Patent Application
20180106161
The application relates generally to the field of gas turbine engines and, more particularly, to shrouding arrangements for surrounding the blades of gas turbine engine rotors.
In gas turbine engines, rotor tip clearance is an issue that affects turbine performance. Shrouds are used to address this issue. In typical gas turbine engines, the vane ring assembly is allowed some movement in the radial direction relative to the engine case: this is desirable to account for the thermal expansion of such vane assembly during operation of the gas turbine engine. The shrouds are integrated to such vane ring assembly, for example by being secured to the vane ring; however, as the vane ring assembly moves radially during operation as a result of thermal expansion, so do the shrouds, thereby reducing their sealing effectiveness. In more recent engines, shroud assemblies are directly secured to the engine case and made to move independently of the vane assembly. As the engine case temperature is lower than that of the vane assembly, radial movement due to thermal expansion is reduced during operation, thereby improving the shroud assemblies' sealing effectiveness. Such shroud assemblies have however certain design complexities, in order to be able to both support the sealing element and be secured to the engine case. Therefore, whenever the shroud assemblies need to be replaced/overhauled, there is a significant cost associated therewith. There is therefore a continued need for alternative shroud arrangements.
In one aspect, there is provided a gas turbine engine apparatus comprising: an engine case; a circumferential array of rotor blades located within the engine case and rotatable about a centerline; and a stator vane assembly located within the engine case, and axially spaced from the array of rotor blades, said stator vane assembly comprising a plurality of stator vane segments disposed circumferentially one adjacent to another, each stator vane segment comprising: an outer endwall, a plurality of vanes extending radially from the outer endwall towards the centerline, and a shroud segment extending axially from the outer endwall configured to extend to and surround the array of rotor blades, the shroud segment including an abradable portion surrounding the rotor blades; wherein the vane assembly is secured relative to the engine case.
In another aspect, there is provided a method for sealing a rotating circumferential array of rotor blades in a gas turbine engine having an adjacent vane assembly, the method comprising: surrounding the array of rotor blades with an abradable element assembly configured to abrade when contacted by the rotor blades; securing the abradable element assembly to an outer shroud of the vane assembly; and securing the vane assembly to the engine case.
In a further aspect, there is provided a stator vane segment for use in a gas turbine engine, the stator vane segment comprising a plurality of vanes extending between an outer endwall and an inner endwall, the outer endwall extending axially to provide a shroud, the shroud including an abradable portion configured to surround a rotating array of rotor blades; wherein the stator vane segment is configured to be securable to an engine case.
Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description and drawings included below.
Reference is now made to the accompanying figures in which:
The engine case 30 is concentrically mounted about centerline A. Engine case 30 may, in turn, may be structurally connected to nacelle 10 through a plurality struts 18 extending radially through a bypass passage 16 of the engine. It may also be appreciated that a tail cone 25 may be positioned at an aft end of engine case 30.
In operation, hot combustion gases discharged from combustor 23 power and flow through high and low pressure turbines 19 and 15, and are then exhausted into the atmosphere.
Pursuant to an embodiment of the invention, a stator vane assembly of a low pressure turbine will be described. More specifically, as shown in
The stator vane segment 40, shown by itself in
Stator vane segment 40 further comprises a shroud segment 44 which is integral to and extends axially from outer endwall 41. When stator vane segment 40 is installed in a gas turbine engine, shroud segment 44 surrounds the circumferential array of rotor blades 52. Shroud segment 44 is positioned radially further away from centerline A than outer endwall 41, as it is preferable that array of rotor blades 52 extends radially further away from centerline A in relation to position of outer endwall 41.
An abradable element 45 is secured to shroud segment 44. The qualifier “abradable” is meant to signify that element 45 is made of a material that, when the gas turbine engine is in operation, wears away when array of rotor blades 52 enters in frictional contact with it, more specifically when shrouded end 55 of array of rotor blades 52 enters in frictional contact with. It is understood that in sections of the gas turbine engine where rotor blades are not or cannot be shrouded, it is the unshrouded end (or tip) of the rotor blade that will wear away abradable element 45. An example of an acceptable material for abradable element 45 is honeycomb. Abradable element 45 is also positioned radially further away from centerline A than outer endwall 41, as it is preferable that array of rotor blades 52 extends radially further away from centerline A in relation to position of outer endwall 41.
As shown in more details in
In the embodiment shown in
It will be understood that other techniques for radially securing each stator vane segment 40 to engine case 30 and for assisting in the structural integrity of stator vane segment 40 as it is secured to engine case 30, such as the embodiment described in more details below (and shown in
As discussed above and partially shown in
The anticipated level of thermal expansion that such vane assembly will need during operation of the gas turbine engine may also be addressed by ensuring that, when stator vane segments 40 are secured to engine case 30, in the embodiment shown in
As discussed above, other techniques for radially securing each stator vane segment 40 to engine case 30 and for assisting in the structural integrity of stator vane segment 40 as it is secured to engine case 30 are possible pursuant to the invention. For example, as shown in
engine case connecting element 135 comprises C-shape ends 136 and 137, which are facing downstream (towards right hand side of
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 departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention 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.
