Patent Application
20080120841
This invention relates generally to turbine engines, and more particularly to methods and apparatus for reducing convection and aerodynamic bleed losses in turbine engines.
The efficiency of at least some known turbines is at least partially affected by the clearances defined between the rotating components and stationary components. Specifically, the magnitude of steady state clearances and transient radial clearances between the components may affect the turbine efficiency and/or operability margin. For example, a large transient clearance, or a clearance with significant variation around the circumference of the rotating component may adversely decrease the turbine efficiency and may result in engine stalls.
As described above, clearances may be affected by the rotor and the stator's transient thermal responses. Generally, known stators are built to be as lightweight as possible to meet engine weight metrics. This low stator weight makes the stator's transient thermal response typically faster than that of known rotors. Since the stator expands faster than the rotor, rotor tip clearances may increase transiently. Known stator assemblies include a plurality of stator rings coupled together. Specifically, such stator rings are coupled to each other with fasteners which extend through flanges, spaced about the outer circumference of the stator rings. To facilitate slowing the transient thermal response of the stator rings, at least some known turbine assemblies include U-shaped shields that cover the flanges. The shields accomplish this by reducing the convective film coefficients of the stator rings such that the stator rings experience a slower temperature-displacement response.
However, because such U-shaped shields are positioned adjacent the flowpath, the shields may adversely impact engine efficiency, specifically, such shields may increase aerodynamic losses associated with the compressor bleed flow. In some known compressors, aerodynamic losses are incurred because of windage, convection, and/or pressure losses due to the discharge of the air flow in a large cavity and the turbulence of the flow associated therewith.
In one aspect a method for assembling a compressor for use with a turbine is provided. The method includes coupling at least a first stator ring to a second stator ring via at least one fastener sized to extend through at least one stator ring opening. The method further includes coupling a shield assembly to at least one of the first stator ring and the second stator ring to facilitate reducing convection and aerodynamic bleed losses of the at least one stator ring. The shield assembly includes a downstream surface, a retaining portion, and a contoured upstream surface extending from the downstream surface to the retaining portion.
In another aspect, a turbine assembly is provided. The turbine assembly includes a compressor assembly including at least one flange coupled to at least one stator ring via at least one fastener sized to extend through at least one stator ring opening. The turbine assembly further includes a shield assembly coupled to the at least one stator ring to facilitate reducing convection and aerodynamic bleed losses of the at least one stator ring. The shield assembly includes a downstream surface, a retaining portion, and a contoured upstream surface extending from the downstream surface to the retaining portion.
In a further aspect, a compressor assembly for use with a turbine is provided. The compressor assembly includes at least one flange coupled to at least one stator ring via at least one fastener sized to extend through at least one stator ring opening. The compressor assembly further includes a shield assembly coupled to the at least one stator ring to facilitate reducing convection and aerodynamic bleed losses of said at least one stator ring. The shield assembly comprises a downstream surface, a retaining portion, and a contoured upstream surface extending from the downstream surface to the retaining portion.
In operation, air flows through fan assembly blades 24 and compressed air is supplied to high pressure compressor 14. The air discharged from fan assembly 22 is channeled to compressor 14 wherein the airflow is further compressed and channeled to combustor 16. Products of combustion from combustor 16 are utilized to drive turbines 18 and 20, and turbine 20 drives fan assembly 22 via shaft 31. Engine 10 is operable at a range of operating conditions between design operating conditions and off-design operating conditions.
Each stator vane assembly 56 includes a vane 74, a radial flange 76, and an annular stator body 58. Each radial flange 76 extends radially outward from stator body 58. As is known in the art, vanes 74 are oriented relative to a flow path through compressor 14 to control air flow therethrough. In addition, at least some vanes 74 are coupled to an inner shroud. Alternatively, compressor 14 may include a plurality of variable stator vanes utilized in lieu of fixed stator vanes 74.
Each stator body 58 includes a radial flange 76 and an opening 102 formed therethrough. More specifically, in the exemplary embodiment, each opening 102 extends through each radial flange 76 of an upstream stator body 58. Stator body 58 may also include a stator ring or flange 104 that extends substantially axially from stator body 58. In the exemplary embodiment, stator ring or flange 104 extends generally upstream from a downstream stator body 58. More specifically, in the exemplary embodiment, each flange 104 of a downstream stator body 58 is coupled to each radial flange 76 of an adjacent upstream stator body 58 via a plurality of fasteners 106. In the exemplary embodiment, fastener 106 extends through stator body opening 102 and through an opening 108 in stator body flange 104 to secure flange 104 to an upstream stator body 58. In the exemplary embodiment, fastener 106 is a D-Head bolt that is secured in position with a breakaway nut 110. Fastener 106 has a fastener head 111 and a fastener body 112. Fastener head 111 has a thickness of T1. Fastener body 112 has a length of L1. In the exemplary embodiment, fastener body length L1 is greater that the length of the breakaway nut 110 to allow flange 104 and a nut 218 to be coupled to fastener 106, as described in more detail below.
In the exemplary embodiment, shield assembly 100 includes a shield 200 having an integrally-formed retaining portion 202, an aerodynamically contoured upstream surface 204, and a downstream surface 205. Upstream surface 204 extends between retaining portion 202 and downstream surface 205. Downstream surface 205 includes a slot 206 extending therethrough and that is sized to receive fastener 106 therethrough, as described in more detail below. Upstream surface 204 and downstream surface 205 each have a thickness of T2. Retaining portion 202 has a width of W1, a depth of D1, and a thickness of T2. Shield 200 is arcuate with a radius R1 (shown in
In the exemplary embodiment, stator body 58 is formed with a retaining channel 208 that extends circumferentially around stator body 58 and is defined between an annular lip 210 and a stepped portion 212 of body 58. Retaining channel 208 has a width W2. Lip 210 has a height of H1. Channel width W2 is larger than retaining portion width W1 such that retaining portion 202 may be inserted in retaining channel 208. Stepped portion 212 extends outward from body 58 and, in the exemplary embodiment, is formed with a plurality of shoulders 214 and 216. Shoulder 214 is counter-bored to a depth D2, where D2 is substantially equal to fastener head thickness T1. Shoulder 216 is counter-bored to a depth of D3. When assembled, fastener head 111 is substantially flush with the outer edge of shoulder 214. In the exemplary embodiment, when retaining portion 202 is positioned in retaining channel 208, a portion of retaining portion 202 extends beyond shoulder 216.
In the exemplary embodiment, shield assembly 100 is positioned just downstream of an annular opening 219 in casing 62 and covers stator body opening 102, fastener 106, and flange 104. Shield 200 is retained in position by inserting shield retaining portion 202 into retaining channel 208. Lip 210 contacts shield 200 approximately at a point 220 where upstream surface 204 is coupled to retaining portion 202. In the exemplary embodiment, lip 210 and upstream surface 204 form a continuous contour from stator body 58 at opening 219 to downstream surface 205. Furthermore, in the exemplary embodiment, shield 200 is further secured by coupling shield 200 at slot 206 to flange 104 and breakaway nut 110 by utilizing shield slot 206. Shield 200 is secured in position by coupling nut 218 to fastener body 112 downstream of breakaway nut 110, slot 206, and flange opening 108. When shield assembly 100 is secured in position over stator body 58, shield assembly 100 creates an aerodynamic surface between stator body 58 and the airflow.
In the exemplary embodiment, first overlap portion 222 is recessed from shield 200 by offset O1. More specifically, in the exemplary embodiment, offset O1 is substantially equal to shield thickness T2. First overlap portion 222 has an upstream surface 226 and a downstream surface 228. Upstream surface 226 and downstream surface 228 each have a thickness of T3. In the exemplary embodiment, thickness T3 is substantially equal to shield thickness T2. Upstream surface 226 is aerodynamically contoured and has a contour substantially equal to that of upstream surface 204. An aperture 230 having a radius R2 extends through downstream surface 228.
In the exemplary embodiment second overlap portion 224 is co-planar with shield 200. Second overlap portion has an upstream surface 232, a downstream surface 234, and a retaining portion 236. Upstream surface 232 and downstream surface 234 each have a thickness T4. In the exemplary embodiment, thickness T4 is equal to thickness T2. Upstream surface 232 is configured to have substantially the same aerodynamic contour as upstream surface 204. Retaining portion 236 is configured to have the same features and dimensions as retaining portion 202, described above. Downstream surface 234 has an aperture 238 extending therethrough. More specifically, in the exemplary embodiment, aperture 238 has a radius R3 that is equal to aperture radius R2.
In the exemplary embodiment, first overlap portion 222 is inserted between second overlap portion 224 of an adjacent shield 200 and stator body 58. First overlap portion 222 and second overlap portion 224 are configured to mate and form overlap engagement 300. Aperture 230 is configured to align with aperture 238 of adjacent second overlap portion 224. Apertures 230 and 238 are further configured to align with a second opening 302 extending through stator body 58. Moreover, in the exemplary embodiment, flange 104 has a second opening 304 extending therethrough. Flange second opening 304 is sized to receive a retainer 306. More specifically, second opening 302 has a radius R4 where R4 is greater than R2 and/or R3 such that radius R4 is sized to receive retainer 306. Furthermore, in the exemplary embodiment, retainer 306 is a shank nut. Retainer 306 is positioned within stator body second opening 302 and flange second opening 304. Apertures 230 and 238 are configured to align with retainer 306 positioned in openings 302 and 304. Overlap portions 222 and 224 are secured to stator body by inserting a second fastener 308 through apertures 230, 238 and into retainer 306. More specifically, in the exemplary embodiment, second fastener 308 is a traditional bolt. In the exemplary embodiment, when apertures 230 and 238 are coupled to retainer 306, shield slot 206 is aligned with stator body opening 102.
While engine 10 is in operation, shield assembly 100 facilitates reducing aerodynamic bleed losses by providing an aerodynamic surface over which air may flow and experience a pressure recovery. Further, stator body 58, stator body flange 104, and fastener 106 assembly is shielded from airflow of heated fluids. When in position, shield assembly 100 facilitates reducing the thermal expansion of stator body 58, which thereby facilitates slowing the growth of the stator during transient conditions and reducing tip clearances. When first overlap portion 222 and second overlap portion 224 form overlap engagement 300, overlap engagement 300 facilitates reducing leakage of air between shields 200 of shield assembly 100 and reduces aerodynamic windage losses over the shield.
The above-described apparatus facilitates reducing losses in a compressor. The shield assembly facilitates minimizing losses by creating an aerodynamic surface in the air flow path and aiding in pressure recovery. In the exemplary embodiment, a secondary air flow bled from the main compressor airflow flows over the aerodynamic surface. The airflow across the stator body increases in temperature of the stator body because of friction between the fluid and the surface of the stator body (windage). By coupling the shield assembly upstream of the stator body, the fluid has an aerodynamic surface across which to flow, reducing friction between the fluid and the stator body. The reduction in windage maintains the secondary air flow at a lower temperature than in other known compressors. Furthermore, since the bleed air flows over the shield and does not directly impinge on the stator ring, the stator ring is shielded from the convection air flow. The overlapping shields create a low convection cavity around the stator ring such that the shield facilitates insulating the stator ring from the air flow. Therefore, the shield assembly also facilitates maintaining the desired stator thermal-displacement response to passively control the clearance between the rotating tip and the stationary inner surface of the compressor flow path. Because of the insulation effects of the shield assembly, the mass of the fastener at the stator body joints can be reduced while achieving the same time constant as a fastener with more mass.
Exemplary embodiments of a method and apparatus to facilitate reducing losses in a compressor are described above in detail. The method and apparatus is not limited to the specific embodiments described herein, but rather, components of the method and apparatus may be utilized independently and separately from other components described herein. For example, the shield assembly may also be used in combination with other turbine engine components, and is not limited to practice with only stator body assemblies as described herein. Rather, the present invention can be implemented and utilized in connection with many other windage loss reduction applications.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
