Experimental and theoretical investigating on measurement of dynamic response characteristics of the semi-infinite pressure tube with non-uniform temperature

In combustion instability experiments, oscillatory pressure is commonly sampled using a semi-infinite pressure tube, but the non-uniform temperature distribution adds complexity to the correction of oscillatory pressure. This paper innovatively investigates the impact of non-uniform temperature distribution on the dynamic response characteristics of semi-infinite pressure tubes using a one-dimensional discrete method for sound propagation, obtaining the distribution of sound pressure gain and phase difference in the pressure tube. The results indicate that the end of the semi-infinite pressure tube can be approximated as a non-reflective boundary; however, the presence of sensor mounts on the sidewalls of the pressure tube creates small cavity structures that reflect sound waves, leading to non-monotonic characteristics in the dynamic response of the pressure tube. An increase in pressure tube root temperature reduces the traveling wave specific acoustic impedance, amplifying the pressure tube gain. At a pressure tube root temperature of 500 °C, the temperature non-uniformity effect overall amplifies the gain by about 1.2 times. By establishing a one-dimensional sound wave propagation theory analysis, combined with acoustic simulation and experimental verification, this paper reveals the mechanism of action of non-uniform temperature fields on the dynamic response within pressure tube, providing theoretical guidance for correcting oscillatory pressure measurements in combustion instability of gas turbines and aero-engines.