1. Field of the Invention
The present invention relates to a blade for a rotor, and is particularly, although not exclusively, concerned with a blade such as a turbine blade for a rotor to be used in a gas turbine engine.
2. Description of the Related Art
With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 110 has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 111, a propulsive fan 112, an intermediate pressure compressor 113, a high-pressure compressor 114, combustion equipment 115, a high-pressure turbine 116, and intermediate pressure turbine 117, a low-pressure turbine 118 and a core engine exhaust nozzle 119. A nacelle 121 generally surrounds the engine 110 and defines the intake 111, a bypass duct 122 and a bypass exhaust nozzle 123.
The gas turbine engine 110 works in a conventional manner so that air entering the intake 111 is accelerated by the fan 112 to produce two air flows: a first air flow A into the intermediate pressure compressor 113 and a second air flow B which passes through the bypass duct 122 to provide propulsive thrust. The intermediate pressure compressor 113 compresses the air flow A directed into it before delivering that air to the high pressure compressor 114 where further compression takes place.
The compressed air exhausted from the high-pressure compressor 114 is directed into the combustion equipment 115 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 116, 117, 118 before being exhausted through the nozzle 119 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 114, 113 and the fan 112 by suitable interconnecting shafts.
GB 2462131 discloses a turbine rotor blade for use in e.g. the high-pressure turbine of such an engine. The blade has, at its radially outer end, a cavity or passage defined by a peripheral wall which has an opening at the trailing edge of the blade. The function of the cavity is to trap gas which leaks past the peripheral wall on the pressure side of the blade. The trapped gas forms a vortex within the cavity, and flows from the cavity through the opening at the trailing edge. This configuration serves to reduce losses in efficiency caused by gas leakage over the turbine blade tips and also to reduce losses caused by flow disturbances set up by the leakage flow.
Such configurations at the tip of a rotor blade are sometimes referred to as “squealer tips”.
The blade from GB 2462131 shown in FIGS. 2 and 3 has an aerofoil surface made up of a pressure side 2 and a suction side 4, both extending from a leading edge 6 to a trailing edge 8. The radial tip of the blade is formed as a squealer tip, comprising a partition 10 and a peripheral wall 14, which define a cavity 12. The cavity 12 is open at the radial tip of the blade, and, through an opening 16 at the trailing edge 8 of the blade.
The peripheral wall 14 comprises a first region 18 which extends from the trailing edge 8 over the suction surface 4, round the leading edge 6 and part of the way along the pressure surface 2. This first region 18 extends generally radially, and its outer surface 20 is a smooth continuation of the profile of the aerofoil surface, both on the pressure side 2 and the suction side 4.
The peripheral wall 14 also has a second region 22 which is in the form of a winglet extending generally over the rear (i.e. nearer the trailing edge 8) portion of the pressure side of the blade tip. This second region 22, as is clear from sections S4 and S5 in FIG. 3, inclines outwardly of the cavity 12 with respect to the radial direction. The outer surface of the winglet is thus also inclined to the pressure side of the aerofoil surface. Between the first region 18 and the second region or winglet 22, there is a transition region 26, shown in sections S2 and S3 in FIG. 3. In the transition region 26, the peripheral wall 14 has two portions, namely a first portion 28 which extends radially, like the first region 18, and a second portion 30, which is inclined, like the second region or winglet 22. Thus, as the transition region 26 extends away from the leading edge 6, the second portion 30 becomes larger, to merge with the second region 22, while the first portion 28 becomes smaller.
Because the winglet 22 is inclined from the radial direction, it has the effect of widening the cavity 12 as it approaches the trailing edge 8. The result is that, in use of the blade, gas leaking over the peripheral wall 14 on the pressure side 2 will, over the full extent of the pressure side 2, encounter a region of the cavity 12 having a width which is sufficiently large to enable the overflowing air to reattach within the cavity 12 and so remain captured until it is discharged through the opening 16 at the trailing edge 8.
As described in GB 2462131, such winglets may also be formed on the suction side of the blade tip.