Far-field Plume Research Articles

Coupled Navier–Stokes/Direct Simulation Monte Carlo Simulation of Multicomponent Mixture Plume Flows

A coupled particle-continuum simulation method is presented to compute the multicomponent mixture plume flow from the attitude-control engines of a satellite through the use of the Navier–Stokes solver and direct simulation Monte Carlo method. In this study, the implicit hybrid flux iteration scheme for the axisymmetric compressible Navier–Stokes equations is constructed to solve the inner flowfield of the nozzle. The Navier–Stokes computing technique is implemented considering slip boundary theory for the near-continuum slip flow near the nozzle exit. Direct simulation Monte Carlo methods for the axisymmetric core plume and three-dimensional far-field plume flows of multispecies mixture gas are developed by using a radial weighted factor, by tracking the molecular motion trajectory, and with secondary Cartesian and unstructured cell processing techniques. A multiregion decomposition and hybrid Navier–Stokes/direct simulation Monte Carlo algorithm with two-way and one-way coupling is established to solve the internal and external flow of the thruster, including the near-field, far-field, backflow, and gas-surface contaminated regions. After constructing the coupled Navier–Stokes/DSMC simulation scheme, the present method is applied to solve the plume flowfield and impinging contamination effects from the satellite attitude-control engine and solar array panel; the simulation results correspond well with the experimental measurements from the low-density wind tunnel and the theoretical predictions. To study the contamination effects produced by the multicomponent mixture plume, the current method is employed to simulate a five-component mixture plume flowfield of tens of meters from two representative attitude-control engines installed in different locations of a satellite in orbit. The results of the nonreacting multicomponent flow with equivalent mole fractions can be achieved with a one-component gas simulation if the species is assigned the properties of the mixture. The deposition rate of the plume flows produced by the two teamwork engines can be superimposed on each other. This method can be used to efficiently predict the impingement contamination effects of the gas-fired mixture plume flow on the satellite and solar array panels.

Effect of External Cathode Azimuthal Position on Hall-Effect Thruster Plume and Diagnostics

The T-220HT Hall-effect thruster was tested with the external cathode at different azimuthal locations to determine the effect of an external cathode on the far-field plume. The cathode is mounted in two configurations: 1) on top of the thruster, perpendicular to the plane of plume measurements, and 2) in the plane of plume measurements. The thruster was tested at discharge voltages of 150–300 V at a constant discharge current of 9 A on krypton propellant. The vacuum facility operating pressure was below for all operating conditions. Noticeable changes in the plume ion current density were measured that indicate plume asymmetry. With the cathode in the plane of the probes, the ion current density peak increases by up to 43% and the divergence angle decreases by up to 2.6 deg. However, there is less than a 5 V shift in the ion energy distribution, and the distribution shape remains constant. The results indicate that an external cathode alters the plume symmetry and creates a region of increased ion flux. An analysis of the cathode generated species densities indicates that the increase in ion current density is caused by nonuniform ingestion of cathode neutrals and nonuniform electron density near the cathode. This phenomenon can affect thruster plume measurements as well as the orientation of thrusters for satellite integration.

The Use of SF<sub>6</sub> and GIS to Study Farfield Modeling of Ocean Outfall Plumes in Florida

In June, 2004 and February, 2007, in field tracer studies were conducted on the Hollywood and South Central outfalls, using sulfur hexafluoride (SF6) as a tracer. The objective of these studies was to determine if the tracer could be detected in the farfield at significant distance, and if so, could this data be used to construct a model of the farfield plume. Prior models for farfield plume movement do not appear to comport well with the conditions in southeast Florida. Extensive research was conducted in southeast Florida on 4 outfalls, which led to the development of nearfield dilution equations for same. However farfield modeling of outfall plumes was difficult to accomplish because the tracers used are not detectable for significant distances. The SF6 resolved that problem and as a result the Hollywood outfall was used to construct a model. Two methods were investigated for modeling the plume, 1) the Eureqa formulation method and 2) the Gamma-Curve method. The concentrations in the x-y plane were first found by using the Eureqa formulation to calculate the concentration at each grid point given its depth and the concentration of the centerline at the same latitude. The plume models were generated using MATLAB that matched with the results actually seen in the field.

Electron flow properties in the far-field plume of a Hall thruster

The plasma properties were investigated in the far-field plume of a 1.5 kW class Hall thruster using a single, cylindrical Langmuir probe. The plasma potential, the electron temperature and the electron density were measured at 191 positions, providing a detailed map of the plume pattern. This map shows that the plasma plume of a Hall thruster is an expanding jet that is symmetric about the thruster axis. The large data set was also used for a detailed analysis of the electron flow properties. This analysis reveals that the plasma plume of a Hall thruster is an isentropic expansion. In addition, the momentum conservation equation shows there is a polytropic relationship between the plasma potential and the electron density with a γ smaller than that for an atomic gas due to ionization.

Modelling of Far-field Pressure Plumes for Carbon Dioxide Sequestration

We apply both numerical modelling, by means of single-phase and two-phase models, and analytical calculation for estimation of far-field pressure buildup, considering a generic scenario of dipping aquifer and a site-specific scenario for the Scania site, southwest Sweden. We examine the effect of depth-dependent fluid and material properties as well as formation geometries on far-field pressure buildup. The use of simple analytical calculations, including the Theis equation and superposition based on the method of images, for the estimation of pressure buildup is evaluated. The results are also discussed in terms of comparison between the numerical simulations and simple analytical calculations.

Time-resolved measurement of plasma parameters in the far-field plume of a low-power Hall effect thruster

Time-resolved measurements using electrostatic probes are performed in the far-field plume of a low-power permanent magnet Hall effect thruster. These measurements are necessary in order to account for the non-stationary behavior of the discharge. The plasma potential is measured by means of a cylindrical Langmuir and a sufficiently heated emissive probe, the electron temperature and density are measured with a cylindrical Langmuir probe. The thruster is maintained in a periodic quasi-harmonic oscillation regime by applying a sinusoidal modulation to a floating electrode in the vicinity of the cathode in order to guarantee repeatable conditions for all measurements. The modulation depth of the discharge current does not exceed approximately 10%. In order to achieve synchronism, the frequency of the modulation has to be close to the natural frequency of the observed phenomena. It is different depending on whether the discharge current or the plasma potential is selected as a reference. The measurements show that the fluctuations of the electron density follow the discharge current fluctuations. The time evolution of the plasma potential and the electron temperature is similar. The time-averaged properties of the discharge remain almost uninfluenced by the modulation. Measurements of the plasma potential with the two different probes are in good agreement. The observed phenomena are similar for Xe and Kr used as propellant gases.

Measurement of plasma parameters in the far-field plume of a Hall effect thruster

The far-field plume of a 1.5 kW Hall effect thruster is mapped with a Langmuir probe and an emissive probe. Time-averaged measurements of the plasma potential, the electron temperature and the electron number density are performed for different operating conditions of the thruster. The influence of the discharge voltage, the cathode mass flow rate as well as the magnetic field strength is investigated. The plasma potential decreases from 30 V at 300 mm on the thruster axis to 5 V at 660 mm and at 60°, the electron temperature decreases from 5 to 1.5 eV. The electron number density drops from 3.5 × 1016 to 1 × 1015 m−3 in the far-field plume. The values of the plasma potential and electron temperature measured with the Langmuir probe and the emissive probe are in good agreement.

Comments on “Simulation of Jeddah multi–port sea outfall” by Abdullah S. Al-Ghamdi [J. Coast. Conserv.] (2010) 14:63–69

In a paper published recently in the Journal of Coastal Conservation, Al-Ghamdi (J Coast Conserv 14:63–69, 2010) analyzes the wastewater multi-pot outfall of Jeddah using CORMIX2 for average ambient conditions. Both the near–field and the far–field mixing are calculated with CORMIX2. It is found in Al-Ghamdi (J Coast Conserv 14:63–69, 2010) that the near-field extends 187.5 m downstream from the diffuser, where the dilution reaches 1,047.8. It is at this same distance, 187.5 m, that the plume touches the water surface. The far-field dilution and plume width is calculated as the plume finally fills the entire water depth at a distance of 18,927 m downstream. From these analyses, it is concluded that local and international standards for treated wastewater are met and that the plume “will not pose any treats to the local venerable environment”. These findings, if correct, will help to protect the surrounding marine environment. However, is argued here that the use of CORMIX2, particularly for the far-field environment is not well justified and that the inherent simplifications in the software and its use, mainly the characterization of the physical environment, undermine the main conclusions.

Entrainment and flushing time in the Fraser River estuary and plume from a steady salt balance analysis

[1] A passenger ferry equipped with oceanographic instrumentation made eight transects across the Fraser River plume in the Strait of Georgia, British Columbia, each day for 4 years. Estimates of average plume salinity and volume were made from the observations and used in a quasi-steady budget to estimate the net upward flux of ambient salt water into the plume. This entrainment flux increases from a minimum of 17,000 m3s−1 at low river flow to a maximum of about 27,000 m3s−1 at intermediate flow. The entrainment flux then becomes essentially independent of river flow, although we argue on physical grounds it must eventually decrease. Entrainment velocities of a few mm s−1 were estimated from the entrainment flux when assuming that mixing primarily occurs along the salt wedge estuary or in the near-field plume. These values are consistent with previous estimates. This, in turn, suggests that entrainment is not important over most of the plume's full extent and that bulk plume properties are set in the near field. Finally, the observations are used to estimate a plume freshwater flushing time of 2.2 days, with essentially no dependence on river discharge, even though discharge varies seasonally by almost an order of magnitude. This value lies in between the expected time scales for near-field and far-field plumes and is long enough for rotation to play an important role. There is no evidence, however, of a coherent bulge as observed in other systems.

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.

Numerical modeling of aquaculture dissolved waste transport in a coastal embayment

Marine aquaculture is expanding rapidly without reliable quantification of effluents. The present study focuses on understanding the transport of dissolved wastes from aquaculture pens in near-coastal environments using the hydrodynamics code SUNTANS (Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier–Stokes Simulator), which employs unstructured grids to compute flows in the coastal ocean at very high resolution. Simulations of a pollutant concentration field (in time and space) as a function of the local environment (bathymetry), flow conditions (tides and wind-induced currents), and the location of the pens were performed to study their effects on the evolution of the waste plume. The presence of the fish farm pens cause partial blockage of the flow, leading to the deceleration of the approaching flow and formation of downstream wakes. Results of both the near-field area (area within 10 to 20 pen diameters of the fish-pen site) as well as far-field behavior of the pollutant field are presented. These detailed results highlight for the first time the importance of the wake vortex dynamics on the evolution of the near-field plume as well as the rotation of the earth on the far-field plume. The results provide an understanding of the impact of aquaculture fish-pens on coastal water quality.

High-speed dual Langmuir probe

In an effort to temporally resolve the electron density, electron temperature, and plasma potential for turbulent plasma discharges, a unique high-speed dual Langmuir probe (HDLP) has been developed. A traditional single Langmuir probe of cylindrical geometry (exposed to the plasma) is swept simultaneously with a nearby capacitance and noise compensating null probe (fully insulated from the plasma) to enable bias sweep rates on a microsecond timescale. Traditional thin-sheath Langmuir probe theory is applied for interpretation of the collected probe data. Data at a sweep rate of 100 kHz are presented; however the developed system is capable of running at 1 MHz-near the upper limit of the applied electrostatic Langmuir probe theory for the investigated plasma conditions. Large sets (100,000 sweeps at each of 352 spatial locations) of contiguous turbulent plasma properties are collected using simple electronics for probe bias driving and current measurement attaining 80 dB signal-to-noise measurements with dc to 1 MHz bandwidth. Near- and far-field plume measurements with the HDLP system are performed downstream from a modern Hall effect thruster where the time-averaged plasma properties exhibit the approximate ranges: electron density n(e) from (1x10(15))-(5x10(16)) m(-3), electron temperature T(e) from 1 to 3.5 eV, and plasma potential V(p) from 5 to 15 V. The thruster discharge of 200 V (constant anode potential) and 2 A (average discharge current) displays strong, 2.2 A peak-to-peak, current oscillations at 19 kHz, characteristic of the thruster "breathing mode" ionization instability. Large amplitude discharge current fluctuations are typical for most Hall thrusters, yet the HDLP system reveals the presence of the same 19 kHz fluctuations in n(e)(t), T(e)(t), and V(p)(t) throughout the entire plume with peak-to-peak divided by mean plasma properties that average 94%. The propagation delays between the discharge current fluctuations and the corresponding plasma density fluctuations agree well with expected ion transit-times observed with distinct plasma waves traveling away from the thruster at velocities >10 km/s.

Dissolved and particulate aluminum in the Columbia River and coastal waters of Oregon and Washington: Behavior in near-field and far-field plumes

The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80 nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000 nM and 18,000 nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100 km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf.

A conceptual model of the strongly tidal Columbia River plume

The Columbia River plume is typical of large-scale, high discharge, mid-latitude plumes. In the absence of strong upwelling winds, freshwater from the river executes a rightward turn and forms an anticyclonic bulge before moving north along the Washington coast. In addition to the above dynamics, however, the river plume outflow is subject to large tides, which modify the structure of the plume in the region near the river mouth. Observations based on data acquired during a summer 2005 cruise indicate that the plume consists of four distinct water masses; source water at the lift-off point, and the tidal, re-circulating and far-field plumes. In contrast to most plume models that describe the discharge of low-salinity estuary water into ambient high-salinity coastal water, we describe the Columbia plume as the superposition of these four plume types. We focus primarily on a conceptual summary of the dynamics and mutual interaction of the tidal and re-circulating plumes. The new tidal plume flows over top of the re-circulating plume and is typically bounded by strong fronts. Soon after the end of ebb tide, it covers roughly 50–100% of the re-circulating plume surface area. The fronts may penetrate well below the re-circulating plume water and eventually spawn internal waves that mix the re-circulating plume further. The re-circulating plume persists throughout the tidal cycle and corresponds to a freshwater volume equivalent to 3–4 days of river discharge. Finally, the plume water masses are distinguished from one another in term of surface chlorophyll concentration, suggesting that the above classification may also describe different biological growth regimes. The low-salinity re-circulating plume serves as an extension of the estuary into the coastal ocean, or an “estuary at sea”, because residence times during periods of high river flow are greater than those in the estuary.

An investigation on spill plume temperature of large space building fires

In fire safety engineering, rapid fire detection and suppression in large spaces are very important issue. Development of new techniques is always based on the good understanding of the basic principle of smoke movement, especially the temperature of spill plume. Aiming to this objective, this paper specifies the multi-sectional characteristics on spill plume free developing out of a wide-door cabin in a large space atrium by means of full-scale experiment, theoretical analysis and CFD modeling. First the physical development process of the spill plume is analyzed from the horizontal curved regime at the door, the near-field two-dimensional linear plume regime, through to the far-field axisymmetric plume regime. It demonstrates the coupling correlation existing between the linear virtual origin, critical transition height from linear to axisymmetric regime, the axisymmetric virtual origin and other parameters, such as the spill plume depth at the door, the mass and heat flow rate outside the cabin door, the cabin door width and height etc. The basic mathematic equations regarding each regime's centerline temperature have been obtained. The virtual origin position of linear plume regime and axisymmetric plume regime are given, the critical transition height of spill plume from the two-dimensional linear plume to axisymmetric plume regime is also proposed, and finally the double-part prediction model (MEDP) for the spill plume centerline temperature is put forward. By validation with the full-scale experiment and the large eddy CFD modeling, it shows that the proposed spill plume model is capable to well describe the centerline temperature varying characteristics of the spill plume free developing out of the cabin.

Plume impingement investigation using Monte-Carlo computations

Numerical simulations have been performed to explore the effects of important design parameters on impingement disturbance properties of multiple hydrazine thruster plumes. The particle behaviour of the far-field plume flows near the impingement surfaces is modelled using the collisionless molecular direct simulation Monte-Carlo method with the inflow boundary condition derived from the velocity and temperature profiles at the nozzle exit. The entering molecular motions and the impact interactions between molecules and solid boundaries are treated on a probabilistic basis, whereas the main flow properties are preserved from the transformation of the microscopic fluid activities of simulated molecules. To validate the present computer code, the predicted transverse Pitot pressure profile was compared with the measured data in the far plume region of an MBB/ERNO 0.5-N conical nozzle. On the basis of the ROCSAT-1 design configuration, the calculated plume disturbance torques are examined in the yaw, roll, and pitch directions for different settings of the canted angle of the thruster mounting and the satellite centre-of-mass (CM) offset. Predictions show that the normalized yaw impingement disturbance torque reaches 6.3 per cent at the cant angle of 30°, indicating that the associated plume collision effect on the attitude control can be important at large cant angles. In addition, the location change of the satellite CM in the axial axis reveals insignificant influence on the impingement torque for the offset value varying from −5.0 to 5.0 cm.

Top hat electrostatic analyzer for far-field electric propulsion plume diagnostics

The design, development, and testing of the top hat electric propulsion plume analyzer (TOPAZ) are presented for far-field electric propulsion plume diagnostics. The trend towards high-power thruster development will require plume diagnostic techniques capable of measuring high-energy particles as well as low-energy ions produced from charge-exchange collisions due to elevated facility background pressures. TOPAZ incorporates a “top hat” design with a geometrical analyzer constant of 100 resulting in a wide energy range and a high-energy resolution. SIMION, an ion trajectory analysis program, was used to predict characteristics of the analyzer. An ion beam accelerator system confirms the computational results. TOPAZ provides an energy resolution of 2.7%, field of view of 112°×26° (azimuthal by elevation) with an angular resolution in each direction of 2°, and a demonstrated energy-per-charge acceptance range of 5–15keV. An energy profile measurement of the NASA-173Mv1 Hall thruster demonstrates instrument operation in a Hall thruster plume.

Relating River Plume Structure to Vertical Mixing

Abstract The structure of a river plume is related to the vertical mixing using an isohaline-based coordinate system. Salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows. This coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume. Vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind-forced river plume. Vertical mixing, and the corresponding entrainment of background waters, is greatest near the estuary mouth where inertial shear mixing is large. This region is defined as the near field, with the more saline, far-field plume beyond. Wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field. Wind mixing is weaker at high salinity classes that have already been mixed to a critical thickness, a point where turbulent mixing of the upper layer by the wind is reduced, protecting these portions of the plume from further wind mixing. The work done by mixing on the plume is of similar magnitude in both the near and far fields.

Development of A Two-Dimensional Analytical Model for Predicting Toxic Sediment Plumes Due to Environmental Dredging Operations

A two-dimensional analytical transport model is developed to predict the dredge induced plume concentration in the horizontal plane under steady-state for simple hydraulic conditions. The derivation of the analytical solution is based on the solution to the advection-diffusion equation. The application of this analytical model is limited to mechanical dredge operations, bucket dredge, which has continuous point source in the water column. The analytical model developed herein is used to simulate sediment concentration distributions from a hypothetical dredging site and compared to results from a similar model using Stokes’ settling. The result shows that Stokes’ settling underestimates settling in the near-field and overestimates settling in the far-field plume. In summary, the model provides the ability to account for the rapid settling of larger particles in the suspended sediment near the dredging operations while simulating the slower settling and diffusive transport of smaller particles moving away from the dredging sites.

Determination of plume impingement disturbance characteristics for the ROCSAT-1 satellite

The impingement disturbance characteristics of the hydrazine thruster plumes have been examined comprehensively for the ROCSAT-1 satellite. In this study, the velocity and temperature distributions at the nozzle exit are obtained from the nozzle flowfield analysis. The axial velocity, transverse velocity and temperature profiles are further correlated with the curve-fitting procedure for resolving inflow properties of molecules ejected into a vacuum. The free-molecular direct simulation Monte Carlo technique is used to describe the particle nature of the distant plume flow behaviour near the impingement surface. The inflow molecular motions as well as the collision interactions between the molecules and the solid surface are treated on a probabilistic basis. On the other hand, the inter-collisions among molecules are considered to be relatively unimportant in the far-field plume region. A reasonable number of simulated molecules is also employed to reproduce the fluid behaviour in the macroscopic level. The predicted disturbance torques and thrust loss are found to be much less than the design control torques and the nominal thrust force for ROCSAT-1 satellite, indicating that the plume impingement effect will not cause any performance deterioration of the propulsive function.