Gas Turbine Rotor Centering Cooling System for Exhaust Diffuser
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Solution Overview
Problem
In gas turbine engines, the uneven heating of struts at top and bottom dead center positions causes the exhaust bearing body to become off-center, leading to potential tip rub of turbine blades during hot restarts due to insufficient cooling, resulting in misalignment and clearance issues.
Innovation Solution
A rotor centering cooling system is implemented, which includes an exhaust cooling manifold and internal cooling systems within struts to reduce thermal gradients by supplying cooling fluid through rotor centering cooling channels that entrain ambient air, purging the shroud cavity and cooling the turbine casing exhaust flange, thereby maintaining a centered exhaust bearing body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling air is supplied to support struts and adjacent components of the turbine exhaust case, then the turbine exhaust case temperature is maintained below a predetermined temperature, but the thermal gradient between top and bottom struts causes the exhaust bearing body to move off-center
Solution Approach 1:
The cooling system applies different cooling strategies to different locations: top struts receive cooling air through internal passages to reduce thermal expansion and prevent upward movement, while bottom struts are cooled through the rotor centering cooling system to prevent downward movement. This localized differential cooling maintains thermal balance and keeps the exhaust bearing body centered.
Solution Approach 2:
The cooling system proactively counteracts the thermal gradients before they can cause significant off-center movement. By continuously supplying cooling air to both top and bottom struts, the system prevents the thermal expansion that would otherwise cause the exhaust bearing body to shift position.
2Device complexity
If the exhaust bearing body is allowed to move off-center due to thermal gradients, then cooling air flow is simplified, but turbine blade tip clearance becomes non-uniform causing tip rub during hot restarts
Solution Approach 1:
The cooling system targets specific struts based on their thermal environment. Top struts, which experience higher temperatures, receive cooling air through internal passages. Bottom struts are cooled through the rotor centering cooling system. This localized cooling approach maintains uniform blade tip clearance without requiring a completely complex distributed cooling system.
Solution Approach 2:
The patent replaces mechanical adjustment mechanisms with a thermal management approach. Instead of mechanically adjusting strut positions or bearing body location to maintain centering, the system uses controlled cooling air flow to thermally manage the struts and maintain geometric stability, thereby keeping the exhaust bearing body centered.
3Stability of the object's composition
If cooling channels are extended through the turbine casing exhaust flange to purge the shroud cavity, then thermal gradients are reduced and bearing centering is improved, but the device complexity increases
Solution Approach 1:
The rotor centering cooling system merges multiple functions into a single integrated cooling network. The cooling channels serve dual purposes: they cool the turbine casing exhaust flange structurally and simultaneously purge the shroud cavity by directing cooling air flow through it. This consolidation achieves bearing centering without adding separate purging systems.
Solution Approach 2:
The extended cooling channels perform multiple functions: they cool the turbine casing exhaust flange to reduce thermal gradients, purge the shroud cavity to remove hot gases and debris, and contribute to maintaining exhaust bearing body centering. This multi-functionality reduces the need for separate systems and minimizes overall device complexity.
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 system effectively reduces thermal gradients and prevents the exhaust bearing body from moving off-center, minimizing tip rub during hot restarts by ensuring uniform cooling and reducing clearance discrepancies between top and bottom turbine blade tips.
Implementation Method 1
The cooling fluid flowing through the rotor centering cooling channel entrains ambient air within the shroud cavity, thereby purging the shroud cavity and cooling the turbine casing exhaust flange
Implementation Method 2
the rotor centering cooling system may be positioned, in part, within struts in the exhaust diffuser downstream from a turbine assembly for limiting thermal gradients of a turbine case and between top and bottom struts
Data Source
AI summary
A gas turbine engine having a rotor centering cooling system for cooling struts within an exhaust diffuser and turbine case to reduce tip rub during hot restarts is disclosed. In particular, the rotor centering cooling system may be positioned within struts in the exhaust diffuser downstream from a turbine assembly for limiting thermal gradients between top and bottom struts to prevent the exhaust bearing body from becoming off-center during steady state operation as a result of the top struts becoming hotter than the bottom struts. The rotor centering cooling system may reduce the temperature at the exhaust diffuser and turbine case, thereby reducing the thermal gradient between the top and bottom struts and top and bottom of the turbine case. As such, the exhaust bearing body remains centered, thereby preventing a tighter blade tip clearance at the top of the turbine assembly than at the bottom of the assembly.