The invention relates to turbine engines and variable guide vanes and/or inlet guide vanes for turbine engines in particular.
In a gas turbine engine having a multi-stage axial compressor the rotor is turned at high speed so that air introduced into the compressor is accelerated by the rotating blades and swept rearwards onto an adjacent row of stator vanes. Each rotor stage increases the pressure of the air passing through the stage and at final stage of the compressor the air is many times that of the inlet air pressure.
In addition to converting the kinetic energy of the air into pressure the stator vanes also serve to correct the deflection given to the air by the rotor blades and to present the air at the correct angle to the next stage of the rotor blades.
As compressor pressure ratios have increased it has become more difficult to ensure that the compressor will operate efficiently over the operational speed of the engine. This is because the inlet to exit area ratios of the stator vanes required for high pressure operation can result in aerodynamic inefficiently and flow separation at low operational speeds and pressures.
In applications where high pressure ratios are required from a single compressor spool the above problem can be overcome by using variable stator vanes which permit the angle of one or more rows of stator vanes in a compressor to be adjusted while the engine is running in accordance with the rotational and mass flows of the engine.
Existing designs for variable inlet guide vanes typically incorporate an integral outer platform which provides for an interface between the aerofoil and also that of the outer spindle. Often known as a “penny”, these platforms are round in geometry and positioned within a counterbore incorporated into a suitable casing to provide for a continuous aerodynamic profile at the casing/penny interface as the vane rotates.
A non metallic thrust washer may be sandwiched between the penny and the inner base surface of the counterbore to prevent metal to metal contact.
The counterbore must be sufficiently robust to accommodate the penny and platform and not distort in use. With large vanes the size and depth of the counterbore significantly increases the machining time and cost of the casing. Alternative manufacturing methods, such as forging, to form the casing can exhibit high levels of distortion in manufacture.
It is an object of the present invention to seek to address these and other problems.
According to a first aspect of the invention there is provided a variable guide vane assembly comprising a variable guide vane having an aerofoil and a spindle at one end of the aerofoil; wherein the vane further comprises a platform having a non-circular plan positioned between the aerofoil and the spindle, the platform having a surface facing in the direction of the spindle and at least one side face; the assembly also having a washer having a circular plan with an aperture through which the spindle extends, the washer having a portion which overhangs the at least one side face. Preferably the washer is supported by the platform surface and portion overhangs one or more of the side faces of the platform. Preferably the plan of the washer is circular. The plan of the platform may be non-circular and may be rectangular, fluted or lobed.
Advantageously, the washer may be secured to the platform by its positioning between the platform and a further component or by an interference fit between the platform and the washer. Adhesive, or another coating, may be used to further secure the platform with the washer.
Preferably the washer is formed from plastic. An exemplary plastic is polyimide.
The washer may be formed from metal having a surface coating.
The variable guide vane assembly may further comprise a casing having a chamber containing the platform and the washer. Preferably the chamber is stepped from a casing surface wherein a surface of the platform opposing the spindle facing surface is flush with the casing surface.
a to 5d are plan views (5a-5b) and side views (5c-5d) of alternative washer arrangements.
In the arrangement shown in
The actuating lever 16 has a mount which surrounds the vane spindle 20 and has an inner profile which engages the driving teeth 40 on the spindle (
The thrust washer 26 is shown in more detail in
A top view of the vane 22, washer26 and platform 24 is shown in
It will be appreciated that the invention offers a number of advantages. The overhang of the thrust washer, when presented to the platform of the vane, forms a full circular aerodynamic surface at the vane interface with the casing. For large stator vanes in particular the arrangement provides a significant reduction to the time and cost required to machine the vane by virtue of a more efficient utilisation of the aerofoil initial material envelope as machining a platform with a circular cross-section requires significantly more material. By contrast the thrust washer can be made of both cheaper and lighter material which also leads to an overall reduction in the weight of the engine.
The depth of the washer 26 has a significantly lower profile 48 than the conventional combinations of platform and washer. Accordingly, the manufacturing costs of the casing is reduced.
The use of a thrust washer can also reduce the profile of the vane which allows the vane, if forged, to be manufactured from smaller stock which results in reduced manufacturing cost of the aerofoil as less material is used with reduced machining time.
a and 5b are top views of alternative washer arrangements. In 5a the washer has a star-shaped feature which engages a complementary star shaped platform. In 5b the washer has a cross-shaped feature which engages a complementary cross shaped platform.
Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be effected without further inventive skill and effort. For example, the platform 24 is shown as rectangular but may be any other appropriate shape provided the thrush washer may fit around it.
Number | Date | Country | Kind |
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1206603.1 | Apr 2012 | GB | national |