This invention was made with government support under Contract No.: N00019-02-C-3003 with the United States Navy. The government therefore has certain rights in this invention.
The present invention relates to gas turbine engines having a cooling liner, and more particularly to an attachment hanger system for a circumferential cooling liner within a swivelable exhaust duct.
In order to improve engine operation and performance, the usage of exhaust duct cooling air is carefully rationed. Since the cooling air is generally extracted from the engine and is then not utilized for producing thrust, this extracted cooling air is a penalty to the overall performance of the engine. In current gas turbine engine exhaust ducts, a liner is disposed between the engine's working medium (exhaust gas path) and the engine outer casing or duct. Cooling air typically extracted from the engine's compressor is flowed between the cooling liner and duct then discharged over the seals and flaps of the nozzle located at the rear end of the exhaust duct.
A relatively significant quantity of cooling air is required to properly cool the generally annular area to maintain a positive pressure within the cooling liner while being subjected to large core pressure gradients at various operating conditions. The cooling airflow is typically based at an airflow required for the most adverse pressure gradient during the most adverse operating condition. Furthermore, recent aircraft include exhaust ducts which can vector through relative swiveling between exhaust duct segments which are interconnected through bearing arrangements may further complicate cooling liner arrangements.
To accommodate the multiple duct segments and intermediate bearing systems, a multitude of individual cooling liner segments are assembled within the duct to permit passage and assembly through the upstream bearing obstructions. Although effective, each liner segment needs to be individually fastened to the duct case and each liner segment needs to be sealed to the adjoining liner segment. This may result in a weight and manufacturing penalty for redundant parts, loss of sealing efficiency and a significant number of non-desirable joints between each individual liner segment.
Accordingly, it is desirable to provide a cooling liner assembly for a swivelable exhaust duct which minimizes the number of cooling liner segment joints to increase sealing efficiency while reducing weight, maintenance requirements, and assembly complications.