Similarity laws of pressure fluctuations for vertical dual-directional pumping system
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Abstract:
The vertical dual-directional pumping system is more and more widely used in plain region because it can meet the two operating conditions of pumping station drainage and irrigation. Due to the closed space at the other end of the inlet and outlet flow channel, “dead water area” will be formed at the other end of the vertical dual-directional pumping system. The water flow has backflow in both vertical and horizontal directions, which makes the flow pattern in the bidirectional flow channel more disordered. At the same time, there will be phenomena such as defluidization and backflow, which may lead to the structural vibration of the unit and the unstable operation of the pump station. The pressure fluctuation is one of main factors impacting on the operational stability of vertical dual-directional pumping system, and the pressure pulsation amplitude and frequency of the pump device are the key indicators to measure the stability of the system, so that the study on the similarity laws between model and protype systems of this pump system is necessary. The pressure fluctuations of model and protype pumping systems were predicted with 3D unsteady simulation under various operational conditions, taking an example of one vertical dual-directional pumping station. The corresponding fluctuations in the model test system and protype pumping station were measured with sensors installed in the same locations. Finally, the similarity laws were analyzed. The result showed that the numerical simulation predicted pressure fluctuations and the test results have pressure fluctuations peaks at 3, 6, and 9 times the rotation frequency. The variation law of the pressure fluctuations deviation between the protype and the model was basically consistent with the variation law of the head and efficiency characteristics. The numerical simulation predicted pressure fluctuations were similar to the test results. And the pressure fluctuations amplitude predicted by the numerical simulation were slightly larger than the test value. The pressure fluctuations amplitude and frequency calculation results of the prototype pump system were highly similar to the calculation results of the model pump system. There was little difference between the model numerical simulation and the model test in the prediction of the main frequency amplitude of the pressure fluctuations. The amplitude at the secondary main frequency was relatively small, and the relative deviation was large. Comparing the pressure fluctuations prediction and measured amplitude of the protype and model pump systems, the test value of the model test was the closest to the test amplitude of the prototype pump system. However, the test of the model pump system was affected by many interference factors, so the spectrum of the test pulsation signal was much richer than that of the prototype pump system. Under high flow conditions, the deviation between the protype and model pressure fluctuations values increases, and the deviation between head and efficiency also increases. The deviation between the protype and model measurement was about 3% while the deviation between the protype measurement and simulation was close to 16% under main frequency. These results indicated that there was a certain correlation between the pressure fluctuations value and the external characteristics of the pump system. The pressure fluctuations of the prototype pump system can be predicted by numerical simulation. The model pump system can be used to convert the calculation results, and the deviation was very small. Compared with protype measurement the simulation and model test were tending towards safety so that they can meet the requirement of engineering design and operation.
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