Patent Application
20160208626
This application relates to an integrally bladed rotor wherein the thickness of a blade is locally increased at a radially inner span and at the trailing edge.
Gas turbine engines are known and, typically, include a fan delivering air into a compressor. The air is compressed and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, causing them to rotate.
One recent development is an integrally bladed rotor utilized as a fan rotor. An integrally bladed rotor can generally be described as a fan rotor having a hub with a plurality of blades formed integrally with the hub, and extending radially outwardly of the hub. As known, the fan blades define an airfoil shape with a pressure side, a suction side, and extending between a leading edge and a trailing edge.
As known generally, a fillet, or curved portion, merges the airfoil into the hub over a relatively small portion of the radial extent of the airfoil, also known as its span.
Some prior art integrally bladed rotors have a problem with surge, which is an undesirable aerodynamic effect that may be experienced by a fan rotor. Surging is essentially an unstable airflow which can have detrimental effect on the operation of the fan.
In a featured embodiment, an integrally bladed rotor comprises a hub centered about an axis and having a plurality of blades extending radially outwardly of the axis across a span. Each of the blades includes an airfoil extending between a leading edge and a trailing edge, and having a pressure side and a suction side. The airfoil has a thicker portion at the trailing edge, and at a radially inner portion of the span, and over a limited percentage of the span, such that the thicker portion does not extend beyond 50 percent of the span. An axial distance is defined between the trailing edge and the leading edge. The thicker portion extends for less than 50 percent of the axial distance, and is on the pressure side.
In another embodiment according to the previous embodiment, an increased thickness of the thicker portion area becomes greater in a direction moving from a radially outermost end of the end toward the hub.
In another embodiment according to any of the previous embodiments, the thickness increases by greater than 100 percent of a thickness of that at the radially outermost end to a portion of the thicker portion which merges into the hub.
In another embodiment according to any of the previous embodiments, a fillet merges the airfoil into the hub at locations along the axial distance and spaced toward the leading edge from the increased thickness portion.
In another embodiment according to any of the previous embodiments, the thicker portion also has a fillet merging the thicker portion into the hub.
In another embodiment according to any of the previous embodiments, a ratio of the thickness of the thicker portion at a radially innermost end to a diameter of an outer periphery of the hub is less than 0.025.
In another embodiment according to any of the previous embodiments, the thicker portion extends radially outwardly for less than 40 percent of the span.
In another embodiment according to any of the previous embodiments, the thicker portion extends for less than 40 percent of the axial distance.
In another embodiment according to any of the previous embodiments, a ratio of the thickness of the thicker portion at a radially innermost end to a diameter of an outer periphery of the hub is less than 0.025.
In another embodiment according to any of the previous embodiments, the thicker portion extends radially outwardly for less than 40 percent of the span.
In another embodiment according to any of the previous embodiments, the thicker portion extends for less than 40 percent of the axial distance.
In another featured embodiment, a gas turbine engine comprises a fan, a compressor rotor, a combustor and a turbine section. The fan is formed by an integrally bladed rotor including a hub centered about an axis and has a plurality of blades extending radially outwardly of the axis for a span. Each of the blades includes an airfoil extending between a leading edge and a trailing edge, and having a pressure side and a suction side. The airfoil has a thicker portion at the trailing edge, and at a radially inner portion of the span, and over a limited percentage of the span, such that the thicker portion does not extend beyond 50 percent of the span. An axial distance is defined between the trailing edge and the leading edge. The thicker portion extends for less than 50 percent of the axial distance, is on the pressure side.
In another embodiment according to previous embodiment, an increased thickness of the thicker portion area becomes greater in a direction moving from a radially outermost end of the end toward the hub.
In another embodiment according to any of the previous embodiments, a fillet merges the airfoil into the hub at locations along the axial distance and spaced toward the leading edge from the increased thickness portion.
In another embodiment according to any of the previous embodiments, the thicker portion also has a fillet merging the thicker portion into the hub.
In another embodiment according to any of the previous embodiments, a ratio of the thickness of the thicker portion at a radially innermost end to a diameter of an outer periphery of the hub is less than 0.025.
In another embodiment according to any of the previous embodiments, the thicker portion extends radially outwardly for less than 40 percent of the span.
In another embodiment according to any of the previous embodiments, the thicker portion extends for less than 40 percent of the axial distance.
In another embodiment according to any of the previous embodiments, the thicker portion extends radially outwardly for less than 40 percent of the span.
In another embodiment according to any of the previous embodiments, the thicker portion extends for less than 40 percent of the axial distance.
These and other features may be best understood from the following drawings and specification.
The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.
The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.
The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.
The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second).
A modified portion 92 of the airfoil defining the blade 84 is formed adjacent or at the trailing edge 88. The portion 92 includes an increased airfoil thickness portion 94 extending radially outwardly to a radially outward most point 96. Point 96 is preferably at less than 50 percent of the span of the airfoil of the blade 84. More narrowly, it is less than 40 percent and, in one embodiment, it is approximately 30 percent.
Modified portion 92 also includes a fillet 98 formed at the radially inner end of the thicker portion 94 to merge the thicker portion 94 into the hub 82. As shown, the thicker portion 94 extends for only a small portion of an axial distance between the trailing edge 88 and the leading edge 86 to a forwardmost point 99. In embodiments, the thicker portion 94 extends for less than 50 percent of the distance and for less than 40 percent of the distance. In one embodiment, it extended for 30 percent of this distance.
The increased thickness of the thicker portion becomes greater, as can be appreciated from
Of course, the blade 84 can be seen to be relatively thin and, thus, the total increase may be less than 0.05 inch, for an integrally bladed rotor having a diameter to an outer surface of the hub 82 of 14 inches. In one embodiment, the 150 percent thickness increase was approximately 0.021 inch (0.053 centimeters). In embodiments, the thickness increases by at least 100%. The increase as a percentage compares the increase to a nominal thickness of the airfoil at point 96.
Thus, as is clear, the thickness increases by greater than 100% between the radially outermost end, or the top point 96, and to a portion of the thicker portion 94 which merges into the hub 82. A ratio of the thickness of the thicker portion at a radially innermost end to a diameter of the hub 82 is less than 0.025.
With the modified portion 92, the occurrence of a surge is dramatically reduced. On the other hand, the additional material is limited both in span and in the axial length and, thus, unnecessary weight is not added.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
