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1、第 9卷? 第 14期? 2009年 7月 1671?1819(2009) 14?4080?06?科 ? 学 ? 技 ? 术? 与? 工? 程 Science Technology and Engineering?Vol ?9? No?14?July 2009 ? ?2009?Sci ? Tech?Engng ?航空航天翼型大攻角的振动对气动性能影响的初步分析解亚军? 叶正寅(西北工业大学翼型、 叶栅空气动力学国防科技重点实验室, 西安 710072)摘? 要? 通过求解非定常 Navier?Stokes方程, 模拟了风洞实验中模型振动条件下的流场, 以翼型振动对流场和气动力的影响为突破口,
2、研究了模型振动对流场、 尤其是大迎角流场的影响, 并考虑了模型弹性轴不同位置对结果的影响。研究结果表明:在临近传统定常失速迎角的大迎角条件下, 翼型的振动可以引起翼型大尺度的分离, 导致翼型失速的提前发生, 其提前量取决于振动的幅度、 频率。风洞模型设计中的弹性轴所处的翼型弦向位置也对结果有一定影响。其研究结果对大展弦比机翼的风洞实验结果分析、 模型设计有指导意义。关键词? Navier ?Stokes方程? ? 分离流? ? 失速? ? 大展弦比模型机翼? ? 弹性振动中图法分类号? V211. 24; ? ? ? ? 文献标志码? A2009年 4月 13日收到?In recent yea
3、rs, many w ind tunnel experi ments a?bout large aspect ratio aircraft indicate that the airfoilofmodel presences obvious vibration ,as shown in F ig.1 that illustrates the demonstration of airfoil vibration ina low speed wind tunnel ofNorthwestern PolytechnicalUniversity .The arrow in Fig . 1 right
4、down region re?presents the amplitudes of vibration . According to theliterature 1? 3,it is well known that the reason ofproducing vibration of large aspect ratio airfoil mainlycom es from elastic vibration of airfoilmodel itsself andvibration of supporting system.However ,due to thesecrecy of aircr
5、aftmodel dealingw ithm ilitary ,it isdif?ficult to find the valuable infor mation from the existingreports .Farther ,it is of great i mportance to be able toi mprove the precision and reliability of wind tuunel ex?peri ments .W ith the development of high?speed computer andnu m erical computational
6、methods,the computationalfluid dyna m ics ( CFD) was introduced in this paper .This method possesses some superior characteristics,F ig . 1?airfoil ofmodelsuch as low cost and easy controlling of the propertiesof fluid , which makes it highly valued by researchersand developed quickly. Therefore ,in
7、 this paper ,theCFD approach is e mployed to investigate the effect ofmodel vibration on the airfoil flow field by designingseveral different vibration mode. l Using the method itis pri m ari found that the elastic vibration of the modelairfoilmay cause the stall attack ahead.1? Numericalmethod and
8、exampleDue to the ti m e consum ing of computation on theunsteady flow field ,a t wo? di mensional airfoil model ofhigh aspect ratio is approxi m ately considered to investi?gate the aerodynam ic performance .Consequently,theevolved infinite interpolation approach is employed tointroduce the C grid
9、of airfoi.l And the compressibleand unsteadyN- S equation is described as follows :? ?t?V? Qdv+?V? F? nds = 0(1)where ? Q = ? , ? u, ? v, eT,inwhich ?denotes the fluiddensity; u and v denote components of the velocity inthe direction x and direction y respectively ;e denoteswhole internal energy of
10、unit volu m e ; ? n denotes a unitnor mal vector of integral boundary; v denotes the inte?gral energy of a unit flow field ;?v denotes the bounda?ry of integral region ;?F denotes flux,which can beclassified two categories :non?viscosity ?FEand viscosity?Fv:?F = ?FE+ ?Fv(2)?In order to i mprove the
11、reliability of the computa?tion ,in the case of unsteady condition ,double ti m emethod is applied to figure out the unsteady N?S equa?tion , where the SST model is e mployed based on the k? equation .In addition ,for the sake of comparing theresults in different conditions,the computation in dif?fe
12、rent vibration model and different parameters adoptsthe sa m e grid and viscous coefficien. t And when thephysical ti me is advanced ,the m axi mumerror ad?vanced about pseudo ti me in every step is controlledbelow 10- 5. Thesem easures can be used to ensure thecompulating results reliability .To id
13、entify the reliability of the numericalmethodand program,the airfoilNACA0015w ith quarter?chordlength which perfor m s pitching motion is consideredand investigated .During the analysis ,the Reynoldsnu mberRe is considered to be 1 950 000 ,andM achnu mberMa is considered to be 0. 29 ,the mathe matic
14、expression ofmotion is defined by ?= ?m+ ?0sin(?t),reduced frequency k= ?c/2V?,where ?mdenotesmean incidence angle ,?0denotes incidence anglemagnitude of pitching motion ,? denotes the angularfrequency.In the study, ?m= 17? , ?0= 4 . 2? , k= 0. 1 .The relation bet ween lift coefficient cland inciden
15、ceangle is shown in F ig. 2 .It is evident from the figurethat themethod and progra m adopted in this paper canaccurately si mulate the unsteady separate flow field .F ig . 2? The curve of the aerofoil? s liftcoefficientwith incident angle2? Results and discussionTo si mulate the vibration of large
16、aspect ratio air?craft ,theNACA0008 airfoilw ith the lesser thickness iscarried out to investigate . According to the low speedinw ind tunne,l the Reynolds number of airfoil is con?sidered to be 106,andM ach number is considered tobe 0 . 15 .In the case of ?m= 15? ,the plunging modeand pitching mode and teir various combinations arechoosed to be investigated .For the purposes of accurately capturing the histo?ry variation of airfoil? s lift coefficient and plungingmodew ith non?di mens
