Influence of specific speed on hydraulic performances and pressure fluctuations in mixed-flow pumps.pdf
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1、排灌机械工程学报Journal of Drainage and Irrigation Machinery Engineering2023年10 月第41卷第10 期Oct.2023Vol.41No.10Influence of specific speed on hydraulicperformances and pressure fluctuationsin mixed-flow pumpsFU Yanxial*,JIA Qil,SHEN Yang,PACE Giovanni?.3(1.School of Energy and Power Engineering,Jiangsu Univer
2、sity,Zhenjiang,Jiangsu 212013,China;2.Zhenjiang Fire and RescueDivision,Zhenjiang,Jiangsu 212000,China;3.Sitael S.P.A.,Pisa 56121,Italy)FU YanxiaAbstract:A series of steady and unsteady numerical calculations of the internal flow in mixed-flowpumps with three different specific speeds were carried o
3、ut based on the N-S equation coupled with thestandard k-turbulence model under different operating conditions to investigate the relationship be-tween the impeller specific speed and the pump performance as well as pressure pulsations.Meanwhile,the pump performance and pressure pulsations inside the
4、 mixed-flow pump with three dif-ferent specific speeds were also analyzed and compared with the corresponding test data.From the re-sults,the averaged deviations between the predicted and tested head among different impellers are be-low 5%,and with respect to the equivalent impeller specific speeds
5、of 280 and 260,the values are4.30%and 3.69%,respectively.For all the impeller schemes,the best efficiency point of the mixed-flow pump is found at the flow rate of 1.2Qa and the higher head deviation occurs at lower flow rates.Especially,it can be found that the specific speed has a slight effect on
6、 the pressure fluctuation in theimpellers.Eventually,it is determined that the pump performance curves calculated by numerical simu-lations have good agreement with the relevant experimental results,which verifies that the numericalmethods used in the present study are accurate to a certain extent.F
7、urthermore,the results alsoprovide some references to the pressure pulsation analysis and the performance improvement of themixed-flow pump design.Key words:mixed-flow pumps;impeller specific speed;hydraulic performance;pressure pulsation;numerical simulation;experimentCLC Number:S277.9 Document Cod
8、e:A Article No:1674-8530(2023)10-0981-07D01:10.3969/j.issn.1674-8530.23.0085FU Yanxia,JIA Qi,SHEN Yang,et al.Influence of specific speed on hydraulic performances and pressure fluctuations in mixed-flowpumps J.Journal of drainage and irrigation machinery engineering(JDIME),2023,41(10):981-987.A mixe
9、d-flow pump has an intermediate specificspeed with characteristics of both axial flow and centri-fugal pumpsl-a,he pump s ecific speed is typieallycalculated considering the maximum hydraulic efficien-cy at the design point and can be used to identify ordesign the optimal blade shape since the shape
10、 of theReceived date:2023-05-10;Accepted date:2023-08-04;Publishing time online:2023-10-13Online publishing:https:/ information:National Natural Science Foundation of China(51976078);Senior Personnel Scientific Research Foundation of Jiangsu Uni-versity:(15JDG073);Open Research Subject of Key Labora
11、tory of Fluid and Power Machinery,Ministry of Education(szj2016-065)First author information:FU Yanxia(1986),female,Ph.D,associate professor(corresponding author,yanxiafu ),researchingin flow instability in turbomachinery,numerical simulation.Second author information:JIA Qi(1997-),male,master stude
12、nt(470023519 ),researching in seal performance,numerical simulation.blade passage varies as the pump specific speed(n,)changs(-01Since the blade shape is closely related to the per-formance of the pump,the pump specific speed has astrong impact on the shape of the head-flow performan-ce curve,cavita
13、tion,unstable vibration,as well as un-982排灌机械工程学报第41卷desired noises.For example,MIYABE et al.7 foundthat a rotating stall occurred in a low-specific-speedmixed-flow pump at a 65%flow rate of the best effi-ciency point(BEP)t o g e t h e r w i t h p e r i o d i c a l l a r g e-scale abrupt backflow ge
14、nerated from the vaned diffuserto the impeller outlet in their experimental tests.KIMet al.8 designed a new mixed-flow pump using thetrend of the design variables versus the specific speedand found that the specific speed was closely related tothe shape and performance of the mixed-flow pump.They al
15、so indicated that the pump efficiency first in-creased and then decreased as the specific speed in-creased.ZOTOv9 found that the higher the specificspeed,the lower the load and the pressure drop,andthe better the cavitation performance.More efforts arerequired to understand the relationship between
16、the pumpspecific speed and the performance of mixed-flow pumps.So far,many researchers have observed that com-plex flow phenomena can be involved in the blade tipclearance flow in a mixed-flow pump,and havefocused on analyzing the influence of the tip clearancesizeonpressurefluctuation in a mixed-fl
17、owp1-2,ZHANG et al,10 found that the separationpumptbetween the main leakage vortex and the secondaryleakage vortex was strengthened with the increase inthe tip clearance size.JI et al.experimentally foundmore complicated frequency domain features occurringin the pump impeller due to the effect of t
18、he tip clea-rance flow.ZHANG et al.12 found that the clearancevariation had less effect on the pressure fluctuations inthe guide vane.Therefore,it is necessary to investigatethe dynamic characteristics at different specific speedsto reduce their power consumption and improve theirefficiency.In the p
19、resent research,the hydraulic performan-ce of a mixed-flow pump at different flow rates was pre-dicted using the ANSYS CFX sofware packagl 13 Thepressure fluctuation in the impeller outlet was furtherstudied based on frequency domain analysis.11Modeling and numerical methods1.1Geometrical dataThe mi
20、xed-flow pump in this study has been typi-cally applied inSouth-to-NorthPrjects in China 141.As illustrated in Fig.1,the computational modelof the mixed-flow pump included five-bladed impellerswith different specific speeds,the ring,a p u mpcasing,a guide vane,and the inlet and outlet pipeswith thei
21、r extended portions,respectively.Fig.1Three-dimensional view of model mixed-flowpumpThe main dimensions and characteristics of themixed-flow pump impellers with different specificspeeds are as demonstrated in Tab.1,where Qa is thedesign flow rate,H,is the design head,n is the rota-tional speed,Z,is
22、the blade number of the impeller,Z,is the blade number of the guide vane,D,is the im-peller inlet diameter,and D,is the impeller outletdiameter.The impellers in accordance with the threedifferent equivalent specific speeds of 280,270 and260,are labeled as Impeller A,Impeller B andImpeller C,respecti
23、vely.Tab.1IDesign and geometrical parameters of Im-peller A,B,CImpellerQd/(m3.h-I)A(n,=280)1 350B(n,=270)1 400C(n,=260)1 260The big difference for these impellers lies in thedesign parameters such as the different design flowrates and design head.1.2 Mesh generation and grid independence checkStruct
24、ured hexahedron cells were applied as thenumerical mesh using ANSYS ICEM CFD commercialsoftware.In particular,five computational grids of thewhole computational domain,as demonstrated in Tab.2,were chosen to analyze the impact of mesh size on theprediction of the hydraulic performance of the mixed-f
25、low pump operating with Impeller A(n,=280)at theWaterDiversionParameterHa/mn/(r:min-1)261.450281450281.450Z122D/mD2/m570.28570.28570.280.370.370.37第FUYanxia,tlInfueneofimpelersecifcseedonhydraulic pefomanesand pesurefuctuationsimixd-fow pumps983design point in detail based on the steady numericalcal
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