Negative Thermal Expansion Compressor Case Tip Clearance Control
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Solution Overview
Problem
The existing gas turbine engines face inefficiencies due to increasing tip clearance between compressor blades and the casing as the engine heats up, leading to over-tip leakage and higher specific fuel consumption, as the casing expands more slowly than the blades and disc, resulting in reduced compressor efficiency over time.
Innovation Solution
Incorporating a negative thermal expansion material in the compressor case that contracts when heated, allowing for active control of tip clearance through air flow management, using a collection and distribution manifold system with a valve and controller to adjust the temperature of the material and thus the case dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the tip clearance is set small when the engine is cold to improve compressor efficiency, then the compressor efficiency is improved, but the blades will rub against the casing when the engine heats up due to thermal expansion
Solution Approach 1:
The patent applies parameter changes by using a material with negative thermal expansion coefficient for the compressor casing. This causes the casing to contract radially when heated, maintaining a consistent tip clearance between the blades and casing across different temperature conditions, thereby resolving the contradiction between cold-start efficiency and hot-operation reliability
Solution Approach 2:
The patent directly applies thermal expansion principles by selecting a material with negative thermal expansion properties. As the engine operates and temperature increases, the negative thermal expansion material contracts instead of expanding, compensating for the thermal expansion of the blades and disc, and maintaining optimal tip clearance to prevent blade rubbing while preserving compressor efficiency
2Reliability
If the tip clearance is set large when the engine is cold to prevent blade rubbing, then blade rubbing is prevented, but the compressor efficiency decreases due to over-tip leakage
Solution Approach 1:
The patent changes the thermal expansion parameter of the casing material to negative values. This ensures that as the engine heats up, the casing contracts to maintain optimal tip clearance, preventing both the excessive clearance (which causes over-tip leakage) and the negative clearance (which causes blade rubbing), thereby maintaining compressor efficiency while ensuring reliability
Solution Approach 2:
By utilizing materials with negative thermal expansion properties, the patent creates a system where the casing dimension changes in the opposite direction to the blades and disc during thermal cycling. This compensates for the thermal growth of rotating components, maintaining a consistent tip clearance that prevents over-tip leakage and maintains compressor efficiency across all operating temperatures
3Strength
If conventional materials with positive thermal expansion are used for the compressor casing, then the casing is structurally sound, but the tip clearance increases over time as the casing expands with heat
Solution Approach 1:
The patent employs composite materials or materials with negative thermal expansion properties for the compressor casing. These materials maintain the structural integrity required for casing strength while providing the unique property of contracting when heated, thereby stabilizing the tip clearance and preventing the increase in clearance that occurs with conventional positive thermal expansion materials
Solution Approach 2:
The patent applies thermal expansion principles by selecting materials with negative thermal expansion coefficients. This causes the casing to contract radially when heated, counteracting the thermal expansion of the blades and disc, and maintaining stable tip clearance throughout the engine's thermal cycle, thus resolving the contradiction between structural integrity and clearance stability
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
This solution maintains optimal tip clearance, enhancing compressor efficiency, reducing fuel consumption, and extending the life of high-pressure compressor components by actively controlling the thermal expansion of the compressor case.
Implementation Method 1
an inner case (62) comprising a negative coefficient of thermal expansion material; the tip clearance (74) located between the inner case (62) and the blade tip (75); wherein the collection manifold (78) and the distribution manifold (80) are configured to direct air to the negative coefficient of thermal expansion material and change the tip clearance
Implementation Method 2
the collection manifold (78) and the distribution manifold (80) are configured to direct air to the negative coefficient of thermal expansion material and change the tip clearance
Data Source
Figure 1
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Figure 5
AI summary
A compressor (61) with negative coefficient of thermal expansion case material (50) comprising a rotor having blades with tips (76), the case including an inner case (62) comprising a negative coefficient of thermal expansion material (50), and a tip clearance (74) located between the tips (76) and the inner case (62); wherein the tip clearance (74) is maintained responsive to a flow of air (70) over the negative coefficient of thermal expansion material (50).