Under pressure: turbulent plumes in a uniform crossflow

2021 ◽  
Vol 932 ◽  
Author(s):  
Owen H. Jordan ◽  
Gabriel G. Rooney ◽  
Benjamin J. Devenish ◽  
Maarten van Reeuwijk
Keyword(s):  
Current Model ◽  
Perturbation Expansion ◽  
Flow Speed ◽  
Conservation Equation ◽  
Buoyancy Flux ◽  
Centre Of Mass ◽  
Buoyant Plumes ◽  
Leading Role ◽  
Field Lines ◽  
Good Agreement

Direct numerical simulation is used to investigate the integral behaviour of buoyant plumes subjected to a uniform crossflow that are infinitely lazy at the source. Neither a plume trajectory defined by the centre of mass of the plume $z_c$ nor a trajectory defined by the central streamline $z_{U}$ is aligned with the average streamlines inside the plume. Both $z_c$ and $z_{U}$ are shown to correlate with field lines of the total buoyancy flux, which implies that a model for the vertical turbulent buoyancy flux is required to faithfully predict the plume angle. A study of the volume conservation equation shows that entrainment due to incorporation of ambient fluid with non-zero velocity due to the increase in the surface area (the Leibniz term) is the dominant entrainment mechanism in strong crossflows. The data indicate that pressure differences between the top and bottom of the plume play a leading role in the evolution of the horizontal and vertical momentum balances and are crucial for appropriately modelling plume rise. By direct parameterisation of the vertical buoyancy flux, the entrainment and the pressure, an integral plume model is developed which is in good agreement with the simulations for sufficiently strong crossflow. A perturbation expansion shows that the current model is an intermediate-range model valid for downstream distances up to $100\ell _b$ – $1000 \ell _b$ , where $\ell _b$ is the buoyancy length scale based on the flow speed and plume buoyancy flux.

scholarly journals Dispersion in two-dimensional turbulent buoyant plumes

2015 ◽  
Vol 774 ◽  
Author(s):  
Stefano Rocco ◽  
Andrew W. Woods
Keyword(s):  
Leading Edge ◽  
Buoyancy Flux ◽  
Two Dimensional ◽  
Centre Of Mass ◽  
Mean Flow ◽  
Buoyant Plumes ◽  
Longitudinal Mixing ◽  
Resolution Imaging ◽  
The Mean ◽  
Averaged Model

Using high-resolution imaging and dye studies, we investigate experimentally the mixing of a tracer by the eddies within a two-dimensional turbulent buoyant plume. Instantaneously, the plume consists of a series of eddies, and at each point along the centreline of the plume, the along-plume speed of the leading edge of the eddies $w_{e}\approx 1.3f^{1/3}$, where $f$ is the buoyancy flux, while the product of the length scale, $A$, and frequency, ${\it\omega}$, of the eddies ${\it\omega}A\approx 0.15f^{1/3}$. The circulation and flow associated with the eddies lead to longitudinal mixing relative to the mean flow. To illustrate this mixing, we analyse the evolution of the horizontally averaged dye front produced by adding a constant flux of dye to a steady plume for times $t>0$. We show that the centre of mass of the horizontally averaged dye front has an along-plume speed ${\approx}1.04f^{1/3}$. This is consistent with the predictions of a time-averaged model for the evolution of the horizontally averaged mass, momentum and buoyancy flux in the plume. The new data also show that the longitudinal spreading of the horizontally averaged dye front can be described in terms of a dispersivity ${\approx}\,0.02f^{1/3}z$, where $z$ is the vertical distance below the source. This model of longitudinal mixing enables calculation of the residence time distribution of material in the plume, which may be key to modelling the products of a reaction in which the reaction time is comparable to the travel time in the plume.

An Analytical Drain Current Model for Dual-material Gate Graded - channel and Dual-oxide Thickness Cylindrical Gate (DMG-GC-DOT) MOSFET

2019 ◽  
Vol 9 (2) ◽  
pp. 291-297
Author(s):  
Hind Jaafar ◽  
Abdellah Aouaj ◽  
Ahmed Bouziane ◽  
Benjamin Iñiguez
Keyword(s):  
Current Model ◽  
Drain Current ◽  
Oxide Thickness ◽  
Subthreshold Current ◽  
The Poisson Equation ◽  
Strong Inversion ◽  
Cylindrical Form ◽  
Silvaco Atlas ◽  
Dual Material ◽  
Good Agreement

Background: A novel Dual Material Gate Graded Channel and Dual Oxide Thickness Cylindrical Gate (DMG-GC-DOT) MOSFET is presented in this paper. Methods: Analytical model of drain current is developed using a quasi-two-dimensional cylindrical form of the Poisson equation and is expressed as a function of the surface potential, which is calculated using the expressions of the current density. Results: Comparison of the analytical results with 3D numerical simulations using Silvaco Atlas - TCAD software presents a good agreement from subthreshold to strong inversion regime and for different bias voltages. Conclusion: Two oxide thicknesses with different permittivity can effectively improve the subthreshold current of DMG-GC-DOT MOSFET.

scholarly journals The Balloon-Borne Investigation of Temperature and Speed of Electrons in the Corona (BITSE): Mission Description and Preliminary Results

Solar Physics ◽  
2021 ◽  
Vol 296 (1) ◽  
Author(s):  
N. Gopalswamy ◽  
J. Newmark ◽  
S. Yashiro ◽  
P. Mäkelä ◽  
N. Reginald ◽  
...  
Keyword(s):  
Heliocentric Distance ◽  
Signal To Noise Ratio ◽  
Flow Speed ◽  
Science Data ◽  
Uncertainty Interval ◽  
Heliospheric Observatory ◽  
Flash Storage ◽  
Goddard Space Flight Center ◽  
Good Agreement ◽  
Polarization Camera

AbstractWe report on the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission launched recently to observe the solar corona from $\approx 3$ ≈ 3  Rs to 15 Rs at four wavelengths (393.5, 405.0, 398.7, and 423.4 nm). The BITSE instrument is an externally occulted single stage coronagraph developed at NASA’s Goddard Space Flight Center in collaboration with the Korea Astronomy and Space Science Institute (KASI). BITSE used a polarization camera that provided polarization and total brightness images of size $1024 \times 1024$ 1024 × 1024 pixels. The Wallops Arc Second Pointer (WASP) system developed at NASA’s Wallops Flight Facility (WFF) was used for Sun pointing. The coronagraph and WASP were mounted on a gondola provided by WFF and launched from the Fort Sumner, New Mexico station of Columbia Scientific Balloon Facility (CSBF) on September 18, 2019. BITSE obtained 17,060 coronal images at a float altitude of $\approx \mbox{128,000}$ ≈ 128,000 feet ($\approx 39$ ≈ 39  km) over a period of $\approx 4$ ≈ 4  hrs. BITSE flight software was based on NASA’s core Flight System, which was designed to help develop flight quality software. We used EVTM (Ethernet Via Telemetry) to download science data during operations; all images were stored on board using flash storage. At the end of the mission, all data were recovered and analyzed. Preliminary analysis shows that BITSE imaged the solar minimum corona with the equatorial streamers on the east and west limbs. The narrow streamers observed by BITSE are in good agreement with the geometric properties obtained by the Solar and Heliospheric Observatory (SOHO) coronagraphs in the overlapping physical domain. In spite of the small signal-to-noise ratio ($\approx 14$ ≈ 14 ) we were able to obtain the temperature and flow speed of the western steamer. In the heliocentric distance range 4 – 7 Rs on the western streamer, we obtained a temperature of $\approx 1.0\pm 0.3$ ≈ 1.0 ± 0.3  MK and a flow speed of $\approx 260$ ≈ 260  km s−1 with a large uncertainty interval.

scholarly journals Bottom Sediments Reveal Inter-Annual Variability of Interaction between the Ob and Yenisei Plumes in the Kara Sea

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
A. A. Osadchiev ◽  
En. E. Asadulin ◽  
A. Yu. Miroshnikov ◽  
I. B. Zavialov ◽  
E. O. Dubinina ◽  
...  
Keyword(s):  
Bottom Sediments ◽  
Vertical Structure ◽  
Suspended Sediments ◽  
Kara Sea ◽  
Local Wind ◽  
River Plumes ◽  
Buoyant Plumes ◽  
Sea Bottom ◽  
Mixing Dynamics ◽  
Good Agreement

AbstractRiver discharge is the main source of terrigenous sediments in many coastal areas adjacent to estuaries and deltas of large rivers. Spreading and mixing dynamics of river plumes governs transport of suspended sediments and their deposition at sea bottom at these areas. Generally river plumes have very large synoptic and seasonal variability, which cannot be reconstructed from structure of bottom sediments due to their small accumulation velocity. However, bottom sediments can be indicative of variability of river plumes on inter-annual and decadal time scales. In this study we focus on the large Ob and Yenisei buoyant plumes formed in the central part of the Kara Sea. These plumes interact and mix in the area adjacent to the closely located Ob and Yenisei gulfs. Suspended sediments carried by these river plumes have significantly different geochemical characteristics that can be used to detect Ob or Yenisei origin of bottom sediments. Using new geochemical methods we revealed dependence between spreading patterns of these plumes and spatial distribution and vertical structure of bottom sediments in the study area. This relation is confirmed by a good agreement between local wind and discharge conditions reconstructed for 1948–2001 and vertical structure of bottom sediments.

scholarly journals Structure of the poleward wall of the trough and the inclination of the geomagnetic field above the EISCAT radar

1997 ◽  
Vol 15 (6) ◽  
pp. 740-746 ◽  
Author(s):  
D. G. Jones ◽  
I. K. Walker ◽  
L. Kersley
Keyword(s):  
High Resolution ◽  
Electron Density ◽  
Time Scale ◽  
Geomagnetic Field ◽  
Energy Input ◽  
Current Model ◽  
Soft Particle ◽  
Dynamic Feature ◽  
Eiscat Radar ◽  
Good Agreement

Abstract. A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.

Macroscopic Simulation of Pedestrian Flow through a Bottleneck

2011 ◽  
Vol 97-98 ◽  
pp. 1168-1175 ◽  
Author(s):  
Yan Qun Jiang ◽  
Peng Zhang
Keyword(s):  
Traffic Congestion ◽  
Mass Conservation ◽  
Flow Speed ◽  
Conservation Equation ◽  
Comfort Level ◽  
Macroscopic Model ◽  
Pedestrian Flow ◽  
Macroscopic Simulation ◽  
Flow Through ◽  
Mass Conservation Equation

The paper deals with the macroscopic type modelling of the unidirectional pedestrian flow moving through a corridor with a bottleneck. The macroscopic model of pedestrian flow is the two-dimensional Lighthill-Whitham-Richards model described as a mass conservation equation. The characteristic feature of pedestrian route choice is that pedestrians in the corridor try to minimize the instantaneous travel time and improve the comfort level. The model equation is solved numerically by the discontinuous Galerkin method. Numerical results visualize the ability of the model to predict macroscopic characteristics of pedestrian flow through bottlenecks, i.e. the spatial distribution of the flow speed and density, as well as the formation and dissipation of traffic congestion in the corridor. They also validate that congestion is caused by the limited capacity of the bottleneck.

scholarly journals Storm-time ring current: model-dependent results

2012 ◽  
Vol 30 (1) ◽  
pp. 177-202 ◽  
Author(s):  
N. Yu. Ganushkina ◽  
M. W. Liemohn ◽  
T. I. Pulkkinen
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Boundary Conditions ◽  
Electric Fields ◽  
Ring Current ◽  
Current Model ◽  
Current Data ◽  
Storm Events ◽  
Boundary Location ◽  
Field Lines

Abstract. The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6–7 November 1997 and one intense (SymH minimum of −230 nT) on 21–22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 RE gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.

scholarly journals Three-dimensional modeling of chromospheric spectral lines in a simulated active region

2019 ◽  
Vol 631 ◽  
pp. A33 ◽  
Author(s):  
Johan P. Bjørgen ◽  
Jorrit Leenaarts ◽  
Matthias Rempel ◽  
Mark C. M. Cheung ◽  
Sanja Danilovic ◽  
...  
Keyword(s):  
Active Region ◽  
Three Dimensional ◽  
Coherent Scattering ◽  
Opposite Polarity ◽  
Conservation Equation ◽  
Spectral Lines ◽  
Equilibrium Equations ◽  
Nonthermal Electrons ◽  
Three Dimensional Modeling ◽  
Field Lines

Context. Because of the complex physics that governs the formation of chromospheric lines, interpretation of solar chromospheric observations is difficult. The origin and characteristics of many chromospheric features are, because of this, unresolved. Aims. We focus on studying two prominent features: long fibrils and flare ribbons. To model these features, we use a 3D magnetohydrodynamic simulation of an active region, which self-consistently reproduces both of these features. Methods. We modeled the Hα, Mg II k, Ca II K, and Ca II 8542 Å lines using the 3D non-LTE radiative transfer code Multi3D. To obtain non-LTE electron densities, we solved the statistical equilibrium equations for hydrogen simultaneously with the charge conservation equation. We treated the Ca II K and Mg II k lines with partially coherent scattering. Results. This simulation reproduces long fibrils that span between the opposite-polarity sunspots and go up to 4 Mm in height. They can be traced in all lines owing to density corrugation. In contrast to previous studies, Hα, Mg II h&k, and Ca II H&K are formed at similar height in this model. Although some of the high fibrils are also visible in the Ca II 8542 Å line, this line tends to sample loops and shocks lower in the chromosphere. Magnetic field lines are aligned with the Hα fibrils, but the latter holds to a lesser extent for the Ca II 8542 Å line. The simulation shows structures in the Hα line core that look like flare ribbons. The emission in the ribbons is caused by a dense chromosphere and a transition region at high column mass. The ribbons are visible in all chromospheric lines, but least prominent in Ca II 8542 Å line. In some pixels, broad asymmetric profiles with a single emission peak are produced similar to the profiles observed in flare ribbons. They are caused by a deep onset of the chromospheric temperature rise and large velocity gradients. Conclusions. The simulation produces long fibrils similar to what is seen in observations. It also produces structures similar to flare ribbons despite the lack of nonthermal electrons in the simulation. The latter suggests that thermal conduction might be a significant agent in transporting flare energy to the chromosphere in addition to nonthermal electrons.

scholarly journals Greenland Ice Mapping Project: ice flow velocity variation at sub-monthly to decadal timescales

2018 ◽  
Vol 12 (7) ◽  
pp. 2211-2227 ◽  
Author(s):  
Ian Joughin ◽  
Ben E. Smith ◽  
Ian Howat
Keyword(s):  
Flow Speed ◽  
Velocity Variation ◽  
Landsat 8 ◽  
North West ◽  
South West ◽  
Speed Up ◽  
Ice Velocity ◽  
Year 2000 ◽  
The Impact ◽  
Good Agreement

Abstract. We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbræ and Køge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbræ began slowing substantially in 2017, with a midsummer peak that was even slower than some previous winter minima. Over the last decade, we identify two major slowdown events at Køge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in north-west and south-west Greenland to produce a record of speed-up since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speed-up. In addition, we computed trends in winter flow speed for much of the south-west margin of the ice sheet and find little in the way of statistically significant changes over the period covered by our data. Finally, although the consistency of the data is generally good over time and across sensors, our analysis indicates that substantial differences can arise in regions with high strain rates (e.g. shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.

scholarly journals Assessment of ice flow dynamics in the zone close to the calving front of Antarctic ice shelves

2015 ◽  
Vol 61 (230) ◽  
pp. 1194-1206 ◽  
Author(s):  
Martin G. Wearing ◽  
Richard C.A. Hindmarsh ◽  
M. Grae Worster
Keyword(s):  
Flow Speed ◽  
Flow Dynamics ◽  
Rheological Parameters ◽  
Ice Thickness ◽  
Scaling Analysis ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Shelves ◽  
The Relationship ◽  
Good Agreement

AbstractWe investigate the relationship between four ice-shelf characteristics in the area close to the calving front: ice flow speed, strain rate, ice thickness and shelf width. Data are compiled for these glaciological parameters at the calving fronts of 22 Antarctic ice shelves. Clarification concerning the viscous supply of ice to the calving front is sought following the empirical calving law of Alley and others (2008), derived from a similar but smaller dataset, and the scaling analysis of Hindmarsh (2012). The dataset is analysed and good agreement is observed between the expected theoretical scaling and geophysical data for the flow of ice near the calving front in the case of ice shelves that are laterally confined and have uniform rheology. The lateral confinement ensures flow is aligned in the along-shelf direction, and uniform rheological parameters mean resistance to flow is provided by near-stationary ice in the grounded margins. In other cases, the velocity is greater than predicted, which we attribute to marginal weakening or the presence of ice tongues.

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