Identification of vortices in a transonic compressor flow and the stall process

第22卷第9期航空动力学报Vol. 22 No. 92007年9月Journal of Aerospace PowerSept. 2007文章编号: 1000-8055<2007)09-1455-06Identification of vortices in a transoniccompressor flow and the stall processHUANG Xu-dong, CHEN Hai-xin, FU Song,David Wisler, Aspi Wadia, G. Scott McNulty(School of Aerospace, Tsinghua University, Beijing 100084;GE Aircraft Engines, Mail Drop A411, One Neumann Way, Cincinnati, OH 45215, USA)Ahstract: A novel vortex intification method for the visualization of the flow field is used for the study of thestall process of a transonic compressor. The parameter n，which is one of the five invariants formed by thestain tate and vorticity tensors from the theory of modern rational mechanics, is found to have good ability to identify vortcx stretching and vortcx relaxation/breakdown processes, is introduced here to identify the tipleakuge vortices. Compare with former generally used DP H( dynarnic pressurc head) contour, the new methodreveals much more flow details which may advance our understanding of the compressor behaviors. The Vorti-ces details are revealed in both peak eficiency and near stall condition. A possible stall process is also sugges-ted based on the vortices analysis. The tip leakage flow from mid-chord, besides leading edge leakage flow, isalso considered to play an imporlant role in the stall process.Key words: transonic compressor; stall; vortex identification; tip leakage vortexCLC number: V231.3Docoment code: Ahave good ability to identify vortex stretchingIntroductionand vortex relaxation/ breakdown processesi].Vortex is often the essential element re-The definition of this parameter is η= S, Wg,sponsible for triggering stall and surge in com-with the strain rate tenisor Sg≈0. 5(u, + u..;)pressors. So the identification and the analysisand vorticity tensor W。=0.5(u.,- u,). On theof the vortices in compressor are usually quiteprincipal axes of the strain rate tensor, it can behelpful for the understanding of the compressorshown that η=SW3s+ S2W3十SssW72. Fur-behavior. However, the generally used dynamicthermore, if the vortex is dominated by W23 withpressure head (DPH) contours and the stream-its axis along SI, as often to be the case, p≈lines are not enough for the identification of theS11 W2. Thus, the vortex stretching mechanismblade tip leakage vortices (BTLV). It is oftenis associated with n>0 since a positive Su re-difficult to reveal the details of the BTLV onlypresents the flow acceleration. When S1 is nega-by the DPH contours and streamlines. Some-tive, i.e. , n<0 the vortex breakdown or relax-times they may even lead to confusion and mis-ation occurs. However, the determination of theunderstanding of the flow.principal axes of the strain rates in a complexAn early study showed that the parameterflow. good choice be-m，which is one of the five invariants formed by中国煤化工causethe stain rate and vorticity tensors from the the-TYHCNMHGxhascomparedory of modern rational mechanics, is found tothe加method and the DPH method in detail,Received: 2007-06 -28 ;revision received date :2007-07-191456航空动力学报第22卷which proves that the n method is not only validtour and the n contour, and with the help of ve-but also resultful on the revealing of the vortexlocity vector we can find the basic features of thedetails. Based on those results, the authors willvortices at maximum efficiency condition:try to open out the stall process of the transoniccompressor in a certain configuration in this pa-per.NomenclatureCGCT circumferential grooves casing treat-mentBTLV blade tip leakage vortexDPH dynamic pressure head1Configuration of current studyThe NASA Rotor 378] is a high pressure(a) 96.6% sponratio transonic comnpressor rotor. With compre-hensive measured data and flow images, it wasused as a blind test case for CFD codes in the“IGTI Gas Turbine Conference" in 1994.The parameters for this rotor are listed inTable 1. The detailed numerical methods fothis study and the code validation can be found inReferences [4]and [5].Table1 Parameters of NASA Rotor 37ParameterValue- Vortex INumber of blades36Vote 1一-Rotation speed/ 85% ajanFig. 11 Relative location in spanwise ofvortices at near stall condition■名moves upstream and becomes strongers mean-while the mass flow rate decreases. Those chan-ges make the leading edge BTLV (Vortex II)become looser and weaker , and undergo a break-down when it interacts with the shock. The ex-pand of the Vortex II jostles Vortex III to theblade suction side, which makes the latter in-Fig.8 Vortices at the trailing edge of the bladeduce the large separation ( Vortex V) at theblade trailing edge. The spill forward region( Vortex VII), as explained before, is consideredto be only a flow phenomenon at the near stallcondition but not the reason for the stal. So thetwo large low DPH regions (Fig. 5 (c), (d))riggering of thestall中国煤化工ne is more fatal(a) 95% Span(b)99% Spannow.:YHCNMHGmuchlargerreFig. 9 Spill forward region at the leadinggion, it is more probable to be the key factor.edge at near stell condition (Top view)When the back pressure increases further, those1460 .航空动力学报第22卷two low DPH regions will block the flow pas-dation of China (NSFC) project No. 10477012.sage and trigger the compressor stall.References:3 Conclusions[1] FU Song, LI Qibing, WANG Minghao. Depicting vortexstretching and vortex relaxing mechanisms [J]. CHIN.With the help of a novel vortex identifica-PHYS. LETT. 2003 ,20(12);2195 2198.tion method, the detailed vortices structures and[2] HUANG Xudong, CHEN Haixin, FU Song. Identificationtopology in a transonic compressor have been re-of vortices in the transonic compressor flows [ R].vealed. The study distinguishes different vorti-11ACFM D06 , 2006.ces structures in the compressor, as well as their[3] Hathaway M. Slrecirculating casing treatment conceptfor enhanced compressor performance [R]. ASME paperdevelopment at different operating condition.GT -2002 30368, 2002.From comparison of the vortices in maximum ef-[4] CHEN Haixin, FU Song, HUANG Xudong. CFD investi-ficiency condition and near stall condition, a pos-gation on tip leakage flow and casing tretment of a tran-sible stall process has been revealed and the vor-sonie compressor [R]. ISABE 2005-1098, 2005.tex, which comes from the interaction between[5] HUANG Xudong, CHEN Haixin, FU Song, CFD investi-the tip leakage flow from mid-chord and the pas-gation on circumferential grooves casing treatment of atransonie compresor [R]. AJCPP 2006 _C015, 2006.sage main flow, is considered to be the most[6] Bergner J, Henecke DK, Hah C. Tip clearance variationsprobable direct reason for the happening of stall.of如axial highrspeed single -stage transonic compressorAcknowledgments[R]. ISABE 2005-1096 , 2005.This research work is supported by the GE-AE USA Programme and National Science Foun-中国煤化工MYHCNMHG