Three-dimensional flow and turbulence structure around Sea Cucumber Apostichopus japonicus

Abstract

The sea cucumber Apostichopus japonicus (A. japonicus) is a benthic invertebrate with a quasi-cylindrical body and several rows of papillae (conical prominence) on its body wall. As nutrient recyclers, A. japonicus plays a fundamental role in marine ecosystems and is one of the most important commercial aquaculture species in eastern Asia. Despite its ecological and economical importance, little is known concerning the flow characteristics surrounding A. japonicus on the organism scale. Research on the detailed flow structure at such a scale may serve as a significant step toward understanding the transport of sediment and nutrients in the vicinity of A. japonicus. This study sets up the D3Q27 multiple-relaxation-time lattice Boltzmann method to obtain the three-dimensional flow structure around an individual A. japonicus placed at the bottom of a flat-bed channel. The numerical model is validated by a water flume experiment. The flow patterns exhibit distinctive features at three different angles of attack (0°, 45°, 90°). The increasing inflow velocity (0.1m/s, 0.25m/s, 0.4m/s) brings no fundamental change to the structure of flow fields but induces more small-scale vortices and larger velocity fluctuations. This study investigates the complex turbulent flow fields around the A. japonicus and provides new insight for future studies on the interaction between water flow and A. japonicus.