Surface flow and subsurface flow constitute a naturally linked hydrologic
continuum that has not traditionally been simulated in an integrated
fashion. Recognizing the interactions between these ...systems has encouraged
the development of integrated hydrologic models (IHMs) capable of treating
surface and subsurface systems as a single integrated resource. IHMs are
dynamically evolving with improvements in technology, and the extent of their
current capabilities are often only known to the developers and not general
users. This article provides an overview of the core functionality,
capability, applications, and ongoing development of one open-source IHM,
ParFlow. ParFlow is a parallel, integrated, hydrologic model that simulates
surface and subsurface flows. ParFlow solves the Richards equation for
three-dimensional variably saturated groundwater flow and the
two-dimensional kinematic wave approximation of the shallow water equations
for overland flow. The model employs a conservative centered finite-difference scheme and a conservative finite-volume method for subsurface
flow and transport, respectively. ParFlow uses multigrid-preconditioned
Krylov and Newton–Krylov methods to solve the linear and nonlinear systems
within each time step of the flow simulations. The code has demonstrated
very efficient parallel solution capabilities. ParFlow has been coupled to
geochemical reaction, land surface (e.g., the Common Land Model), and atmospheric
models to study the interactions among the subsurface, land surface, and
atmosphere systems across different spatial scales. This overview focuses on
the current capabilities of the code, the core simulation engine, and the
primary couplings of the subsurface model to other codes, taking a
high-level perspective.
•Flow patterns for zeotropic hydrocarbon mixtures were observed.•A new flow pattern transition line between annular and non-annular flow pattern was proposed.•An improved heat transfer correlation ...was proposed.
An experimental and simulation investigation of condensation flow pattern and heat transfer characteristics of zeotropic hydrocarbon mixtures methane/propane and ethane/propane in a helical tube was presented. Flow visualization was conducted to capture flow pattern during flow condensation. The flow mechanisms were categorized into six different flow patterns: slug flow, stratified flow, transition flow, wavy flow, half-annular flow and annular flow. In addition, several existing two-phase flow pattern maps in horizontal tube were compared with the flow pattern data. Then a new flow pattern transition line between annular and non-annular flow pattern was proposed. Based on the flow pattern transition line, the heat transfer data under different flow pattern were compared with the existing heat transfer corrections. Finally, an improved heat transfer correlation was proposed and well coincided with the data with a mean absolute relative deviation (MARD) of 13.8%.
•KEEP consists of global KE conservation, local KE preservation, and IEC.•Consistency conditions and a set of numerical fluxes are proposed to achieve KEEP.•Coarse-grid simulations of compressible ...two-phase flows at infinite Re are presented.•Density ratio effect on droplet-laden compressible isotropic turbulence is analyzed.•The proposed KEEP scheme is also applicable for multicomponent systems.
Accurate numerical modeling of compressible flows, particularly in the turbulent regime, requires a method that is non-dissipative and stable at high Reynolds (Re) numbers. For a compressible flow, it is known that discrete conservation of kinetic energy is not a sufficient condition for numerical stability, unlike in incompressible flows.
In this study, we adopt the recently developed conservative diffuse-interface method (Jain et al., 2020 30) for the simulation of compressible two-phase flows. This method discretely conserves the mass of each phase, momentum, and total energy of the system and consistently reduces to the single-phase Navier-Stokes system when the properties of the two phases are identical. We here propose discrete consistency conditions between the numerical fluxes, such that any set of numerical fluxes that satisfy these conditions would not spuriously contribute to the kinetic energy and entropy of the system. We also present a set of numerical fluxes—which satisfies these consistency conditions—that results in an exact conservation of kinetic energy and approximate conservation of entropy in the absence of pressure work, viscosity, thermal diffusion effects, and time-discretization errors. Since the model consistently reduces to the single-phase Navier-Stokes system when the properties of the two phases are identical, the proposed consistency conditions and numerical fluxes are also applicable for a broader class of single-phase flows.
To this end, we present coarse-grid numerical simulations of compressible single-phase and two-phase turbulent flows at infinite Re, to illustrate the stability of the proposed method in canonical test cases, such as an isotropic turbulence and Taylor-Green vortex flows. A higher-resolution simulation of a droplet-laden compressible decaying isotropic turbulence is also presented, and the effect of the presence of droplets on the flow is analyzed.
Dynamic analyses have been applied to the temporal signals from an Electro Capacitance Volume Tomography instrument located near mid-height on the riser of an industrial-scale cold-flow circulating ...fluidized bed to characterize gas-solids flow behavior in the riser. Twelve capacitance electrodes surround the cylindrical riser over a height of 1.3 m. The instrument used a neural network deconvolution algorithm to determine the spatially resolved solids fraction recorded at 52 Hz. Experiments were carried out over a range of gas and solids flows in the transport regime using a Geldart Group B bed material, high density polyethylene with mean particle size of 880 μm. The radial solids distribution was found to vary from one-time step to the next between profiles typical of laminar and turbulent flow. The duration of time spent in each of these flow profiles depended upon the operating regime – dilute, core-annular, or fast fluidized bed. The chaotic structure of the temporal data was characterized using the three conventional approaches: the first 4 moments from the distribution of signal in time, system memory parameters from the autocorrelation function and the Hurst exponent, and analysis of the correlation entropy and correlation dimension of the attractor. These signal analysis techniques were used to clearly distinguish differences between different transport operating regimes. Specifically, it was experimentally observed that a riser transitions from core annular flow profile to dilute and dense regimes via increasing the frequency of short term transients to either dilute or dense flow profiles, respectively. A regime map was generated based upon these dynamics using solids flux and gas velocity axes. Fast fluidized, core annular, and dilute each exhibited different degree of dynamic characteristics typical of fluid dominated or particle compromising behavior. It should be noted that the magnitude for the different statistics? was in the same range regardless of the regime, it was the radial profile for the statistic that changed and subsequently identified that there was a change in the regime. Finally, a reduced regime map was developed consisting of plotting the gas velocity normalized by the upper transport velocity versus the solids flux normalized by the saturation carrying capacity. The use of this reduced plot allowed the data from widely different conditions to be plotted and compared on the same graph. Note that in many instances, some of the statistics identified the operating point as being in one regime while others indicated that it was in another indicating a transition region between dilute or core annular regimes and between the core annular and fast fluidization regimes. This now provides a tool that can be used to optimize process performance, identify changes in operating states, or replicate process dynamics during process scaling or changing operating parameters.
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•Dynamic analyses have been applied to the temporal signals from an ECVT device.•The radial solids distribution varied between profiles of laminar and turbulent flow.•The duration of time spent in each of these flow profiles depended upon the operating regime.•A regime map was generated based upon these dynamics.•Fast fluidized, core annular, and dilute each exhibited different characteristics.
•Linear stability analysis of stably stratified annular Poiseuille flow is carried out for a wide range of curvature parameter and the Prandtl number.•Instability of the pipe flow with a thin rod ...placed at the center even for a very small value of heat source intensity has been found.•Three types of instability have been observed through kinetic energy analysis.•For a large value of curvature parameter, the least stable azimuthal number may vary as large as 40.
The stability of non-isothermal Poiseuille flow in a coaxial annular domain is studied using normal mode analysis. The stably stratified flow (i.e., when buoyant force is in the direction of forced flow) is induced due to external pressure gradient and maintenance of linear variation of the temperature of the inner cylinder. We have emphasized the impact of the gap between cylinders in terms of curvature parameter (C) and Prandtl number (Pr) on the instability of the flow under axisymmetric as well as non-axisymmetric disturbances. In general, it has been found that the flow of low Pr fluids under axisymmetric disturbance is more stable in comparison with the flow under non-axisymmetric disturbance. When the gap between cylinders is relatively small (i.e. C is large), the flow under non-axisymmetric is most stable for the fluids having high Pr. It is known that the Newtonian pipe flow is linearly stable for all values of Reynolds number (Re). However, in the present study, we have seen the instability of the pipe flow with a thin rod placed at the center even for a very small value of heat source intensity (in terms of Rayleigh number) at Re=2000. Here the disturbance velocity is concentrated in the vicinity of the inner wall and instability is due to transfer of kinetic energy from the basic flow through Reynold’s stress. Depending on the value of controlling parameters, three types of instability: thermal-shear, interactive, thermal-buoyant have been observed. In general, for a fixed value of Pr, the type of instability is not affected by C and Re. The non-isothermal Poiseuille flow of low Pr (including mercury and gases) is governed by thermal-shear instability and the same of high Pr (including liquid and oil) is governed by thermal-buoyant instability.
•The gas-liquid two-phase flow was visualized within the pump impeller.•A classification was proposed for the two-phase gas-liquid flow patterns.•The flow patterns were correlated to pump ...performance.•The surging phenomenon was related to the Gas Pocket Flow pattern.•The gas locking phenomenon was related to the Segregated Flow pattern.
This paper aims, through experiments, at determining gas–liquid flow patterns inside a centrifugal pump impeller, as well as to correlate the topological distribution of the phases of pump performance. For this, an experimental facility was built that would allow flow visualization inside the impeller. The construction of the visualization prototype was based on the stage of an Electrical Submersible Pump (ESP) widely used in petroleum industry. High-speed imaging was used as a technique to visualize the flow. The images obtained allowed us to classify the gas-liquid flow into four patterns, which are: Bubble Flow, Agglomerated Bubble Flow, Gas Pocket Flow and Segregated Flow. It was observed that the intensity of pump performance degradation is directly influenced by the flow pattern within the impeller. The occurrence of the Gas Pocket Flow pattern is linked to the intensification of the deterioration of pump performance and the appearance of operating instabilities. When it comes to the Segregated Flow, data has shown that the severity of performance degradation may make the pump incapable of generating pressure. Maps correlating flow pattern and pump performance were set for different operating conditions. These maps showed that the higher the rotational speed, the greater the no-slip gas void fraction where the transition occurred between the phases inside the impeller.
•The volume of fluid method with a detached eddy simulation turbulence are used.•The flow distribution in the feeders depends on the leak mass flow rate.•The pressure loss in the header can be ...predicted well by using available correlations.
Extensive numerical simulations of isothermal air/water flow in an idealised model of the header/feeder system of a CANDU nuclear reactor were performed under conditions that are relevant to postulated loss-of-flow accidents (LOFA) and small-break loss-of-coolant accidents (SBLOCA). Following our recent work, in which the present CFD methodology was validated against in–house experimental results, we used the volume of fluid method to solve the system of multi-phase flow governing equations and the detached eddy simulation model to close this system in turbulent flow. We computed the steady-state liquid flow distribution to the different feeders for different combinations of inlet water and air mass flow rates and different mass extraction rates, namely, values of the ratio of the leak liquid mass flow rate and the inlet liquid mass flow rate, and found that, in general, this distribution tends to become more uniform as the inlet flow rate of either the liquid or the gas increases. A “free surface” separating air above from an air–water mixture below was observed in many cases, generally moving downward with decreasing inlet flow rates and increasing mass extraction ratio. The liquid distribution to non-leaking feeders was not affected significantly by a change in the location of the leak. Time histories of flow properties following a step change in boundary conditions showed that the change of flow rate through each feeder can be represented by a first-order model with a time constant of roughly 1 s. As part of the validation of the present CFD analysis, the computed local pressure loss coefficient for a leaking feeder was found to be in excellent agreement with previously published experimental results. The static pressure loss across the header, estimated from available semi-empirical two-phase flows models was, in most cases, found to be within 10% of the CFD solution.
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