Research On The Relationships Between Area Ratio And Hydraulic Performance And Excitation Characteristics In Centrifugal Pumps

The performances of vibration and noise have been focused broadly over the past few years.The reasons to vibration and noise are mechanical and hydraulic factors.It is known transparently for mechanical factors lead to vibration and noise in academic and engineering field,and some measures already have been applied to solve these problems.However,it is unclear that hydraulic factors result in vibration and noise yet,and some measures are not enough.Some works have been done about hydraulic induced vibration and noise,which the main direction was internal flow in pump.There are significantly relationships between internal flows and flow passages and channels.But the parameters of inner passages and channels are not independent.And the cross section area is a bridge that connects all kinds of geometry parameters.Investigating the relationship between cross section area progression?area ratio?and hydraulic performance,excitation characteristics instead that the single factor effect on the performance.This approach could develop a new thought and support a new method.In order to show the common sense,this paper covers usual range of specific speed for centrifugal pump,6 specific speeds were chose as research objectives.The critical cross-sectional area ratios were built and numerical method was carried out.Hydraulic performance,excitation characteristics with different area ratios for specific speeds were analyzed and the relationships between area ratios and performance were summarized.Finally,hydraulic performance and pressure pulsation were tested on closed test loop.The main works and some conclusions are below:1.The parameters of good hydraulic models were counted in a wide range of specific speeds.And the range of area ratios value was summarized.The range of low and medium specific speed is wide but high specific speed is narrow.The standards for hydraulic performance and excitation characteristics assessment was mentioned through analyzing influence that different area ratios on performance and excitation characteristics.2.Six medium and low specific speeds were degined by using area ratio from impeller inlet to volute throat and all the cases were steadily calculated by CFD at different flow rates and unsteadily simulated at nominal flow.The comparison between numerical value and experimental value were made and both match well,which validates numerical results are reliable.Some approaches and standards are mentioned to value hydraulic and excitation performance,such as ??,Cp,?Cp and RMS.3.The hydraulic and excited performance were analyzed from the inlet to the blade edge.Re is badly different with different specific speeds.Re has a little effect on impeller performance in some range but great effect on amplitude of pressure pulsation.The impeller hydraulic performances are almost not change but the amplitude at fBPF would decline and arise in the range of Re=5.49⁶.06×105.The area ratio S₁/S₀ change a little with different specific speed.The performances and amplitudes of different specific speeds and area ratios change a lot.And the principle about area ratio and performance and amplitude is not transparent.4.The values of the area flow passage discharge divide the inlet are almost same,the range is 1.1¹.5.The impeller hydraulic and excitation characteristics are sensitive to area ratios,but there is no laws between area ratio and hydraulic and excited performance.The spiral inlet area of volute divide the discharge area of impeller S₃/S2,when the discharge area is larger,the whole pump hydraulic and excited performances are effected on.Conversely,the S2 stay the same,the hydraulic performance would stay the same as well with S₃/S2 changing a lot while amplitude of pressure pulsation would decline as S₃/S2 increasing.5.The volute throat area,as a matter of fact,reflects discharge capacity,which would deadly influence the whole pump's hydraulic performance.The throat area domains within the equation S₄/S₃.The whole pump hydraulic efficiency,radial force and amplitude would decline with area ratio arise.The progression of volute crosssectional area has great effect on not only hydraulic performance but also radial force and pressure pulsation,convex and S type progression are benefit of hydraulic head and efficiency,while the impeller radial force of convex progression is huge than that of original pump.So S type should be chosen to consider hydraulic,radial force and pressure fluctuation.The discharge area of impeller divide throat area of volute Y has a little influence on head and hydraulic efficiency in range of Y=2.93³.32,while the amplitude of pressure pulsation would decrease as Y up to 3.6.The low specific speed model pumps were tested on the close platform to acquire the signs of pressure pulsation and hydraulic head.And the experimental data shows that the different Y have the similar pressure pulsation spectrum characteristics,the amplitude at the shaft rotational frequency remains constant for different flow rates and points.The experimental and numerical results are matched,which smaller Y applied properly could lower effectively lower pressure fluctuation level.