Gas Turbine Compressor Transition Duct for Rotor Stress Reduction
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Solution Overview
Problem
The aft rotor stages of gas turbine engine compressor sections face high rotational and thermal stresses due to elevated temperatures, necessitating cooling that reduces engine efficiency by bleeding off compressor air.
Innovation Solution
A compressor section design featuring a transition duct with a radially inwardly spaced outlet, reducing rotor blade tip speed and stress in downstream stages, and a bearing system radially inward from the transition duct to support the spool, potentially reducing cooling needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling air is bled off to cool the aft rotor stages, then the ability to withstand elevated temperatures is improved, but the engine efficiency deteriorates
Solution Approach 1:
The invention extracts the bearing system from the traditional location within the rotor assembly and relocates it to the transition duct. This separation allows the bearing to be cooled independently without requiring cooling air to be bled from the compressor stages, thus maintaining engine efficiency while still protecting the aft rotor stages from thermal stress
Solution Approach 2:
The transition duct serves as an intermediary structure that houses the bearing system away from the hot compressor airflow. By positioning the bearing in this intermediate zone with access to cooler air, the system can withstand thermal loads without compromising the main compressor airflow and engine efficiency
2Strength
If the transition duct outlet is spaced radially inward, then the rotor blade tip speed and stress are reduced, but the structural complexity increases
Solution Approach 1:
The transition duct is designed to perform multiple functions: it serves as the structural connection between upstream and downstream compressor sections, houses the relocated bearing system, and creates the optimized airflow path with the radially inward outlet. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in structural complexity while achieving reduced blade stress
3Loss of energy
If the bearing system is located radially inward from the transition duct, then the cooling requirements are reduced, but the space for rotor support is constrained
Solution Approach 1:
The bearing system is positioned in the axial dimension within the transition duct rather than in the radial dimension of the rotor assembly. This dimensional relocation provides adequate space for rotor support while placing the bearing in a region with lower thermal loads, thereby reducing cooling air requirements without compromising rotor support capability
Data Source
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Figure 2
AI summary
A compressor section (52) for a gas turbine engine comprises an upstream portion (82) that includes at least one upstream rotor stage (60) und a downstream portion (84) that includes at least one downstream rotor stage (60) configured to rotate with the upstream rotor stage (60). A transition duct (88) separates the upstream portion (82) from the downstream portion (84). A method of operating a compressor section in a gas turbine engine (20) comprises the steps of: rotating at least one upstream rotor stage (60) of the compressor section (52) at the same rotational speed as at least one downstream rotor stage (60) of the compressor section (52); and reducing a tip speed of the at least one downstream rotor stage (60) relative to a tip speed of the at least one upstream rotor stage (60) by locating a transition duct (88) axially between the at least one upstream rotor stage (60) and the at least one downstream rotor stage (80).