Patent Application
20100229618
The technical field relates to mixers for use in turbofan gas turbine engines.
In the production of aircraft engines, the geometric complexity of sheet metal components and the accuracy required can be very challenging. An example of a complex sheet metal component is an exhaust mixer of a turbofan gas turbine engine. This component is provided to mix the cold bypass flow and hot engine core flow at the aft of the engine. The inner surface of the turbofan mixer is designed to alter the outer portion of the engine core flow and the outer surface of the turbofan mixer is designed to alter the inner portion of the by-pass flow. These flow alterations result in an improved mixing of the two flows behind the engine. Turbofan mixers are often fabricated by cutting and forming individual segments in a sheet metal die press, then assembling the individual segments together in a complex welding jig. This procedure can be very time consuming and very demanding in terms of craftsmanship. Needs for improvements in this area exist.
In one aspect, the present concept provides a method of forming a turbofan mixer, the method comprising: providing a single monolithic and generally flat annular sheet metal blank; providing a die surface substantially corresponding in shape to a turbofan mixer shape; positioning the blank with reference to the die surface; and forcing the blank against the die surface to transform the blank into a monolithic turbofan mixer.
In another aspect, the present concept provides an apparatus for forming turbofan mixers from monolithic sheet metal blanks, the apparatus comprising: a die having a central axis, the die including a plurality of outwardly-projecting and circumferentially disposed bulges provided around a central core of the die, each two adjacent bulges having a respective channel therebetween, the die having an outer shape substantially corresponding to a turbofan mixer interior shape; and a plurality of circumferentially-disposed strikers provided around the die, each striker in registry with a respective one of the channels, the strikers being movable substantially simultaneously with reference to the die.
Further details of these and other aspects will be apparent from the detailed description and figures included below.
As can be seen, the turbofan mixer 20 includes a plurality of intercalated outward and inward mixer lobes 24, 26 circumferentially distributed around the periphery of the rear end portion 20b. Outward mixer lobes 24 can be axisymmetric or not all around the circumference, depending on the design. Likewise, inward mixer lobes 26 can be axisymmetric or not all around the circumference, depending on the design. The exact mixer lobe pattern is something that a skilled turbofan mixer designer will know how to create and does not need to be further discussed herein.
The strikers 34 correspond in number to the inward mixer lobes 26 of the turbofan mixer 20. Each striker 34 is substantially in registry with a respective channel 40 formed between each two adjacent bulges 38. Each striker 34 also has an interior portion that cooperates with the corresponding channel 40 and the sides of the bulges 38. It should be noted that
To shape the blank 50 into a turbofan mixer 20, the center of the blank 50 is set against the front side of the die 32, for instance coaxially with reference to the central axis 42. The blank 50 is held in that position using a suitable holding arrangement. For instance, the blank 50 can be held by the inner tips of the strikers 34 abutting against the front side of the blank 50. Other arrangements are possible as well. The strikers 34 are then moved substantially simultaneously in a radial plane towards the rear and the central axis 42 of the die to draw the blank 50. The lobes 24, 26 will be formed as the strikers 34 move towards the end of their stroke, thereby forcing the sheet metal wall of the blank 50 over the die surface.
Each striker 34 follows a direction that is somehow oblique with reference to the central axis 42 of the die 32, although it does not necessarily need to be in perfect alignment therewith. Arrow 60 in
As can be appreciated, forming turbofan mixers 20 using the apparatus 30 and the method described herein can be made quickly and very efficiently. A turbofan mixer can even be shaped in a single pressing stroke, depending on the exact configuration.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For instance, the exact shape of the turbofan mixer can be different from the one illustrated. The shape of the die, the shape of the strikers and the shape of the blank can be different as well. When moving the strikers simultaneously, some can be slightly delayed in their initial movement and the speed of all strikers need not necessarily be the same. Strikers can get to the end of their stroke at slightly different intervals and the speed of their movement can vary during the forming. Still, the relative position of the strikers at the beginning and/or at the end of their stroke may not be the same. Strikers can have a different angle with reference to the central axis of the die compared to others. The movements of some or of all strikers do not necessarily need to be entirely linear and variants are possible. Once formed, the turbofan mixers can be subjected to additional manufacturing procedures, if required, for instance heat treatments, coatings, etc. Other modifications which fall will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
