scholarly journals Plasma flow patterns in and around magnetosheath jets

2018 ◽  
Vol 36 (3) ◽  
pp. 695-703 ◽  
Author(s):  
Ferdinand Plaschke ◽  
Heli Hietala
Keyword(s):  
High Speed ◽  
Flow Patterns ◽  
Propagation Direction ◽  
Bow Shock ◽  
Mhd Waves ◽  
Plasma Flows ◽  
Plasma Motion ◽  
Core Plasma ◽  
Mhd Waves And Instabilities ◽  
Jet Plasma

Abstract. The magnetosheath is commonly permeated by localized high-speed jets downstream of the quasi-parallel bow shock. These jets are much faster than the ambient magnetosheath plasma, thus raising the question of how that latter plasma reacts to incoming jets. We have performed a statistical analysis based on 662 cases of one THEMIS spacecraft observing a jet and another (second) THEMIS spacecraft providing context observations of nearby plasma to uncover the flow patterns in and around jets. The following results are found: along the jet's path, slower plasma is accelerated and pushed aside ahead of the fastest core jet plasma. Behind the jet core, plasma flows into the path to fill the wake. This evasive plasma motion affects the ambient magnetosheath, close to the jet's path. Diverging and converging plasma flows ahead and behind the jet are complemented by plasma flows opposite to the jet's propagation direction, in the vicinity of the jet. This vortical plasma motion results in a deceleration of ambient plasma when a jet passes nearby. Keywords. Magnetospheric physics (magnetosheath; MHD waves and instabilities; solar wind–magnetosphere interactions)

MHD Waves and Instabilities in Space Plasma Flows

2011 ◽  
Vol 158 (2-4) ◽  
pp. 505-523 ◽  
Author(s):  
Y. Taroyan ◽  
M. S. Ruderman
Keyword(s):  
Space Plasma ◽  
Mhd Waves ◽  
Plasma Flows ◽  
Mhd Waves And Instabilities

scholarly journals Compressional waves in the Earth's neutral sheet

2004 ◽  
Vol 22 (1) ◽  
pp. 303-315 ◽  
Author(s):  
M. Volwerk ◽  
W. Baumjohann ◽  
K. H. Glassmeier ◽  
R. Nakamura ◽  
T. L. Zhang ◽  
...  
Keyword(s):  
Current Sheet ◽  
Power Density ◽  
Plasma Flow ◽  
High Speed ◽  
Rest Frame ◽  
Spectral Power ◽  
Spectral Power Density ◽  
Mhd Waves ◽  
Plasma Flows ◽  
Compressional Waves

Abstract. Compressional waves in the Earth's current sheet, driven by the high-speed plasma flows connected to substorms, are investigated using the Cluster magnetometer and plasma instrument. During the time that Cluster had its apogee in the magnetotail (July through October 2001), we have studied 5 events in detail. We find compressional waves in the 30–60mHz band, at a spectral power density that is dependent on when and where the event is observed. There is a difference of two orders of magnitude in power density between waves at substorm onset and waves during quiet times. Strong plasma flows are the driver of the wave power. The spacecraft location in the current sheet is also important for the spectral power density. Having four spacecraft available we can discern spatial from temporal variations. We have determined the propagation direction of the waves in the 30–60mHz band and found that in the Cluster rest frame they propagate in the same direction as the plasma flow at an angle 30° < ∆φ < 40° with respect to the plasma flow direction in the spacecraft' rest frame. Key words. Magnetospheric physics (magnetotail; MHD waves and instabilities; plasma sheet)

scholarly journals Correlation of Pc5 wave power inside and outside themagnetosphere during high speed streams

2004 ◽  
Vol 22 (2) ◽  
pp. 629-641 ◽  
Author(s):  
R. L. Kessel ◽  
I. R. Mann ◽  
S. F. Fung ◽  
D. K. Milling ◽  
N. O'Connell
Keyword(s):  
Solar Wind ◽  
Central Region ◽  
High Speed ◽  
Leading Edge ◽  
Bow Shock ◽  
Mhd Waves ◽  
Clear Correlation ◽  
Wave Power ◽  
Data Set ◽  
Interplanetary Physics

Abstract. We show a clear correlation between the ULF wave power (Pc5 range) inside and outside the Earth's magnetosphere during high speed streams in 1995. We trace fluctuations beginning 200RE upstream using Wind data, to fluctuations just upstream from Earth's bow shock and in the magnetosheath using Geotail data and compare to pulsations on the ground at the Kilpisjarvi ground station. With our 5-month data set we draw the following conclusions. ULF fluctuations in the Pc5 range are found in high speed streams; they are non-Alfvénic at the leading edge and Alfvénic in the central region. Compressional and Alfvénic fluctuations are modulated at the bow shock, some features of the waveforms are preserved in the magnetosheath, but overall turbulence and wave power is enhanced by about a factor of 10. Parallel (compressional) and perpendicular (transverse) power are at comparable levels in the solar wind and magnetosheath, both in the compression region and in the central region of high speed streams. Both the total parallel and perpendicular Pc5 power in the solar wind (and to a lesser extent in the magnetosheath) correlate well with the total Pc5 power of the ground-based H-component magnetic field. ULF fluctuations in the magnetosheath during high speed streams are common at frequencies from 1–4mHz and can coincide with the cavity eigenfrequencies of 1.3, 1.9, 2.6, and 3.4mHz, though other discrete frequencies are also often seen. Key words. Interplanetary physics (MHD waves and turbulence) – Magnetospheric physics (solar wind-magnetosphere interactions; MHD waves and instabilities)

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

scholarly journals Oxidation Resistance of a Si–TiSi2–MoSi2–TiB2–CaSi2 Coating on a Cf/C–SiC Substrate in High-Speed High-Enthalpy Air Plasma Flows

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2637
Author(s):  
Alexey Astapov ◽  
Lev Rabinskiy ◽  
Olga Tushavina
Keyword(s):  
Oxide Film ◽  
Oxidation Resistance ◽  
High Speed ◽  
Protective Action ◽  
Structural Phase ◽  
Silicon Monoxide ◽  
Air Plasma ◽  
Plasma Flows ◽  
Main Layer ◽  
Static Conditions

The results of a study on the development and testing of a heat-resistant coating in a Si–TiSi2–MoSi2–TiB2–CaSi2 system to protect Cf/C–SiC composites from oxidation and erosional entrainment in high-speed flows are presented here. The coating was formed using firing fusion technology on the powder composition. Oxidation resistance tests were carried out under static conditions in air at 1650 °C and under conditions of interaction with high-speed air plasma flows, with Mach numbers M = 5.5–6.0 and enthalpy 40–50 MJ/kg. The effectiveness of the protective action of the coating was confirmed at surface temperatures of Tw = 1810–1820 °C for at least 920–930 s, at Tw = 1850–1860 °C for not less than 510–520 s, at Tw = 1900–1920 °C for not less than 280–290 s, and at Tw = 1940–1960 °C for not less than 100–110 s. The values of the rate of loss of the coating mass and the rate constant of heterogeneous recombination of atoms and ions of air plasma on its surface were estimated. The performance of the coating was ensured by the structural-phase state of its main layer, and the formation and evolution on its surface during operation of a passivating heterogeneous oxide film. This film, in turn, is composed of borosilicate glass with titanium and calcium liquation inhomogeneities, reinforcing TiO2 microneedles and in situ Si2ON2 fibers. It was shown that at Tw≥ 1850–1860 °C, the generation of volatile silicon monoxide was observed at the “oxide layer–coating” interface, followed by the effects of boiling and breakdown degradation of the oxide film, which significantly reduced the lifespan of the protective action of the coating.

An experimental and simulation study of the flow pattern characteristics of water jet impingements in boreholes

2021 ◽  
pp. 014459872110520
Author(s):  
Yabin Gao ◽  
Xin Xiang ◽  
Ziwen Li ◽  
Xiaoya Guo ◽  
Peizhuang Han
Keyword(s):  
High Speed ◽  
Impact Force ◽  
Jet Impingement ◽  
Flow Patterns ◽  
Water Jet ◽  
Solid Boundary ◽  
Force Model ◽  
Water Jets ◽  
Contact Surfaces ◽  
The Impact

Hydraulic slotting has become one of the most common technologies adopted to increase permeability in low permeability in coal field seams. There are many factors affecting the rock breaking effects of water jets, among which the impact force cannot be ignored. To study the influencing effects of contact surface shapes on jet flow patterns and impact force, this study carried out experiments involving water jet impingement planes and boreholes under different pressure conditions. The investigations included numerical simulations under solid boundary based on gas–liquid coupling models and indoor experiments under high-speed camera observations. The results indicated that when the water jets impinged on different contact surfaces, obvious reflection flow occurred, and the axial velocity had changed through three stages during the development process. Moreover, the shapes of the contact surfaces, along with the outlet pressure, were found to have impacts on the angles and velocities of the reflected flow. The relevant empirical formulas were summarized according to this study's simulation results. In addition, the flow patterns and shapes of the contact surfaces were observed to have influencing effects on the impact force. An impact force model was established in this study based on the empirical formula, and the model was verified using both the simulation and experimental results. It was confirmed that the proposed model could provide important references for the optimization of the technical parameters water jet systems, which could provide theoretical support for the further intelligent and efficient transformation of coal mine drilling water jet technology.

Magnetosheath high speed jets and foreshock transients observed by Cluster and MMS

2021 ◽  
Author(s):  
C.-Philippe Escoubet ◽  
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
Cone Angle ◽  
Bow Shock ◽  
Magnetic Data ◽  
Energetic Ions ◽  
Dust Clouds ◽  
Simultaneous Measurements ◽  
Wind Measurements ◽  
Dominant Period

&lt;p&gt;Magnetosheath High Speed Jets (HSJs) are regularly observed downstream of the Earth&amp;#8217;s bow shock. Determining their origin from spacecraft observations is however a challenge since (1) L1 solar wind monitors are usually used with their inherent inaccuracy when plasma and magnetic data are propagated to the bow shock, (2) the number of measurement points around the bow shock are always limited. Various mechanisms have been proposed to explain HSJs such as bow shock ripples, solar wind discontinuities, foreshock transients, pressure pulses or nano dust clouds and it is difficult to relate these to HSJs with the lack of simultaneous measurements near the bow shock and immediately upstream. &amp;#160;We will use a special Cluster campaign, where one spacecraft was lagged 8 hours behind the three other spacecraft, to obtain near-Earth solar wind measurements upstream of the bow shock, together with simultaneous measurements in the magnetosheath. The event of interest is first observed by ACE on 13 January 2019 as a short 10 minutes period of IMF-Bx dominant (cone angle around 140 deg.). This IMF-Bx dominant period is also observed, one hour later, by THEMIS B and C (ARTEMIS) and Geotail, which were at 60 and 25 R&lt;sub&gt;E&lt;/sub&gt; from Earth on the dawnside. Cluster 1 and Cluster 2 just upstream of the bow shock, at 17 R&lt;sub&gt;E&lt;/sub&gt; from Earth, observed also such IMF-Bx dominant period together with energetic ions reflected from the bow shock and foreshock transients. Preliminary analysis indicate that these transients would be hot flow anomalies. Finally, Cluster 3 and 4 and MMS1-4, a few R&lt;sub&gt;E&lt;/sub&gt; from each other downstream of the shock, observed a turbulent magnetosheath with HSJs for 15 minutes. The HSJ characteristics are investigated with the constellation of 6 spacecraft, as well as their relation to hot flows anomalies observed upstream.&lt;/p&gt;

scholarly journals Evolution of High‐Speed Jets and Plasmoids Downstream of the Quasi‐Perpendicular Bow Shock

2020 ◽  
Vol 125 (6) ◽  
Author(s):  
O. Goncharov ◽  
H. Gunell ◽  
M. Hamrin ◽  
S. Chong
Keyword(s):  
High Speed ◽  
Bow Shock

scholarly journals Magnetospheric lion roars

2000 ◽  
Vol 18 (4) ◽  
pp. 406-410 ◽  
Author(s):  
W. Baumjohann ◽  
E. Georgescu ◽  
K.-H. Fornacon ◽  
H. U. Auster ◽  
R. A. Treumann ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

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