US2305136A - Centrifugal blower construction - Google Patents

Description

Dec. 15], 1942 K. CAMPBELL f CENTRLFUGALBLOWER CONSTRUCTION Filedqan. 31, 1941 V V INVENTR Kenneh CampbeLL.

` ATTORNEY y Patented Dec. Il5, 1942 CENTRIFUGAL BLOWER CONSTRUCTION Kenneth Campbell, Ridgewood, N. J., assignor to Wright Aeronautical Corporation, a corporation of New York Application January 31, 1941, Serial No. 376,757

2 Claims.

Thisvinvention relates to centrifugal blowers and is particularly concerned with improvements in the construction of blowers which are adapted for very high speed operation along with large delivery and substantial pressure rise.

The .provisions ofthe invention are particularly applicable to aircraft engine superchargers but the teachings of the invention may likewise be utilized in connection with centrifugal blowers in general. 'I'he desideratum in a. supercharger is to delivera large air volume at a pressure rconsiderably in excess of atmospheric, and to do this with a blower impeller and diffuser of very compact size. must rotate at very high speed and that air velocity through the impeller must b high. To get high pressure rise without an excessive velocity, the use of an impeller having backwardly sloping self diffusing vanes is indicated; the vanes should be wide for good blower capacity and for effective diffusion.

The impeller vanes according to this invention are carried by a curvedhub membersupporting the vanes only at 'one end in spaced parallel relation with the impeller axis to lave a clear axial air inflow opening. Since the curved vanesv Thus it is apparent that the impeller;

up by the impeller vanes for delivery to the diffuser embracing the impeller. The vanes in particular serve to change the entering air direction so that it ows smoothly through the zone l'along the inner face of the impeller shroud, which would otherwise be full of turbulent, low pressure air due to the lfailure of incoming air to make the necessary sharpturn around the shroud inner edge.`

Thus the several features of the structure herein disclosed combine to afford a supercharger assembly which is sound structurally and efficient aerodynamically.

In prior impellers and superchargers, two common faults includedthe lturning of air through passages of lolw aspect ratio, and the breaking away of air from one face or shroud of the im peller due to too sharp a turn from the axial to the radial path, causing turbulent ilow, poor velocity distribution, and curtailment in blower capacity and emciency. These faults are wholly overcome in the present invention. It might here be Amentioned that conventional supercharger impellers have. utilized radial vanes and stationary outer ends are supported by an integral shroud ring, which ring provides structure vto resist centrifugal force and likewise provides a mask at the ends of the intervane passages to suppress turbulence of airflow through the passages.v To be highly desirable to maintain a uniform velocity of air at all points in the cross section ofthe When the leading edges of the impeller passage. impeller vanes are substantially parallel to the impeller axis, as is herein contemplated, it is necessary to turn the air in as uniform a manner as possible from its axial incrw direction to aradial outflow direction, at the same time maintainingV good distribution across the ,impeller vane entrance spaces. 'I'his I propose to accomplish by placing annular stationary turning vanes in the impeller eye, Whose own aspect ratio as to the entering air ,is high. These vanes pick up con- `secutive annular incrementscf entering air and 'discharge them radially outwardly, whence they blend into a radially owing mass which is .picked I8 the foregoing.

shrouds. `It has been realized that the integral rotating shroud has advantages in Vpreventing slip vof air from one impeller passage to the next, and

in preventing the turbulatingeifect dueto air friction whichoccursI between the fast moving air and the stationary shroud. However, an integral shroud inthe old type impeller would not be likely. to secure all the advantages 'possible .unless the air .is properly turned. from axial to radial. iiow to avoid separation of air from the shroud surface, to enable an even velocity distribution across impeller passages, as gained by vpercharges of any type to which they are appli-v cable.

`To indicate thefnecessity of extreme reflne- I ment .in supercharger design as `herein taught, for an-` aircraft engine of 1,000 H. P., the impeller speed is of the order of 18,000 R. P. M.; .the impeller diameter is of the order of 11 inches; the air mass moved at sea level is of the order of 1450 cu. ft./min., or 110 lbs. per min.; andthe air velocity at the impeller outlet as it addresses the diffuser vanes is of the order of 1200 ft./sec. For high altitude, air mass* moved increases to 125 lbs/min. and 3100 cu. ft./min. Some of the objects of theinvention will be 4apparent from 2 e asoman An object ofthe invention is to provide statlonary, annular guide vanes in a centrifugalV blower rotor system which serve to alter the axial.I

entering air to a radial path, the radial air flow leaving the guide vanes then being vpicked up by the blower vanes. Still another object is to provide an impeller construction having spiral vanes and having an integral shroud, i. e'., integral side plates bordering the ,impeller blades for their mechanical support and for their greater aerodynamic efficiency.-

/The invention is susceptible to various changes and modiilcations as will be pointed out in the from an axial direction or now to annoia! d1rec.

' and velocity distribution across the impellerpas-V Y sages. `To attain uniform pressure across the passage a plurality of annular turning vanes 28,

detailed description below in connection with the 4 of the figures, and the detailed'diierences in the turning vane provisions will be taken up thereafter.

the general housing structure provided with bearings, not shown, in which an impeller yshaft II is carried. To the shaft il an impeller I2 is keyed as at I3, the impeller comprising a hub 'Il blending into a backplate l5 in clearance relation with a skirt I6 on the diffuser housing I0. The outersurface of the backplate Il may be either plane or slightly dished while the inner surface of thel backplate is preferably substan tially planef` as at i8, blending in a smooth curve into the hubv portion i4. Integralwith the backplate I8 are a plurality of spirally-shaped blower A diiluser housing ID comprises a portion of vanes 20 whose inner Lentering edges 2| intersect the baokplate i5 substantially at the juncture thereof with the hub il and extend nearly par- ,allel to the impeller axis. The outer trailing edges 22 of the blower vanes 20 are also substantially parallel to the axis oi rotation of the impeller. 'These vanes define inter-vane passages of relatively high aspect ratio for eil'ective velocity distribution throughout cross sections of the passages. passage is fairly small compared with the length of the leadingr edge of the vane. Integral with the righthand edges of the vanes 20 is a vshroud element 23 whose inner surface 2| is substantially plane and whosel outer surface is dished and runs in clearance relation with an inner skirt portion 2l of the diffuser III. The innermost portion of the shroud 23 is formed as an enlarged bead as at 25 to provide a ring having great strengthy against bursting under the centrifugal loads imposed thereon by high speed impeller rotation.4

It will thus be seen that the shroud 23 and the impeller backplate I8 support themselves and'the vanes 20 against centrifugal force. The impeller passages between the shroud andthe baclrplate.7 are substantially radial which is necessary to" allow of economical distribution of impeller material against centrifugal stress.

That is, the circumferential width of each 28' and 3l are carried by 'spokes Il secured to aring 32' attached to the diffuser housing i0. The ,severaly vanes 28, 2l, and IIL-in cross sectional prole, are concentric withone another and are substantially concentric with the impeller eye in its transition from axial to radialform, the turning vanes gradually increasing in lchord or width toward the impeller axis. Likewise their leading edges are long compared with their relative spacing. It will be apparent that these turning vanes will guide the air toward a radial path in several strata, preventing high velocity near the surface I8 and low velocity near the surface 24. These vanes. being' non-rotative,

are not subject to the effect. of centrifugal force."

. In Fig. 3 a plurality of Vturning vanes u are shown, supported by spokes 3l on the diifuser backplate face I8. The vanes 3l, being of equal.

chord, will have substantially the same drag so as not to upset distribution of air ow to the rotating part of the impeller by drag differences.

In Fig. 4 a plurality of short chord turning vanes Il, 3l and lunare shown, these annular vanes being supported by spokes 4I secured tor the diii'user housing. The vane il is the innermost radially, and upstream from the others,

'while' the vane 4l is outermost and is downstream `of the others. The vanes have a t'urning effect on different annular strata of entering air, the downstream vanes also affecting that air leaving the upstream vanes. The echelon vane arrangement tends to prevent `separation on the convex or. cambered vane sides,4 and laminar flow without turbulence is thus maintained throughout the passage. y

It will be appreciated that forany impeller design the turningvane arrangements may have to be changed and experimented with in order to secure an even pressure distribution between the backplate inner surface Il and the shroud inner surface 2|. Thus, anyone of the ythree vane systems of Figs. 1,- 43, or 4,'may be used The air intake to the impeller, commonly called Athe impeller eye, is deflnedbetween the impeller hub and the shroud innerborder, and entering air must accordingly make a right-angled turn initially, and changed in their adjustment yto secure -the desired' degree of pressure distribution.

The use of backwardiy sloped impeller vanes 20 endows the impeller itself with someLdiifusing action-that is; that air deliveredfat the impeller periphery will have a lower velocity head and a higher pressure head than is obtainable with impellers having radial,` rather than retreating spiral, vanes.

vradial form in order to be adequately supported i against centrifugal force.

The nattenea spokes u, al and u :or un" sev- The tendency of the vanes of f eral types of turning vanes have the functions not only of supporting' the" turning vanes but also of acting 'as axial flow guides tending to prevent rotation of the air mass entering the impeller eye before same has been attacked by the leading edges of the impeller vanes.

While I have described my invention in detailY in its present preferred embodiment, it will be surface of revolution and being staggered successively closer to the impeller axis and disposed more remotely from the`leading edges of said blower vanes.

obvious to those' skilled in the art, after underV standing. my invention, that various changes and modications may be made therein-without departing from thevspirit or scope thereof. I aim in the appended claims to cover al1 such modifications and changes. t

I claim as my invention:

l. In a blower assembly, an impeller comprising a hub element secured to a shaft, the element having a concave surface of revolution,

the outer part of said surface blending into a plane surface, integral blower yanes extendingy therefrom in an axial direction, the inner leading edges of said vanes lying substantially at the junction of the curved surfaceV and plane surface and extending to the impeller periphery. a shroud element radially substantially coextensive with said blower vanes at their other ends, the zone, inward of the vane leading edges comprising the Iimpeller eye, and a plurality of stationary annular guide vanesf in said eye, said guide vanes being curved in cross section in sub- 5 stantial complement to the curvatureof said tion as the first, having both its leading and trailing edges disposed upstream of the leading and trailing edges respectively of the first vane, the

chord of the rst vane being sloped at a greater angle to the impeller axis than the chordof the ysecond vane whereby the air passing from between said vanes influences the airflow leaving the other passages defined in the impeller eye, all of said vanes being spaced more closely to the shroud inner edge than to the impeller backplate, whereby a clear air passage of substantial width,

' unencumbered by vanes, is dened between the impeller backplate andthe innermost turning vane. o AKENITE'I'H CAMPBELL.

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