The open-water performance of podded propulsors of different sizes are numerically simulated by using the RANS method with a realizable k - ε turbulence model to study the scale effect of each component of the podded propulsor. It focuses on the scale effect associated with the pod body and the strut. Based on the analysis of the pod body drag and the strut drag at different scales, a correction method is proposed for the frictional drag coefficients of the pod body and the strut by recalculating the Reynolds number with the modified characteristic length and characteristic velocity.
The podded electric propeller becomes more popular in the practical engineering due to its advantages of high modularity, easy maintenance, and low noise, etc. Both of the experimental test and numerical simulation method can be used in the research of the podded propulsor. Many institutes, such as HSVA (Germany), VTT (Finland) and MARIN (the Netherlands), have conducted experimental studies on podded propulsors, including the scale effect analysis, the performance prediction and the cavitation performance of the podded propulsor under open-water conditions. Islam (2007) presented experimental research on the effect of the gap distance on the propulsive characteristics of puller and pusher podded propulsors in straight-ahead and azimuthing open water conditions. Though great progress has been made in the technology of podded propulsion tests for podded propulsors with different sizes in various applications, the analysis of the interactions between different components of the podded propulsor or variations in viscous forces due to scale effects requires more flow field details.
The numerical simulation of the podded propulsor can be carried out based on the potential flow theory and/or the viscous flow theory. Ma et al. (2009) established steady and unsteady numerical calculation methods for the podded propulsor based on the potential flow theory, in which the blades were calculated by the lifting surface theory, and the pod and the strut were calculated by the panel method. The hydrodynamic performance of the podded propulsor was predicted accurately, but with insufficient flow field details. Guo et al. (2009) studied the hydrodynamic performance of the podded propulsor based on the RANS method. Islam (2017) evaluated the propulsive characteristics of a puller podded propulsor in extreme azimuthing condition by using a RANS-based CFD code.
