Multilayer Ring Damped Turbomachine Rotor Assembly

Abstract

The disclosure illustrates a centrifugal compressor comprising an inducer hub telescoped over an adjacent shoulder of an impeller hub. The inducer hub has an inner annular surface which receives a plurality of stacked annular relatively thin split ring elements. When the compressor rotates at high r.p.m.'s the split rings frictionally engage one another and the inner annular surface of the inducer hub to provide a highly effective means for damping vibrations in the inducer.

Description

The present invention relates to turbomachine rotor assemblies and more particularly to assemblies of the type that have provisions for damping.

In the gas turbine art there have been numerous approaches directed at providing damping in rotor assemblies. A departure from the usual method of providing damping at the tips of rotor blades may be found in the copending patent application entitled "Damped Turbomachine Rotor Assembly" in the name of Wayne C. Shank, Ser. No. 77,969, filed Oct. 5, 1970, and of common assignment with the present invention. The present invention constitutes an improvement over this copending application.

It is an object of the present invention to provide a highly effective means for damping a turbomachine rotor.

The above end is achieved by a damped turbomachine rotor comprising a generally annular hub spaced outward from its axis of rotation and having an inner annular surface. A plurality of annular, relatively thin stacked ring elements are received within and conform to the surface so that centrifugal force urges the ring members into frictional engagement with one another and with the inner surface to damp vibrations in the blades.

The above and other related objects and features of the present invention will be apparent from a reading of the description of the accompanying drawing and the novelty thereof pointed out in the appended claims.

In the drawing:

FIG. 1 is a longitudinal sectional view of a centrifugal compressor rotor assembly embodying the present invention;

FIG. 2 is a view taken on lines 2--2 of FIG. 1 which illustrates the fundamental mode of vibration of the compressor hub;

FIG. 3 is a perspective illustration of a plurality of split ring elements incorporated in the impeller of FIG. 1.

Referring now to FIG. 1, there is shown a centrifugal compressor rotor assembly 10 with which the present invention may be used. The rotor assembly comprises a first generally annular shaped hub 12 spaced outwardly from its axis of rotation A. The hub 12 has a series of radially extending blades 14 to form the impeller portion of the rotor assembly 10. A second hub 16 is positioned upstream of the hub 12 and is also annular and spaced outwardly from the axis of rotation A. An annular surface 15 is formed on the inner side of hub 16. Hub 16 has a series of inducer blades 18 which extend radially outward but are cambered so as to efficiently receive air from an axially directed inlet, shown in phantom and designated by reference character 21. The inducer blades 18 are spaced from but correspond with the impeller blades 14 to form a generally annular flow path across the centrifugal compressor rotor 10.

Hub 12 has an elongated shaft portion 26 over which hub 16 is telescoped. A tapered pilot diameter 28 on the elongated shaft portion 26 and a corresponding tapered diameter 30 on the inducer hub 16 centers it on elongated shaft portion 26 of hub 16. An internally threaded nut 32 is screwed onto the threaded portion 35 of the elongated portion 26 by a suitable tool which engages slots 34 in element 32. Element 32 holds the inducer hub 16 against a shoulder 20 on the impeller hub 12.

A plurality of annular, relatively thin ring elements 36 are received within and conform to the inner annular surface 15 of hub 12. Preferably the rings 36 are split at 38, as shown in FIG. 3 which shows the individual rings peeled away for illustrative purposes. The rings are formed so that they fit within one another in stacked fashion and the outermost ring element has an outside diameter slightly greater than the diameter of the inner annular surface 15. The plurality of ring elements 36 are then compressed for insertion into the inner annular surface and once they are in position they are yieldably maintained in place.

In operation the centrifugal compressor rotor assembly many rotates at a high rate of speed. Due to manny exciting forces the blades 18 and 14 tend to vibrate in their several modes. As shown in FIG. 2, the resultant vibration causes deflection of the inner annular surface 15 of annular inducer hub 16 from which the blades 18 extend radially. The deflection of the hub for a swing of blades 18 to the left is shown in exaggerated proportion by the phantom lines of FIG. 2. It can be seen that this deflection generally resembles a sine wave superimposed on the annular shape of the inner annular surface 15. A swing of the blades to the right causes a similar deflection in the opposite direction.

The outermost ring element 36 is urged radially outward by centrifugal force into frictional engagement with the deflected portion of the inner annular surface 15. In addition, the adjacent ring element 36 is urged against the outermost ring element by centrifugal force. Centrifugal force urges each of the ring elements into its adjacent outer element.

As the blades swing, the ridges and valleys in the inner annular surface 15 rub against the outermost ring element 36. The resultant frictional engagement of this element and the other ring elements absorbs the energy created by the blade vibration.

It can be seen that the provision of the multilayered rings greatly increases the surface area over which there is frictional engagement. This provides a substantial increase in damping over the copending application referred to above without necessitating any increase in the diameter of the inner annular surface 15. The reason for this is that the individual ring elements have a very thin section, for example, 0.001 inch thick, and the effective radius of the rings is approximately that of the inner annular surface. This causes approximately an equal centrifugal force on the rings when compared to the force on the single ring set forth in the above patent application.

For a rotational speed of over 50,000 r.p.m. the weight of the individual rings is magnified approximately 100,000 times their radius in inches. However, the frictional area for damping is greatly increased over the copending application referred to above, since it has a single ring whose outer surface only is in frictional contact. In the multilayer arrangement both sides of each ring element, except for the innermost element, provide a frictional engaging surface. It can be seen that the rubbing area is increased to a high degree, thereby providing a very effective means to damp the vibrations.

While the present invention has been described in connection with the inducer portion of a centrifugal compressor, it is believed that those skilled in the art can adapt the invention to other turbomachine rotors, such as axial flow type or centripetal turbine assemblies without departing from the spirit and scope of the present invention.

Claims

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. A damped turbomachine rotor assembly adapted to rotate at relatively high rates, said rotor assembly comprising:

a generally annular hub spaced outward from its axis of rotation having an outer surface defining the inner bounds of a flow path for fluid and an inner annular surface;

a plurality of blades extending radially outward from the outer surface of said hub substantially radially outward from said inner annular surface, said blades being subjected to vibratory bending forces, thereby producing deflections in said interior surface; and

a plurality of stacked, annular, relatively thin ring elements coaxial with one another and received within the inner annular surface of the hub member and having the outermost ring element conforming thereto, whereby centrifugal force urges said ring members into frictional engagement with one another and the outermost ring element with the inner surface of said hub for damping vibrations.

2. A rotor assembly as in claim 1 wherein each of said ring elements are split and the outermost ring element has an outside diameter slightly larger than the diameter of said inner annular surface, whereby the stacked ring elements are compressed for insertion into said inner annular surface and are yieldably maintained in position.

3. A rotor assembly as in claim 1 wherein said hub and blades comprise an inducer of a centrifugal radial outflow compressor and said rotor assembly further comprises:

a downstream radial outflow impeller hub;

a plurality of blades extending radially outward from said impeller hub, said blades being out of contact with said inducer blades.

4. A rotor assembly as in claim 3 wherein said stacked rings each have a thickness of approximately 0.001 inch.