Complete propulsion system simulation with ReFRESCO


Within the EU project STREAMLINE, the ReFRESCO team


developed new tech- niques facilitating


advanced simulations of the complete


(ship-propeller-rudder) propulsion system. This article outlines this achievement and how the research work is already opening new doors.


Guilherme Vaz g.vaz@marin.nl


18 report I


n the framework of numerical simu- lations, analysis of the flow around a ship is usually done in several


independent stages: ship resistance tests, propulsor analysis, seakeeping behaviour and manoeuvring tests. However, this obviously disregards the interaction between them. One relevant interaction that should be considered is the ship propulsion system (Figure 1 illustrates an example of a ship, propeller and rudder configuration).


Traditional approaches The traditional numerical approach for this propulsion problem has been to analyse the different components separately. This would involve examining the flow around the ship using steady viscous-flow RANS codes, extracting the wake field at the propeller plane, and analysing the propulsion characteristics of the propeller by using an unsteady poten- tial-flow BEM code, together with the so-called “effective-wake” field (which has to be determined using simplified models). A more integrated approach is to directly couple the RANS and BEM codes. This RANS-BEM approach (also used at MARIN) has low CPU costs and for design purposes is a suitable choice. However, it is still a split approach based on potential-flow and modelling simplifications. The new


numerical features facilitate an accurate analysis of this complex problem with no simplifications, by modelling less and simulating more.


Achievements ReFRESCO could already accurately predict the flow around open and ducted propellers in open-water configura- tions, at both model and full-scale, back in 2010 [1]. The prediction of the flow on a propeller in-behind conditions and the complete ship+propulsion system needed three major CFD-related developments: modelling rigid-body motions, non-confor- mal interfaces and sliding-interfaces. These developments have been accomplished within the European Union FP7 STREAM- LINE project, where innovative marine propulsion concepts have been proposed, experimentally tested, and computed using newly developed tools. With the first feature we now have the possibility to simulate any kind of imposed motion in different reference systems and with the second we can simulate the quasi-steady interaction of objects having different imposed motions. In the third we consider the fully unsteady interaction of these different moving objects. Important numeri- cal aspects such as boundary conditions, conservation properties close to these


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