Variable Area Turbine Section for Three-Spool Gas Engine
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Solution Overview
Problem
Turboprop and turbofan engines face challenges in balancing the relative contributions of turboprop and turbofan operations, particularly at higher speeds, due to noise issues and the need for precise control of working fluid flow and spool loading, which existing designs struggle to address effectively.
Innovation Solution
A three-spool gas turbine engine with a variable area turbine section positioned between the intermediate and low-pressure turbines, allowing for control of rotational speeds and thrust output by adjusting the expansion ratio, combined with a reduction gearbox and adjustable pitch mechanism to optimize power distribution between the fan and propeller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a turboprop engine operates at higher speeds, then thrust output increases, but noise levels increase and shock wave formation occurs
Solution Approach 1:
The engine is divided into three independent spools (high, intermediate, low pressure), each capable of operating semi-independently. This segmentation allows the propeller spool to be controlled separately from the fan spool, enabling optimization of propeller speed to reduce noise and shock waves while maintaining overall thrust output through coordinated fan operation.
Solution Approach 2:
The engine incorporates variable geometry components including variable inlet guide vanes and variable pitch propeller blades. These dynamic elements allow real-time adjustment of airflow angles and blade pitch to optimize performance across different flight conditions, reducing noise and shock wave formation at higher speeds while maintaining thrust.
2Power
If a turboprop engine operates at higher speeds, then thrust output increases, but shock wave formation and loss effects increase
Solution Approach 1:
Variable pitch propeller blades allow dynamic adjustment of blade angle to maintain optimal aerodynamic efficiency at different forward speeds. This prevents excessive shock wave formation and associated energy losses that would occur with fixed-pitch propellers operating at high speeds.
Solution Approach 2:
The engine changes operating parameters including propeller rotational speed, blade pitch angle, and inlet guide vane positioning to optimize the balance between thrust generation and energy loss prevention across the flight envelope.
3Measurement precision
If a three-spool engine configuration is used, then control precision of spool loading improves, but device complexity increases
Solution Approach 1:
The three-spool configuration segments the engine into independent rotational systems (high, intermediate, low pressure spools), each with its own turbine-compressor pairing. This allows independent control of each spool's loading and speed, providing precise control over power distribution to the fan and propeller, though it increases mechanical complexity.
Solution Approach 2:
The intermediate pressure spool acts as an intermediary between the high-pressure core and low-pressure propeller system. It provides an additional degree of freedom for controlling power split and spool loading, enabling more precise management of the complex three-spool system through the variable inlet guide vane and other control mechanisms.
Data Source
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AI summary
A gas turbine engine (10) comprises a high spool (46), a low spool (30) and an intermediate spool (38). The high spool comprises a high pressure turbine coupled to a high pressure compressor. The intermediate spool comprises an intermediate pressure turbine (34) coupled to a ducted fan (16). The low spool comprises a low pressure turbine (24) coupled to an open-rotor propeller (12). A variable area turbine section (50) positioned between the intermediate pressure turbine and the low pressure turbine variable turbine section is configured to vary an expansion ratio across the intermediate pressure turbine to control rotational speeds of the low spool and the intermediate spool.