Dynamic Characteristics Analysis of Blade of Fan Based on Ansys

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1 Powr and Enrgy Enginring Confrnc 1 Dynamic Charactristics Analysis of Blad of Fan Basd on Ansys Junji Zhou, Bo Liu, Dingbiao Wang, Xiaoqian li School of Chmical Enginring Zhngzhou Univrsity Scinc Road NO.1 Zhngzhou 51 Abstract: In this papr, th finit lmnt modl of blad of R axial-flow fan has bn built, using this modl, th dynamic charactristics of blad hav bn analyzd with Ansys softwar. W can gt th first 1 natural frquncis of blad undr ratd and rsonant oprating conditions, and gt th harmonic rspons of xciting forc. h rsults show that R axial-flow fan runs stabl undr rsonant oprating conditions, rsonanc dos not occur; th largr rotation spd can incras th natural frquncis of blad; th blad has th maximum rspons of th xciting forc at 1Hz. Ky words: Blad; Finit Elmnt; Dynamic; modal analysis; harmonic rspons 1 Introduction Blad as an important componnt of fluid mchanical, its structur is rasonabl or not dirctly affcts th prformanc of th fan, whil th advantags and disadvantags of blad prformanc ar mainly rflctd in th static and dynamic charactristics [1]. Blad will b affctd by cntrifugal forc and stady or unstady flow forc, unstady flow forc is th main sourc of xcitation among th all of th forc. If th blad occurrd bnding and torsion dformation undr th action of th xciting forc, th dformation will lad to arodynamic of blad chang. Whn th intraction btwn air forc and mchanical vibration is rducd, th motion is stabl, othrwis vibration and unstabl movmnt will occur. Blad Vibration will gnrat dynamic strss, rsulting in blad fatigu, or vn ruptur [-]. hrfor, it is grat significanc to analyz th dynamic charactristics of th fan blads. Structural Dynamics Analysis is to study th natural frquncis and mod shaps of blad [5], analyz and prdict dynamic rspons of blad undr th loads to avoid rsonanc. In this papr, th finit lmnt modl of blad of R axial-flow fan has bn built, using this modl, th dynamic charactristics of blad hav bn analyzd with Ansys softwar. W can gt th first 1 natural frquncis of blad undr ratd and rsonant oprating conditions, and gt th harmonic rspons of xciting forc. Blad finit lmnt modl and msh.1 Study objct In this papr, th blad of R axial fan is usd as rsarchd objct. Blad is CLARK-Y airfoil, its rlativ thicknss is 1%.h spd of work is 1rpm. h paramtrs of blad control sction shown in abl 1. Matrial of blad is FRP, and Dnsity is kg /m3. Elastic modulus is 7. 1 MPa, Poisson ratio is.3. abl 1. th paramtrs of blad control sction paramtrs control sction r r R Chord C/m orsion angl h modl of blad is dfind by paramtrs of control sction, w can stablish blad modl by surfac connction. hrfor, in th modling procss, using th point to a lin and thn to plan, to th body modling []. h modl of blad is shown in figur 1.. Finit lmnt quation In this papr, w slctd Solid 18 to discrt unit of blad (h disprsd grid shown in Figur ). Solid 18 is a high-nd 3D solid unit which has -nods, it with quadratic displacmnt modl can bttr simulat SciRs. 3

2 Powr and Enrgy Enginring Confrnc 1 th irrgular grid. Unit dfind by nods, ach nod has thr translational dgrs of frdom along th xyz dirctions. Solid 18 can hav any spatial anisotropy, unit support plastic, supr-lastic, crp, and has th ability to simulat larg dformation and larg strain. h balanc quations of blad undr th cntrifugal forc fild ar as follows [7] : Figur1. Blad modl of grid incrasd [8]. As th computr rsourc constraints, w can not gt vry fin msh, but th nd to nsur that th rsult of numrical is indpndnt to grid. In this papr, thr grid systms wr usd. Elmnt dg lngth is.1,.75 and.; Spacing btwn two adjacnt grid systm lvl changs is larg nough, th blad first mod and rlativ strss along X-axis is calculatd. h rsults ar shown in Figur.3 and Figur. As can b sn from Figur.3, th rsult of first mod calculatd using diffrnt nods numbr not chang significantly. With th incras of nods numbr, th rsult of first mod calculatd by two adjacnt grid systms is mor similar. Figur. shows that th rsult of rlativ strss along X-axis has a littl diffrnc, but th diffrnc is vry small whn lmnt dg lngth is.75 and.. hrfor, w bliv that Elmnt dg lngth =.75 has bn to mt th rquirmnt of accuracy, and can b obtaind th rsult indpndnt to grid th first mudl Figur. Msh NODE numbr B dv N f dv N p ds R B strain matrix N shap function matrix p prssur pr unit ara R nod concntration loading vctor (1) strss vctor f inrtia forc vctor pr unit volum h finit lmnt quation is: M C K M C () Q C P F R M total mass matrix C damping matrix K stiffnss matrix M C cntrifugal forc mass matrix.3 Examination of grid indpndnc In th diffrntial quations discrt procss, th discrt rror would b introducd. For th sam discrt schm, discrt rror is usually rducd with th dns 应力 Figur3. First mod Rsult analyss 沿程长度 X( m) Figur. Rlativ strss along X-axis Static mod analysis h root of blad was bound compltly. Using SciRs.

3 Powr and Enrgy Enginring Confrnc 1 Lanczos mthod to calculat th first 1 natural frquncis of blad, th rsults shown in Figur 5. rlativ strss of th laf blad. As can b sn from figur, whn th frquncy of th laf is 1.99Hz, first-ordr rsonanc will occur, th main form of first-ordr rsonanc is wav vibration, th closr to th tip of th sit, th gratr amplitud is, maximum dynamic strss appars in blad root; whn th frquncy of th laf is.59hz, scond-ordr rsonanc will occur, th main form of scond-ordr rsonanc is shimmy, th tip and th cntral of th blad hav largr amplitud, dynamic strss will mainly concntrat in th location of nar th blad root and from 1/3.Bcaus th procss of movmnt of th blad is affctd by th first two bands vibration, roots and th uppr is pron to fatigu and vn appars crack or fractur. In practic, from th collctd fractur fragmnts of lavs, w can s most of th fractur appar in th two placs of abov-mntiond[9], th rsult is provd corrct 固有频率/HZ 阶次 Figur5. h first 1 natural frquncis of blad Figur shows first two vibration mod and a a First-ordr mod shap and rlativ strss 1.99Hz b Scond-ordr mod shap and rlativ strss (3.11Hz) Figur. Mod shap and rlativ strss abl. th first 1 natural frquncis of blad in diffrnt spds 3. Modal analysis of a pr-strss In th procss of rotation, blad is affctd by cntrifugal forc. Load cntrifugal forc on blad as Pr-strss and calculat th first 1 natural frquncis of blad in diffrnt spds. h rsult is shown in abl. As can b sn from ab., with th spd incras, th natural frquncy of blad also will bcom largr, which is du to stiffnss matrix K incras. h frquncy of xciting forc is: N n spd ordr 3 Whr:N indicats th numbr of blad, n indicats th spd of fan pr minut. As can b sn from th formula, whn th working spd of th fan is 1rpm,th frquncy of th xciting strss is 9Hz, this frquncy is diffrnc mor than 15% to first-ordr natural frquncy(1.33hz).h fan runs stabl, rsonanc dos not occur. With th incrasing spd of fan, th frquncy of th xciting strss gts largr, whn th SciRs. rpm 1rpm 175rpm rpm spd incrasd to rpm,its frquncy is Hz, this frquncy is closr to th first-ordr natural 3

4 Powr and Enrgy Enginring Confrnc 1 frquncy (131.9Hz), blads will occur unstabl vibration and affct th arodynamic prformanc of th blad and rduc th fficincy of fan. If fan runs undr this condition in long-trm, th blad will fatigu and asily appar crack or vn fractur. hrfor, whn adjust to th spd in th actual opration procss, w should tak full account of th natural frquncy of blad, avoiding rsonanc and xtnding th srvic lif of fans. 3.3 Harmonic rspons analysis of xciting forc Application of computational fluid dynamics softwar Flunt to simulat th flow fild, w can gt th xciting forc on blad is 1.9N. Load xciting forc on blad and calculat rspons displacmnt and strss. h rsults ar shown in Figur 7 and Figur 8. dramatically, so w can mak sur that rsonanc occurs in narby 1Hz and point A radial rspons displacmnt is 5.7mm now, it is 3.9 tims of xciting forc frquncy in 9Hz corrspondnc rspons displacmnt(.155mm). Figur 1 shows us point B on th blad rspons forc siz whn xciting forc frquncy changs, its tndncy is similar to Figur 9 and maximum rspons strss 5.7Mpa, it is 7.5 tims of frquncy in 9Hz corrspondnc rspons strss(.93mpa). rspons sss/mm frquncy/hz Figur 7. Rspons displacmnt Figur 9. rspons displacmnt changs with th xcitation frquncy at point A 3 7 Figur 8. Rspons strss As can b sn from th figur7 and figur 8, th maximum displacmnt rspons to xciting forc is.919 mm, th maximum strss valu of 1.8MPa. h maximum strss is lowr than th allowabl strss of th matrial and mts th dsign rquirmnts. With th changs of th xciting forc frquncy, Figur 9 shows us point A on th blad rspons displacmnt siz, as w can s from th pictur, whn xciting forc frquncy incrass from 11Hz to 1 Hz, point A radial rspons displacmnt incrass dramatically, whn xciting forc frquncy adds to 1Hz, point A radial rspons displacmnt dcrass qunlnt strss/mpa frquncy/hz Figur 1. rspons strss changs with th xcitation frquncy at Conclusions point B In this papr, th dynamic charactristics of blad hav bn analyzd with Ansys softwar. W can gt th first 1 natural frquncis of blad undr ratd and rsonant SciRs.

5 Powr and Enrgy Enginring Confrnc 1 oprating conditions, and gt th harmonic rspons of xciting forc. h following conclusions can b drawn: (1) R axial-flow fan runs stabl undr rsonant oprating conditions, rsonanc dos not occur. h maximum strss is lowr than th allowabl strss of th matrial and mts th dsign rquirmnts. () h largr rotation spd can incras th natural frquncis of blad. In actual opration, w should fully considr th impact of natural frquncy to avoid rsonanc. (3) h blad has th maximum rspons of th xciting forc at 1Hz. Rfrncs [1] Liang Gui. Rsarch on Static and Dynamic Charactristic of th Blad in Axial-Flowing Comprssor[D]. XiAn Univrsity of chnology. 8(Ch). [] Jinxiang Xi. h Caus Analysis of Fatigu for th First Stag Blad of Axial-flow Comprssor [J]. Comprssor, Blowr & Fan chnology. 7, ():-7(Ch). [3] Jianghong Wan. Braking Rason Analysis for Axial-Cntrifugal Comprssor Blad[J]. Comprssor,Blowr & Fan chnology., ():53-55(Ch). [] C.Konga,J.Banga. Structural invstigation of composit wind turbin blad considring various load cass and fatigu lif[j]. Enrgy 3(5):11-11(Ch). [5] Hongxin Zhang. Slf-Study Manual Of ANSYS[M]. Machinry Industry Prss(Ch) [] Wnjun Hang. Rsarch on thr dimnsional solid modling for stam turbin twist blad basd on th Solid Works[J]. Machinry Dsign & Manufactur. 7, (5):7-9(Ch). [7] Xianchng Rong. Finit Elmnt Mthod[M]. Southwst Jiaotong Univrsity. 7(Ch). [8] Wnquan ao. Numrical Hat ransfr[m]. Xian Jiaotong Univrsity. 1(Ch). [9] Bingli Wu. Axial fan Of Air Cooling[M]. Harbin Univrsity of chnology. 7(Ch) SciRs. 38