Hydraulic Characteristic Of The Free-surface-pressure Flow In The Outlet Pipeline With Steep Base Slope

In the delivery pipeline with varying level of upper reservoir, the transitional state between flow in open air and pressure flow often appears. Alternative free-pressure flow is complicated and unstable in water system. It often engenders breakage such as impulsion and cavitations to construction. It is a question having research value and economy content to avoid free surface-pressure flow in the high-speed pressure flood discharge-pipe design. This paper primarily studies the free surface-pressure flow hydraulic characteristics in high-speed delivery pipeline with steep base slope. Since the free-surface-pressure flow engendering has direct relation with inspiration swirl before water inlet, by studying the arrangement of water inlet and structures before water inlet, this paper educes the infection of water inlet arrangement to free-pressure flow. If the water inlet arrangement is rational and its pressure distribution is reasonable, the free-surface-pressure flow range will minish in case that great pressure gradient is small. The swirl-removing measure can block off and destroy the swirl effectively, so this also has restraining effect to free surface-pressure flow. The flow characteristic has its special attribute in the pipeline of steep base slope. In the condition of high-velocity flow, water with airflow in pipeline doesn't come into gliding in velocity. Because it has double characters including free flow and flowing flow, hydraulic characteristic is similar to the character of free flow at low fall head. Along with elevation of reservoir, the affection in fall head strengthens gradually. The discharge increases quickly. the discharge relates to level of reservoir with linearity. After having compared stress distribution in pipeline in every kind of condition, it is found that the range of the free-surface-pressure flow is greater when the pressure of the part of infall is lower. It proves farther that the shape of the infall has direct effect to the appearance of he free-surface-pressure flow. The narrow of the outfall is good to improve stress distribution. After analyzing the pressure fluctuating in every pivotal point, it is found that if the angle of the joint is greater, the pressure fluctuating is greater. While the velocity of flow in steep pipeline continually increases, the extent of fluctuation pressure is correspond to increase. However, it has less amplitude of fluctuation in pipeline with the level or gentle slope. Lastly, maximum and minimum pressure in the free-surface-pressure flow is computed through attempting to set up mathematics model. Because of interaction between air and water, the free-surface and pressure flow is complexly and the result of numerical simulation may have some error. So simulation should be perfected farther. As a whole, the mathematic model is reasonable.