Computational Study On The Noise Radiation Of A Centrifugal Pump Based On 3-D Flow Field With Varying Working Condition

With the development of industrial technology, the centrifugal pump noise has become a new kind of environmental pollution sources and brought massive downsides, which could deteriorate the pump performance, make the pump deviate from the best efficient point, reduce the operation efficiency, increase the energy consumption, and influence the economy and stability of the pump. What’s more, the noise could exacerbate the working environment of the staff and the living quality of city residents around. Therefore, it is extremely urgent to study the mechanism of generated noise to improve the noise pollution.In this paper, a 3-D unsteady hydro/aero acoustic model based on one of IS series centrifugal pumps with a design rotational speed of 1450r/min with the LES closure has been established. Here, the Ffowcs Williams-Hawkings model (FW-H) is employed to predict the noise generation by the impeller as well as the volute through setting up outside monitoring points. The noise radiation in a centrifugal pump at different rotational speed and flow rate has been studied with the method of spectrum analysis. The calculation model is validated through comparing the design parameters, the numerical simulation and experimental results. The good agreement between them reveals that the model can yield good results on the noise and the flow field.Firstly, the changing rule of radiation noise in a centrifugal pump has been studied along with the rotate speed from 1000r/min to 6000r/min, which reveals the responding relationship between the radiation noise and the rotate speed, the simulation result shows that the total sound pressure level of the impeller radiation noise fluctuates between 65dB and 100dB with a nonlinear and monotonous increase, when the rotational speed rises from 1000r/min to 1450r/min, the amplitude of the impeller radiation noise rockets rapidly, about 13dB averagely, however, that of remaining speed range climbs steadily, with a increase of 3.3dB per 1000r/min, the radiation noise average growth slope in this interval is about 1/6 of that between 1000r/min to 1450r/min. On the other hand, the total sound pressure level of the volute radiation noise fluctuates between 72dB to 100dB, it is interesting to find a similar increasing trend as that of variable rotational speed, the sound pressure level increases slowly when the rotational speed is less than 2000r/min as well as more than 2500r/min, the sound pressure level increases about 4dB per 1000r/min, and it increases sharply when the rotational speed is between 2000r/min to 2500r/min, the sound pressure level rises about 14dB per 1000r/min, the increasing slope in this rotate speed interval is much higher than others apparently (about 3.5 times).Secondly, the changing rule of radiation noise of the centrifugal pump is also researched through numerical simulation under varying flow rate condition. The simulation results show that as the flow rate rises from 0.25Q to the rated flow, the radiation noise of the impeller appears monotonous and downward trend, and then reaches the minimum at the rated conditions. as the flow continues to increase, the radiation noise increases dramatically. The slope is about 3 times of that when the flow rate is between 0.25Q and the rated condition. The radiated noise of volute also shows a similar trend, but more uneven compared with the descent of the radiation noise of the impeller with a drop-steady-drop variation, in which the flow rate increases from 0.5Q to 0.75Q, the radiated noise keeps nearly the same. It is also interesting that when the flow rate rise from 0.75Q to 1.25Q, the radiated noise shows a mirror symmetry trend at the rated flow.It is interesting to find that the profiles of TSPL of directivity field for the impeller-generated noise demonstrate the dipole characteristic behavior, whereas the ones for the volute-generated noise exhibit an apparent asymmetric behaviour. Additionally, the design operation(lQ) generates the lowest TSPL than off-design operations for all the flow rates studied. In general, as the flow rates decrease from 1Q to 0.25Q, TSPL initially increase significantly before 0.75Q and then level off afterwards.Lastly, the difference and relationship between the impeller and volute radiation noise have been revealed. The difference is that the noise radiation directivity of the impeller and volute has been studied. The impeller-generated noise demonstrates the dipole characteristic behavior, whereas the ones for the volute-generated noise exhibit an apparent asymmetric behavior that the noise in the direction facing the tongue is higher than that of the direction against the tongue. On the other hand, when running with both varying flow rate and variable rotational speed, the two parts show a similar changing rule, indicating that the varying flow rate or variable rotational speed has a similar impact on both. Meanwhile, the direct and the root reasons inducing the impeller and volute radiation noise have been discussed, it is found that the direct cause is wall pressure fluctuation, and the root one is the heterogeneous distribution of the flow field of the impeller and the volute.The conclusion could provide guidance to avoid the high radiation noise effectively when running, and lay a foundation for the design of low-noise centrifugal pump and the noise-control technology of the centrifugal pumps existing.