GB1597376A - Nose bullet for a gas turbine engine - Google Patents

Description

(54) A NOSE BULLET FOR A GAS TURBINE ENGINE (71) We, ROLLS-ROYCE LIMITED a British Company of 65 Buckingham Gate, London SW1E 6AT, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a nose bullet for a gas turbine engine.

A gas turbine engine normally has an air intake into which the air required for its operation passes. In order to direct the air into this intake and to divide it, it is normal to provide a streamlined projection or nose bullet. In the case of an annular air intake, this nose bullet normally comprises a streamlined surface of revolution, while in the case of the linear type of intake referred to as a two-dimensional intake, this nose bullet would normally comprise a longitudinal member having a streamlined crosssection.

The present invention relates to a nose bullet which is shaped so as to enable the boundary layer of air on the bullet to be energised.

According to the present invention a nose bullet for a gas turbine engine comprises a projection which diverges in the direction of the air flow round the bullet, a concave wall portion immediately downstream of the projection which at least partly turns back on itself so that the air flowing over it is encouraged to form and maintain a vortex in the concavity parallel with the surface, the direction of movement of the air in the vortex being such as to energise the boundary layer adjacent the surface in the general direction of the air flowing round the bullet and a convexly curved wall portion immediately downstream of the concavely curved wall portion adapted to entrain air from the vortex and to cause it to flow smoothly into the intake of the engine associated with the bullet.

In one embodiment the nose bullet and the concave and convex wall portions all comprise surfaces of revolution about the axis of the bullet, which may coincide with the axis of the intake of the associated engine.

The invention is particularly applicable to the nose bullet which is fixed to and rotates with the fan rotor of a fan engine.

In order to allow water to escape from the concave wall portion, water drain holes may be provided in that portion.

The invention will now be particularly described merely by way of example, with reference to the drawing filed with the provisional specification in which: Fig. 1 is a partly broken away view of a gas turbine fan engine having a nose bullet in accordance with the invention, Fig. 2 is an enlarged sectional view of the fan rotor and nose bullet of the engine of Fig. 1, and Fig. 3 is a perspective view of an alternative embodiment of a nose bullet in accordance with the invention.

In Fig. 1 there is shown a gas turbine engine comprising a core engine casing 10 within which are mounted in flow series a compressor 11, combustion chamber 12, high pressure turbine 13 and low pressure turbine 14. The compressor and the high pressure turbine are drivingly interconnected by a high pressure shaft 15. In front of the compressor 11 is mounted a fan 16 comprising a single stage of rotor blades mounted on a fan rotor 17. The fan rotor is drivingly interconnected with the low pressure turbine 14 by a low pressure shaft 18.

A fan casing 19 extends round the forward portion of the casing 10 to define therewith an annular fan duct 20.

Operation of the engine is conventional as so far described in that the fan compresses air part of which passes through the fan duct 20 to provide propulsive thrust and part of which enters the compressor 11. Within the compressor it is further compressed before being mixed with fuel in the combustion chamber 12. The hot gases then drive the turbines 13 and 14 in series, these turbines in turn driving the compressor 11 and fan 16.

It will be seen that the air must enter the fan 16 as an annular flow. The forward extremity of the fan casing 19 forms the outer boundary of this annular flow, but some provision must be made to divide the centre of the flow aerodynamically so as to prevent it impinging directly on the front face of the rotor 17 and producing turbulence.

In Fig. 2 the detailed construction of the nose bullet in accordance with the invention which effects this division of the air is illustrated. It will be seen fan rotor 17 is provided with a forwardly extending flange 21 having bolts 22 which attach to the rotor a nose bullet generally indicated at 23. It will be seen that the bullet comprises a central forwardly extending projection 24 which diverges in the direction of flow of the air past the bullet and is a substantially conical surface of revolution about the axis of the bullet which coincides with the axis of the engine. Immediately downstream of the projection 24 there is a concave wall portion 25. This wall portion turns back on itself to have a maximum forward extension on the point 26. The wall portion 25 is substantially part circular in cross-section and therefore part toroidal in surface shape.The point 26 thus comprises an annular forwardly extending rim, and the bullet is then provided with a convexly curved wall portion 27 which extends rearwardly from the rim 26. The surface 27 terminates at the rear face of the bullet 23 where it coincides with the forward edge of the platform 28 of the rotor blades of the fan.

The effect which this bullet has on the air flow past it is indicated by arrows, and it will be seen that the forward projection 24 splits the flow which then passes into the concave portion 25. Because the surface of this portion turns back on itself, the air is also caused to reverse direction and forms into a toroidal vortex 29. The direction of this vortex is such as to accelerate the boundary layer air on the bullet in the direction of general flow of air past the bullet. On leaving the concave portion 25 past the rim 26 the curvature of the surface 27 is arranged to be such as to cause the air to stick to that surface through the Coanda effect; this thus has the effect of changing the direction of flow from being radially outwards with a small forward component to being axially reanvards with a small radial component.

The air leaving the surface 27 then flows onto the platforms 28.

Because of the high velocities of air produced in the toroidal vortex the air flow adjacent the surface of the bullet is also accelerated and in this way the boundary layer which passes over the rim 26 and the surface 27 into the fan 16 is energised and becomes less of a penalty on the efficiency of the fan near to its hub. Also because the vortex and associated Coanda surface comprise an efficent way of dividing the air and directing it into the intake of the fan, the axial depth of the nose bullet from the tip of the projection 24 to its back face may be reduced compared with the normal aerodynamic profile.

It will be understood that in some circumstances rain or other precipitation could collect in the concave portion 25 and be held there by the airflow. In order to allow this water to escape, drillings 30 are provided which extend from the outer wall of the concave portion 25 to the back face of the bullet adjacent its periphery. Water collecting in the concavity will thus flow under the influence of centrifugal forces through the ducts 30 and back into the airflow of the engine.

Because of the high air velocities involved in this design of bullet, it is expected that ice will be unable to form on it and it may therefore be possible to reduce or completely eliminate any arrangements for anti-icing.

It will be appreciated that although the maximum benefit of the invention is obtained in the case of a circular rotating bullet the invention could be applied to the two-dimensional intake and Fig. 3 shows how this could be done. The intake shown is a rectangular intake which divides air to two engines generally indicated at 35 and 36.

The centre body of the rectangular intake is a longitudinally extending member 37 having a cross-section identical to that of the bullet 23 described above. Operation of this bullet is similar to that of the bullet 23, however in this case instead of a toroidal vortex the bullet will produce two linear vortices. Because of the fact that the air must enter an annular intake to an engine after it leaves the bullet 37 the same advantages with regard to fan efficiency may not be realised, but this will still provide a short and efficent splitter device.

It will be understood that the invention could be modified in a number of ways; in particular the details shape of the bullet as shown at 23 could well be varied for an optimum result in different conditions, but it is essential in all cases that the bullet comprise a projection followed by a concave wall portion which induces the form of a vortex and a convex wall portion which then entrains the air in the correct direction to be fed to the engine.

WHAT WE CLAIM IS: 1. A nose bullet for a gas turbine engine comprising a projection which diverges in the direction of the air flow round the bullet, a concave wall portion immediately downstream of the projection which at least partly turns back on itself so that the air flowing over it is encouraged to form and maintain a vortex in the concavity parallel with the surface, the direction of movement of the air in the vortex being such as to energise the boundary layer adjacent the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. extremity of the fan casing 19 forms the outer boundary of this annular flow, but some provision must be made to divide the centre of the flow aerodynamically so as to prevent it impinging directly on the front face of the rotor 17 and producing turbulence. In Fig. 2 the detailed construction of the nose bullet in accordance with the invention which effects this division of the air is illustrated. It will be seen fan rotor 17 is provided with a forwardly extending flange 21 having bolts 22 which attach to the rotor a nose bullet generally indicated at 23. It will be seen that the bullet comprises a central forwardly extending projection 24 which diverges in the direction of flow of the air past the bullet and is a substantially conical surface of revolution about the axis of the bullet which coincides with the axis of the engine. Immediately downstream of the projection 24 there is a concave wall portion 25. This wall portion turns back on itself to have a maximum forward extension on the point 26. The wall portion 25 is substantially part circular in cross-section and therefore part toroidal in surface shape.The point 26 thus comprises an annular forwardly extending rim, and the bullet is then provided with a convexly curved wall portion 27 which extends rearwardly from the rim 26. The surface 27 terminates at the rear face of the bullet 23 where it coincides with the forward edge of the platform 28 of the rotor blades of the fan. The effect which this bullet has on the air flow past it is indicated by arrows, and it will be seen that the forward projection 24 splits the flow which then passes into the concave portion 25. Because the surface of this portion turns back on itself, the air is also caused to reverse direction and forms into a toroidal vortex 29. The direction of this vortex is such as to accelerate the boundary layer air on the bullet in the direction of general flow of air past the bullet. On leaving the concave portion 25 past the rim 26 the curvature of the surface 27 is arranged to be such as to cause the air to stick to that surface through the Coanda effect; this thus has the effect of changing the direction of flow from being radially outwards with a small forward component to being axially reanvards with a small radial component. The air leaving the surface 27 then flows onto the platforms 28. Because of the high velocities of air produced in the toroidal vortex the air flow adjacent the surface of the bullet is also accelerated and in this way the boundary layer which passes over the rim 26 and the surface 27 into the fan 16 is energised and becomes less of a penalty on the efficiency of the fan near to its hub. Also because the vortex and associated Coanda surface comprise an efficent way of dividing the air and directing it into the intake of the fan, the axial depth of the nose bullet from the tip of the projection 24 to its back face may be reduced compared with the normal aerodynamic profile. It will be understood that in some circumstances rain or other precipitation could collect in the concave portion 25 and be held there by the airflow. In order to allow this water to escape, drillings 30 are provided which extend from the outer wall of the concave portion 25 to the back face of the bullet adjacent its periphery. Water collecting in the concavity will thus flow under the influence of centrifugal forces through the ducts 30 and back into the airflow of the engine. Because of the high air velocities involved in this design of bullet, it is expected that ice will be unable to form on it and it may therefore be possible to reduce or completely eliminate any arrangements for anti-icing. It will be appreciated that although the maximum benefit of the invention is obtained in the case of a circular rotating bullet the invention could be applied to the two-dimensional intake and Fig. 3 shows how this could be done. The intake shown is a rectangular intake which divides air to two engines generally indicated at 35 and 36. The centre body of the rectangular intake is a longitudinally extending member 37 having a cross-section identical to that of the bullet 23 described above. Operation of this bullet is similar to that of the bullet 23, however in this case instead of a toroidal vortex the bullet will produce two linear vortices. Because of the fact that the air must enter an annular intake to an engine after it leaves the bullet 37 the same advantages with regard to fan efficiency may not be realised, but this will still provide a short and efficent splitter device. It will be understood that the invention could be modified in a number of ways; in particular the details shape of the bullet as shown at 23 could well be varied for an optimum result in different conditions, but it is essential in all cases that the bullet comprise a projection followed by a concave wall portion which induces the form of a vortex and a convex wall portion which then entrains the air in the correct direction to be fed to the engine. WHAT WE CLAIM IS:

1. A nose bullet for a gas turbine engine comprising a projection which diverges in the direction of the air flow round the bullet, a concave wall portion immediately downstream of the projection which at least partly turns back on itself so that the air flowing over it is encouraged to form and maintain a vortex in the concavity parallel with the surface, the direction of movement of the air in the vortex being such as to energise the boundary layer adjacent the

surface in the general direction of the air flowing round the bullet, and a convexly curved wall portion immediately downstream of the concavely curved wall portion adapted to entrain air from the vortex and to cause it to flow smoothly into the intake of the engine associated with the bullet.

2. Nose bullet according to claim 1 comprising a surface of revolution about an axis coinciding with the axis of the intake of the associated engine.

3. Nose bullet for a gas turbine engine substantially as described herein with reference to the drawing filed with the provisional specification.