Patent Application
20140017061
The subject matter disclosed herein relates to the art of gas turbomachines and, more particularly, to a gas turbomachine including a purge flow reduction system.
Many turbomachines include a compressor portion linked to a turbine portion through a common compressor/turbine shaft or rotor and a combustor assembly. The compressor portion guides a compressed air flow through a number of sequential stages toward the combustor assembly. In the combustor assembly, the compressed air flow mixes with a fuel to form a combustible mixture. The combustible mixture is combusted in the combustor assembly to form hot gases. The hot gases are guided to the turbine portion through a transition piece. The hot gases expand through the turbine portion rotating turbine blades to create work that is output, for example, to power a generator, a pump, or to provide power to a vehicle. In addition to providing compressed air for combustion, a portion of the compressed airflow is passed through the turbine portion for cooling purposes. Additional cooling/heating is provided by introducing purge flows from the turbine portion into various regions of the turbomachine. For example, purge flows are often employed to cool/heat aft portions of the turbine. The purge flow also helps to maintain desired thermal expansion of adjacent parts
According to one aspect of the exemplary embodiment, a gas turbomachine includes a turbine portion including at least one turbine wheel, and a wheel shaft operatively connected to the at least one turbine wheel. The wheel shaft includes an outer surface. A stationary member includes an inner surface positioned outward of the outer surface of the wheel shaft to form a purge flow passage. A bearing housing is linked to the stationary member and spaced radially outward of the wheel shaft. The bearing housing includes at least one purge flow passage configured and disposed to guide a purge flow toward the wheel shaft. At least one of the outer surface of the wheel shaft and the inner surface of the stationary member includes a roughness inducing coating configured and disposed to increase drag and residence time of purge flow in the purge flow passage.
According to another aspect of the exemplary embodiment, turbomachine system includes a rotating component including an outer surface, a stationary member including an inner surface positioned outward of the outer surface of the rotating component to form a fluid flow passage, and a bearing housing linked to the stationary member and spaced radially outward of the rotating component adjacent the stationary member. The bearing housing includes at least one fluid flow passage configured and disposed to guide a fluid flow toward the fluid flow passage. At least one of the outer surface of the rotating component and the inner surface of the stationary member includes a roughness inducing coating configured and disposed to increase drag and residence time of fluid flow in the purge flow passage.
According to yet another aspect of the exemplary embodiment, a method of decreasing purge flow in a gas turbomachine includes guiding a purge flow into a purge flow passage defined between a rotating component and a stationary member, and inducing the drag in the purge flow through an interaction with a roughness inducing coating provided on one of the rotating component and the stationary component. The drag leads to an increased temperature and residence time of the purge flow in the purge flow passage that reduces an amount of required purge flow.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification.
The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
A gas turbomachine in accordance with an exemplary embodiment is indicated generally at 2 in
Turbine wheel 8 is operatively coupled to a rotating component or wheel shaft 19. Wheel shaft 19 rotates in response to rotation of turbine wheel 8. Wheel shaft 19 includes an axial portion 22 having an axial portion outer surface 24 and an angled portion 28 having an angled portion outer surface 30. As shown in
Stator 40 includes a first section 50 that extends to a second section 51 and a third section 52. Second section 51 is angled to correspond to angled portion 28 of wheel shaft 19. Third section 52 extends generally parallel to axial portion 22 of wheel shaft 19 and first section 50 extends generally perpendicularly to third section 52. First section 50 includes a first inner surface 54, second section 51 includes a second inner surface 55, and third section 52 includes a third inner surface 56. Bearing housing 44 includes a bearing housing body 60 including a first end portion 62 that extends to a second end portion 63 through an intermediate portion 64. First end portion 62 supports a plurality of seal members, one of which is indicated at 67. Seal members 67 prevent lubricant and/or coolant (not shown) flowing along axial portion 22 to pass toward angled portion 28. Seal member 67 is shown to include a purge flow nozzle 69 that passes a purge flow through bearing housing 60. The purge flow passes into a purge flow passage 75 that extends between angled portion outer surface 30 and first, second, and third inner surfaces 54-56 of stator 40. The purge flow may originate from a component operatively coupled to turbomachine 2 such as a compressor (not shown) or from an external source such as a blower (also not shown).
The purge flow is controlled to condition rabbet portion 33 to achieve a rate of thermal expansion that aligns with a rate of thermal expansion of turbine wheel 8. During start up, blades mounted to turbine wheel 8 are exposed to combustion gases flowing along hot gas path 11. As a result, turbine wheel 8 thermally expands faster than rabbet portion 33. In order to offset the difference in rates of thermal expansion, a large amount of purge flow is passed into purge flow passage 75 to cause angled portion 28 and rabbet 33 to heat up faster and match the rate of thermal expansion of turbine wheel 8. The amount of purge flow passing into purge flow passage 75 represents lost work that results in efficiency losses for turbine portion 4.
In accordance with the exemplary embodiment, turbine portion 4 includes a purge flow reduction system 88 that leads to a reduced amount of purge flow required to heat rabbet 33. Purge flow reduction system 88 includes roughness inducing coating 90 provided on angled portion 28 and another roughness inducing coating 94 provided on second inner surface 55 of stator 40. Roughness inducing coatings 90 and 94 induce a drag on the purge flow in purge flow passage 75 that increases a residence time and temperature of the purge flow. The increased residence time of the purge flow leads to a reduction in the amount of purge flow required to condition angled portion 28 and rabbet 33 to achieve a rate of thermal expansion that more closely aligns with the rate of thermal expansion of turbine wheel 8.
In accordance with one aspect of the exemplary embodiment, roughness inducing coatings 90 and 94 comprise thermal or flame sprayed coatings 98 and 100 respectively. Thermal coatings allow for the application of a melted or heated material to a substrate having a desired thickness. The desired thickness may be varied to achieve the desired drag and residence time of the purge flow. Flame spray coating may include coatings applied through a cold spray process. The roughness inducing coating may be applied to one or the other of angled portion 28 or second inner surface 55 of stator 40. The overall surface area, thickness, and location of the roughness inducing coating may vary depending on the desired flow modification within purge flow passage 75. For example, the roughness inducing coating may entirely cover an entire surface or may be applied in strips. Although described in terms of being incorporated into a turbomachine, the roughness inducing coating may be employed in fluid passages of other systems to create a desired restriction.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
