A reheat burner includes a channel with a lance projecting thereinto to inject a fuel over an injection plane perpendicular to a channel longitudinal axis. The channel and lance define a vortex generation zone upstream of the injection plane and a mixing zone downstream of the injection plane in the hot gas direction. The mixing zone has a cross section with diverging side walls in the hot gas direction. The diverging side walls define curved surfaces in the hot gas direction having a constant radius.
1. A reheat apparatus comprising:
a reheat burner comprising:
a channel with an entry for a gas flow which flows in a downstream direction; and
a lance projecting into the channel and configured to inject a fuel over an injection plane perpendicular to a channel longitudinal axis,
wherein the channel and the lance define a vortex generation zone upstream of the injection plane and a mixing zone downstream of the injection plane, the vortex generation zone having a converging portion in the downstream direction with vortex generators extending radially inward from the channel,
the mixing zone comprising:
a diverging portion with diverging sidewalls, wherein throughout the diverging portion, a minimum distance of the diverging side walls from the channel longitudinal axis increases in the downstream direction;
wherein throughout the diverging portion, a concave surface of each diverging sidewall has a constant radius of curvature in the downstream direction.
2. The reheat apparatus as claimed in claim 1 , wherein ends of the diverging side walls define with the channel longitudinal axis an angle larger than 8 degrees.
3. The reheat apparatus as claimed in claim 1 , wherein the channel has a mixing zone terminal portion with plane diverging side walls downstream of the diverging side walls.
4. The reheat apparatus as claimed in claim 3 , wherein the plane diverging side walls are flush with the diverging side walls.
5. The reheat apparatus as claimed in claim 4 , wherein the plane diverging side walls define with the channel longitudinal axis an angle larger than 8 degrees.
6. The reheat apparatus as claimed in claim 1 , wherein a width and a height of the vortex generation zone increase toward the injection plane in the 1 R-et downstream direction and then decreases.
7. The reheat apparatus as claimed in claim 1 , wherein at least those side walls of the mixing zone between the diverging side walls define a constant mixing zone height.
8. The reheat apparatus as claimed in claim 1 , wherein a ratio between a width w at mid-height and a height h of a channel cross-section at the injection plane is equal to 1.
9. The reheat apparatus as claimed in claim 8 , wherein downstream of the injection plane, a mixing zone cross-section decreases and then increases defining a throat.
10. The reheat apparatus as claimed in claim 9 , wherein a lance tip is located upstream of the throat.
11. The reheat apparatus as claimed in claim 1 , wherein an inner wall of the mixing zone has a protrusion defining a line where hot gases detach from the walls.
12. The reheat apparatus as claimed in claim 11 , wherein the protrusion extends over a plane perpendicular to the longitudinal channel axis.
13. The reheat apparatus as claimed in claim 1 , wherein the channel has a quadrangular, square or trapezoidal cross section.
14. The reheat apparatus as claimed in claim 2 , wherein ends of the diverging side walls define with the channel longitudinal axis an angle larger than 15 degrees.
15. The reheat apparatus as claimed in claim 5 , wherein the plane diverging side walls define with the channel longitudinal axis an angle larger than 15 degrees.