This invention relates to combustors for gas turbine engines and, more particularly, to double wall gas turbine combustors.
Gas turbine engine combustors are generally subject to high thermal loads for prolonged periods of time. To alleviate the accompanying thermal stresses, it is known to cool the walls of the combustor. Cooling helps to increase the usable life of the combustor components and therefore increase the reliability of the overall engine.
In one cooling embodiment, a combustor may include a plurality of overlapping wall segments successively arranged where the forward edge of each wall segment is positioned to catch cooling air passing by the outside of the combustor. The forward edge diverts cooling air over the internal side, or xe2x80x9chot sidexe2x80x9d, of the wall segment and thereby provides film cooling for the internal side of the segment. A disadvantage of this cooling arrangement is that the necessary hardware includes a multiplicity of parts. A person of skill in the art will recognize that there is considerable value in minimizing the number of parts within a gas turbine engine, not only from a cost perspective, but also for safety and reliability reasons. Specifically, internal components such as turbines and compressors can be susceptible to damage from foreign objects carried within the air flow through the engine.
A further disadvantage of the above described cooling arrangement is the overall weight which accompanies the multiplicity of parts. A person of skill in the art will recognize that weight is a critical design parameter of every component in a gas turbine engine, and that there is considerable advantage to minimizing weight wherever possible.
In other cooling arrangements, a twin wall configuration has been adopted where an inner wall and an outer wall are provided separated by a specific distance. Cooling air passes through holes in the outer wall and then again through holes in the inner wall, and finally into the combustion chamber. An advantage of a twin wall arrangement compared to an overlapping wall segment arrangement is that an assembled twin wall arrangement is structurally stronger. A disadvantage to the twin wall arrangement, however, is that thermal growth must be accounted for closely. Specifically, the thermal load in a combustor tends to be non-uniform. As a result, different parts of the combustor will experience different amounts of thermal growth, stress, and strain. If the combustor design does not account for non-uniform thermal growth, stress, and strain, then the usable life of the combustor may be negatively affected.
U.S. Pat. No. 5,758,503, assigned to the assignee of the instant application, discloses an improved combustor for gas turbine engines. The advantage of the combustor of the ""503 patent is its ability to accommodate a non-uniform heat load. The liner segment and support shell construction of the present invention permits thermal growth commensurate with whatever thermal load is present in a particular area of the combustor. Clearances between segments permit the thermal growth without the binding that contributes to mechanical stress and strain.
The support shell and liner construction minimizes thermal gradients across the support shell and/or liner segments, and therefore thermal stress and strain within the combustor. The support shell and liner segment construction also minimizes the volume of cooling airflow required to cool the combustor. A person of skill in the art will recognize that it is a distinct advantage to minimize the amount of cooling airflow devoted to cooling purposes. Improved heat transfer at minimal change in liner-shell pressure drop is beneficial. At fixed combustor aerodynamic efficiency, the foregoing translates to reduced coolant requirements.
It would be highly advantageous to improve the heat transfer efficiency of a gas turbine engine combustor while not adversely effecting the pressure drop across the combustor or cooling flow requirement.
It is a further object of the present invention to provide a combustor as above wherein improved heat transfer is achieved with negligible increase in pressure drop.
It is an object of the present invention to provide a lightweight combustor for a gas turbine engine having improved heat transfer efficiency.
According to the present invention the foregoing objects are achieved by providing a combustor for a gas turbine engine is provided which includes a plurality of liner segments and a support shell. The support shell includes an interior and an exterior surface, a plurality of mounting holes, and a plurality of impingement coolant holes extending through the support shell. Each liner segment includes a panel and a plurality of mounting studs. The panel includes a face surface and a back surface, and a plurality of coolant holes extending therethrough. The back surface of the panel has a surface profile for improving the heat transfer properties of a liner segment without substantial increase in pressure drop across the twin walls formed by the liner segment and support shell of the combustor.
Further features and advantages of the present invention will become apparent in light of the detailed description of the best mode embodiment thereof, as illustrated in the accompanying drawings.