An axial swirler, in particular for premixing of oxidizer and fuel in gas turbines, includes a series of swirl vanes with a streamline cross-section. Each swirl vane has a leading edge, a trailing edge, and a suction side and a pressure side extending each between the leading and trailing edges. The swirl vanes are arranged around a swirler axis, wherein the leading edges extend essentially in radial direction. Flow slots are formed between the suction side of each swirl vane and the pressure side of its nearest neighboring swirl vane. Furthermore, at least one swirl vane has a discharge flow angle between a tangent to its camber line at its trailing edge and the swirler axis that is monotonically increasing with increasing radial distance from the swirler axis. The invention also relates to a burner with such a swirler and a method of operating the burner.
1. An axial swirler for premixing of oxidizer and fuel in gas turbines, the axial swirler comprising:
a series of swirl vanes with a streamline cross-section, each swirl vane having a leading edge, a trailing edge, and a suction side and a pressure side extending each between said leading and trailing edges, the swirl vanes being arranged around a swirler axis, wherein said leading edges extend radially outwardly from said axis, wherein flow slots are formed between the suction side of each swirl vane and the pressure side of its circumferentially adjacent swirl vane, wherein at least one swirl vane has a discharge flow angle (α) between a tangent to its camber line at its trailing edge and the swirler axis that is monotonically increasing with increasing radial distance (R) from the swirler axis, and wherein the trailing edge of each of the swirl vanes is rotated with respect to the leading edge; and
wherein a discharge flow angle (α) on said radial distance (R) is given by a function:
tan [α( R )]= K·R β +H,
wherein β is ranging from 1 to 10, and K and H are constants chosen such that the discharge flow angle (α(R min )) at a minimum radial distance (R min ) is from 0 degrees to 20 degrees and the discharge flow angle (α(R max )) at a maximum radial distance (R max ) is from 30 degrees to 50 degrees.
2. The axial swirler according to claim 1 , wherein the leading edge of each of the swirl vanes is an essentially straight edge extending in a radial direction and/or the camber line of the swirl vane is curved to form a C-shape or an S-shape.
3. The axial swirler according to claim 1 , wherein the trailing edge of each of the swirl vanes is rotated with respect to the leading edge, such that the trailing edge extends with increasing radial distance (R) increasingly in the direction in that the pressure side of the swirl vane faces.
4. The axial swirler according to claim 1 , wherein the leading edge and/or the trailing edge of each of the swirl vanes extend radially outwardly from the swirler axis in a plane perpendicular to the swirler axis.
5. The axial swirler according to claim 1 , wherein all the vanes of the series of swirl vanes are identically formed and/or in that the swirl vanes are arranged around the swirler axis in a circle.
6. A burner for a combustion chamber of a gas turbine comprising:
an axial swirler comprising:
a series of swirl vanes with a streamline cross-section, each swirl vane having a leading edge, a trailing edge, and a suction side and a pressure side extending each between said leading and trailing edges, the swirl vanes being arranged around a swirler axis, wherein said leading edges extend radially outwardly from said axis, wherein flow slots are formed between the suction side of each swirl vane and the pressure side of its circumferentially adjacent swirl vane, wherein at least one swirl vane has a discharge flow angle (α) between a tangent to its camber line at its trailing edge and the swirler axis that is monotonically increasing with increasing radial distance (R) from the swirler axis, and wherein the trailing edge of each of the swirl vanes is rotated with respect to the leading edge; and
wherein a discharge flow angle (α) on said radial distance (R) is given by a function:
tan [α( R )]= K·R β +H,
wherein β is ranging from 1 to 10, and K and H are constants chosen such that the discharge flow angle (α(R min )) at a minimum radial distance (R min ) is from 0 degrees to 20 degrees and the discharge flow angle (α(R max )) at a maximum radial distance (R max ) is from 30 degrees to 50 degrees; and
wherein at least one of the swirl vanes is configured as an injection device with at least one fuel nozzle for introducing at least one fuel into the burner.
7. The burner according to claim 6 , wherein fuel is injected on the suction side and/or the pressure side of at least one swirl vane.
8. The burner according to claim 6 , wherein each flow slot has a gas entrance region that extends downstream from the leading edges and a gas discharge region that extends upstream from the trailing edges of its defining swirl vanes, wherein the fuel is injected into the flow slot in the gas entrance region, in the upstream third of the swirl vane and/or in a cross-flow injection.
9. The burner according to claim 6 , wherein the fuel is injected by a series of fuel nozzles being preferably arranged one adjacent another in a radial direction.
10. The burner according to claim 6 , wherein cooling air is introduced through the axial swirler so as to avoid flashback, wherein at least one swirl vane is provided with cooling elements, wherein the cooling elements are given by internal circulation of cooling medium along sidewalls of the swirl vane and/or by film cooling holes, located near the trailing edge, and wherein the cooling elements are fed with air from a carrier gas feed also used for the fuel injection.
11. A method for operating a burner for a combustion chamber of a gas turbine, the burner comprising an axial swirler, the axial swirler comprises a series of swirl vanes with a streamline cross-section, each swirl vane having a leading edge, a trailing edge, and a suction side and a pressure side extending each between said leading and trailing edges, the swirl vanes being arranged around a swirler axis, wherein said leading edges extend radially outwardly from said axis, wherein flow slots are formed between the suction side of each swirl vane and the pressure side of its circumferentially adjacent swirl vane, wherein at least one swirl vane has a discharge flow angle (α) between a tangent to its camber line at its trailing edge and the swirler axis that is monotonically increasing with increasing radial distance (R) from the swirler axis, and wherein the trailing edge of each of the swirl vanes is rotated with respect to the leading edge; and
wherein a discharge flow angle (α) on said radial distance (R) is given by a function:
tan [α( R )]= K·R β +H,
wherein β is ranging from 1 to 10, and K and H are constants chosen such that the discharge flow angle (α(R min )) at a minimum radial distance (R min ) is from 0 degrees to 20 degrees and the discharge flow angle (α(R max )) at a maximum radial distance (R max ) is from 30 degrees to 50 degrees, the method comprising:
introducing air through the axial swirler and determining a number of fuel nozzles through which fuel is injected as a function of a total injected fuel flow; and
injecting fuel into the number of the fuel nozzles determined as the function of the total injected fuel flow.
12. The method according to claim 11 , comprising:
staging the fuel injection below a threshold fuel flow such that the fuel is injected only on the suction side or the pressure side and/or only through every second or third fuel nozzle of a swirl vane and/or that fuel is only injected through the fuel nozzles of every second or third swirl vane of the burner.
13. The method according to claim 11 , wherein the fuel is a highly reactive fuel.
14. The axial swirler according to claim 1 , wherein the axial swirler is in an annular combustor, can combustors, or a single or reheat engine.
15. The axial swirler according to claim 1 , wherein β is from 3 to 8.
16. The axial swirler according to claim 1 wherein β is 7.
17. The burner according to claim 6 , wherein the fuel nozzles are circular.
18. The burner according to claim 6 , wherein the fuel nozzles are elongated slot nozzles extending essentially parallel to the leading edge of the swirl vane.
19. The burner according to claim 6 , wherein the fuel nozzles comprise a first nozzle for injection of liquid fuel, and/or a second nozzle for injection of a gaseous fuel and a third nozzle for injection of carrier air, which encloses the first nozzle and/or the second nozzle.
20. The method according to claim 13 , wherein the highly reactive fuel consists of natural gas fuels, hydrogen rich fuels, and hydrogen fuel.