Numerical Study of Ultrasound-Based Level Sensors in Liquid Hydrogen Tanks

Abstract

Liquid hydrogen (LH2) holds immense potential for decarbonizing aviation, offering a sustainable alternative to conventional fuels. However, its adoption is constrained by its lower volumetric energy density, necessitating storage in liquid form at 20 K. Precise LH2 level measurement in cryogenic aircraft tanks under varying flight conditions presents significant challenges due to its low viscosity, thermal stratification, and the risk of hydrogen embrittlement. This study explores the use of ultrasonic sensors for LH2 level detection, employing FEM simulations in COMSOL Multiphysics 6.2. The findings reveal that placing the sensor within the LH2 medium makes level detection feasible due to the low transmission of acoustic waves at the LH2-H2 interface. Under the stationary fluid assumption, using a 50 kHz frequency, the sensor achieved a relative error of 0.65% at a fuel level of 1.9 m, with absolute errors ranging from 12.3 to 12.5 mm. However, cryogenic temperature variations between 18 K and 20 K directly influenced sensor accuracy, with lower temperatures leading to higher absolute errors. Additionally, increasing sloshing angles reduced the sensor’s accuracy and detectability. These findings demonstrate the feasibility of ultrasound sensors for reliable LH2 level measurement. However, practical implementation must address the challenges posed by sloshing e ects, thermal stratification, and hydrogen embrittlement to ensure long-term reliability and operational safety.