Computational sedimentation modelling calibration: a tool to measure the settling velocity under different gravity conditions

Abstract. Research in zero or reduced gravity is essential to prepare and support planetary sciences and space exploration. In this study, an instrument specifically designed to measure the settling velocity of sediment particles under normal-gravity, hypergravity and reduced-gravity conditions is presented. The lower gravity on Mars potentially reduces drag on particles settling in water, which in turn may affect the texture of sedimentary rocks forming in a standing or moving body of water with settling particles. An environment to test such potential errors is the parabolic flight, which offers reduced gravity for up to 30 s. Exact tracing of particle tracks while settling is essential to assess the impact of gravity on flow hydraulics, drag and settling velocity. In this study, we present an advanced version of previous instruments, including the approach to particle tracking and track analysis. The trajectories of particles settling in water were recorded under reduced Martian and lunar gravity, the hypergravity phases during the pull-up of the plane and at terrestrial gravity on Earth. The data were used to compute the terminal settling velocity of isolated and small groups of particles and compared with the results calculated using a semi-theoretical formula derived in 2004 by Ferguson and Church (Ferguson and Church, 2004). The analysis showed that with improved design of settling chambers, particle recording and tracking, a highly precise measurement of settling velocity is possible. This illustrates that the parabolic flight environment is suited not just for broad qualitative comparisons between different gravity environments but also for highly precise data acquisition on flow hydraulics associated with particle settling.