Patent Application
20170241434
The application relates generally to gas turbine engines and, more particularly, to spigot joints of gas turbine engine casing apparatuses.
In gas turbine engines a casing assembly is provided to house and support a number of rotors such as fan, compressor and turbine rotors. A conventional casing assembly may include a fan case, an intermediate case, a compressor case, a gas generator case, a turbine case and turbine exhaust case arranged about a central axis of the engine. The individual cases may be connected one to another for example by flanges and fasteners. A spigot joint may be provided between two connected cases such as the intermediate and compressor cases in order to provide concentricity control of the two cases. However, different cases may be made of different materials which have different thermal expansion coefficients. This may cause excessive tightening of the spigotted joint which can in turn cause high stress areas near the spigotted joint during engine operation. These high stress areas may be at locally stiff features such as bosses, discrete struts or supports, etc. and therefore may be at risk of component damage such as strut cracking.
Therefore, improved case joints are needed to relieve local loads generated by a tight spigot while maintaining concentricity control of the mating parts.
In one aspect, there is provided a gas turbine engine casing apparatus comprising a first annular case and a second annular case axially connected by a spigot joint, the spigot joint including a projection having a first annular mating surface axially projecting from an end of the first annular case and a recess having a second annular mating surface axially extending into an end of the second annular case, the projection being received in the recess such that the first and second annular mating surfaces mate each other, and a plurality of circumferentially extending intermittent scallops circumferentially spaced from one another and formed on at least one of the first and second annular mating surfaces, the scallops being located at selected circumferential locations to reduce a local contact area between the mating surfaces of the projection and the recess.
In another aspect, there is provided a gas turbine engine casing apparatus having a first case including at least a first annular wall integrated with and supported by a plurality of circumferentially spaced apart and radially extending struts and a second case including at least a second annular wall, the first and second annular walls being axially connected by a spigot joint, the spigot joint comprising: an annular projection having outer-diameter and inner-diameter surfaces co-axially projecting from an end of the first annular wall and an annular recess having outer-diameter and inner-diameter surfaces axially extending into an end of the second annular wall, the annular projection being received in the annular recess such that the two outer-diameter surfaces mate with each other or the two inner-diameter surfaces mate with each other, and a plurality of circumferentially extending and spaced apart grooves formed on one of the surfaces, the grooves being located circumferentially adjacent the respective struts to reduce a local contact area between the projection and the recess.
In a further aspect, there is provided a gas turbine engine comprising an intermediate case axially connected to an annular compressor case by a spigot joint, the intermediate case including a plurality of annular walls connected by a plurality of radially extending struts, the spigot joint including an annular projection having first outer-diameter and first inner-diameter surfaces extending axially from an end of one of the annular walls and an annular recess formed radially between second outer-diameter and second inner-diameter surfaces extending axially into an end of the annular compressor case, the annular projection being received in the annular recess such that the first and second outer-diameter surfaces mate with each other or the first and second inner-diameter surfaces mate with each other, and a plurality of circumferentially extending and spaced apart grooves formed on one of the first and second outer-diameter surfaces, the grooves being located circumferentially adjacent the respective struts to reduce a local contact area between the projection and the recess.
Reference is now made to the accompanying figures in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
It should be noted that the terms “axial”, “radial” and “circumferential” used for various components throughout the description and appended claims are defined with respect to the longitudinal central axis 12 of the engine.
A generally cylindrical casing assembly 32 envelops the engine 10 and thereby defines a main flow path (indicated by arrows) 36 through a core of engine 10 and a bypass flow path (indicated by arrows) 37.
Is should be noted that the terms “upstream”, “downstream”, “front” and “aft” are defined with respect to the direction of the air flow entering into and passing through the main flow path 36 of the engine 10.
The casing assembly 32 according to one embodiment may include a generally cylindrical fan case 44, which houses the fan rotor assembly 13, a generally cylindrical intermediate case 46 downstream of the fan case 44 and a gas generator case 52 downstream of the intermediate case 46. The intermediate case 46 may include a bearing seat 58 for mounting an HP bearing 59 thereto. The cylindrical casing assembly 32 may further include a cylindrical bypass duct case 56 generally surrounding the gas generator case 52 and a cylindrical compressor shroud 48 which encircles blade tips of the HPC assembly 16. The cylindrical compressor shroud 48, gas generator case 52 and the bypass duct case 56 are located downstream of and are connected to the intermediate case 46.
Referring to
The intermediate case 46 may further have a plurality of radially extending struts 40 which may each be configured as a hollow structure. The radially extending struts 40 may be circumferentially spaced apart one from another, each connecting or being integrated with the respective cylindrical walls 41, 42, 43, and 45 and thus in combination support all the cylindrical walls 41, 42, 43 and 45 in an integrated configuration to form the intermediate case 46.
Referring to
A tight fit of the spigot joint 60 is required for concentricity control of the cylindrical wall 42 of the cylindrical intermediate case 46 and the cylindrical compressor shroud 48 for the purpose of blade tip clearance control of the HPC blades 50 with respect to the cylindrical compressor shroud 48. Nevertheless, during engine operation the spigot joint 60 may become excessively tight between the outer-diameter surfaces 66 and 70 due to different thermal expansion coefficients of the two mating parts. For example, the intermediate case 46 according to one embodiment may be made of magnesium and the compressor shroud 48 may be made of titanium which has a thermal expansion coefficient lower than the thermal expansion coefficient of magnesium. At a cold assembly condition according to this embodiment, the spigot joint 60 may be tight between the inner-diameter surfaces 68 and 72. However, under operating conditions such a thermal mismatch of the two mating parts of the spigot joint 60 may result in high compressive stresses developing in a plurality locally stiffer regions indicated by “A”, adjacent the respective struts 40. Such local high compressive stresses may cause an elevated risk of stress cracking.
According to one embodiment, a plurality of circumferentially spaced intermittent scallops or shallow grooves 74 (see
Alternatively, the scallops or shallow grooves 74 may be provided on the outer-diameter surface 70 of the annular recess 64. Alternatively, scallop the scallops or shallow grooves 74 may be provided on both surfaces 66 and 70.
Optionally, the scallops or shallow grooves 74 may be circumferentially located symmetrically about a radial central axis 80 of the respective radially extending struts 40. Optionally, the scallops or shallow grooves 74 may be configured in an arc profile equal to or less than 20 degrees because the scallops or shallow grooves 74 are provided for locally reducing the presences of an over-tight spigot fit conditions in selected circumferential locations while maintaining concentricity control of the spigotted connection. As noted, the scallops or shallow grooves 74 are circumferentially intermittent, as the skilled reader will appreciate in light of this disclosure that a fully-annular groove may disadvantageously affect spigot fit, such as required for concentricity control of the spigotted connection. The scallops or shallow grooves 74 according to one embodiment may have a depth of 0.015 inches (0.37 mm) or less.
The above-described subject matter may be applicable to spigotted connections between first and second annular engine cases of other types, not limited to the spigotted connection between an intermediate case and a compressor shroud. Furthermore, the plurality of circumferentially extending and spaced apart scallops or shallow grooves 74 may be formed on one of the outer-diameter surfaces 66, 70 or on one of the inner-diameter surfaces 68, 72, and may be located in selective circumferential locations adjacent respective enhanced stiff areas of two connected annular cases. Depending on the particular configuration of the cases, the enhanced stiff areas may be formed with bosses, discrete struts or supports, etc. wherein the local areas may be stiffer than surrounding areas.
As a general example, the plurality of scallops or shallow grooves may be formed on the outer-diameter surface of the annular projection and/or of the annular recess when one of the connected cases which is integrated with the annular projection has a thermal expansion coefficient higher than a thermal expansion coefficient of the other of the connected case which defines the annular recess therein.
As another general example, the plurality of scallops or shallow grooves may be formed on the inner-diameter face of the annular projection or of the annular recess when one of the annular cases which is integrated with the annular projection has a thermal expansion coefficient lower than a thermal expansion coefficient of the other of the connected cases which defines the annular recess.
As a note, spigot connections also exist where there is not a second mating diameter (i.e. 68 and 72 do not exist) where the described subject matter could still apply.
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 described subject matter. For example, in the above-described embodiments, it is a high pressure compressor (HPC) tip clearance control that is being preserved but the described subject matter is also applicable for low pressure compressor (LPC) tip clearance control. 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.
