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Патент USA US2405282

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Aug., @9 w46.
R. BlRwaANN
lVARIABLE RATIo'coMPREssoR
Fil-ed Feb. 2, 19384>
, WWA/53s.
¿4659282
2 Sheets-Sheet l
Aug., 6, E46,
R. BIRMANN
2,4%@
VARIABLE RATIO COMPRESSOR
Fílèd Feb. 2, 1938
2 Sheets-Sheet 2
/m/f/yra@ _
WVU
y
Patented Aug. 6, 1946
2,405,282
'UNITED STATE-s >Perret-Vr oFFl-CE
mesne assignments, to Federal Reserve Bank
of Philadelphia, a `ccrporation of the United
‘States of America
Application February 2, 1938, Serial No. 188,231
V8 Claims. (Cl. 230-47)
1
.
This invention relates to a variable compression
ratio centrifugal compressor, and particularly to
a compressor of that type adapted to -be'driven at
constant speed and used Yforthe sup'ercharging of
aircraft engines.
All modern aircraft engines `of medium and
large sizes are equipped with gear driven super
V2
practically constant, and also since th-rottlingof
the suction does -not >bring about a temperature
reduction of the air entering the supercharger,
the manifold temperature is greatly increased,
High manifold temperature, however, cannot
be tolerated, kbecause it results in overheating of
the cylinders, burning >of the exhaust valvesg'de
structive preignition `or detonation, `and loss of
chargers that are commonly‘built into the engine
as an integral part thereof. These superch'argers
have two purposes. First, 'they Jare designed to 10 power due to the high speciiic' volumeof the air lin
the manifold. Hence, to make operation >of an
increase the manifold pressure to Vcrowd more
altitude supercharger equipped engine at jall p‘o's
oxygen and fuel into vthe cylinders to thereby in
vsibie near sea level, it has 'been'necessar'y to limit
crease the charge density and the horsepower
its power output to substantially less than full
'out-put of the engine. Secondly, they are designed
to maintain a certain manifold pressure, and 15 Power. >In other words, at sea'level where maxi
mum' power Ashould be available, _the 4engine def
thereby the horsepower developed bythe engine,
velops
less power than at thelaltitude‘s for which
at high altitudes Where the pressures `and 'densi
the arrangement is properly designed,
ties of the air ~are reduced to such extent that
"ro avoid these difficulties, the following
without a supercharger there would resulta rapid
schemes have 'been proposed:
u
decrease of power output of the engine with in 20
First,
superchargers
have
been
driven
by
the
creased altitudes, For example, whereas at sea
engine not with a constant speed up gear' ratio,
level the -absolute pressure of the atmosphere may
but by means 'of a gear'arrangement that permits
be 30 'inches of mercury and the vtemperature 60°
two or more speed up ratios rso that the super
F., at 35,000 feet at the same time the pressure
charger can be operated at a'lower speed, and
may be 7 inches of mercury andthe temperature 26 consequently at a lower pressure and ,temperature
~66° F.
ratio, at or lnear sea level >and a higher speed at
So far as the design of a >centrifugal compressor
a higher altitude to suit the pressure and 'tem
‘is concerned, the aforementioned duties do not
pera‘ture conditions existing thereat. A continu
l offer <any particular problem, There is, however,
ously
speed up ‘gear has been proposed
a‘difficulty which has given the aircraft engine -30 to givevariable
the best results.
designer a considerable amount -of trouble, -and
Secondly, va 'supercharger has been proposed
the elimination of which has been the object of
with two or more stages, only one of which, 'the
much developmental and experimental work.
last one, is used at sea level, while 'the others are
This'diiiiculty is due to the fact that a given
made operative at higher altitudes where the
supercharger operating at a constant speedmcan
increased pressure rat'ios’s'o obtained are required
be practically designed to give a certain manifold
to maintain the manifold pressures. Obviously,
>pressure at one 'altitude only. At higher altitudes
the increase in pressure ratio can only be secured
this manifold pressure will drop and the horse
in step-s.
power »ofthe engine will fall off as a consequence.
Again, >without resorting to throttling its suction 40 Third,v it has been- proposed that the pressure
at the impeller inlet may be lowered, but instead
at lower altitudes, the ’supercharger discharge
of doing this by throttling it is to be done `by ex
pressure increases to such extent that vthe engine
pansion
in a turbine. Accordingly, »the tempera
`cannot stand the- increased power output that
ture at the impeller inlet, and consequently 'the
would result. Throttlin-g has, therefore, been
necessary to prevent the `manifold pressure from 45 discharge temperature, are reduced and some’of
the power required to drive the compressor is
exceeding a maximum safe value.
Y
saved, being reduced by the amount that is `ob
lIn throttling at the lower altitudes, the air `and
tainable from the expansion in the turbine. This l
gas mixture is admitted to the supercharger at
approximately a pressure equal to the one that
`exists at the altitude for which the supercharger
is designed. However, at the designed altitude
the air temperature is vert7 much lower than it is
at or near sea level, and since the pressure ratio,
and consequently the temperature ratio, produced
by any constant speed centrifugal compressor are
arrangement, however», is not only structurally
complicated, but is incapable of giving eiiiciently
a large range of compression `ratios such as is re
quired for normal aircraft operation, the reason
being the occurrence of excessive power Vlosses
due to the existence of improperly directed pas
sages for operation outside a limited compression
2,405,282
3
4
ratio range. Furthermore the arrangement in
volves large impact losses.
All of the above arrangements are quite corn
plicated, cumbersome, heavy and expensive and
have not been practical for general adoption.
It is the object of the present invention to avoid
above, but also ci, the absolute fluid velocity at
the entrance, c2, the absolute fluid velocity at the
discharge, w1, the velocity of the ñuid relative
the difficulties above mentioned by the utilizasI
cussed more fully hereafter. Y »- 4
to the impeller at the entrance, and wz, the ve
locity of the fluid relative to the impeller at the
discharge. These vector diagrams will be dis
i
.The above formula, which -nepresents a close
approximation to normal conditions which are
the pressure ratio of a centrifugal compressor
operating at constant speed may be changed by.' ,105 encountered, indicates that the pressure rise de
tion of an arrangement of »Simple type in which
Y pends exclusively on the inlet and discharge con
simple adjustments of parts which are normally
stationary during operation and without
Yditions and is independent of the path of flow
between the linlet and discharge. Since nor
mally it is desirable to obtain the maximum pos
sible pressurerise' from a Wheel of given outside
diameter >and eye diameter at a given speed of
rotation, the negative term of the above formula
is made zero `by so arranging the construction that
the absolute inlet velocity is perpendicular to the
any - f
modification of a conventional rotor construction
and without the addition of any conventional
parts rotating at high speeds, for example, tur
bine rotors, which involve large energy losses by
increase in the number ofentrances and exits
for the air besides providing for'only a‘limited
range of over-all compression ratios. specifi-‘_ ,
cally, the object is accomplished by modifying in
let conditions without thro-ttling and its objec
tionable consequences in accordance with princi
ples hereafter disclosed, while at the same time
20 face of the impeller so that its peripheral com
ponent cui is zero. This construction, of course.
has the further advantage of obviating the neces- '
sity for suction guide vanes because the flow cor
responding to such condition of the absolute inlet
securing in fashion a long range of compression
ratios.)
'
»
. l velocity is the normal inlet flow to the impeller.
In accordance with the present invention, the
second term of the above formula is made positive
to an adjustable extent serving to cut down the
'
The accomplishment of this general object,
and of more specific objects, relating primarily
to details of arrangement and construction, will
be apparent from the following description read
in conjunction with the accompanying drawings,
pressure rise, and consequently the pressure ratio,
Si)
in which: y
v Figures 1, 2 vand13 are axial Sections through an
impeller construction embodying the principles
of vthe invention, the` several figures showing vari
ous conditions of adjustment to secure different
pressure ratios;
'
`
to thef desired amount at lower altitudes, while
for operation at the designed altitude, this term
is made zero so that the compressor functions in
its most efficient normal manner. The values of
ai and u2 are ñxed by the rangesV of inlet and dis
charge radii of the impeller. cui and cu2 depend,
respectively, on'the arrangement of inlet and dis
'
chargepassages with respect to the passages of
Figure 4 is a transverse section taken on the
the rotor. Since in general design considerations
plane indicated at ¿_A in Figure l;
make it impractical to vary the discharge Das
` Figure 5 is a section taken on the broken plane
sages,-there is leeft vfor practical variation the ar
indicated at 5-5 in Figure 2;
rangement of the inlet a proach passages -where
` Figures 6 and '7 are vectorl diagrams illustrat
byv the quantity cuifmaë be controlled, to vary
'ing approximately the respective velocity condi
tions accompanying operations according to the
from its normal zero value to such values as will
serve Ato make the second term of the above
adjustments of Figures l and'3; and
„ Figure _8 is Ya diagrammatic View illustrating
equation sufficiently large.
By doing the above, it is possible to have the im
the'nature of the blading preferably used.
peller function in quite conventional fashion,
with axial flow through `the inlet approach pas
W To enable- the principles of the invention to be
understood, a general explanation of the theory
may be made as follows:-
y
sages, when the maximum pressure ratio is de
’
sired, with maximum efficiency and minimum
' >If it is 'assumed that there are no friction or
lossesl at high'altitudes, while when a low com
now losses, the pressure rise produced by a cen
t'rifugal` compressor is expressed by the well
pression ratio Vis desired, ~this is secured merely
by changing the direction of inlet,V flow to give
an increase-¿of the peripheral component of the
known equation:
`
I
`
absolute velocity. Doing this involves no increase
in impact losses norvthrottling over a large range
Vof compression ratios as will be evident hereafter.
>This mayy be contrasted with the inevitable im
Aîp=â<uèca-uictd
in Èwhich z>
A
pactV losses f in the turbine-impeller arrangement
referred to above, which additionally has only a
small range of moderately efficient operation and
is «particularly unsatisfactory for high compres
u1 is the peripheral velocity of the impeller at
_the entrance,
ì
'
_
_
»
cur is the peripheral component of vthe absolute
fluid velocity at the entrance, '
us' »is the peripheral velocity of the impeller at
sion ratio conditions since the -air at all times
~
passes Ythrough the turbine. .
:the discharge,- .`>
'
"
' fluid vvelocity at the discharge,
Ap is the total pressure rise,'p2-pi,
'
.
mechanical embodiment of the invention illus
trated the drawings.
_Í
.
`At 2 there is illustrated a shaft of a centrifugal
'
'y is‘the mean specific weight ofthe iiuid, and
y is the acceleration due to gravity.
`
significance of these and other quantities l
compressor adapted to be driven at substantially
constant/'speed by the engine whichA drives the
airplane propeller and which is> being supers
charged..l The kshaft 2 carries the impeller 4, of
substantially conventional type, ‘rotating within a
may be seen by a preliminary reference to Fig
ures '6 and 7, in which flow conditions in a
centrifugal compressor are represented in con
ventional 'vector diagrams, in which there are
indicated not` onlyï u1,-u2,lcu1,~and cua-defined
'
' >*Before discussing further matters of the theory
of operation -referer'ice may be ’madeV to a desirable
cuz- is' 'the >peripheral component of the absolute
75
suitable housing 6, providing intake and discharge
:2,405,282
passages, .and provided with passages vindicated
'ati8, of whichîmore «will-besaidìlaten» Discharge
Sfromthe impeller passages f8 'takes place lthrough
a suitable idii’fuser l0 'into fthe passage 't2 lf-rom
`.which the compressed air vmay befdelivered -to the
»engine to be supercharged.
’
ysion-‘ratio lat :higher »altitudes where lower ítem'
pera'tures prevail. Consequently, adjustment 'is
¿made ~.by >rotation I»of the shaft 32 ìto Jmover-the
‘plate >ZI‘I -‘to :the left, causing fthe Ivanes ¿34 to f-ob
struct' -*more kand -more :of ¿the ‘inlet Ipassage
-eventually .arriving »at «the >condition illustrated ¿in
'The supply of Vair to the compressor takes place
Figure >2. As the vanes approach the -ring I8 -a
-through M. At 'the normal altitude -for which
greater Aproportion of the vinflowing »air must »flow
design is made substantially -all ’o'f -theßair thus
entering liiows Laxially `to'the impeller passages -8 10 'between them and 4they will `>impart Ato the .air
rentering `the impeller va, swirling motion in lthe
giving ~rise to a »zero valueofcui. Consequently,
direction/of -rotationof `the impeller. 'This action
`the second term lof -«the above equation ¿is zero
is :accomplished without throttling, the‘energ-vyio'î
and `a maximumcompression -ratio fissecured, the
¿the Linflowing `air being converted `into Ikinetic
-impeller «operating lin conventional, vhighly e’iïì
energy `rather than into heat as in the lcase -of
cientïashion.
Unlike conventionalcomp-ressor arrangements,
throttling. As a result of `this action «theeen'ter
`ing fair 'now «moves Yin -a »spiral »direction yin -«its
the :entrance portions of the impeller passages 8
are «not »surrounded by »an Aannular closure wall;
but, »on ¿the contrary, »there are 'provided around
these portions of the Limpeller «passages guide
4approach tothe impeller‘inlet, and consequently
the peripheral component of the absolute 'fluid
velocity 4at -the entrance, namely cui, takes »on-‘a '
»vanes i6 extending in ithe/direction indicated 'in 20 positive -value with the result »that >'the ‘second
term Jof the l'above lformula decreases »the value
Figure 4. An annular Vring íI-ß -is slotted -as in
of the’pressure rise. The -pressure ratio is there
dicated at >20, "the slots being vformed «to ñt the
by decreased to the proper extent in a-continuous
»vanes i6 so that the ring may Amoveaxially-over
¿fashion 'from its maximum vaïlue attained by'ïtlhe
the vanes. The ring is urged outwardly lby lcom
«adjustment iin Figure il through the «approach -to
pression springs indicated at -22 >to 'a position
the -condition -of »adjustment illustrated lin IFig
limited ïby suitable stops formed by the «semi
ure -‘2.
cylindrical elements housing tha-springs.
There is a limit, however, ‘to the vrotational
velocity which itis desirable to impart tothe
`meshing with an elongated pinion l(it) -'mounted 30 ~inllowïing :air by this action -of the 'vanes 34.
AThe limi-t is achieved when, due to the daction -of
lupon-a shaft 32 which may be `rotated lmanually
the inlet swirl, the `impeller passages at the-nor
for adjustment purposes. Rotation ofthe shaft
mal entrance lreceive 'the 'air at >an Aangle that 'is
V32 V`Willvcause the plate -24 to move =axially:between
'approximately y'about 15° Ylarger than the “vane
the -»limiting ypositionsïindicated -in Figures 1 and
angle Awhich is designed -»to -be correct for ‘the
’3. At its >periphery the plate 24 carries *a series
quite open suction «condition applying 'at Í‘hi'gh
Aof 'guide vanes 34 of theform‘illustrated in Figure
altitudes. As will Vbe 'pointed out hereafter, ‘the
'5., the inner-‘ends of which are design‘edto’ñt over
impeller Yvanes are preferably `of a-type present
the periphery Ñt5 ofthe Jring i8, the arrangement
ing straight ‘line elements inthe direction of ,'?low
being such that movement of the 'plate 24‘to the
and are streamlined yat their-intake edges. vOli/‘ing
left, Ías viewed in th-e'succ' sive Figures 1, 2 and 3,
AA plate ¿24 is threaded upon -a íixed lhub 26 V‘and
‘is provided at its periphery with gear teeth 23
to -this fact, each vane acts very imuch like an
-will first cause the lvanes 4 to'belocatediadjac'ent
the ring i8 ‘and then -wil'l cause the'plate 241150
engage :the Aring I8, moving it to Ythe left 'hand
>airfoil. It is known that a suitable airfoil 4can
llimiting position indicated 'in Figure 3 against ‘the ‘ '
an angle of incidence of about 15°. I_t -will ¿be
compressed'springsZZ. "The ring ‘i8 and the'plate
obvious, therefore, that the angle of 15° or ¿less
with which -the entrance air >blows against the
trailing side Aof the ‘vanes does not constitute a
24 are `provided with >`guide >surfaces î'33 and '36
designed for the v'smooth guidance 'of air tothe
‘impeller inlet during 'normal operation.
Work eiliciently and ydevelop maximum lift 'with
shock angle, but, owing to the airfo'il character
-Thenormal high 'altitude condition of the “com 50 istie of the vanes, they Will deflect the entering
v-pressor is illustrated ‘in Figure 1. Under such con
ditions the plate ’24 is moved to its extremeright
>handposition 'as viewed in 'that'?lgura providing
Va"`la1”ge'open‘passage for the air "flowing from 14 y
v»to the radially extending ‘in‘let lipsof the impeller
ya'ir in the proper Vmanner to >resultin a substan
tial driving Vcomponent at the entrance tending
'to provide a‘net reduction of the power'necessary
to drive the compressor. At anglesgreaterfthan
1f5° the airfoil effect rapidly drops off so that, as
‘just indicated, an entrance langle of about 15°
greater ‘than the vane angle represents the limit
passages 8. At such time 'the guide passages be
tween the 'vanes 16 are ’fully open but-due to the
ing condition desirably `achieved through the
comparatively small passagearea and also due to
action of the vanes’34.
_
,
' '
"
the normal inlet ñow in an axial direction, 'little
if any air flows through these passages and the 60 `As Ja specific example of 'the above, the vinlet
»angle of the vanes- corresponding exactly to the
operation is the same as 'if ’the portion of the im
angle of the lrelative inlet velocity under the con
peller at the location of these passages was sur
ditions of operation of Figure 1 may be 20°. "In
rounded by a closed wall. The guide vanes 34
the approach to the condition of Figure 2, due
interrupt only a relatively insigniñcant portion
of the intake passage and consequently vdo not 65 to the increase in the absolute'velocity of theair,
the proper value for theinlet angle will increase
substantially ‘influence the "in'ilow'ing vair, which,
‘to a value of, for example, 35-40° when the con
accordingly, „passes to the 'impeller in an axial
dition of Figure 2 is secured. Such an angle,
direction, 'giving rise ‘to operation at the maximum
compression ratio.
n
'If "the altitude is decreased, -the high com
pression ratio previously Vresulting may 'be .too
great, resulting `in the yproduction of too high a
pressure in the 'intakemanifo'ld accompanied by
an undesirable rise in ltemperature rover that ef
fected ‘by vthe-compression at «the same >com-pres
'being only 15°-20° larger than -the provided angle
of 20°, will, nevertheless, be consistent with satis
-factory operation due to the fact that the air
does not Istrike the impeller`- vanes at an angle
_ lgreater -than the
permissible one considering Íits
~airfoil characteristics. However, "if the design 'is
made -for normal high altitude .operation ,a‘ su’f
xñcient increase -in the value of cui to’sa‘tis'fa'œ
2,405,282
.
7
8
toit and theabsolute entrance velocity as illus
trated in the triangle. At the discharge the pe
ripheral velocity is uz and the absolute discharge
torily reduce lthe pressure ratio at >low altitudes
Vwould resultin an inlet angle _requirement of
from 45°-120°_. A ñow angle of such values would
create high impact losses and very unsatisfactory
velocity is c2. The relative velocity is wz.
At sea level, on the other hand, the conditions
indicated in Figure 7 may prevail. The corre
operation the effect of the guide vanes IE. As
spondence of the various velocities to those indi
will be obvious from Figures 2 and 3, a movement
cated in Figure 7 will be obvious. The principal
of lthe plate 24 to the left beyondthe position of
change is that c1, the absolute velocity at the en
Figure 2 will first result in cutting oíî the pas
trance, now has a very considerable peripheral
sagesbetween the vanes v3ft, and then the move 10 component due not only to its absolute value, but
ment of the ring I8 against the action of the
also to its direction. Consequently, the second
springs 22 to cut down the cross-sectional areas
term of the equation given above is relatively
of the passages between the vanes I6, this taking
small. It will be noted also from the vector dia
place until there isreached the limiting condi
gram that the ratio of w1 to wz is small, approxi
tion illustrated in Figure 3.
mating unity, so that there is very little compres
"After passage to the normal entrance of the
sion taking place. By suitable design it will be
impeller is very substantially reduced or cut off,
obviousthat any intermediate conditions may be
as illustrated in Figure 2, for example, auxiliary
secured, these being obtained in the adjustment
or exclusive entrance of air takes place through
from the condition of Figure 1 to the condition of
the passages deñned by the Vanes I6 between the 20 Figure 3 by the gradual change in the direction
1 peripheral portions of .the entrance ends of the
and absolute value of ci. Note that the inlet
impeller vanes 8. The average direction of flow
angle theoretically required in Figure 7 is less
through the passages defined Aby the vanes IB
than the vane angle of 90° plus the permissible
when the passages are in their most fully open
shock angle.
position is such as to approximate as closely as
l It will be noted that the matter of the resulting
possible impactless entrance between the vanes' 8
temperature is automatically taken care of by
of the impeller, which have radially extending
the above arrangement. When the temperature
inlet edges adjacent the varies I6. The net
is low, as at high altitudes, and a high compres
result is a still further increase in the last term
sion
ratio is used, the temperature is substan
of the above formula, thereby further cutting 30 tially raised to a satisfactory extent. On the
down the compression ratio for sea level lcondi
other hand, at low altitudes where the compres
tions. By continued decrease of the passages be
sion ratio approaches unity, little temperature
tween the blades I6 the velocity c1 is increased
rise will occur; and in the case of the extreme
to such an extent that if no supercharging is to
condition illustrated in Figure 3 with a pressure
35
be attempted the compression ratio may be unity.
ratio of substantial unity, the temperature rise
AS the velocity is increased beyond the wide open
above the temperature of the entering gases is
f condition of the passages vbetween the blades i6,
quite small and is due primarily to friction con
and the velocity ci increases, there again enters
ditions being well within the upper limits which
operation. ‘ Consequently there now comesl into
into the situation _the airfoil characteristics of
are permissible.
i
the'vanes with the result that shocklessentrance 40 The impeller blades are preferably designed in
of the air occurs though the relative flow angle
accordance with the eßnsiderations indicated in
may increase to 105° >to 110,". „In case a still
my application Serial No. 176,979, i'lled November
larger angle is required, a smooth inlet flow may
be provided by slight curvature of the inlet edges
of the vanes adjacent the finally active portions
of the passages i6, or alternatively, smooth en
29, 1937, and my Patents Nos. 1,926,225 and
1,959,703, dated September 12, 1933, and May 22,
1934, respectively.
In Figure 8 there is illus
trated (in a fashion similar to Figure 8 of my
trancemay be obtained by the arrangement de
Patent 1,959,703) the nature of the blades and
scribed in my application Serial No. 176,979, ñled
passages` In this figure OL represents the axis
November 29, 1937.
of rotation and OM a radial line deñning the
50
Since, when the compression ratio is unity, no
origin of a blade. As described in said patent,
compression is >taking place the compressor does
there are two sets of straight lines involved in the
no Work, and consequently does not absorb power
design, the straight lines A of one set extending
except for that incidental to the losses of „its idle
in. the direction of normal flow during entrance
operation. By means of a design such as that il
under normal conditions in an axial direction,
lustrated, for example, it is possible to attain a 55 while the straight lines B extend radially as in
continuous variation in compression ratio from,
dicated. The two sets indicate the actual fact
say, 2.2'to 1. Under the lastv named-condition
the unavoidable flow losses result in a.V certain
power consumption which is only a small fraction
that the blades are built up on relatively hat sur
'faces of smooth form so that entrance may take
value by means of suction throttling, in which
case power consumption remains practically con
choice of entrance lip in the case of turbine pas
sages based on my improved construction may be
used to achieve the result of impactless entrance
place inwardly as provided by the vanes I6 with
vof the power that would have .to be expended if 60 >the insurance of smooth flow. As pointed out in
the discharge pressure were reduced to the same
my application above mentioned, the proper
stant at its full load value.
,
.
The extreme conditions described above are 65 and desired relationships between peripheral ve
graphically illustrated in Figures'fì and 7. Re
locity of the turbine passages and spouting ve
ferring ñrst to the former, it illustrates the rela
locity ‘of the driving gases. This principle may be
tionships of the various velocities >under consider
obviously embodied as indicated above in the de
ation corresponding to the adjustment of Figure 1
sign of the lips of the impeller passages where
for high altitude operation. c1, representing the 70 they receive air from the passages deiined by the
absolute fluid velocity` at the entrance, extends
guide varies l5 so as to secure proper iiow as the
axially and has no peripheral component so that
passages I6 are reduced in cross-sectional'area
the second: term of the eliluation- given» above is
zero. ' The relative velocity 'un resulting from the
>in the adjustment between the‘positions of Fig
peripheral velocity ui-'at the 'entrance is related 75 ures 2 and 3. Both at the normal radial entrance
2,405,282
edge, and Where entrance occurs from the vanes
I 6, the blades are provided with airfoil type edges
-to secure impactless entrance through the sub
stantial ranges of approach angles mentioned
above, 'I‘hus the vanes form acute angles with
axial planes and extend substantially along
straight lines in the direction of flow from their
entrance portions to their discharge portions and
10
able to control flow to the second series of inlet
edge portions to provide varying velocity of flow
of gas thereto, and means for controlling both
of said adjustable means for their successive
operation to provide progressive variation of the
peripheral component of the absolute velocity of
iloW to the passages.
5.. A centrifugal compressor having a variable
are provided With airfoil type edges at their en
compression ratio comprising a rotor provided
trance portions to provide smooth entrance and
With impeller vanes defining gas passages, said
ñow over said vanes through substantial ranges of
vanes having one series of inlet edge portions
approach angles of flow.
arranged to receive gas approaching them in an
What I claim and desire to protect by Letters
axial direction, and another series of inlet edge
Patent is:
1. A centrifugal compressor having a variable 15 portions arranged to receive gas approaching
them with a radially inward component of flow,
compression ratio comprising a rotor provided
means adjustable to control ílow to the ñrst men
with impeller vanes deñning gas passages, and
tioned series of inlet edge portions to provide
means -for varying the peripheral component of
either substantially axia1 110W thereto or flow
the absolute velocity of the gas at the entrance
to said passages, said vanes forming acute angles 20 having a variable peripheral component in the
direction of rotation of the rotor, and means ad
with axial planes and extending substantially
justable to control ¿flow to the second series of
along straight lines in the direction of flow from
inlet edge portions to provide varying velocity
their entrance portions to their discharge por
of IloW of gas thereto.
`
tions and being provided with airfoil type edges
6. A centrifugal compressor having a variable
at their entrance portions to provide smooth en
compression ratio comprising a rotor provided
trance and ñow over said vanes through sub
with impeller vanes deñning gas passages, said
stantial ranges of approach angles of flow.
vanes having one series of inlet edge portions
2. A centrifugal compressor having a variable
arranged to receive gas approaching them in an
compression ratio comprising a rotor provided
with impeller vanes defining gas passages, and 30 axial direction, and another series of inlet edge
portions arranged to receive gas approaching
normally stationary but adjustable means for
them With a radially inward component of flow,
varying the peripheral component of the absolute
and means for controlling ñow to both said series
velocity of the gas at the entrance to said pas
of inlet edge portions to secure diiîerent pe
sages, said vanes forming acute angles with axial
ripheral components of the absolute velocity of
planes and extending substantially along straight 35 flow
thereto.
lines in the direction of now from their entrance
7. A centrifugal compressor having a variable
portions to their discharge portions and being
compression ratio comprising a rotor provided
provided with airfoil type edges at their entrance
with impeller vanes deñning gas passages, and
portions to provide smooth entrance and iloW
over said vanes through substantial ranges of 40 means for varying the peripheral component of
the absolute velocity of the gas at each of a
approach angles of IioW.
plurality of series of inlet edge portions of said
3. A centrifugal compressor having a variable
vanes, the inlet edge portions of one series hav
compression ratio comprising a rotor provided
ing inlet angles substantially different from those
with impeller vanes defining gas passages, said
gas passages being provided with inlet portions 45 of the inlet edge portions of the other series, the
passages receiving at one of said series of inlet
arranged to normally receive gas approaching
edge portions the major portion of the gas during
them in an axial direction, and means adjust
operation Within one range of peripheral com
able to control flow to said inlet portions to
ponents of the absolute velocity, and receiving
provide either substantially axial ilow thereto, or
flow having a variable peripheral component in 50 at another of said series of inlet edge portions
the major portion of the gas during operation
the direction of rotation of the rotor, said vanes
Within another range of peripheral components
forming acute angles with axial planes and eX
of the absolute velocity.
tending substantially along straight lines in the
8. A centrifugal compressor having a variable
direction of flow from their entrance portions to
their discharge portions and being provided with 55 compression ratio comprising a rotor provided
With impeller vanes deñning gas passages, and
airfoil type edges at their entrance portions to
normally stationary but adjustable means for
provide smooth entrance and iiow over said
varying the peripheral component of the absolute
vanes through substantial ranges of approach
velocity of the gas at each of a plurality of series
angles of flow.
4. A centrifugal compressor having a variable 60 of inlet edge portions of said vanes, the inlet
edge portions of one series having inlet angles
compression ratio comprising a rotor provided
substantially different from those of the inlet
with impeller vanes deñning gas passages, said
edge portions of the other series, the passages re
vanes having one series of inlet edge portions ar
ceiving at one of said series of inlet edge por
ranged to receive gas approaching them in an
axial direction, and another series of inlet edge 65 tions the major portion of the gas during oper
ation Within one range of peripheral components
portions arranged to receive gas approaching
of the absolute velocity, and receiving at an
them with a radially inward component of flow,
other of said series of inlet edge portions the
means adjusta-ble to control ilow to the ñrst men
major portion of the gas during operation with
tioned series of inlet edge portions to provide
in another range of peripheral components of the
either substantially axial flow thereto or ñow 70 absolute
velocity.
having a variable peripheral component in the
RUDOLPH ‘BIRMANN~
direction of rotation of the rotor, means adjust
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