Experimental Research On Characteristics And Effect Factors Of Finger Flow

This paper was supported by Project about Colleges and Universities Key Laboratory Visited Scholar Plan in Shannxi province. The experiments were designed for two different water transmission processes including the water infiltration process with continuous water supply and the water redistribution process with insufficient or sufficient water supply. Three different soils (a coarser sand, a finer sand and a Xifeng soil of Gansu province) were used in the experiments. The effect factors included the structure and the texture of soil, the conditions of the water supply, the fluid characteristics and the initial/boundary conditions. With a purpose to disclose the basic laws of the finger flow, enrich the theory of finger flow research and provide practical guidance, the characteristics and the effects of different factors on the development of finger flow were studied during the research. Based on extensive review on finger flow research achievements from domestic and abroad, then through the systematic experiments indoors as well as the processing and analyzing of the experimental data, the major results are as follows:1. The wetting front instability exists in both processes of water transmission including the water infiltration process with continuous water supply and the water redistribution process with insufficient or sufficient water supply, and can grow into finger flow under certain conditions.2. Varying the intensity of water supply within certain extents can bring both positive and negative effects on the development of finger flow, and when the intensity of water supply is too high or too low, the wetting front always tends to be stable.3. During the two different water transmission processes studied in this paper, the effect of soil texture on the development of finger flow is similar, that is, finger flow always tends to occur in coarser-texture soil.4. During both the water infiltration and the water redistribution process, high initial water content always has disadvantageous effects on the development of finger flow. The underdeveloped finger flow is wider and slower the downward movement of the wetting front while the high initial water content accelerates it. So the speed of the wetting front is affected by both the form of underdeveloped finger flow and the magnitude of the initial moisture content, and its varying trend is undefined.5. The layered structure of soil may results from the difference of soil texture and humidity. In the texture-layered soil (a coarser-texture sublayer), the ringer flow is promoted in both the water transmission processes. The humidity-layered soil structure (a wetter-soil sublayer) has negative effect on the development of finger flow in the water redistribution process with sufficient water supply and positive effect on it in the water infiltration process with continuous water supply and in the water redistribution process with insufficient water supply; however, the positive effect is very limited and unconspicuous.6. To some extent, increasing the quantity of water supplied in prior process of infiltration can act as an obvious stimulus to the form and speed of the finger flow development in the water redistribution process with insufficient water supply. In the water redistribution process with sufficient water supply, the quantity of water increased in prior process of infiltration has little influence on the final form of finger flow developed, whereas quickens the speed of the finger flow development.7. With the same soil and other factors, considering the simplex solute (KN03) dissolved in distilled water, the finger flow develops faster with its form clearer if more solute (KN03) is added in the water redistribution process with sufficient water supply.8. Keeping other factors the same, compared with the experiment aforementioned in which the KN03 solution concentration is 7214mg/l (max.) in distilled water, the finger flow tends to occur more easily in the experiment in which tap water is used, which is of Low-density and consisted of various kinds of ions or compounds.Fund of Project: Project about Colleges and Universities Key Laboratory Visited Scholar Plan in Shannxi Province.