| Pumps are acting more and more important roles in both daily life, economic production, fire extinguishing and rescue. As a pump never works without the pipeline system, the study of pump cannot focus on the pump only. Hydraulic transient processes sometimes bring with it violent or dramatic unsteady phenomenon, which will interfere the normal operation or even damage the system. The situation will be more complex if cavitation is also considered. However, the hydraulic systems usually combine with kilometers long pipelines and hydraulic machines, and they influence each other’s behavior under transient processes.Conventional transient process calculation methods (Method of Characteristics, which will be called MOC hereafter), developed with the analysis of water hammer, treat the whole system as a combination of 1D components. Results can be obtained quickly with this method, however the inner flow details are missed.3D numerical simulations (Computational Fluid Dynamics, which will be called CFD hereafter) are widely used in the flow analysis in hydraulic machines. However, it is still difficult when the object is the whole flow system because of the huge computational cost. Coupling of ID (for the pipeline part) and 3D (for the hydraulic machines part) simulation thereby came to people’s eyes. The reality of guided by the same fluid flow equations makes this theory practical, this method is accomplished in this research and was used in a centrifugal pump starting up analysis. The main content of this thesis includes the following aspects:First, a pump testing system was selected as a lot of work had been done on this system for studying the starting up process and large numbers of results were given. In order to make the simulation match the tests, the 1D system and 3D models were build based on known data. The 3D model were simulated and the 1D system was calculated to compare the running characteristics of both the pump and the system with the original test data. And the results match well. Cavitating characteristics of the centrifugal pump was also simulated and compared.Second, the coupling simulation was established between MOC and CFD. The influence of weighting factor, iteration numbers in each time step was analyzed and the best solution was selected for the following simulation.Third, the startup process of the pump was simulated with the coupling simulation method. The pressure and mass flowrate of the pump outlet and inlet obtained from the coupling simulation agreed well with the tests. And the flow information inside the pump were analyzed. And a slower starting up process was co-simulated to compare the influence of the starting up speed to the stability of the system.Forth, with cavitation model ZGB considered in Fluent simulation, the centrifugal pump starting up under lower pressure were analyzed, the pump run in the cavitation region, and cavities appeared form 0.4s, and they gain in volume quickly and led to a significant pump head decrease. The pressure pulsation of monitoring points in the case and in the system were analyzed. And the reason for the two pressure drops were analyzed based on the simulation results.Fifth, compared the startup process coupling simulation with cavitation model results with cavitation simulation from Flowmaster only and unsteady cavitation simulation from Fluent only, the advantage of the coupling simulation was pointed out. The pulsation of the fluid domain and development of the bubbles under transient processes were compared with steady conditions, they do behave differently under two different conditions.In this theis, MOC-CFD coupling method were proposed to simulate the starting up process of a pump testing system, and the results agreed well with the test data. When cavitation model was added in to the cosimulation, the pump starting up process under cavitation process was simulated and analyzed. This research have a positive and guiding significance for the pump and system transient process and cavitation condition study. |
PDF Full Text Request