| Noise pollution,which is parallel with air pollution,water pollution,soil pollution and solid waste pollution,is one of the major environmental problems facing mankind.Controlling,reducing and even eliminating noise pollution has increasingly become an important issue in the construction of ecological civilization.Jet centrifugal pump(JCP)has several flow passage components,its internal flow is very complex,and strong noise is often accompanied in operation.With the increasingly stringent environmental protection standards and the continuous improvement of people’s quality of life,users have higher requirements on the acoustic performance of JCP.In this paper,the unsteady flow and its acoustic response characteristics in JCP were researched by theoretical analysis,experiment and numerical simulation.The purpose is to provide theoretical and technical reference for the high efficiency and low noise design,as well as for the controlling and optimization of hydrodynamic noise of other types of pumps.The main work and innovative achievements of the paper are as follows:(1)The hydraulic performance and hydrodynamic noise characteristics of the JCP were studied by experimental method,which is to master the variation rule of the hydraulic performance and hydrodynamic noise with flow rate,the time and frequency distribution characteristics of internal hydrodynamic noise,as well as verify the accuracy of the numerical research of the flow field and hydrodynamic noise.The results showed that the fluctuating period of sound pressure in time domain is the same as the rotating period of impeller;the peak value of sound pressure is mainly at the axis frequency and the blade frequency,and the noise level at the axis frequency is the most obvious;the hydrodynamic noise is mainly in the middle and low frequency band within 400 Hz.Except for the distinct discrete noise at characteristic frequencies,such as the axis frequency and blade frequency,it also presents broadband noise in other frequency bands that can not be ignored.(2)The unsteady flow mechanism and fluctuation characteristics in JCP under 4 typical working conditions were studied and analyzed by numerical method.The results showed that it is mainly related to two factors that the hydraulic performance and the flow fluctuation characteristics in the JCP.One is that the flow in the pump body is asymmetric in all directions and is very complex,which destroys the flow stability in time and balance in space in the guide vane,impeller and ejector,resulting low hydraulic efficiency of the pump,the other is that the rotor-stator interaction between the impeller and the guide vane is the most critical factor affecting the unsteady flow fluctuation rule in JCP.(3)Based on the theory and method of acoustic analogy,the radiation characteristics of hydrodynamic noise induced by flow passage components under three different working conditions are studied and analyzed.The results showed that the the rotor-stator interaction between impeller and guide vane,the resonance between fluid and pump body structure,both of that are important factors of affecting the hydrodynamic noise in internal and external fields of JCP.The structure and material properties of the flow passage components themselves have an important influence on the hydrodynamic noise.The impeller-induced noise is the greatest contributing factor to the internal hydrodynamic noise,and the guide vane-induced noise is the greatest contributing factor to the external hydrodynamic noise.(4)Response surface method(RSM)combined with CFD/CFA(Computational Fluid Dynamics/Computational Fluid Acoustic)technology were employed to analyze the influence of blade profile on the hydraulic performance and impeller rotating noise characteristics of the JCP.The results showed that blade wrap angle,blade outlet angle and blade inlet diameter are the most significant three factors of affecting the hydraulic and acoustic performance of the JCP.There is restriction between the optimal hydraulic performance and the optimal acoustic performance,smaller wrap angle,larger outlet angle and smaller blade inlet diameter are helpful to improve the hydraulic performance of the JCP,but when the acoustic performance is the optimal,the control parameters should not be too large or too small.The mapping of acoustic performance and hydraulic performance has the ability to approach Pareto solution in the samples space of blade profile.The Pareto frontier solution is distributed along a convex curve,in which is the optimal solution combination of blade selection.(5)It was studied by numerical simulation that the influence of rotor-stator interaction on the mechanism and characteristics of flow field and induced noise in impeller and guide vane.The results showed that good design of guide vane blade profile can improve the hydraulic and acoustic performance of impeller,and good design of impeller blade profile can improve the hydraulic and acoustic performance of guide vane.The influence of rotor-stator interaction on the fluctuation intensity of flow field in impellernd guide vane is more sensitive than that of its time-averaged value.The existence of guide vane blades destroy the stability and balance of flow field in impeller,but it can restrain the impeller-induced noise to a certain extent.The impeller-induced noise is most obviously affected by the blade inlet angle of guide vane and the clearance between rotor and stator,and the guide vane-induced noise is most obviously affected by the blade outlet angle of impeller and the clearance between rotor and stator;the evolution process of internal flow field in rotor and stator is mainly related to the blade numbers of impeller or guide vanes,other structural parameters only affect the strength of the vortex,but do not change the basic evolution law.(6)The multi-objective optimization design of rotor and stator matching was carried out by orthogonal experiment combined with CFD/CFA technology.It was determined by matrix analysis method that the optimizing scheme of comprehensive performance considering hydraulic performance index and acoustic performance index.The results showed that under the rated conditions,after optimization,the water head remains unchanged,hydraulic efficiency increases by 0.5%,and the overall noise in the rotor and stator cascades decreases significantly,the impeller-induced noise decreases by 7.1% and the guide vane-induced noise increases by 2.1%.Different matching schemes of rotor and stator cascades are more sensitive to the water head of the JCP than to its efficiency,and more sensitive to the guide vane-induced noise than to impeller-induced noise.The key of the design of a low noise JCP is to determine the clearance between stator and rotor as well as the blades number of stator and rotor.It is an effective method to achieve high efficiency and low noise design of the JCP by the matching design of rotor and stator cascades.(7)A Gappy proper orthogonal decomposition(POD)method combined with CFD/CFA technique was proposed to reconstruct and predict the unsteady flow field fluctuation intensity and flow-induced noise in impeller region.The results showed that based on the mapping relationship between the geometry and flow field fluctuation intensity of sample set,or between the geometry and impeller-induced hydrodynamic noise of sample set,the relative error of pressure fluctuation intensity field is less than 4.0%,velocity fluctuation intensity field is less than 3.0%,turbulent kinetic energy fluctuation intensity field is less than 4.5%,impellerinduced hydrodynamic noise is less than 10%.Taking the method as a surrogate model to predict the flow field fluctuation intensity and the radiation level of hydrodynamic noise in the optimization process of centrifugal pump impeller,it could not only reduce the calculation amount and time significantly,improve optimization speed and efficiency greatly,but also could provide reference for vibration characteristics of the models. |
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