US3642379A - Rotary gas-handling machine and rotor therefor free of vibration waves in operation - Google Patents

Abstract

A rotary gas-handling machine and rotor therefor in which the number of puffs of gas affecting the rotor so as to tend to excite vibrations therein on each revolution will be such that for the designed speed of operation of the rotor the resulting frequency of excitation puffs will be different from each of the resonant frequencies of the rotor, such as the resonant frequency for ''''saddle'''' vibration, blade vibration, rotational and outer edge vibration of the shroud, etc. The excitation frequency is also made to differ from one-half of each of the resonant frequencies. In the case of such a machine in the form of a turbine the number of excitation puffs per revolution is determined by the number of circumferentially spaced nozzles carried by the housing to direct the gas against the rotor, while in the case of a compressor rotor the number of excitation puffs per revolution is determined by the number of blades. The blades and the shroud are preferably made thicker adjacent their inner extremities both to deter vibration by inherent stiffness of such thicker members and to change their natural frequencies by the mass of the thickened members. The same sort of structure makes the shroud more resistant to vibration by stiffening an important component of the ''''spring'''' of the resonant mode while strengthening it against shear. Another expedient is to cause the blades to protrude from the wheel outwardly past the plane of the eye of the shroud and be joined to the hub out beyond such plane so as to provide bracing for both the shroud and the disk of the rotor against axial vibration.

Description

United States Patent Swearingen 51 Feb. 15,1972

[54] ROTARY GAS-HANDLING MACHINE AND ROTOR THEREFOR FREE OF VIBRATION WAVES IN OPERATION [72] Inventor: Judson S. Sweariugen, 500 Bel Air Road,

Los Angeles, Calif. 90024 [22] Filed: June 27, 1969 [211 App]. No.: 837,178

[52] U.S.Cl ..415/1l9,415/181,415/2l1, 415/185,4l6/l79 [51] Int. Cl ..F04b 39/00, F04d 29/00 [58] FieldofSearch AIS/119,211,18l;4l6/186, 416/185, 180

[56] References Cited UNITED STATES PATENTS 3,194,487 7/1965 Tyler et a1 415/119 786,384 4/1905 Richards 415/211 1,350,927 8/1920 Gomborow. 415/21 1 1,350,941 8/ 1920 Rice .415/211 2,764,944 10/ l 956 Lawrence .415/21 1 3,006,603 10/1961 Caruso et a1 .415/211 2,285,266 6/1942 Fiilleman. .416/186 2,625,365 1/1953 Moore ..416/186 3,305,165 2/1967 Gregory ..415/2l1 FOREIGN PATENTS OR APPLICATIONS 421,964 1/1935 Great Britain ..415/2l1 906,975 3/1954 Germany ..4l6/l 86 Primary Examiner-Henry F. Raduazo AttorneyRalph R. Browning [57] ABSTRACT A rotary gas-handling machine and rotor therefor in which the number of pufis of gas afiecting the rotor so as to tend to excite vibrations therein on each revolution will be such that for the designed speed of operation of the rotor the resulting frequency of excitation puffs will be different from each of the resonant frequencies of the rotor, such as the resonant frequency for saddle vibration, blade vibration, rotational and outer edge vibration of the shroud, etc. The excitation frequency is also made to differ from one-half of each of the resonant frequencies. In the case of such a machine in the form of a turbine the number of excitation puffs per revolution is determined by the number of circumferentially spaced nozzles carried by the housing to direct the gas against the rotor, while in the case of a compressor rotor the number of excitation puffs per revolution is determined by the number of blades. The blades and the shroud are preferably made thicker adjacent their inner extremities both to deter vibration by inherent stiffness of such thicker members and to change their natural frequencies by the mass of the thickened members. The same sort of structure makes the shroud more resistant to vibration by stiffening an important component of the spring of the resonant mode while strengthening it against shear. Another expedient is to cause the blades to protrude from the wheel outwardly past the plane of the eye of the shroud and be joined to the hub out beyond such plane so as to provide bracing for both the shroud and the disk of the rotor against axial vibration.

9 Claims, 4 Drawing Figures PATENTEDFEB 15 I972 SHEET 1 BF 2 F/G.2A

- Judson Swaringen /N VE N TOR A TTORNE Y PATENTEBFEB15 m2 SHEET 2 BF 2 ROTARY GAS-HANDLING MACHINE AND ROTOR TI-IEREFORFREE OF VIBRATION WAVES IN OPERATION BACKGROUND OF THE INVENTION This invention relates in general to the structures of gashandling machines such as radial turbines, centrifugal compressors and the like having rotors adapted to operate at exceedingly high blade tip speeds and to the inhibition or suppression of vibratory waves therein during such rotation.

In centrifugal pump or compressor impellers and in rotors of radial reaction turbines (which have rotors similar to pump impellers) the rotor is of moderately light weight because of the passages through the wheel, and they are very well braced by the blades, so vibrations of this type have previously not been recognized in them.

Vibrations in the liquid in centrifugal liquid pumps have been recognized in cases where the number of blades and the speed and the length of the volute have been favorable for establishment of a standing wave in the liquid.

The applicant, in his work, has found several significant vibrations in rotors. He operates rotors in his work at unusually high tip speeds in the order of 1,000 feet per second; and he puts a great deal of power into a small rotor. Also, he has a type of configuration which creates a very high excitation frequency.

To illustrate this high excitation frequency, consider a radial reaction turbine rotor surrounded with a group of primary nozzles from which the expanding gases jet generally tangentially into the periphery of the rotor. Each of these nozzles provide a puff" so that the rotor is subjected to a series of these puffs, the frequency of which is equal to the number of nozzles multiplied by the rotating speed. This frequency is of the order of thousands per second. In the case of impellers for centrifugal pumps and compressors the excitation frequency is the number of blades multiplied by the rotational frequency. As each blade at the periphery or inlet of the rotor passes a disturbance in the main stream a force impulse is applied to the rotor. If the rotor has a resonance frequency that coincides with this excitation frequency, the resonance vibration in the rotor will be actuated and built up to an amplitude which will soon fatigue members of the rotor and cause failure.

At least five modes of vibration, and quite possibly more, have been identified in a typical rotor which can be excited and can cause fatigue and failure of the rotor. They are as follows:

l. Saddle" vibration, as described above, with four nodes.

2. Saddle" vibration with six nodes.

3. Blade vibration (the vibration of the long span of blade edge at the eye of the impeller).

4. Rotation of the shroud of the impeller with respect to the disk of the impeller.

5. Vibration of the outer edges of the shroud between the impeller blades.

6. There are numerous, 50 or more other complex modes of vibration such as higher order saddle vibrations and second harmonic blade vibrations, usually in the frequency range of 1,000 per second up to 20,000 per second.

It is the object of this invention to inhibit these or reduce them to practically tolerable amplitude.

This invention provides for substantially inhibiting these vibrations. Consider the third one, the blade vibration. One solution to this problem in the case of a turbine can be either operation with excitation frequency above the resonant frequency as by increasing the number of nozzles to increase the excitation frequency or reducing the resonance frequency as by making the blades thinner. The resonance frequency is approximately linearly proportional to blade thickness. Another solution is making the blade thicker to increase the resonance frequency and/or the number of nozzles lower to reduce the excitation frequency so that the excitation frequency never reaches the resonance frequency in operation.

It has also been found, especially in large rotors where the power is great, that resonant vibration can be excited by an excitation frequency which is half the resonance frequency. This is no doubt due to the first overtone of the excitation frequency. Overtones above that appear not to have sufficient power to cause much trouble. Also, they are usually at such high frequency that the problem is minimized for that reason by radiation of energy to the surrounding members and fluid.

The saddle vibrations (first and second listed above) are overcome by increasing the bending strength or the rigidity of the rotor about a diameter and this is done by axially thickening the rotor, that is, extending the blades out far into the eye (or beyond the plane of the eye) so that the section modulus of the rotor about a diameter is increased sufficiently to raise the saddle vibration frequency higher than the excitation frequency. Reducing the mass around the outer periphery of the rotor by thinning the shroud and click also raises the saddle vibration frequency and tends to make it different from the excitation frequency.

The saddle vibrations may result in blade failure in the eye because the blades are stressed excessively by such vibration. Saddle vibrations may also result in a notching of the shroud at the periphery where the shroud is fatigued by stressing in a wrinkling manner. It is characterized by failure sections of shroud between alternate blades. Evidently, when a section of shroud fails, then the mode of vibration changes and it cannot change to the section between the next two blades because the rigidity is not on one side to flex it, so it skips past the second blade.

The shroud rotation resonance (number 4 above) is complicated in the respect that it is the band around the eye which vibrates at the largest amplitude. It rotates circularly back and forth while the blades extending to the hub are bent back and forth and the shroud which is outside of its diameter is deformed in a shear manner or by wrinkling. The outer periphery of the shroud vibrates much less because the wheel is thin there and the blades brace it rather well. The effect of this rotation is to fatigue the blades and break them at the eye and also to wrinkle the shroud and cause it to crack radially and cause notches of material to fall out of it. It tends to notch the shroud between every blade. If it is more violent, it will break the shroud loose from the blades and the shroud will fall off. If the shroud is of narrow extent in a radial direction (does not extend to the periphery of the rotor), then it will cause the blades to fail at the hub first and finally the blades to fail completely and come off the hub.

Finally, the shroud vibrations between the blades around the periphery of the wheel (number 5 above) can move up and down. Their natural frequency can be increased by putting in more blades to shorten the span of the shroud sections. Their frequency can also be increased by thickening the shroud. The excitation frequency in any case can be reduced by reducing the number of primary nozzles in the turbine.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein is set forth by way of illustration and example, but not by way of limitation a preferred embodiment of the invention.

In the drawings:

FIG. I shows a drawing in axial cross section of a rotor of a machine embodying this invention.

FIG. 2 is a fragmentary view in cross section through one of the blades of the rotor illustrated in FIG. I, along the line 22 of FIG. I, for the purpose of illustrating the variation in cross section from the tip to the inner end thereof.

FIG. 2A is a fragmentary view similar to FIG. 2 but taken along the line 2A-2A of FIG. 1 and showing the blade thickness taper from disk to shroud.

FIG. 3 is a view taken along the line 3-3 of FIG. 1 showing the rotor illustrated in FIG. 1 and illustrating in surrounding relation thereto and similarly in cross section the nozzles used with the rotor in FIG. 1 and the housing thereabout to make up the turbine.

Referring first to FIG. 1, the rotor illustrated is one such as customarily embodied in a turbine. A similar rotor for a compressor would appear much the same in cross section and for purposes of this invention it is believed unnecessary to illustrate both although the invention is applicable to both, because it is thought that the illustration of one will serve for both.

It will be seen that the rotor has a hub portion 1 through which there is an opening 2 to receive a shaft on which the rotor is supported for rotation. Extending in a generally radial direction outwardly from one end of the hub is a disk portion 3 which gradually tapers to a relatively thin edge at its outer extremity shown at 4. Intermediate its radial extent this disk is provided with a laterally projecting annular portion 5 on the surface of which is provided one part of a type of seal known as a labyrinth seal 6 such as customarily used in high-speed seal locations.

At circumferentially spaced positions on that portion of the disk which faces toward the opposite end of the hub 1 there are located numerous radially inwardly extending blades whose tips 7 are located along the outer periphery of the disk 3 adjacent the edge 4 and whose opposite ends 8 are located near the opposite end of the hub 1 these blades being secured to the'disk and hub along one edge substantially throughout their respective lengths.

It will be noticed also from FIG. 2A that each of these blades tapers from its outer edge adjacent the shroud to its inner or hub and disk attachment edge, being much thinner at its outer edge than at its inner edge. This serves to provide in the blade as well as in the disk 3 a thicker inner portion so that the blade and disk provide mutual supports for one another against lateral blade vibrations. The blade edge adjacent the shroud is made thin so as to provide a higher frequency natural harmonic, and this sizing is so selected, empirically or otherwise, that the natural period of vibration of both parts will be different from the excitation frequency of the machine involved determined as elsewhere set forth. By this-means, therefore, the natural frequency of vibration of these parts is made distinctly different from the excitation frequency of the machine in its operation as designed. Also FIG. 2 shows that the blades taper from their outer tips to the hub ends 8, where they are thicker.

Along the opposite edges of the various blades from the disk 3 is a shroud in the form of an annular shield 9. This shroud has its inner end 10 spaced somewhat outwardly from the outer surface of thehub l and its outer end 11 preferably sub,- stantially flush with the outer ends of the blades and the outer edge of the disk 4. At an appropriate position surrounding its exterior is one portion ofa seal 12 similar to the seal 6 which is carried on the disk on the opposite surface of the rotor. Both of these seals are for the purpose of sealing against the interior ofa housing surrounding the rotor.

Nominally the open central portion of the annular shroud 9 inwardly of the edge 10 is known as the eye." Through this eye gas emerges from the rotor in the event the rotor is being used as the turbine and through this eye gas enters the rotor in the event ofits use as a compressor.

It will be noted in this case that the blades, in accordance with this invention, project through the eye to a position beyond the plane of the smaller opening or eye of the shroud and exteriorly of said opening are secured all the way to their respective extremities to the hub. This serves the purpose of enabling the blades to brace the inner edge of the shroud against vibration to a much better degree than they would if they did not project through the eye.

For reasons similar to those hereinbefore expressed, the shroud 9 is also made thicker at its inner edge 10 then at its outer edge 11, having a tapering cross section from one to the other.

Referring now to FIG. 3, it will be seen that surrounding the rotor is a housing 14 within which are located in circumferentially spaced surrounding relationship to the rotor nonrotating but preferably adjustable nozzle blades 15. These are employed in a turbine construction and in such construction serve to provide nozzles through which gas to be expanded in the turbine is directed in a generally tangential direction against the radially outer edge of the rotor and into the openings provided between the outer tips 7 of the blades. It has been discovered by the applicant that the number of such nozzles provided by blades 15, multiplied by the rotational speed of the rotor, determines the excitation frequency tending to excite portions of the rotor into vibration as it is rotated. For purposes of reference in connection with a turbine, each pair of nozzle blades 15 with the nozzles spaced between them will be considered to be a means for producing an excitation puff of gas so that the number of nozzles will determine the number of excitation puffs of gas into the turbine rotor during each revolution, and such number of nozzles multiplied by the number of revolutions per minute will give the frequency per minute of the excitation puffs. In accordance with this invention such frequency is made different not only from each resonant frequency of possible vibration of parts of the rotor at the intended speed of rotation, but is made different from one-half of each such frequency for reasons hereinbefore stated.

In the event of the use of a similar rotor as the impeller for a compressor, the gas leaving the outer end of the space between each adjacent pair of blades would constitute a means for producing an excitation puff of gas and there is high probability of a nearby structure capable of reflecting this puff back against the wheel. Hence the number of blades in the rotor would determine the number of excitation puffs of gas between the exterior and interior of the passages through the rotor for each revolution of the rotor. A modification of the number of puffs so produced in one revolution of the rotor by the number of the revolutions per minute, would, of course, determine the excitation frequency of puffs of gas during operation of the rotor. At the inlet, the stream is, in general, nonuniform, and as each blade passes through a stream irregularity it receives a force impulse. The number of blades times the revolutions per unit time will determine the frequency of excitation impulses or puffs. In accordance with this invention such frequency of excitation would be designed into the rotor by a determination of the number of blades with respect to the intended speed of rotation, that the excitation frequency so determined would be different from each resonant frequency known to be present in connection with possible natural in contrast to forced vibrations in the rotor. It would also be difierent from one-half of each such known resonant frequencies.

Certain embodiments having been fully set forth and described which are capable of carrying out the objects and advantages of this invention, what is claimed is:

1. In a rotary gas-handling machine designed for rotation at a predetermined fixed speed and in which gas is converted from one pressure to another and which comprises a housing, a rotor rotatably mounted therein and having generally radially and axially extending blades each confined between and joined to a hub and a disk along one axially directed edge, said disk being continuous with and projecting generally radially from said hub, and an annular shroud opposed to the disk along the other axially directed edge forming generally radially directed gas passageways between the said blades, hub, disk and shroud, and having predetermined resonant frequencies for known types of rotation vibration, the improvement which comprises said housing and rotor combination including means for rotating said rotor at said predetermined speed and means for producing a predetermined number of excitation puffs of gas between exterior and interior of said passages for each revolution of the rotor so that said number of excitation puffs multiplied by said speed of rotation will produce an excitation frequency of puffs which differs from each of said resonant frequencies.

2. A rotary gas-handling machine in accordance with claim 1 in which the machine is a turbine and the means for producing excitation puffs for each revolution comprises a plurality of circumferentially spaced nozzles carried by the housing,

disposed about and adjacent the outer ends of said passageways and adapted to direct gas tangentially and slightly radially into said outer ends of the passageways.

3. A machine as set forth in claim 1 in which the machine is a compressor and the means for producing excitation puffs for each revolution comprises the ends of the several blades.

4. A machine as set forth in claim 1 in which the machine is a turbine and the means for producing excitation puffs for each revolution comprises the ends of the several blades.

5. A machine as set forth in claim 1 in which an inner periphery of said annular shroud is axially and radially spaced from that end of said hub which is more remote from said disk, and in which said blades project axially through the annular space between said hub and said inner periphery of said shroud and are continuously joined to said hub to a position beyond said inner periphery of said shroud from said disk.

6. A machine as set forth in claim 1 in which said blades are thicker near said disk and said hub than at their opposite portrons.

7. A machine as set forth in claim 1 in which said shroud is of greater bending strength adjacent itsinner than adjacent its outer periphery.

8. [n a rotary gas-handling machine designed for rotation at a predetermined fixed speed, and in which gas is converted from one pressure to another and which comprises a housing, a rotor rotatably mounted therein and having generally radially and axially extending blades each joined to a hub and a disk along one axially directed edge, said disk being continuous with and projecting generally radially from said hub, and forming generally radially directed gas passageways between the said blades, hub and disk, and having predetermined resonant frequencies for known types of rotation vibration, the improvement which comprises said housing and rotor combination including means for rotating said rotor at said predetermined speed and means for producing a predetermined number of excitation puffs of gas between exterior and interior of said passages for each revolution of the rotor so that said number of excitation puffs multiplied by said speed of rotation will produce an excitation frequency of puffs which differs from each of said resonant frequencies.

9. A rotary gas-handling machine in accordance with claim 8 in which said number of excitation puffs multiplied by said rate of rotation will produce an excitation frequency of puffs which differs from one-half of each of said resonant frequencies also.

Claims (9)

1. In a rotary gas-handling machine designed for rotation at a predetermined fixed speed and in which gas is converted from one pressure to another and which comprises a housing, a rotor rotatably mounted therein and having generally radially and axially extending blades each confined between and joined to a hub and a disk along one axially directed edge, said disk being continuous with and projecting generally radially from said hub, and an annular shroud opposed to the disk along the other axially directed edge forming generally radially directed gas passageways between the said blades, hub, disk and shroud, and having predetermined resonant frequencies for known types of rotation vibration, the improvement which comprises said housing and rotor combination including means for rotating said rotor at said predetermined speed and means for producing a predetermined number of excitation puffs of gas between exterior and interior of said passages for each revolution of the rotor so that said number of excitation puffs multiplied by said speed of rotation will produce an excitation frequency of puffs which differs from each of said resonant frequencies.

2. A rotary gas-handling machine in accordance with claim 1 in which the machine is a turbine and the means for producing excitation puffs for each revolution comprises a plurality of circumferentially spaced nozzles carried by the housing, disposed about and adjacent the outer ends of said passageways and adapted to direct gas tangentially and slightly radially into said outer ends of the passageways.

3. A machine as set forth in claim 1 in which the machine is a compressor and the means for producing excitation puffs for each revolution comprises the ends of the several blades.

4. A machine as set forth in claim 1 in which the machine is a turbine and the means for producing excitation puffs for each revolution comprises the ends of the several blades.

5. A machine as set forth in claim 1 in which an inner periphery of said annular shroud is axially and radially spaced from that end of said hub which is more remote from said disk, and in which said blades project axially through the annular space between said huB and said inner periphery of said shroud and are continuously joined to said hub to a position beyond said inner periphery of said shroud from said disk.

6. A machine as set forth in claim 1 in which said blades are thicker near said disk and said hub than at their opposite portions.

7. A machine as set forth in claim 1 in which said shroud is of greater bending strength adjacent its inner than adjacent its outer periphery.

8. In a rotary gas-handling machine designed for rotation at a predetermined fixed speed, and in which gas is converted from one pressure to another and which comprises a housing, a rotor rotatably mounted therein and having generally radially and axially extending blades each joined to a hub and a disk along one axially directed edge, said disk being continuous with and projecting generally radially from said hub, and forming generally radially directed gas passageways between the said blades, hub and disk, and having predetermined resonant frequencies for known types of rotation vibration, the improvement which comprises said housing and rotor combination including means for rotating said rotor at said predetermined speed and means for producing a predetermined number of excitation puffs of gas between exterior and interior of said passages for each revolution of the rotor so that said number of excitation puffs multiplied by said speed of rotation will produce an excitation frequency of puffs which differs from each of said resonant frequencies.

9. A rotary gas-handling machine in accordance with claim 8 in which said number of excitation puffs multiplied by said rate of rotation will produce an excitation frequency of puffs which differs from one-half of each of said resonant frequencies also.

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