Patent Application
20110116917
Not applicable.
The present invention generally relates to a compressor component having an airfoil and more specifically to an improved airfoil profile that has a variable thickness along the airfoil span in order to raise the natural frequency of the compressor component and minimize excitation of the component.
A compressor typically comprises a plurality of stages, where each stage includes a set of stationary compressor vanes which direct a flow of air into a rotating disk of compressor blades, where each stage of the compressor decreases in diameter, causing the pressure and temperature of the air to increase. Compressor components having an airfoil, such as compressor blades and compressor vanes, are held within disks or carriers and are designed to aid in compressing a fluid, such as air, as it passes through stages of blades and vanes of the compressor.
Axial compressors having multiple stages are commonly used in gas turbine engines for increasing the pressure and temperature of air to a pre-determined level at which point a fuel can be mixed with the air and the mixture ignited. The hot combustion gases then pass through a turbine to provide either a propulsive output or mechanical output.
Compressor components, such as blades and vanes, have an inherent natural frequency, and when the compressor component is excited, as would occur during normal operating conditions, the compressor component shakes or moves at different orders of the engine natural frequency. When the natural frequency of the compressor component coincides or crosses an engine order, the compressor component can start to resonate or vibrate in such away that it is excited and can cause cracking or failure of the compressor component.
In accordance with the present invention, there is provided a novel and improved compressor component having a non-linear airfoil thickness that results in an altered natural frequency of the airfoil. The location of the airfoil thickness has been modified at a distance along the airfoil span so as to shift the natural frequency of the blade with minimal impact to blade aerodynamics and efficiency.
In an embodiment of the present invention, a compressor component has an attachment and an airfoil extending radially outward from the attachment, where the airfoil has a leading edge and a trailing edge, concave and convex surfaces, and a thickness. The thickness of the airfoil between the concave and convex surfaces varies non-linearly along the span of the airfoil.
In an alternate embodiment of the present invention, a compressor component is disclosed having an attachment and an airfoil extending radially outward from the attachment. The airfoil has an uncoated profile substantially in accordance with Cartesian coordinate values of X, Y, and Z as set forth in Table 1, where Z is a distance measured radially from a bottom of the attachment to which the airfoil is mounted. The X and Y values are joined by smooth connecting splines to form a plurality of airfoil sections and the sections are joined to form the airfoil profile.
In yet another embodiment, a compressor stator having an increased natural frequency is disclosed in which the compressor stator comprises an attachment and an airfoil extending radially outward from the attachment with the airfoil having a variable thickness with at least a first and second maximum thicknesses and a non-linear variation of the thickness.
The enhancements made to the airfoil along its chord length and span are made without impacting the throat area between adjacent blades or overall efficiency while also increasing the natural frequency of the compressor component. As such, parts of the compressor vane have a reduced thickness compared to the prior art, while other areas of the compressor component have an increased thickness. Although disclosed as an airfoil that is uncoated, it is envisioned that an alternate embodiment of the present invention can include an airfoil that is at least partially coated with an erosion resistant coating, corrosion resistant coating, or a combination thereof. In this case, the coordinates of the airfoil as listed in Table 1 would be prior to a coating being applied to any portion of the airfoil.
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 instant invention will now be described with particular reference to the accompanying drawings.
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 thickness 114 varies non-linearly along an airfoil span 116 as measured in a radial direction from the attachment 102 to a tip 118 of the airfoil 104. The non-linear variation in thickness can be seen with reference to
Referring to
From approximately 35% span until approximately 60% span, the airfoil thickness again increases non-linearly, at which point a second decrease in thickness occurs, roughly from approximately 60% -85% span. However, the thickness over at least the 40% -80% span is greater than the thickness at approximately 15%-25% span. For an embodiment of the present invention the maximum thickness of the airfoil 104 is located at approximately 60% along the span, as depicted by
Unlike the prior art, the maximum thickness of the airfoil 104 is not at the tip 118. In an embodiment of the present invention, the airfoil 104 has a first maximum thickness and a second maximum thickness at points along the airfoil span. As depicted in
The changes in airfoil thickness and distribution of material along the airfoil alters the natural frequency of the compressor component 100. As one skilled in the art of blade and vane airfoil design will understand, the airfoils move at various modes due to their geometry and the aerodynamic forces being applied thereto. Should this excitation occur for prolonged periods of time at a natural frequency or order thereof, the airfoil 104 can fail due to high cycle fatigue. Such modes include bending, torsion, and various higher order modes. For example, a critical bending mode for the compressor component of the present invention is the fourth bending, which is also referred to as 42E or 42 times the 60 Hz frequency of the engine. For this mode, the fourth bending results in a critical frequency of 2512 Hz. The prior art component had a higher order operating mode that corresponded to this frequency, and as such, the excitation at this frequency caused high cycle fatigue cracking at approximately 40%-60% span. Increasing the thickness of the airfoil 104 along this portion of the airfoil span, serves to alter the natural frequency of the component such that the natural frequency at this higher engine order is above the critical frequency of 2512 Hz. More specifically, the embodiment of the present invention discussed with reference to
A compressor component for a land-based compressor is typically fabricated from a relatively low temperature alloy since air temperature of the compressor typically only reaches upwards of 700 deg. F. One such material for the compressor component 100 is a hardenable stainless steel alloy. For compressor components in this region of the engine, a common durability issue exhibited by prior art components is erosion of the airfoil leading edge. The airfoil leading edge (see 106 in
In an embodiment of the present invention, the airfoil 104 is solid and fabricated from a material such as a hardened steel alloy. The airfoil 104 has an uncoated profile substantially in accordance with Cartesian coordinate values of X and Y, for each distance Z, in inches, as set forth in Table 1 below. The distance Z is measured radially outward from a bottom surface 126 of the attachment 102. The X and Y coordinates are distances relative to coordinate plane origin established at each of the radial Z heights.
Referring to
The airfoil 104 can be fabricated by a variety of manufacturing techniques such as forging, casting, milling, and electro-chemical machining (ECM). As such, the airfoil has a series of manufacturing tolerance for the position, profile, twist, and chord that can cause the airfoil 104 to vary by as much as +/−0.090 inches from a nominal state. In addition to manufacturing tolerances affecting the overall size of the airfoil 104, it is also possible to scale the airfoil 104 to a larger or smaller airfoil size. However, in order to maintain the benefits of this airfoil shape and size, in terms of stiffness and stress, it is necessary to scale the airfoil uniformly in X and Y directions, but Z direction may be scaled separately.
As previously discussed, the profile generated by the X, Y, and Z coordinates of Table 1 is an uncoated profile. While an embodiment of the present invention is an uncoated compressor component 100 such as a stator vane, it is possible to add a coating to at least a portion of the airfoil 104 in an alternate embodiment. This coating would have a thickness of up to approximately 0.010 inches
An alternate embodiment of the present invention is shown in
An additional benefit of the carrier 124 is its ability to provide dampening of vibrations of the compressor component 100. The prior art arrangement of the carrier was fabricated from A515 steel and the compressor component was fabricated from a precipitation-hardenable grade of Carpenter Custom 450 stainless steel (CC 450), which together were subject to corrosion, and because of this corrosion the prior art compressor component locked with the carrier during operation. As a result, any damping benefit gained by the interaction of the component and carrier segment was lost due to the corrosion.
The compressor component 100 slides into the carrier 124, and due to the associated tolerances, the compressor component 100 can move relative to the carrier 124 during operations, and such movement allows for dampening of vibrations in the airfoil 104. The compressor component 100 is fabricated from CC 450 stainless steel and the carrier 124 is fabricated from Nitronic 60, a more corrosion-resistant material. The difference in materials significantly reduces any corrosion between the compressor component 100 and carrier 124, and as such, the carrier 124 is capable of dampening vibrations of the compressor component 100.
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.
As a result of the thickness change, other factors such as airfoil shape, pressure loss, and overall compressor performance are impacted. Care is taken to minimize any adverse effects from the airfoil thickness changes. Despite the thickness change, the general airfoil shape is maintained while the pressure loss across this stage compressor vane has increased approximately 6.3%. However, because most axial compressors have multiple stages, the overall performance impact on the compressor is negligible (approximately 0.01% loss in efficiency). Therefore, the benefits of an alternate natural frequency through airfoil thickness changes can be achieved without adverse effect to the overall compressor performance.
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.
