Flexible Leaf Member for Gas Turbine Fan Case Clearance Control
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Solution Overview
Problem
Gas turbine engine fan sections face challenges in maintaining a minimized clearance seal between fan blades and the fan case due to large temperature fluctuations, which existing technologies fail to adequately address through thermal expansion and contraction accommodation.
Innovation Solution
A composite septum and honeycomb structure with a flexible leaf member, constructed from aluminum alloy, is used to connect the adhesive and the honeycomb, providing a rub strip between the liner and the blade, with undulations and straps to maintain radial blade tip clearance by accommodating the thermal expansion and contraction of the liner and fan blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid seal structure is used between fan blades and fan case, then structural strength is improved, but thermal expansion and contraction cannot be accommodated, causing clearance variations
Solution Approach 1:
The seal structure transitions from a rigid static configuration to a dynamic one where the Z-band can move axially and change its cross-sectional shape. The Z-band's ability to deform and shift position allows it to adapt to thermal expansion and contraction of the fan case while maintaining sealing contact with the fan blades throughout the temperature range.
Solution Approach 2:
The Z-band is designed as a thin, flexible metallic element with a specific cross-sectional geometry that allows it to bend and deform. This flexible structure can accommodate the dimensional changes of the fan case due to thermal effects while maintaining the seal, replacing the need for a rigid seal structure.
2Adaptability or versatility
If a flexible seal structure is used to accommodate thermal expansion, then adaptability is improved, but sealing effectiveness deteriorates due to excessive movement
Solution Approach 1:
The Z-band's dynamic characteristics are carefully controlled through its geometric design. It possesses sufficient flexibility to move with thermal expansion but maintains enough structural rigidity in its cross-section to preserve sealing contact. The dynamic behavior is optimized so that movement occurs in a controlled manner that does not compromise seal integrity.
Solution Approach 2:
The cross-sectional dimensions and geometry of the Z-band are specifically designed to provide the right balance between flexibility and sealing effectiveness. By controlling parameters such as band thickness, width, and cross-sectional shape, the structure achieves adequate movement capability while maintaining sufficient contact pressure and geometric integrity for effective sealing.
3Ease of manufacture
If multiple discrete pins are used to support the liner, then manufacturing ease is improved, but clearance consistency deteriorates due to localized expansion points
Solution Approach 1:
Multiple discrete pin support points are merged into a continuous Z-band structure that provides uniform support and clearance control around the entire fan case circumference. This continuous structure eliminates the localized expansion and clearance variations that occur with discrete pins, achieving more consistent clearance while remaining manufacturable.
Solution Approach 2:
The Z-band can be manufactured as separate segments that are then assembled around the fan case, combining the manufacturing advantages of discrete components with the performance benefits of a continuous structure. This segmentation approach allows for easier fabrication and installation while achieving uniform clearance control when the segments are properly positioned and connected.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively maintains a consistent radial blade tip clearance throughout varying operating temperatures by using a flexible leaf member that absorbs thermal expansion and contraction, ensuring a tight seal and reducing wear between the fan blades and the fan case.
Implementation Method 1
accommodating the thermal expansion and contraction of the liner and fan blades
Implementation Method 2
accommodating the thermal expansion and contraction of the liner and fan blades
Implementation Method 3
A composite septum and honeycomb structure with a flexible leaf member, constructed from aluminum alloy, is used to connect the adhesive and the honeycomb
Data Source
Figure 1
Figure 2~4B
Figure 5~10B
AI summary
A section (18) of a gas turbine engine (10) includes a case structure (30) having a first coefficient of thermal expansion. A continuous, ring-shaped liner (44) has a second coefficient of thermal expansion that is substantially different than the first coefficient of thermal expansion. A flexible leaf member (46) operatively connects the liner (44) to the case structure (30). The leaf member (46) is configured to accommodate diametrical change in the liner (46) throughout various fan section-operating temperatures.