Measurement of jet gas-liquid interface fluctuations based on ultrasonic scattering

Aero-engines and rocket engines regularly experience unstable combustion phenomena. In order to reveal the complex mechanism, it is necessary to measure the jet gas-liquid interface disturbances. However, most techniques require optical access and the measurement fails when the optical access is limited. Ultrasonic method can be considered as an alternative under this condition. The present work proposes an acoustic approach for measuring the jet gas-liquid interface based on ultrasonic scattering. A thorough investigation of the scattered acoustic field by the jet is conducted by experimental methods. The high-speed imaging technology is used to verify the ultrasonic measurement results. The direct measurement results demonstrate a relationship between the perturbation of the jet gas-liquid interface and that of ultrasonic scattered acoustic pressure in certain measuring direction. The scattered acoustic field is analyzed theoretically and practically by using customized metal scatters of certain size. Based on these findings, a database is created to enable the ultrasonic measurements to be calibrated. The corrected result shows that the correlation of ultrasonic measurements and results from cameras has been greatly improved, and the maximum relative error of the ultrasonic measurements is 30.9%, the average relative measurement error is 2.1%. It is proved that the method of determining the gas-liquid interface of jet by ultrasonic scattering wave is feasible. The method may also be used for the measurement of the overall jet fluctuations and breakup.