UNITED STATES PATENTS 6/1971 Rethorst /41. 6/1965 Hiersch P 9/1953 Hoadley. 181/33 HB. 7/1957 Stephens /41

Transcription

1 Unitd Stats Patnt 19 Kuth 54 CONTROL OF NOISE AND INSTABILITIES IN JET ENGINES, COMPRESSORS, TURBINES, HEAT EXCHANGERS AND THE LIKE 76 Invntor: Arnold M. Kuth, 490 Barton (51) 58) North Dr., Ann Arbor, Mich Fild: May 10, 1971 Appl. No.: 141,617 U.S. Cl /33 C, 181/33 HC, 181/33 P, 244/1 N, 244/41, 41.5/119, 416/2 int. Cl.... F01d 5/16, B64c 23/06 Fild of Sarch /33 P, 36 A, 33 H, 18 1/33 HA, 33 HB, 33 HC, 33 HD, 43, 51, 33 C; 41.5/119, DIG. 1; 244/41, 1 N, A; 416/500, 2, ) Rfrncs Citd 3,588,005 2,934,889 3, ,0,752 2,800,291 2,899,0 2,9, 136 2,944,623 3,000,1 3,523,661 UNITED STATES PATENTS 6/1971 Rthorst /41 5/19 Poulos /33 HC 6/19 Hirsch P 9/1953 Hoadly. 181/33 HB 7/1957 Stphns /41 8/1959 Ellis /41 12/ Ringlb /33 HB 7/19 Bodin /33 HC 9/1961 Ringlb /33 HB 8/1970 Rthorst /41 FOREIGN PATENTS OR APPLICATIONS 587,211 1/19 Franc /41 11 () Dc. 4, ,841 12/19 Franc... o 244/ ,398 5/1967 Franc /41 791,563 3/1958 Grat Britain /41 885,093 12/1961 Grat Britain. 181/33 HC 6,118 5/1962 Italy /41 Primary Examinr-Richard B. Wilkinson Assistant Examinr-John F. Gonzals Attorny-Marchal, Bibl, Frnch & Bugg 57 ABSTRACT Intrinsic sound, nois and instabilitis dirctly or indi rctly du to th shdding of cross-stram vortics causd whn air or fluid movs ovr th trailing dg of a plat, blad, van or th lik ar rducd by th formation of rlativly stady-stat stramwis vorti cs upstram of th trminal dg. Th invntion is applid to turbin and comprssor blads, jt tub in lts and xits, hat-xchangr tubs and th lik by placing or forming stramwis vortx-inducing gnra tors within th boundary layr on th shdding itm so. that th inducd stramwis vortics trail off of th trailing dg and supprss th formation of cross stram disturbancs. Through this procss, nois dis turbancs which would othrwis amplify to high sound intnsitits and/or larg flow disturbancs, high structural strsss and loss of fficincy through pas sag ovr succssiv shdding itms ar supprssd in thir arly stags of dvlopmnt. 12 Claims, 7 Drawing Figurs -24b 24

2 PATENTEDDEC SE 2 3, 776,363 O S. S. S. y o ARNOLD M. KUETHE 2wll 3 (3.43 A 77OAPWAYS

3 PATENTED DEC SHEET 2 OF 2 s -2 r a. -" - 1 1

4 1 CONTROL OF NOISE AND INSTABILITIES IN JET ENGINES, COMPRESSORS, TURBINES, HEAT EXCHANGERS AND THE LIKE BACKGROUND OF THE INVENTION Th prsnt invntion is dirctd to tchniqus, mthod and apparatus for th rduction of sound and flow instabilitis producd in th wak of a body mov ing rlativly through a fluid. It is known that whn a fluid passs ovr a two-dimnsional body, such as a blad, a surfac of rvolution of othr surfac which has a trailing dg alignd gnrally transvrsly to th dirction of fluid flow, thr is formd a cross-stram or transvrs priodic succssion of flow and prssur disturbancs known as a Karman wak or vortx trail.... This is actually an altrnating sris of transvrs vorti cs formd in th wak of th objct. Th Karman trail producs sound by rason of th fact that th prssur disturbanc varis with tim; and oftn this sound is in th audibl frqunc rang. Th sound producd by a singl body in a low-spd fluid stram is of rlativly small amplitud. Howvr, th sound and th fluctuating structural strsss that accompany th gnration of th Karman trail at high spds, such as occurs in flow past high spd propl lrs, fans, and hlicoptr blads and th lik at nar Sonic and suprsonic spds, can b of significant am plituds. Furthrmor, th sound prssur is aug.. mntd whn thr ar a larg numbr of bodis mov ing, togthr, through a fluid stram. This is th condi tion which obtains, for xampl, in a jt ngin in which sound is producd at th jt inlt, at th stator and rotor blads. Each individual trailing dg or blad producs a wak, and this wak includs a trail of cross-stram vortics. Sinc th blads ar arrangd in cascad fash ion, th succding blad must pass through th wak cratd by th prcding blad and this wak imping mnt crats additional nois. Th disturbancs du to Karman vortics and that du to th passag of blads through th waks of prcding rotor and stator stags gnrat major contributions to th nois mittd by jt ngins. In addition, rsonanc charactristics of nclosurs, such as fan or ngin housings and hat xchangrs, can caus th unstady flow, vorticity or prssur dis turbancs, such as thos dscribd, to amplify by x changing nrgy with ach othr and with th main stram. Instabilitis in th functioning of turbins, com prssors and hat xchangrs and non-uniform tmpr atur and flow proprtis, ar frqunt dirct or indi rct consquncs of ths nrgy transfrs and rso nanc phnomna. This gnral problm has bn d scribd by Chn, Flow-Inducd Vibration and Nois in Tub-Bank Hat Exchangrs Du to von Karman Strts, Journal of Enginring for Industry, Fb. 1968, p. 134 t. sq. Jt ngin nois is tratd in a papr by Ribnr Proc. Air Forc Offic of Scintific Rsarch - Univrsity of Toronto Institut of Aro spac Scincs Symposium, May, 1968, Univrsity of Toronto. SUMMARY OF THE INVENTION Th prsnt invntion is dirctd to mthods and ap paratus for supprssing th formation of Kármán vorti cs and to rducing flow disturbancs in th waks of bodis in rlativ motion through fluids. Th invntion has particular utility whn applid in th form of O stramwis vortx-inducing surfacs and lmnts in turbins, comprssors, hat xchangrs and th lik. I hav discovrd that Karmain vortics can b sup prssd by th formation of stramwis vortics up stram of th trailing dg in such a mannr that th stramwis vortics trail off from th dg and into th wak rgion. I prfr to form th stramwis vortics by using vortx-inducing surfac discontinuitis or sur fac lmnts positiond within th boundary layr a short distanc upstram of th trailing dg at which Karman shdding occurs. Th stramwis vortx tho rtically producs no sound sinc it is ssntially a stady-stat phnomnon in that thr is no prssur chang with tim. Thus, by forming stramwis vortics and in doing so, supprssing th formation of Kármán vortics, I can substantially rduc th sound which would othrwis b causd by th sam structur in th absnc of my invntion. I prfr to crat th stramwis vortics by utilizing vortx-producing lmnts, within th boundary layr, of th typ disclosd in my U.S. Pat. No. 3, , now schduld to issu May 11, 1971 (also disclosd in Grman Offnlgungsschrift No ). Th vor tx-producing lmnts may thus compris ithr a dis crt raisd portion or a dprssion, alignd to intr cpt th flow of fluid or air and to caus a transfr of. stramwis momntum from th xtrior flow to th boundary layr immdiatly adjacnt th surfac in qustion. Such vortx gnrating lmnts may b formd or placd on on sid or on both sids of th surfac in qustion, such as adjacnt th trailing dg of a blad, jt mouth or th lik. Mor complt sup prssion of th Karman trail is achivd by using vortx gnrators on both surfacs lading to th trailing dg. Th lmnts may b ithr curvd or straight, and ar prfrably inclind at an acut angl to th dirction of air flow for maximum utilization of th boundary layr vorticity.. It is accordingly an important objct of this invntion to provid apparatus and mthod for rducing th sound mittd by, and th flow instabilitis within, comprssors, turbins, hat xchangrs and th lik. A furthr important objct of th invntion is th supprssion of a trail of cross-stram sound-inducing vortics by th cration of an array of stramwis vorti cs upstram of th trailing dg or flow sparation lin. A furthr objct of th invntion is th provision of a jt ngin, or a comprssor, a turbin or a hat x changr having improvd sound mission charactris tics. A still furthr objct of th invntion is that of th limination or rduction of th intnsity of cross stram vortics by th formation of stramwis vortics within th boundary layr. Ths and othr objcts and advantags of th invn tion will b apparnt from th following dscription, th accompanying drawings and th appndd claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of an airfoil lmnt, such as a comprssor or turbin blad, diagrammatically illus trating th formation of Karman vortics at th trailing dg; FIG. 2 is a fragmntary plan viw of a blad of FIG. 1 to which my tchniqu has bn applid;

5 3 FIG. 3 is a diagram of a stramwis vortx pattrn formd by this invntion; FIG. 4 is a fragmntary nlargd sction through a positiv surfac lmnt takn gnrally along th lin 4-4 of FIG. 2; FIG. 5 is a similar sction through a ngativ surfac lmnt; FIG. 6 is a diagrammatic rprsntation showing th mannr in which a singl surfac lmnt forms a stramwis vortx; and - FIG. 7 is a modification showing a curvd vortx gn rator. DESCRIPTION OF PREFERRED EMBODIMENT Rfrring first to FIG. 1, a two-dimnsional objct of an air stram, in th form of an airfoil-shapd turbin or comprssor bladr 10 is shown crating an instabl wak 12 of Karman-typ vortics, with air flowing in th dirction of th arrow. 13. Actually, such as instabil ity wak may b producd by any transvrsly lon gatd objct in a moving stram. Th cross-stram vor tics of altrnating opposit sign within th wak 12 ar diagrammatically illustratd at 14. Th formation of cross-stram vortics is rfrrd to as shdding.' Th frquncy in by which vortics ar shd from th trail ing surfacs of a flat plat paralll to a fluid stram may b givn by th formula: whr v is th vlocity of th mainstram air, t is th thicknss of th objct at th trailing dg, and 8 is th boundary layr thicknss. Whil th spcific application of this invntion is il lustratd hrin as applid to a typical turbin blad 10, th mthod can b applid for xampl, ithr to a rotor or to a stator blad, ithr in th comprssor or th turbin sction, and it should b undrstood that th invntion is not intndd to b limitd to its appli cation tp jt ngin blads as such. In fact, th advan tags of th invntion can b ralizd by applying it to jt tub xits or othr surfacs adjacnt trminal or trailing transvrs dgs in ordr to supprss or rduc th formation of cross-stram vortics. From th abov formula, it will b sn that vn a sharp trailing dg will produc a Karman vortx trail. Furthr, th shdding frquncy in for a convntional turbin blad, particularly if it is highly loadd, will b lowr bcaus flow sparation from th suction (con vx) surfac will tak plac slightly upstram of th trailing dg, thus rsulting in an ffctiv thicknss t gratr than that of a corrsponding flatplat. Shd ding frquncis in th ordr of 5,000 to 10,000 cps can b xpctd. I achiv th supprssion of th Kárman vortx trail by crating at a rgion upstram of th trailing dg 19, a transvrs sris of stramwis vortics which trail off th dg 19 (or th flow sparation lin) and into th rgion of th wak boundary 12. Such stramwis vor tics ar prfrably formd by suitabl vortx gnrat ing lmnts 20, positiond on both th uppr and lowr surfacs 21 and 22 of th sound producing l mnt, although it is within th scop of my invntion to utiliz gnrators slctivly on ithr of such surfacs or altrnativly on such surfacs. Th gnrators 20 ar prfrably constructd ac cording to th tachings of U.S. Pat. No. 3,578,264, abov rfrrd to, and thus consist of surfac lmnts of ithr th positiv or ngativ typ applid to or formd on th xposd surfac 21 or 22 of th blad 10, and which xtnd partially into th boundary layr as dfind or masurd at a rgion upstram of th sur fac lmnts. Th vortx-producing lmnts or gn rators 20 ar shown in FIG. 2 as bing applid to both th uppr and lowr surfacs of th blad 10 adjacnt th trailing dg 19. Th gnrators 20 shown in full lin ar applid to surfac 21 and thos shown in bro kn lin ar applid to th opposit surfac 22. Th l mnts 20 may thus b formd ithr intgrally with th surfac of th blad or may b applid to th surfac. Thy may b positiv as shown in FIG. 4 or ngativ as shown in FIG. 5, and prfrably xtnd in an array of lmnts 20 along straight transvrs rgions and ar orintd gnrally paralll to ach othr. FIG. 2 illus trats such an array in which all of th lmnts 20 ar paralll to ach othr. Howvr, V-shapd or zig-zag lmnt arrays as disclosd in U.S. Pat. No. 3,578,264 may also b usd. Th placmnt of th vortx gnrating or inducing lmnts with rspct to th airfoil surfac of th blad 10 diffrs somwhat from convntional placmnt of vortx-producing dvics which ar usd for dlaying flow sparation. In th lattr cas, th vortx gnra tors ar commonly placd narr th cntr of th chord lngth of th blad or airfoil structur in qus tion. Howvr, for th purpos of supprssing th Kar man trail, I hav found it dsirabl to plac th vortx inducing lmnts narr to th trailing dg or th flow sparation lin. Also, my mthod as it rlats to nois supprssion is not limitd to th us of vortx including lmnts on airfoil or curvd sctions sinc this tchniqu and mthod may b applid to flat plats, or surfacs which ar not curvd in th dirction of fluid flow, such as th rgion adjacnt xit ducts, or whrvr thr is a trminal dg in a mainstram of flow, for supprssing th shdding of transvrs vorti cs. Furthr, my invntion is not limitd spcifically to th us of th boundary layr vortx gnrator as dis closd in U.S. Pat...No. 3,578,264, and gnrators of th convntional typ as shown in U.S. Pat. Nos. 2,800,291 and 2,558,816 may b usd. Howvr, I pr fr to mploy th boundary layr vortx gnrator b caus of its small dimnsions, low cost, ruggdnss and simpl surfac configuration. Th mchanism by which a givn stramwis vortx is gnratd by a surfac lmnt inclind at an angl to th dirction of mainstram flow dos not admit of prcis graphic analysis. FIG. 6 is an illustration of a typical singl gnrator 20 shown as bing applid to th xposd surfac of a blad 10 or th lik. Th boundary layr vorticity is dflctd to form, in this in stanc, a vortx 24 having a countr-clockwis rotation as viwd oppositly to th dirction travl of th main stram air. It will b sn that som of th stramlins 26 ar divrtd by th lading dg of th lmnt 20 and ar displacd latrally along th dg and trail off at th trailing dg of th lmnt and ar joind by som of th stramlins 27 which pass ovr th lmnt and ar dflctd and causd to rotat in th stram wis dirction to form th vortx 24. This may or may not b accompanid by a rvrsal of flow of th flow componnt normal to th axis of gnrator 20 in th r gion clos to its downstram dg 30. In all cass, th stramlins closst to th surfac at th downstram dg 30 of th gnrator 20 ar dflctd to a gratr

6 S xtnt than th stramlins in th boundary layr mor rmot from th surfac. Rfrnc may b had to U.S. Pat. No. 3,578,264 for a fullr discussion of th m chanics of stramwis vortx formation by a gnrator lmnt 20. Th diagram of FIG. 6 furthr illustrats th mannr in which th thicknss of th boundary layr 8 has bn dcrasd as indicatd by 8". Obsrvations by vorticity mtrs hav shown that two adjacnt gnrators 20, having th sam rlativ incli nation with rspct to th mainstram flow, will ach produc a primary vortx 24 rotating in th prdictd dirction, and if th spanwis spacing 32 btwn th gnrators is nar optimum, thy will also produc thrbtwn a scondary vortx rotating in th oppo sit dirction. Thus, rfrring to FIGS. 2 and 3, th in dividual gnrators 20 on th uppr surfac will pro duc a corrsponding transvrs sris of primary vor tics indicating gnrally at 24a which rotat in th sam dirction as shown in FIG. 3. Th primary vorti cs 24 also produc intrmdiat scondary, rlativly countr-rotating vortics as indicatd at 24b in FIG. 3. Th mchanism of th formation of th vortics 24b. may b undrstood by looking at FIG. 3. Th down ward motion of th fluid indicatd at 33 and th up ward motion indicatd at 34 st up a motion btwn thm which inducs th formation of th vortx 24b in th spac btwn th adjacnt co-rotating vortics. Vorticity mtr obsrvations indicat that th countr rotating intrmdiat vortx 24b is of substantially th sam intnsity of that of a primary vortx 24a. This tnds to show th compltnss by which th boundary layr vorticity has bn utilizd by th gnrator arrays in th production of stady-stat stramwis vortics for th supprssion of th formation of th Kármán cross-stram vortx trail. Th mchanism by which my invntion supprsss th Karman vortics can bst b undrstood by consid ring th dtails of th flow nar th lin whr th flow sparats from th body; on an airfoil-shapd body, this lin is vry nar th trailing dg 19. In a two dimnsional flow, that is, in th absnc of a spanwis vlocity componnt, a flow instability occurs which causs th sparation lin to shift back and forth as Karman vortics form and ar shd into th wak. Th ffct of th stramwis vortics gnratd by my in vntion is to provid a strong spanwis vlocity compo nnt at th sparation lin with th rsulting tndncy to stabiliz th flow in that rgion and prvnt th gn ration of Karman vortics. This tndncy is accntu atd if th stramwis vortics ar of altrnating sns so that th spanwis vlocity componnts altrnat as on movs along th sparation lin and thr would thus b no sufficintly long spanwis intrval in nar two-dimnsional flow to gnrat th Kármán vortics. As indicatd abov, I prfr to mploy an array of vortx gnrators 20 on ach of th two opposit sur facs of th objct with rspct to which supprssion of transvrs vortics is dsird. In th mbodimnt of th turbin blad 10 shown in FIG. 2, an array of th gnr ators 20 is shown as bing formd on th top surfacs and anothr array is formd on th bottom surfac, in gnrally th sam rgion as th top array and having th sam rlativ inclination whn viwd from th sam sid. In a turbin blad, th surfacs ar rspc tivly known as prssur and suction surfacs. How vr, th cross-stram spacing of th gnrators on th prssur sid, for xampl, ar staggrd with rspct to that of th gnrators on th suction sid. Th rsult is that a primary vortx 24a from on surfac will flow from th trailing dg at th sam rgion as a scondary vortx 24b from gnrators on th opposit surfac. Th rotations of ths pairs of vortics 24a and 24h from opposit surfacs ar in th sam dirction, and thus th arrangmnt is on in which th vortics formd by th gnrators on th opposit surfacs tnd to augmnt and rinforc ach othr at a rgion down stram of th trailing dg 19. Whil th spacing numbr, lngth, hight (or dpth) and angl of th inclination of th gnrators 20 may vary widly, I hav found that good rsults ar obtaind whn th ratio of gnrator hight h (or dpth h) to boundary layr thicknss 8 is in th ordr of 0.5, as shown in FIGS. 4 and 5. In th mbodimnt of FIG. 5, it may b dsird to round out th downstram dg as shown at 34. Th ratio of gnrator lngth to boundary layr thicknss can b in th ordr of 8, and th angl of inclination p to th mainstram 13 may b in th ordr of. Furthr, th ratio of cross-stram projc tion 36 (gnrator lngth multiplid by sin p) to th cross-stram spacing 32 may b in th ordr of 0.5, and th spacing 37 upstram of th trailing dg 19 or th flow sparation lin in th ordr of approximatly tims th upstram boundary layr thicknss or lss. As notd, ths dimnsional ratios ar not critical; how vr, if th distanc of th gnrator from th trailing dg is too grat, th gnratd vortics may b dampd by viscous dissipation, thus rducing thir f fctivnss in supprssing th cross-stram vortics. Whil I prfr to us gnrators 20 formd along gn rally straight lins as shown in FIG. 2, ths gnrators nd not b straight and may in fact b curvd as shown at in FIG. 6 with an upstram nd 41 at an angl p of -20 and th downstram nd 42 substantially paralll to th flow dirction with th shap approxi matly th arc of a circl. It will thus b sn that on of th important advan tags is th provision of an apparatus and mthod by which th sound producing instability of lmnts mov ing through a fluid stram, such as air, can b rducd with a minimum of altration to ths lmnts and at a low cost. Th gnrators ar not subjct to misalign mnt in us or asy dstruction. Thy hav an xcd ingly low profil and thus do not rquir a major chang in dsign or th spacing of th parts, which could b critical in a jt ngin for xampl. Furthr, th rduction of nois by th supprssion of th nois producing cross-stram vortics is in itslf a masur of incrasd fficincy. Whn my mthod is applid to th quiting of a jt ngin, it is prfrrd that th gnra tors b applid to th blads of both th comprssor and th turbin, and to substantially all of ths blads. Furthr, th lmnts may b similarly applid to th insid and outsid surfacs of th jt xit mouth to r duc shdding, and to th surfacs of tub-bank hat xchangrs to rduc flow-inducd nois and vibration. Whil th mthods hrin dscribd, and th forms of apparatus for carrying ths mthods into ffct, constitut prfrrd mbodimnts of th invntion, it is to b undrstood that th invntion is not limitd to ths prcis mthods and forms of apparatus, and that changs may b mad in ithr without dparting from th scop of th invntion. What is claimd is:

7 7 1. Th mthod of rducing nois and vibration induc ing Karman vortics at th trailing dg of a turbin blad or van in a jt ngin or th lik comprising th stp of forming a spanwis sris of stramwis vortics at locations on th surfac of th blad or van up stram of th trailing dg throf and no highr than th hight of th boundary layr so that said vortics flow past said trailing dg and downstram throf to provid an incras spanwis flow componnt at said trailing dg. 2. Th mthod of claim 1 in which said stramwis vortics ar formd by positioning longatd wav l mnts on said surfac at an acut angl to th dirction of flow throvr. 3. A jt ngin, turbin or comprssor blad lmnt having rducd sound producing charactristics in which a curvd flow control surfac trminats at a cross-stram trailing dg, th improvmnt compris ing mans dfining at last on longatd vortx pro ducing lmnt on said surfac positiond slightly up stram of said trailing dg at an acut angl to th di rction of flow ovr said surfac and situatd ntirly within th boundary layr air ffctiv to produc a stramis vortx xtnding off said trailing dg and into th rgion normally occupid by Karmancross stram vortics. 4. Th blad of claim 3 furthr comprising a plurality of said lmnts positiond in a spanwis row adjacnt said trailing dg. 5. Th blad of claim 4 in which said lmnts ar formd on ach of th prssur and suction surfacs of said blad adjacnt said trailing dg. 6. Th mthod of supprssing th shdding of nois or vibration-producing cross-stram unstady vortics which ar othrwis producd downstram of th flow sparation lin of a body such as a tub, duct, turbin blad or van, in a fluid stram comprising th stps of forming wholly within th boundary layr a plurality of spanwis-sparatd primary stramwis rlativly stady-stat vortics at locations adjacnt th surfac of said body upstram of th sparation lin, simulta nously inducing th formation of a plurality of coun tr-rotating stramwis vortics intrmdiat said pri mary vortics, and causing said stramwis vortics to xtnd downstram of such sparation lin into th downstram rgion normally occupid by cross-stram vortics to ffct a spanwis vlocity componnt at th O 30 8 flow sparation lin for th supprssion of th shdding of cross-stram vortics. 7. Th mthod of claim 6 in which said stramwis primary vortics ar formd by longatd wavs l mnts on said surfac positiond at an acut angl to. th dirction of flow of said fluid stram. 8. In a jt ngin having comprssor and turbin blads, th improvmnt in jt ngin structur rduc ing intrinsic sound mission thrfrom, comprising mans on th surfac of a substantial numbr of said blads dfining, longatd vortx-producing lmnts, said lmnts bing longatd in th stramwis sns, positiond wholly within th boundary layr upstram of th trailing dg of said blads and xtnding at an acut angl to th dirction of air flow ovr th blad surfac to produc stramwis, rlativly stady-stat vortics xtnding rarwardly of th corrsponding trailing dgs to supprss th formation of sound producing cross-stram prssur disturbancs bhind said blads. 9. A body in a rlativly moving fluid stram having. a rducd tndncy for producing nois and vibrations and having a surfac xposd to said stram trminat ing in a trminal dg or a flow sparation rgion, com prising mans on said surfac upstram of said dg or rgion dfining a spanwis sris of longatd surfac lmnts positiond wholly within th fluid stram boundary layr and xtnding at an acut angl to th dirction of flow of said fluid stram and which utiliz th boundary layr vorticity to form a plurality of stramwis vortics in said fluid stram which trail downstram of said dg or rgion and which induc spanwis componnts of flow to supprss th formation of nois and vibration-inducing Karman vortics. 10. Th body of claim 9 having opposd said surfacs which ffctivly trminat at a common dg dfining said trminal dg or rgion, and said vortx-forming lmnts bing associatd with ach of said surfacs. 11. Th body of claim 10 in which th vortx-forming mans on said surfacs ar rlatd in spanwis spacing to ach othr to form mutually rinforcing vortics downstram of said dg. 12. Th body of claim 9 in which th spacing btwn adjacnt spanwis said lmnts is sufficint to induc th formation of a countr-rotating vortx btwn an adjacnt pair of primary lmnt-inducing vortics. ck k k k >k 50