US 2656096 A
Description (OCR text may contain errors)
Oct. 20, 1953 M. G. SCHWARZ CENTRIFUGAL PUMP AND COMPRESSOR 5 Sheets-Sheet 1 Filed Dec. 27. 1946 \D 5 g 5 v m k .J
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Oct. 20, 1953 M. e. SCHWARZ CENTRIFUGAL PUMP AND COMPRESSOR 5 Sheets-Sheet Filed Dec. 27, 1946 'FigS INVQNT'OR Oct. 20, 1953- M. G. SCHWARZ CENTRIFUGAL PUMP AND COMPRESSOR Filed Dec. 27, 1946 Y 5 Sheets-Sheet 4 uwlmv l /l. 3 WM 7 i z? 7 W h u 2 Iv y i a 4 w H M Ml V6? n fl ATTORNEYS Oct. 20, 1953 M.- G. SCHWARZ 2,656,096
CENTRIFUGAL PUMP AND COMPRESSOR Filed Dec. 27, 1946 5 Sheets-Sheet 5 Fig.7
H Patented Oct. 20, 1953 CENTRIFUGAL PUMP AND COMPRESSOR Marcel G. Schwarz, Paris, France, assignor to Societe Rateau (Societe Anonyme), Paris,
France, a company of France Application December 27, 1946, Serial No. 718,798 In France January 4, 1946 Claims. 1 It is a well known fact that centrifugal pumps and compressors include chiefly in their more recent form: a distributor which directs the fluid stream in the desired direction providing a smooth inlet into the wheel, the centrifugal wheel proper wherein the mechanical energy provided appears simultaneously under its potential and its kinetic form and lastly a diffusing member generally followed by a delivery pipe inside which the major part of the kinetic energy available at the output of the wheel is transformed into potential energy.
Numerous improvements have been already proposed for reducing to a minimum the losses affecting separately the different transformations of energy of which the centrifugal pumps and compressors are the seat. However the quantitative examination of the different losses proves in particular that the diffuser inside which the flow of fluid is produced with a damping of the speed shows comparatively high losses.
The object of my invention consists in reducing to a minimum the internal losses of the centrifugal pumps and compressors and more particularly those occurring in the diffuser. It consists chiefly in designing means for removing the boundary layers having a reduced energy, and which are formed on the stationary walls of the diffuser, preferably in combination with means adapted to regularize the flow inside the wheel itself and inside the intake thereof.
A further improvement in the efficiency may be obtained by recovering the energy contained in the fluid removed from said boundary layers. This recovery may be obtained either by using the energy as it is or by increasing it so as to bring it to a higher level, according to the point at which it is desired to reintroduce into the circuit of the pump or compressor the fluid that is removed from the boundary layers.
In the following description and corresponding accompanying drawings there are illustrated by way of example forms of execution of the invention. In said drawings:
Fig. 1 shows in partial cross-sectional view a diffuser for a compressor and the boundary layers that form in contact with the stationary walls of the diffuser.
Figs. 1a and 1b are illustrative curves of the speed and pressure of fluid flowing through the diffuser.
Fig. 2 shows a form of execution of the invention with a partial exhaust of the boundary layer as applied to a diffuser with parallel side walls.
Figs. 3 and 4 show further forms of execution of my invention as applied to a diffuser with diverging walls.
Fig. 5 is an axial half cross-section of a pump or compressor and shows recovering means for part of the residual energy contained in the fluid removed from the boundary layer and returned through injection into the intake of the pump or compressor.
Fig. 6 illustrates a modification wherein the recovery is obtained by admitting the amount of fluid removed into an intermediary point of the compression stage in a movable wheel.
Fig. '7 is a cross-sectional view of a modification.
Fig. 7a is a similar view of another embodiment.
Fig. 8 illustrates diagrammatically an arrangement for increasing the energy contained in the fluid removed for ensuring its introduction at the delivery end of the pump or compressor.
Lastly Fig. 9 shows the manner of using the removed fluid with a view to applying it to auxiliary purposes such as the cooling of a gas turbine when the compressor forms part of a motor group including such a gas turbine.
Returning to Fig. 1 it shows the cross section (by a plane passing through the axis of the pump or compressor) of a flat diffuser without any blades located at the output of a centrifugal wheel; a designates the periphery of a removable wheel, I) and c the side walls of the diffuser which are supposed to be parallel and d the delivery pipe. By reason of the friction of the fluid stream over the walls b and c of the diffuser and of the viscosity of the fluid, there is established perpendicularly to the walls a distribution of speeds illustrated in Fig. 1a which is a cross section through XX. The speed is zero in the immediate vicinity of the wall and reaches substantially the speed 1) of the sound flow only at a pertain distance from the wall. The layers of fluid which are slowed down in the vicinity of the wall show therefore only a reduced kinetic energy which is not sufiicient for producing the increase in pressure which is sought for in the diffuser. Experience shows that the thickness of these boundary layers increases along the wall together with the damping of the flow as occurs in a diffuser. Fig, 1 shows the boundary layers e and f as illustrated by cross-hatched zones and it is found that the presence of these layers fills up more and more the cross sectional area available for the flow inside the diffuser which hinders thus the desired damping. Fig. 1b illustrates the increase in pressure Ap which would be obtained if the distribution of speeds were uniform throughout each cross-section of the diffuser in the absence of any boundary limit as shown by the curve m, l, 12. while the increase of pressure Api actually obtained in practice is given out by D. q. Thus the boundary layers initiate a reduced damping in the diffuser and moreover through a non-reversible exchange of moment between the fluid streamlets advancing at difl'erent speeds, they produce frictional losses which reduce the eiflciency of the difluser and consequently that .of the pump or compressor. Their importance may become such that the flow may break away from the diffuser walls and increase thereby the losses of efllciency.
According to my invention the above disclosed drawbacks are removed by providing in the side walls of the diffuser at suitable locations exhaust ports or openings for the fluid contained inside the boundary layers. Fig. 2 shows by way of example and by no means in a limitative sense a form of execution of the invention as applied to a diffuser with parallel side walls. The arrangement includes then annular slots i, 2 and 3, 4 located at one or more pressure levels. The slots open into collecting chambers 71., i, 7', k. The output of the boundary layers reaches altogether only a few hundredths of the total output of the pump or compressor and it is important that the output of these slots may be limited to the value strictly required for this purpose. The discharges of the collecting chambers h, i, a, k which may be interconnected when the corresponding slots lie on the same pressure level are adjusted either through diaphragms or valves or through any other members playing the same part, so that the output flowing through said chambers is not higher than the output of the boundary layers.
Of course the ports for taking off the fluid from the boundary layers may be constituted by slots, bores or slots of any suitable shape and kind. In practice it is possible to obtain a satisfactory result by providing a partial removal of the boundary layer from a single pressure level, which latter is located preferably at a point corresponding to an increase between the first third and one half of the theoretical increase in pressure inside the diifuser.
By reason of the compression already produced inside the wheel and inside the fraction of the diffuser preceding the exhaust slots for the boundary layer it is always possible to find inside the apparatus a point at a lower pressure allowing the exhaust towards said point of the fluid which it is desired to remove. In the case of an air compressor, the adjusted exhaust of the boundary layer may be performed directly into the outer air (Fig. 2); when the fluid circulating is a gas, a vapour or a liquid, the exhaust may be provided into the suction pipe or intake of the apparatus to which are connected the collecting chambers so that the fluid of the boundary layers is automatically sucked out from the diffuser. In particular in the case of an air compressor forming part of an arrangement including gas turbines, the flow of air produced by the exhaust of the boundary layers may be used directly for cooling the stationary and movable blades and wheels of the gas turbine or turbines.
Of course, rm; invention is applicable to diffusers of any type or shape. In the case of diffusers with blades or blade carrying grids, the blades may be hollow and include intakes for the boundary layers at one or more suitable pressure levels. Fig. 3 ShOWs how the invention is applicable by way of example to the hollow blades of a difluser made of sheet metal, the removal of fluid being performed at a single pressure level. Each blade ki, k2, k3 etc., is hollow and is mm vided at 1-2, i-2 with exhaust slots through which the fluid from the boundary layers ma? enter said blades. At the same time the blades show a transversal bore SS, communicating with the slots t provided in the lateral walls of the difiuser. The exhaust arrangement includes then as above one or more collecting chambers into which open the bores S and the slots 1. while means are provided for adjusting the output of the fluid and channel for the final exhaust into a point at a lower pressure level.
Lastly, as the invention disclosed prevents any premature breaking away of the fluid, it is possible, as shown in Fig. 4, to give a larger divergency to the side walls of the difiuser in a meridian plane, which allows increasing the damping without increasing to an exaggerated extent the transversal bulk of the device. The removal of the boundary layer of the difiuser is executed at y, z with a return of the exhausted flow into the suction end, with an adjustment obtained for instance through a valve or.
The efiiciency of the arrangement described requires that the fluid stream at the output of the wheel may be as homogeneous as possible; the invention is therefore applied preferably in combination with the known means satisfying said condition such as for instance a movable wheel with a sufllciently large number of blades. movable or stationary distributors providing 'or an inlet into the intake of the movable wheel without any shock or breaking away. The invention is also applicable to all diilusers whatever may be the rate of flow, either underneath or above the speed of sound.
Lastly, when the pump or compressor is of th multistage type, it is possible to apply the invention to any of the stages considered separately, the exhaust of the boundary limit of a diffuser stage being performed for instance into the suction intake of said stage.
The comparatively low amount of fluid circulating and removed from the boundary limits along a wall of the diffuser in accordance with the above described features incorporate still a certain amount of potential energy which is of the same magnitude as that contained therein at the rutput of the movable wheel, while it is lower than that of the fluid in the sound flow at the output of the diffuser by reason of the internal friction afiecting it in the diifuser. This residual energy is lost when the fluid taken oil the boundary layer is exhausted either into the free air or in the absence of any particular contrivances, into the suction end of the pump or compressor.
In accordance with the invention, it is possible to recover a fraction of the fluid energy removed from the boundary layers of the diffuser and to communicate said energy either to the fluid to be compressed under its aerodynamic or hydrodynamic form or else mechanically to the movable member of the pump or compressor.
Fig. 5 shows by way of example and by no means in a limitative manner a first form of execution of such energy recovering means; it shows cross-sectionally a fan constituted by a suction pipe III, a movable wheel ll provided with blades a and a diffuser d with its collecting volute d. The diffuser d is provided with two annular slots I and 2 through which it is possible to remove the boundary layers formed against the wall of the difluser. The fluid thus collected in the two chambers h, i into which open the annular slots is then removed by the pipes l2 and 13; thus the fluid output is adjustable for instance by a valve H and is finally led under pressure into an annular chamber l5 surrounding the suction pipe of the fan. The residual energy is then partly recovered and transmitted to the fluid circulating in the fan through an annular nozzle IS with an exchange of momenta as in the case of a waterblast. The annular nozzle'may moreover be provided with directing blades H, which gives the fluid returning towards the suction end the correct direction for ensuring a smooth inlet into the movable wheel.
When the fan wheel includes no flange on at least one of its sides, the preceding arrangement may be improved by feeding the fluid removed from the boundary layers of the diffuser into an intermediary point of the movable wheel as illustrated in Fig. 6. As a matter of fact, the pressure in the wheel increases when the circulating fluid is considered further away from the axis of rotation. It is then sufllcient to return the fluid removed from the boundary layers into the wheel through an annular slot located at a distance such from the axis of rotation that the pressure inside the chamber preceding the annular slot may be sufficient for allowing the reintroduction of the removed flow into the pump or fan wheel along a suitable direction, ensuring an input without any shock on the wheel blades.
Fig. 6 illustrates by way of example a form of application of the invention to a blowing engine with two symmetrical fluxes; the engine includes 2 two suction pipes l0, III", a wheel ll carrying the blades (1', a" without any lateral flanges, a difliuser d with parallel or even diverging walls and lastly a delivery pipe d. The arrangement for removing fluid from the boundary layers of the diffuser may be executed as precedingly through two annular slots I, 2 and two collecting chambers h, i. Each collecting chamber is connected through a pipe with a distributing chamber l5, l5" which allows the reintroduction of the exhaust flow into an intermediary point of the movable wheel through the annular slots 16', I6" provided with directing blades giving the fluid the desired direction for a smooth entrance into the wheel. The exhaust output is adjusted to its optimum value through the valves II' III.
Obviously, the method for executing the invention may include fluid tappings from the boundary layers of the diffuser at different pressure levels or stages, the preceding arrangements being applied individually to each tapping.
According to a further form of application of the invention. the residuary energy of the fluid taken off the boundary layers of the diffuser may be recovered mechanically, the power thus obtained being restored to the shaft or the movable wheel of the centrifugal pump or compressor. Fig. 7 illustrates such a form of execution wherein the fluid removed from the boundary layers of the diffuser is caused to expand down to the suetion pressure of the pump or compressor on an annular arrangement of turbine blades rigid with the wheel of the apparatus.
The fluid removed from the boundary layers in the diffuser is collected in the chambers i, 1 and the pipes l2 and I3 and is then led into the distributing torus 20 of a turbine including annular nozzles 2|, the cross-sectional area of which corresponds to the optimum output of removed fluid while an annular arrangement of movable receiving blades 22 is carried by the movable wheel ll of the pump or fan rotor. It is always possible to give the nozzles and movable blades of the turbine an outline such that the pressure and direction of the fluid streamlets at the output of the annular arrangement of movable blades 22 may be those which are to prevail at the inlet of the blades of the pump or fan wheel. This embodiment is given by way of example but it is also possible to imagine a separate recovering turbine connected with a movable member of the pump or compressor through any known or suitable coupling means while the exhaust is fed for instance into the suction pipe of the pump or compressor for instance.
Fig. 7a illustrates an embodiment of this kind wherein the pipes l2 and I3 feed the fluid removed from the boundary layers into the admission torus 20a of turbine of which the wheel 22a is keyed to a shaft 22b forming an extension of the shaft carrying the wheel ll of the fan.
According to a different embodiment of the invention, it is possible to incorporate to the amount of fluid removed from the boundary layer the additional energy which it is lacking for allowing said amount of fluid to be brought into the delivery pipe of the pump or compressor. Fig. 8 illustrates diagrammatically the corresponding arrangement. The fluid removed at l or 2 from the boundary layers of the diffuser d of the compressor is urged through a small auxiliary compressor 23 into the delivery pipe 11' at the outlet of the diffuser. The auxiliary compressor may be of any type whatever whether of the piston, centrifugal or any other type and its output will be only a few hundredths of that of the main compressor. It may be driven by an auxiliary motor the speed of which is variable or otherwise or else by a mechanism connected with the control mechanism of the main compressor so as to ensure a predetermined correspondency between the rotary speeds of the main and auxiliary compressors.
Lastly, andaccording to a further form of execution of the invention, the amount of fluid removed from the boundary layers of the diffuser may be used directly for auxiliary purposes such as the feeding of the fluidtight packings located along the compressor or pump shaft, the lubrication of the bearing through emulsions etc. A particularly interesting application consists, in the case where the air compressor forms part of a motor group incorporating a gas turbine, in making use of the fluid removed from the boundary layers of the centrifugal compressor orcompressors for the cooling of the bearings, shafts,
wheels or blades of the gas turbine or turbines. Fig. 9 shows diagrammatically such an embodiment. The gas turbine engine in its simplest form is constituted by a centrifugal air compressor H, one or more combustion chambers 24 and an expansion turbine 25. The air removed from the annular slots I and 2 on the walls of the diffuser or of the compressor is fed through the pipes 26 provided with valves 21 for adjusting its output into the wall of the wheel 28 of the turbine for taking a part in the cooling of said wheel.
In the preceding application, only one compression stage in the centrifugal pump or compressor has been considered; however the features described are applicable separately or together to the different stages of a multicellular centrifugal pump or fan.
What I claim is:
1. A centrifugal machine of the type disclosed, comprising an impeller, a diffuser at the discharge end of said impeller, including two opposed substantially planar walls, slot-like passages through both of said opposed walls, the passages through one of said walls being in register with corresponding passages through the otherof said walls, connecting means between corresponding pas sages, piping means between said connecting means and a zone upstream of said discharge end, and means for adjusting the cross-section of said piping means.
2. A centrifugal machine according to claim 1 in which the connecting means are fluid-tight chambers located exteriorly of said difluser.
3. A centrifugal machine according to claim 1 in which the walls of the diffuser are formed of two opposed annular flanges around the periphery of the impeller, and each passage extends over at least part of a circumference coaxial with said impeller.
4. A centrifugal machine of the type disclosed, comprising an impeller, a diffuser at the discharge end of said impeller, including two opposed substantially planar walls, slot-like passages through both of said opposed walls, piping means for connecting said passages to a zone upstream of said 25 impeller, nozzles at the outlet of said piping means into said zone, said nozzles being annularly distributed around the rotation axis of said impeller and being directed parallel to said axis and a turbine wheel coaxial and fast with said impeller, said wheel including blades located opposite said nozzles.
5. A centrifugal machine according to claim d, in which the turbine blades are integrally formed with the impeller.
MARCEL G. SCHWARZ.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,084,463 Stalker June 22, 1937 2,305,226 Stalker Dec. 15, 1942 2,344,835 Stalker Mar. 21, 194% 2,399,072 Thompson Apr. 23, 1946 FOREIGN PATENT S Number Country Date 495,838 Great Britain Nov. 21, 1938 701,509
Germany Jan. 17, 19a