Patent Publication Number: US-11021975-B2

Title: Gas turbine engine and rotary assembly therefor

Description:
TECHNICAL FIELD 
     The application related generally to gas turbine engines and, more particularly, to a structure having a connector joining two rotary components to one another. 
     BACKGROUND OF THE ART 
     It was known to structurally join rotary components to one another using a spigot fit, i.e. an arrangement where a male portion of a first one of the rotary components was press-fitted into a female portion of a second one of the rotary components, with an annular, radial interference fit being formed therebetween. Over the use of fasteners, for instance, such an arrangement can provide the benefit of greater simplicity. However, such arrangements were not suitable for all conditions. Indeed, there is a limit to the amount of interference which can be achieved upon press fitting, and in some conditions of use, the deformation between the rotary components in conditions of use can be unequal, and the growing of the first rotary component relative to the second rotary component can lead to progressively diminishing interference of the fit therebetween, and ultimately to the formation of a gap and to the loss of the structural joint. There thus remained room for improvement. 
     SUMMARY 
     In one aspect, there is provided a rotary assembly comprising a first and second rotary components structurally joined to one another via a connector, a first radial fit between the connector and the first rotary component, the first radial fit forming an interference fit at a first operating condition of the rotary assembly and forming a gap at a second operating condition, a second radial fit between the connector and the first rotary component, the second radial fit forming an interference fit at the second operating condition and forming a gap at the first operating condition, the rotary assembly being further configured to form a radial interference fit between the connector and the second rotary component in both the first and the second operating conditions. 
     In another aspect, there is provided a gas turbine engine comprising a first and second rotary components structurally joined to one another via a connector, a first radial fit between the connector and the first rotary component, the first radial fit forming an interference fit at a first operating condition and forming a gap at a second operating condition, a second radial fit between the connector and the first rotary component, the second radial fit forming an interference fit at the second operating condition and forming a gap at the first operating condition, the gas turbine engine being further configured to form a radial interference fit between the connector and the second rotary component in both the first and second operating conditions. 
     In a further aspect, there is provided a method of operating a gas turbine engine having a first radial fit between a connector and a first rotary component and a second radial fit between a connector and the first rotary component, the connector structurally joining the first rotary component to a second rotary component, the method comprising: in a first operating condition, providing an interference fit at the first radial fit, and a loose fit at the second radial fit; transitioning from the first operating condition to a second operating condition, including gradually reducing the interference fit of the first radial fit, the first radial fit forming a gap at the second operating condition, and gradually reducing the gap of the loose fit, the second radial fit forming an interference fit at the second operating condition; maintaining at least one radially-oriented interference fit between the second rotary component and the connector throughout the transitioning. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIGS. 2A and 2B  are cross-sectional views show a portion of a first embodiment of a rotary assembly, with  FIG. 2A  in a first operating condition, and  FIG. 2B  in a second operating condition. 
         FIG. 3  is a graph schematically illustrating the transition between the first operating condition and the second operating condition; 
         FIG. 4  is a cross-sectional view similar to  FIG. 2A , showing a second embodiment; 
         FIG. 5  is a graph schematically illustrating the transition between the first operating condition and the second operating condition for the embodiment of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrated a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. 
     The compressor section  14  can include, for instance, a plurality of rotors and stators. The rotors can be formed of separately manufactured rotor discs and blades which are assembled to form the rotor, such as via a dovetail engagement for instance, or be provided in the form of integrally bladed rotors, to name two relatively common examples. 
     Integrally bladed rotors, in particular, are subjected to a significant amount of design testing, which can be performed using a device referred to as a test rig, such as a cold flow test rig for instance. In such a test environment, it can be desired to test a rotary assembly including two adjacent rotors at different inter-rotor spacings. In this context, it can be useful to provide a plurality of connectors designed to be assemblable to the two adjacent rotors in a manner to structurally join the two adjacents rotors to one another for a given test, during which the test rig rotates the rotary structure with a first inter-rotor spacing. Following a given test, the connector can then be removed, and replaced with a connector having a different axial thickness, to test the same rotors again, but with a different inter-rotor spacing. 
       FIGS. 2A and 2B  show an example of a rotary structure  20  which has two rotary components  22 ,  24  structurally joined to one another via a connector  26 . The connector  26  has a first radial fit  28  with the first rotary component  22 , and a second radial fit  30  with the second rotary component  24 . As will be explained below, the first radial fit  28  forms an interference fit in a first operating condition shown in  FIG. 2A , during which the second radial fit  30  forms a gap/loose fit, and vice-versa in the second operating condition shown in  FIG. 2B , maintaining an interference fit between the connector  26  and the first radial component  22  in both operating conditions. It will be noted that an interference fit is also maintained between the connector  26  and the second rotary component  24  in both operating conditions, effectively structurally joining the two rotary components  22 ,  24  in these two operating conditions. In the radial fits, the faces which engage one another extend axially and are pressed against one another in the radial orientation (relative to the engine axis  11 ). The faces typically extend annularly, around an entire circumference (cylindrically), and the resulting interference fit can be referred to as a spigot fit. In this example, the two rotary components  22 ,  24  are corresponding integrally bladed rotors configured for testing in a test rig. It will be understood that the two rotary components  22 ,  24  can be other components in alternate embodiments. 
       FIG. 2A  shows the rotary structure  20  in a first operating condition. The first operating condition, in this example, is the rest condition. The first radial fit  28 , which is an interference fit in this operating condition, can be formed by press-fitting an outer diameter face of the connector  26  into an inner diameter face of the first rotary component  22 , for instance. In this first operating condition, the second radial fit  30 , which can be formed between a radially inner diameter face of the connector  26  and a radially outer diameter face of the first rotary component  22  can be loose, and have a small gap between the two components. In this embodiment, the second operating condition can correspond to a condition in which the rotary assembly is rotated at a relatively high RPM, which can impart stress to the components due to centripetal acceleration, resulting in growth of the components. This stress can be greater in components which are heavier than in components which are lighter, and in components which have a more radially-outwardly distributed mass. In the case of an integrally bladed rotor, for instance, the integrally bladed rotor can have a significantly greater weight and have a mass which is significantly more radially-outwardly distributed than the connector  26 , for instance. In such a scenario, even if the connector  26  is made of a material having the same elasticity than the rotor, such as the same metal for instance, the rotor will nonetheless be subjected to greater growth than the connector  26 . 
     A similar effect can occur if the first rotary component  22  and the connector  26  have a different thermal growth coefficient and the second operating condition is at a higher temperature than the first operating condition, for instance, or simply if they have a different level of elasticity (e.g. Young&#39;s modulus). In the transition to the second operating condition, the growth of the first rotary component  22  leads to progressively lesser interference in the first radial fit  28 . However, simultaneously, it also leads to a progressively lesser gap in the second radial fit  30 , and eventually to progressively increasing interference fit in the second radial fit  30 . At the second operating condition, the interference fit of the first radial fit  28  can be completely lost, and replaced with a gap, but the structural joint between the connector  26  and the first rotary component  26  can nonetheless be maintained via the second radial fit  30 . 
     It will be noted here that the radial direction, or relative orientation, of the first rotary component  22  and of the connector  26  is inversed from the first radial fit  28  to the second radial fit  30 , and that the initial gap of the second radial fit  30  is designed to be sufficiently small to allow it to become an interference fit in the second operating condition. Moreover, throughout the transition, a third radial fit  32  is maintained in an interference fit condition, between a radially-outwardly facing cylindrical face of the connector  26  and a radially-inwardly facing cylindrical face of the second rotary component  24 . In this embodiment, this was achieved while avoiding to subject the connector  26 , or any of the two rotary components  22 ,  24 , to critical deformation stresses which could have led to a failure, such as a crack formation. 
     The design of the fit was achieved using ANSYS software, a finite element type analysis software, which can allow to simulate the conditions, and resulting stresses, using a computer and virtual models of the components of the rotary assembly. It will be noted that the initial interference fit conditions themselves, at the first radial fit and the third radial fit, impart stresses, and thus deformation into the components, including the connector, which must be taken into account in designing such a structural joint. However, simulations performed using the ANSYS software led to the conclusion that using such a three radial fit solution to join two rotary components using a connector, could lead to a workable solution, and such a workable solution may be of use in a test rig or in a gas turbine engine environment, for instance. Though the calculations are more complex than modeling single radial fits, the ANSYS software was nonetheless able to perform them. 
     The varying conditions during the transition are schematized in the graph shown in  FIG. 3 . The progressive reduction of the interference in the first radial fit  28  is shown by a line which begins with a significant interference fit in condition A, and which progresses to a gap/spacing at condition B. The portion of the graph where the interference fit of the first radial fit  28  is maintained can be referred to as the first radial fit interference zone  34 . Similarly, the second radial fit  30  is shown to have a negative value at condition A which progresses until reaching zero, and then an increasing positive value along a second radial fit interference zone  36 . It will be noted that in this embodiment, there is a zone  38  in the graph where both the first and the second radial fits  28 ,  30  are in an interference fit scenario, which can be referred to as a zone of overlapping interference  38 . Such a zone  38  can be useful in ensuring that a structural joint is maintained throughout the transition. It will also be noted that in this embodiment, the third interference fit  32  is maintained in the positive values of interference throughout the transition. 
       FIG. 4  shows an other embodiment. In this other embodiment, a double radial fit engagement is used not only between the connector  126  and the first rotary component  122 , but also between the connector  126  and the second rotary component  124 . More specifically, the double radial fit ( 128 ,  130 ) between the connector  126  and the first rotary component  122  is as illustrated in  FIG. 2A , but rather than using a single radial fit between the connector  126  and the second rotary component  124 , a third  132  and a fourth  133  radial fits are used. The third radial fit  132 , in this embodiment, can be similar to the third radial fit of the embodiment of  FIG. 2A . However, in this embodiment, it was not found suitable to provide a third radial fit having an interference level sufficient to be maintained at the second operating condition, where a gap was instead present. In this embodiment, this was compensated by providing a fourth radial fit  133 , having again an inversed radial direction compared with the other radial fit  132 , which begins with a gap, but eventually reaches engagement, and ultimately a suitable level of interference to maintain an interference fit between the connector  126  and the second rotary component  124  throughout the transition, similarly to what was achieved in  FIG. 2A-2B  using a single radial fit  32  between the connector  26  and the second rotary component  24 . 
     In a gas turbine engine environment, the first condition can be an engine idle condition, for instance, and the second condition can be a full thrust condition, for instance. 
     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. For example, the radial fits can be positioned in different configurations than those illustrated in the examples, and can be axially spaced apart from one another, for instance. In some embodiments, each radial fit can include more than one set of engaging cylindrical surfaces. Moreover, and if different growth phenomena are present for instance, it can be preferable to use more than two radial fits between the connector and any one of the two rotary components, such as a second one which becomes engaged due to thermal growth and a third one which becomes engaged due to centripetal acceleration, for instance. If applied in a gas turbine engine context, the connector and dual radial fit-based structural joining concept presented above can be applied between various gas turbine engine components, such as between a coverplate and a disc, between two discs, between a disc and an impeller, between attachments, etc. 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.