Effects of Inlet Air Distortion on Gas Turbine Combustion Chamber Exit Temperature Profiles

Localized damage to turbine inlet nozzles is typically caused by non-uniform temperature distributions at the combustion chamber exit. This damage results in decreased turbine performance and can lead to expensive repair or replacement. A test rig was designed and constructed for the Rolls-Royce Allison 250-C20B dual-entry combustion chamber to investigate the effects of inlet air distortion on the combustion chamber’s exit temperature fields. The rig includes a purposely built water cooled thermocouple rake to sweep the exit plane of the combustion chamber. Test rig operating conditions simulated normal engine cruise conditions by matching the quasi-non-dimensional Mach number, equivalence ratio and Sauter mean diameter. The combustion chamber was tested with an even distribution of inlet air and a 4% difference in airflow at either combustion chamber inlet. An even distribution of inlet air to the combustion chamber did not produce a uniform temperature profile and varying the inlet distribution of air exacerbated the profile’s non-uniformity. The design of the combustion chamber promoted the formation of an oval-shaped toroidal vortex inside the combustion liner, causing localized hot and cool sections separated by 90° that were apparent in the exhaust. Uneven inlet air distributions skewed the oval vortex, increasing the temperature of the hot section nearest the side with the most airflow and decreasing the temperature of the hot section on the opposite side.