Combustor and method for improving combustor performance

A method for improving performance of a combustor, the combustor including a tubular body including a plurality of cooling flow paths formed inside a wall surface, extending in a flow direction of a combustion gas, and configured to allow cooling air to flow through the plurality of cooling flow paths, and a throttle ring having an annular shape, protruding radially inward from an inner circumferential side of the tubular body, including a throttle surface extending radially inward from the inner circumferential side of the tubular body, and extending in a circumferential direction on the inner circumferential side of the tubular body, the method comprising the steps of:

• forming a pair of cavities in an outer circumferential surface of the tubular body, the pair of cavities being spaced apart in the flow direction, being recessed radially inward from the outer circumferential surface, and extending in the circumferential direction across the plurality of cooling flow paths;
• forming, by dividing the tubular body along the pair of cavities into three in the flow direction, an upstream side divided body, an intermediate divided body, and a downstream side divided body;
• attaching the throttle ring to an inner circumferential side of the intermediate divided body;
• joining each of the upstream side divided body and the downstream side divided body to the intermediate divided body to which the throttle ring is attached;
• and
• attaching lids configured to cover the pair of cavities.