Plume Separation Research Articles

Circulation and Retention of River Plumes Around Capes

AbstractRiver plumes often interact with capes in the coastal ocean, impacting local hydrodynamics and the transport of scalars. However, our current knowledge on how capes affect river plume separation, mixing, and retention is limited. Here, we conducted idealized numerical experiments with Gaussian‐shaped capes of varying curvature radii, constant river discharge, a sloping bottom, and scenarios with and without downwelling winds. We found that river plumes separate from capes when the Rossby number is above 1, a criterion that had not been tested for plume separation. This Rossby number is based on the plume velocity, the Coriolis factor, and the radius of curvature of the cape. Freshwater accumulation is greatest at the lee of narrow (i.e., pointy) capes under calm winds, but decreases significantly in downwelling winds or around broader capes.

Optical emission features of laterally colliding laser-produced plasmas at different ambient pressures

Optical emission characteristics of seed plasma and stagnation region of laterally colliding laser produced aluminium plasmas are investigated under various background gas pressures of air and argon ambient. The intensity of ionic and neutral emissions from seed plasma region increases with the increase of ambient pressure. Neutral emission from the stagnation region increases whereas the intensity of ionic emission decreases with the increase of ambient pressure. Decrease of collision rate between the seed plasmas results in the decrease of ionic emission from the interaction region. For higher inter seed plume separation, maximum spectral emission from stagnation region is observed at an intermediate pressure range of 10−2 mbar. Emission intensity and the life time of both ionic and neutral emission are greater in heavier Ar ambient. In the case of seed plasmas, the electron density decreases whereas the electron temperature increases with the increase of ambient gas pressure and is greater in Ar ambient. The variations of plasma parameters are quite less in stagnation region.

Characteristic of spatiotemporal evolution of hydrogen isotope in laser-induced plasma under low-pressure environment

The elemental analysis of hydrogen (H) and its isotopes, deuterium (D) and tritium (T) is important for fuel retention detections in plasma-facing materials of nuclear fusion devices, H abundance assessment in geochemistry and so on. Laser-induced breakdown spectroscopy (LIBS) is one of the most promising technology to analyze the H isotopes due to its excellent real-time and in situ analytical ability. However, the laser ablation plasma is a transient plasma with inhomogeneous spatiotemporal evolution. Especially in low-pressure background, the particles with different masses may separate in the plasma plume. This will result in the loss of accuracy of LIBS measurement. In this work, the characteristic of spatiotemporal evolution of spectra from laser-induced plasma on the frozen D2O-H2O mixture under low-pressure environment has been investigated. The spectral intensity of Dα and electron density decrease with radial direction and delay time. The intensities ratio of Dα and Hα, ID/(ID + IH), are almost constant at different radial positions and delay times under the background pressure of 1 × 10−1 mbar. However, when the pressure decreases to 1 × 10−4 mbar, ID/(ID + IH) decreases from the center to the edge of the plasma due to plume separation by the different atomic masses of isotopes. The degree of separation increases from the center to the edge of the plasma. The results will be useful for better understanding of characteristic of spatiotemporal evolution of LIBS plasma in low pressure and improvement of LIBS measurement for H isotopes.

Geometrical Analysis of the Stagnation Zone in Laterally Colliding Plasmas: Effects of Plasma Plume Separation and Ablating Target Material

The influence of an ablating target’s atomic mass on the development and growth of the interaction zone in laterally colliding plasmas has been investigated. As diagnostic tools, fast imaging and optical emission techniques were used to evaluate the characteristics of the seed plasma as well as the interaction zone created by different target materials (i.e., aluminum and silicon). The current findings show that the dynamical, spectral, and geometrical properties of the generated interaction zone are affected by the features of the ablated species and the geographical separation of the interacting plumes. The interaction of aluminum plume species results in a sharper, more intense, and more directed stagnation zone than that reported for silicon targets using a 450 nm filter. Furthermore, the investigation of the interaction area emission from both regions for aluminum (Al) and silicon (Si) plasma explains the variation in plasma properties in the stagnation zone. As a part of this work’s description, a comparative study of the dynamics and characteristics of the homogenous interaction region produced by colliding plasma plumes by laser ablation of flat Al and Si targets has been presented, which can provide deep insight into the characterization of colliding laser-produced plasma expansion and related physical and technical properties.

Expansion Dynamic and Characterization of Stagnation Layer in Laterally Colliding Plasmas: Dependence of Observation Bandwidth and Plasma Plume Separation

The colliding laser-produced plasma (CLPP) has a wide range of applications in various contexts, that might start with astrophysical applications or pulsed laser deposition or Laser-Induced Breakdown Spectroscopy (LIBS), which is a powerful analytical technique for elemental analysis and material identification.In CLPP experiments, the stagnation layer might form at the interface region when two dense laser-induced plasmas collide, and the degree of stagnation can be diagnosed by the collisionality parameter that is used to determine what kind of interaction will take place, i.e., soft or hard stagnation.Our experimental work presents the results of the temporal, spatial and semi-spectrally imaging of colliding plasmas of aluminium and silicon targets. The analysis is focused on describing the velocity of the expanding plasma front for the interaction zone. The aim of the work presented here is to further advance and study colliding plasma techniques, as well as other methods to realize and control species density and expansion, with a view to a deep understanding of these complex mechanisms and optimising emission in the visible wavelength range.All investigation sequences were based on a similar experimental setup, where two different focusing lenses were used with an effective focal length (EFL) of approx. 100mm or 125mm to achieve seed separation around 1.66mm or 2.16mm, respectively. Time-resolved emission imaging was employed to track the stagnation layer‛s size and shape, which might act as a signature of hard versus soft stagnation.The study provides a considerable amount of detailed data related to the expansion velocity of the interaction zone which extends the understanding of the behaviour of particular species within colliding laser-produced plasmas.

Preferential Retention and Transport of Perfluorooctanesulfonic Acid in a Dolomite Aquifer.

Per- and polyfluoroalkyl substances (PFAS) can represent a significant human health risk if present in aquifers used as a drinking water source. Accurate assessment of PFAS exposure risks requires an improved understanding of field-scale PFAS transport in groundwater. Activities at a former firefighter training site in University Park, Pennsylvania introduced perfluorooctanesulfonic acid (PFOS) to the underlying dolomite aquifer. Groundwater sampling from 2015 to 2018 delineated a PFOS plume with two concentration maxima located approximately 20 and approximately 220 m downgradient of the training site, separated by a zone of lower concentrations. We use a combination of analytical and numerical models, informed by independent measurements of aquifer porosity, hydraulic conductivity, and organic carbon content, to interpret the field observations. Our analysis demonstrates that preferential retention and transport resulting from simple heterogeneity in bedrock sorption, as caused by organic carbon (OC) content variability, provides a plausible explanation for plume separation. Dissolved PFOS partitions strongly to organic solids (high Koc ), so even a small OC (<1wt%) significantly retards PFOS transport, whereas zones with little to no OC allow for transport rates that approximate those of a conservative solute. Our work highlights an important consideration for modeling the groundwater transport of PFOS, and other compounds with high Koc . In aquifers with discrete layers of varying OC, models using a uniform site-average OC will underestimate transport distances, thereby misrepresenting exposure risks for downgradient communities.

Assessing JUICE's ability of in situ plume detection in Europa's atmosphere

ESA's upcoming JUpiter Icy moons Explorer (JUICE) is scheduled to perform two flybys of Jupiter's moon Europa. Here, we present the results of our investigation into JUICE's capability to detect plumes and to separate them from the background water in the atmosphere as a function of their source's location and mass flux on the Europan surface using the neutral mass spectrometer NIM. For both of the currently planned flybys we evaluate different scenarios to estimate how feasible such a detection is, using a Monte Carlo particle tracing model of a plume. We also incorporate the putative plume candidates reported by Roth et al. (2014b), Sparks et al. (2016), Sparks et al. (2017), Jia et al. (2018), Arnold et al. (2019) and Sparks et al. (2019) into this investigation. We come to the conclusion that the first flyby trajectory is better suited to detect the potential plume candidates listed above as they are detectable down to mass fluxes of approx. 100 ​kg/s. The second flyby requires mass fluxes between 100 ​kg/s and 500 ​kg/s for all suggested plume candidates to be detectable. This discrepancy is caused by the first flyby's closer proximity to the locations of the suggested plume sources which lie mainly on the southern hemisphere. Separation of water plumes from the atmospheric water vapour density is dependent on the mass flux of the respective plume source. The only plume separable from the background water in the atmosphere at the lowest investigated plume source mass flux of 1 ​kg/s is the one suggested by Roth et al. (2014b). It is therefore the most likely plume to be detected by JUICE. Furthermore, we investigate the detectability of trace gas contents in a plume and analyse how these impact upon plume detection. The spacecraft will be able to detect whether lighter-than-water trace gas species are present within the plume down to trace gas source mass fluxes of 0.1 ​kg/s. Provided this is the case, such species constitute a means to identifying plumes in the Europan atmosphere. Finally, the effects of lowering the flyby altitude are examined. We find that lowering the altitude of the CA does not increase the region of separability. Therefore, lowering the second flyby trajectory will not suffice for the spacecraft to be able to identify plumes that originate from the locations of the candidates mentioned above. Considering that the second flyby is the most likely to be lowered, this case study provides an example of the importance of arranging the second trajectory in a manner such that its ground track lies in close proximity to the locations of the suggested plume candidates listed above. This approach to the mission planning maximises the chance of separating the presumptive plumes from the atmospheric background water even at the lowest plume source mass fluxes.

Spectroscopic investigation of stagnation region in laterally colliding plasmas: Dependence of ablating target material and plasma plume separation

The effect of the atomic mass of the ablating target on the formation and expansion of the interaction region in laterally colliding plasmas has been studied. Fast imaging and optical emission spectroscopy have been utilized as diagnostic tools to investigate the characteristic features of the seed plasma as well as interaction zone formed by different target materials (i.e., carbon, aluminium, and nickel). The present results reveal that dynamical, spectral, and geometrical features of the induced interaction zone depend on the mass of the ablated species and spatial separation between the interacting plumes. It has been observed that a sharp, intense, and more directional interaction zone is formed by the interaction of heavier plume species in comparison to that observed for a lighter atomic mass target. Further, the difference in the plasma parameters in seed and interaction regions are explained from the analysis of emission from both the regions for aluminium plasma.

Assessment of gasoline direct injector fouling effects on fuel injection, engine performance and emissions

The current optical and thermal experimental tests were mainly focused on obtaining a comprehensive understanding of the effects of gasoline direct injector fouling on mass flow rates, spray characteristics, engine emissions and engine performance. A robust injector fouling cycle was employed to produce coked injectors in a multi-cylinder thermal engine. Deposit build-up in the coked injectors and fouling cycle repeatability was first examined by measurements of fuel flow rate. Macroscopic spray characteristics of the clean and the coked injectors were carried out using high-speed imaging and Planar Laser Induced Fluorescence (PLIF) of sprays foot-print. Fuel droplets size and velocity were characterised with a two-dimensional Phase Doppler Particle Analyser (PDPA). It was observed that the deposit build-up inside injector nozzles and on injector tips reduced the plume cone angle while increased plume penetration length, plume separation angles, mean droplet velocity and size for the coked injector. Impact of injector fouling was further investigated by PLIF measurements of in-cylinder charge inhomogeneity and repeatability in mixture preparation. The coked injectors showed higher degree of inhomogeneity and poorer repeatability in mixture preparation. These were in agreement with combustion analysis results where the coked injectors showed lower load and lower combustion stability compared with the clean injector under same operating conditions. Significantly higher unburned hydrocarbon emissions and particulate number concentration were also observed for the coked injectors. This work was carried out to obtain a broad picture of injector cooking effects in GDI engines.

Plume dynamics in Hele-Shaw porous media convection.

Mass transport in multi-species porous media is through molecular diffusion and plume dynamics. Predicting the rate of mass transport has application in determining the efficiency of the storage and sequestration of carbon dioxide. We study a water and propylene-glycol system enclosed in a Hele-Shaw cell with variable permeability that represents a laboratory analogue of the general properties of porous media convection. The interface between the fluids, tracked using an optical shadowgraph technique, is used to determine the mass transport rate, the spatial separation of solutal plumes, and the velocity and width characteristics of those plumes. One finds that the plume dynamics are closely related to the mass transport rate.This article is part of the themed issue 'Energy and the subsurface'.

Turbulent Rayleigh–Bénard convection in spherical shells

We simulate numerically Boussinesq convection in non-rotating spherical shells for a fluid with a Prandtl number of unity and for Rayleigh numbers up to $10^{9}$. In this geometry, curvature and radial variations of the gravitational acceleration yield asymmetric boundary layers. A systematic parameter study for various radius ratios (from ${\it\eta}=r_{i}/r_{o}=0.2$ to ${\it\eta}=0.95$) and gravity profiles allows us to explore the dependence of the asymmetry on these parameters. We find that the average plume spacing is comparable between the spherical inner and outer bounding surfaces. An estimate of the average plume separation allows us to accurately predict the boundary layer asymmetry for the various spherical shell configurations explored here. The mean temperature and horizontal velocity profiles are in good agreement with classical Prandtl–Blasius laminar boundary layer profiles, provided the boundary layers are analysed in a dynamical frame that fluctuates with the local and instantaneous boundary layer thicknesses. The scaling properties of the Nusselt and Reynolds numbers are investigated by separating the bulk and boundary layer contributions to the thermal and viscous dissipation rates using numerical models with ${\it\eta}=0.6$ and with gravity proportional to $1/r^{2}$. We show that our spherical models are consistent with the predictions of Grossmann &amp; Lohse’s (J. Fluid Mech., vol. 407, 2000, pp. 27–56) theory and that $\mathit{Nu}(\mathit{Ra})$ and $\mathit{Re}(\mathit{Ra})$ scalings are in good agreement with plane layer results.

Modelling CO2 migration in aquifers; considering 3D seismic property data and the effect of site-typical depositional heterogeneities

Geological sequestration is one proposed measure for greenhouse gas mitigation; and deep, saline aquifers are considered to hold large storage potentials for CO2. The Johansen Formation has been suggested by Norwegian authorities as a potential reservoir candidate due to its relative proximity to land and point sources for CO2. Reservoir evaluations must consider the given premise of zero interference with ongoing gas production in the Troll Field, providing geographical constraints. Recent data contributions; new 3D seismic data, attribute analyses, and revision of the depositional model form the basis of this modelling study. Porosity distributions were generated from quantified relations with acoustic impedance. The reservoir quality varies according to sedimentary facies, and differentiated relative permeability curves were assigned accordingly. Effects of directional anisotropy and site-typical geological heterogeneities were considered through scenario-modelling. The potential for dissolution and residual trapping of CO2 varies according to migration paths; and was estimated to 50–80% of injected CO2 after 150 years. Immobilisation was more efficient with increased sweep through reservoir zones with high irreducible gas fractions, and in scenarios where plume separation occurred. The main determinant, however, for improving trapping efficiency is the well location and injection scheme.

Plume separation from an adiabatic horizontal thin fin placed at different heights on the sidewall of a differentially heated cavity

The separation of plumes from an adiabatic horizontal thin fin attached to a sidewall of a differentially heated cavity at quasi-steady stage is experimentally and numerically studied at three Rayleigh numbers (0.92×109, 1.84×109 and 3.68×109) and over a range of fin positions. Regular plume separation is observed over the present range of parameters during the quasi-steady stage. Both experimental and numerical results reveal that the plume separation frequency increases with the Rayleigh number and decreases with the fin height measured from the leading edge. A higher Rayleigh number leads to a more unstable flow above the horizontal thin fin which in turn leads to a higher plume separation frequency. The decrease of the plume separation frequency with the increasing fin height is mainly due to the reduction of the adverse temperature gradient in the unstable layer above the thin fin as a result of the cavity-wide temperature stratification. It is further revealed that the heat transfer through the sidewall is improved by the presence of the thin fin. An optimum fin height for maximum heat transfer enhancement has been identified for the case with a Rayleigh number of 0.92×109. For the other two higher Rayleigh number cases considered in this study, the heat transfer through the sidewall monotonically decreases with the fin height.

A new model for coupled multicomponent NAPL dissolution and aqueous-phase transport, with application to creosote dissolution in discrete fractures

[1] This paper concerns a new modeling approach to multicomponent NAPL dissolution and transport, based on analytic solutions and Laguerre series. This approach allows virtually any of the numerous existing 1-D analytic transport solutions in the literature to be coupled with arbitrary boundary conditions stemming from nonlinear NAPL dissolution, as dictated by Raoult's Law. A computer implementation of this approach to coupled dissolution and transport in parallel fractures—which no other screening tool known to the authors covers—is presented. This is verified against an existing analytic transport solution that assumes a constant boundary condition. Subsequently, the model is demonstrated via a study of separation of PAH and phenolic plumes generated by dissolution of creosote, using the new computer implementation. The PAH and phenolic constituents of creosote strongly differ in both their dissolution and their transport behavior, and this is shown to necessitate the use of a tool that can account for both processes, such as the one developed here. We also find the possibility of PAH and phenolic plumes becoming entirely disjoint.

Tidal modulation on the Changjiang River plume in summer

[1] Tide effects on the structure of the near-field Changjiang River plume and on the extension of the far-field plume have often been neglected in analysis and numerical simulations, which is the focus of this study. Numerical experiments highlighted the crucial role of the tidal forcing in modulating the Changjiang River plume. Without the tidal forcing, the plume results in an unrealistic upstream extension along the Jiangsu coast. With the tidal forcing, the vertical mixing increases, resulting in a strong horizontal salinity gradient at the northern side of the Changjiang River mouth along the Jiangsu coast, which acts as a dynamic barrier and restricts the northward migration of the plume. Furthermore, the tidal forcing produces a bidirectional plume structure in the near field, and the plume separation is located at the head of the submarine canyon. A significant bulge occurs around the head of the submarine canyon and rotates anticyclonically, which carries a large portion of the diluted water toward the northeast and merges into the far-field plume. A portion of the diluted water moves toward the southeast, which is mainly caused by tidal rectification. This bidirectional plume structure is more evident under certain wind conditions. During the neap tide with the reduced tidal energy, the near-field plume extends farther offshore, and the bulge becomes less evident. These dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents, although in the far field the wind forcing and shelf currents eventually dominate the plume extension.

Experimental and theoretical investigations of a laser-produced aluminum plasma

The formation and dynamics of a laser-produced aluminum plasma have been experimentally and theoretically investigated. The visible-emitting regions of the plasma form two structures with different lifetimes and expansion velocities. The first part of the transient ionic signal simultaneously recorded by a Langmuir probe presents an oscillatory structure. A hydrodynamic model in a nondifferentiable space-time has been established. The numerical simulation of the plasma expansion showed the plasma plume separation into two patterns. Moreover, the self-structuring of the interface appears through a negative differential conductance and the current oscillations are explained as being induced by thermal fluctuations that appear in the plasma cooling processes.

Field Evidence for Strong Chemical Separation of Contaminants in the Hanford Vadose Zone

Water and chemical transport from a point source within vadose zone sediments at the Hanford Site in Washington State were examined with a leak test consisting of five 3800‐L aliquots of water released at 4.5‐m depth every week over a 4‐wk period. The third aliquot contained bromide, D2O, and 87Sr. Movement of the tracers was monitored for 9 mo by measuring pore water compositions of samples from boreholes drilled 2 to 8 m from the injection point. Graded sedimentary layers acting as natural capillary barriers caused significant lateral spreading of the leak water. Shortly after injections were completed, D2O was found at the 9‐ to 11‐m depth at levels in excess of 50% of the tracer aliquot concentration, while sediment layers with elevated water content at the 6‐ to 7‐m depth had less than 3% of the D2O tracer concentration, suggesting deep penetration of the D2O tracer and limited mixing between different aliquots of leak fluids. Initially, high bromide concentrations decreased more rapidly over time than D2O, suggesting enhanced transport of bromide due to anion exclusion. No significant increase in 87Sr was detected in the sampled pore water, indicating strong retardation of Sr by the sediments. These results highlight some of the processes strongly affecting chemical transport in the vadose zone and demonstrate the significant separation of contaminant plumes that can occur.

Mantle Plume Separation and the Expanding Earth

Summary Previous studies of mantle plume motions have assumed that any movement occurred within an Earth of fixed size. A comparison of distances between pairs of hot spots and their traces for different ages generally indicates less separation further back in time. The apparent changes in great circle distances between plumes may be consistent with constant separations in terms of geocentric angles, with an increase in the Earth's radius of up to 12 per cent over the past 120 My. The evidence for an expansion over the past 50 My may be inconclusive, due to the errors in the data for plume locations.

Subtidal flow structure at the turning region of a wide outflow plume

A series of underway current velocity profiles and near‐surface temperature and salinity measurements were combined with temperature and salinity profiles to characterize the subtidal flow structure at the turning region of a wide plume, the Chesapeake Bay outflow plume. In this context, “wide” refers to the ratio of lateral plume expansion to internal radius of deformation being greater than one. Observations were obtained in September and November of 1996 and in February and May of 1997 with the idea of capturing the variability in forcing conditions typically associated with these seasons. However, regional precipitation patterns yielded similar buoyancy forcing conditions for the four surveys and among the wettest years on record. This buoyancy forcing produced a well‐delineated outflow plume that separated from the coast on its way out the estuary. The plume separation acted in conjunction with frictional effects to delineate an inshore front, in addition to the customarily described offshore front. The outflow plume was markedly constrained by the Chesapeake Channel, which was also the main conduit of shelf waters toward the estuary. The bathymetric influence was also evident in the surface salinity field, the mean flows and the volume fluxes. The offshore extent of the plume was found between the scale predicted by geostrophic dynamics (internal Rossby radius) and that predicted by cyclostrophic dynamics. Such offshore extent was most likely linked to the plume interactions with the bathymetrically steered up‐estuary flow. This was corroborated by an analytical solution that explored the dynamical balance among pressure gradient, Coriolis accelerations and friction. In addition to being influenced by bathymetry, the Chesapeake Bay outflow plume was modified by local and remote effects related to atmospheric forcing.

Submarine tailings placement by a copper mine in the deep anoxic zone of the Black Sea

Copper mine tailings are discharged to the anoxic zone of the Black Sea at 350 m depth, and there is currently consideration of reducing this discharge depth. Oceanographic sampling has provided data allowing calculating whether dilute buoyant plumes will separate from the tailings density current as predicted. Calculations for various discharge rates and slurry dilutions indicate that such plumes will rise ∼89 m above the discharge depth, hence will remain in the deep anoxic zone below the permanent pycnocline at ∼150 m depth at both the present and currently proposed sites. There is some indication from relative seawater density measures that these plumes will drift rather than spreading diffusely. Plume separation from controlled discharges of the tailings slurry was confirmed by visual observations in an experimental tank. The oceanographic sampling also showed that trace element levels in the seawater by the discharge point remained below Turkish marine receiving water quality criteria.