The present disclosure relates to a blade tip clearance control system, more specifically a fan blade tip clearance control system, to be used in engines such as gas turbine engines.
In a gas turbine engine, fan blades may be formed from an aluminum material, while the casing surrounding the fan blades may be formed from a composite material. There can be large differences in the thermal growth of these two materials. As a result, blade tip clearances may go beyond a desired range and fan efficiency may decrease.
A system which helps maintain control of the blade tip clearance is highly desirable from the standpoint of obtaining fan efficiency.
In accordance with the present disclosure, there is provided an engine which broadly comprises a blade, a casing surrounding the blade, a seal ring, and a passive system for connecting the seal ring to the casing and for accommodating thermal expansion of the seal ring relative to the casing so as to maintain blade tip clearance control.
Further in accordance with the present disclosure, there is provided a method for maintaining blade clearance tip control in a fan section of an engine, which method broadly comprises the steps of: providing a fan casing formed from a composite material and a plurality of fan blades formed from an aluminum containing material; providing an annular seal ring; and providing a passive system for connecting the seal ring to the casing and for accommodating thermal expansion of the seal ring relative to the casing so as to maintain the blade tip clearance control.
Other details of the fan blade tip clearance control via Z-bands are set forth in the following detailed description and the accompanying drawings, wherein like reference numerals depict like elements.
Referring now to
The fan section 12 includes a fan casing 30 and a plurality of fan blades 32 which rotate about the centerline 22. The fan blades 32 are each connected to a fan rotor disk 34 which may be driven by a spool or shaft 33 connected to a low pressure turbine array 35 in the turbine section 18. If desired, each fan blade 32 may be formed from an aluminum containing material such as an aluminum or an aluminum alloy where aluminum is present in an amount greater than 50 percent by weight.
The fan casing 30 may be formed from any suitable material. If desired, the fan casing 30 may be formed from a composite material such as an organic matrix composite material.
Referring now to
It is desirable to maintain a clearance distance between the seal ring 40 and the tip 46 of each fan blade 32. To this end, a passive system 48 for connecting the seal ring 40 to the fan casing 30 is provided. The passive system 48 accommodates thermal expansion of the seal ring 40 relative to the fan casing 30 so as to maintain blade tip clearance control. The system 48 is passive because it does not require the use of sensors, heating elements, piezoelectric materials, shape memory metal elements, fluid control systems, and the like.
The passive system 48 may comprise a plurality of Z-bands 50 extending between an inner wall 52 of an annular duct portion 54 of the fan casing 30 and the abradable seal ring 40. Each Z-band 50 may be formed from a non-corrugated, solid piece of metallic material such as nickel sheet material, a nickel alloy sheet material such as INCO 718, a steel sheet material, a titanium sheet material, an aluminum sheet material or a composite sheet material. The material which is used for each Z-band may have a thermal growth which falls between the thermal growth of the material forming the fan casing and the thermal growth of aluminum. Each Z-band 50 may have an annular configuration and extend about the entire inner periphery of the duct portion 54. Alternatively, each Z-band 50 may comprise an arc segment which extends about a portion of the inner periphery of the duct portion 54. If metallic, each Z-band may have a thickness in the range of 0.015 to 0.030 inches. If composite, each Z-band may have a thickness in a wider range of 0.015 to 0.060 inches due to fiber orientation and lay-up possibilities.
Each Z-band 50 may be attached to the inner wall 52 and to the exterior surface 56 of the backing ring 44. Any suitable means may be used to attach each Z-band 50 to the inner wall 52 and to the exterior surface 56. For example, nuts and bolts may be used to join each Z-band 50 to the inner wall 52 and the exterior surface 56.
As can be seen from the foregoing discussion, the fan casing 30 and the backing ring 44 are formed by different materials having different thermal expansion coefficients.
The Z-bands 50 allow the backing ring 44 to thermally expand relative to the fan casing 30. Each Z-band 50 may be provided with a thickness which is sufficiently thin so that the alpha thermal differences between the Z-bands 50 and the backing ring 44 have minimal influence on the backing ring 44 and hence blade tip clearance is maintained.
If desired, the passive system 48 may comprise multiple Z-bands, for example, three Z-bands 50 with a first of the Z-bands 50 being attached to a leading edge portion 60 of the seal ring 40, a second of the Z-bands 50 being attached to a trailing edge portion 62 of the seal ring 40, and a third of the Z-bands 50 is attached to the seal ring 40 intermediate of the first and second ones of the Z-bands 50.
The passive system 48 further comprises a slip joint 64 between the fan casing 30 and the abradable seal ring 40. The slip joint 64 may be located adjacent the leading edge and trailing edge portions 60 and 62 respectively of the seal ring 40 and a wall 70 of the fan casing 30.
The passive system 48 allows the seal ring 40 to grow different from the fan casing 30 and move thermally independent of the fan casing 30. As a result, increases in fan efficiencies may be obtained.
There has been provided in accordance with the instant disclosure a blade tip clearance control via z-bands. While the fan blade tip clearance control via z-bands has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
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Number | Date | Country | |
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20130149098 A1 | Jun 2013 | US |