Patent Application
20080310956
This invention generally relates to a gas turbine engine, and more particularly to a nacelle assembly for a turbofan gas turbine engine.
In an aircraft gas turbine engine, such as a turbofan engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. The hot combustion gases flow downstream through turbine stages which extract energy from the hot combustion gases.
Combustion gases are discharged from the turbofan engine through a core exhaust nozzle while fan air is discharged through an annular fan exhaust nozzle defined at least partially by a nacelle assembly which surrounds the core engine. A majority of propulsion thrust is provided by the pressurized fan air which is discharged through the fan exhaust nozzle, while the remaining thrust is provided from the combustion gases discharged through the core exhaust nozzle.
The fan section of the turbofan engine may be geared to control a tip speed of the fan section. Reduced fan section tip speed results in decreased noise because the fan section tip speed is lower in speed than the speed of the rotating compressor. Also, controlling the fan section tip speed allows the fan section to be of a larger diameter, which further decreases noise generation.
The performance of turbofan engines varies relative to flight conditions experienced by the aircraft. A conventional inlet lip section located at a forward most section of the nacelle assembly is a compromise design which generally reduces airflow separation from the inlet lip section of the nacelle assembly during these flight conditions. Although effective, a compromised “thick” inlet lip section designed for a takeoff flight condition may operate at a somewhat reduced efficiency in another flight condition, such as a cruise condition which may be better served by a “thin” inlet lip section. Furthermore, a “thick” inlet lip section may, during some flight conditions, suffer from boundary layer separation that may decrease efficiency.
Small vortex generators which increase the velocity gradient of oncoming airflow near the effective boundary layer and synthetic jets which introduce airflow at the boundary layer have been conventionally utilized to reduce the onset of boundary layer separation from the nacelle assembly. These attempts, however, have proved complex, expensive and may not fully reduce the onset of boundary layer separation.
Accordingly, it is desirable to provide a turbofan gas turbine engine fan nacelle assembly which is aerodynamically optimized for particular flight conditions.
A nacelle assembly includes an inlet lip section and a cowl section positioned downstream of the inlet lip section. At least a portion of the cowl section includes a flexible portion which is selectively movable to influence an effective boundary layer thickness of the nacelle assembly. A controller identifies an operability condition and selectively flexes the cowl section in response to the operability condition. The flexible portion is selectively driven by a nanoelectromechanical system
A method of an effective boundary layer thickness management of an inlet lip or cowl section of a nacelle of a gas turbine engine, to minimize flow separation, includes sensing an operability condition, and selectively flexing at least a portion of a cowl section positioned downstream of the inlet lip section in response to sensing the operability condition.
Accordingly, the present invention provides a turbofan gas turbine engine fan nacelle assembly which is aerodynamically optimized for particular flight conditions.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
In a two-spool design, the high pressure turbine 20 utilizes the extracted energy from the hot combustion gases to power the high pressure compressor 16 through a high speed shaft 19, and a low pressure turbine 22 utilizes the energy extracted from the hot combustion gases to power the low pressure compressor 15 and the fan section 14 through a low speed shaft 21. However, the invention is not limited to the two spool gas turbine architecture described and may be used with other architectures such as a single spool axial design, a three spool axial design and other architectures.
The gas turbine engine 10 is in the form of a high bypass ratio turbofan engine mounted within a nacelle assembly 26 in which a significant amount of air pressurized by the fan section 14 bypasses the core engine for the generation of propulsion thrust. The nacelle assembly 26 partially surrounds an engine casing 31, which houses the core engine 39. The disclosed embodiment depicts a high bypass flow arrangement in which approximately 80% of the airflow entering the fan section 14 may bypass the core engine 39 via a fan bypass passage 30 which extends between the nacelle assembly 26 and the engine casing 31 for receiving and communicating a discharge airflow F1. The high bypass flow arrangement provides a significant amount of thrust for powering an aircraft.
In the disclosed embodiment, the bypass ratio (i.e., the ratio between the amount of airflow communicated through the fan bypass passage 30 relative to the amount of airflow communicated through the core engine 39 itself) is greater than 10 and the fan section 14 diameter is substantially larger than the diameter of the low pressure compressor 15. The low pressure turbine 22 has a pressure ratio that is greater than five, in one example. The engine 10 may include a gear train 23 which reduces the speed of the rotating fan section 14. The gear train 23 can be any known gear system, such as a planetary gear system with orbiting planet gears, a planetary system with non-orbiting planet gears, or other type of gear system. In the disclosed example, the gear train 23 has a constant gear ratio. It should be understood, however, that the above parameters are only exemplary of a contemplated geared turbofan engine 10, and the invention is applicable to traditional turbofan engines as well as other engine architectures.
The discharge airflow F1 is discharged from the engine 10 through a fan exhaust nozzle 33. Core exhaust gases C are discharged from the core engine 39 through a core exhaust nozzle 32 defined between the engine casing 31 and a center plug 34 disposed coaxially around a longitudinal centerline axis A of the gas turbine engine 10.
The nacelle assembly 26 defines a contraction ratio. The contraction ratio represents a relative thickness of the inlet lip section 38 of the nacelle assembly 26 and is represented by the ratio of a high light area HA (ring shaped area defined by a highlight diameter Dh) and a throat area Ta (ring shaped area defined by throat diameter DT of the nacelle assembly 26. Current industry standards typically use a contraction ratio of approximately 1.330 to prevent the separation of the oncoming airflow F2 from the inlet lip section 38 during engine operation, but other contraction ratios may be feasible. “Thick” inlet lip section designs, which are associated with large contraction ratios, increase the maximum diameter Dmax and increase weight and drag penalties associated with the nacelle assembly 26. In this embodiment, the ratio of Dmax to Dh is less than 1.5.
The flexible portion 52 transforms the cowl section 50 aft of the inlet lip tip section 38 in response to a detected operability condition. While a single flexible portion 52 of the cowl section 50 is illustrated, it should be understood that the flexible portion 52 may circumferentially extend about the entire nacelle assembly 26 such that it forms a “thick” lip function occurs around the entire circumference of the inlet lip section 38 (
A sensor 61 detects the operability condition and communicates with a controller 62 to adjust the flexible portion 52 of the cowl section 50 into a desired shape. The actual shape of the flexible portion 52 of the cowl section 50 will vary depending upon design specific parameters including but not limited to the operability conditions experienced by the aircraft (
The flexible portion 52 is selectively driven by a nanoelectromechanical system 64 such as a multitude of nano-jacks 66 contained therein (
The airflow F2 is forced to flow around the flexible portion 52 of the cowl section 50 as required during certain operability flight conditions (see
By changing the nacelle surface to represent a “thick” inlet lip section 38 during specific flight conditions, the aircraft may be designed having a thin inlet lip section 38 (i.e., a slim line nacelle having a reduced contraction ratio such that efficiency is improved during cruise operations. By specifically tailoring the effective boundary layer 35 thickness for each operability flight condition, overall performance of the gas turbine engine 10 is improved. A reduced maximum diameter of the nacelle assembly 26 may therefore be achieved while reducing weight, reducing fuel burn and increasing the overall efficiency of the gas turbine engine 10. The flexible portion 52 in the disclosed embodiment need only provide a maximum diameter increase of approximately 20% reducing aircraft drag and weight to provide mission fuel burn rate decrease of approximately 2%-5%.
It should be understood that relative positional terms such as “forward,”“aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.
It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.
The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The disclosed embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
