Flow Analysis for the Development of the Coanda Vortex Ring Thruster (CoVoRT)*

 The vortex ring thruster (VRT) is a propulsion system mimicking the propulsive technique of cephalopods, such as squids and jellyfish. VRT's acknowledged advantages include low noise generation, delicate attitude control, and precise maneuverability. However, due to the low propulsion efficiency, its application is limited to low-speed micro-scale vessels only. In the present study, VRT enhanced by the Coanda effect, dubbed CoVoRT, is proposed, aiming for propulsion efficiency improvement. The flows around the typical VRT and CoVoRT were analyzed using Computational Fluid Dynamics (CFD) simulations. For computational validation, the CFD results for the flow around VRT were compared with the previous simulations and experimental results. Then the propulsion performance of VRT and CoVoRT was compared in terms of the propulsion performance evaluation index (PPEI), and the vortex ring formation process. The results showed that CoVoRT's PPEI is approximately 50% higher than that of VRT. Also, the vortex ring formation by CoVoRT was more stable compared to that by VRT.