US2819838A - Centrifugal compressors - Google Patents

Description

Jan. 14, 1958 D. K. WARNER CENTRIFUGAL COMPRESSORS Filed July 23, 1952 This invention relates to the compression of gases in centrifugalcompressors-in which the vanes =a-reslotted :to permitsomeof-thefastest-movingair on-theface of a-blade'to 'slipback to the reverse side thereof tospeed up the.stagnant airthere and thus'give a moreuunifonn flow of .air'into. .thedifl-user -andsoreduce thesonic disturbanceslin .the. diffuser-which reduce efiiciency,-:and,

*by reflection: backto the rotor,-cause =the latter to prematurely crack. These'slots differ vfrom previously disclosed devices in that they are in the trailing portion of the blade instead -of-its'leading portion and instead of reducing the shock loss of -the air-entering the blade prevent-the shockloss-in the "diffuser" from air-velocity changes from supersonic flow to reverse flow, ahead of and behind the blades.

The object of my invention is to prevent the diffuser shocks which are normally reflected back to thick blade tips and thence transferred to the highly stressed inner portion of the blade resulting in cracks and short life.

A continuous flow of air outwardly from all parts of the rotor is essential to prevent diffuser shocks. This type of fiow requires radial blades with thin outer edges and slots inwardly thereof, a short distance, to correct the reverse flow behind the blades. A further object of the invention is to continually increase the air speed in the passages between rotor blades by sharp narrowing of said passages outwardly to the rotor rim, as opposed to the usual constant speed, and to give the trailing edge of both blade and rotor disc a thin trailing edge. A further object is to prevent sonic disturbances reflected back from the diffuser from destroying the edge of rotor circumference.

This objective is attained in two manners, first by slotting the ccrnpressor vanes near their trailing edges to prevent reversal of air flow at the back side of the blade, and second by injecting wet steam into the difiuser passage at a velocity higher than the air velocity leaving the rotor blades and so maintaining flow in the diffuser even if rotor discharge pulsates. The wet steam jet moving only slightly faster than the air entrains air efliciently and the evaporation of the moisture in the steam effects isothermal compression or better depending on the partial pressure of the steam in the air as moisture evaporates. This permits higher pressures w th the same power input and gives cool air to an engine for much greater power output. u

The compressor is illustrated on the drawing m which:

Figure l is an end view of a portion of the compressor above its center line.

Fig. 2 is a section thru 22 of Fig. 1 and Fig. 3 1s a section through 33, Fig. 1.

Similar numbers refer to similar parts in each v1ew.

In Fig. 1 three blades are shown as 1. Their slots 2 leave an airfoil shaped tip portion 3 sloping slightly forward of radial at a positive attack angle as compared with a straight radial blade thereby increasing air velocity over its forward surface 3:1, as well as creating a high velocity outwardly over the rear of its surface 3b. The leading edge 30 of the air-foil-shaped tip portion of the States Patent 2,819,838 .iliatentedsalanail-l 19558 .12 -..blade,isurlirected toward-the rotors.axisvwhilesitstrailing -.:or .outeryport-iongis :.d-ir.eeted-.-.away tfromrthe axisnand slightlyforwardly at :the -.r.otor-?s circumference -.'I he.,blac1es, 1 have: the standard: forwardly: bentside 5 :entranceaand ,are. deeply,.slot-teclsat-that location of-:mini- .,:mum.stress...near :theirauter tip port-io xtpyritheimforrvard ;portion- 11 curving-.backwardlyoat:12; l-:it meetsvtherflat .rear.side..13.aat a, sharp-zed-genm. heeleading edge. 30 ...of.,the.-airfoil shaped t'tip portion-:3.:;is-Ilocated Eforwardly 10.. ,and..outwardly of 14:;3111 \said:. t;ip1;portion',;;is rnearlyi in radiate-ligament with/blade.ilt leavingtithefslot'l between them. The-air ivelocityslosteinrtheislotzwhile increasing (air Yvelocitysat;ihackaofnblade:tisrmere. than: recovered by this forward; slope. tSteaan jetsA fromzeachsideiofidiifuser passage. 5 discharge tverynwetrsteameintorsaidipassagetim- .tmediatelytadjacentitherim; of said rotor.

While; the tconventional; mompressonadenelops-.- cracks .snearrthetzblade roots when operatednat;tspeedsrzattaining --4 /2 .ratios of 1 compressionithi'szis :duecto :the sonic ivibra- 20. .qtions :reflected. basin 1 from the tdi'liusemrwhere; athey. t are vtic-reared-;by thesharpwvariations:inwelocitynofi alLiattfIOnl wand back-10f each-Mane. tliothithe-rrvet:stearmjetaandtme -..sl,ot-tedvanes- .-he1-p -:t0. ere'ducel :these t-sharp sQnio s disturb- @ances wi'thuthet IGStlli'r'thfiir-ihfl. ifanamay'ibez safely :o-perated v .at higher-t speeds: and Wi;thrlfl'IlI1litI3lliI1gl6dg6S ofaweb and znblaideamhe 'lhlnntmiliflgltGClgfistflllltheb enhanceithesflow .1aonditiansrincreasinguefficiencyf bvnthezr'eduetionlzofnd-isturbance. The higher permissible R. P. M. gives an air speed nearer the steam speed so improving entrainment efficiency. The steam added to the air is useful in engines in that it permits higher compression without knock and permits using a premixed fuel-air charge with higher than the usual diesel engine pressures. In the double flow compressor shown, wet steam jets entering oppositely from both sides meet in the center of the passage and thence flow straight down the center thereof permitting little erosion of the side walls, and in the single flow compressor, not shown, the diffuser has an axial-radial slope in order that the steam jets travel through the center of passage. (Instead of the usual straight radial flow from the impeller, the air flows slightly axially and the steam'jets entering from the air input side move down the center of the diffuser passage.)

It is not essential that steam jets be directed into all diffuser passages, it being preferable to direct them only into those passages which carry air to the driving engine. Thus a stall which often starts in one passage and works around from passage to passage will be stopped when it reaches the steam jetted passage. In slotting the vanes I prefer to slot them diagonally as shown at 7 and to extend the slot only to the edge of the large fillet 8 on the forward face of blade where it joins disc 9.

This slot being made where the blade stress is least and where disc and blades are rapidly thinning does not affect the rotor strength. Steam jets entering from both sides keep water in center of passages.

In the diifuser 5 are passages 15 of gradually increasing cross sectional area outwardly where both air and steam are slowed down with resulting pressure increase.

I claim:

1. A centrifugal compressor comprising a housing, a centrifugal impeller mounted rotatably in said housing, said impeller having outwardly extending blades and said blades having sharp leading edge portions directed with rotation of said impeller and radially extending portions attached to said leading edge portions, said radial portions having rearwardly outwardly inclined slots, said slots being located adjacent to the outer ends of said radial portions of said impeller blades and said slots being disposed at the point of minimum stress in said blades whereby said slots provide an outward high velocity air flow stream adjacent the down-stream side of said blade 3 Y tip portion, said housing having a diffuser peripherall disposed about said impeller and said dilfuser comprising a plurality of forwardly inclined walls having sharp leading edges wherein adjacent walls form downstream outwardly diverging flow passages, aplurality of downstream outwardly inclined nozzles in said diffuser adjacent the periphery of said impeller and located between the said adjacent forwardly inclined walls whereby wet steam flowing through said nozzles at a higher velocity 1 than the air leaving the tips of said blades increases the air velocity and aids said slots in keeping the air velocity uniform across the diffuser passage so eliminating shock waves in the diffuser and the reflection of those waves back to the rotor periphery whence in other compressors it is carried back to the blade roots cracking same.

2. In a centrifugal compressor a housing including a diffuser, a rotor including a web portion mounted within said housing, centrally of said difluser, blades mounted radially on said web portion, said blades having thin outer trailing edges, the outer portion of each of said blades being separated from their inner portion and a slot formed therebetween, said outer portion of said blades forming an airfoil shaped section approximating the standard cambered fiat-bottomed-wing airfoil having a leading edge bluntly rounded and directed inwardly and located forwardly relative to said rotors rotative direction and outwardly of the trailing edge of the inner portion of said blade, said inner portion being swept back and outwardly terminating in a thin trailing edge in line with the blades rear surface, said outer portion being the portion of the said blade which is radially outwardly beyond the inner portion with said slot therebetween, and said outer portion commencing at location of minimum stress in said rotor close to the rim thereof, whereby air flows rearwardly outwardly through the slot so preventing inward flow of air behind the tip portion of said blade and whereby the resulting sonic bangs in said diffuser are avoided which in blades without such outwardly located slots are transmitted back through said blades to the inner highly stressed portions thereof causing cracks.

3. A compressor as set forth in claim 2 in which said airfoil-shaped tip portion has a positive attack angle with respect to the radial direction of the inner portion of a blade whereby velocity lost by air passage through said slot is regained.

References Cited in the file of this patent UNITED STATES PATENTS 1,075,300 Moss Oct. 7, 1913 1,383,354 Wareing et al July 5, 1921 1,622,930 Von Karman et a1 Mar. 29, 1927 2,228,194 Birkigt Jan. 7, 1941 2,314,572 Chitz Mar. 23, 1943 2,399,072 Thompson Apr. 23, 1946 2,576,700 Schneider Nov. 27, 1951 FOREIGN PATENTS 162,580 Germany Sept. 21, 1905 226,523 Switzerland July 16, 1943 571,750 France Feb. 8, 1924

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