Scroll Case Lug-Slot Mounting for Turbine Tip Clearance
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Solution Overview
Problem
Aircraft engine scroll cases experience thermal growth that affects surrounding components, leading to increased tip clearance and impaired performance due to radial movement of the turbine exhaust case.
Innovation Solution
A turbine support case is secured to the bearing housing, with spokes extending through the scroll case and locked via lugs and slots to allow radial expansion, while sealing members limit gas leakage and maintain tip clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the scroll case is rigidly connected to the turbine support case, then structural stability is improved, but thermal growth causes increased tip clearance and impaired performance
Solution Approach 1:
The connection between the scroll case and turbine support case is changed from rigid to dynamic through the lug-slot mechanism. The slots allow radial movement of the scroll case relative to the turbine support case, enabling the system to adapt to thermal growth while maintaining structural integrity. This dynamic connection resolves the contradiction by allowing stability through structural connection while accommodating thermal expansion to prevent performance degradation.
Solution Approach 2:
The invention changes the physical state of the connection from fixed to movable by introducing slots that permit radial displacement. This parameter change allows the scroll case to expand radially with thermal growth while remaining circumferentially locked, thus maintaining structural stability while preventing the harmful effects of rigid connection during thermal expansion.
2Temperature
If the scroll case is allowed to expand freely, then thermal growth is accommodated, but tip clearance increases and performance deteriorates
Solution Approach 1:
The connection mechanism is segmented into lugs and slots, where the lugs provide circumferential locking and the slots provide radial movement freedom. This segmentation allows the scroll case to expand radially to accommodate thermal growth while the lugs prevent circumferential movement that would affect tip clearance, thus resolving the contradiction between thermal accommodation and clearance control.
Solution Approach 2:
The lug-slot mechanism acts as an intermediary between the scroll case and turbine support case. It mediates the thermal growth by allowing controlled radial movement while preventing unwanted circumferential displacement, thus accommodating thermal expansion without compromising tip clearance control.
3Adaptability or versatility
If lugs and slots are used to connect the scroll case and turbine support case, then radial expansion is allowed, but device complexity increases
Solution Approach 1:
The connection structure is segmented into simple geometric elements (lugs and slots) that can be easily manufactured and assembled. This segmentation achieves radial expansion capability through a relatively simple mechanism compared to more complex articulated or flexible connections, thus resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The lug-slot mechanism provides local quality by allowing radial movement only where needed (in the slot direction) while maintaining rigidity in other directions (circumferential locking). This localized freedom of movement achieves the required adaptability without requiring complex mechanisms throughout the entire structure.
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 maintains consistent tip clearance and improves engine performance by isolating the scroll case from thermal loads, preventing force transmission to the turbine support case.
Implementation Method 1
aerodynamic flow distributors, such as scroll or volute structures, are used to receive combustion gases and to regulate them... Such structures are subjected to thermal growth
Data Source
AI summary
An aircraft engine, has: a turbine rotatable about a central axis; a scroll case having an inlet and an outlet connected to the turbine, and a conduit extending around the central axis from the inlet to the outlet; a bearing housing extending around the central axis and including a support flange; and a turbine support case secured to the bearing housing, the turbine support case having spokes distributed around the central axis and extending along a direction having an axial component relative to the central axis, the spokes extending through the scroll case and radially supported by the bearing housing, one of the turbine support case and the scroll case defining lugs circumferentially distributed around the central axis, the other of the turbine support case and the scroll case defining slots, the turbine support case and the scroll case circumferentially locked to one another via the lugs engaging the slots.