Study On Numerical Simulation Method Of Flow-induced Noise In A Centrifugal Pump

Noise generation within centrifugal pumps is receiving increasing attention because of increasingly strict enviromental requirements. In centrifugal pumps, noise includes two parts, one is mechanical noise which is generated by mechanical vibration, and the other is flow-induced noise which is generated by flow field. Although there are many kinds of different methods to reduce vibration and noise level obviously, it is difficult to reduce noise further if researches only foucus on the noise propagation. Flow-induced noise generation related to flow field in centrifugal pumps is especially important. Hydrodynamic sources can be characterized by computational fluid dynamic methods, so numerical simulation is able to help studying principles of noise generation in centrifugal pumps and optimizing acoustic performance of centrifugal pumps. In a centrifugal pump, impeller is the component to provide enengy, whose rotation causes unsteady flow and pressure fluctuation in the flow field. Impeller optimization is able to improve flow-induced noise reduction at sources. This thesis adds a link of acoustic performance analysis in the traditional process of impeller optimization. The specific work is to build a numerical simulation method of flow-induced noise in a centrifugal pump based on commercial software FLUENT. With this method, causes of flow-induced noise is analyzed and the thinking of impeller optimization aimed to improve pumps acoustic performance is applied as well. The achievements of this thesis are:1 Three dimentional models of pumps with three different impellers are built. According to real situations of flow field in centrifugal pumps, viscous model, boundary conditions and pressure-velocity coupling method is determined. Numerical method using large eddy simulation is applied to solve the three dimentional unsteady flow of whole flow field in centrifugal pumps.2 According to the results at design point, causes of unsteady pressure fluctuation in pumps are analyzed. It is shown that interaction betweent impeller and volute tongue is the main cause of unsteady pressure fluctuation. Specifically, spatial fluid flow nonuniformity in the paths leads to temporal changes in pressure while blades sweeping the volute tongue.3 Thinking of impeller optimization is advanced, and it is shown that changing impeller type such as adding splitter blades is able to reduce unsteady pressure fluctuation effetively. Comparison of prototype impeller and optimized ones proves the thinking of impeller optimization is correct and feasible.4 Using the computational results of three dimentional unsteady flow of the whole flow field in centrifugal pumps and referring to acoustic analogy method, rapid method of comparison of impeller acoustic performance is built. 5 The three centrifugal pumps acoustic performances at off design point are computed and compared. The results show that pressure fluctuation is weaker in large flow condition. In addition, it is shown that impellers optimized at design point may not have good acoustic performances at off design point.