Abstract
Symbiotic relationships have developed through natural evolution. For example, that of the remora fish attached to the body of a shark. From the remora’s perspective, this could be associated to an increased hydrodynamic efficiency in swimming and this needs to be investigated. To understand the remora's swimming strategy in the attachment state, a systematic study has been conducted using the commercial Computational Fluid Dynamics (CFD) software, STAR-CCM + to analyse and compare the resistance characteristics of the remora in attached swimming conditions. Two fundamental questions are addressed: what is the effect of the developed boundary layer flow and the effect of the adverse pressure gradient on the remora’s hydrodynamic characteristics? According to the results, the resistance of the remora can generally be halved when attached. Besides, the results have also demonstrated that the drag reduction rate increases with the developed boundary layer thickness and can be estimated using the boundary layer thickness ratio and velocity deficit. The paper demonstrates that the most frequent attachment locations are also the areas that provide the maximum drag reduction rate.
Highlights
Natural cooperative relationships have developed throughout the evolution process
An investigation has been conducted to study the hydrodynamic characteristics of the remora fish in attached swimming conditions
This research has primarily focused on the investigations of the effect of the boundary layer flow and the attachment locations of the remora to the body of a shark
Summary
The section below describes the details of the simulated models for the remora fish and the shark model. It is to note that when the remora attaches to the host, four pectoral fins of the remora open, with two of them staying close to the host This will be modelled in the simulation. Numerical simulations were performed with the CFD software STAR-CCM + to investigate the hydrodynamic free-swim characteristics of the remora and the shark and to set out our benchmark cases. According to ITTC Practical Guidelines for Ship CFD Applications g uidelines[16], the surrounding planes are defined as symmetry boundary conditions 1.5L from the body, while the shark and the remora models are set to non-slip wall conditions. A more refined grid is used in the vicinity of the models which is about 0.1L There are three different grid groups to be implemented in the CFD software STAR-
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