Flow behavior of large-scale pyroclastic flows ? Evidence obtained from petrofabric analysis

1989 ◽  
Vol 51 (2) ◽  
pp. 115-122 ◽  
Author(s):  
Tadahide Ui ◽  
Keiko Suzuki-Kamata ◽  
Rumi Matsusue ◽  
Kei Fujita ◽  
Hideya Metsugi ◽  
...  
Keyword(s):  
Large Scale ◽  
Flow Behavior ◽  
Pyroclastic Flows

scholarly journals Shallow Water Magnetohydrodynamics in Plasma Astrophysics. Waves, Turbulence, and Zonal Flows

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 314 ◽  
Author(s):  
Arakel Petrosyan ◽  
Dmitry Klimachkov ◽  
Maria Fedotova ◽  
Timofey Zinyakov
Keyword(s):  
Shallow Water ◽  
Large Scale ◽  
Fundamental Problem ◽  
Flow Behavior ◽  
Magnetohydrodynamic Equations ◽  
Plasma Astrophysics ◽  
Wave Interactions ◽  
Zonal Flows ◽  
New Applications ◽  
The Universe

The purpose of plasma astrophysics is the study and description of the flow of rotating plasma in order to understand the evolution of various objects in the universe, from stars and planetary systems to galaxies and galaxy clusters. A number of new applications and observations have appeared in recent years and actualized the problem of studying large-scale magnetohydrodynamic flows, such as a thin layer under the convective zone of the sun (solar tachocline), propagation of accreting matter in neutron stars, accretion disks in astrophysics, dynamics of neutron star atmospheres, and magnetoactive atmospheres of exoplanets tidally locked with their host star. The article aims to discuss a fundamental problem in the description and study of multiscale astrophysical plasma flows by studying its general properties characterizing different objects in the universe. We are dealing with the development of geophysical hydrodynamic ideas concerning substantial differences in plasma flow behavior due to the presence of magnetic fields and stratification. We discuss shallow water magnetohydrodynamic equations (one-layer and two-layer models) and two-dimensional magnetohydrodynamic equations as a basis for studying large-scale flows in plasma astrophysics. We discuss the novel set of equations in the external magnetic field. The following topics will be addressed: Linear theory of magneto-Rossby waves, three-wave interactions and related parametric instabilities, zonal flows, and turbulence.

Active Flow Control of Turbulent Refractive Interfaces in Separated Shear Layers for Laser Beam Propagation

2007 ◽  
Author(s):  
Fazlul R. Zubair ◽  
Haris J. Catrakis
Keyword(s):  
Laser Beam ◽  
Large Scale ◽  
Flow Behavior ◽  
Direct Reduction ◽  
Active Flow Control ◽  
Beam Propagation ◽  
Shear Layers ◽  
Plasma Actuators ◽  
Pulsed Plasma ◽  
Laser Beam Propagation

The behavior of turbulent refractive interfaces, and means for the optimization of these interfaces, is essential in various basic and applied studies concerning the propagation of optical wavefronts such as laser beam wavefronts through turbulence or optical imaging through turbulence. In this study, the structure of turbulent refractive interfaces and aero-optical interactions along laser beam propagation paths, in unforced and forced separated compressible shear layers, are examined through use of direct imaging and pulsed plasma actuators. Dielectric-barrier discharge (DBD) pulsed plasma actuators are used to excite the flow prior to separation. Our interest is in searching for the frequencies and amplitudes of the forcing that produce direct suppression of the large scale turbulent interfaces and, thereby, direct reduction of the laser wavefront aberrations. Whole-field shadowgraph imaging of pure-air separated shear layers is conducted for control off vs. control on cases at various forcing frequencies, in order to explore the effects of plasma forcing on the large-scale flow behavior. Direct profiling of forced vs. unforced turbulence-aberrated laser wavefronts propagated transversely through shear layers is conducted using high-resolution Shack-Hartmann microlens arrays. Evidence is presented showing significant reduction of the turbulence-induced laser aberrations, for forced vs. unforced shear layers, indicating the presence of a mechanism of suppression, i.e. disorganization, of large-scale organized structures by high-frequency pulsed plasma forcing.

Establishment of Testing Methodology for Forge Welded Tubular Products

2012 ◽  
Author(s):  
Ganesan S. Marimuthu ◽  
Per Thomas Moe ◽  
Bjarne Salberg ◽  
Jan Inge Audestad
Keyword(s):  
Material Flow ◽  
Large Scale ◽  
Flow Behavior ◽  
Treatment Options ◽  
Full Scale ◽  
International Standards ◽  
Small Scale ◽  
Test Plan ◽  
Welding Machine

A state-of-the-art small-scale solid state forge welding machine has been fabricated for checking weldability by Shielded Active Gas Forge Welding (SAG-FW) of tubular products applicable predominantly for, but not limited to offshore Industries. Effective, fast and inexpensive welding and testing of joints make this small-scale method suitable for evaluating weldability of a material before starting regular qualification and fabrication in a full-scale welding machine normally located in spool base or offshore. The small-scale machine provides a complete package for pre-qualification studies, including assessment of welding conditions, material flow behavior, heat treatment options. However, there are considerable challenges relating to application of international standards of testing as well as interpretation and use of results in the context of large-scale welding. In this paper results from small-scale welding and weld characterization of an API 5L X65 quality are presented. First, a detailed test plan for analyzing the weld is outlined. This procedure is subsequently applied for checking the welds to be produced in the full-scale machine. Short-comings in using the small-scale process as well as the possible remedies are discussed in detail.

Numerical Investigation of a Cryogenic Liquid Turbine Performance and Flow Behavior

2008 ◽  
Author(s):  
Wei Zhao ◽  
Jinju Sun ◽  
Hezhao Zhu ◽  
Cheng Li ◽  
Guocheng Cai ◽  
...  
Keyword(s):  
Numerical Investigation ◽  
Large Scale ◽  
Flow Behavior ◽  
Cryogenic Liquid ◽  
Air Separation ◽  
Design Flow ◽  
Suction Surface ◽  
Navier Stokes Equation ◽  
Separation Unit ◽  
Turbine Performance

A single stage cryogenic liquid turbine is designed for a large-scale internal compression air-separation unit to replace the Joule-Thompson valve and recover energy from the liquefied air during throttling process. It includes a radial vaned nozzle, and 3-dimensional impeller. Numerical investigation using 3-D incompressible Navier-Stokes Equation together with Spalart-Allmaras turbulence model and mixing plane approach at the impeller and stator interface are carried out at design and off-design flow. At design condition, recovered shaft power has amounted to 185.87 kW, and pressure in each component decreases smoothly and reaches to the expected scale at outlet. At small flow rates, flow separation is observed near the middle section of blade suction surface, which may cause local vaporization and even cavitation. To further improve the turbine flow behavior and performance, geometry parametric study is carried out. Influence of radial gap between impeller and nozzle blade rows, and nozzle stagger angle on turbine performance are investigated and clarified. Results arising from the present study provide some guidance for cryogenic liquid turbine optimal design.

The Response of Injection of Vortex Generator Jets to a Backward Facing Step Flow

2003 ◽  
Author(s):  
Koichi Yamagata ◽  
Manabu Saito ◽  
Tadashi Morioka ◽  
Shinji Honami
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Flow Behavior ◽  
Velocity Ratio ◽  
Vortex Generator ◽  
Step Response ◽  
Backward Facing Step ◽  
Longitudinal Vortices ◽  
Step Flow ◽  
Vortex Generator Jets

In this paper, the flow behavior of a reattachment process over a backward facing step flow is reported. The reattachment process is controlled by injection of vortex generator jets. The injection of jets upstream of the step produces the co-rotating longitudinal vortices in a separating shear layer. The experiment of the step response of the injection jet is also conducted in order to investigate the evolution process of the longitudinal vortices. A large scale of primary and counter vortices are observed, when the velocity ratio of the free stream to injected jet is 6. The detailed structure of the longitudinal vortices is clarified. The remarkable effect of the vortices on the separating shear layer downstream of the step is observed.

3-D Time Domain Unsteady Computation of Rotating Instability in Steam Turbine Last Stage

2012 ◽  
Author(s):  
L. Y. Zhang ◽  
L. He ◽  
H. Stüer
Keyword(s):  
Mass Flow ◽  
Large Scale ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Frequency Pattern ◽  
Last Stage ◽  
Rotating Instability

The rotating instability phenomenon in a last stage of steam turbines at low mass flow conditions has been previously identified experimentally. Recently, the rotating instability has also been numerically studied in a whole annulus domain on 2D blade sections. In the present work, 3D simulations of unsteady flows are carried out on two model steam turbines over a range of mass flow conditions. The pressure-ratio volume-flow characteristics in rotor row tip region under different flow conditions are well captured in the computations in comparison with the experiment. The effect of blade scaling is examined to identify the influence of changing blade counts for a circumferential domain reduction, showing relatively small effects on the overall performance characteristics. The present 3D unsteady solutions on a reduced multi-passage domain have been able to predict a rotating instability in the rotor blade tip region, in accord with the corresponding experiment. Further Fourier analysis is carried out to examine the frequency pattern and spatial modal features. The 3D flow behavior is highlighted by comparison between the 3D and 2D calculations. The present results seem to suggest that the rotating instability onset in the rotor tip region is largely independent of the large scale flow separation in the downstream diffusor.

scholarly journals Modelling erosion and deposition in geophysical granular mass flows

2021 ◽  
Vol 52 (1) ◽  
pp. 29-32
Author(s):  
Sylvain Viroulet ◽  
Chris Johnson ◽  
Nico Gray
Keyword(s):  
Debris Flows ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Pyroclastic Flows ◽  
Small Scale ◽  
Snow Avalanches ◽  
Erosion And Deposition ◽  
Granular Rheology ◽  
Scale Models ◽  
Mass Flows

During hazardous geophysical mass flows, such as rock or snow avalanches, debris flows and volcanic pyroclastic flows, a continuous exchange of material can occur between the slide and the bed. The net balance between erosion and deposition of particles can drastically influence the behaviour of these flows. Recent advances in describing the non-monotonic effective basal friction and the internal granular rheology in depth averaged theories have enabled small scale laboratory experiments (see fig. 1) to be quantitatively reproduced and can also be implemented in large scale models to improve hazard mitigation.

Flow Simulation and Diagnosis Through Hydraulic Turbines Using a RNG k-ω Turbulence Model

2010 ◽  
Author(s):  
Shuhong Liu ◽  
Xiaojing Wu ◽  
Yulin Wu
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Hydraulic Turbine ◽  
Francis Turbine ◽  
Design Stage ◽  
Hydro Power ◽  
Large Power ◽  
Power Stations

Francis turbine is widely employed in large scale hydro-power stations in the world with main characteristics of efficiency, stability and cavitation. In practical establishment, each large power station must develop a new Francis turbine for its special natural condition and requirement, such as higher efficiency for utilization of natural resources. CFD has been developed greatly and helped a lot in hydraulic design stage of the turbine. In this paper, firstly, a new RNG k–ω turbulence model is proposed based on the RNG k–ε model, which brings the nonlinear term of the mean fluid flow transition to the ω equation in the original k–ω model. And, this RNG k–ω model has been used to predict the energy performances for Francis turbine. Then, the flow diagnosis method in the turbine runner based on vorticity parameters is presented, following the detailed flow behavior revealed. Finally, the simulation results for different model Francis turbines have been compared and analyzed for optimizing the energy performances of the turbine. The model test results indicate that the efficiency of hydraulic turbine has been improved from 93.6% to 94.5%.

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