Patent Publication Number: US-8540480-B2

Title: Aerofoil having a plurality cooling air flows

Description:
The present invention relates to an aerofoil, particularly but not exclusively an aerofoil for a gas turbine engine. 
     Conventionally, turbine blades and nozzle guide vanes within gas turbine engines include aerofoils which are hollow. Each aerofoil defines an interior and passages through the aerofoil walls from the interior to the exterior. Cooling air flows radially outwardly along the interior and along the passages, so as to form an external cooling film over the external surfaces of the aerofoil, protecting the material of the aerofoil from hot combustion gases. The design of the cooling passages must satisfy a number of requirements. The flow rate along the passages must be sufficient to prevent back flow of combustion gases while providing a cooling film rather than a jet. The flow rate must be minimised to minimise the amount of air bled from the compressor. The flow rate must be sufficient to ensure adequate cooling of the aerofoil surfaces, and thus provide a satisfactory working life of the engine components. 
     One problem encountered is blocking of the cooling passages by a build up of internal and external dirt. Such blockages alter the cooling air flows, changing the relatively delicate balance of design parameters outlined above and thus affecting either the efficiency of the engine or the working life of the components, or both. The fact that blockages will occur has to be taken into account by the designer, who thus has to provide an initial excess of holes and/or larger holes with consequently increased manufacturing costs, increased complexity and reduced operating efficiency. The provision of larger holes reduces cooling efficiency. 
     According to a first aspect of the present invention, there is provided an aerofoil for a gas turbine engine, the aerofoil including at least one wall defining an interior along which in use cooling air flow&#39;s in a first direction, the at least one wall defining a passage extending from an interior surface of the one wall to an exterior surface of the at least one wall to permit in use a cooling air flow in a second direction therealong, the passage including an inlet area defined by the interior surface, the inlet area having a shape which is elongated along one axis, the elongate axis of the inlet area extending along or being substantially parallel with the first cooling air flow direction an external fluid flowing across the exterior surface of the at least one wall in a third direction. The cooling air on exiting the passage flowing in the third direction. The passage including an outlet area, which may be defined by the exterior surface, and which may have a shape which is elongated along one axis. 
     Possibly, the elongate axis of the inlet area lies on a first plane, and the first and second directions lie on the same plane. 
     Possibly, the elongate axis of the outlet area extends along or is substantially parallel to the third direction. Possibly the third direction is substantially at an angle to the first direction when viewed along the length of the passage, which angle may be substantially 90°. Possibly, the elongate axis of the outlet area lies on a second plane, and the second and third directions lie on the same plane. 
     Possibly, the second plane is orientated at an angle to the first plane, and may be orientated at substantially 90° to the first plane. 
     Possibly, the aerofoil has a length, and the interior extends along the length. Possibly, the passage extends laterally through the wall. Possibly, the first direction is along the length. Possibly, the second direction is at an angle to the first direction, and may be substantially at 90° to the first direction. 
     The inlet area may be elliptical or oval in shape. The outlet area may be elliptical or oval in shape. 
     The aerofoil may define a plurality of passages, which may be regularly spaced, and may be arranged in rows, which may extend along the length of the aerofoil. 
     The aerofoil may be formed by soluble core casting, and may be formed using a laser. The aerofoil may form part of a turbine or a nozzle guide vane for a gas turbine engine. 
     According to a second aspect of the present invention, there is provided a gas turbine engine, the engine including an aerofoil, the aerofoil being as described in any of the preceding statements. 
     According to a third aspect of the present invention, there is provided a method of cooling a gas turbine engine, the method including providing an aerofoil, the aerofoil being as described in any of the said preceding paragraphs. 
    
    
     
       An embodiment of present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:— 
         FIG. 1  is a side sectional view of part of a gas turbine engine; 
         FIG. 2  is a perspective view of part of an aerofoil; 
         FIG. 3  is a side sectional view of part of a wall of the aerofoil, as indicated by section line III-III in  FIG. 4 ; 
         FIG. 4  is a sectional view from above of the part of the wall of  FIG. 3  as indicated by section line IV-IV in  FIG. 3 ; and 
         FIG. 5  is a side view of the wall of the aerofoil, along arrow G as indicated in  FIG. 3 . 
     
    
    
     Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high pressure compressor  14 , combustion equipment  15 , a high pressure turbine  16 , an intermediate pressure turbine  17 , a low pressure turbine  18  and an exhaust nozzle  19 . 
     The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which produces two air flows: a first air flow, indicated by arrow A into the intermediate pressure compressor  13  and a second air flow indicated by arrow B which provides propulsive thrust. The intermediate pressure compressor compresses the air flow A directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
     The compressed air exhausted from the high pressure compressor  14  is directed into the combustion equipment  15  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  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13  and the fan  12  by suitable interconnecting shafts. 
       FIG. 2  shows a section of an aerofoil  20 . The aerofoil  20  could form part of a turbine blade or nozzle guide vane of one of the high, intermediate or low pressure turbines  16 ,  17 ,  18 . The aerofoil  20  includes walls  22  which define an interior  24  and a plurality of through passages  26  which extend from an interior wall surface  28  to an exterior wall surface  30 . As shown in  FIG. 2 , the passages  26  are arranged in a row at a regular spacing extending along the length of the aerofoil  20 . The interior  24  extends along the length of the aerofoil  20 . 
     Each of the passages  26  includes an inlet area  32  defined by the interior wall surface  28  and an outlet area  34  defined by the exterior wall surface  30 . 
     Referring to  FIGS. 3-5 , the inlet area  32  has an elliptical or oval shape which is elongated along one axis  36 . The elongate inlet area axis  36  extends generally along the length of the aerofoil  20 . 
     The outlet area  34  has an elliptical or oval shape which is elongated along an elongate outlet area axis  38 . The elongate outlet area axis  38  extends substantially laterally across the aerofoil  20 . 
     For reference,  FIGS. 3 and 4  each include a reference axis  56 , which shows X, Y and Z axes. Referring to  FIG. 3 , a first plane  46  is defined, which by reference to the reference axis  56  is the XY plane, and a second plane  48  is defined, which, by reference to the reference axis  56  is the XZ plane. The inlet area axis  36  lies on first plane  46 . The outlet area axis  38  lies on the second plane  48  which is orientated substantially at 90° to the first plane  46 . The plane in which the outlet area axis  38  lies is thus orientated at substantially 90° to the plane in which the inlet area axis  36  lies. 
     When viewed from the side, as shown in  FIG. 3 , passage surfaces  54  defining the passage  26  appear to converge from the inlet area  32  to the outlet area  34 . When viewed from above, as shown in  FIG. 4 , the passage surfaces  54  diverge from the inlet area  32  to the outlet area  34 . 
       FIG. 5  shows a view along the passage axis  58  as seen by a viewer viewing along arrow G shown in  FIG. 3 . The outlet area axis  38  and the second plane  48  are at substantially 90° to the inlet area axis  36  and the first plane  46 . 
     In use, cooling air flows in a first direction  40  along the interior  24  as shown by arrows C. The first direction  40  is generally along the length of the aerofoil and along the length of the longitudinal axis of the interior  24 . A cooling air flow flows through the passage  26  in a second direction  42  as shown by arrow E. In a gas turbine engine, the first direction could be a radial direction relative to an engine shaft. 
     The elongate inlet area axis  36  is substantially parallel to the first direction  40 . The first direction  40  and second direction  42  lie in the first plane  46 , and thus are substantially coplanar with the inlet area axis  36 . 
     As shown in  FIG. 4 , the symbol comprising a dot within a circle indicates an arrow coming out of the paper towards the viewer. 
     The passage cooling air flow exits the passage  26 , where it meets with an external fluid flow in a third direction  44  as indicated by arrows D across the exterior surface  30  which could be a flow comprising combustion gases. In a gas turbine engine, the third direction could be a rotational direction around an engine shaft. The cooling air flow meets the external fluid flow and flows in the third direction  44  along the exterior surface of the walls  22  of the aerofoil  20 . The third direction  44  generally extends along or is parallel with the orientation of the elongate outlet area axis  38 , and lies in the second plane  48 , and thus is coplanar with the elongate outlet area axis  38 . 
     The advantages provided by the invention are as follows. The cooling air flowing in the first direction  40  as shown by arrow C along the interior  24  includes particles of dirt. The inlet area  32  of the passage  26  defined in the walls  22  forms a trap for the dirt particles, which can cause build up on those surfaces which are opposed to the motion of the cooling air. Thus, dirt build up will tend to occur along the uppermost (as shown in  FIG. 3 ) or downstream part of the inlet area  32  as indicated by reference numeral  50 . 
     Dirt build up also occurs at the inlet area  32  as a result of the change in direction of the cooling air entering the passage  26 . Dirt particles entrained in the cooling air flow are carried by centrifugal force towards the uppermost or downstream part of the inlet area  32  and can result in dirt build up in this area. 
     By elongating the inlet area  32  along the inlet area axis  36  parallel with the first direction  40 , the size of the uppermost or downstream area of the inlet area  32  is reduced, thus reducing the amount of build up, and when build up does occur, this has relatively less effect upon the available inlet area remaining, thus providing a passage  26  which is resistant to blockage at the inlet area  32 . 
     Similarly, dirt particles can build up in the downstream part of the outlet area  34  as indicated by reference numerals  52 . Such dirt build up can be caused by dirt particles entrained in the external flow indicated by arrows D, or by dirt particles entrained in the cooling passage flow indicated by arrow E. In either case, the dirt build up is reduced by elongating the outlet area axis  38  along the third direction  44 , which reduces the area available for dirt build up, and also reduces the effects of any dirt build up which does occur, thus providing a cooling passage  26  which is resistant to blockage at the outlet area  34 . 
     Aerofoils  20  of the invention can be formed by soluble core casting, and could be formed by using a laser. Such aerofoils could be formed of high temperature metal alloys, which could be nickel or titanium alloys. 
     Various other modifications could be made without departing from the scope of the invention. The inlet areas and outlet areas could be of any suitable size and elongate shape and could be orientated in any suitable way relative to each other. For example, the outlet area could be offset laterally relative to the inlet area, and/or could be offset vertically relative to the inlet area. Depending on the flow directions of the cooling air and external flows, the elongate axis of the inlet area and the outlet area could be orientated at different angles to each other. The aerofoil could be formed in any suitable way, of any suitable material. 
     There is thus provided an aerofoil which is resistant to blockage of film cooling passages. As a result of the reduced rate of build up of dirt and reduced rate of blockage, fewer, smaller cooling passages are required, resulting in reduced manufacturing costs, and improved engine and cooling efficiency.