International Industrial Informatics and Computer Engineering Conference (IIICEC 2015)

Transcription

1 Inernaional Indusrial Informaics and Compuer Engineering Conference (IIICEC 015) Effec of impeller blades on waer resisance coefficien and efficiency of mied-flow pump Du Yuanyinga, Shang Changchunb, Zhang Kepengc, Hao Yuyud and Wang Penge Engineering raining Cener, Xi an Universiy of Science and Technology, Xi an, , Shaani, China. a 56959@qq.com, b @qq.com, c @qq.com. Keywords: mied-flow pump; waer resisance coefficien; number of impeller blades; efficiency; numerical simulaion. Absrac.In order o invesigae effecs of impeller blades on performance in mied -flow pump, using unsrucured erahedral mesh and SIMPLE algorihm, he simulaion of hree-dimensional flow inside a mied-flow pump were done in Fluen. Adoping he ime-averaged coninuiy equaion, N-S equaion and RNG -ε urbulence model in a relaive coordinae sysem. The saic pressure and absolue velociy disribuions of impeller blades and saor blades were simulaed. Under differen blades, he flow resisance coefficien across pump was esimaed in saic, performance parameer was esimaed in dynamic condiion. I s found ha waer resisance coefficien and head were gradually increased, and efficiency firsly increased and hen decreased wih unobvious rend while res geomerical unchanged. The resuls showed ha: under special environmen, design condiion, number of impeller blades should as small as possible o mee efficiency requiremen under a paricular applicaion. In addiion, he opimum performance was achieved a 4 blades and 3 guide vanes. Inroducion Mied flow pump is a basic ype of vane pump, he scope of he specific speed is from 300 o 600, which is easy o sar and have high efficiency, i have broad prospec in cooling waer circulaion sysem of nuclear power plan, propulsion sysem, waer cycle of power plan and waer desalinaion devices. Currenly, Li Yibin ec have sudied performance of inernal flow field in mied-flow pump [1], he resuls have guiding significance for design efficien and running sable pump. Some researchers have sudied effec of parameers of mied-flow pump [-3], Yang Congin ec have sudied he disance beween impeller and guide vane in mied-flow pump[4]. Bu maerials abou effecs of impeller blades on waer resisance coefficien and efficiency in mied-flow pump were less. In his paper, under design condiions, specific speed is 504, hrough simulaion of he hree-dimensional flow inside mied-flow pump by Fluen, rying o find some rules of waer resisance coefficien and performance of mied flow pump. The basic heory 1.1 Calculaion model Assumed fluid is incompressible, saionary, ecluding influence of graviy, Chose Reynolds-average equaions as conrol equaions [5]. I s form as follow: 015. The auhors - Published by Alanis Press 94

2 ρu + ρvy + ρω = 0 ( ρuu) + ( ρvu) y + ( ρω u) eu) ( µ euy) y ( µ eu) = Su p Fc ( ρuv) + ( ρv) y + ( ρω v) ev) ( µ evy) y ( µ ev) = Sv py Fc y ( ρuω) + ( ρvω) y + ( ρωω ) eω) ( µω e y) y ( µω e ) = Sω p In he equaion: p = ω, p y = ω y, y p = ; Fc = vω, F c y = uω. (1) RNG ε model considering precision of large curvaure, i s more suiable for calculaion of flow field in he hydraulic machinery [5]. S i, j v ν i = ν + + r i i σ i In he equaion: p ε viε ν ε Cε1ε pr Cεε = ν + + i i σ ε i () v v i j vi pr = ν +, ν = C µ, η = S, C = ; µ i i j ε ε S = S i, j S i, j, 1 v v i j = ( + ); β = ; C =1. 68; ε C = ; σ = j i 1. Boundary condiions (1)Inle and oule condiions: used incompressible waer as medium, inle was velociy-inle, urbulen flow was full-blown, oule was ouflow [5]. ()Solid wall condiions: impeller was roaing wall and no-slip mesh, inle pipe, guide blade and oule pipe all used saic wall and no slip mesh. 1.3 Performance predicion model Head and efficiency of pump s predicion formula are as follow. In he equaion: Z sands for verical disance beween oule and inle of pump, P ou, P in sand for average pressure of pump a inle and oule, H d for design condiion head. Pou Pin H = + (3) ρg ρg φ = H (4) H d ρgqh η = (5) P 1.4 The formula of saic waer resisance coefficien Waer resisance coefficien is posiive, when pump is saic and fluid flow from guide vane and diffuser. Resisance coefficien is defined as follows: =gδh/v (6) In he equaion: Δh sands for hydraulic loss of pump a inle and oule, v sand for cross-secion velociy of reference. The descripion of model and numerical mehod.1 ey parameer The flow rae of mied flow pump Q=1400 m 3 /s, roaional speed n = 900r/min, impeller diameer D=40 mm, oule widh of impeller b = 76 mm, blade number of impeller Zg= 4, guide vane number Z = 3, lengh-widh raio of guide vaneλ= Solid Meshing Mehods Overflow of pump included inle pipe, impeller, guide vane and diffusion ube. The grid meshed by Gambi. In order o improve calculaion accuracy, compuaional domain used grid refinemen mehod, ensuring calculaion resul did no depend on grid number, he minimum number of grid was deermined abou The calculaion model is shown in figure 1. 95

3 Fig.1 Calculaion model of mied-flow pump.3 Numerical compuaion mehod Finie volume mehod was used o discree conrol equaions, in order o srenghen convergence of calculaion, discreion and convecive erm adoped firs order upwind. The couple of pressure and velociy used SIMPLEC algorihm. Resuls and analysis 3.1 The resuls and analysis of numerical calculaion The saic pressure disribuion of mied flow pump blades and guide vane were simulaed by FLUENT, i is shown in figure. Fig. Saic pressure disribuion under design condiion.(uni: Pa) I can be seen from Fig. ha: liquid obain energy from roaion impeller, saic pressure disribuion of sucion surface a impeller blade increased gradually and reached maimum a he ip of blade, here was obvious one of negaive pressure a inle of sucion surface, his posiion is easy o appear caviaion, Guide vane made flow smooh, which ranslaed ineic energy ino pressure energy, pressure reached maimum in he middle of guide vane,bu i reduced a oule of guide vane, overall flow condiion was smooh and in accordance wih he acual siuaion. Absolue velociy disribuion under design condiion is shown in figure 3. I can be seen from Fig. 3 ha: from inle o oule of blade, he absolue velociy disribuion increased gradually wih blade heigh direcion, overall flow was smooh, and did no eis laeral flow and flow separaion. Sreamline of liquid which was flow from oule of impeller was smooh, The velociy was gradually decrease, in which ineic energy was ranslaed ino pressure energy, flow rend from inle o oule of guide vane was smooh. Fig.3 Absolue velociy disribuion under design condiion (uni: m/s) 3. The predicion and analysis of performance Impeller is vial par of pump, The blade numbers have significan influence on head, efficiency and resisance. In generally, he impac was non-linear, bu from he poin of opimal performance, mied flow-pump mus have opimal blade number The influence of impeller blades number on waer resisance coefficien. When impeller saic, under design condiions, guide vane number was 3, oule angle of guide blade was 90, wihin limied space, oher parameers were consan, he number of blades (Zg) 96

4 were 4,6,8, mied flow pump was simulaed, he formula (6) was used and waer resisance coefficien was calculaed as shown in able 1. Table 1 waer resisance coefficien under differen impeller blade number Number of impeller blades Waer resisance coefficien I can be seen from able 1: Resisance coefficien was lowes a 4 impeller blades and 3 guide blades, waer resisance coefficien was gradually increased wih number from 4 o 8 of impeller blades. There are mainly wo reasons: (1) wih increase of impeller blade numbers, epulsion of blades were gradually increased, angen surface area was increased, so fricion of blade surface was increased, he moivae paricle has o overcome increased resisance, so energy loss and waer resisance coefficien were increased. () he disance beween impeller blades was decreased, binding effec of impeller blades was increased, desabiliaion by impeller blades of fluid paricle which flow nearby impeller was increased, which made hem deviae from original pah, he mechanical energy which was overcome echange momenum was increased, he energy loss and waer resisance coefficien were increased. 3.. The effecs on head and efficiency of number of impeller blades. When he impeller roaed, under design condiions, mied flow pump was simulaed when impeller blades were 4, 6, 8, formula (3), (4), (5) were used o simulae head and efficiency, curves of head and efficiency VS number of saor blades were ploed. I s shown in figure 4. I can be seen from he figure4: wih number of impeller blades increased, head showed a rend of increasing, efficiency firsly increased and hen decreased wih unobvious rend. There are mainly wo reasons: (1) Wih he increasing of blade number, he resricion of liquid by blades was increased, he sliding coefficien increased, while loss of separaion and spread of impeller blade were reduced, so head was increased.()blades ransmied orque o liquid, increased surface of blades made liquid flow more smooh, and loss of separaion and diffusion were wea, so head was increased. The reason of efficiency firsly increased was ha: due o eddy moion, slip phenomenon, loss of separaion were weaen, efficiency was increased; he reason of efficiency decreased was ha: due o epulsion was increased, fricion of blade surface was increased, mechanical energy which was overcame resisance was increased, so efficiency was declined. Summary Fig.4 Curves of head and efficiency VS impeller blades number (1)Under special environmen, in order o ensure whole sysem have well circulaion and sable sysem, which required low waer resisance coefficien. So he number of blades should as less as possible in he premise of efficien. 97

5 ()I s found ha he opimum performance of mied flow pump was achieved a 4 blades and 3 guide vanes, a which could obain requiremen and have he lowes waer resisance in saic and highes efficiency in dynamic, ha have some references for design similar ype pump. References [1] Li Yibin,Li Rennian,Wang Xiuyong,Han Wei,Gao Qiang. Numerical analysis of pressure flucuaion in low specific speed mied-flow pump [J]. Journal of Drainage and Irrigaion Machinery Engineering, 013,31(3):05-09 [] Feli A.Muggli Peer Holbein. CFD calculaion of a mied flow pump characerisic from shuoff o maimum flow[j].asme, 00: [3] Liu Zhenyi,Huang Xiaojun,Cheng Kuangmin. The analysis and calculaion of hydraulic fricion resisance in he impeller of mied flow pump [J]. fluid machinery,1995, 10(4):1-5 [4] Yang Congin,Du Yuanying, Li Yibin. Effecs of guide vanes parameers on waer resisance coefficien and efficiency of mied-flow pump[j]. Journal of Drainage and Irrigaion Machinery Engineering, 001:9(35): [5] Wang Fujun. The dynamics analysis of compuaional fluid, principle and applicaion of CFD sofware [M].Beijing: Tsinghua Universiy Press,