Plume Shape Research Articles

Influence of initial plume shape on miscible porous media flows under density and viscosity contrasts

The effect of the initial condition upon the transport dynamics of miscible flowing fluids in a porous medium is investigated under viscosity and density contrasts. Such flows have attracted significant attention due to their importance in many fields of science and engineering, such as $\mathrm {CO}_2$ sequestration and aquifer remediation. Using high-resolution two-dimensional numerical simulations, we illustrate the impact of viscosity and density contrasts on the temporal evolution of the spreading and mixing quantities. We show that such impact depends on the initial shape of the source distribution where the solute is injected and on the intensity of the horizontal background flux. We find that rates of mixing are dependent on whether the solute is more or less viscous than the ambient fluid, a result usually not taken into consideration in studies on gravity fingering. At higher background flux, the effects due to horizontal viscous fingering dominate over gravitational fingering. Our computational analysis also suggests a non-trivial relationship between mixing and the length of the plume's interface under fingering instabilities. Finally, we show how a stratified permeability field can interact with these sources of instabilities and affect the transport behaviour of the plume.

Numerical studies of gasoline direct-injection sprays (ECN Spray G) under early- and late-injection conditions using Large Eddy Simulation and droplets-statistics-based Eulerian–Lagrangian framework

This paper presents an approach that uses Large Eddy Simulation under the Eulerian–Lagrangian framework to model the gasoline direct-injection (GDI) spray from Engine Combustion Network (ECN) multi-hole and counter-bore injectors. The approach considers the significant role that cavitation plays in primary atomization due to the counter-bore configuration. The local Weber number (We) and Reynolds number (Re) for GDI sprays are much smaller than those for a diesel spray, which renders conventional diesel spray approaches unsuitable. The proposed one uses a statistics-based droplet distribution function to address this and incorporates necessary information from a DNS inner-nozzle flow simulation. The corresponding models for drag, heat transfer, evaporation, and breakup consider the effects of viscous and distorted spray droplets. The approach has been applied to two different operating conditions, with simulation results that agree well with experimental data. Compared to the blob method assuming the ejected droplets are at the size of the injector diameter, the proposed CFD framework can reproduce a more accurate plume shape in the Spray G3 case. Applying the late-injection condition (Spray G1), the proposed approach improves the projected liquid volume (PLV) extinction compared to the blob method by providing a more accurate droplet evaporation prediction. These findings demonstrate the significance of the proposed approach for modeling GDI sprays and highlight its potential for future research in this area.

Experimental study of interface behavior and sound pressure oscillation of direct contact condensation of a steam jet in flowing water

Direct contact condensation of a vapor jet in liquid is frequently encountered in lots of industrial applications because of its high heat and mass transfer rates. However, severe interface and sound pressure oscillation associated with condensation might cause vibration and even failure of pipeline systems. In this paper, the interface behavior and the sound pressure oscillation of a steam jet in flowing water are captured respectively by a high-speed camera and a high-frequency hydrophone. According to the gray profile of the image, an identification method is proposed to determine the interface characteristics, including the plume shape, width, and penetration length of the jet. The statistical intensity and power spectrum density of the interface position and sound pressure oscillation of the steam jet are calculated. Two typical condensation regimes of Chugging and Oscillation-I under low steam mass flux (Gs < 346 kg/m2s) are observed. The intensities of the interface oscillation and sound pressure oscillation decline with increasing steam mass flux and a significant correlation coefficient of about 0.94 between them is revealed. With the incorporation of sound pressure parameters, two correlations of the dimensionless jet length and its oscillation intensity are established, with relative deviations of 20% between the experimental and predicted values. For Oscillation-I, the dominant frequencies of the interface oscillation and sound pressure oscillation are quantitatively consistent. From the time and frequency domain perspectives, it is quantitatively confirmed that the sound pressure oscillation of the steam jet under low steam mass flux is caused by its interface oscillation.

CLASP: CLustering of Atmospheric Satellite Products and Its Applications in Feature Detection of Atmospheric Trace Gases

AbstractSatellite instruments have the most potential of capturing trace gas variability as they continually observe the atmosphere and its composition over wide regions. Yet the increasingly large data size of satellite products poses a challenge for their use as traditional data processing methods (e.g., averaging) may not be effective to extract the spatiotemporal variability without prior knowledge of an emission source's spatial and temporal behavior, such as location, time, and plume shape. Here, an agile clustering algorithm entitled CLustering of Atmospheric Satellite Products (CLASP) is presented to identify the spatiotemporal variability of trace gases captured in satellite observations. We find the knowledge discovery method for large data sets, clustering, is suited for identifying the variability of trace gases in satellite observations, as such CLASP is rooted in density‐based clustering methods. CLASP detects features from satellite observations and identifies their spatial, magnitude, and temporal axis leading to a better understanding of the spatiotemporal variability of atmospheric trace gases. To test the applicability of CLASP, the algorithm is applied to TROPOspheric Monitoring Instrument NO2 observations illustrating some of its different capabilities. Implementing CLASP for event identification, capturing plume variability, and source detection, CLASP identified wildfires, observed disruptions from COVID‐19 lockdown restrictions, and detected irregular emissions from oil and gas operations.

Efficient Numerical Simulation of Biochemotaxis Phenomena in Fluid Environments.

A novel dimension splitting method is proposed for the efficient numerical simulation of a biochemotaxis model, which is a coupled system of chemotaxis-fluid equations and incompressible Navier-Stokes equations. A second-order pressure correction method is employed to decouple the velocity and pressure for the Navier-Stokes equations. Then, the alternating direction implicit scheme is used to solve the velocity equation, and the operator with dimension splitting effect is used instead of the traditional elliptic operator to solve the pressure equation. For the chemotactic equation, the operator splitting method and extrapolation technique are used to solve oxygen and cell density to achieve second-order time accuracy. The proposed dimension splitting method splits the two-dimensional problem into a one-dimensional problem by splitting the spatial derivative, which reduces the computation and storage costs. Finally, through interesting experiments, we show the evolution of the cell plume shape during the descent process. The effect of changing specific parameters on the velocity and plume shape during the descent process is also studied.

Numerical study on density-driven convection of CO2-H2S mixture in fractured and sequential saline aquifers

Dissolution trapping stands as a critical mechanism for the geological carbon storage (GCS) and can be notably improved through density-driven convection. However, to the best of the author’s knowledge, the discussion on density-driven convection of CO2-H2S mixture has been limited to the exclusion of intersected fractures and lithology sequence effects. Therefore, this study aims to systematically investigate the impact of H2S concentration, fractures, and lithology sequence on convective mixing. Four distinct mechanisms that influence convective mixing of CO2-H2S mixtures in the presence of fractures were identified: 1) accelerated downward solute transportation in fractures, 2) coalescence between plumes around fractures and primary down-swelling plumes, 3) high fracture conductivity inhibiting plume migration across fractures, and 4) upward flow in fractures facilitating the transport of high-concentration solute out of the system. Additionally, the effects of lithology sequence on the shape of CO2 plumes and the curve shape of the total flux at the top boundary were described. The results demonstrated that density-driven convection is enhanced with decreasing H2S concentration and increasing fracture interaction angle and fracture conductivity ratio. The magnitudes of density-driven convection, ranked from high to low, are fining downward, uniform, and fining upward lithology sequences. Furthermore, the H2S concentration affects the flow direction within fractures and alters the relative magnitude of the dimensionless concentration in the noise sequences. The findings of this study on a small scale were proven to be applicable on a large scale.

Monte Carlo simulation of the maximum migration distance of CO[formula omitted] in a sloping aquifer

Carbon capture and storage in saline aquifers is broadly considered a viable technology for reducing anthropogenic impact on the environment. However, a secure CO2 storage can be compromised by the depositional environments of target reservoirs, which can influence the CO2 migration in subsurface. The disposal of CO2 in a sloping aquifer can result in a substantial gas migration in the updip direction from the injection well until all gas becomes trapped. It thus can reach far more than desired regions from the well where the potential leakage paths to the surface can exist. This study aims at understanding the principal parameters that the maximum migration distance in the updip direction depends on, which can be important for estimating the risks of CO2 leakage through old abandoned wells in the regions of intensive subsurface exploration. Using the Monte Carlo method, an extended parametric study is performed by running 3-D reservoir simulations of CO2 storage in random aquifers characterized by various petrophysical and thermobaric parameters, saturation functions and brine salinity, and for the wells operated under different target rates. Herewith, the modeling accounts for such relevant physical phenomena as the phase transitions, the gravity and capillary forces, the hysteresis behavior of the relative permeability, etc. It is shown that the maximum migration distance at the post-injection stage is characterized by just two similarity criteria and the critical gas saturation for the drainage and imbibition processes. It is found that the CO2 plume shape at the moment of the well shut-in influences the subsequent gas transport. A new simple relation parameterizing the revealed dependence is proposed and validated against the sampled maximum migration distances. The relation is useful for an instant estimating the size of the contaminated zone around a projected CO2 well and for ranking the potential storage sites.

Numerical Exploration of Low Altitude Rocket Plume in Aircraft Vicinity

Low altitude plume of a solid rocket motor is numerically explored. The effects of free stream Mach number, altitude and presence of launch platform wing on plume shape are studied. Three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations along with k-ε turbulence model and species transport equations are solved using commercial CFD software CFX-11. Thermochemical parameters (Mach number, pressure, temperature and propellant hot gas mass fraction) are analysed to characterize the plume. Mixing layer boundaries, its thickness and the attainment of self-similarity are evaluated to study the plume structure. With the increase of free stream Mach number, the computed plume diameter reduces. Centerline pressure, temperature and radial expansion of the plumes increases with the increase in altitude. Plume is found to be elongated and narrowed with relatively warm core region due to the presence of platform wing.

Shelf slope, estuarine dynamics and river plumes in a z* vertical coordinate, unstructured grid model

The finite element, unstructured grid model SHYFEM has been used to carry out some fundamental studies on the quality of a specific type of Generalized Vertical Coordinate (GVC) system, the so-called z∗ coordinates versus z−geopotential coordinates. Idealized and realistic test cases are shown to assess the impact of the vertical coordinates on key physical processes, i.e. the internal tide generation at a continental slope, a river plume shape and intensity and the salt water intrusion.The results showed that the z∗ coordinates produce a stronger water column stratification than the z−geopotential ones and together with the unstructured grid modeling they can better solve the coastal sea dynamics.An idealized twin experiment configuration of the model was carried out to verify the proper implementation of the GVC z∗ by simulating the production of internal tides at the continental slope. The results confirmed that the z∗ coordinate model reproduces the expected internal tide fields better than z−geopotential model. A set of realistic experiments in the Po river delta coastal region, demonstrated that the representation of the dynamical processes at the coastal scales is conditioned by the high resolution (25 cm layers), which was only possible by the z∗ formulation in the upper water column.

CFD Simulation on Pressure Profile for Direct Contact Condensation of Steam Jet in a Narrow Pipe

In the published experimental results, it has been observed that when high-speed steam spurt into the subcooled waterflow, the total pressure along the axial direction at trailing edge of the steam plume shows a pressure-lift. To reveal the mechanism behind this phenomenon, this study utilizes a particle model to investigate the pressure profile of steam jet condensation in subcooled water flow in a narrow pipe. A numerical model based on the Eulerian–Eulerian multiphase model has been developed to accurately simulate the characteristics of pressure profile along the axial direction. The model’s validity is established by comparing the steam plume shape and temperature profiles with the experimental data. By analyzing the total pressure profile of the axis and the contours of gas volume fraction, it is found that there exists a pressure-lift phenomenon at trailing edge of the steam plume. The dynamic pressure of the water also shows a pressure-lift at this position, so it can be inferred that the dynamic pressure of the water is the main factor of the total pressure-lift.

Effect of energy input on the discharge characteristics of a microcathode arc thruster

To explore the effect of energy input on the discharge characteristics of a micro cathode arc thruster, the relationships between the different input PPU voltages of the micro cathode arc thruster and the plume shape, arc characteristics, thruster propulsion performance, and working fluid ionization are characterized in this research. The results obtained using a high-speed camera indicate that the change in the thruster's energy input affects the plume contraction. Further, the results of spectroscopy and electrical testing analyses show that an increase in the thruster input voltage prolongates the arc duration, ionization rate of the arc, and degree of plume contraction. When the thruster is in a low input voltage state, the arc ionization rate primarily affects thrust-to-power ratio. However, when the thruster is in a high input voltage state, the degree of plume contraction primarily affects propulsion efficiency.

Near-surface wind variability over spatiotemporal scales relevant to plume tracking insects.

Odor plume tracking is important for many organisms, and flying insects have served as popular model systems for studying this behavior both in field and laboratory settings. The shape and statistics of the airborne odor plumes that insects follow are largely governed by the wind that advects them. Prior atmospheric studies have investigated aspects of microscale wind patterns with an emphasis on characterizing pollution dispersion, enhancing weather prediction models, and for assessing wind energy potential. Here, we aim to characterize microscale wind dynamics through the lens of short-term ecological functions by focusing on spatial and temporal scales most relevant to insects actively searching for odor sources. We collected and compared near-surface wind data across three distinct environments (sage steppe, forest, and urban) in Northern Nevada. Our findings show that near-surface wind direction variability decreases with increasing wind speeds and increases in environments with greater surface complexity. Across environments, there is a strong correlation between the variability in the wind speed (i.e., turbulence intensity) and wind direction (i.e., standard deviation in wind direction). In some environments, the standard deviation in the wind direction varied as much as 15°-75° on time scales of 1-10 min. We draw insight between our findings and previous plume tracking experiments to provide a general intuition for future field research and guidance for wind tunnel design. Our analysis suggests a hypothesis that there may be an ideal range of wind speeds and environment complexity in which insects will be most successful when tracking odor plumes over long distances.

Uncertainty Quantification Analysis of Exhaust Gas Plume in a Crosswind

The design of naval exhaust funnels has to take into account the interaction between the hot gases and topside structures, which usually includes critical electronic devices. Being able to predict the propagation trajectory, shape and temperature distribution of an exhaust gas plume is highly strategic in different industrial sectors. The propagation of a stack plume can be affected by different uncertainty factors, such as those related to the wind flow and gas flow conditions at the funnel exit. The constant growth of computational resources has allowed simulations to gain a key role in the early design phase. However, it is still difficult to model all the aspects of real physical problems in actual applications and, therefore, to completely rely upon the quantitative results of numerical simulations. One of the most important aspects is related to input variable uncertainty, which can significantly affect the simulation result. With this aim, the discipline of Uncertainty Quantification provides several methods to evaluate uncertainty propagation in numerical simulations. In this paper, UQ procedures are applied to a CFD simulation of a single plume in a crossflow. The authors test the influence of the uncertainty propagation of the chimney exit velocity and the main flow angle on the plume flow development. Two different UQ methods are applied to the analysis: the surrogate-based approach and the polynomial chaos expansion method. A comparison of the two methods is performed in order to find their pros and cons, focusing on the different and detailed quantities of interest.

Machine learning-based prediction of operation conditions from plasma plume images of atmospheric-pressure plasma reactors

A technique was proposed in this paper to monitor the key operating conditions of a plasma abatement system, which are the concentration of the carbon-containing process gas and the treatment flowrate, from a plasma plume image acquired using an inexpensive color camera. The technique is based on the observation that the shape and color of the plasma plume vary with the variations in the specific energy input and plasma gas composition. In addition, because these variations are marginal and it is challenging to identify an analytical relationship between these variations and the operating conditions, the prediction model is obtained in a data-driven manner. Specifically, the model was composed of a set of convolutional autoencoders (CAEs) and a dense neural network. Furthermore, it was trained only with images captured under normal operation so that (1) images captured under abnormal operations could be identified based on the reconstruction error of the trained CAEs and (2) predictions are made only on normal images. As a demonstration, methane was tested as a process gas, and oxygen was used as a reaction agent in a nitrogen-rich environment. The test results showed that the optimized model could predict the treatment flowrate and process gas concentration with 96% probability within ±3.08 slpm and ±300 ppm, respectively.

Impact of variable density on electrokinetic transport and mixing in porous media

Electrokinetic (EK) techniques can effectively mobilize amendments and contaminants in porous media and therefore have a great potential for in situ subsurface remediation of a wide variety of organic and inorganic contaminants. However, the fundamental mechanisms governing EK applications in porous media are complex and entail coupling between different flow, transport, electrostatic and geochemical processes. In this study we investigate the interactions between density driven effects and electrokinetic transport in permeable porous media and we compare the observed dynamics with the outcomes of analogous scenarios in which advection and dispersion are the only transport mechanisms. We perform a series of multidimensional experiments and we demonstrate the strong interplay between Coulombic interactions among charged species in pore water and density-driven effects during electrokinetics. Our study illuminates non-trivial interactions between the pore water composition and the macroscopic behavior of variable density dye tracer plumes, showing different sinking and floating patterns, distinct plume shapes and spreading, as well as different extent of mixing depending on the chemical composition of the pore water. A numerical model, based on the Nernst-Planck-Poisson formulation and on the coupling with the geochemical code PHREEQC, was developed to simulate variable density flow and transport and to update the density of the aqueous solution resulting from mixing and electrostatic interactions between all chemical species in the injected plume and in the surrounding pore water electrolyte. The model allowed us to interpret the experiments and to visualize the impact of small density gradients and Coulombic effects on the macroscopic transport of the dye tracer. The outcomes of this study highlight the importance of density-driven flow also during EK transport, where the electrostatic interactions not only influence the concentration of charged species but can also affect the density and result in complex flow patterns, plume shapes and mixing behavior, radically different from the ones generated during advective-dispersive transport.

Experimental study on condensation and acoustic characteristics of steam underwater injection

Introduction: Bubbling deaeration is widely applied in marine steam power system, and direct contact condensation (DCC) of steam injected into water under low sub-cooled water is the thermodynamic foundation of this technology. The deaeration process involves complex thermal and hydraulic behaviors, such as violent turbulence, interfacial mass transfer, and multiphase flow etc., which induce significant pressure fluctuation and radiated noise. In this paper, the two-phase flow regimes and acoustic characteristics of DCC of steam injected into water were studied for sub-cooled temperature ranging from 3℃ to 17℃.Methods: Using high-speed camera to capture the dynamic plume shape, four typical plumes are found: external chug with encapsulating bubble, oscillating bubble jet, conical and cylindrical jet and cap jet; The underwater acoustic signal is measured synchronously, and the acoustic spectrum is obtained by Fast Fourier transform (FFT).Results and Discussion: Combined with the plume image, the component sources of the acoustic signal are analyzed. It is found that the first dominant frequency and the second dominant frequency of the acoustic are caused by the evolution of the jet main steam zone and the downstream large steam column respectively; By analyzing the influence of injection parameters on acoustic signal, it is found that steam flow and sub-cooled temperatures have a great influence on acoustic root mean square value and spectrum characteristics. With the decrease of sub-cooled temperature, the main frequency of injection noise signal gradually moves to low frequency. Low frequency noise dominates the radiated noise when the flow field approaches the saturation temperature.

Spatiotemporal characterization of evaporated atoms during electron beam melting additive manufacturing by advanced laser diagnostics

Electron powder bed fusion (E-PBF) is an additive manufacturing technology used to produce parts layer-wise for advanced aerospace, biomedical, and other applications. Precise control over the energy transferred to the powder by the electron beam is key to further process improvements. Here, we used tunable diode laser absorption spectroscopy to characterize the evaporated titanium atoms above the molten area of a TA6V powder alloy, and, thus, the effects of the energy transferred to it by the electron beam. This unconventional diagnostic tool achieves analyses at very high temporal (&amp;lt;1 μs) and spatial (&amp;lt;100 μm) resolutions, thus, offering valuable information on the microsecond-scale dynamics of the micro-melting zone and the effectiveness of the electron beam spot at diameters as small as ∼200 μm. Our measurements highlighted sharp fluctuations during the evaporation process that were independent of the power and scan speed of the electron beam; instead, the molten pool surface itself seems to drive these fluctuations. Our analysis also documented the shape and density of the vapor plume, which was oriented perpendicular to the surface under common E-PBF conditions.

Numerical simulation of density-driven non-Newtonian fluid flow

Abstract Density-driven flow is numerically studied. The sinking fluid is set as a power-law non-Newtonian fluid with a higher density than the environmental fluid. During the simulation process, saturation concentration is fixed on the upper boundary; thus downward plumes are formed because of gravitational instability. The dissolution flux undergoes a series of changes, from the initially diffusion-dominated regime to the convection-dominated regime due to the appearance of finger structures, and then to the transition of finger structures merging into larger plumes. Finally, it enters the shutdown regime as the plumes start to reach the impermeable bottom boundary. In the process of plume sinking, different fluid properties have an important impact on the downward velocity, shape of plumes and the dissolution flux of the flow field. The tip velocity of the plumes is slowed until the high-concentration fluid is supplied to further push the plumes downward. For the shear-thinning fluid ambient fluid, this phenomenon is even more drastic. However, for shear-thickening fluid, this phenomenon is almost not observed. In addition, unlike the condition of a Newtonian fluid, protoplumes on the original interface appear at the early stage. Prominent protoplumes have developed between the primary plumes in non-Newtonian fluids throughout the entire process.

Axisymmetric plumes due to fluid injection through a small source in a wet porous medium

A small spherical source discharges a fluid into a porous medium that is already fully saturated with another fluid. The injected fluid has higher density than the ambient fluid, and so it forms a plume that moves downward under the effects of gravity. We present a simple asymptotic analysis assuming the two fluids do not mix that gives the width of the plume far from the source as a function of the injected volume flux. A spectral method is then developed for solving the full nonlinear problem in Boussinesq theory. Accurate numerical solutions are presented, which show in detail the evolution of the plume of heavier injected fluid over time. Close agreement with the asymptotic plume shape far from the source is demonstrated at later times.

Modelling underwater dispersion of gas released from seabed soil considering current and wave

Subsea gas release incidents may result in catastrophic consequences, e.g., overturning of offshore floating structures, fire, and explosion. This paper developed a model to investigate the dispersion behavior of underwater gas released from the seafloor soil under combined action of current and wave. Eulerian-Eulerian model is used to track underwater gas dispersion trajectory. Porous model is utilized to describe the seafloor soil and simulate the penetration of gas released from seafloor soil. The numerical model is validated by comparing with small-scale experiments. The effect of release rate, current velocity and soil porosity is investigated. The parameters, e.g., rising time, horizontal dispersion distance and surfacing area are estimated. The uniqueness of this study is that underwater gas plumes are simulated considering the seafloor soil and the combined action of current and wave. The results indicate that the presence of seafloor soil has a significant effect on the migration shape and trajectory of underwater gas plume. The combined action of current and wave increases the dispersion distance of gas plume. This study can support risk assessment and emergency planning of subsea gas release accidents.