Patent Application
20110081253
The subject matter relates generally to gas turbine engines, and more particularly, to balancing a gas turbine engine rotor.
A rotor assembly of a gas turbine engine may require balancing, for example, by addition of balancing weights in selected locations of the rotor assembly. Balancing weights are conventionally provided through dedicated attachments points on the rotor. These configurations however, may introduce stress concentrations on the rotor assembly.
Accordingly, there is a need to provide for improved balancing or gas turbine engine rotors.
In one aspect, the described subject matter provides an apparatus for balancing a gas turbine engine rotor assembly, the apparatus comprising at least one annular balancing weight having a central aperture defined therethough, the at least one weight inserted into a the cooling hole defined in the rotor assembly, the at least one balancing weight installed asymmetrically on the rotor assembly to thereby assist in balancing the rotor assembly.
In another aspect, the described subject matter provides a balanced rotor of a method for balancing a gas turbine rotor assembly, the method comprising steps of: (a) providing a rotor assembly having a rotational imbalance, the rotor assembly having a plurality of cooling holes defined therein, the cooling holes communicating with a cooling path through a disc of the rotor assembly; (b) providing at least one balancing weight defining a cooling passage; and (c) inserting the at least one cooling weight into a said cooling hole in a manner which permits cooling air access to the cooling path through said cooling passage of the weight
Further details of these and other aspects of the described subject matter will be apparent from the detailed description and the drawings included below.
Reference is now made to the accompanying drawings depicting aspects of the described subject matter, in which:
Referring to
An annular front coverplate 46 may be mounted to the front side 36 of the disc 32 to rotate together with the rotating disc. The annular front coverplate 46 is configured and cooperates with the disc 32 such that a cavity 48 is formed between the coverplate 46 and the front side 36 of the disc 32 and is in fluid communication with the cooling air passage 40. A plurality of cooling holes 50, as more clearly shown in
In a rotor balancing process according to one embodiment, a first step is to observe rotational imbalance of the rotor assembly 30, which is known in the art and will not be further described. As a result of the observation, a magnitude of imbalance caused by an eccentric rotation mass which is a function of the weight of the eccentric rotating mass and the radial distance of the mass from an axis of rotation, is determined. The angular direction of imbalance is also determined by the angular position of the eccentric mass relative to an arbitrary reference angular direction. The magnitude and angular direction of imbalance may be determined in a radial plane 68 normal to the engine rotating axis in which plane the cooling holes 50 of the coverplate 46 are substantially defined. Therefore, one or two or even more cooling holes 50 adjacent to the determined angular direction of imbalance may be selected for receiving balancing weights therein for balancing adjustment of the rotor assembly 30. The annular coverplate 46 is also configured and cooperates with a stationary structure (not numbered) to perform a seal function to maintain the supply of the cooling air 42 in appropriate pressure.
A plurality of balancing weights 52 (more clearly shown in
The balancing weights 52 according to one embodiment may include a stem 54 extending axially from an enlarged head 56. The stem 54 has a diameter snugly fit in the individual cooling holes 50. Different masses for the individual balancing weights 52 may be achieved by varying the dimension of the head 56 or changing the axial length of the stem 54, or both. Optionally, the balancing weights 52 may define a central bore 58 axially extending therethrough such that when the stem 54 of the balancing weight 52 is inserted in a selected cooling hole 50, the central bore 58 of the balancing weight 52 allows the cooling air to pass therethrough, thereby preventing the selected cooling hole 50 which receives the balancing weight 52 from being blocked, resulting in less interference with the cooling of the rotor assembly 30. In alternate configurations, the weights may be provided in any suitable shape which provides cooling access through or past the weight, into the associated cooling passage.
Suitable means for securing the balancing weight 52 in the selected cooling hole 50 may be provided. For example, appropriate adhesive may be applied to the stem 54 of the balancing weight 52, the weight may be force-fit in the hole, mating threads may be provided to the respective stems 54 of the balancing weights 52 and the cooling holes 50 in the annular coverplate 46, or any other suitable method of attachment may be provided.
Optionally, a retainer such as a split ring 60 may be provided to retain one or more balancing weights 52 in position when the one or more balancing weights are inserted into selected cooling holes 50 of the annular coverplate 46. The split ring 60 is received in an annular groove defined in the annular coverplate 46 and abuts the enlarged head 56 of the one or more balancing weights 52 inserted in the selected cooling holes 50, thereby preventing the one or more balancing weights 52 from withdrawal from the selected cooling holes 50.
Alternatively, the above described balancing procedure using cooling holes in the rotor assembly 30 may also be applicable at the aft side 38 instead of at the front side 36 of the rotating disc 32. For example, an annular aft coverplate 62 may be mounted to the rotating disc 32 at its aft side 38. The annular aft coverplate 62 which may be configured differently from the annular front coverplate 46 depending on the specific configuration of the rotating disc, cooperates with the rotating disc 32 to form an annular cavity 64 between the annular aft coverplate 62 and the rotating disc 32 and is in fluid communication with the cooling air passage 40 of the rotor assembly 30. Similar to the annular coverplate 46, the annular aft coverplate 62 defines a plurality of circumferentially spaced cooling holes 66 in a radial plane 70 normal to the engine rotating axis. The cooling holes 66 are in fluid communication with the annular cavity 64 and therefore form as individual outlets (not numbered) of the cooling passage 40. The cooling holes 66 in the annular aft coverplate 62 may be used for selectively receiving one or more balancing weights 52 which are configured to fit with the size of the cooling holes 66, to perform the rotor balancing procedure as described above. The similar balancing process will not be redundantly described. The balancing weights used with the cooling holes 66 may be similar to or different from the balancing weights 52, and are not shown and further described.
It has been known that a static balancing process for a rotor involves balancing performance in one radial plane which is normal to the rotating axis of the rotor, such as the radial plane 68 in which the cooling holes 50 of the annular coverplate 46 are defined, or the radial plane 70 in which the cooling holes 66 of the annular aft coverplate 62 are defined. However, performing rotor balancing process in two radial planes which are normal to the rotating axis of the rotor and axially spaced apart from each other, such as the radial planes 68 and 70, may provide more desirable balancing results Therefore, a dynamic balancing process can be achieved by performing the above described rotor balancing process by using both cooling holes in the annular coverplate 46 and the cooling holes 66 in the annular aft coverplate 62, according to a further embodiment.
By employing cooling holes already provided in a disc assembly to retain balancing weights, additional features are not required on the disc assembly to retain weights. This simplifies the disc and minimizes stress concentrations, which may be beneficial where materials are used which are sensitive to stress concentrations, such an IN100 or ME16 superalloys.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departure from the scope of the invention disclosed. For example, the described apparatus and method may be applicable to rotors in a gas turbine engine different from the described and illustrated turbofan engine, and the rotor assemblies, particularly the rotating disc of the rotor assembly may be configured different from that described and illustrated in the described embodiments. Still other modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
