Experimental Investigation of Hysteretic Dynamic Capillarity Effect in Unsaturated Flow

Zhuang, Luwen; Hassanizadeh, S. Majid; Qin, Chao; Waal, Arjen de

doi:10.1002/2017wr020895

Cited by 35 publications

(39 citation statements)

References 44 publications

(79 reference statements)

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“…Dynamic effects in our simulations are small (less than 5.5 Pa s) for saturation values higher than 0.82 whereas for saturation values lower than 0.82, dynamic effects barely exist (i.e.,

τ

is close to zero). However, experimental studies typically obtain larger values of

τ

, for example, Zhuang et al () reported a value of

τ

in the range of 5 × 10 4 to 3 × 10 6 Pa s. But in experiments the sample size is larger than that of our simulations. The domain size in our model is 3.2 × 3.2 × 3.2 mm 3 whereas the sample size in experiments by Zhuang et al () was 30 × 30 × 20 mm 3 .…”

Section: Resultsmentioning

confidence: 50%

See 1 more Smart Citation

Dynamic Pore‐Scale Model of Drainage in Granular Porous Media: The Pore‐Unit Assembly Method

Sweijen

Hassanizadeh

Zhuang

2018

Water Resources Research

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Dynamics of drainage is analyzed for packings of spheres, using numerical experiments. For this purpose, a dynamic pore‐scale model was developed to simulate water flow during drainage. The pore space inside a packing of spheres was extracted using regular triangulation, resulting in an assembly of grain‐based tetrahedra. Then, pore units were constructed by identifying and merging tetrahedra that belong to the same pore, resulting in an assembly of pore units. Each pore unit was approximated by a volume‐equivalent regular shape (e.g., cube and octahedron), for which a local capillary pressure‐saturation relationship was obtained. To simulate unsaturated flow, a pore‐scale version of IMPES (implicit pressure solver and explicit saturation update) was employed in order to calculate pressure and saturation distributions as a function of time for the assembly of pore units. To test the dynamic model, it was used on a packing of spheres to reproduce the corresponding measured quasi‐static capillary pressure‐saturation curve for a sand packing. Calculations were done for a packing of spheres with the same grain size distribution and porosity as the sand. We obtained good agreement, which confirmed the ability of the dynamic code to accurately describe drainage under low flow rates. Simulations of dynamic drainage revealed that drainage occurred in the form of finger‐like infiltration of air into the pore space, caused by heterogeneities in the pore structure. During the finger‐like infiltration, the pressure difference between air and water was found to be significantly higher than the capillary pressure. Furthermore, we tested the effects of the averaging, boundary conditions, domain size, and viscosity on the dynamic flow behavior. Finally, the dynamic coefficient was determined and compared to experimental data.

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“…Dynamic effects in our simulations are small (less than 5.5 Pa s) for saturation values higher than 0.82 whereas for saturation values lower than 0.82, dynamic effects barely exist (i.e.,

τ

is close to zero). However, experimental studies typically obtain larger values of

τ

, for example, Zhuang et al () reported a value of

τ

Section: Resultsmentioning

confidence: 50%

“…To test our model, we simulated the fast drainage experiments reported by Zhuang et al (). In those experiments, fast drainage was studied for a filter sand having a particle diameter of 0.0–0.50 mm (with an average diameter of 0.20 mm) and porosity value of 0.39.…”

Section: Simulation Setupmentioning

confidence: 99%

Dynamic Pore‐Scale Model of Drainage in Granular Porous Media: The Pore‐Unit Assembly Method

Sweijen

Hassanizadeh

Zhuang

2018

Water Resources Research

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“…The results obtained with the ESD model deviated substantially from the data, while the results from the IFA model showed much better agreement. The fitted values of L im and L dr are different from those of Zhuang et al (2017b) but have the same order of magnitude. Because L is a material property, different values may reasonably be expected for different sands.…”

Section: Resultsmentioning

confidence: 70%

“…For example, it is not clear what the importance of various terms are and how the various material coefficients should be determined experimentally. Also, to our knowledge, only two studies exist where the interfacial area model has been used to simulate experiments (Zhuang et al, 2016, 2017b). These two studies were both related to horizontal redistribution, which has a flow regime and experimental design that is very different from downward water infiltration studies.…”

mentioning

confidence: 99%

Experimental and Numerical Studies of Saturation Overshoot during Infiltration into a Dry Soil

Zhuang

Hassanizadeh

Duijn

et al. 2019

Vadose Zone Journal

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Core Ideas Experiments measured saturation overshoot during infiltration of water into dry soil. Two models based on Richards' equation with a dynamic capillarity term simulated the data. The IFA model is an alternative approach to simulate saturation overshoot. The IFA model and dynamic capillarity equation were combined to simulate experiments. Downward infiltration of water into almost dry soil, when there is no ponding at the soil surface, often occurs in the form of fingers, with saturation overshoot at the finger tips. While this is well known, there is still uncertainty about the exact saturation pattern within fingers. We performed a series of one‐dimensional water infiltration experiments into a dry soil to study the non‐monotonicity of the saturation. We observed that saturation showed a non‐monotonic behavior as a function of time. The overshoot was somewhat plateau shaped at relatively low flow rates but was quite sharp at higher flow rates. Two mathematical models, referred to as the extended standard (ESD) model and the interfacial area (IFA) model, were used to simulate the experimental results. Both models were based on extended forms of the Richards equation by including a dynamic capillary term. In the ESD model, standard equations for hysteresis were used. In the IFA model, the specific interfacial area was introduced to simulate hysteresis. Parameter values for both models were obtained from preliminary experiments or using empirical formulas. Only one parameter, the dynamic capillarity coefficient τ, was optimized to model saturation overshoot. While the ESD model did not reproduce the form of saturation overshoot for any combination of parameter values, the IFA model could provide good agreement with the data. To our knowledge, this is the first time where a combination of the IFA model and the dynamic capillarity equation has been used to simulate a set of experiments.

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“…Nevertheless, during the past few decades, studies conducted under nonequilibrium conditions have indicated that the soil water retention curve may depend on the dynamics of water flow [14,15]. Water content measured under transient flow conditions has been shown to be significantly different from that measured under static and steady-state conditions [16][17][18][19][20][21]. Considering the soil water retention curve based on thermodynamics, Hassanizadeh and Gray [22], postulated the existence of a dynamic component in the unsaturated water flow.…”

Section: Introductionmentioning

confidence: 99%

Effects of the Grain Size on Dynamic Capillary Pressure and the Modified Green–Ampt Model for Infiltration

et al. 2018

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Darcy-scale capillary pressure is traditionally assumed to be constant. By contrast, a considerable gap exists between the measured and equilibrium capillary pressures when the same moisture saturation is considered with a high flow rate, and this gap is called the dynamic effect on the capillary pressure. In this study, downward infiltration experiments of sand columns are performed to measure cumulative infiltration and to calculate the wetting front depth and wetting front velocity in sands with different grain sizes. We estimate the equilibrium capillary pressure head or suction head at the wetting front using both the classical Green–Ampt (GAM) and modified Green–Ampt (MGAM) models. The results show that the performance of MGAM in simulating downward infiltration is superior to that of GAM. Moreover, because GAM neglects the dynamic effect, it systematically underestimates the equilibrium suction head in our experiments. We also find that the model parameters α^ and β of MGAM are affected by the grain size of sands and porosity, and the dynamic effect of the capillary pressure increases with decreasing grain size and increasing porosity.

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Experimental Investigation of Hysteretic Dynamic Capillarity Effect in Unsaturated Flow

Cited by 35 publications

References 44 publications

Dynamic Pore‐Scale Model of Drainage in Granular Porous Media: The Pore‐Unit Assembly Method

Dynamic Pore‐Scale Model of Drainage in Granular Porous Media: The Pore‐Unit Assembly Method

Experimental and Numerical Studies of Saturation Overshoot during Infiltration into a Dry Soil

Effects of the Grain Size on Dynamic Capillary Pressure and the Modified Green–Ampt Model for Infiltration

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