Applied Ocean Research 39 (2012) 1–10 Contents lists available at SciVerse ScienceDirect Applied Ocean Research journal homepage: www.elsevier.com/locate/apor Simulation of turning circle by CFD: Analysis of different propeller models and their effect on manoeuvring prediction Riccardo Broglia a, * , Giulio Dubbioso a , Danilo Durante a , Andrea Di Mascio b a Maritime Research Centre, CNR-INSEAN, 00128 Rome, Italy b Istituto per le Applicazioni del Calcolo, CNR-IAC, 00161 Rome, Italy article info Article history: Received 27 January 2012 Received in revised form 11 September 2012 Accepted 12 September 2012 Keywords: Computational methods Marine engineering Twin screw ship Manoeuvring Propeller loads abstract Propeller modelling in CFD simulations is a key issue for the correct prediction of hull-propeller interactions, manoeuvring characteristics and the flow field in the stern region of a marine vehicle. From this point of view, actuator disk approaches have proved their reliability and computational efficiency; for these reasons, they are commonly used for the analysis of propulsive performance of a ship. Nevertheless, these models often neglect peculiar physical phenomena which characterise the operating propeller in off-design condition, namely the in-plane loads that are of paramount importance when considering non-standard or unusual propeller/rudder arrangements. In order to emphasize the importance of these components (in particular the propeller lateral force) and the need of a detailed propeller model for the correct prediction of the manoeuvring qualities of a ship, the turning circle manoeuvre of a self-propelled fully appended twin screw tanker-like ship model with a single rudder is simulated by the unsteady RANS solver χnavis developed at CNR-INSEAN; several propeller models able to include the effect of the strong oblique flow component encountered during a manoeuvre have been considered and compared. It is emphasized that, despite these models account for very complex and fundamental physical effects, which would be lost by a traditional actuator disk approach, the increase in computational resources is almost negligible. The accuracy of these models is assessed by comparison with experimental data from free running tests. The main features of the flow field, with particular attention to the vortical structures detached from the hull are presented as well. c  2012 Elsevier Ltd. All rights reserved. 1. Introduction The numerical prediction of the trajectory followed by a self- propelled hull in free motion exhibits all the computational issues that can be met in naval hydrodynamics; the main difficulties arise in the accurate evaluation of the hydrodynamic forces and moments on the appendages, which are of paramount importance when assessing the dynamic response of the vessels and its trajectory. With regards to the mathematical model, the equations of rigid body motion must be coupled with the unsteady Reynolds averaged Navier–Stokes (uRANS) equations and many numerical aspects must be carefully considered. From the discretization point of view, at least in the context of uRANS solvers for structured grids (like the one used here), a dynamic over- lapping grid method must be implemented in order to let the ship move in a fixed background and allow the rudder to move with re- spect to the hull. Moreover, due to memory and CPU requirements, it would be difficult to obtain results accurate enough for practical purposes with a serial code, and therefore parallelization must be considered. However, in spite of all these difficulties, simulations performed * Corresponding author. Tel.: +39 0650299297; fax: +39 065070619 . E-mail address: riccardo.broglia@cnr.it (R. Broglia). by means of the numerical solution of the uRANS equations can be extensively used for the analysis of both static and dynamic manoeu- vres, as the latest workshops and international conferences (see for example [15–17,20,21]) have demonstrated. In this work, the prediction of the free turning manoeuvre of a tanker-like ship, already considered in a recent study [7], has been further analysed to gain further insight into some aspects of propeller modelling when operating under strong oblique flows. The test case considered is particularly challenging, since the unusual propeller/ rudder configuration (i.e. the twin screw vessel with a single rudder) provides a poor stability qualities of the ship. In the previous work, satisfactory results have been obtained in terms of trajectory, drift and speed drop in the stabilized phase of the turning only with the use of a “suitable” lateral force acting in the propeller plane; this approach was necessary because the simple actuator disk model used (the Hough and Ordway model [9]) in its original version provides only thrust and torque. As a matter of fact, detailed measurements of hydrodynamic loads and flow features [1] for a twin-screw frigate-type vessel during a steady turn have shown that the side forces generated by the pro- peller can be relevant (15–20% of the total lateral force) and therefore their contribution to the total hydrodynamic loads acting on the hull 0141-1187/$ - see front matter c  2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apor.2012.09.001