Method and apparatus for relieving stress in a combustion case in a gas turbine engine

A system for a gas turbine engine, comprising:

• a) a generally cylindrical or conical combustion case;
• b) a number, N, of primary apertures in the combustion case;
• and
• c) a number, T, of T-shaped slots distributed among the primary apertures, wherein T is not equal to N.

A system, comprising:

• a) a gas turbine engine which includes a combustion case;
• b) an annulus defined within the combustion case which
• i) contains apertures extending from an inner side to an outer side;
• ii) bosses surrounding individual apertures on the outer side;
• iii) no bosses surrounding individual apertures on the inner side;
• and
• iv) a T-shaped slot on the inner side between at least one pair of individual apertures.

A system, comprising:

• a) a gas turbine engine which includes a combustion case;
• b) an annulus defined within the combustion case which
• i) contains apertures extending from an inner side to an outer side;
• ii) bosses surrounding individual apertures on the outer side;
• and
• iii) no bosses surrounding individual apertures on the inner side,
• wherein multiple apertures are contained within a single boss on the inner side.

A system, comprising:

• a) a gas turbine engine which includes a combustion case;
• b) an annulus defined within the combustion case which
• i) contains apertures extending from an inner side to an outer side;
• ii) bosses surrounding individual apertures on the outer side;
• and
• iii) no bosses surrounding individual apertures on the inner side,
• wherein the inner side contains T-shaped slots, which do not fully penetrate the combustion case.

A method of constructing an annular combustion case, having inner and outer faces, for a gas turbine engine, comprising:

• a) constructing apertures in the case;
• b) on the outer face of the case, surrounding each aperture with a respective boss;
• and
• c) on the inner face of the case, surrounding multiple apertures with a single boss.

A method of constructing an annular combustion case, having inner and outer faces, for a gas turbine engine, comprising:

• a) constructing apertures in the case;
• b) on the outer face of the case, surrounding each aperture with a respective boss;
• c) maintaining the inner face of the case in a smooth cylindrical shape;
• and
• d) disrupting smoothness of the inner face by forming periodic T-shaped slots in the inner face.

A combustion case having inner and outer faces for a gas turbine engine, comprising:

• a) an annulus having radially facing holes extending therethrough;
• b) on the outer face of the annulus, individual bosses surrounding individual holes;
• c) on the inner face of the annulus, a plurality of bosses
• i) each of which surrounds two, or more, holes;
• and
• ii) adjacent pairs of which have edges which cooperate to define T-shaped depressions in the inner face.

A system, comprising:

• a) a gas turbine engine;
• and
• b) a combustion case which includes an annular body comprising
• i) an inner surface and an outer surface
• ii) primary apertures extending through the body, from the inner surface to the outer surface;
• iii) bosses on the outer surface surrounding primary apertures;
• iii) no bosses on the inner surface which surround individual primary apertures;
• and
• iv) a plurality of T-shaped slots penetrating the inner surface, but not extending through to the outer surface.

A system, comprising:

• a) a gas turbine engine;
• and
• b) an annular combustion case which includes
• i) an inner surface and an outer surface;
• ii) a plurality of T-slots on the inner surface, with adjacent T-slots being separated by a respective space;
• iii) in every space except a unique space, a single aperture extending from the inner surface to the outer surface;
• and
• iv) in the unique space, either no aperture, or more than one aperture.

A system, comprising:

• a) a gas turbine engine;
• and
• b) an annular combustion case which includes
• i) an inner surface and an outer surface;
• ii) N slots
• A) which are T-shaped,
• B) which are distributed along a circumferential band on the inner surface, and
• C) of which, every adjacent pair defines a space therebetween, thereby defining a total of N spaces;
• iii) in each space except the Nth space, a single aperture which extends from the inner surface to the outer surface;
• and
• iv) in the Nth space, a n umber of apertures other than one.