1,297 research outputs found
Remote sensing of the river Rhine plume
No full textThe data content of remote sensing (RS) images of sea surface temperature (SST) and normalized water-leaving radiance (nLw), for the year 1998, with respect to the River Rhine plume, is investigated. Questions that this study tries to answer are: is it possible to identify the plume from the available RS images, and under which conditions is this possible? How much information on the plumes behaviour can be derived from these images? Does or can this information contribute to our general knowledge of the plume? The images provide a spatial resolution of I km2 and a temporal resolution of I or 2 images per day per sensor for nLw and SST, respectively (in the case of a cloudless atmosphere). In the presence of clouds, no signal is detected for the area of surface water underneath the clouds. Two hypotheses are set up to explain how the RS images can be used to trace the plume. In the hypotheses links are established between salinity gradients that delimit the plume and SST and nLw respectively. The results are based on these hypotheses. From the available images, 9 SST images in spring provide detailed information on the stratified plume and allow for derivation of indirect information on sub-surface processes. In winter the temperature gradients as visible on SST imagery seem to indicate the broad plume patterns. From the nLw images it was not possible to identify the boundaries of the plume. However it is expected that the nLw images are an excellent source for monitoring suspended particulate matter (SPM) in the North Sea. The general conclusion of this study is that the RS data used in this project provide a valuable source of information, with respect to the Dutch coastal zone, in addition to the currently available measurement techniques and computer models. The SST imagery turns out to be particularly useful for tracing stratification, whereas nLw imagery seems to be an excellent source for monitoring SPM in the North Sea. For detailed monitoring of the DCZ and the plume, increased spatial and temporal resolutions are required.Hydraulic EngineeringCivil Engineering and Geoscience
The effect of temperature fluctuations on the spread of a buoyant plume
No full textEmissions from many natural and anthropogenic sources are hot compared with the surrounding ambient air. Such buoyancy effects cause the emitted plume to rise, increasing the effective source height and significantly decreasing the maximum ground level concentrations (in the vicinity of the source). A major aspect that distinguishes buoyant and passive dispersion is that buoyant fluid particles create their own turbulence and hence exchange processes between the plume and its environment need to be accounted for. The inclusion of plume rise in Lagrangian stochastic models (LSMs) of turbulent dispersion has been considered by many authors but the interaction of the buoyant plume with the environment (by means of entrainment) is difficult to model in a Lagrangian framework. Webster and Thomson [8] formulated a hybrid model in which the mean flow is calculated from a simple plume model and the fluctuations of velocity are calculated using an LSM. They model the effect of turbulence generated by the plume by an additional random increment to the position of a particle. Here, instead of including this extra term, we add a stochastic differential equation (SDE) for the temperature fluctuations suitably coupled with the SDE for the velocity fluctuations. The interaction of temperature and velocity fluctuations, directly related to the turbulence within the plume, determines the plume’s spread. The results of the model are compared with large-eddy simulation (LES) of buoyant plumes in a uniform crosswind and also with the plume generated by the explosion and fire at the Buncefield oil depot in 2005 using realistic profiles of the wind speed and direction and thermal stratification
A Study on Plume Dispersion Characteristics of Two Discrete Plume Stacks for Negative Temperature Gradient Conditions
No full text© 2021, The Author(s). The dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions
Modelling the Rhine River Plume
No full textWhen a river discharges into the sea it forms a river plume. The main property of these plumes is their buoyancy; fresh water discharged by rivers is less dense than the receiving, saline waters. Due to the rotation of the Earth, these plumes tend to turn to the right in the Northern Hemisphere after entering the sea. Previous studies investigated the advection of buoyant river plumes due to wind forcing and ambient currents. However, most studies have neglected the influence of tidal motions. Consequently in this study attention is paid to the spring-neap tidal cycle and tidal straining, in order to investigate the effects of tidally generated turbulence to the stratification. The objective of this study was to investigate the role of tidal forcing on the evolution of a river plume in a shallow frictional sea. The numerical experiments presented employ a three-dimensional, idealised coastal basin set-up. The basic physical properties of the basin are an approximation to the typical conditions associated with the Rhine River Plume. In addition the effects of wind stress and a high discharge are brieflydiscussed. The model set-up enabled the performance of a large number of simulations concerning the sensitivity to open boundaries, forcing conditions and numerical properties. The most apparent effect of tidal forcing appeared to be the on- and offshore movement of the plume and the recurrent mixed and stratified conditions associated with the spring-neap tidal cycle. A pulsed discharge and instabilities (see figure) in the coastal current are also identified. Despite a number of simplifications, the results of the study exhibit a fair resemblance with the behaviour of the Rhine plume. This indicates the significance of tidal forcing on a buoyant plume in a shallow basin; it appeared to be the most important process controlling the stratification.Hydraulic EngineeringCivil Engineering and Geoscience
The thermal and mechanical structure of a two-dimensional plume in the earths mantle
No full textOn the condition that the distribution of velocity and temperature at the mid-plane of a mantle plume has been obtained (pages 213–218, this issue), the problem of determining the lateral structure of the plume at a given depth is reduced to solving an eigenvalue problem of a set of ordinary differential equations with five unknown functions, with an eigenvalue being related to the thermal thickness of the plume at this depth. The lateral profiles of upward velocity, temperature and viscosity in the plume and the thickness of the plume at various depths are calculated for two sets of Newtonian rheological parameters. The calculations show that the precondition for the existence of the plume, δT/L 1 (L = the height of the plume, δT = lateral distance from the mid-plane), can be satisfied, except for the starting region of the plume or near the base of the lithosphere. At the lateral distance, δT, the upward velocity decreases to 0.1 – 50% of its maximum value at different depths. It is believed that this model may provide an approach for a quantitative description of the detailed structure of a mantle plume
Variability of Yellow River turbid plume detected with satellite remote sensing during water-sediment regulation
No full textWater Sediment Regulations (WSRs) of the Yellow River (YR) have fundamentally altered the dynamics of freshwater and sediment transport in YR estuary and might profoundly affect water quality and ecosystem of the adjacent Bohai Sea. In this study, empirical algorithms were established to infer sea surface salinity and turbidity of YR plume using on surface reflectance products of MODIS and GOCI satellites in combination with observations from hydrographic surveys during the 2014 WSR event. Inter- and intraday variability of salinity and turbidity were quantitatively assessed and correlated with external forces including river discharge, tides, Coriolis force, and wind-driven circulation. The results revealed the enhanced offshore extension of turbid plume as WSR drastically increased freshwater and sediment discharge to river mouth. During WSR event, the area of low salinity plume ( < 25 psu) increased to 267 km(2), while sediment plume (SR645 > 0.12sr(-1)) occupied a maximum area of 162 lung. Intraday variation observed from geostationary GOCI data clearly illustrated the dominance of tidal current on short term dispersal pattern of freshwater and sediment plume. In comparison, wind field dominated the seasonal variation in flume transport but had insignificant impact on short term river plume dynamic during WSR. Overall, this study demonstrated that the spatial and temporal dynamic of YR plume was successfully captured by satellite remote sensing, which provided an effective tool for evaluating the environmental and ecological impact of WSRs
Observations of Multiple Internal Wave Packets in a Tidal River Plume
No full textRemotely sensed images document the occurrence of multiple packets of internal solitary waves (ISWs) in the Rhine River plume at the same time. We use a combination of field observations, and non-hydrostatic and hydrostatic modeling to understand the processes that lead to the generation and retention of multiple ISW packets within the Rhine plume. Previous numerical modeling shows that the tidal plume front is trapped in the mid-field plume for more than one tidal cycle due to tidal straining and recirculation within the plume, resulting in the presence of multiple fronts in the near-and mid-field plume regions. In this work, we show how variations in the strength of these fronts can lead to the release of ISW packets. We conclude that the retention of the fronts in the mid-field region of the plume and modulation in the strength of the fronts can explain the presence of multiple ISW packets. A frontal Froude number analysis shows that fronts generated during the previous ebb tide can release ISWs in addition to the newly released tidal plume front.Environmental Fluid Mechanic
Icy moon plume simulator chamber: The design of a laboratory recreation of an icy moon plume
No full textSince the discovery of plumes on Saturn's icy moon Enceladus' southern pole by Cassini in 2005, these phenomena have been observed and simulated by computer models. This study takes a next step in icy-moon plume research and proposes a design for a laboratory set-up that recreates such a plume here on Earth. This set-up consists of a cylindrical ice-block with a crevasse reaching from the top to the reservoir of liquid water at the bottom, tailored such that a hypersonic plume will form when placed in a vacuum chamber. This laboratory set-up can for example assist in proving current hypotheses on the plumes’ mechanism, subsurface ocean content, grain growth, organic macromolecular material origin, serve as a test ground for future landers and much more.Aerospace Engineering | Space Fligh
Modelling far-field dredge plume dispersion
No full textBy its very nature dredging is an environmental impact, since dredging includes the excavation and/or relocation of sediment in a river, sea or estuary. One of the environmental impacts related to dredging is increased suspended sediment concentration (SSC) levels, forming plumes of sediment. These so called dredge plumes originate from spillage of dredged material. Especially the fine sediment can stay in suspension on long time and spatial scales. Environmental Impact Assessments (EIAs) are conducted prior to the project's start to assess impact of dredging activities. One of the concerns of an EIA is to determine dredge induced rise of SSC levels. Forecast modelling is often applied to simulate dredge plumes in order to verify SSC and sedimentation levels. However, due to large uncertainties about the project, input parameters and ambient parameters, forecast modelling of dredge plumes is often challenging. In this study the most important parameters involved in far-field dredge plume dispersion were identified. Furthermore, by means of a numerical model experiment the influence of these parameters on far-field plume results was tested. Subsequently, the model was compared to data from several measurement campaigns concerning dredge plumes. This helped to verify the applicability of the model and made comparison possible between the comparison model output and experimental results. Recommendations were developed, supporting more informed selection of modelling techniques and model input regarding forecast modelling far-field plume dispersion. All recommendations use the requested output as starting point, based on both parameter (concentration or flux) and plume age.Hydraulic EngineeringHydraulic EngineeringCivil Engineering and Geoscience
Shadowgraphy of the end-effects regime produced by clustered rockets
No full textThe plume produced by a cluster of two high area-ratio thrust optimized parabolic contour nozzles is visualized by way of retroreflective shadowgraphy. Both steady and transient operations of the nozzles (start-up and shut-down) were conducted in the anechoic chamber and high speed flow facility at The University of Texas at Austin. Both nozzles exhibit free shock separated flow, restricted shock separated flow and an end-effects-regime prior to flowing full. Radon transforms of the shadowgraphy images are used to identify the locations in the flow where sound waves are being generated. During these off design operations of the nozzles, most sound waves are generated by turbulence interactions with the shock cells located in the supersonic annular plume. During the end-effects-regime, this supersonic annular plume is shown to flap violently, thus providing a first principals understanding of the sources of most intense loads during engine ignition
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