scholarly journals The Effects of Exchange Flow on the Karst Spring Hydrograph under the Different Flow Regimes: A Synthetic Modeling Approach

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1189
Author(s):  
Malihe Shirafkan ◽  
Zargham Mohammadi ◽  
Vianney Sivelle ◽  
David Labat
Keyword(s):  
Flow Regime ◽  
Spring Discharge ◽  
Exchange Flow ◽  
Flow Conditions ◽  
Spring Hydrograph ◽  
Conduit Flow ◽  
Discharge Fluctuations ◽  
Recession Coefficient ◽  
The Matrix ◽  
Synthetic Modeling

In this study, a synthetic modeling approach is proposed to quantify the effect of the amount and direction of the exchange flow on the karstic spring discharge fluctuations under different hydrologic conditions corresponding to high and low flow conditions. We hypothesis that the spring discharge fluctuations constitute a valuable proxy to understand the internal processes of the karst system. An ensemble of spring hydrographs was synthetically produced to highlight the effect of exchange flow by exploring the plausible range of variability of coefficients of exchange flow, conduit diameter, and matrix hydraulic conductivity. Moreover, the change of the rate of point recharge through the karst conduit allows for the quantifying of the sensibility of the spring hydrograph to the directions of exchange flow. We show that increasing the point recharge lies to a remarkable linear recession coefficient (β) as an indication of the conduit flow regime. However, a reduction in and/or lack of the point recharge caused the recession coefficient to change to exponential (α) due to the dominant effect of the matrix restrained flow regime and/or conduit-influenced flow regime. The simulations highlight that the exchange flow process from the conduit to the matrix occurred in a short period and over a restricted part of the conduit flow regime (CFR). Conversely, the exchange flow dumped from the matrix to the conduit occurs as a long-term process. A conceptual model is introduced to compare spring hydrographs’ characteristics (i.e., the peak discharge, the volume of baseflow, and the slope of the recession curve) under the various flow conditions with the directions of the exchange flow between the conduit and the matrix.

scholarly journals The dynamics of miscible viscous fingering from onset to shutdown

2018 ◽  
Vol 837 ◽  
pp. 520-545 ◽  
Author(s):  
Japinder S. Nijjer ◽  
Duncan R. Hewitt ◽  
Jerome A. Neufeld
Keyword(s):  
Numerical Simulations ◽  
Flow Regime ◽  
Peclet Number ◽  
Viscous Fingering ◽  
Linear Stability Theory ◽  
Late Time ◽  
Exchange Flow ◽  
Mixing Rate ◽  
Péclet Number ◽  
Single Finger

We examine the full ‘life cycle’ of miscible viscous fingering from onset to shutdown with the aid of high-resolution numerical simulations. We study the injection of one fluid into a planar two-dimensional porous medium containing another, more viscous fluid. We find that the dynamics are distinguished by three regimes: an early-time linearly unstable regime, an intermediate-time nonlinear regime and a late-time single-finger exchange-flow regime. In the first regime, the flow can be linearly unstable to perturbations that grow exponentially. We identify, using linear stability theory and numerical simulations, a critical Péclet number below which the flow remains stable for all times. In the second regime, the flow is dominated by the nonlinear coalescence of fingers which form a mixing zone in which we observe that the convective mixing rate, characterized by a convective Nusselt number, exhibits power-law growth. In this second regime we derive a model for the transversely averaged concentration which shows good agreement with our numerical experiments and extends previous empirical models. Finally, we identify a new final exchange-flow regime in which a pair of counter-propagating diffusive fingers slow exponentially. We derive an analytic solution for this single-finger state which agrees well with numerical simulations. We demonstrate that the flow always evolves to this regime, irrespective of the viscosity ratio and Péclet number, in contrast to previous suggestions.

scholarly journals Calibration of hydrological models for ecologically relevant streamflow predictions: a trade-off between fitting well to data and estimating consistent parameter sets?

2020 ◽  
Vol 24 (3) ◽  
pp. 1031-1054 ◽  
Author(s):  
Thibault Hallouin ◽  
Michael Bruen ◽  
Fiachra E. O'Loughlin
Keyword(s):  
Flow Regime ◽  
River Flow ◽  
Freshwater Ecosystems ◽  
Living Environment ◽  
Rate Of Change ◽  
Low Flow ◽  
Hydrological Models ◽  
Flow Conditions ◽  
Local Flow ◽  
Trade Off

Abstract. The ecological integrity of freshwater ecosystems is intimately linked to natural fluctuations in the river flow regime. In catchments with little human-induced alterations of the flow regime (e.g. abstractions and regulations), existing hydrological models can be used to predict changes in the local flow regime to assess any changes in its rivers' living environment for endemic species. However, hydrological models are traditionally calibrated to give a good general fit to observed hydrographs, e.g. using criteria such as the Nash–Sutcliffe efficiency (NSE) or the Kling–Gupta efficiency (KGE). Much ecological research has shown that aquatic species respond to a range of specific characteristics of the hydrograph, including magnitude, frequency, duration, timing, and the rate of change of flow events. This study investigates the performance of specially developed and tailored criteria formed from combinations of those specific streamflow characteristics (SFCs) found to be ecologically relevant in previous ecohydrological studies. These are compared with the more traditional Kling–Gupta criterion for 33 Irish catchments. A split-sample test with a rolling window is applied to reduce the influence on the conclusions of differences between the calibration and evaluation periods. These tailored criteria are shown to be marginally better suited to predicting the targeted streamflow characteristics; however, traditional criteria are more robust and produce more consistent behavioural parameter sets, suggesting a trade-off between model performance and model parameter consistency when predicting specific streamflow characteristics. Analysis of the fitting to each of 165 streamflow characteristics revealed a general lack of versatility for criteria with a strong focus on low-flow conditions, especially in predicting high-flow conditions. On the other hand, the Kling–Gupta efficiency applied to the square root of flow values performs as well as two sets of tailored criteria across the 165 streamflow characteristics. These findings suggest that traditional composite criteria such as the Kling–Gupta efficiency may still be preferable over tailored criteria for the prediction of streamflow characteristics, when robustness and consistency are important.

scholarly journals Experimental Analysis of Gas–Liquid–Solid Three-Phase Flows in Horizontal Pipelines

2020 ◽  
Vol 105 (4) ◽  
pp. 1035-1054
Author(s):  
Paolo Sassi ◽  
Youssef Stiriba ◽  
Julia Lobera ◽  
Virginia Palero ◽  
Jordi Pallarès
Keyword(s):  
Flow Visualization ◽  
Flow Regime ◽  
Solid Particles ◽  
High Complexity ◽  
Flow Conditions ◽  
Two Phase Flows ◽  
Two Phase ◽  
Three Phase ◽  
Inner Diameter ◽  
The Individual

AbstractThe dynamics of three-phase flows involves phenomena of high complexity whose characterization is of great interest for different sectors of the worldwide industry. In order to move forward in the fundamental knowledge of the behavior of three-phase flows, new experimental data has been obtained in a facility specially designed for flow visualization and for measuring key parameters. These are (1) the flow regime, (2) the superficial velocities or rates of the individual phases; and (3) the frictional pressure loss. Flow visualization and pressure measurements are performed for two and three-phase flows in horizontal 30 mm inner diameter and 4.5 m long transparent acrylic pipes. A total of 134 flow conditions are analyzed and presented, including plug and slug flows in air–water two-phase flows and air–water-polypropylene (pellets) three-phase flows. For two-phase flows the transition from plug to slug flow agrees with the flow regime maps available in the literature. However, for three phase flows, a progressive displacement towards higher gas superficial velocities is found as the solid concentration is increased. The performance of a modified Lockhart–Martinelli correlation is tested for predicting frictional pressure gradient of three-phase flows with solid particles less dense than the liquid.

scholarly journals CONTRIBUTION OF SEASONAL STOCHASTIC MODELS SARIMA TO THE RATIONAL WATER RESOURCES MANAGEMENT. THE CASE OF THE KRANIA ELASSONA KARST SYSTEM, THESSALY, GREECE

2004 ◽  
Vol 36 (4) ◽  
pp. 2012
Author(s):  
A. Μανάκος ◽  
Γ. Δημόπουλος
Keyword(s):  
Time Series ◽  
Stochastic Model ◽  
Groundwater Flow ◽  
Stochastic Models ◽  
Groundwater Resources ◽  
Spring Discharge ◽  
Karst System ◽  
Flow Conditions ◽  
Discharge Time ◽  
Monthly Discharge

Several stochastic models, known as Box and Jenkins or SARIMA (Seasonal Autoregressive Integrated Moving Average) have been used in the past for forecasting hydrological time series in general and stream flow or spring discharge time series in particular. SARIMA models became very popular because of their simple mathematical structure, convenient representation of data in terms of a relatively small number of parameters and their applicability to stationary as well as nonstationary process.Application of the seasonal stochastic model SARIMA to the spring's monthly discharge time series for the period 1974-1993 in Krania Elassona karst system yielded the following results. Logarithms of the monthly spring discharge time series can be simulated on a SARIMA (4,1,1)(1,1,1)12 type model. This type of model is suitable for the Krania Elassona karst system simulation and can be utilised as a tool to predict monthly discharge values at Kafalovriso spring for at least a 2 year period. Seasonal stochastic models SARIMA seem to be capable of simulating both runoff and groundwater flow conditions on a karst system and also easily adapt to their natural conditions.Adapting the proper stochastic model to the karst groundwater flow conditions offers the possibility to obtain accurate short term predictions, thus contributing to rational groundwater resources exploitation and management planning

Bivariate Log-Normal Distribution of Stimulated Matrix Permeability and Block Size in Fractured Reservoirs: Proposing New Multilinear-Flow Regime for Transient-State Production

SPE Journal ◽  
2018 ◽  
Vol 23 (04) ◽  
pp. 1316-1342 ◽  
Author(s):  
Salam Al-Rbeawi
Keyword(s):  
Normal Distribution ◽  
Flow Regime ◽  
Fractured Reservoirs ◽  
Block Size ◽  
Analytical Models ◽  
Matrix Permeability ◽  
Matrix Block ◽  
The Matrix ◽  
Log Normal ◽  
Log Normal Distribution

Summary This paper investigates the impacts of varied stimulated matrix permeability and matrix-block size on pressure behaviors and flow regimes of hydraulically fractured reservoirs using bivariate log-normal distribution. The main objective is assembling the variance in these two parameters to the analytical models of pressure and pressure derivative considering different porous-media petrophysical properties, reservoir configurations, and hydraulic-fracture (HF) characteristics. The motivation is eliminating the long-run discretization treatment in the porous media required by applying analytical models to describe the variance in the previously discussed parameters with the distance between HFs. Several analytical models for pressure response were generated in this study for hydraulically fractured reservoirs with rectangular-shaped drainage areas. These models take into account the change in stimulated matrix permeability from the maximum value close to the HF face to the minimum value at the so-called no-flow boundary between fractures. They also consider the change in the matrix-block size, corresponding to the change in the induced-fracture density (number of fractures per foot of length), from the minimum value close to the fracture face to the maximum value at the no-flow boundary. Bivariate log-normal distribution was used to describe the change in the stimulated matrix permeability and matrix-block size. The formations of interest are composed of stimulated reservoir volume (SRV), where the matrix is stimulated by the fracturing process, and unstimulated reservoir volume (USRV), where the stimulation process does not affect the matrix. The outcomes of this study can be summarized as Generating new analytical models for pressure and pressure derivative in hydraulically fractured reservoirs that consider the change in stimulated matrix-block size and permeability using bivariate log-normal distribution Understanding the effect of using the probability-density function (PDF) of matrix-block size and permeability in the pressure distribution of different reservoirs Observing the new multilinear-flow regime that develops at intermediate production time and represents several simultaneous linear-flow regimes inside HFs, SRV, and USRV Developing analytical models for the new multilinear-flow regime Studying the effects of petrophysical properties of HFs, induced fractures, and matrix as well as reservoir size and configuration on pressure behavior The most interesting points in this study are The applicability of bivariate log-normal distribution for describing the variance and nonuniform distribution of matrix-block size and permeability. The large variance in the matrix-block size and permeability causes significant decrease in wellbore-pressure drop. Small value of standard deviation of matrix-block size and permeability indicates the possibilities for significant decrease in wellbore pressure drop. The means of matrix-block size and permeability may not have significant effects on reservoir-pressure distribution. The new multilinear-flow regime is characterized by a one-eighth slope on the pressure-derivative curve and is seen always after HF linear flow and before boundary-dominated flow regime. Multilinear-flow regime develops to bilinear-flow regime with a one-quarter slope for uniform distribution of equal matrix-block size and permeability.

Characterising transition towards more ephemeral streams in Australian catchments

2020 ◽  
Author(s):  
Margarita Saft ◽  
Murray Peel ◽  
Tim Peterson
Keyword(s):  
Surface Water ◽  
Flow Regime ◽  
Water Availability ◽  
Environmental Flows ◽  
Future Climate ◽  
Ephemeral Streams ◽  
Flow Conditions ◽  
Spatial And Temporal Patterns ◽  
Millennium Drought ◽  
Zero Flow

<p>Many streams experienced a prominent increase in proportion of cease to flow conditions during and after the multiyear drought in Australia (Millennium drought, circa 1997 – 2009). Change in zero flow occurrence frequency reflects the general transition of stream reaches from gaining to losing conditions, from losing to losing more, and ultimately to the disconnected state. We track and characterise these changes in groundwater-surface water connection using zero flow conditions as a proxy and explore the spatial and temporal patterns in flow regime transformation. The implications for upstream / downstream water availability and management of environmental flows and ecosystems are discussed in view of projected drier future climate.</p>

Adipose fin condition and flow regime in catfish

2008 ◽  
Vol 86 (9) ◽  
pp. 1079-1082 ◽  
Author(s):  
N. F. Temple ◽  
T. E. Reimchen
Keyword(s):  
Turbulent Flow ◽  
Flow Regime ◽  
Body Shape ◽  
Paired Comparisons ◽  
Flow Conditions ◽  
Habitat Types ◽  
Variable Expression ◽  
Adipose Fin ◽  
Hydrodynamic Function ◽  
Turbulent Flow Conditions

Based on recent evidence suggesting a hydrodynamic function of the small adipose fin in salmonids to turbulent flow conditions, we test for associations between presence and absence of the adipose fin and flow regime in Siluriformes, one of the largest freshwater groups of fish with variable expression of this fin. Among 1906 species from multiple families, those living in habitats with flow (streams or rivers) exhibited an adipose fin significantly more frequently than expected relative to no-flow habitats (lakes, marine, parasitic). These trends were robust and occurred on different continents and among multiple paired comparisons within sister groups. Exceptions to these trends generally had atypical body shape or occupied divergent habitat types. These results are concordant with the hydrodynamic function of this small fin.

An experimental study of low-Reynolds-number exchange flow of two Newtonian fluids in a vertical pipe

2011 ◽  
Vol 682 ◽  
pp. 652-670 ◽  
Author(s):  
F. M. BECKETT ◽  
H. M. MADER ◽  
J. C. PHILLIPS ◽  
A. C. RUST ◽  
F. WITHAM
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Viscous Fluid ◽  
Flow Regime ◽  
Low Reynolds Number ◽  
Velocity Profiles ◽  
Newtonian Fluids ◽  
Exchange Flow ◽  
Volume Flux ◽  
Two Fluids

We present an experimental study of a buoyancy-driven, low-Reynolds-number (Re < 1) exchange flow of two Newtonian fluids in a vertical cylindrical pipe (length 1 m and diameter 38.4 mm) connecting two fluid reservoirs. The denser, more viscous fluid was golden syrup and the less dense, less viscous fluid was a golden syrup–water solution; the ratio of the viscosities of the two fluids (β) ranged from 2 to 1180. Flows were initiated by removing a bung in the base of the upper reservoir or sliding out a gate positioned at the top, middle or bottom of the pipe. We observe the flows over long time durations (up to 356 h), and define the development of the flow with reference to a non-dimensional time (τ). The initial transient development of the flow was dependent on which of the two fluids initially filled the pipe, but this did not systematically affect the flow regime observed at τ ≫ 1. Two distinct flow regimes were observed: axisymmetric core-annular flow (CAF), in which the less viscous fluid occupies a cylindrical core and the denser fluid flows downwards in an annulus, and side-by-side (SBS) flow where both fluids are in contact with the pipe and there is a single interface between them. CAF formed at β ≥ 75 and SBS flow at β ≤ 117. In several experiments, for 5 ≤ β ≤ 59, a slowly developing transitional SBS (TSBS) flow was observed where SBS flow and CAF occurred simultaneously with SBS in the lower portion of the pipe; SBS existed throughout most of the pipe and in one case grew with time to entirely fill the pipe. Velocity profiles determined by tracking tracer particles show that the observed CAFs are adequately described by the formulation of Huppert & Hallworth (J. Fluid Mech., vol. 578, 2007, pp. 95–112). Experimental SBS velocity profiles are not well produced by the formulation of Kerswell (J. Fluid Mech., 10.1017/jfm.2011.190), possibly because the latter is restricted to flows whose cross-section has an interface of constant curvature. Despite the variations in flow regime, volume fluxes can be described by a power-law function of β, Q1 = 0.059 β−0.74. A comparison of experimental data with the theoretical approaches of Huppert Hallworth (2007) and Kerswell (2011) indicates that fluids are not arranged in the regime that maximises volume flux (e.g. SBS or CAF), nor do they adopt the geometry that maximises volume flux within that particular regime.

scholarly journals Continuous flow synthesis of terpene-based monomers for green polymers production

2019 ◽  
Author(s):  
Lucas Pera Fernandes ◽  
Julio Cezar Pastre ◽  
Renan Galaverna ◽  
Gustavo Rodrigues Gomes
Keyword(s):  
Maleic Anhydride ◽  
Flow Regime ◽  
Continuous Flow ◽  
Cycloaddition Reaction ◽  
Hydrogenation Reaction ◽  
Diels Alder ◽  
Flow Conditions ◽  
Flow Synthesis ◽  
Green Polymers

The synthesis of monomers for the production of novel green polymers was evaluated in continuous flow conditions using terpenes as dienes and maleic anhydride as dienophile for the [4+2] Diels-Alder cycloaddition reaction. The hydrogenation reaction was also evaluated to prevent the retro-Diels-Alder and to expand the reactional scope by producing adducts with distinct characteristics of structures and reactivity. Fourteen different monomers were obtained in good yields in flow regime.

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