oct. 1,1946. ~ ` A. A. GRIFFITH >2,408,632 FLUID- SOLID CONTACT-_SURFACE Filed Aug.> l2, 1945 rf w PI" 2”' 22l f '13 , 2f ’ 129.5? ÄTTOK/VEY 2,408,632 Patented Oct. 1, 1_946 >unirsi) A‘srlwrlëls PATENT OFFICE y 2,408,632 ~ . FLUmï-SOLID CCINÍI'Afyl.` 1. Alan Arnold-Griffith, Derby; England, assigner to - . . . Rolls-Royce Limited, Derby; England,fa com-l Panyof Great Britain - ~ l _ . ~ Appli'catien Angustia, 1943',"seriàifNq. 492;',414 ' “ ` In Great Britain August 2.5, 1942 t *l . 5 claims. (cran-4.o)V 1 2 . According to another feature of my invention,` This invention relates to aeroplanes and other vehicles and also to pumps, compressors, turbines the shape of the surface is so chosen that there ,occurs a suitable‘slow fall of pressure in the direc and like machines and ancillary appliances where, tion of ñow, both upstream of the slot and down stream from the 'stagnation point associated with the slot, so that withmotion at large- ReynoldsV in the relative motion of a solid and avñuid; it is necessary for the proper functioning of the ve hicle or ïmachine that the ñuid pressure on the number the boundary layer is in known manner surface >ofthe 'solid shall increase in the general maintained in the laminar condition, with conse direction of motion of the îiluid past the surface. quent benefit in decreased skin friction; . " " A basic'factor governing the design`of such sur According to a further feature-of the invention, faces is that if such rise of pressure betoo rapid, 10 the slot extends into the solid in a direction tan- _ the íiow will break away from the surface with gential to the less'convex portion ofthe surface consequent increase of‘drag'orî other loss. It is knownl that vsuch'a» tendency', Ywhen it exists, may bev mitigated by ¿introducing `into the'.> surface ¿a at'the entrance ‘to the slot'so'that Vthere isv no sharp vchange of’ direction between theslot and slótv Vor slots, or vthe like, through which the ñuid itsstagnation'point. boundary layer may b'e- sucked away by a pump ‘ or’other device». When this ~is done there exists on" the .surface of the solid a stagnation point a short distance downstream from'the slot. At this point the fluid further from the surface, just be yondr the layer sucked away, is -brought to> rest ' ` ì ~ ` ` now ‘be'described by wayof'example only,fwithV reference to theaccompanying drawing, in which: Figurel 1 shows diagrammatically the known 20 arrangement `ofsolid-fluid boundary andthe pres sure lg'radients'occurring along a boundary; ‘ ¿Figure 2'is a diagrammatic section through a on 'the surface, thereby generating. the corre-Y solid-fluid boundary according 'to thisy invention and showsthe pressure gradient- along this bound sponding dynamic pressure. In general, there fore, there is'a sharp rise of pressure from the slot to the >stagnation point followed by a sharp but smaller fallzand then a more- gradual rise. The sharp rise from‘the` slot tothe stagnation point has no’ tendency tokcaus'e a breakaway vbecause ' `An embodiment ofthe present inventi‘onwill v25 „ Maand/-..N Y vFigure 3 ‘is a diagrammatic section through a modification ‘ofthe fluid-solid boundary shown in ` y Likèrefer'ence numerals indicate like parts in inY this- restricted'region .the direction of ñow of ’w ’ ' the-boundaryV layer is reversed; that is, it runs 30 the ñgures of the ‘drawing ï " ' l " ' _ AS'îshÖWniIi Figure, lair or'otl'ie? fluid iS flow: from the stagnation point to the slot.` `The tend- ing fò’ve'r the surface I0 of a "solid I I inthe direc-` ' ency >’still'texistavhowever, in the later, more grad tiön'shown bythe arrow I2. y Slots’l3- (the sizev» ualrisef'ï'»V " " ' " ` ' Accordirig‘to my invention, aïlluid-solidibound-ï of which'is‘greatly exaggerated Ainthevdrawing) ` ary containing'one or more ’suction slots Yor the 35 are formed in the surface I0 and suctionis'a'pplied like îisso shaped that norise of pressure occurs ` toY these slots by suitable means so`as toy suck away apart or the whole of the boundary layer- , onïthesurface in the general direction of flow of thefluid adlaçent the surface ID. The suction eXcept'in’the interval between the slot, or each causes theboundary'layer to'flow vin the manner ` ofä them, and Vitsv associated stagnation point, where the boundary> layer is Vlocally reversed inV 40 indicated bythe arrows-III', I5, I6 and I‘I. A short ’ distance' downstream of each slot I3 there isa direction. Thisk may be done by providingthat the surface curvature suddenlyY changes onpass-vv ing 'acrossthe slot, in the _sense of being less con from stagnation'point the surface, I8justbeyondfthe at which the’iluidvfurther layer_siiclçedVA awayßisnbrought" to" rest onmthe surface. TheV veX tothe fluidvonfthe'do'wnstream side of the" slot.» Iriaddition, there may be a sudden change 45 ydirecti'onbf 'flow’of theboundarylayer is locally reversed, as indicated by the arrow I5, between of direction at the slot, in the sense to form a. each slot I3 and the adjacent stagnation point re-entrant angle with respect to the solid. Known downstream. l methods of calculation, used for determining ythe The pressure curve in Figure 1 shows the pres shapes of the surfaces having prescribed pressure distributions, may be used for ascertaining the 50 sure on the surface in the plane of the section as opposed to lift, or reduction in pressure, as is precise shapes which are suitable for carrying out conventional. The pressure gradient comprises this invention. In general, it is found that the a sharp rise I9 from each slot I3 to the adjacent surface is convex to the fluid upstream of the stagnation point I8 followed by a sharp fall ZI]ì slot and concave downstream, with the greatest arithmetical curvature at the slot in each case. 55 and a. more gradual rise 2| to a point just up-V 2,408,632 3 4 stream of the next slot i3 when the pressure will fall as shown at 22 to a value dependent upon appended claims to changes of curvature of the surface mean changes other than any progressive the pressure produced by the suction device in change in general mean curvature that the sur face may have. My invention is of advantage in that the ill effects of contrary pressure gradients which ' the next slot I3. The rise 2! tends to cause the boundary layer to break away as indicated by the arrows Il with consequent increase of drag or other loss. The surface Hl'shown in Figure 2 isshaped' ink usually arise in the relative motionfof solids and fluids, arenot merely mitigated but~ eliminated altogether. The long slender shapes which have vlhitherto been an aerodynamic necessity are no accordance with this invention so as to be convex to the fluid at 23 upstream of each slot i3 andY longer needed. concave to the fluid at 24 downstream of the slot. . The arithmetical curvature of both the' concave" ' I claim: ‘ and the convex portions of the surface a'ref'great-u 1.; A solid'A having a surface over which ñuid fiows¿.which:~is~provi`ded with at least one suction .xslotzand- which surface is convex to the iluid .upstream ofthe slot and is concave to the fluid downstream of'th‘e slot with the greatest arith metic'al'curvature at the slot in each case, and meansfor» sucking some of the fluid through the est near the slot. The curves 23 ands24~--are dis continuous at the slot, so that there is a sudden change of direction at the slot» to form~a~reThe curve 2?ï'merges»witl'iïv one> wall of the slot so that there is no sharp change of direction between the stagnation pointlandthe slot. The curve 23, upstream of the slot, is . rounded to'merge with the. other surface of the slot.: entrant angle. slot. ‘ 2;v A -solid having, a surface overy which fluid flows; which is providedwith at least one suction slot, and which surface is convex to the fluidv its adjacent stagnationpcint l Biwill occur as with upstream of the slot> and concave to the fluid the existing arrangementisee the curve in Figf 25 downstream of the slot, with the greatest arith ure 2,»w-hich is drawn onytheflsame convention as metical curvature at the slot in each case and thatin Figure l, but the sharp fall 20 and subse- ' withthe curvatures on either side of the slot dis quent` rise 2'! are replacedby a gradualslow fall continuous to forma re-entrant anglewith re 25 in pressure to the'next; slot 131v downstream. spect to the~solid, and' meansl for sucking;` some. The rise -i 9i in -fpressure betweenl each .slot and - Any _tendencyt for theV boundary layer; tof break 30 of - theriluid v through> the slot'.l away thus` completely@ eliminated. SLA» solid having,v a surface: over which. ñuid Anyv known'V form of; purnp„,fan, ejector, venturi ilows, which surfaceis providedwith at/leastpone` ortheV like YInaysbe used tor-.suck awaytherboundary suction slot and-¿which surfacenis' convex-utothe.. uuid through the slots andv this> means-is shown fluidupstream of. the slot and ltconcave .to .the :iiuid in Figure 2 as comprising acentriiugalifan 26 , downstream of the> slot;, and .which slot ,. extends drivenby a suitable primefmover 21fandhaving into thesol-idiinadirection4 tangential to the’con. its intakeconnected-.byça passage ZS‘tothe slots-I 3. cavefportionI` ofsthe surfacev at the entrance .to the: In‘the :modification¿shown` in Figure 3 the slot l3~is.m'ade wider' than is> necessary to admit the slot; and . means -for' sucking; some: of? the: fluid.; through the slot.: boundaryè layer - and. lthea curve 2 3 .upstream s of ` the > 40 4. A solidfhaving-j a- surface. over. which:l fluid slot ends in-.af sharp edgeî 3S, the tangent '.31 f to' flows andzwhich‘has a- convex portionfand a. cone thecurve 23.» at the edge Sûrbeing normal to the direction` ofthe slot. cave-portion;r` the-< concave portion. being down. strearniofv the convex portion, andwhich iszfornred with- a :slot1betweenzthe said: portionszand 'extend-l It'fis »to- be. understood that the `above".reference ' to sucking away the boundary layer includesuthe. ` .ingsintorthe solid inwaidirection: tangential 4to .the removal -of Athe whole or a partthereof; the-,pres sureproduced lby the suctionzdevice must be'. less than the pressure existing at the slot in orderto" remove-thefluid.` The suction' pressure deter. mines the pressure which obtains at the-stagna, tion npoint downstream from the- slot,»which ymay be equal-toforless :than the` Pitot pressure :accord concaver portion of". theV surface> atA the. entrance. to :thefsloit ,withion‘ewall .mergingywith the con cave.: portion and; the: otherv wall merging“y with. the convex portion:VV of.' ther. surface; through a> f smooth‘curvefofïsmallradius;.and:means` for suck». ing-.some of theîfluid through thej'slot; .5. A solidV having, a surface‘oyer which fluidA ing as` the boundary layerY is wholly or> partly' removed.. No» additional»v advantage is- obtained flows and which has a convex portion and a-con-;-` by removing. a layer of: greater. thicknessfthanß stream ofith'e convex'fportion,A „and which isîí‘ormed the boundary layer. with -a-islot between the: said portions and extend ingfinto the solid' in‘a‘idirection tangential-to the'V concave portion of the. surface at 'the'. entrance A Y _Itfvvillalso be’understood that‘surfaces of the kind to which this `invention relates are: usually curved-.in the direction of-fiow of thel fluid over cave portion,` thev concave: portion being; down, to»the~slot~ with» one wall4 merging with the con x them,` as shown in .Figure 1, and thatr this general 60. cave’portion andthe other joining;v the convex curvature acrossthe surface isY not, in general, uniform but changes,y along the surface. The changesy inv curvature required by the present invention are additional Àto such general progres sivefchangesof curvature and referencesfin the; portion of the surface atk a sharp corner alongça-l line where the. tangent. at: the surface isnormal tothe direction-ofthe slot,_and means `for-sucking, some of~ the -fiuid through the slot. ` ALAN «» ARNOLD'GRIFFITH.