March 13, 2017
Computational Study of the Noise Radiation in a Centrifugal Pump with Varying Flow Rate
In this paper, a three-dimensional unsteady hydro/aero acoustic model with Large Eddy Simulation (LES) closure is developed to explore noise radiation patterns in a centrifugal pump at different flow rates. Specifically, the Ffowcs Williams-Hawkings model (FW-H) is employed to predict noise generation by the blades as well as the volute. The model is rigorously validated by comparing the numerical predictions with the measured/analytical results reported. The ensuing good agreement obtained reveals that the model can yield qualitative/quantitative results of engineering significance regarding the noise and the flow field. The simulated flow fields reveal that the interactions of the blades with the volute induces strong pressure fluctuations and further lead to noise radiation. Moreover, the sources of noise generated by the blade surfaces and the volute at different flow rates are the subject of interest in this study. It is interesting to find that the profiles of Total Sound Pressure Level (TSPL) regarding the directivity field for the impeller-generated noise demonstrate a typical dipole characteristic behavior, whereas strictly the volute-generated noise exhibits an apparently asymmetric behavior. Additionally, the design operation 1Q (Here, Q represents the design flow rate) generates the lowest TSPL vis-a-vis the off-design operations for all the flow rates studied. In general, as the flow rates decrease from 1Q to 0.25Q, TSPL initially increases significantly before 0.75Q and then levels off afterwards. A similar trend appears for cases having the larger flow rates (1Q~1.25Q). The TSPL deviates with the radiation directivity and the maximum is about 50%. It is also found that TSPL by the volute and the blades can reach ~87 dB and ~70 dB at most respectively.
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