Mixing ducts for a gas-turbine annular combustion chamber

A method of operating a gas-turbine annular combustion chamber having a front plate with at least one row of premix burner arranged in an annular form, a plurality of combustion-air ducts, each combustion-air duct being designed as a diffuser and arranged to guide combustion-air directly downstream of a compressor outlet from guide vanes of a last compressor row to each premix burner, wherein at a downstream end of each combustion-air duct at least one longitudinal-vortex generator is disposed, and at least one fuel injection means is disposed in or downstream of the at least one longitudinal-vortex generator, and having a mixing duct extending from the at least one fuel injection means to a combustion chamber, each mixing duct having a constant height (H) and a length (L) which corresponds approximately to twice the value of a hydraulic duct diameter (D) of the mixing duct, the method comprising the steps of:

• dividing the combustion air, directly after discharge from the compressor into individual air flows for the burners and for cooling of the combustion chamber and the turbine, decelerating a velocity of the air for the burners in the combustion-air ducts to about half the value of the compressor outlet velocity, generating at least one longitudinal vortex in the air per combustion-air duct, and injecting fuel during or downstream of the longitudinal-vortex generation forming a fuel/air mixture, the mixture flowing along in a mixing duct and flowing with an overall swirl imposed on it into the combustion chamber and being burnt there.