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Analytic, High-beta Solutions of the Helical Grad-Shafranov Equation

Description: We present analytic, high-beta ({beta} {approx} O(1)), helical equilibrium solutions for a class of helical axis configurations having large helical aspect ratio, with the helix assumed to be tightly wound. The solutions develop a narrow boundary layer of strongly compressed flux, similar to that previously found in high beta tokamak equilibrium solutions. The boundary layer is associated with a strong localized current which prevents the equilibrium from having zero net current.
Date: May 19, 2004
Creator: Smith, D.R. & Reiman, A.H.
Partner: UNT Libraries Government Documents Department

Oscillations of a Turbulent Jet Incident Upon an Edge

Description: For the case of a jet originating from a fully turbulent channel flow and impinging upon a sharp edge, the possible onset and nature of coherent oscillations has remained unexplored. In this investigation, high-image-density particle image velocimetry and surface pressure measurements are employed to determine the instantaneous, whole-field characteristics of the turbulent jet-edge interaction in relation to the loading of the edge. It is demonstrated that even in absence of acoustic resonant or fluid-elastic effects, highly coherent, self-sustained oscillations rapidly emerge above the turbulent background. Two clearly identifiable modes of instability are evident. These modes involve large-scale vortices that are phase-locked to the gross undulations of the jet and its interaction with the edge, and small-scale vortices, which are not phase-locked. Time-resolved imaging of instantaneous vorticity and velocity reveals the form, orientation, and strength of the large-scale concentrations of vorticity approaching the edge in relation to rapid agglomeration of small-scale vorticity concentrations. Such vorticity field-edge interactions exhibit rich complexity, relative to the simplified pattern of vortex-edge interaction traditionally employed for the quasi-laminar edgetone. Furthermore, these interactions yield highly nonlinear surface pressure signatures. The origin of this nonlinearity, involving coexistence of multiple frequency components, is interpreted in terms of large- and small-scale vortices embedded in distributed vorticity layers at the edge. Eruption of the surface boundary layer on the edge due to passage of the large-scale vortex does not occur; rather apparent secondary vorticity concentrations are simply due to distension of the oppositely-signed vorticity layer at the tip of the edge. The ensemble-averaged turbulent statistics of the jet quickly take on an identity that is distinct from the statistics of the turbulent boundary layer in the channel. Large increases in Reynolds stress occur due to onset of the small-scale concentrations of vorticity immediately downstream of separation; substantial increases at locations further ...
Date: September 19, 2000
Creator: Lin, J.C. & Rockwell, D.
Partner: UNT Libraries Government Documents Department

Schlieren investigation of the wing shock-wave boundary-layer interaction in flight

Description: Report presenting data obtained in flight using a schileren apparatus that photographed the shock-wave interaction with a thick turbulent boundary layer on a wing. Local Mach number and boundary-layer characteristics obtained from pressure measurements in the vicinity of the shock wave are also presented.
Date: September 19, 1951
Creator: Cooper, George E. & Bray, Richard S.
Partner: UNT Libraries Government Documents Department

An evaluation of four experimental methods for measuring mean properties of a supersonic turbulent boundary layer

Description: From Summary: "Surveys were made through a turbulent boundary layer on a flat plate by means of a pitot probe, an x-ray densitometer, and hot-wire and cold-wire probes. Results from these surveys were analyzed to determine (a) the reliability of the basic data and hence the methods by which they were obtained, and (b) how well the actual distributions of properties in the boundary layer compare with those commonly assumed in semiempirical and theoretical analyses. All surveys were made at the same longitudinal station on the flat plate. The tests were conducted in a an 8- by 8-inch supersonic nozzle. The free-stream Mach number was 3.03 and the Reynolds number was approximately 210,000 based on boundary-layer thickness."
Date: April 19, 1956
Creator: Nothwang, George J.
Partner: UNT Libraries Government Documents Department

Final Technical Report ARM DOE Grant #DE-FG02-03ER63520 Parameterizations of Shortwave Radiactive Properties of Broken Clouds from Satellite and Ground-Based Measurements

Description: This study used DOE ARM data and facilities to: 1) study macroscopic properties of continental stratus clouds at SGP and the factors controlling these properties, 2) develop a scientific basis for understanding the pocesses responsible for the formation of boundary layer clouds using ARM observations in conjunction with simple parametric models and LES, and 3) evaluate cumulus cloud characteristics retrieved retrieved from the MMCR operating at TWP-Nauru. In addition we have used high resolution 94 GHz observations of boundary layer clouds and precipitation to: 1)develop techniques for using high temporal resolution Doppler velocities to study large-eddy circulations and turbulence in boundary layer clouds and estimate the limitations of using current and past MMCR data for boundary layer cloud studies, 2) evaluate the capability and limitation of the current MMCR data for estimating reflectivity, vertical velocities, and spectral under low-signal-to-noise conditions associated with weak non-precipitating clouds, 3) develop possible sampling modes for the new MMCR processors to allow for adequate sampling of boundary layer clouds, and 4) retrieve updraft and downdraft structures under precipitating conditions.
Date: June 19, 2006
Creator: Albrecht, Bruce, A.
Partner: UNT Libraries Government Documents Department

Consequences of the Large-Scale Subsidence Rate on the Stably Stratified Atmospheric Boundary Layer Over the Arctic Ocean, as seen in Large-Eddy Simulations

Description: The analysis of surface heat fluxes and sounding profiles from SHEBA indicated possible significant effects of subsidence on the structure of stably-stratified ABLs (Mirocha et al. 2005). In this study the influence of the large-scale subsidence rate on the stably stratified atmospheric boundary layer (ABL) over the Arctic Ocean during clear sky, winter conditions is investigated using a large-eddy simulation model. Simulations are conducted while varying the subsidence rate between 0, 0.001 and 0.002 ms{sup -1}, and the resulting quasi-equilibrium ABL structure and evolution are examined. Simulations conducted without subsidence yield ABLs that are deeper, more strongly mixed, and cool much more rapidly than were observed. The addition of a small subsidence rate significantly improves agreement between the simulations and observations regarding the ABL height, potential temperature profiles and bulk heating rates. Subsidence likewise alters the shapes of the surface-layer flux, stress and shear profiles, resulting in increased vertical transport of heat while decreasing vertical momentum transport. A brief discussion of the relevance of these results to parameterization of the stable ABL under subsiding conditions in large-scale numerical weather and climate prediction models is presented.
Date: January 19, 2006
Creator: Mirocha, J D & Kosovic, B
Partner: UNT Libraries Government Documents Department

The Use of Kruskal-Newton Diagrams for Differential Equations

Description: The method of Kruskal-Newton diagrams for the solution of differential equations with boundary layers is shown to provide rapid intuitive understanding of layer scaling and can result in the conceptual simplification of some problems. The method is illustrated using equations arising in the theory of pattern formation and in plasma physics.
Date: February 19, 2008
Creator: Fishaleck, T. & White, R. B.
Partner: UNT Libraries Government Documents Department