COMBINED ACOUSTIC DAMPING-COOLING SYSTEM FOR OPERATIONAL FLEXIBILITY OF GT26/GT24 REHEAT COMBUSTORS

In the development process of gas turbine combustion chambers, finding countermeasures for thermoacoustically induced pressure pulsations is a major focus. This paper presents a novel system consisting of a multi-layered and multi-functional high frequency damping and cooling structure that is implemented on the sequential burner front panel of the GT26/GT24 gas turbines. The device features multiple single Helmholtz dampers and an advanced convective near wall cooling system to improve the cooling capability and to reduce the cooling mass flow and thereby reducing NO emissions. The acoustic properties of the dampers and their placement have been defined as function of the identified acoustic mode shapes. The latter is very important since the dampers are designed to counteract screech tones that have acoustic wave lengths of the order of one burner front face width. In order to identify the acoustic mode shapes, multiple dynamics pressure measurements are applied in the full scale engine. The near wall cooled damping front panel design represents a new technology which has been developed and successfully validated at engine level in fuel gas and oil operation. The restrictions of the stable operating range due to pulsations are completely eliminated resulting in an increase of operational flexibility and lifetime. In addition to a thorough treatment of the damper's acoustic performance, information on the improved near wall cooling scheme is given in the paper, too.