凌庄子水厂保水堰流量系数试验

Experiment on discharge coefficient of water conservation weir in Lingzhuangzi water plant

凌庄子水厂蓄水池进水口处有一保水堰,为非标准薄壁堰,不能使用已有堰流公式对其过流量进行准确计算。为了得出较为精确的过流流量,按照重力相似准则制作几何比尺为1∶5的模型进行试验研究。在已有自由出流公式的基础上,对自由出流流量系数进行修正并对淹没情况下流量变化过程进行研究。对该非标准堰自由出流流量系数的实测值与经验值进行分析比较,发现堰板槽降低了实际自由出流过流能力。淹没出流的流量系数主要与下游尾水位有关,试验中形成的淹没式堰流受实际堰型尺寸影响,下游尾水位和堰上水位近似相等,不完全适用已有淹没出流流量公式,通过试验给出了修正淹没系数随h/p的变化关系。结果表明利用堰前、堰后水位初步计算过流流量是可行的,可为该工程提供参考,也可为实际工程中非标准矩形堰的流量计算提供思路。

Lingzhuangzi waterworks in water processing adopts drug concentration of water body method to monitor and to determine the reasonable dosage.The method first dosing and monitoring of drug concentrations,after initial dosage judging by experience,which wastes manpower and cannot guarantee the result accurately.The determined dosage must first clear streamflow,reservoir a submerged inlet for the non-standard rectangle thin-wall weir,therefore,unable to use the existing flow formula calculation flow of traffic.At the entrance of the weir,there are both free outflow and submerged outflow.To obtain a more accurate flow rate,the physical model test method was adopted,and the model with a geometric scale of1∶5 was made according to the gravity similarity criterion for experimental research.The experiment is carried out to analyze the flow change process of the weir.The appropriate position of the weir before and after the weir at the inlet of the water plant reservoir is set up,and the corresponding physical model is made.The actual flow capacity of a rectangular thin-walled weir is reduced due to the influence of the weir plate groove.The empirical value of the flow coefficient was Cd1=0.0569 h/p+0.597,and the measured value was Cd2=0.828 h/p+0.5438,respectively.The free flow formula was calculated by Cd2 without considering the influence of surface tension.Submerged discharge conditions can be used to scale according to different valve opening and close the valve opening as a group,the outlet valve opening corresponding to the actual engineering of the middle and lower reaches of reservoir level can be carried out on the downstream water level"sectional processing",namely the designated several water level range,as a set of each water level range,according to the flood discharge formula in the calculation,flow coefficient,different groups of corresponding parameters aand b values.Through the model test,the flow variation law of free flow and submerged flow of the weir in Lingzhuangzi waterworks are studied,the test results show that it is feasible to preliminarily calculate the overflow by the water level in front of the weir and behind the weir,and the calculation ideas of the flow are given respectively.Compared with the standard rectangular thin-walled weir,the weir plate groove of the water conservation weir in the waterworks reduces the free flow capacity,and the measured flow coefficient is Cd2=0.828 h/p+0.5438.The free outflow can be calculated directly by formula using flow coefficient Cd2.When the outlet valve has a certain opening,the submerged water depth increases with the increase of the incoming flow;when the flow rate is constant,the submerged depth decreases with the increase of the opening of the outlet valve;and when the downstream valve opening is certain,the submergence coefficient Cfhas a mathematical relationship with h/p,and the submergence coefficient Cfof several similar valve openings applies to the same value of aand b.Outlet valve opening corresponding to the actual engineering of the middle and lower reaches of reservoir level,according to different groups,the downstream water level giving to the flood discharge formula,refer to historical traffic data,the relationship between the primary parameter values constantly in the process of practical application to modify parameters,the accurate calculation formula can be obtained,and then the automatic control of dosage can be realized.