations as a measure of atmospheric turbulence

Description: From Introduction: "Increments in structural loads due to atmospheric turbulence can be accurately expressed in terms of flight speed and effective gust velocities (reference 4). Data from which the effective gust velocities could be computed were also obtained during the flights of the XC-35 airplane. These data have been used to determine the significance of the fluctuations in the pilot's indicated-airspeed readings in relation to structural loads to due to atmospheric turbulence."
Date: July 1945
Creator: Tolefson, H B
Partner: UNT Libraries Government Documents Department

An analysis of the indications of the University of Chicago airborne turbulence indicator in gusty air

Description: From Introduction: "The present report has been prepared to discuss the indications obtained from the University of Chicago turbulence indicator in relation to simultaneous measurement of atmospheric gustiness made by the NACA, which are summarized herein."
Date: August 1946
Creator: Pratt, K G
Partner: UNT Libraries Government Documents Department

Geometry Dependence of Stellarator Turbulence

Description: Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes.
Date: August 10, 2009
Creator: H.E. Mynick, P. Xanthopoulos and A.H. Boozer
Partner: UNT Libraries Government Documents Department

An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear

Description: The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.
Date: May 11, 2011
Creator: J. L. Peterson, G.W. Hammett, D.R. Mikkelsen, H.Y. Yuh, J. Candy, W. Guttenfelder, S.M. Kaye, and B. LeBlanc
Partner: UNT Libraries Government Documents Department

Electromagnetic Transport From Microtearing Mode Turbulence

Description: This Letter presents non-linear gyrokinetic simulations of microtearing mode turbulence. The simulations include collisional and electromagnetic effects and use experimental parameters from a high beta discharge in the National Spherical Torus Experiment (NSTX). The predicted electron thermal transport is comparable to that given by experimental analysis, and it is dominated by the electromagnetic contribution of electrons free streaming along the resulting stochastic magnetic field line trajectories. Experimental values of flow shear can significantly reduce the predicted transport.
Date: March 23, 2011
Creator: Guttenfelder, W; Kaye, S M; Nevins, W M; Wang, E; Bell, R E; Hammett, G W et al.
Partner: UNT Libraries Government Documents Department

Huygens-Fresnel Wave-Optics Simulation of Atmospheric Optical Turbulence and Reflective Speckle in CO

Description: The measurement sensitivity of CO{sub 2} differential absorption LIDAR (DIAL) can be affected by a number of different processes. Two of these processes are atmospheric optical turbulence and reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. The effects of this phenomenon include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. The authors have previously developed a Huygens-Fresnel wave optics propagation code to separately simulate the effects of these two processes. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, the authors briefly review a description of the model including the limitations along with a brief summary of previous simulations of individual effects. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, simulation studies have been performed to demonstrate the utility and limitations of the model. Examples presented include assessing the effects for different array sizes on model limitations and effects of varying propagation step sizes on intensity enhancements and intensity probability distributions in the receiver plane.
Date: July 18, 1999
Creator: Nelson, D.H.; Petrin, R.R.; Quick, C.R.; Jolin, L.J.; MacKerrow, E.P.; Schmidtt, M.J. et al.
Partner: UNT Libraries Government Documents Department

Gyrokinetic Statistical Absolute Equilibrium and Turbulence

Description: A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence [T.-D. Lee, "On some statistical properties of hydrodynamical and magnetohydrodynamical fields," Q. Appl. Math. 10, 69 (1952)] is taken to study gyrokinetic plasma turbulence: A finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N + 1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperature states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.
Date: January 10, 2011
Creator: Zhu, Jian-Zhou & Hammett, Gregory W.
Partner: UNT Libraries Government Documents Department

Turbulence studies in Tokamak boundary plasmas with realistic divertor geometry

Description: Results are presented from the 3D nonlocal electromagnetic turbulence code BOUT [1] and the linearized shooting code BAL[2] to study turbulence in tokamak boundary plasmas and its relationship to the L-H transition, in a realistic divertor plasma geometry. The key results include: (1) the identification of the dominant, resistive X-point mode in divertor geometry and (2) turbulence suppression in the L-H transition by shear in the ExB drift speed, ion diamagnetism and finite polarization. Based on the simulation results, a parameterization of the transport is given that includes the dependence on the relevant physical parameters.
Date: October 14, 1998
Creator: Xu, X.Q.
Partner: UNT Libraries Government Documents Department

Subgrid-scale model for the scalar dissipation rate in nonpremixed combustion

Description: A subgrid-scale model is presented for the scalar dissipation rate in nonpremixed turbulent reacting flows. Inputs to the model are the filtered density, the Favre- filtered temperature and the Favre-filtered misture-fraction. The model contains a coefficient which is determined by assuming a form for the scalar energy spectrum. Inputs to the presumed spectrum are the integral and dissipation length scales of the scalar field. These quantities are estimated locally from the Favre-filtered velocity field, resulting in a model coefficient which is spatially and temporally dependent. The model is tested a priori using data from a Direct Numerical Simulation (DXS) of a temporal reacting mixing layer. Estimated values of the dissipation rate are found in good agreement with dissipation rates computed directly from the DXS data. Furthermore, the presumed spectrum methodology is found to accurately predict the mean value of the model coefficient as well as its spatial and temporal variations.
Date: August 31, 1998
Creator: Bushe, W. K. & Cook, A. W.
Partner: UNT Libraries Government Documents Department

Manifold methods for methane combustion

Description: Objective is to develop a new method for studying realistic chemistry in turbulent methane combustion with NO{sub x} mechanism. The realistic chemistry is a simplification to a more detailed chemistry based on the manifold method; accuracy is determined by interaction between the transport process and the chemical reaction. In this new (tree) method, probability density function or partially stirred reactor calculations are performed. Compared with the reduced mechanism, manifold, and tabulation methods, the new method overcomes drawbacks of the reduced mechanism method and preserves the advantages of the manifold method. Accuracy is achieved by specifying the size of the cell.
Date: December 31, 1995
Creator: Yang, B. & Pope, S.B.
Partner: UNT Libraries Government Documents Department

Implementation and Validation of a Reynolds Stress Model in the COMMIX-1C/RSM and CAPS-3D/RSM Codes

Description: A Reynolds stress model (RSM) of turbulence, based on seven transport equations, has been linked to the COMMIX-1C/RSM and CAPS-3D/RSM computer codes. Six of the equations model the transport of the components of the Reynolds stress tensor and the seventh models the dissipation of turbulent kinetic energy. When a fluid is heated, four additional transport equations are used: three for the turbulent heat fluxes and one for the variance of temperature fluctuations. All of the analytical and numerical details of the implementation of the new turbulence model are documented. The model was verified by simulation of homogeneous turbulence.
Date: August 1995
Creator: Chang, F. C. & Bottoni, M.
Partner: UNT Libraries Government Documents Department

Atmospheric Turbulence

Description: Some characteristics of turbulence near the ground can begin to be interpreted There is yet little information about others (even near the ground) such as spectra measured along the vertical lines, or cross spectra between two variables. Further, results of turbulence characteristics over water are few and confusing, and no information exists about the effects of cities and deserts. As we go aloft, our information about spectra becomes more scanty, although the general areas of large turbulence intensity are fairly well known (auth)
Date: September 1, 1959
Creator: Panofsky, H. A.
Partner: UNT Libraries Government Documents Department

Progress in Simulating Turbulent Electron Thermal Transport in NSTX

Description: Nonlinear simulations based on multiple NSTX discharge scenarios have progressed to help differentiate unique instability mechanisms and to validate with experimental turbulence and transport data. First nonlinear gyrokinetic simulations of microtearing (MT) turbulence in a high-beta NSTX H-mode discharge predict experimental levels of electron thermal transport that are dominated by magnetic flutter and increase with collisionality, roughly consistent with energy confinement times in dimensionless collisionality scaling experiments. Electron temperature gradient (ETG) simulations predict significant electron thermal transport in some low and high beta discharges when ion scales are suppressed by E x B shear. Although the predicted transport in H-modes is insensitive to variation in collisionality (inconsistent with confinement scaling), it is sensitive to variations in other parameters, particularly density gradient stabilization. In reversed shear (RS) Lmode discharges that exhibit electron internal transport barriers, ETG transport has also been shown to be suppressed nonlinearly by strong negative magnetic shear, s<<0. In many high beta plasmas, instabilities which exhibit a stiff beta dependence characteristic of kinetic ballooning modes (KBM) are sometimes found in the core region. However, they do not have a distinct finite beta threshold, instead transitioning gradually to a trapped electron mode (TEM) as beta is reduced to zero. Nonlinear simulations of this "hybrid" TEM/KBM predict significant transport in all channels, with substantial contributions from compressional magnetic perturbations. As multiple instabilities are often unstable simultaneously in the same plasma discharge, even on the same flux surface, unique parametric dependencies are discussed which may be useful for distinguishing the different mechanisms experimentally.
Date: July 17, 2013
Creator: Guttenfelder, Walter; Kaye, S. M.; Ren, Y.; Bell, R. E.; Hammett, G. W.; LeBlanc, B. P. et al.
Partner: UNT Libraries Government Documents Department

Theoretical Studies of Drift-Alfven and Energetic Particle Physics in Fusion Plasmas

Description: Nonlinear equations for the slow space-time evolution of the radial drift-wave envelope and zonal flow amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent four-wave drift wave-zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7, 3129 (2000)]. Solutions clearly demonstrate turbulence spreading due to nonlinearly dispersiveness and, consequently, the device-size dependence of the saturated wave intensities and transport coefficients.
Date: July 6, 2005
Creator: Chen, Liu
Partner: UNT Libraries Government Documents Department

Final Report - Investigation of Intermittent Turbulence and Turbulent Structures in the Presence of Controlled Sheared Flows

Description: Final Report for grant DE-FG02-06ER54898. The dynamics and generation of intermittent plasma turbulent structures, widely known as "blobs" have been studied in the presence of sheared plasma flows in a controlled laboratory experiment.
Date: June 27, 2013
Creator: Gilmore, Mark A.
Partner: UNT Libraries Government Documents Department

Zonal Flow as Pattern Formation: Merging Jets and the Ultimate Jet Length Scale

Description: Zonal flows are well known to arise spontaneously out of turbulence. It is shown that for statisti- cally averaged equations of quasigeostrophic turbulence on a beta plane, zonal flows and inhomoge- neous turbulence fit into the framework of pattern formation. There are many implications. First, the zonal flow wavelength is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.
Date: January 30, 2013
Creator: Krommes, Jeffrey B. Parker and John A.
Partner: UNT Libraries Government Documents Department