Influence of droplet on energy field of ultrasonic transducers in pipelines of hydrogen-blended natural gas

Leveraging existing natural gas pipelines to transport hydrogen-blended natural gas is a practical route for large-scale hydrogen delivery. Ultrasonic flowmeters are essential for pipeline metering, but residual water vapor may condense into droplets on the transmitting surface of the transducer, disturbing ultrasonic propagation and energy distribution. In this study, a multiphysics model was developed in COMSOL Multiphysics to investigate the effects of attached droplets on the acoustic and flow fields in hydrogen-blended natural gas pipelines. The influences of droplet diameter, emission frequency, hydrogen blending ratio, and droplet position were systematically analysed. The results show that droplet diameter has a significant attenuation effect on the received signal. As the droplet diameter increased from 1 to 4 mm, the peak acoustic intensity at the receiving end decreased from 2.69 × 10⁵ to 2.59 × 10² W/m². Increasing the emission frequency from 15 to 60 kHz shortened the acoustic-wave arrival time from 550 to 380 μs, but intensified wave interference. When the hydrogen blending ratio increased from 5 % to 20 %, the average acoustic energy density decreased from 8.42 to 6.88 J/m³. Moreover, off-centre droplets weakened the influence on arrival time but still affected local instantaneous acoustic intensity. These findings guide ultrasonic flowmeter deployment and signal correction in hydrogen-blended natural gas pipelines.