US2983434A - Turbocompressor - Google Patents

Description

May 9, 1961 P. PISA 2,983,434

TURBOCOMPRESSOR Filed Dec. 24, 1957 7 Sheets-Sheet 1 INVENTOR.

May 9, 1961 Filed Dec. 24, 1957 P. PISA 2,983,434

TURBOCOMPRESSOR 7 Sheets-Sheet 3 4 i 2 Q Ir 10 g I; P

PtETRo PISA INVENTOR.

BYM/MM AIME/V575 P. PISA TURBOCOMPRESSOR May 9, 1961 7 Sheets-Sheet 4 Filed Dec. 24, 1957 Puzmo PISA INVENTOR. Bark/WM, MUM

ATTORNEYS P. PISA TURBOCOMPRESSOR May 9, 1961 7 Sheets-Sheet 5 Filed Dec. 24, 1957 PIETRO PISA INVENTOR. BYMMM MQM A TTORA/E/S P. PISA TURBOCOMPRESSOR May 9, 1961 '7 Sheets-Sheet 6 Filed Dec. 24, 1957 PIETRO PISA INVENTOR. Ba k/M WM P. PISA TURBOCOMPRESSOR May 9, 1961 7 Sheets-Sheet 7 Filed Dec. 24,

United States Patent TURBOCOMPRESSOR' Pietro Pisa, Via di Casaglia, Bologna, Italy Filed Dec. 24, 1957, Set. Np. 704,975 5 Claims. (Cl. zen- 124 The present invention relates to a turbocompressor of centrifugal type, wherein the diffuser is movable instead of being stationary, said diffuser revoluting in reverse direction with respect to the centrifugal impeller, with the purpose of obtaining a high pressure for the air by its passage through said two subsequent elements forming one stage of the turbbcompressor. I

The relativeinflow speed, or air flow speed through the ducts, is therefore the sumof the high peripheral speeds of the centrifugal impeller and of the diffuser rotating in the reverse direction, while a low outflowspeed is obtained and therefore-a great amount of kinetic energy is converted to pressure.

The air path through the turbocompressor is part-way radial and part-way axial, and the shape of the machine issomewhat similar to that of -a centrifugal turbocompressor.- I a A feature of the contra-rotating dilfuser resides in that it keeps unaltered the efficiency when-the number of revolutions changes, in that the air moves always therethrough withoutstriking the blades and the flow defining walls. The machine, in onesimple embodiment given only by way of example is shown in the attached drawings, wherein: I

Fig. 1'is an axial cross-sectional view of the turbocompressor according to the invention;- t

Fig. '2 shows in enlargedfscale the details of the-conis transmitted from the impeller to the facing difiuser' (Figs. 1, 2, 4 and4a), I The air which comes fromthe intake 9, and moves in a mainly axial direction, is first radially deflected through the ducts of the centrifugal impeller 2 and its axial flow is then'restored at the outlet from said impeller (Figs. land 2). v

The direction changes are obtained in the impeller with great radii of curvature.

The air enters the contra-rotating diffuser in axial direction, then the air stream is deflected by the difluser blades towardthe rotation axis, and finally an axial flow direction is restored at the outlet from the machine (Figs. 1 and 2). The path of the ducts of the impeller 2 is very similar to that found in'the centrifugal compressors where the blades 10-have a radial direction (Figs. 1 and 3).

The air stream through the contra-rotating diifuser has however a different shape, in that said stream progressively comes nearer to the center 0 of the diffuser while moving through ducts defined by spiral shaped blades 11; (Fig. 3a). Theseducts'have attheir outer portion a narroW'cross-sectional inlet area (almost tangential inlet), said area continuously-increasing while nearing to the center due to change of'dire'ction (almost radial outfl'ow+-Fig. 3 a);

The progressiveincrease of the cross-sectional passage area causes a slowing down of the air stream and there fore an increase of the pressure. The inflow velocity into the-diffuser ducts is high, for being equal to the sum 7 of the two equalandcontrary peripheral velocitiesj of the impeller and of the diffuser, respectively, while the nection between the'cent-rifugal impeller and the contrarotating diffuser; t

Fig. i 3' is a cross-sectional view taken al'ong line IIIIII of Fig. 1;

Fig; 3a is" a cross-sectional='view taken-along line Fig. 4* is a cross-sectional view taken I V IVmt Fig.1; a Fig. 4a is a cross s"ectional view'taken IVaIVa of Fig. 1. I

along s.

gl-lig. 3 5 shows: graphs 'ora velocity tr'iangle's} 'fo 'rmedE Figs. 6a, 6b and show the's'hape' o-f" he bottom-walls of thei contra rotating diffuser. Iii r The shaft: 1 is' actuated rea m-the: en of the machine corresponding to the outlet manifoldg slai'd shaft is-"s'fip= ported attits en'ds and'in nt'erfnediate zone-(Fig ly u Aicent rifuga'l impeller '2 s keyed to said driving 's'haft,

while the' contr'a-rotating "diifuser 3, fa'cing the impeller and co-axial with said impeller, rotates -oiifwsleeve '4 i n which is; held sta'tionary'fin' that it f'is rigidly connected to-the"compressorshell*(Figs, 1 andZ),i i Both"the impeller" 2 and the contra=rotatingl difiuser threade'd'to the sleeve} (Figs. 1 man." .1;

shaft- '1 re sleeve sup 99m difeQtidfiS-E h re Qtthe it 4 mm 7 outflow 'veloc ity'is low, owing to the, remarkable increase of the passage-eross-sectional area (Figs. land 2).

last portion ofthe contra-rotating diffuser 3 directly con tact's the -statio'nary walls of'the case 12 within'which glides; through suitablejackets 13,'t he cooling water, the inlet and the outlet of which are formed by the'fittings 14 (Figs. 1, 3 and 3a).

- The blades" 10' o'ffthe' impeller 2 haveno outer connecting :wall (open ducts) while, for constructional and s'tu'rdin'es reasons,--the blades 11 of thecontra-rotating 'diihiser fii near'to the inlet zone are bodily connected to a cone shaped 'conneeting' wall o'router shroud "ring 15 (Figs. 1, 2 an'd s p 1- 'Fhe'se two movable members are sufliciently compact to withstand both the stresses of the centrifugal force and the moment or st-ressthat said members must impart to the' ai-r stream (blade pressure); 'Ihe'axesof both the impeller-I and the" contra-rotating diflus'er 3"arecoinci dent; itis'; however, tobe noted-that these two members are co-axi-al but do not rotate above one another (Figs: Ira 1:2, I 1 1 i he sleev "4, by ne intervenfiqn of roller-bear supports: the inter ediate portion f the driving" orts the hell w-shaft 16 of the difius er also in thisease by the intervention" f roller Bearings (Figs: lila'lldlz 1 a L 'J. I. .;.-I The s1eeve 4; which-carries at ifits free end the spider 51ca'rrying ithe intermediate bevel pinions 8, 'must. bfe

t a t'o th'e pinions8(twist"moment);' Thisstres'sfis v the driving momentappliedbythe impeller 2t catedffland itm-usit withstand the stress imposed b'evel gea'r .6: and '7,,respectively 1, audio);-

"Thie's'l'eeve. is provided,;. at its end remote from' the,

ta a blades 20,; rigid.- or, integral; Wi hI-said tinge-11, V

Theair' streammoving throughthe impeller 2 and the.

ed ther n, while the outer surfaceofs'aid ;du ,.to "t e. I v a p I contra-rotating difluser .3"by,1m eansof the'respective the 'sprocket'8' mounted by thestationary spider' 5 scr'iew i 3 bear against the inner walls of the shell 12 compressor (Figs. 1 and 2).

The shell 12 is comprised of two halves' and may be opened along a horizontal plane (Figs. 1, 3, 4 and 4a). Both the fore cover, carrying the intake 9, and the rear cover 19,'carrying the outlet manifold 22, are fastened to the shell 12, when the latter has been closed, andsaid two covers, by means of the cast vanes 23 and 24 .are rigidly connected to the supporting hubs for the driving shaft 1, at its ends, also in this case by the interposition of ball bearings and thrust bearings for adjusting purposes, as shown in Figs. 1 and 2. The operation of the turbocompressor is evident from the velocity triangles of the air stream and of the movable members (Fig. 5).

The air reaches the impeller from the intake with an absolute inflow velocity G which, when composed with the inner peripheral velocity-U gives, as resultant, the relative inflow velocity W (Fig. 5).

The stream is moved, by the centrifugal force through the conduits of the impeller 2 defined between the blades which have a perfectly radial direction. The air outflows in axial direction, the deflection of the stream be ing obtained by the curvature of the walls of the shell of the turbo- 12 and of the impeller 2 (Figs. 1 and 2). The relative outflow velocity W is less than the outer peripheral velocity U and than the relative inflow velocity W as readily seen from Fig. 5.

The air pressure increases due to the effect of the centrifugal force (proportional to the difference of the squares of thevelocities) and due to the slowing down ofthe flow speed through the ducts of the impeller.

The stream leaves the impeller 2 with an outflow absolute velocity C which is the resultant of the outflow relative velocity W and of the outer peripheral velocity U of the impellenas shown in Fig. 5. The velocity C has a certain inclination with respect to the inlet plane of the diffuser and passes through said plane. (The peripheral velocities U as well as the relative velocities and the absolute ones, are calculated on the base of the medium radius of the inlet and outlet cross,- sectional areas of both the impeller and the diffuser).

As the contra-rotating diffuser 3 has a peripheral velocity U equal and contrary to the velocity U of the impeller 2, the relative inflow velocity W in the diffuser is given by the resultant of the absolute outflow velocity C from the impeller 2 and;of the peripheral -U (with the inverted sign) proper of the contrarotating difiuser 3, as shown in Fig. 5.

Therefore the inflow relative velocity W into the diflfuser will have a very remarkable value, as it is to be noted from Fig. 5, said value being the sum of the peripheral velocities of the impeller and of the difluser.

-The relative inflow velocity W will therefore have a small inclination (angle 'yFig. 5) with respect to the rotation plane of the inlet cross-sectional area of the diffuser. a

Fig. 6 shows as by a graphical method has been found the inclination 'y with respect to said plane that the corner or common line between the convex wall (back wall) of the blades 11 makes with the bottom conical Wall of the shroud ring 15 of the difiuser (Figs. 1 and 2). Byv

the projections method for six points of the blade backside, as illustrated in Fig. 6a, said points being decreasingly spaced apart from the center 0 of rotation, the corresponding axial depths have been found, as shown in Fig. 6 in thickened lines, .for theducts defined by the spiral shaped blades and the bottom conical wall of the difiuser. v

These segments begin at, the right-hand zone of the line b-b, as it will be seen in Fig. 6b, while in the righthand zone there is' the inlet zone of the difiuser, where the blades 11 presentto the air stream a very sharpened edge, in order to avoid any impact in the inlet stream (Figs. 1 and 2). Taking the distances 0-l, 0-2 and soon, as abscissae and the corresponding segments" 1, 2

and so on, as ordinates, the line or corner common to both said walls has been plotted as shown in Fig. 6c, said corner presenting with respect to the rotational plane the same angle 7 that makes the inflow relative velocity W when entering the diffuser. This line or corner represents the profile of all the conical bottom wall of the diffuser which is therefore tangent at any point to the inflow relative velocity W1 Having thus avoided any shock of the stream against the bottom wall of the diffuser, the air is progressively I deflected towards the rotation center 0 by the concave wall of the spiral shaped blades 11, as shown in Figs. 2 and 3a. The air issuing from the impeller due to both its own velocity and the velocity of the difluser moving towards said air, is very quickly picked up by the diffuser.

Through the diffuser ducts, having a progressively increasing cross-sectional area, the air flow velocity is progressively slowed down, and therefore a remarkable conversion of kinetic energy into pressure occurs, which is proportional to the differential between the squares of the inflow and outflow relative velocities W and W respectively. I

In the contra-rotating diffuser, the return stream, directed from down upstream, i.e. the airj amount tending to escape along the edge 25 (Fig. 2) is held by the extended outer wall of the conical ring 15 which glides with a small clearance against thewall of the shell 12.

At the end of the hub 16 of the contra-rotating diffuser 3, along the flat wall faced to that of the stationary sleeve 4, i.e. at the portion 26 (Fig. 2), the necessary clearance originates an air leakage, said air tending to move in reverse directionthrough the passagebetween the hub 16 of the diffuser, and the outer cylindrical sur face, on which the difiuser rotates (Fig. 2). The air enters, therefore the space comprised between the conical dise27 of the impeller and the inner disc 28 of the dif-. fuser, best shown in Fig. 2, within said space being received the bevel ring gears 6 and 7, as well as the pinions 8 (Figs. 1 and'2).

In order to reduce this leakage, a labyrinth seal is carried by the flat edges of said two discs, said seal being formed by the insert rings 29 projecting from the disc 27 and entering the registering grooves provided in the faced disc 2 8, as clearly shown in Fig. 2.

These rings are made of antifriction material, so that they originate a little, friction resistance and are easily replaceable.

For concision, the turbocompressor according to the present invention, has been disclosed with a single compression stage, while it mustcomprise at least another subsequent stage, in order to obtain that. high compression feature which is the main feature of this great debelow the normal rating.

livery compressor.

In this case, between the first and the second .stage,

an intermediate cooling stage, must be provided,,obtained I by extended walls which are. cooled from outside by Another feature of thepturhocompressoraccording to the present invention. resides in thatthis machine-keeps almost unchanged its efliciency, i.e. this turbocompressor affords the elimination of any shock of the air stream against the blades and the difiuser walls when the number of revolutionsper minute ofthev machine falls down,

'In fact, from the examination of'the velocity triangles, it is evident that for a lower number of revolutions,-theperipheral velocities of both the impeller and the difluser equally decrease due to the existing connection, and therefore also the absolute and relative velocities of the air stream at the inlet and at the outlet of the V difiuser, proportionally are changed.

The new velocity triangles, which are thus obtained, aresimilar to those obtained in the normal operation and-therefore remains unaltered the inclination'y'to be provided for the bottom wall of thecontra-rotatingdiffuser.

At parity of obtained compression, the machine according to the present invention rotates at a lower number of revolutions per minute (about one half) of the number of revolutions necessary in the conventional turbocompressors according to the prior art, with an obvious advantage due to the reduced stresses produced by the centrifugal force. The turbocompressor according to the present invention, having the features of a high compression and a great delivery, besides having a minor number of stages or passages, in comparison with the prior art machines, has been disclosed in the at-' tached drawings only by way of example.

What is claimed is as follows:

1. A turbocompressor of the centrifugal type, which comprises in combination a casing having an intake therein and an outlet therefrom, a driving shaft rotatably mounted in said casing for rotation around an axis of rotation, an impeller mounted on said driving shaft within said casing, a diffusor rotatably mounted for rotation around said driving shaft and within said casing, gear means connected between said impeller and said diffusor for rotating said diifusor in a direction opposite to the direction of the rotation of the impeller and at the peripheral speed equal and opposite to the peripheral speed of said impeller, said impeller having a plurality of blades therein defining a first plurality of ducts each having an inlet and an outlet, and said diffusor having a plurality of blades thereon defining a second plurality of ducts each having an inlet and an out let, the inlets to said first plurality of ducts'being at the said intake of said casing and the outlets of said second plurality of ducts being at said outletfrom said casing, and the outlets of said first plurality of ducts being opposed to the inlets to said second plurality of ducts, said first plurality of ducts extending away from the axis of rotation in a plane with the axis of rotation and an angle to the axis of rotation, said first plurality of ducts having a cross section gradually decreasing from the inlet toward the outlet of the ducts, and the ducts of said second plurality of ducts curving spirally inwardly toward the axis of rotation in the portions thereof adjacent to the outer periphery of said diffusor and curving toward a direction which is substantially parallel to the axis of rotation, having a cross section which increases from the inlets toward the outlet, the inclination of the spiral portions being at a small angle to the plane of the face of the said difiusor in the initial section of the spiraland at the greatest inclination in the final section of'thespiral toward the outlet of the ducts. f

2. A turbocompressor of the centrifugal type, which comprises in combination a stationary casing, a front cover on the said casing and having an air'intake therein, a rear cover on the said casing, an outlet manifold for the air attached-to said cover, a stationary sleeve fastened at one'end to the said casing and tothe said rear cover and rigid with the rear cover and extending into said casing, a driving shaft rotatab-ly mounted in the said sleeve for rotation around an axis of rotation, an impeller mounted on the said said second plurality of ducts,

driving shaft Within 6 let, said dilfusor comprising an inner disc, an outer disc and a plurality of blades therebetween which define a second plurality of ducts each having an inlet and an outlet, the disc of the said impeller and the inner disc of the said diifusor having edges which are opposedto each other and delimitate a chamber wherein the said spider is contained, a first gear ring fastened to the disc of the said impeller and engaging the said sprocket mounted on said spider, a second gear ring fastened to the inner disc of the said diifusor and engaging with the said sprocket mounted on the said spider for rotating said diffnsor in a direction opposite to the direction of the rotation of the impeller and at a peripheral speed equal and opposite to the peripheral speed of said imjeller, the second plurality of ducts of the said diffusor registering'during rotation with the said first plurality of ducts of the said impeller and receiving from the said first plurality of ducts of the said impeller air having a speed equal to the sum of the peripheral speed of the said impeller and the said diffusor.

3. A turbocompressor according to claim 2, wherein the disc of the said impeller and the inner disc of the said diffusor have a labyrinth seal therebetween closing the chamber delimited by the last mentioned discs, said labyrinth seal 'comprisinga plurality of rings fixed in the edge of the impeller disc, said inner diffusor disc having a plurality of grooves in the edge, said rings extending into the said grooves and sliding therein during rotation of said impeller and said diffusor and reducing the leakage therebetween.

4. A turbocompressor as claimed in claim 2, wherein said first plurality of ducts of the said impeller extend away from the axis of rotation in a plane with and at an angle to theaxis of rotation, said first plurality of ducts having a cross section gradually decreasing having a cross section which increases from the inlet toward the outlet, the inclination of the spiral portions the said casing, a spider fastened to the portion of the said sleeve within said casing and spaced frorn said one end of the sleeve and leaving a the said spider, a diffusor'rotatably mounted on the said intermediate free portion'of said sleeve, said r-impeller comprising a disc and a plurality of blades defininga first plurality of ducts each free intermediate portion on the said sleeve, a sprocket rotatably mounted on having an inlet and an outbeing at a small angle to the plane of the face of the said-dilfusor in the initial section of the spiral and at the greatest inclination in the final section of the spiral toward the outlet of the ducts. I

5. A turbocompressor as claimed in claim 4, wherein the spiral shaped blades of the diffusor have greatly tapered edges in the inlet zone to avoid shocksin the inflowing. air stream, and have very sharp'edges in the outlet zone to avoid eddy movements in theair stream leaving the ducts of the ditfusor, the central portion of the said blades of the difiusor being thickened for rigid connection between the inner and outer discs of said diffusor;

2,318,990 Doran. May 11, 2,344,366 Price a M31114, 1944 2,575,682 Price Nov. 20, 1951 2,620,624 Wislicenus' Dec. 9," 1952 2,853,227 Beardsley. Sept. 23, 1958 FOREIGN PATENTS 1 7 539,882 France Apr. 8, 1922 621,065 Great Britain Apr. 4, 1949 706,213 1941 7 Germany -a May 21,

from the inlet toward the outlet of the ducts, and the ducts of said ducts in said diifusor curving spirally

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