船舶螺旋桨射流对湘江河床底泥扰动影响分析

船舶航行时螺旋桨产生的射流会对河道水流产生扰动,这种扰动是否能引起河床底泥的再悬浮需要更深入的论证分析。通过对比分析螺旋桨射流发展规律的研究成果,以湘江典型河段为研究对象,结合实船测量结果和此段河流地质资料,探讨了螺旋桨射流对湘江长株潭段河床底泥扰动的影响,并对此段河床底泥起动和悬浮条件进行了理论分析。结果表明:在周围环境流速较低的条件下,螺旋桨射流初始速度、河床水深及泥沙粒径是决定泥沙是否运动的主要因素。湘江长株潭河段已基本库区化,大部分河道平均水深远大于航道的标准水深2.8 m,河床泥沙平均粒径大于0.87 mm,其中细颗粒泥沙很少,由于螺旋桨射流断面平均流速小于泥沙起动流速,悬浮指标计算值远大于4,因此可以判断船舶正常航行在该段河流时底泥难以起动和再悬浮。

AN ANALYSE ON THE EFFECT OF PROPELLER JET FLOW ON THE XIANGJIANG RIVERBED SEDIMENT DISTURBANCE

Jet flow generated by the tail propeller can cause disturbance to river flows, and a further analysis is required to investigate whether such disturbance will result in re-suspension of bed sediment. Then,a comparative analysis was conducted on the research findings on the development rule of propeller jet flow .Meanwhile, a typical section of Xiangjiang River was chosen as an instance, and results from observing and measuring the prototype of propeller jet flow in the Changsha-Zhuzhou-Xiangtan section of Xiangjiang River were combined, together with geological survey data about the bed in this section. Also, the conditions for bed sediment incipient motion and suspension in this river section were calculated and analyzed, so as to determine whether the propeller jet flow affects the bed bottom sediment. The calculated results suggest that when the ambient velocity is low, the initial velocity of propeller jet flow, the water depth of riverbed and the sediment grain size are the main factors that determine the existence of sediment movement. The Changsha-Zhuzhou-Xiangtan section of Xiangjiang River basically become a reservoir;the average water depth in most river channels is much larger than the standard depth (2.8 m);the average gain size of bed sediment in this section exceeds 0.87 mm, and there is little fine-grained sediment;calculation and analysis of the disturbance caused by propeller jet flow in dry season shows that the mean velocity on the jet flow cross-section is less than the sediment incipient velocity;the sediment suspension indicator is above 4 in most cases. The above suggests that the possibility of bed sediment incipient motion and sediment re-suspension occurrence is tiny small in this section. Therefore, it can be judged that the influence on bed bottom sediment is negligible during normal ship navigation in this reservoir area.