The invention relates generally to an exhaust strut and gaspath for a gas turbine engine and, more particularly, to airfoil profiles suited for thin and thick exhaust struts of an auxiliary power unit (APU).
A gas turbine engine typically includes an exhaust duct through which hot combustion gases are flowed during operation of the engine. The exhaust duct conventionally comprises an inner cylindrical member forming the inner wall of the gaspath and an outer cylindrical member forming the outer wall of the gaspath. A plurality of radially extending struts spans the gaspath between the inner and outer cylindrical members.
Hot combustion gases discharging from the turbine into the exhaust duct during operation of the engine have a residual velocity component in the tangential direction with respect to the inner annular gaspath. The tangential velocity component of the hot combustion gases is undesirable as it detracts from the momentum increase that produces a forward axial thrust in the gas turbine engine. Conversion of the tangential velocity to axial velocity increases the axial thrust produced in the mixer and is essential for optimum operation of the turbine engine.
The tangential velocity component of the flow is redirected axially by the struts of the exhaust duct. More specifically, each strut has an airfoil for axially straightening the flow, the airfoil profiles being configured so as to aerodynamically affect the turning of the flow of gases.
In an exhaust duct following a single stage low pressure (LP) turbine, and particularly where the duct has forced mixer component following it, the strut airfoil shape must remove a substantial amount of residual swirl in the flow leaving the single stage LP turbine, in order to ensure that the forced mixer component which follows can function correctly. The amount of swirl will vary from the inner to the outer annulus and from one engine operating condition to another. At altitude, the flow Reynolds Number will be such that the flow is subject to flow separation unless great care is taken in determining the airfoil profile shape. Thus, the flow regimes this type of airfoil is exposed to will vary substantially with engine operating conditions and will be subject to flow separation. Therefore, improvements in airfoil design are sought.
It is therefore an object of this invention to provide an improved airfoil shape for a strut of a turbine exhaust duct of a high power APU.
In one aspect, the present invention provides a strut extending across an exhaust duct of a gas turbine engine, comprising an airfoil having at least a portion defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 to 7 set forth in one of Table 2 and Table 3, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the strut in the exhaust duct, the Z values are radial distances measured along the stacking line, the X and Y are coordinate values defining the profile at each distance Z.
In another aspect, the present invention provides a strut extending across an exhaust duct of a gas turbine engine comprising an uncoated airfoil having at least one portion defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 to 7 set forth in one of Table 2 and Table 3, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the strut in the exhaust duct, the Z values are radial distances measured along the stacking line of the airfoil, the X and Y are coordinate values defining the profile at each distance Z, and wherein the X and Y values are scalable as a function of the same constant or number.
In another aspect, the present invention provides an exhaust duct for a gas turbine engine comprising a plurality of thin struts, each thin strut including an airfoil having at least one portion defined by a nominal profile substantially in accordance with Cartesian coordinate values of X, Y, and Z of Sections 3 to 7 set forth in Table 2, wherein the point of origin of the orthogonally related axes X, Y and Z is located at an intersection of a centerline of the gas turbine engine and a stacking line of the struts, the Z values are radial distances measured along the stacking line, the X and Y are coordinate values defining the profile at each distance Z.
In another aspect, the present invention provides an exhaust strut comprising at least one airfoil having a surface lying substantially on the points of Table 2, the airfoil extending between inner and outer end portions defined generally by Table 1, and wherein the values of Table 2 are subject to relevant tolerance.
This design profile advantageously removes a substantial amount of residual swirl in the flow leaving the LP turbine. The unique airfoil shape is optimized to minimize flow separation at low Reynolds number. According to another aspect, the thin and thick aerofoils are optimized and integrated for oil system access.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
a and 4b are respectively cross-sections of the thin exhaust strut and the thick exhaust strut shown in
The gas turbine engine 10 further includes a turbine exhaust duct 20 which is exemplified as including an annular core portion 22 and an annular outer portion 24 and a plurality of thin struts 26 circumferentially spaced apart, and radially extending between the inner and outer portions 22, 24. Specifically, the turbine exhaust duct 20 includes 5 thin struts 26a and 3 thick strut 26b.
The turbine section 18 has a high pressure turbine (HPT) stage located downstream of the combustor 16 and a low pressure turbine (LPT) stage located further downstream in the gaspath 27. The turbine exhaust duct 20 is shown downstream from the LPT stage.
Referring to
The HPT includes 14 HP vanes and 65 HP blades, the LPT include 38 LP vanes and 59 LP blades, and there are 5 thin and 3 thick airfoils in the turbine exhaust case.
The novel airfoil shape of each strut 26a, 26b is defined by a set of X-Y-Z points in space. This set of points represents a novel and unique solution to the target design criteria discussed above, and is well-adapted for use in a single-stage LPT design. The set of points are defined in a Cartesian coordinate system having mutually orthogonal X, Y and Z axes. The X axis extends axially along the turbine rotor centerline 29, i.e., the rotary axis. The positive X direction is axially towards the aft of the turbine engine 10. The Z axis extends along the strut stacking lines 52 and 53 of each respective strut 26a,b in a generally radial direction and intersects the X axis. The positive Z direction is radially outwardly toward the outer portion 24 of the turbine exhaust duct 20. The Y axis extends tangentially with the positive Y direction being in the direction of rotation of the rotor assembly 38. Therefore, the origin of the X, Y and Z axes for the thin and the thick struts is respectively defined at the point of intersection of all three orthogonally-related axes: that is the point (0,0,0) at the intersection of the center of rotation of the turbine engine 10 and the stacking line 52 and the staking line 53.
In a particular embodiment of the turbine exhaust duct 20, the set of points which define the airfoil profile of a portion of the thin strut 26a relative to the axis of rotation of the turbine engine 10 of the stacking line 52 thereof are set out in Table 2 below as X, Y and Z Cartesian coordinate values. Particularly, the strut airfoil profile is defined by profile sections 56a at various locations along its height, the locations represented by Z values. It should be understood that the Z values do not represent an actual radial height along the airfoil 54a but are defined with respect to the engine centerline. For example, if the thin struts 26a are mounted about the inner portion 22 of the turbine exhaust duct 20 at an angle with respect to the radial direction, then the Z values are not a true representation of the height of the airfoils 54a of the thin struts 26a. Furthermore, it is to be appreciated that, with respect to Table 2, Z values are not actually radial heights, per se, from the centerline but rather a height from a plane through the centerline—i.e. the sections in Table 2 are planar. The coordinate values are set forth in inches in Table 2 although other units of dimensions may be used when the values are appropriately converted.
Thus, at each Z distance, the X and Y coordinate values of the desired profile section 56a are defined at selected locations in a Z direction normal to the X, Y plane. The X and Y coordinates are given in distance dimensions, e.g., units of inches, and are joined smoothly, using appropriate curve-fitting techniques, at each Z location to form a continuous airfoil cross-section. The strut airfoil profiles of the various surface locations between the distances Z are determined by smoothly connecting the adjacent profile sections 56a to one another to form the airfoil profile.
The coordinate values listed in Table 2 below represent the desired airfoil profiles in a “cold” (i.e. non-operating) condition. However, the manufactured airfoil surface profile will be slightly different as a result of manufacturing tolerances. The coordinate values listed in Table 2 below are for an uncoated airfoil. According to an embodiment of the present invention, the struts remain uncoated. Likewise, the set of points which define the airfoil profile of a portion of the thick strut 26b relative to the axis of rotation of the turbine engine 10 of the stacking line 53 thereof are set out in Table 3 below as X, Y and Z Cartesian coordinate values.
The Table 2 and 3 values are generated and shown to three decimal places for determining the profile of the thin and thick strut airfoils. However, as mentioned above, there are manufacturing tolerance issues to be addressed and, accordingly, the values for the profile given in Table 2 and 3 are for a theoretical airfoil, to which a ±0.010″ manufacturing tolerance is additive to the X and Y values given in Table 2 below. The strut airfoil design functions well within this range. The cold or room temperature profile is given by the X, Y and Z coordinates for manufacturing purposes. It is understood that the airfoil may deform, within acceptable limits, once entering service.
The coordinate values given in Table 2 and 3 below provide the preferred nominal airfoil profile of a portion of the thin strut 26a and thick strut 26b, respectively.
It should be understood that the finished struts 26a and 26b do not necessarily include all the sections defined in Tables 2 and 3. The portion of the airfoil 54a,b proximal to the inner and outer portions 22, 24 may not be defined by a profile section 56a,b. It should be considered that the strut airfoil profile proximal to the inner and outer portions 22, 24 may vary due to several imposed constraints. However the struts 26a,b have an intermediate airfoil portion 54a,b defined between the inner and outer portions 22, 24 thereof and which has a profile defined on the basis of at least the intermediate Sections of the various strut profile sections 56a,b defined in Table 2 and Table 3.
It should be appreciated that the airfoil portion 54a,b of the struts 26a,b is defined between the inner and outer gaspath walls 28 and 30 which are partially defined by the inner and outer portions 22 and 24 of the turbine exhaust duct 20. More specifically, the Z values defining the gaspath in the region of the stacking line 52 fall within the range of Z=3.933 and Z=7.181, which are the z values of the inner and outer walls 28 and 30 of the gaspath near the stacking line 53 (see Table 1). Therefore, the airfoil profile physically appearing on the thin and thick struts includes Sections 3 to 7 of Table 2 and Table 3, respectively. Sections 2 and 8 are partially in the gaspath. Sections 1 and 9 are located completely outside of the boundaries set by the inner and annular outer gaspath walls 28 and 30 at the strut stacking lines 52 and 53, and are provided, in part, to fully define the airfoil surface and, in part, to improve curve-fitting of the airfoil at its radially distal portions. The skilled reader will appreciate that a suitable fillet radius is to be applied between the portions 22 and 24 and the airfoil portion 54a,b of the strut 56a,b.
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 department from the scope of the invention disclosed. For example, the airfoil and/or gaspath definitions of Tables 1, 2 and 3 may be scaled geometrically, while maintaining the same proportional relationship and airfoil shape, for application to gas turbine engine of other sizes. 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.