Patent Application
20180016920
This disclosure claims the benefit of UK Patent Application No. GB1612288.9, filed on 15 Jul. 2016, which is hereby incorporated herein in its entirety.
The present disclosure relates to a rotor assembly for a turbomachine and particularly, but not exclusively, to a rotor assembly for a gas turbine turbofan engine, together with a method assembling the same.
Gas turbine engines are used to power aircraft, watercraft, power generators, pumps, and the like. Gas turbine engines operate by compressing atmospheric air, burning fuel with the compressed air, and then removing work from hot high-pressure air produced by combustion of the fuel in the air. Rows of rotating blades and non-rotating vanes are used to compress the air and then to extract work from the high-enthalpy air produced by combustion. Each blade and vane has an airfoil that interacts with the gasses as they pass through the engine.
Airfoils have natural vibration modes of increasing frequency and complexity of the mode shape. The simplest and lowest frequency modes are typically referred to as the first bending mode, the second bending mode, the third bending mode, and the first torsion mode. The first bending mode is a motion normal to the working surface of an airfoil in which the entire span of the airfoil moves in the same direction. The second bending mode is similar to the first bending mode, but with a change in the sense of the motion somewhere along the span of the airfoil, so that the upper and lower portions of the airfoil move in opposite directions. The third bending mode is similar to the second bending mode, but with two changes in the sense of the motion somewhere along the span of the airfoil. The first torsion mode is a twisting motion predominantly along the span of the aerofoil, on each side of the elastic axis, moves in the same direction.
Blades are subject to destructive vibrations induced by unsteady interaction of the airfoils of those blades with gasses passing through a gas turbine engine. One type of vibration is known as flutter, which is an aero-elastic instability resulting from the interaction of the flow over the airfoils of the blades and the blades' natural vibration tendencies. The lowest frequency vibration modes, the first bending mode and the first torsion mode, are often the vibration modes that are susceptible to flutter. When flutter occurs, the unsteady aerodynamic forces on the blade, due to its vibration, add energy to the vibration, causing the vibration amplitude to increase. The vibration amplitude can become large enough to cause damage to a blade. Another type of vibration is known as forced response, which is an aero-elastic response to inlet distortion or wakes from upstream airfoils, struts, or any other flow obstruction. The operable range, in terms of pressure rise and flow rate, of turbomachinery can sometimes be restricted by flutter or forced response phenomena.
The specific susceptibility of a blade to flutter may be increased if all the blades on a rotor are identical in terms of their vibration frequencies. Sometimes, intentional variations may be introduced into blades during manufacturing to create structural mistuning of a rotor and provide flutter resistance.
According to a first aspect of the present disclosure there is provided a rotor assembly for a turbomachine, the rotor comprising:
By positioning alternate ones of the blade root slots at an angle to the axis of rotation, the rotor assembly can be intentionally de-tuned to improve the stability margin, so taking it away from normal operation of the rotor assembly.
This alternating angled blade root slot arrangement results in more than one set of blades with each of the sets of blades having different mean root heights. This difference in mean root height results in each of the blade sets having a different centre gravity. It is the different centre of gravity between adjacent blades that results in the de-tuning of the rotor assembly.
The arrangement of alternating blade root slot angle requires no change to the annulus line and throat area for the rotor assembly. This means that the aerodynamic efficiency of the rotor assembly is not adversely affected by the mis-tuning effect of the angled blade root slot arrangement, which in turn makes the arrangement convenient for a user.
Optionally, the second radius decreases monotonically along the second blade root slot axial length from the first face to the second face.
In this arrangement, each of the first blade root slots is angled with the first radius increasing monotonically along the blade root slot from the first face to the second face, while each of the second blade root slots is angled with the second radius decreasing monotonically along the blade root slot from the first face to the second face.
In this arrangement, the blade root slots are angled relative to an axis of rotation of the rotor assembly with adjacent ones of the blade root slots being angled in opposing senses. In other words, adjacent ones of the blade root slots alternately slope inwardly and outwardly along an axis of rotation of the rotor assembly from one end of the rotor assembly to the other.
By angling each blade root slot in an opposite sense to its neighbouring blade root slot, each first blade will have a different centre of gravity to the adjacent second blade. This difference in centre of gravity enables the above-mentioned mis-tuning of the rotor assembly.
Optionally, each of the first blades has a first blade tip portion, each of the second blades has a second blade tip portion, and wherein the plurality of first blade tip portions and second blade tip portions together define a tip circumference.
The alternating angled blade root slot arrangement requires that the root portions of the alternating blades be of different height to one another. However, when the blades are assembled into the rotor assembly, the outer diameter swept by all of the blades is a contiguous circle. This maintains the aerodynamic efficiency of the rotor assembly. Optionally, at least one of the first blade root slots, and at least one of the second blade root slots, has a pyriform cross-sectional profile extending radially inwardly into the hub.
In one arrangement, each of the blade root slots is formed with a female pyriform cross-sectional profile. In other words, each blade root slot has a female pear-shaped cross-section extending radially inwardly into the hub of the rotor assembly. The blade root slot width increases as the slot depth increases from an outer surface of the hub.
In this arrangement, each of the blades has a corresponding pyriform cross-sectional profile with a width of the blade root portion increasing as it gets closer to the end of the blade root portion. The pyriform cross-sectional profile of the blade root portion corresponds to the pyriform cross-sectional profile of the blade root slot such that the blade is accommodated within the blade root slot.
The pyriform cross-sectional profile of the blade root slot and the corresponding blade root portion provides for effective load transfer between the blade and the hub, while being straightforward to manufacture.
Optionally, at least one of the first blade root slots, and at least one of the second blade root slots, has a fir-tree cross-sectional profile extending radially inwardly into the hub.
The use of a fir tree cross-sectional profile for the blade root slot and the corresponding blade root portion may provide for an increased area of contact between the blade and the hub. This can increase the amount of force that can be transmitted across the blade root joint. Thus a blade root joint that employs a fir tree root geometry may be able to be operated at higher rotational speeds.
According to a second aspect of the present disclosure there is provided a method of manufacturing a rotor assembly, the method comprising the steps of:
By positioning alternate ones of the blade root slots at an angle to the axis of rotation, the rotor assembly can be intentionally de-tuned to improve the stability margin, so taking it away from normal operation of the rotor assembly.
This alternating angled blade root slot arrangement results in more than one set of blades with each of the sets of blades having different mean root heights. This difference in mean root height results in each of the blade sets having a different centre gravity. It is the different centre of gravity between adjacent blades that results in the de-tuning of the rotor assembly.
The arrangement of alternating blade root slot angle requires no change to the annulus line and throat area for the rotor assembly. This means that the aerodynamic efficiency of the rotor assembly is not adversely affected by the mis-tuning effect of the angled blade root slot arrangement, which in turn makes the arrangement convenient for a user.
Optionally, the step of forming a plurality of alternate first blade root slots and second blade root slots, arranged in a circumferential array, the axial separation between the first face and the second face defining a respective blade root slot axial length, each of the first blade root slots being positioned at a first radius from the axis of rotation at the first face, each of the second blade root slots being positioned at a second radius from the axis of rotation at the first face, and the first radius increasing monotonically along the first blade root slot axial length from the first face to the second face, comprises the step of:
In this arrangement, each of the first blade root slots is angled with the first radius increasing monotonically along the blade root slot from the first face to the second face, while each of the second blade root slots is angled with the second radius decreasing monotonically along the blade root slot from the first face to the second face.
In this arrangement, the blade root slots are angled relative to an axis of rotation of the rotor assembly with adjacent ones of the blade root slots being angled in opposing senses. In other words, adjacent ones of the blade root slots alternately slope inwardly and outwardly along an axis of rotation of the rotor assembly from one end of the rotor assembly to the other.
By angling each blade root slot in an opposite sense to its neighbouring blade root slot, each first blade will have a different centre of gravity to the adjacent second blade. This difference in centre of gravity enables the above-mentioned mis-tuning of the rotor assembly.
Other aspects of the disclosure provide devices, methods and systems which include and/or implement some or all of the actions described herein. The illustrative aspects of the disclosure are designed to solve one or more of the problems herein described and/or one or more other problems not discussed.
There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:
It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
A turbofan gas turbine engine 10, as shown in
Referring to
The rotor assembly 100 comprises a hub 110, a plurality of first blades 120, and a plurality of second blades 130. Each of the first blades 120 comprises a first blade root portion 122. Each of the second blades 130 comprises a second blade root portion 132.
The hub 110 comprises a plurality of first blade root slots 140 and a plurality of second blade root slots 150 arranged in a circumferential array around an axis of rotation 112 of the hub 110.
The hub 110 further comprises a first face 114 and an opposite second face 116. An axial separation 118 between the first face 114 and the second face 116 defines a respective blade root slot axial length 141,151. In other words, each of the first blade root slots 140 has a first blade root slot axial length 141, and each of the second blade root slots 150 has a second blade root slot axial length 151.
Each of the plurality of first blade root portions 122 is accommodated within a respective one of the first blade root slots 140. Each of the plurality of second blade root portions 132 is accommodated within a corresponding one of the second blade root slots 150.
Each of the first blade root slots 140 is positioned at a first blade root slot radius 142 from the axis of rotation 112 at the first face 114. Each of the second blade root slots 150 is positioned at a second blade root slot radius 152 from the axis of rotation 112 at the first face 114.
In the embodiment shown in the figures, the first radius 142 increases monotonically along the first blade root slot axial length 141 in a direction extending from the first face 114 to the second face 116. In addition, the second radius 152 decreases monotonically along the second blade root slot axial length 151 in a direction extending from the first face 114 to the second face 116. In other words, the circumferential array of first and second blade root slots 140,150 comprises an alternating sequence of sloped blade root slots 140,150, with adjacent blade root slots 140,150 being sloped in an opposite sense to each other.
In an alternative arrangement, each of the first blade root slots 140 may be angled as outlined above, whilst each of the second blade root slots 150 may be parallel to the axis of rotation 112.
Respective ones of the first blade root slots 140 and second blade root slots 150 are arranged in an alternating sequence circumferentially around the axis of rotation 112. Respective ones of the plurality of first blade root portions 122 are accommodated in corresponding ones of the first blade root slots 140, and respective ones of the plurality of second blade root portions 132 are accommodated in corresponding ones of the second blade root slots 150.
Each of the first and second blades 120:130 has a respective blade tip portion 124:134. For each of the first and second blades 120:130, the corresponding blade tip portion 124:134 is positioned radially outwardly of the respective blade root portion 122:132. The plurality of blade tip portions 124:134 together define a blade tip circumference 126.
Each of the first blade root slots 140 is angled at a first blade root slot angle 143 to the axis of rotation 112, and each of the second blade root slots 150 is angled at a second blade root slot angle 153 to the axis of rotation 112. In one arrangement, the first blade root slot angle 143 is 3°, and the second blade root slot angle 153 is 3°. In other embodiments of the disclosure, the first blade root slot angle 143 and the second blade root slot angle 153 may be other than 3°. In further arrangements, the first blade root slot angle 143 may be different to the second blade root slot angle 153.
In the embodiment shown in
Referring to
Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.
The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the disclosure as defined by the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1612288.9 | Jul 2016 | GB | national |
