GB2046849A

GB2046849A - Turbomachine strut

Info

Publication number: GB2046849A
Application number: GB7913290A
Authority: GB
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1979-04-17
Filing date: 1979-04-17
Publication date: 1980-11-19

Abstract

In combination with a stator vane assembly 15 arranged within a fluid flow duct of a turbo-machine, there is provided a strut 16 projecting across the duct downstream of the stator vanes 17 and having a first axis 18 extending along the duct, the leading edge 19 of the strut 16 being of an assymmetric shape about axis 18 and comprising two surfaces 20, 21 which meet at an apex 22 positioned to one side of axis 18. <IMAGE>

Description

SPECIFICATION Struts for gas turbine engines This invention relates to turbo-machines and in particular to the design of struts which extend across fluid flow passages of such machines.

It is frequently necessary to provide such turbo-machines with one or more struts which extend across fluid flow passages of the machine. Usually such a strut is generally symmetrical about an axis extending in a direction along the duct. However, such a design causes a perturbation of the flow in the duct and when such a strut is positioned downstream of a row of stator blades the perturbation may be assymmetric in that it tends to increase the flow turning effect on one side of the strut and to decrease it on the other side of the strut, just ahead of the strut so that some of the stators become more highly loaded than others and could stall.

In our British Patent No 1,291,235 (Agent's reference case 629A) there is described a turbo-machine in which the stator blades are arranged along a helical path and the strut or pylon is designed to be effectively the equivalent of a stator blade and constitutes an essential part of the stator assembly design.

In many designs of aero-engines it is not practical to incorporate the pylon or strut as a part of the stator blade design. Furthermore, it is undesirable to design stator assemblies made from a plurality of individual differently designed stator blades. It is far better to employ a common design of blade so that there is uniformity in production and assembly.

In general, the perturbation of the air flow in the duct extends over a field of effect a distance of two and a half times the width of the pylon ahead of the leading edge of the pylon strut. Therefore, if the pylon or strut can be positioned more than say two and a half times the width of a pylon downstream of the stator blades then the perturbation in the flow of air in the duct will not seriously effect the operation of the stator blades. However, in many designs of engine it is not possible to position the pylon or strut, such a distance away from the stator blade assembly.

Accordingly, it is an object of the present invention to provide a design of strut for location closely adjacent a stator blade assembly and which is designed so that the perturbation in the air flow in the duct does not deleteriously effect the flow of air through the stator blade assembly.

According to the present invention there is provided in combination with a stator vane assembly arranged within a fluid flow duct of a turbo-machine, a strut which projects across the duct and has a first axis extending in a direction along the duct, the strut being positioned downstream of the stator vanes of the assembly so that a leading edge of the strut is spaced downstream of the trailing edges of all the stator vanes of the assembly, the leading edge of the strut being of an assymetric shape about the first axis of the strut.

Preferably, the leading edge of the strut comprises two surfaces which meet at an apex, the first axis of the strut passes through a trailing edge of the strut, and the apex is positioned to one side of the first axis of the strut.

The stator vanes deflect fluid flowing through the duct in a curved path. Preferably, the leading edge of the strut has a surface which is curved in the same sense as the curved path so as to present a concave surface to air issuing from between those vanes of the assembly adjacent to the concave surface.

Preferably, the leading edge of the strut has a second surface which is curved in the same sense as the curved path so as to present a convex surface to the air issuing from between those stator vanes of the assembly adjacent to the second surface. Alternatively, the leading edge of the strut may have a second surface which is curved in the opposite sense to that of the curved paths so as to present a concave surface to air issuing from between those stator vanes of the assembly adjacent to the second surface. In a further alternative arrangement the leading edge of the strut may have a second surface which is generally planar and lies in a plane extending along the duct.

The present invention will now be described, by way of an example, with reference to the accompanying drawings in which: Figure 1 shows a gas turbine front fan bypass engine incorporating the present invention; Figure 2 is a cross-sectional view through the strut which projects across the bypass duct of the engine of Fig. 1, illustrating, schematically, part of the stator vane assembly; Figure 3 illustrates an alternative shape of a strut to that shown in Fig. 2; and Figure 4 illustrates a further alternative shape of a strut to that-shown in Fig. 2.

Referring now to the drawings Fig. 1 shows a ducted fan gas turbine engine 10 having an engine casing 11 which accmmodates a core engine comprising compressor means, combustion equipment and turbine means (not shown). The turbine means drives a shaft 1 2 on which is mounted a front fan assembly 1 3 for rotation within a bypass duct 1 4. The bypass duct 1 4 is supported from the engine casing 11 by streamline struts 1 6 (one of which is shown) constructed in accordance with the present invention. Located between the leading edge of the struts 1 6 and the front fan assembly 1 3 is a stator vane assem bly 1 5 comprising a plurality of spaced curved stator vanes.

The curved stator vanes 1 7 are shown in greater detail in Fig. 2. The vanes 1 7 are of aerofoil section and are spaced apart around a circumferential line and arranged so that their trailing edges lie in a common plane. The gap between the guide vanes is a diverging gap and the guide vanes serve to deflect the air from the front fan assembly 1 3 in a curved path so that it issues in a generally axial direction along the bypass duct 14.

The strut 1 6 is spaced downstream of the trailing edges of the stator vane assembly 1 5 and as shown in Fig. 2 the central cored and trailing regions of the strut 1 6 are generally symmetrical about a centre line 18. The leading edge region 1 9 of the strut 1 6 is, however, of an assymmetric shape relative to the centre line 1 8. The leading edge region 1 9 of the strut 1 6 comprises two surfaces 20, 21 which meet at an apex 22 which is positioned to one side of the centre line 1 8. One of the surfaces 20 is curved in the same sense as the curved path followed by the air as it flows through the stator vane assembly so as to present a concave surface to the air issuing from the stator vane assembly 1 5. The other surface 21 is generally planar from the apex 22 to the mid-chord region 24.

It will be seen from Fig. 2 that the assymmetric shape of the strut 1 6 minimises the effect of perturbations in the air flow immediately ahead of the strut 1 6. The generally concave surface 20 has the effect of increasing the turning of the air flow whereas the straight line surface 21 reduces the turning effect, which, in the case of the symmetric shaped strut (shown dotted in Fig. 2) is in the opposite direction to the curved path of air through the stator vane assembly.

The preferred shape for the surface 21 is a straight line. However, other considerations of air supplies etc. and the like, may dictate a non-optimum shape. Figs. 3 and 4 show two alternative shapes for the leading edge region 19 of the strut 16. In Fig. 3 the curved surface 20 is generally concave as shown in Fig. 2 but the other surface 21 constituting the leading edge portion 1 9 is curved in the opposite sense to the curved path of air flowing through the stator vane assembly so as to present a concave surface to air issuing from the stator vane assembly in the gaps between the vanes that are adjacent to the surface 21. The apex 22 is, however, still offset from the centre line 1 8.

Referring to Fig. 4 the surface 20, is again curved in the same sense as the curved path through the stator vane assembly so as to present a concave surface to the air issuing from the stator vane assembly from the gaps between those vanes adjacent to the surface 20. The surface 21 is also curved in the same sense as the curved path of air flowing through the stator vane assembly so as to present a convex surface to the air issuing from the stator vane assembly from the gaps between those vanes adjacent the surface 21.

Here again the apex 22 is positioned to one side of the centre line 1 8 of the strut and the strut is generally symmetrical from the midchord position to the trailing edge.

Claims

1. In combination with a stator vane assembly arranged within a fluid flow duct of a turbo-machine, a strut which projects across the duct and has a first axis extending in a direction along the duct, the strut being positioned downstream of the stator vanes of the assembly so that a leading edge of the strut is spaced downstream of the trailing edges of all the stator vanes of the assembly, the leading edge of the strut being of an assymetric shape about the first axis of the strut.

2. The combination as claimed in claim 1 wherein the leading edge of the strut comprises two surfaces which meet at an apex, the first axis of the strut passes through a trailing edge of the strut, and the apex is positioned to one side of the first axis of the strut.

3. The combination as claimed in claim 1 or claim 2 wherein the stator vanes deflect fluid flowing through the duct in a curved path and the leading edge of the strut has a surface which is curved in the same sense as the curved paths so as to present a concave surface to air issuing from between those vanes of the assembly adjacent to the concave surface.

4. The combination as claimed in claim 3 wherein the leading edge of the strut has a second surface which is curved in the same sense as the curved paths so as to present a convex surface to air issuing from between those stator vanes of the assembly adjacent to the second surface.

5. The combination as claimed in claim 3 wherein the leading edge of the strut has a second surface which is curved in the opposite sense to that of the curved paths so as to present a concave surface to air issuing from between those stator vanes of the assembly adjacent to the second surface.

6. The combination as claimed in claim 3 wherein the leading edge of the strut has a second surfce which is generally planar and lies in a plane extending along the duct.