Gas turbine combustor

1. A gas turbine combustor comprising:

a pilot burner;

a plurality of main burners disposed around said pilot burner; and

a basal plate for supporting said pilot burner and said main burners,

wherein each of said main burners includes an extension tube provided at a downstream end thereof,

wherein an outlet of said extension tube is formed so as to have two radial edges extending in a radial direction, and circumferential edges connecting said radial edges,

wherein said extension tubes are located downstream of said basal plate, wherein and said basal plate is provided with openings for allowing sweep air to flow therethrough toward downstream, and

wherein an opening ratio of said openings in regions between said extension tubes is set larger than an opening ratio of said openings in other regions by setting a diameter of said openings in the regions between said extension tubes larger than that of said openings in the other regions or by forming a larger number of said openings in the regions between adjacent radial edges of each of said extension tubes as compared to a number of said openings formed in the other regions of said basal plate.

2. The gas turbine combustor according to claim 1 , wherein said outlet of said extension tube is shaped so that corner portions at which said radial edges are connected with said circumferential edges are rounded.

3. The gas turbine combustor according to claim 1 , wherein an opening ratio of said openings in the regions between said extension tubes and the openings on the inner side of said extension tubes with respect to the radial direction of the gas turbine combustor is set larger than the opening ratio of said openings in other regions of said basal plate.

4. The gas turbine combustor according to claim 1 , wherein each of said main burners further includes:

a main swirler for swirling premix gas and feeding the premix gas to said extension tube;

wherein said openings are formed so that said sweep air is swirled in the same direction as a swirl direction of said premix gas.

5. The gas turbine combustor according to claim 1 , wherein each of said main burners further includes:

a burner outer liner which accommodates a nozzle for injecting fuel to air and a swirler for swirling premix gas containing said fuel and said air; and

a plurality of spacers provided outside of said burner outer liner between said burner outer liner and said extension tube, and separated from each other,

wherein said extension tube is inserted onto a downstream end of said burner outer liner so as to be located outside of said burner outer liner, and

wherein said spacers are tapered down toward downstream.

6. The gas turbine combustor according to claim 1 , wherein each of said main burners further includes:

a burner outer liner which accommodates a nozzle for injecting fuel to air and a swirler for swirling premix gas containing said fuel and said air; and

a spacer provided outside of said burner outer liner between said burner outer liner and said extension tube,

wherein said extension tube is inserted onto a downstream end of said burner outer liner so as to be located outside of said burner outer liner, and

wherein said spacer has an opening which is gradually enlarged toward downstream.

7. The gas turbine combustor according to claim 6 , wherein said spacer is shaped into a ring, and connected to an outer side of said burner outer liner so as to surround said burner outer liner.

8. The gas turbine combustor according to claim 1 , wherein each of said main burners further includes:

a burner outer liner which accommodates a nozzle for injecting fuel to air and a swirler for swirling premix gas containing said fuel and said air; and

a spacer provided outside of said burner outer liner between said burner outer liner and said extension tube,

wherein said extension tube is inserted onto a downstream end of said burner outer liner so as to be located outside of said burner outer liner, and

wherein said spacer is formed of a porous body.

9. The gas turbine combustor according to claim 8 , wherein said spacer is shaped into a ring, and connected to an outer side of said burner outer liner so as to surround said burner outer liner.

10. The gas turbine combustor according to claim 1 , wherein each of said main burners further includes:

a burner outer liner which accommodates a nozzle for injecting fuel to air and a swirler for swirling flow containing said fuel and said air to generate premix gas,

wherein said burner outer liner comprises:

an outer liner body; and

a front end portion which is provided at a downstream end of said outer liner body, and is smaller than said outer liner body in diameter

wherein said extension tube is inserted onto said burner outer liner so as to contact against said outer liner body and to be opposed to said front end portion at a position downstream of said outer liner body, and has an opening at a position opposed to said front end portion.

11. The gas turbine combustor according to claim 10 , wherein said opening is located so as to satisfy the following equation:

L/g> 2,

which is represented by a radial width g of a gap between said front end portion and said extension tube and a distance L between a downstream end of said opening and a downstream end of said front end portion along said extension tube.

12. The gas turbine combustor according to claim 10 , wherein said burner further includes a guide which is provided outside of said extension tube to guide air into said opening.

13. The gas turbine combustor according to claim 12 , wherein said guide comprises:

a connecting portion connected to said extension tube at a position downstream of said opening; and

an opposed portion which extends upstream from said connecting portion and is located as opposed to said opening.

14. The gas turbine combustor according to claim 1 , wherein:

said opening ratio of said openings in the regions between said adjacent extension tubes is set larger than said opening ratio of said openings in the other regions by setting a density of said openings in the regions between said adjacent extension tubes larger than a density of said openings in the other regions of said basal plate.