US2258773A

US2258773A - Elastic-fluid turbine

Info

Publication number: US2258773A
Application number: US386442A
Authority: US
Inventors: Reinout P Kroon
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1941-04-02
Filing date: 1941-04-02
Publication date: 1941-10-14
Anticipated expiration: 1958-10-14

Description

Oct. 14, 1 941. R. P KRQON 2,258,773

ELAsTIc-FLUIp TURBINE Filed April 2, 1941 wrrNEssr-:s: F, 4 mvENToR www 'C1' v RfNou'rEKRooN.

ATTO' 'EY a Curtis stage, and.'in general.

Patented Oct. 14, 1941.

UNITED .STATES PATENT lOFFICE 2,258,713 Reinout Prfdrtmh'more, Pa., assigner to Westinghouse Electric d: Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 2, 1941, Serial No. 386,442

'Cl3ims. j (Cl. 253-39) The invention relates to stages oi.' elastic uid turbines, and it has for an object to resist effectively the inducement of blade vibration because of non-uniform flow of elastic uid issuing from nozzle or vane passages.

Tests have shown, not only that the invention is eiective for the purpose indicated, but also that it is particularly desirable to employ it where the pressure ratio across a stage is relatively high, the elastic iluid ow disturbances inducing blade vibration increasing as the velocity and the pressure ratio increase and such disturbances increasing quite rapidly whenthe acoustic velocity is exceeded. Accordingly, a further object of the invention is to provide a stage of the highpressure ratio type and embracing vanes and blades, particularly short blades, and it has for an object to connect the blades together in groups and to provide such relation of .nozzle or vane pitch, blade pitch, and the number of blades connected together in each group that blade vibration, due to irregularities in flow caused by the l presence of vanes, is eiectively resisted.

These and other objects are effected Vby the invention as will be apparent from the following description and claims taken in connection with the accompanying drawing forming a part of this application, in which:

Figs. 1 and 2 are diagrammatic views showing cooperating nozzles and blade groups:

Fig. 3 is a fragmentary view showing blade groups; and

Fig. 4 is a diagrammatic view. i

Referring to Figs. 1 and 4, the iiow of elastic fluid issuing from the vane or nozzle passages l0 is not uniform because oi' the wakes occurring in the iiow behind each stationary vanel l. In Fig. 4, this non-uniform flow condition is diagrammatically shown, there being wakes, disturbances, .or reduced velocity zones a back of each vane Il and joined by zones b o! more unifor it to travel from one nozzle to the next.- vWhile this capability of non-uniformity of iow to restricted 50 induce blade vibration is necessarily near the inlet end of the turbine, may come within the above frequency range. In Fig. 4, the top curve indicates the condition of dangerous blade vibration where a blade goes through one vibration cycle while traveling a distance equal the nozzle pitch p.

In accordance with the present invention, the blades I2 of the rst moving row of an initial stage are connected byshroud elements i3 to form blade groups, at I4. In Fig. 1, showing an initial Curtis stage of the high-pressure ratio type, both the iirst and second moving rows of blades are connected together in such groups;

l are similarly connected together in groups. The

number of blades connected in a group is such that the combined eect on all the blades in the group does not involve any exciting forces of dangerous frequencies.. The blade pitch.' nozzle or vane pitch, and number of blades connected together in each group are so .arranged that the destructive forces fon the individual blades balance each other. Balancing is secured when the nozzle pitch, the blade pitch, andthe number of blades in each group have the following relation P-:Pq where p is'the nozzle pitch, in. the blade pitch, n, the number of blades connected together in m is the number of vane passages covered by the blades in a group.

The number represented by m is a whole number,l it is neither equal to nor a multiple of n, and it is preferably equal to n-1. If m is equal to n-l, then the above equation becomes Assuming that n=3 (3 blades per segment) and to blades having high frequencies of vibration,

nevertheless, the first moving blade row of an initial Curtis stage, the moving row o! an initial Bateau stage, possibly the second moving row of that the moving blade pitch p1 is 1.20 inches, a stationary vane or nomle pitch p of 1.80 inches may be used and blade vibration, due to irregularities in ow caused by the presence of the vanes, is effectively resisted or avoided.

Referring to Fig. 2, it will be noted that the vane pitch and the blade pitch are related so that two vane passages supply three blade passages; and that,inthisview,misequaltothe number ot nozzle passages i0 covered by the any short blade bladesotagroup ,tbatisnnisequalto2.

Having conceived of the possibility of disturbances making themselves felt on the blades as they pass the nozzle jets and of vibration or a dangerous resonant condition which might be built up, tests have shown the existence of such disturbances and the effects thereof. Furthermore, tests show the degree of disturbance, that is, up to the critical pressure ratio, the pressure ratio necessary for acoustic velocity, the inuence of the wakes behind the nozzle vanes is not very important `but it becomes of increasing consequence as the pressure ratio is further increased.

While the invention is shown as applied to two forms of turbine stages, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims. I

What is claimed is:

. 1. In a turbine stage comprising stationary vanes, moving blades each having such natural frequency as to be likely to be resonant with I elastic fluid flow disturbances due to the presence of the vanes, and means for connecting together in groups' the blades of the rst moving row of the stage; the vane pitch, the blade pitch and the number of blades connected together in each group having the relation,

where p is the vane pitch, pi the blade pitch, n the number of blades connected together in each group, and m is a whole number which is neither equal to nor a multiple of n.-

2. In an arrangement for resisting moving .blade vibration of an elastic fluid turbine initial where p is the vane pitch, p1 the blade pitch, n the number of blades connected together in each group, and m is a whole number which is neither equal to nor a multiple of n.

3. In a turbine stage comprising stationary vanes,A moving blades each having such natural frequency as to be likely to be resonant with elastic uid :dow disturbances due to the presence of the vanes. and means for connecting together in groups the blades of the first movig row of the stage; the vanepitch, the blade pitch and the number of blades connected together in each group having the relation,

where p is the vane pitch, 1n is the blade pitch. A

and n is the number of blades connected together in each group.

4. In an arrangement for resisting moving blade vibration of an elastic iluid turbine initial impulse stage having the elastic iluid pressure ratio thereacross suiiicient to produce elastic iluid velocity' which is acoustic or greater, said initial stage comprising stationary vanes and moving blades, the individual moving blades having such natural frequency as to b likely to'be resonant with elastic iiuid flow disturbances due to the presence of the vanes, and means for connecting together in groups the blades of the moving row of the stage; the vane pitch, the blade pitch and the number of blades connected togeth'er in each group having the relation,

where p is the vane pitch, p1 is the blade pitch, and n is the number of blades connected together in each group.

5. In an arrangement for resisting moving blade vibration of an elastic huid, turbine initial impulse stage comprising a row of stationary vanes providing vane passages, a row of moving blades providing blade passages receiving elastic iiuid issuing from the vane passages, the individual moving blades having such natural frequency as to be likely to be resonant with elastic iiuid flow disturbances due to the presence of the vanes, said vanes and blades being spaced circumferentially so that the blade pitch is twothirds of the vane pitch, and means for connecting the blades together in groups of three.

' REINOUT P. KROON. y