Dynamic Gas Temperature Measurements in a Gas Turbine Transition Duct Exit

Abstract

Wide bandwidth gas temperature measurements in the transition duct exit of a gas turbine show that large gas temperature fluctuations occur at any point in the duct exit. The temperature fluctuations increase with engine thrust level, exceeding 1000 deg F at takeoff. Probabilistic and spectral analyses of the data indicate that the gas temperature fluctuations are due to nonaxial displacements of partially mixed secondary air jet zones in the transition duct exit. The jet zones are driven by the combustion processes in the forward sections of the main burner. The combustion processes regeneratively and nonlinearly amplify the longitudinal resonant acoustic pressure modes of the diffuser duct and the main burner and generate periodic velocity fluctuations in the combustion products leaving the forward sections of the main burner. Surface temperature waves induced at the leading edge of the first-stage turbine nozzle guide vanes by the main burner exhaust gases are also obtained from the data. Surface temperature fluctuations exceeding 30 deg F occur at takeoff. The fluctuations are of sufficient amplitude to cause a significant increase in the rate of oxidation of the turbine components.