TECHNICAL FIELD

The present invention relates to a gas turbine combustor.

BACKGROUND ART

In recent years, more and more gas turbine combustors employ the premixed combustion method for reduction of NOx and other similar purposes. Such a gas turbine combustor, employing the premixed combustion method, includes a pilot burner that performs diffusion combustion in addition to main burners (premix burners) that perform premixed combustion. In this way, the main burners can use a diffusion flame generated by the pilot burner as a pilot to generate premixed flames. Thus, by using this diffusion flame to combust a premixed gas produced by the main burners, premixed combustion is possible.

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: Japanese Patent Application Publication No. 2014-92286

Patent Document 2: Japanese Patent Application Publication No. 2005-315457

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, around the exit of each main burner, the premixed gas flows along its inner peripheral surface. Thus, due to the development of a boundary layer, a spot with lower flow speed appears. At this spot with lower flow speed, a region with a high fuel concentration is sometimes formed from the premixed gas. If a low speed, high fuel concentration region is formed around the exit of the main burner as above, so-called flashback may possibly occur, in which a flame generated downstream of this region spreads to it.

For this reason, various gas turbine combustors that can suppress the occurrence of flashback have been studied (see Patent Documents 1 and 2). For example, as illustrated inFIG. 4, a gas turbine combustor100includes a plurality of swirler tubes131that are provided radially outward of a pilot cone121and impart a swirl to a premixed gas Fp, and an outer ring115that is disposed radially outward of the plurality of swirler tubes131with a gap141provided between the outer ring115and a combustor basket111. By injecting compressed intake air through the gap141, film-shaped air Af flows along the inner peripheral surface of a combustor transition piece (or exit outer ring)112. In this way, the gas turbine combustor100prevents (wall surface) flashback fb along the inner peripheral surface of the combustor transition piece112, which is a low flow speed region within the boundary layer.

However, in the above gas turbine combustor100, as illustrated inFIG. 5, a downstream end portion115aof the outer ring115forms a step. As the compressed air and the premixed gas Fp flow downstream along an outer peripheral surface115cand an inner peripheral surface115bof the outer ring115, the flow of the compressed air separates from the outer peripheral surface115cof the outer ring115and forms a stagnation S1, while the flow of the premixed gas Fp separates from the inner peripheral surface115bof the outer ring115and forms a stagnation, so that a low flow speed region is formed at this spot. Thus, there is a possibility that the region with the stagnations become a flame holding spot and flashback occurs there.

Given the above, the present invention has been made to solve a problem as described above and an object thereof is to provide a gas turbine combustor capable of suppressing the occurrence of flashback at a downstream end portion of its outer ring with a simple configuration.

Means for Solving the Problem

A gas turbine combustor according to a first aspect of the invention to solve the above problem includes:

a plurality of swirler tubes that are disposed inside a combustor basket and impart a swirl to a premixed gas, the premixed gas being obtained by premixing a fuel and air for combustion; and

an outer ring that is disposed between the plurality of swirler tubes and the combustor basket with a gap provided between the outer ring and the combustor basket, and generates film-shaped air inside a combustor transition piece connected to the combustor basket via injection through the gap into the combustor transition piece, and

at a downstream end of the outer ring, the outer ring includes a tapered surface formed such that the outer ring gradually decreases in thickness from an upstream side toward a downstream side.

A gas turbine combustor according to a second aspect of the invention to solve the above problem is the gas turbine combustor according to the first aspect of the invention, in which the tapered surface is formed on an inner peripheral surface side of the outer ring.

A gas turbine combustor according to a third aspect of the invention to solve the above problem is the gas turbine combustor according to the first aspect of the invention, in which the tapered surface is formed on both of an inner peripheral surface side and an outer peripheral surface side of the outer ring.

A gas turbine combustor according to a fourth aspect of the invention to solve the above problem is the gas turbine combustor according to the first aspect of the invention, in which the tapered surface is formed on an outer peripheral surface side of the outer ring.

A gas turbine combustor according to a fifth aspect of the invention to solve the above problem is the gas turbine combustor according to any one of the first to fourth aspects of the invention, in which the tapered surface has a shape of a curved line in a cross section thereof taken along a central axis of the outer ring.

A gas turbine combustor according to a sixth aspect of the invention to solve the above problem is the gas turbine combustor according to any one of the first to fourth aspects of the invention, in which the tapered surface has an angle of 30 degrees to 60 degrees with respect to a radial direction.

Effect of the Invention

According to the present invention, at the downstream end of the outer ring, the outer ring includes a tapered surface formed such that the outer ring gradually decreases in thickness from the upstream side toward the downstream side. In this way, a premixed gas or compressed air flows downstream smoothly along the inner peripheral surface or the outer peripheral surface of the outer ring. This prevents separation of the flow of the premixed gas or the compressed air at a downstream end portion of the outer ring, so that the stagnation region formed by separation of the gas flow is smaller. It is therefore possible to suppress the occurrence of flashback at the downstream end portion of the outer ring with a simple configuration.

