Intercooling Turbine Section for Variable Cycle Gas Turbine Efficiency
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Solution Overview
Problem
Variable cycle gas turbine engines face challenges in achieving high specific thrust and low fuel consumption across a range of operating conditions, particularly in optimizing thermodynamic efficiency for cruise and loiter conditions while maintaining performance for high energy maneuvers.
Innovation Solution
The implementation of a two-spool bypass turbofan engine with an intercooling turbine section that selectively expands airflow to reduce inlet temperatures to the low-pressure compressor, utilizing a multistage fan and variable vanes to modulate the intercooling effect, thereby optimizing the bypass ratio and thermodynamic cycle efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a variable cycle engine alters bypass ratio during flight to achieve high specific thrust and low fuel consumption, then performance across different operating conditions is improved, but device complexity increases due to additional control mechanisms and variable geometry components
Solution Approach 1:
The engine employs variable bypass ratio capability through movable fan blades and adjustable guide vanes that can change the flow distribution between core and bypass streams dynamically during flight, enabling optimization of fuel consumption across different operating conditions without requiring complete structural redesign
Solution Approach 2:
The engine cycle parameters including bypass ratio, compressor inlet temperature, and turbine expansion ratio are varied during operation to match different flight conditions, with the intercooling turbine section enabling independent control of compression and expansion parameters to achieve optimal efficiency at each phase
2Loss of energy
If an intercooling turbine section is added to reduce inlet temperatures to the low-pressure compressor, then thermodynamic efficiency is improved, but device complexity increases due to additional turbine stages and airflow path modifications
Solution Approach 1:
The turbine section is divided into high-pressure and low-pressure turbine stages with an intercooling section in between, allowing independent optimization of each stage's expansion ratio and temperature drop, which improves overall thermodynamic efficiency by recovering more work from the exhaust gases
Solution Approach 2:
The intercooling turbine section acts as an intermediary between the high-pressure and low-pressure compressors, extracting energy from the compressed air to drive the low-pressure spool and reducing the temperature before re-compression, thereby improving the density and efficiency of the intake air
3Productivity
If pressure ratio and temperature ratio in the high-pressure compressor section are increased to improve overall engine efficiency, then thrust-to-fuel ratio is improved, but the inlet temperature to the compressor becomes excessively high requiring additional cooling
Solution Approach 1:
The intercooling turbine section performs preliminary cooling of the compressed air before it enters the low-pressure compressor by expanding it through the turbine blades, reducing the temperature and increasing the density of the air that will be re-compressed in the low-pressure stage
Solution Approach 2:
The compressed air undergoes an expansion phase through the intercooling turbine that temporarily reduces its temperature and pressure before being re-compressed, creating a thermal cycle that improves overall efficiency by utilizing the temperature differential
Data Source
Figure 1
Figure 2~3
AI summary
A gas turbine engine (20) includes an intercooling turbine section (24) along an engine axis (X) aft of a fan section (22) and forward of a combustor section (30).