(19) & (11) EP 2 492 484 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.: 29.08.2012 Bulletin 2012/35 F02K 3/072 (2006.01) B64C 11/00 (2006.01) (21) Application number: 12152601.6 (22) Date of filing: 26.01.2012 (84) Designated Contracting States: (72) Inventors: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB • Stretton, Richard Gordon GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO Loughborough, Leicestershire LE11 4NY (GB) PL PT RO RS SE SI SK SM TR • Howarth, Nicholas Designated Extension States: Derby, DE23 6FY (GB) BA ME (74) Representative: Barcock, Ruth Anita et al (30) Priority: 22.02.2011 GB 201102987 Rolls-Royce plc Intellectual Property Dept. WH20 (71) Applicant: Rolls-Royce plc P.O. Box 3 London SW1E 6AT (GB) Filton Bristol South Gloucestershire BS34 7QE (GB) (54) Propfan engine (57) The present disclosure relates to a propfan en- lates to propfan engine (100) comprising: one or more gine (100) comprising: one or more rotor stages (110, rotor stages (110, 120) comprising a plurality of rotors; 120) comprising a plurality of rotors; and an outer wall and an outer wall (130) comprising an outer profile (132), (130) comprising an outer profile (132), at least a portion the outer profile defining a cross-section, wherein the of the outer profile defining a substantially circular cross- cross-section of the outer profile comprises a maximum section, wherein the diameter of the substantially circular diameter (134, 136) at a point upstream of a leading edge cross-section increases in the direction of flow over the (112, 122) of the rotors, the diameter reducing between outer wall and downstream of a leading edge (112, 122) themaximum diameter and the leading edge of the rotors, of the rotors, and the diameter increases at substantially and wherein the outer profile comprises a point of inflec- all points defining the circumference of the substantially tion (135, 137) between the maximum diameter and the circular cross-section. The present disclosure further re- leading edge of the rotors. EP 2 492 484 A2 Printed by Jouve, 75001 PARIS (FR) 1 EP 2 492 484 A2 2 Description high speed. The root has to be thick enough to guarantee the structural robustness of the blades given the high [0001] The present disclosure relates to a propfan en- aerodynamic and mechanical loads acting on the propel- gine and particularly but not exclusively relates to a prop- ler stages 23, 24, which disadvantageously adds signif- fan engine with a contoured outer casing. 5 icant weight to the engine 10. The airflow passing be- tween the blade roots may easily become supersonic if Background the propeller gas turbine engine 10 operates at transonic cruise speed, around Mach 0.8. This results in disadvan- [0002] Referring to Figure 1, a conventional twin- tageous increased noise, aerodynamic losses and pos- spooled, contra-rotating propeller gas turbine engine, 10 sible mechanical excitation, phenomena which it is de- e.g. a propfan engine, is generally indicated at 10 and sirable to avoid or at least limit. has a principal rotational axis 9. The term "propfan" will [0005] The example shown in Figure 1 has a nacelle be understood by the skilled person to refer to a gas 21 with a conventional fore-body extending from the in- turbine engine having an open rotor, i.e. having a rotor take 12 to a point at which the nacelle diameter is at a comprising blades that are not surrounded by a nacelle. 15 maximum. In an alternative configuration, for example, The engine 10 comprises a core engine 11 having, in the General Electric GE36 Unducted Fan, there is then axial flow series, an air intake 12, a low pressure com- a reduction in the nacelle diameter downstream of the pressor 14, a high- pressure compressor 15, combustion maximum diameter point and ahead of the first propeller equipment 16, a high- pressure turbine 17, a low pressure stage. In effect the geometry results in a diffusion up- turbine 18, a free power (or low- pressure) turbine 19 and 20 stream of the first propeller stage such that the flow ve- a core exhaust nozzle 20. A nacelle 21 generally sur- locity is reduced. The annulus line through the propeller rounds the core engine 11 and defines the intake 12 and stages of the GE36 is then close to cylindrical and is nozzle 20 and a core exhaust duct 22. The engine 10 followed by a short curved after-body to close out at the also comprises two contra-rotating propeller stages 23, core exhaust nozzle. By diffusing the flow ahead of the 24 attached to and driven by the free power turbine 19 25 first propeller stage, the Mach number of the flow at the via shaft 26. The configuration having the propeller stag- hub of the GE36 may be reduced and the rotor efficiency es 23, 24 towards the rear of the gas turbine engine 10 may benefit as a result. However, due to the large max- is termed a "pusher" configuration, as opposed to the imum nacelle diameter of the GE36 required to achieve "puller" or "tractor" configuration having the propeller the diffusion, a large free-stream over-speed over the stages 23, 24 towards the front of the engine 10. 30 outer span of the propeller blades occurs and this is det- [0003] The gas turbine engine 10 works in a conven- rimental to the rotor efficiency. tional manner so that air entering the intake 12 is accel- [0006] The present disclosure therefore seeks to ad- erated and compressed by the low pressure compressor dress these issues. 14 and directed into the high-pressure compressor 15 where further compression takes place. The compressed 35 Statements of Invention air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is [0007] According to a first aspect of the present inven- mixed with fuel and the mixture combusted. The resultant tion there is provided a propfan engine comprising: one hot combustion products then expand through, and or more rotor stages comprising a plurality of rotors; and thereby drive the high-pressure, low pressure and free 40 an outer wall comprising an outer profile, at least a portion power turbines 17, 18, 19 before being exhausted of the outer profile defining a substantially circular cross- through the nozzle 20 to provide some propulsive thrust. section, wherein the diameter of the substantially circular The high-pressure, intermediate pressure and free pow- cross-section increases in the direction of flow over the er turbines 17, 18, 19 respectively drive the high and low outer walland downstream of aleading edge of the rotors, pressure compressors 15, 14 and the propellers 23, 24 45 and the diameter increases at substantially all points de- by suitable interconnecting shafts. The propellers 23, 24 fining the circumference of the substantially circular normally provide the majority of the propulsive thrust. In cross-section. the embodiments herein described the propellers 23, 24 [0008] The diameter may increase at an increasing rotate in opposite senses so that one rotates clockwise rate in a first part of the portion of the outer profile. For and the other anti-clockwise around the engine’s rota- 50 example, the first part of the portion of the outer profile tional axis 9. may be at least partially concave, e.g. with respect to the [0004] One problem with a conventional pusher pro- longitudinal axis. The diameter may increase at a de- peller gas turbine engine 10 is that its cruise speed is creasing rate in a second part of the portion of the outer limited to slightly below transonic, predominantly due to profile. For example, the second part of the portion of the the drag rise encountered when flying at higher speeds. 55 outer profile may be at least partially convex, e.g. with One of the main causes of this drag rise is that generally respect to the longitudinal axis. The second part may be the root of each blade forming the propeller stages 23, downstream of the first part of the portion of the outer 24 can not be shaped with the thin profiles required for profile. There may be a point of inflection in the outer 2 3 EP 2 492 484 A2 4 profile between the first and second parts of the portion [0014] In a second embodiment for a puller configura- of the outer profile. The radius of curvature in the first tion with the rotors towards the front of the engine, the part of the portion of the outer profile may be substantially profile of the substantially circular cross section portion 20% of a maximum diameter of the propfan outer wall. may have a gradient of between 10° and 12° with respect The radius of curvature in the second part of the portion 5 to the longitudinal axis between the local minimum and of the outer profile may be substantially 40% of the max- the local maximum, and may have an average gradient imum diameter of the propfan outer wall. of substantially 11°. The increase in diameter of the sub- [0009] In a third part of the portion of the outer profile stantially circular cross section portion between the local the diameter of the substantially circular cross-section minimum and the local maximum may be between 11 % may reduce in the direction of flow over the outer wall. 10 and 13% of the maximum diameter. For example, the third part of the portion of the outer [0015] According to a second aspect of the present profile may be at least partially convex, e.g.