Research On The Flow Pattern Of Low-lift Diving Tubular Pumping System By 3D CFD

Diving tubular pump is a kind of low head large flow horizontal pump types. This type is postpositive bulb pump and the motor is in the same coaxial with pump, which is suitable for irrigation or storm drainage pumping station. Taizhou Madian pump station uses diving tubular pump system in its rebuilding project, because of its excellent hydraulic performance, compact structure, good noise resistance and low operating cost. The design flow of Madian is 60m3/s, and the single pump’s design flow is 12m3/s. The design lifting head of irrigation is 1.17m. The diversion lifting head is 2.5m. The impeller diameter is 2m. It is hard to find researches periodicals, which analysis its performance and pressure pulsation by three-dimensional numerical simulation. This paper focus on the flow characteristics of diving tubular pump in different analysis types of steady and transient.The paper simulates diving tubular pump system and analyzes the inner flow characteristics of different parts of this pump system. The results are as follows:(1) The asymmetry of the longitudinal structure of inlet conduit affects the flow regime in outlet. Especially in small flow condition, this structural asymmetry causes the bad velocity distribution in the outlet of inlet conduit. The axial velocity distribution uniformity is increasing while the flow rate is increasing in the inlet of inlet conduit, and there is a positive correlation between hydraulic loss of inlet conduit and flow rate’s quadratic. The axial velocity distribution uniformity of inlet conduit’s outlet is 90% in design condition.(2) The static pressure of blade’s pressure surface is larger than that of blade’s suction surface, and it is lower in inlet edge of suction surface than other area. The paper finds that cavitation is easy occurred in off-design condition. The flow separation is firstly occurs in the hub, then it develops to the rim.(3) In little flow rate condition, there is large vortex reign in guide vane, and it will have bad effect on hydraulic performance of pump system. The result of energy recovery is better in guide vane, while the range of Q/QD is 1.000 to 1.037. In design flow rate condition, the result of energy recovery is best in guide vane.(4) The bulb of pump system has a role of adjusting and restraining flow out from guide vane. The lowest hydraulic loss of outlet conduit is relative with pump system’s Operating conditions. The performance of outlet conduit is best in design condition.(5) The results of CFD about hydraulic performance of pump system shows the same trend with model test. The ranges of high efficiency area are almost identical, while are predicted by CFD and model test.The paper simulates diving tubular pump system in transient type and analyzes the pressure pulsation of different parts of pump system. The results are as follows:(1) The main frequency of pressure pulsation is low frequency in inlet conduit in design condition. Besides the main frequency is high frequency in inlet conduit in small and large flow rate condition. In large flow rate condition, the flow pattern is significantly affected by the rotation of impellers in inlet conduit.(2) The main frequency of pressure pulsation is the frequency of impeller in the inlet of pump. It means that flow pattern of pump’s inlet is easy affected by rotation of impeller. In design condition, the main frequency is the lower than that in other condition and the flow pattern is better.(3) The amplitude of pressure pulsation of pump’s outlet is smaller in the hub and rim in different condition, In design condition, the circulation is smaller in the hub in the outlet of pump for the reason that the rotation of impeller is hard to affect flow pattern in there. In large flow rate condition, the circulation recovery is little in guide vane, and there is bad flow pattern in pump.(4) The flow pattern is better near wall region in the outlet of guide vane than other area in small flow rate condition, In large flow rate condition, the main frequency is also affected by the rotation of pump. It means that the circulation recovery is bad in guide vane in large flow rate condition.(5) In off-design condition, the pressure pulsation is stronger in outlet conduit, and the result of bad circulation recovery of guide vane is affected the flow pattern in outlet conduit. In design condition, the main frequency is 35.57Hz, which is double rotation frequency. That is same with the main frequency in inlet conduit.