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oct. 1,1946.
~
` A. A. GRIFFITH
>2,408,632
FLUID- SOLID CONTACT-_SURFACE
Filed Aug.> l2, 1945
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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
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_
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Appli'catien Angustia, 1943',"seriàifNq. 492;',414
' “
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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
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`
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.
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