Not applicable.
The present invention generally relates to gas turbine engines. More specifically, a turbine blade is disclosed having an airfoil profile that reduces aerodynamic flutter while increasing the overall power output from the stage of the turbine.
A typical gas turbine engine comprises a compressor, at least one combustor, and a turbine, with the compressor and turbine coupled together through an axial shaft. In operation, air passes through the compressor, where the pressure of the air increases and then passes to a combustion section, where fuel is mixed with the compressed air in one or more combustion chambers and ultimately ignited. The hot combustion gases then pass into the turbine and drive the turbine. As the turbine rotates, the compressor turns, since they are coupled together along a common shaft. The turning of the shaft also drives a generator for electrical applications. The engine must operate within the confines of the environmental regulations for the area in which the engine is located. As a result, more advanced combustion systems have been developed to more efficiently mix fuel and air so as to provide more complete combustion, which results in lower emissions.
As the demand for more powerful and efficient turbine engines continues to increase, it is necessary to improve the efficiency at each stage of the turbine, so as to get the most work possible out of the turbine. To achieve this efficiency improvement, it is necessary to remove any design defects that limit the turbine from achieving its maximum performance. Turbine blades have been known to be limited in power output by a variety of conditions including, but not limited to creep, flutter, and erosion.
Flutter is a dangerous condition caused by the interaction of an airfoil's structural modes of vibration with the aerodynamic pressure distribution on the blade. As the airfoil portion of the turbine blade vibrates, its pressure magnitudes and distributions fluctuate due to the changing flow path geometry. This can result in energy being either added to the flow (a condition know as positive aero-damping) or energy being extracted from the flow (negative aero-damping). If the energy being extracted from the flow is greater than can be dissipated through mechanical damping, the amplitude of the displacements will increase. The cycle repeats itself and is compounded until either the energy input and energy dissipated balance each other, or failure occurs. In order to avoid excessive flutter, which can cause component failure, limitations may be placed upon the operating condition of the turbine. Furthermore, excessive flutter outside of acceptable limits can cause the turbine blade to fail over time.
Embodiments of the present invention are directed towards a system and method for, among other things, a turbine blade having an increased power output which avoids operational limitations found in prior art turbine blade designs.
In one embodiment of the present invention, a turbine blade is disclosed having an attachment, a neck, a platform extending radially outward from the neck, an airfoil extending radially outward from the platform, and a shroud extending radially outward from the airfoil, where the airfoil has an uncoated profile substantially in accordance with Cartesian coordinate values of X, Y, and Z as set forth in Table 1, carried to three decimal places, wherein Z is a distance measured radially from the platform.
In an alternative embodiment of the present invention, an airfoil for a turbine blade is discussed having an uncoated profile substantially in accordance with the Cartesian coordinate values of X, Y, and Z as set forth in Table 1, carried to three decimal places.
In yet another embodiment of the present invention, a turbine rotor stage is disclosed having a plurality of turbine blades secured to a rotor disk, the turbine blades each having an airfoil including an uncoated profile substantially in accordance with the Cartesian coordinate values of X, Y, and Z as set forth in Table 1, carried to three decimal places.
Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention.
The present invention is described in detail below with reference to the attached drawing figures, wherein:
The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies.
Referring initially to
The turbine blade 100 also comprises a recessed region 112 (
The turbine blade 100 is fabricated through a casting and machining process. Specifically, in an embodiment of the present invention, the turbine blade is cast from a nickel-based superalloy. Examples of acceptable alloys include, but are not limited to, Rene 80, GTD111, and MGA2400. For the embodiment disclosed herein, the airfoil 108 of the turbine blade 100 has a modified profile as compared to prior-art airfoils—more particularly, the airfoil 108 includes a modified spanwise stiffness distribution—which improves its natural frequency margin over the vibratory drivers. In addition, the modified airfoil 108 profile reduces bending stress by balancing the hot gas induced bending loads with centrifugal loading.
As a result of the casting process, the profile of the airfoil 108 can vary typically up to 0.030 inches relative to the nominal coordinates shown in Table 1. In order to provide further thermal capability, the airfoil 108 of the turbine blade 100 comprises a MCrAlY bond coating of approximately 0.0055 inches thick, where M can be a variety of metals including, but not limited to Cobalt, Nickel, or a Cobalt Nickel mixture. By application of the bond coating, the turbine blade 100 achieves an improved oxidation resistance over the prior-art configuration.
As previously discussed,
The airfoil 108 of the present invention is generated by connecting X, Y coordinates with a smooth arc at a number of Z positions extending radially outward from the blade platform 106. In one embodiment, twenty-one sections of X, Y coordinate data are first connected together using a smooth arc. These sections, some of which are shown in
For example,
An alternative embodiment of the present invention is directed to the airfoil 108 for the turbine blade 100, which, as discussed, has an uncoated profile substantially in accordance with Cartesian coordinate values of X, Y, and Z as set forth in Table 1 carried to three decimal places. Again, the airfoil 108 is formed by connecting adjacent sections of X, Y coordinate data at a series of Z positions measured radially from a platform. Because the airfoil 108 is cast, there are tolerances in the casting process, and as such the airfoil 108 can vary in profile and position by about +/−0.030 inches.
In yet another embodiment of the present invention, a plurality of turbine blades 100 are secured to a rotor disk to form a rotor stage. The plurality of turbine blades 100 each have an airfoil 108 having an uncoated profile substantially in accordance with Cartesian coordinate values of X, Y, and Z as set forth in Table 1.
The airfoil 108 profile described herein yields a noticeable improvement in predicted flutter margin over prior-art configurations. Thus, the airfoil 108 maintains aerodynamic stability over the complete range of inter-blade phase angles for critical vibratory modes at the design-point operating condition, whereas prior-art configurations exhibited a narrow range of conditional aerodynamic instability mitigated by mechanical damping contributions. This improved flutter resistance provides the ability to attain higher operating mass flow with increased work extraction.
As previously discussed, the turbine blade 100 also utilizes a seal 114 for sealing the axially-extending gap between adjacent platforms 106 in a rotor stage. The seal and its positioning can be seen from
The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope.
From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.