This application is entitled to the benefit of British Patent Application No. GB 0708377.7 filed on May 1, 2007.
The present invention relates to a turbomachine blade, for example, a compressor blade for a gas turbine engine and in particular to a fan blade for a gas turbine engine.
A turbofan gas turbine engine 10, as shown schematically in
The turbine section 20 comprises one or more turbine stages to drive the compressor section 18 via one or more shafts (not shown). The turbine section 20 also comprises one or more turbine stages to drive the fan rotor 24 of the fan section 14 via a shaft (not shown).
One known wide chord fan blade is disclosed in US2004/0018091 to the present applicant and is depicted in
The damping material 56 is a relatively low shear modulus material having viscoelasticity. Viscoelasticity is a property of a solid or liquid which when deformed exhibits both viscous and elastic behaviour through the simultaneous dissipation and storage of mechanical energy. Suitable materials comprise a polymer blend, a structural epoxy resin and liquid crystal siloxane polymer.
One particular and preferred polymer blend comprises, per 100 grams: 62.6% Bisphenol A-Epochlorohydrin (Epophen resin EL5 available from Borden Chemicals, UK); 17.2 grams Amine hardener (Laromin C260 available from Bayer, Germany); 20.2 grams of branched polyurethane (Desmocap 11 available from Bayer, Germany). This polymer blend is then mixed in a mass ratio of 1:1 with a structural epoxy resin, preferably Bisphenol A-Epochlorohydrin mixed with an amine-terminated polymer (e.g. Adhesive 2216 available from 3M).
A fan is susceptible to Foreign Object Damage, or FOD. Composite blades are not as robust as metal blades but offer advantages in terms of reduced mass. Where a hollow blade is provided there is a risk that the blade may burst when impacted by a large object. The use of a viscoelastic filler or core offers damping but also offers a secondary advantage in that the sides of the blade are held together to resist bursting, particularly busting at the trailing edge tip. Blade robustness may be improved through the provision of an internal warren truss arrangement as shown in
The girders inhibit bursting of the blade upon impact by foreign objects but provide a pathway for the transmittal of vibrational loads through the damping material which can render such damping material obsolete.
Accordingly, the present invention seeks to provide a novel turbomachine blade that addresses, and preferably overcomes, the above mentioned problems.
According to the invention, there is provided a turbomachine blade comprising a root portion and an aerofoil portion, the aerofoil portion having a leading edge, a trailing edge, a wall for forming a pressure surface extending from the leading edge to the trailing edge and wall for forming a suction wall extending from the leading edge to the trailing edge, wherein the aerofoil portion includes securing means extending between the pressure wall and the suction surface, wherein the securing means and comprising a first extension extending from the suction wall and a second extension extending from the pressure wall, the securing means having an energy absorbing portion comprising a first catch element provided on the first extension and a second catch element provided on the second extension and wherein the first catch element is arranged to engage with the second catch element for absorbing energy after impact to the blade by the foreign object.
Preferably, the pressure wall is concave. The suction wall may be convex.
Preferably, the first catch element and the second catch element are separated from each other by a volume containing a viscoelastic damper.
a schematically depicts a cross-sectional view of the blade of
b depicts a cross-sectional view of the blade of
a depicts a first embodiment of a blade provided by the present invention in operation.
b is a simplified illustration of the blade of
A blade 51 of
The damping material 57 is a relatively low shear modulus material having viscoelasticity. Viscoelasticity is a property of a solid or liquid which when deformed exhibits both viscous and elastic behaviour through the simultaneous dissipation and storage of mechanical energy. Suitable materials for the damping layer 57 comprise a polymer blend, a structural epoxy resin and liquid crystal siloxane polymer.
One particular and preferred polymer blend comprises, per 100 grams: 62.6% Bisphenol A-Epochlorohydrin (Epophen resin EL5 available from Borden Chemicals, UK); 17.2 grams Amine hardener (Laromin C260 available from Bayer, Germany); 20.2 grams of branched polyurethane (Desmocap 11 available from Bayer, Germany). This polymer blend is then mixed in a mass ratio of 1:1 with a structural epoxy resin, preferably Bisphenol A-Epochlorohydrin mixed with an amine-terminated polymer (e.g. Adhesive 2216 available from 3M).
It is desirable for the damping material to have a modulus of elasticity in the range 0.5-100 MPa.
The viscoelastic material allows the component to withstand high levels of vibration. The spring element 70 is formed integrally with the convex and concave surfaces and has a thickness 74 of about between 30 □m to 1 mm for an aero-fan blade.
The spring element is formed during manufacture of the blade by powder fed laser deposition where a laser is directed at surface of the blade with sufficient power and focus to form a melt pool thereon into which a powder is supplied and melted. The laser translates across the surface and consequently the melt pool also translates across the surface. As the laser moves from an area to which powder has been added the added powder solidifies to form a deposit having a height. By making repeated passes over an area it is possible to add layers to previously added deposits thereby increasing the overall height of the deposit.
As an alternative the springs may be formed using HIPping using an internal structure or a leachable or etchable support media.
The spring may have other forms as embodied in
The tubes preferably run generally radially between the root and the tip though both the length and major axis can be orientated in other directions depending on the damping requirements and/or requirements on structural support.
Upon impact of foreign objects, the blade may burst or deform with drastic changes to the cross-sectional width of the blade, i.e., the distance between the pressure flank and suction flank increases significantly as depicted in
In an alternative aspect to the invention, the spring element is replaced with catches. The catches are not connected in normal use and consequently the vibrational transmit path is minimised.
a) depicts a first embodiment of a blade provided by the present invention in operational condition. The inside face of the concave surface is provided with a series of integral “T” arms 90 that are interleaved with a series of “T” arms 92 on the inside face of the convex surface. The top bars of the “T” arms overlap the top bars of the interleaved bars such that the underside faces of each bar opposes an underside face of an adjacent, interleaved bar.
b) is a simplified illustration of the blade of
The viscoelastic filler is added by pouring, under a slight positive pressure, the material into the internal cavity of the blade.
In an alternative embodiment of the present invention shown in
The thickness of damping material is related to the damping modulus and has a thickness of between 500 and 1000 m.
Although the invention has been described with reference to a fan blade 26, it is equally applicable to a compressor blade.
Although the invention has been described with reference to titanium alloy blades, it is equally applicable to other metal alloy, metal or intermetallic blades.
Number | Date | Country | Kind |
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0708377.7 | May 2007 | GB | national |