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Saturated-unsaturated Flow and Air-water Two-phase Flow in a Vertical Column Drained at Its Bottom at Constant Head

Author: KuangXingXing
Tutor: JinXiaoMei
School: Chinese Geology University (Beijing)
Course: Hydrology and Water Resources
Keywords: Sand column Constant-Head drainage Saturated - unsaturated flow Water vapor two-phase flow Numerical Simulation
CLC: P641.2
Type: Master's thesis
Year: 2010
Downloads: 118
Quote: 0
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Abstract


Vertical sand column during drainage of whether the upper sand layer from experimental and theoretical study, to study air drainage process in porous media. Grit upper sand layer homogeneous sand column saturated - unsaturated water flow the drainage experiments as well as grit upper fine sand layer of water-gas two-phase flow drainage experiment. The lower part of the sand column is saturated and is in hydrostatic equilibrium state, are fixed at the bottom of the head conditions for drainage. The results showed that when the the grit upper sand layer exists, vacuum drainage in the vadose zone in the sand column. The vacuum in the drainage after the start increased rapidly, reaching a maximum and then slowly decreases to zero. In head differential, the initial conditions of 30 cm, the resulting maximum vacuum of 2.58 kPa. The vacuum created by a holding role in the formation of water so that the water can not be discharged smoothly, thus accumulated in the sand column displacement the drainage process most of the time are significantly lower than the no-fine sand layer accumulated displacement. Write a VBA program based on the mixed form of Richards equation and a conservation of mass finite difference scheme, the numerical simulation of saturated - unsaturated flow drainage experiment. Calculation results and experimental data are in good agreement. VBA program based on the theoretical analysis shows that there are a lot of water in the drainage early vadose zone sand column. As time increases, the saturation profile in the sand column gradually close to the stable saturation profiles, soil moisture characteristic curve corresponds to the grit. Total head in the sand columns at the drainage still higher than at the end of the fixed head boundary at the bottom of the head. Described in saturated porous media saturated non-saturated water-gas two-phase flow in the drainage process with interface location and the vacuum of ordinary differential equations group (ODE) equations need only hydraulic characteristics are derived. Comparison with experimental data, the ODE solutions and experimental data agree well and better than TOUGH2 simulation results. Analysis showed that, based on the theory of ODE solution with the interface position are significantly higher than the water table due to vacuum most of the time in the sand column drainage, saturated and unsaturated. Theoretical analysis also showed that the vacuum saturated and unsaturated sand columns in the vadose zone with the rate of decline of the interface is closely related. Based on TOUGH2 theoretical analysis show that the saturation profiles in the sand column drainage process, the sand layer saturation profiles are significantly different.

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CLC: > Astronomy,Earth Sciences > Geology > Hydrogeology and Engineering Geology > Hydrogeology (groundwater hydrology ) > Groundwater Dynamics
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