摘要
为了探明坡度对中行管段倾斜布置的正虹吸管路水力特性的影响,设置11个不同坡度(0、±1/60、±1/30、±1/20、±1/15、±1/10)和2个安装高度(4、6 m)在不同水位差下量测了虹吸管内的气液两相流动现象、含气率、气泡的运动速度、过流能力及总水头损失等水力特性。通过试验得到了正坡和逆坡管路坡度变化对管路水气流动现象的影响规律,揭示了坡度改变对管内含气率和气泡运动速度、虹吸管路流量及管路水头损失的影响规律,并结合理论分析探讨了气体存在对流量和总水头损失的影响。结果表明,随着坡度逐渐增大,管内伪空化现象逐渐减弱,气体的体积逐渐减小,含气率逐渐减小,气泡运动速度逐渐加快,虹吸管路的输水流量逐渐增大,总水头损失也逐渐增大。通过量纲分析的方法,推导出适用于倾斜布置的不同坡度下正虹吸管路输水流量的计算公式;经验证,公式计算值与实测值相接近,逆坡管路中相对误差控制在±6%,正坡管路控制在±7%。以上探究结果为实际工程中管路布置形式提供了参考依据。
With the constant development and application of a large number of surface water resources, the Karez type underground reservoir has become the key of the water conservancy project in Xinjiang in recent years. The siphon pipeline with longer distance and larger vacuum is the most important part of the Karez type underground reservoir. This study explored the impact of gradient change on the hydraulic characteristics of siphon pipeline with inclined arrangement. A total of 11 gradients were designed at the installation height of 4 and 6 m. The waterhead changed from 5 to 135 cm. The experiment was carried out in organic glass pipes. The pipe length was 18.15 m. The observations and measurements included the gas-liquid two-phase flow phenomenon, void fracture, kinematic velocity of bubble, discharge capacity and total head loss inside the siphon. The experimental result shows that in the flat slope pipe, air bubbles were rich with diameter about 4-5 mm in the head of the pipe and the bubbles in diameter of 1 mm were on the wall of pipe. During the movement, the bubbles was clustered into big bubbles and moved in the different directions from the flow. In inverse slope pipe, many small bubbles were on the wall but the air movement direction was same with the flow direction. Different the flat slope, the airbag was concentrated near downstream when it moved downstream. Different from inverse slope pipe, the airbag moved upstream slowly in the opposite direction from the flow direction. With the gradual increasing of gradient, the fake cavitation phenomenon inside the pipe weakened little by little, the volume of bubble or airbag diminished and the quantity dropped off. With the gradual increasing of the gradient, the void fracture in the pipe diminished, the kinetic velocity of bubble accelerated, the water delivery flow in the siphon strengthened gradually, the total head loss also increased gradually, the maximum flow increasing percentage was 23.8% and the total head loss increased by 42.86%. When the gas rate was larger than 11%, flow type in pipe was transitional and air mass type and the effects of gradient on flow rate could not be ignored. When the gas rate was smaller than 30%, the siphon in the pipeline was unstable. The gas-liquid two-phase flow phenomenon induced by the gradient change under such the conditions above made the effect of gas rate on flow resistance different from the liquid phase flow. Thus, based on the experimental data at installation height of 4 m on inverse slope, a formula for flow rate estimation was derived under the condition of transitional and air mass flow with gas rate of 11%-30% on gradient of 1/60-1/10. The flow rate formula was validated by using data at the installation height of 6 m. The validation results showed the relative error of measured and calculated flow rate in the inverse slope pipe was within 6% and it in the positive slope pipe was within 7%. It suggests that the formula is reliable. The results above provide valuable information for the pipe arrangement in the practical engineering.
作者
张小莹
李琳
靳晟
谭义海
吴洋锋
Zhang Xiaoying Li Lin Jin Sheng Tan Yihai Wu Yangfeng(College of Hydraulic and Civil Engineering, Xinjiang Agricultural University, Urumqi 830052, China College of Computer and Information Engineering, Xinjiang Agricultural University, Urumqi 830052, China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2017年第14期122-129,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金资助项目(51369031)
关键词
虹吸管路
坡度
流量
水头损失
含气率
量纲分析
siphon pipeline
gradient
flow rate
head loss
gas rate
dimensional analysis
