Heat Transfer Coefficients Around Cylinders in Crossflow in Combustor Exhaust Gases

Abstract

The local heat-transfer coefficient at the surface of a component placed in combustor exhaust gases can be determined from an analysis of surface temperature oscillations induced by fluctuations of the exhaust-gas temperature. Within a prescribed bandwidth, the relative amplitudes of the Fourier components of the gas and surface temperature waves are a simple function of the local heat-transfer coefficient and the thermal properties of the component. This method of measuring the local heat-transfer coefficient is described in this paper and heat transfer coefficients measured around small cylinders in crossflow (Re = 4000–20,000) are reported. Measurements of the transient response of cylinders abruptly placed in the exhaust-gas stream were conducted to determine the accuracy of the wide bandwidth method. Wide bandwidth gas temperatures and velocities and their cross correlations in the combustor exit were measured to characterize the large-scale exhaust-gas dynamics. It is shown that the stagnation line heat-transfer coefficients are uniformly higher than those obtained in low-turbulence cold gas streams; the magnitude of the stagnation line Nusselt number increases with the measured turbulent intensity. Away from the stagnation line in the unseparated region, the dependence of the local heat-transfer coefficients on the angle from the stagnation line is in agreement with earlier data measured in cold gas streams.