US 2846136 A
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Aug. 5, 1958 T. ZABA 4 2,846,136
MULTI-STAGE AXIAL FLOW coMPREsoRs Filed July 14, 1952 IN VENTOR I BY K ATTORNEYS.
United States Patent MULTI-STAGE AXIAL FLOW COlVIPRESSORS Tadeusz 'Zaba, Wettingen, Switzerland, assignor to Aktiengesellschaft Brown, Boveri 8; Cie., Baden, Switzer- This invention relates to multi-stage axial flow compressors, and more particularly to axial flow compressors in which the kinetic energy of the medium being compressed is transformed into energy of another type, and thereby recovered.
In the previously known axial flow compressors, deflection blades have been provided for the transformation of the peripheral component of the air or gas stream through the compressor, and a diffuser has been provided at the outlet to transform the axial component of the flow velocity into pressure energy. This solution of the problem has the disadvantage that the diffuser operates at poor efliciency unless substantial space in the axial direction is available for this element of the compressor.
Objects of the present invention are to provide multistage axial flow compressors in which the kinetic energy of the medium under compression is transferred to the compressor rotor as mechanical energy. Objects are to provide multi-stage axial flow compressors of higher efliciency and of shorter axial length than the prior compressors which employ difiusers. Objects are to provide axial flow compressors having rotors with one or more rows of blades following a plurality of compressor stages and operating as a turbine stage or stages to lower the axial velocity of the medium under compression while avoiding a decrease in the pressure of the medium. More specifically, an object is to provide a multi-stage axial flow compressor having rows of turbine blades on the rotor at the outlet end of the compressor and at one or more intermediate points between compressor stages.
These and other objects and the advantages of the invention will be apparent from the following specification when taken with the accompanying drawing, in which:
Figs. 1 and 2 are fragmentary longitudinal central sections through multi-stage axial flow compressors embodying the invention;
Fig. 3 is a fragmentary schematic development showing the blade forms of the energy-recovering stages of the Fig. 1 compressor;
Fig. 4 is a vector diagram of the flow velocities at the blade rows of Fig. 3;
Fig. 5 is a fragmentary schematic development showing the blade forms of the intermediate set of energyrecovering stages of the Fig. 2 compressor; and
Fig. 6 is a vector diagram of the flow velocities at the blade rows of Fig. 5.
In Fig. 1 of the drawing, the reference numeral 1 identifies the rotor of a multi-stage axial flow compressor, the rotor being provided with a plurality of rows of blades 2 and being rotatably supported in conventional manner within a casing 3 having rows of guide blades 4 interleaved with the rows of rotor blades. In accordance with the invention, the last blade row a of the compressor, which is here shown as a guide row, is followed by three rows b, c and d respectively, of turbine rotor blades. The medium to be compressed enters the compressor at the inlet 5 and is discharged at the outlet 6.
In the compressor of Fig. 2, the parts corresponding to those of the Fig. 1- compressor are identified by primed reference numerals 1 to 6' respectively. Therotor row g of a first set of compressor stages is followed by two-rows h and i of turbine blades on the rotor, and these are followed by the first row k of another group of compressor stages, the blade row k being a rotor row as shown. Two additional turbine rotor rows b and c are arranged at the compressor outlet, as in the Fig. l compressor, after the last-compressor bladerow a.
The method of operation of the invention will be apparent from a consideration of the blade forms and the vector diagrams of Figs. 3 and 5, and Figs. 4 and 6, respectively.
In Fig. 3, the peripheral velocity of the rotor rows b, c and d is indicated by the arrows u. The medium to be compressed enters the last compressor guide row a at the velocity o and leaves it at the outgoing velocity c see Fig. 4. From the figure it may be seen that the incoming velocity c has been reduced in magnitude to c The kinetic energy of the compressed medium has been converted into a pressure energy. In the following turbine rows [2, c and d, the incoming velocities w W1; and Wm are deflected into the outgoing velocity wzb, W and w respectively. From Figure 4 it may be seen that the deflected velocities w w and W are of equal magnitude to the incoming velocities W W and w According to the invention and by known principles of blade profiledesign, this deflection is effected without a decrease in the pressure of the medium to be compressed, and the deflected outgoing velocity magnitudes are equal to the incoming velocity magnitudes. The absolute outgoing velocity w from the last turbine rotor row d is therefore obtained by vectorial addition of velocity vectors w and u. The difference between vectors c and w may be regarded as the magnitude of the recovery of kinetic energy.
The flow conditions at blade rows g, h, i, k of Fig. 2 are illustrated in the Figs. 5 and 6. The medium to be compressed enters the compressor rotor-row g at the velocity w and leaves it at the velocity w In the following turbine rotor-rows h and i, the incoming velocities W and w are deflected into the outgoing velocities W and W21. This deflection, too, occurs without a decrease in the pressure of the medium to be compressed through design in known manner of the blade profiles. The medium then enters the following compressor rotor-row k at the velocity w and leaves it at the velocity w which has a much smaller axial component in comparison with w Since the axial velocity of the medium to be compressed is again smaller after the turbine rotor-rows than before them, the blades of the following compressor rows can be made longer, thus contributing to the improvement of the stage efiiciency.
While Fig. 2 shows turbine blades at only one intermediate point along the multi-stage axial flow compressor, it is to be understood that the invention is not limited to this particular construction and that a row or a plurality of rows of turbine blades may be provided at a plurality of points along a multistage compressor in place of or in addition to a row or plurality of rows of rotor turbine blades at the outlet of the multi-stage compressor.
1. A multi-stage axial flow compressor comprising a casing provided with rows of guide blades, a rotor journalled in said casing and provided with rows of blades interleaved with said rows of guide blades, and means for recovering and usefully employing the kinetic energy of the medium being compressed, characterized by the fact that said energy-recovering means comprises a row of turbine blades on said rotor between groups of compressor stages thereof, said row of turbine blades being serially arranged in the path of all medium flowing through the compressor and profiled to provide a deflection 0f the medium at constant relative velocity and constant pressure whereby the axial velocity of the medium is lowered Without a corresponding decrease in pressure so that the kinetic energy of the medium is transformed to mechanical energy imparted to the rotor.
2. A multi-stage axial flow compressor as recited in claim 1, wherein said energy-recovering means comprises a row of turbine blades on said rotor after the last compressor stage thereof, and a row of turbine blades on said rotor between groups of compressor stages thereof.
3. A multi-stage axial flow compressor as recited in claim 1, further characterized in that said row of turbine blades on said rotor follows a rotor row of blades of a compressor stage.
References Cited in the file of this patent UNITED STATES PATENTS 879,059 Ludewig Feb. 11, 1908 2,316,452 Pfenninger Apr. 13, 1943 2,326,072 Seippel Aug. 3, 1943 2,579,049 Price Dec. 18, 1951 FOREIGN PATENTS 622,415 Great Britain May 2, 1949