Modeling Techniques of Puller Podded Propulsor in Extreme Conditions

Abstract

This article presents the outcome of a numerical simulation-based research to evaluate the propulsive characteristics of a puller podded propulsor in extreme azimuthing and at multiple initial loading conditions. A Reynolds-Averaged Navier-Stokes (RANS)-based computational fluid dynamics (CFD) code is used to model and predict the propulsive characteristics of the podded propulsor at extreme oblique flow conditions in which highly unsteady, fully 3D, and separated flows exist. The forces and moments of the podded propulsor in the three coordinate directions as well as the thrust and torque of the propeller in static azimuthing conditions in the range of -180°–180° at advance coefficients of 0.20 and 0.8 are predicted and compared with a corresponding dataset obtained in a previous model testing campaign. The predictions of the performance characteristics of the pod unit were within 1–5% of the corresponding measurements, which also captured the nonlinear trends for all the loading conditions, and azimuthing angles. In addition, the velocity and pressure distributions around the podded propulsor as derived from the RANS predictions reveal the highly separated and 3D flow and complex interaction between the propeller and pod-strut bodies, which was more evident in the extreme azimuthing and moderate to light propeller loading conditions. This study demonstrates that the RANS-based CFD code, with proper meshing arrangement, boundary conditions, and setup techniques, can predict the performance characteristics of the podded propulsor in extreme azimuthing and in various loaded conditions with the same level of accuracy of the measurements. 1. Introduction Podded propulsors have the potential to become a popular main propulsion system because they allow more flexibility in the design of the internal arrangement of a ship, potentially reduce noise and vibration, and increase maneuverability (Pakaste et al. 1999; Carlton 2002). The propeller, pod, and strut are the three main components of a podded propulsor. There are multiple propeller-pod-strut configurations that are available commercially, namely the puller type, pusher type, duel-end type, ducted type, and contrarotating type configurations. One of the popular configurations of the podded systems is the puller type, in which the propeller is located upstream of the pod and strut (Islam 2009).