Cooled Dual Wall Liner Closeout for Thermal Expansion
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Solution Overview
Problem
The challenge in gas turbine engines is to accommodate differing thermal expansions and maintain effective cooling at the interfaces between movable segments of exhaust nozzles and ducts, where the hot and cold side liners expand and contract differently, causing stress and complicating the sealing and cooling of the air passage.
Innovation Solution
A dual wall exhaust liner assembly with a closeout member that includes a rotatable front, intermediate, and rear liner assembly, featuring a Z-shaped and C-shaped closeout member to accommodate thermal expansion and provide cooling airflow between movable segments, with the closeout member being riveted or welded to the outer liner and brazed to the inner liner, allowing for relative movement and maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air passage is closed off at the interface between movable segments, then combustion gases are contained within the exhaust nozzle, but cooling airflow to the hot side liner is compromised and the interface becomes complex to seal
Solution Approach 1:
The closeout member includes a flexible membrane that can deform to maintain sealing between the hot and cold side liners at the movable segment interface. This membrane allows relative movement between segments while preventing combustion gas leakage, eliminating the need for complex rigid sealing mechanisms.
Solution Approach 2:
The exhaust nozzle is divided into multiple movable segments with interfaces between them. Each interface includes its own closeout member with membrane, allowing independent movement of segments while maintaining sealing. This segmentation enables articulation while preserving cooling airflow paths.
2Duration of action of stationary object
If the hot side liner is protected from heat, then the liner durability is improved, but thermal expansion differences between hot and cold side liners generate stresses and strains
Solution Approach 1:
The flexible membrane in the closeout member accommodates differential thermal expansion between the hot and cold side liners by deforming as the liners expand and contract at different rates. This flexibility prevents the generation of excessive thermal stresses and strains that would occur with rigid connections.
Solution Approach 2:
The closeout member's membrane changes its physical state from a rigid barrier to a flexible accommodation element under thermal loading. The membrane's ability to deform allows the system to adapt to changing thermal parameters without generating damaging stresses.
3Strength
If a rigid closeout member is used at the movable segment interface, then structural integrity is maintained, but thermal expansion accommodation and cooling airflow are compromised
Solution Approach 1:
The flexible membrane maintains structural integrity by forming a continuous barrier that prevents combustion gas leakage, while simultaneously accommodating thermal expansion through elastic deformation. The membrane's flexibility allows it to adapt to dimensional changes in the liners without compromising its sealing function.
Solution Approach 2:
The closeout member transitions from a static rigid structure to a dynamic flexible membrane that can adapt its shape and position in response to thermal expansion and segment movement. This dynamic behavior allows the structure to maintain integrity while accommodating dimensional changes.
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 solution effectively accommodates thermal expansions and ensures continuous cooling airflow at the interfaces between movable segments, preventing combustion gas leakage and maintaining the structural relationship between the inner and outer liners, thus enhancing the durability and efficiency of the exhaust nozzle and duct assembly.
Implementation Method 1
The cooling air forms an insulating layer along the interior surface of the exhaust nozzle that protects the hot side liner
Implementation Method 2
The cold side liner and hot side liner expand and contract differently in response to thermal conditions
Data Source
AI summary
An example exhaust duct assembly includes a front liner, an intermediate liner and a rear liner. Each of the front, intermediate and rear liners include an inner liner exposed to combustion gases and an outer liner spaced radially apart from the inner liner. An air passage defined between the inner liner and the outer liner provides cooling air utilized for insulating an inner surface of the exhaust duct assembly. A closeout member is provided between the inner and outer liner and defines a portion of an air passage between the closeout member and the inner liner. Air flowing through the air passage is injected into a joint to provide cooling. The closeout member includes a horizontal leg that is bendable in a radial direction to accommodate relative movement between the inner liner and the outer liner.