Numerical Simulation Of Water Flow Research Articles

Impact of climate change on groundwater recharge in shallow young glacial aquifers in northern Poland

We investigated the influence of climate change in the period 1951–2020 on shallow aquifers in the Brda and Wda outwash plains (Pomeranian Region, Northern Poland). There was a significant temperature rise (0.3 °C/10 years), which accelerated after 1980 (0.66 °C/10 years). Precipitation became increasingly irregular – extremely rainy years occurred right after or before extremely dry years, and intensive rainfall events became more frequent after 2000. The groundwater level decreased over the last 20 years, even though the average annual precipitation was higher than in the previous 50 years. We carried out numerical simulations of water flow in representative soil profiles for the years 1970–2020 using the HYDRUS-1D model, developed and calibrated during our earlier work at an experimental site in the Brda outwash plain (Gumuła-Kawęcka et al., 2022). We used a relationship between the water head and flux at the bottom of the soil profiles (the third-type boundary condition) to reproduce groundwater table fluctuations caused by recharge variability in time. The calculated daily recharge showed a decreasing linear trend for the last 20 years (0.05–0.06 mm d−1/10 years), and dropping trends in water table level and soil water content in the entire profile of vadose zone. Field tracer experiments were performed to estimate impact of extremely rain events on water flux in vadose zone. The results suggest that tracer travel times are strongly determined by water content in the unsaturated zone which is determined by precipitation amount in span of weeks, rather than extremely high precipitation events.

A comprehensive experimental and numerical analysis of water flow and travel time in a highly heterogeneous vadose zone

The assessment of water travel time through the vadose zone is known to be critical for a proper estimation of the hydrologic response time of water bodies to evolutions in land use management and global changes. In this study, the hydraulic properties of fifteen samples displaying contrasted lithologies (soil, powdery limestone, calcareous sand, limestone rock) and extracted from three cored boreholes drilled throughout the vadose zone of a vulnerable limestone aquifer were first determined in the laboratory. Three 23 m-deep vadose zone profiles were then reconstituted with the HYDRUS-1D software for the numerical simulation of water flow and the estimation of the water travel time using unimodal and bimodal approaches. The measured hydraulic properties, meteorological and water table level data were used as input for a virtual bromide tracing experiment undertaken over a period of 55 years (1966–2020). The results showed that the experimental hydraulic properties of the samples were more accurately described with a dual porosity approach, since the latter allowed a precise representation of the bimodal characteristic of most of the samples. The water flow and travel time simulated using unimodal or bimodal models for describing the vadose zone hydraulic properties were largely different. The impact of the vadose zone lateral heterogeneities on the simulated water flow and the estimated travel time was relatively limited compared to the influence of the vadose zone vertical heterogeneities and meteorological conditions. The mean travel time of the first concentration, peak concentration and last concentration of bromide simulated with the bimodal model at the maximum water table level of the aquifer was 13.8, 20.9 and 31.5 years, respectively. Increase in travel time was clearly identified since the late 1970s, and could be a consequence of global warming. These results also pointed out the need for conducting extensive studies at larger scales to take into account possible fast transfers of water that might occur through open fractures and karst networks.

Uncertainty of rivulet flows on heterogeneous surfaces – A numerical study

This paper presents a three-dimensional numerical simulation of water flow on an inclined plate using the software package OpenFOAM. We specifically investigate the influence of a heterogeneous surface on the flow pattern and the degree of wetting. By analyzing 400 simulation results a recently developed method for applying random contact angle inhomogeneities to surfaces is investigated. The simulations were carried out using the empirical contact angle model, which enables stable rivulet development. Part of the analysis is conducted with the help of the statistical software Dakota, which provides information about the probability distribution of the amount of wetted area when varying the two important influencing factors: the amplitude of the contact angle disturbance or the size of contiguous hydrophobic or hydrophilic areas. The results show that a variation of the two input parameters as desired leads to the introduction of a random component and thus to a change in the flow behavior. However, the changes remain within a narrow range around the mean value and produce only a few outliers, which occur mainly at large contact angle disturbance amplitudes and thus indicate the determining influence of the amplitude. The method has proven useful for performing several runs of the same simulation configuration for collecting statistics. Furthermore the inclination of the plate and the contact angle using a constant contact angle model are varied. Here, a clear dominance of the influence of the inclination also manifests over a wide contact angle range.

Purification Efficiency for Treated Waste Water in Case of Joint Infiltration with Water Originating from Precipitation

The decentralized treatment of wastewater and its on-site infiltration is common practice, especially in rural areas. However, uncertainties exist on the degradation potential of treated wastewater constituents mixed with additional infiltration of large quantities of water originating from precipitation. The intermixture of these waters is causing a reduction of residence times of the treated wastewater as well as an increased water saturation within the unsaturated soil zone. This can lead to a negative influence on the purification efficiency. Laboratory-scale 1D column experiments, accompanied by numerical simulations of water flow using the software code HYDRUS 1D, have been performed to evaluate the risks for a reduction of the degradation efficiency. Water content measurements and analysis of relevant organic substances in samples taken at different depths were the basis for evaluating the influence of the joint infiltration on the purification efficiency. The results highlight that a joint infiltration of treated wastewater and additional water originating from precipitation is not affecting the degradation efficiency for treated wastewater constituents. Degradation rates under these conditions were similar to the infiltration of treated wastewater alone. Timeframes with high water saturation were limited to the duration of the precipitation event.

Three-dimensional numerical modelling of the flow around a circular bridge pier: a scaling analysis

Three-dimensional numerical simulations of water flow around a vertical circular pier using the 'large Eddy simulation' method are presented. All simulations were performed using the solver 'interFOAM' supplied with OpenFOAM. The objective of this paper is to provide a better understanding of the influence of the free-surface on the velocity and pressure fields. The influence of three parameters, the Froude number (Fr), the Reynolds number (Re) and the geometrical parameter G (ratio between the water depth and the pier diameter), on the behaviour of free-surface is investigated. Qualitative observations and quantitative results are reported. It is shown that downstream the pier, the flow depends on Fr and G. Indeed, a dimensionless number combination of Fr and G describes all the phenomena related with the free-surface deformation (the wavelength size, the free-surface deformation). On the contrary, for estimating the drag coefficient or for describing dynamic phenomena such as the separation of boundary layers in front of the pier a dimensionless number combination of Fr and Re must be used.

Spatial Heterogeneity Enables Higher Root Water Uptake in Dry Soil but Protracts Water Stress After Transpiration Decline: A Numerical Study

AbstractA common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root‐soil interface is neglected. Here the aim was to explore whether a detailed characterization of the microscale heterogeneity at the scale of a single root impacts the relation between flow rate and pressure gradient. Numerical simulations of water flow toward a root surface were carried out in a two‐dimensional domain with a randomized configuration of spatially variable unsaturated hydraulic conductivities and varying boundary conditions, that is, increasing and decreasing root water uptake rates. By employing Matheron's method, the soil hydraulic properties were varied, while the effective hydraulic conductivity (corresponding to the geometric mean) remained unchanged. Results show that domains with a uniform conductivity could not capture important features of water flow and pressure distribution in spatially variable domains. Specifically, increasing heterogeneity at the root‐soil interface allowed to sustain higher root water uptake rates but caused a slower recovery in xylem suction after transpiration ceased. The significance of this is that, under critical conditions, when pressure gradients and flow rates are high, microscale heterogeneity may become an important determinant and should not be neglected in adequate descriptions of water flow from soil to root in dry soil.

3-D Numerical simulation of water flow over a broad-crested weir with openings

ABSTRACT The creation of an opening in a broad-crested weir body increases the discharge coefficient and reduces the water elevation behind the weir. In this study, three-dimensional numerical modeling is applied to investigate the water behavior, free-surface profiles, and velocity distributions over a broad-crested weir with one opening, two vertically arranged openings, and two horizontally arranged openings. The present study is limited to the above-described weir-opening arrangements. To determinate the most accurate turbulence model, results from the numerical simulation were compared with experimental data. Based on this comparison, the RNG turbulence model was chosen. The behavior of two horizontally arranged openings and the no-opening model were similar and critical flow occurred in two other models (one opening and two vertically arranged openings), downstream of the weir. Also, the maximum velocity in the models without openings was higher than in the other cases.

Radial Nozzles for Non-Cavitating Flow of Water at High Pressure Drops

We analyze the conditions under which radial nozzles can be used to measure or regulate the flow of water at high pressure drops. Using the URANS model, numerical simulation of water flow in radial nozzles was carried out. We find a dependence that establishes a relationship between the minimum static pressure on the geometric contour of a radial nozzle and the pressure drop across the nozzle, which leads to an estimate of conditions for the onset of cavitation.

Simulation of water flow in fractured porous medium by using discretized virtual internal bond

The discretized virtual internal bond (DVIB) is adopted to simulate the water flow in fractured porous medium. The intact porous medium is permeable because it contains numerous micro cracks and pores. These micro discontinuities construct a fluid channel network. The representative volume of this fluid channel network is modeled as a lattice bond cell with finite number of bonds in statistical sense. Each bond serves as a fluid channel. In fractured porous medium, many bond cells are cut by macro fractures. The conductivity of the fracture facet in a bond cell is taken over by the bonds parallel to the flow direction. The equivalent permeability and volumetric storage coefficient of a micro bond are calibrated based on the ideal bond cell conception, which makes it unnecessary to consider the detailed geometry of a specific element. Such parameter calibration method is flexible and applicable to any type of element. The accuracy check results suggest this method has a satisfying accuracy in both the steady and transient flow simulation. To simulate the massive fractures in rockmass, the bond cells intersected by fracture are assigned aperture values, which are assumed random numbers following a certain distribution law. By this method, any number of fractures can be implicitly incorporated into the background mesh, avoiding the setup of fracture element and mesh modification. The fracture aperture heterogeneity is well represented by this means. The simulation examples suggest that the present method is a feasible, simple and efficient approach to the numerical simulation of water flow in fractured porous medium.

Modified Feddes type stress reduction function for modeling root water uptake: Accounting for limited aeration and low water potential

Modeling water flow in the soil–plant–atmosphere continuum with the Richards equation requires a model for the sink term describing water uptake by plant roots. Despite recent progress in developing process-based models of water uptake by plant roots and water flow in above-ground parts of vegetation, effective models of root water uptake are widely applied and necessary for large-scale applications. Modeling root water uptake consists of three steps, (i) specification of the spatial distribution of potential uptake, (ii) reduction of uptake due to various stress sources, and (iii) enhancement of uptake in part of the simulation domain to describe compensation. We discuss the conceptual shortcomings of the frequently used root water uptake model of Feddes and suggest a simple but effective improvement of the model. The improved model parametrizes water stress in wet soil by a reduction scheme which is formulated as function of air content whereas water stress due to low soil water potential is described by the original approach of Feddes. The improved model is physically more consistent than Feddes’ model because water uptake in wet soil is limited by aeration which is a function of water content. The suggested modification is particularly relevant for simulations in heterogeneous soils, because stress parameters are uniquely defined for the entire simulation domain, irrespective of soil texture. Numerical simulations of water flow and root water uptake in homogeneous and stochastic heterogeneous soils illustrate the effect of the new model on root water uptake and actual transpiration. For homogeneous fine-textured soils, predicted root water uptake never achieves its potential rate. In stochastic heterogeneous soil, predicted water uptake is more pronounced at the interfaces between fine and coarse regions which has potential implications for plant growth, nutrient uptake and depletion.

Cavitation passive control on immersed bodies

This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm associated with the multiphase and cavitation model. The modified k-e RNG turbulence model equipped with a modification of the turbulent viscosity was applied to overcome the turbulence closure problem. Numerical simulation of water flow over the hydrofoil equipped with the ACG shows that a low-pressure recirculation area is produced behind the ACG and artificially generates stationary cavitation bubbles. The location, shape, and size of this ACG are the crucial parameters in creating a proper control. Results show that the cavitation bubble is controlled well with a well-designed ACG.

Theoretical and experimental study for temperature distribution and flow profile in all water evacuated tube solar collector considering solar radiation boundary condition

This study investigated a three-dimensional transient numerical simulation of water flow inside evacuated tube solar collector connected to a storage tank. It validates the distribution of the temperature inside the evacuated tube with experimental data from other studies. Variation of the solar radiation intensity and angle of incidence were discussed. The Effect of radiation variation on temperature contours and flow circulation inside the tube was discussed as well. The simulation results showed an agreement with the experimental data by an average relative error ranging from 4.2 to 7.8% at the validated points of temperature measurements. The structure of the flow inside the tube is affected by the variation of solar radiation in intensity and incidence angle. This variation causes the streamlines inside the tube to form two different shapes. The first shape is linear profile beside the top surface of the tube upwards and inclined with the tube. The second shape is a helical one inside the tube declared at the end of the simulation time and was confirmed by a vision experiment. The helical shape is formed due to the synchronous motion of the sun rays on the outer surface of the tube and the motion of the flow upwards. This is clear when the buoyancy velocity increases around the solar noon time.

Numerical Simulation of Water Flow from the Coal Seam Floor in a Deep Longwall Mine in China

The study of groundwater flow from the coal seam floor is critical to safe mining operations in China. We developed a numerical simulation model to describe flood water pathways during mining, using the field conditions present at the no. 4196 west work face in the Panxi longwall coal mine, Shandong Province, China, Groundwater flow analysis revealed unusual values for the failure depth of the coal seam floor. The high ground stress and underground pressure, excavation length, width of working face, poor mechanical properties of aquitards, and expansion of fractures by groundwater infiltration all contribute to groundwater flow into the mine. The modeling results predict the time and longwall locations associated with the maximum likelihood of flood occurrence. Such results can be used by decision makers to improve mine design and safety.

Modeling of Thermal Stratification and the Effect on Water Quality in Four Reservoirs in Tunisia

Tunisia is a North African country which is under the Mediterranean climate. This climate is characterized by a clear difference of precipitation between rainy season in winter and dry season in summer. The flood water in winter is stored for irrigation in dry seasons and for urban water supply throughout the year. The historical data analysis shows that reservoirs in Tunisia are characterized by a long retention time (0.5-1) year. This fact participates in the degradation of the quality of surface water resources due to the sedimentation process; it also induces the thermal stratification in the reservoirs. Dynamic numerical simulations of water flow, thermal stratification and sedimentation process constitute the basis of sustainable reservoir management. Indeed, the thermal stratification may have a big influence in the reservoir conditions and the quality of the stored water. In this study, we will begin by simulating the thermal stratification in four reservoirs in the northern side of Tunisia by applying a one dimensional numerical simulation model. Then we will investigate on the behavior of the water quality parameters towards the change of the temperature of the stored water in all the reservoirs. Finally, we will present the effect of a selective withdrawal on one of the four reservoirs.

Numerical simulation of water flow in a large waste rock pile, Haizhou coal mine, China

Waste rock is the large volume of broken rock and low grade ore materials tend to create potential problems, such as acid mine drainage (AMD), leaching of heavy metals, and slope stability problems. These problems are related to the flow of water through the waste rock. In this study, long term numerical simulations of unsaturated flow in a large waste rock pile are conducted to investigate the effect of internal variability in water flow and saturation. The approach first consists of a basic geotechnical properties investigation to define the main features of the pile. This is followed by numerical simulations of the unsaturated flow through the pile based on the results from the field and laboratory characterization. The simulation results showed that pile is unable to fully saturate and drain during the simulated period. It was also found that high evaporation and the high bottom flux rate and also coarse grain nature of waste rock materials results holding few amounts of water in the system.

Numerical Simulation of Water Flow in Mine Waste Rock Pile

As a long-term source of contaminant solutes, the flow of water within a waste rock pile containing reactive sulfide minerals significantly contributes to the solutes transportation. In this paper, a waste rock pile with the internal structures and grain size distribution from a typical waste dump is introduced as the geometric configuration. A numerical model is then applied to simulate unsaturated flow within a waste rock pile constructed with two primary materials. The simulations results show that the water movement within heterogeneous pile mainly depended on the internal structures. The flow of water can be controlled by the fine material layers within the coarse materials. These fine material layers form a capillary barrier which preventing the water infiltrate towards the centre of the pile. They can retain more water than coarse materials and form a ponding effect and/or percolation points within the pile.

Numerical simulations of water flow and contaminants transport near mining wastes disposed in a fractured rock mass

A numerical tool, called Hydro-Geosphere, was used to simulate unsaturated water flow and contaminants migration around an open pit filled with mining wastes. Numerical simulations had been carried out to assess the influence of various factors on water flow and solute transport in and around the surface openings including recharge, properties of the waste material and presence of fractures in the surrounding rock mass. The effect of the regional hydraulic gradient was also investigated. The analyses were conducted by simulating various 2D cases using experimentally obtained material properties and controlled boundary conditions. The effects of the hydrogeological properties of the filling material (i.e., water retention curve and hydraulic conductivity function), fracture network characteristics and conductivity of the joints were assessed. The results illustrate that fractures control water flow and contaminants transport around the waste disposal area. A fracture network can desaturate the system and improve the regional gradient effect.

Numerical simulation of water flow in tile and mole drainage systems

Tile drainage systems are sometimes not sufficient to provide favorable unsaturated conditions in the rootzone. These drainage systems then need to be supplemented with an additional high conductivity material in the trenches above the tiles or by implementing mole drainage. The HYDRUS (2D/3D) model was used to evaluate the impact of such additional measures for heavy clay soil. Three types of drainage systems were simulated: (i) tile drains, (ii) tile drains with gravel trenches, and (iii) tile drains with gravel trenches and mole drains, using either two-dimensional (the former two systems) or three-dimensional (the latter one) transport domains. Three scenarios were considered to test the efficiency of each system: (i) time to drain an initially saturated system, (ii) high intensity rainfall, and (iii) a real case scenario. Different horizontal spacings between tile drains with or without gravel trenches were also compared with the system which included mole drainage. The results showed that the drainage system that included mole drains and gravel trenches was the most efficient. This system provided the largest drainage rate, was the first to reach steady-state in the time to drain scenario, and also efficiently reduced surface runoff. Adding mole drains to a system with tile drains and gravel trenches resulted in a large reduction of surface runoff (75%). Simulations showed that the spacing of tile drains with or without gravel trenches would have to be 40% or 55% smaller, respectively, in order to reproduce the same water table levels as those observed for the drainage system with mole drains. Therefore, introducing mole drains in drainage systems is an efficient practice for reducing waterlogging and runoff.

3D Dynamic Numerical Simulation of Water Flow in Stilling Basin with Flaring Gate Pier

3D numerical simulation is carried out for the water flow in stilling basin with X shaped flaring gate pier when the radial gate uses four different opening velocities. The space-time change law of hydraulic characteristics is obtained. The water level in the stilling basin is relatively higher while using lower opening velocities during the processes. The negative pressure exists on weir surface while the relative opening degree is less than 0.55; the maximal pressure on the slab of ogee section and stilling basin increases and moves to downstream with the gate opening. The results can provide important basis for shape optimization of practical engineering.

Numerical simulation of water flow in unsaturated soils: comparative study of different forms of Richards’s equation

Modelling one-dimensional flow process in unsaturated soils is usually based on the numerical solutions of the Richards’s equation. Richards’s equation may be expressed in water content form, pressure or mixed form. The objective of this paper is to test the accuracy of the results and the ability of the different forms of Richards’s equation to describe the water flow in unsaturated soils. Implicit finite difference scheme is used in the numerical solution of the water content form and the pressure form of Richards’s equation. The solution of the mixed form is obtained using the 1-D Hydrus software. The effect of texture and the initial moisture of the soil on the equation solutions are explored. The results show a significant difference under some conditions. The choice of the empirical model to describe the hydraulic properties like retention curve and hydraulic conductivity may play an important role on the performance of each form, and can lead to remarkably different simulation results. The accuracy of the results is established by comparing numerical results to the semi-analytical solution of Philip and confronting them to the measured results.