One year variations in the near Earth solar wind ion density and bulk flow velocity

1990 ◽  
Vol 17 (1) ◽  
pp. 37-40 ◽  
Author(s):  
Scott J. Bolton
Keyword(s):  
Solar Wind ◽  
Flow Velocity ◽  
Bulk Flow ◽  
Ion Density ◽  
One Year

Small-amplitude Langmuir pulse excited by a planar grid electrode in a flowing plasma

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
John J. Podesta
Keyword(s):  
Solar Wind ◽  
Flow Velocity ◽  
Small Amplitude ◽  
Collisionless Plasma ◽  
Distribution Functions ◽  
Bulk Flow ◽  
Wire Mesh ◽  
High Time Resolution ◽  
Grid Electrode ◽  
Planar Grid

The generation and propagation of a small-amplitude Langmuir pulse excited by a planar grid electrode in a spatially uniform collisionless plasma with a constant flow velocity is studied by solving the linearized Vlasov–Poisson equations. The electrode is transparent to the flow of particles, like a screen or a wire mesh. The particles are assumed to have a Kappa velocity distribution, a reasonable approximation for electron distribution functions in the solar wind. Exact, closed-form solutions are obtained for ${\it\kappa}=1$, the Lorentzian distribution, and for ${\it\kappa}=2$. The explicit form of the solution in the case ${\it\kappa}=2$ has not, to our knowledge, appeared in the literature before. The properties of the solutions are investigated and a practical technique for measuring the bulk flow velocity in plasma experiments is proposed that may be useful for high-accuracy, high-time-resolution measurements of the bulk flow velocity in the solar wind.

Joint Estimation of Bulk Flow Velocity and Angle Using a Lateral Line Probe

2016 ◽  
Vol 65 (3) ◽  
pp. 601-613 ◽  
Author(s):  
Nataliya Strokina ◽  
Joni-Kristian Kamarainen ◽  
Jeffrey A. Tuhtan ◽  
Juan Francisco Fuentes-Perez ◽  
Maarja Kruusmaa
Keyword(s):  
Flow Velocity ◽  
Lateral Line ◽  
Joint Estimation ◽  
Bulk Flow

Boundary Layer Flashback in Premixed Hydrogen–Air Flames With Acoustic Excitation

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Vera Hoferichter ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Excitation Amplitude ◽  
Bulk Flow ◽  
Acoustic Excitation ◽  
Worst Case ◽  
Thermoacoustic Instabilities ◽  
Flame Flashback

Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0% to 36% of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency, the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes, flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.

scholarly journals Cold and Dense Plasma Sheet Caused by Solar Wind Entry: Direct Evidence

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 831
Author(s):  
Yue Yu ◽  
Zuzheng Chen ◽  
Fang Chen
Keyword(s):  
Solar Wind ◽  
Plasma Sheet ◽  
Cross Correlation ◽  
Direct Evidence ◽  
Dense Plasma ◽  
Ion Density ◽  
Average Value ◽  
Magnetospheric Multiscale ◽  
Cross Correlation Analysis ◽  
Solar Wind Entry

We present a coordinated observation with the Magnetospheric Multiscale (MMS) mission, located in the Earth’s magnetotail plasma sheet, and the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) mission, located in the solar wind, in order to understand the formation mechanism of the cold and dense plasma sheet (CDPS). MMS detected two CDPSs composed of two ion populations with different energies, where the energy of the cold ion population is the same as that of the solar wind measured by ARTEMIS. This feature directly indicates that the CDPSs are caused by the solar wind entry. In addition, He+ was observed in the CDPSs. The plasma density in these two CDPSs are ~1.8 cm−3 and ~10 cm−3, respectively, roughly 4–30 times the average value of a plasma sheet. We performed a cross-correlation analysis on the ion density of the CDPS and the solar wind, and we found that it takes 3.7–5.9 h for the solar wind to enter the plasma sheet. Such a coordinated observation confirms the previous speculation based on single-spacecraft measurements.

scholarly journals Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov–Gerasimenko during the intermediate activity period

2018 ◽  
Vol 613 ◽  
pp. A57 ◽  
Author(s):  
L. Berčič ◽  
E. Behar ◽  
H. Nilsson ◽  
G. Nicolaou ◽  
G. Stenberg Wieser ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Field Measurements ◽  
Distribution Functions ◽  
Activity Period ◽  
Ion Density ◽  
Ion Flow ◽  
Velocity Distribution Functions ◽  
Comet 67P

Aims. Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma. We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in the terminator plane. Methods. We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly using plasma moments). We propose a statistical approach over a period of one month. Results. On average, two populations were observed, separated in phase space. The motion of the first is governed by its interaction with the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatible with an ambipolar electric field. Both populations display a consistent anti-sunward velocity component. Conclusions. Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative to the nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometary ion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. There is no corresponding signature in the average magnetic field strength.

PHASE SHIFT METHODOLOGY ASSESSMENT OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE UNDER PULSATING FLOW CONDITIONS

2015 ◽  
Vol 77 (8) ◽  
Author(s):  
M. H. Padzillah ◽  
S. Rajoo ◽  
R. F. Martinez-Botas
Keyword(s):  
Phase Shift ◽  
Flow Velocity ◽  
Combustion Engine ◽  
Bulk Flow ◽  
Phase Shifting ◽  
Power Matching ◽  
Cfd Models ◽  
Turbine Efficiency ◽  
Turbine Performance ◽  
Computational Fluid Dynamics Cfd

The reciprocating nature of an Internal Combustion Engine (ICE) inevitably results in unsteady flow in the exhaust manifold. In a turbocharged engine, it means that the turbine is subjected to highly pulsating flows at its inlet. The finite time taken by the travelling pressure waves necessitates the need for phase-shifting method before any instantaneous parameter can be analyzed. In a turbocharger test-rig where the instantaneous isentropic power is evaluated upstream of the instantaneous actual power, one of the parameter has to be time-shifted in order to obtain meaningful instantaneous turbine efficiency. This research aims to compare two different methods of phase shifting which are by peak power matching and summation of sonic and bulk flow velocity. In achieving this aim, Computational Fluid Dynamics (CFD) models of full stage turbine operating at 20 Hz, 40 Hz, 60 Hz and 80 Hz have been developed and validated. Instantaneous efficiency was calculated at different locations and the order of calculated efficiency throughout the pulse is analyzed. Results have shown that phase shift using summation of sonic and bulk flow velocity indicated more reasonable efficiency values, thus the method could be used with high confidence for analysis involving unsteady turbine performance.

Solar wind temperature anisotropy and its influence on the spectrum of turbulence

2020 ◽  
Author(s):  
Alexander Pitňa ◽  
Jana Šafránkova ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Large Scale ◽  
Power Spectra ◽  
Solar Wind Plasma ◽  
Turbulent Medium ◽  
Thermal Velocity ◽  
Temperature Anisotropy ◽  
Ion Density ◽  
Proton Temperature ◽  
Wind Spacecraft

<p>Nearly collisionless solar wind plasma originating in the solar corona is a turbulent medium. The energy within large scale fluctuations is continuously transferred into smaller scales and it eventually reaches scales at which it is converted into a random particle motion, thus heating the plasma. Although the processes that take place within this complex system have been studied for decades, many questions remain unresolved. The power spectra of the fluctuating fields of the magnetic field, bulk velocity, and ion density were studied extensively; however, the spectrum of the thermal velocity is seldom reported and/or discussed. In this paper, we address the difficulty of estimating its power spectrum. We analyze high-cadence (31 ms) thermal velocity measurements of the BMSW instrument onboard the Spektr-R spacecraft and the SWE instrument onboard the Wind spacecraft. We discuss the role of the proton temperature anisotropy (parallel/perpendicular) and its influence on the shape of the power spectra in the inertial range of turbulence.</p>

Convective Scaling of Intrinsic Thermo-Acoustic Eigenfrequencies of a Premixed Swirl Combustor

2017 ◽  
Author(s):  
Alp Albayrak ◽  
Thomas Steinbacher ◽  
Thomas Komarek ◽  
Wolfgang Polifke
Keyword(s):  
Flow Velocity ◽  
Acoustic Waves ◽  
Feedback Loop ◽  
Feedback Mechanism ◽  
Bulk Flow ◽  
Axial Position ◽  
Low Frequencies ◽  
Swirl Combustor ◽  
Acoustic Modes ◽  
Resonance Frequencies

For velocity sensitive premixed flames, intrinsic thermoacoustic (ITA) feedback results from flow-flame-acoustic interactions as follows: perturbations of velocity upstream of the flame result in modulations of the heat release rate, which in turn generate acoustic waves that travel in the downstream as well as the upstream direction. The latter perturb again the upstream velocity, and thus close the ITA feedback loop. This feedback mechanism exhibits resonance frequencies that are not related to acoustic eigenfrequencies of a combustor and generates — in additional to acoustic modes — so-called ITA modes. In this work spectral distributions of the sound pressure level (SPL) observed in a perfectly premixed, swirl stabilized combustion test rig are analyzed. Various burner configurations and operating points are investigated. Spectral peaks in the SPL data for stable as well as for unstable cases are interpreted with the help of a newly developed simple criterion for the prediction of burner intrinsic ITA modes. This criterion extends the known −π measure for the flame transfer function (FTF) by including the burner acoustic. This way, the peaks in the SPL spectra are identified to correspond to either ITA or acoustic modes. It is found that ITA modes are prevalent in this particular combustor. Their frequencies change significantly with the power rating (bulk flow velocity) and the axial position of the swirler, but are insensitive to changes in the length of the combustion chamber. It is argued that the resonance frequencies of the ITA feedback loop are governed by convective time scales. For that reason, they arise at rather low frequencies, which scale with the bulk flow velocity.

Oblique penetration of solar-wind filaments into the magnetosphere

1998 ◽  
Vol 60 (4) ◽  
pp. 711-729 ◽  
Author(s):  
WENLONG DAI ◽  
PAUL R. WOODWARD
Keyword(s):  
Solar Wind ◽  
Flow Velocity ◽  
Maximum Depth ◽  
Two Dimensional ◽  
Large Excess ◽  
Magnetospheric Field

In this paper, a set of two-dimensional simulations for resistive magneto-hydrodynamical equations are performed to investigate the interaction between a solar-wind filament and the magnetosphere when the filament is obliquely oriented with respect to the direction of the magnetospheric field. Detailed pictures for the interaction are given. For typical parameters near the magnetopause, a filament with a sufficiently large excess flow velocity will penetrate into the magnetosphere, and will then be repelled back towards the magnetopause by the highly compressed and bent magnetospheric field. Finally, the filament will be smeared along the magnetospheric field near the magnetopause. When the angle is small, the filament will penetrate deeply into the magnetosphere before it is repelled back. Therefore there is a maximum depth a penetrated filament may reach into the magnetosphere. The effect of spontaneous reconnections behind a penetrating filament on the penetration appears to be negligible.

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