| The all-adjusted mixed-flow pump is more widely used in engineering, which is due to its wide operating-mode adaptability and high efficiency. In the21st century, the core-pulling diagonal-flow pump has been applied to some large domestic pump stations. The greatest advantage of this kind of pump is that it has a fully out-core rotor with excellent hydraulic design facilitate installation and maintenance procedure. The investment is small because of the bell mouth suction and the wet-pit pump house. However, compared with large pump, which have elbow, bell or dustpan-inlet conduits, this kind of pump suction directly pump water from pump sump so that it can not make further adjustment in flow pattern, meanwhile; there is no stable structure support between the pump and hydraulic buildings. Therefore, the flow stability in pump is difficult to be guaranteed, especially that severe-vibration in operation, which induces safety risk in water supply. In this thesis, numerical simulation and field tests are used to overall analyze abnormal vibration of pumps.In hydraulic calculation, several commonly used k-ε models are used to simulate the inlet flow patterns. Through comparison of simulation data and model experimental data, it is found that Realizable model is more suitable for inlet flow patterns simulation. The effectiveness of rectifying device of the pumping station is validated by the simulation results of inlet flow patterns for different start-up mode of pumping station. The influence of start-up mode on inlet flow pattern and vibration of pump are discussed.Standard k-ε, RNG k-ε, Realizable k-ε and SST k-ω for the steady numerical simulation are used to simulate the internal flow of the diagonal-flow pump, then RNG k-ε model and large eddy simulation method for the unsteady numerical simulation are used. The simulation results are compared with the measured performance curve of the pump. The applicability of different turbulence models and methods of Numerical calculation is analyzed, the accuracy of the obtained results show that RNG k-ε model is more suitable for this issue, and its internal flow characteristics are analyzed based on that.The characteristics of pressure pulsation of the diagonal-flow pump are analyzed for different flow volume. The results show that the maximum pressure pulsation occurs at impeller outlet, and the value increases along radial direction. The results show that the structural design optimization of the impeller outlet and rim is an effective method to reduce pressure pulsation strength; the diagonal-flow pump operated on off-design condition leads to internal pressure pulsation intensifies, and the strength of pressure pulsation increases with the increase of deviation. Therefore the diagonal-flow pump should be avoided operating in low flow rate; the frequency of pressure pulsation is equal to the impeller passage frequency, so modal analysis of the main parts, like the impeller wheel, must be conducted to avoid resonance or low power harmonic resonance. The results of modal analysis show that the internal pressure pulsation would not induce the impeller resonance or low power harmonic resonance.The results of diagonal-flow pump vibration tests show that the vibration amplitude of pumps enhance with the increase of its blade angle, and decrease with the increase of the operation units, and the symmetrical layout of operation pumps can reduce the vibration amplitude. The impact force which is due to the start of pump makes the spindle deviate, and leads to the abnormal vibration of pumps. In order to reduce the vibration of pumps, the frequency of starting and stopping should be reduced as far as possible, and the soft start technology should be used to decrease the impact force. |
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