Ship Propulsor interaction
General information
MARIN has two methods to compute the flow around a ship with a rotating propeller:

• A RANS-BEM method in which the viscous flow around the hull is solved by a RANS code (either PARNASSOS or ReFRESCO) and the flow around the propeller is solved with a BEM (PROCAL). The coupling between the two codes is done through a two-way coupling: interpolation of the propeller induced velocities from BEM in RANS and imposing the total wake field from RANS in the BEM method.
• A full RANS method in which the flow around both ship and propeller are solved in a RANS code (ReFRESCO). This is accomplished using sliding interfaces: the connection between the rotating grid block around the propeller, and the ship-fixed grid around the hull.
Depending on the goal of the calculation a choice can be made between these two methods. A RANS-BEM solves the propeller flow in an invicid way. Advantages are the lower calculation time and the resulting effective wake field which can be very useful in propeller design studies. A full RANS method makes no assumptions with respect to the propeller vortex system, time-averaging, etc. It is therefore slower, but it includes physics which can be very important in studies like: cavitation in behind condition, effect of rudders on propulsion, post-swirl energy saving devices, etc.

Example 1: RANS-BEM
The RANS-BEM has been used successfully in several projects over the last years and presented in several papers. Besides thorough analysis of the ship propulsion interaction it is also used more often to predict the speed power relation.
Below an example of a single screw vessel. The different wake fields are extracted and the effect of the propeller on the flow is visualized

Computed axial velocity field, limiting streamlines and wake field (nominal, total, induced and effective) by means of a PARNASSOS-PROCAL coupling method.

Example 2: Full RANS
The full RANS method with sliding interfaces is one of the latest developments of ReFRESCO. It opens the door towards in-depth analysis of the flow on and behind the propeller and the interaction with hull and appendages.
Below an example of a hull-propeller-rudder calculation for which the details of the flow field can be extracted during the every part of the rotation cycle of the propeller.

Computed distribution of longitudinal velocity in the ship centreplane, with rotating propeller at different blade positions. Computation using ReFRESCO with sliding interfaces.

Computations can be made for a rotating propeller behind a ship, using the ReFRESCO code. To capture the interaction of propeller and hull, a close coupling between both is needed, and this is accomplished using sliding interfaces: the connection between the rotating grid block around the propeller, and the ship-fixed grid around the hull. The figures showing the axial-velocity distribution indicate what detailed information can be provided by CFD today. Another advantage compared with simpler methods (e.g. coupling with a propeller panel code, which we also use) is that no assumptions are made on the propeller vortex system, time-averages, etc.

On the other hand, for more standard cases and ship performance prediction, a coupling between a RANS computation for the hull, and a propeller calculation using PROCAL, is normally adequate and is used by default.

Recent Papers:
Advanced measurements of rim-driven tunnel thrusters --The Wageningen TT-series JIP--
Yvette Klinkenberg, RenĂ© Bosman, Jie Dang and Do Ligtelijn, The 5th international conference on advanced model measurements technology (AMT '17) 11/13-10-2017, 2017

Exploratory measurements of cavitation nuclei in the wake of a ship model
Milos Birvalski and Martijn van Rijsbergen, The 5th international conference on advanced model measurements technology (AMT '17) 11/13-10-2017, 2017

Round Robin test on the underwater radiated noise of a cavitating ship propeller in open water
Frans Hendrik Lafeber and Thomas Lloyd, The 5th international conference on advanced model measurements technology (AMT '17) 11/13-10-2017, 2017

Validation of underwater radiated noise predictions for a merchant vessel using full-scale measurements
Frans Hendrik Lafeber, Thomas Lloyd and Johan Bosschers, Inter.Noise Hongkong 27-30 August , 2017

A Semi-Empirical Method to Predict Broadband Hull Pressure Fluctuations and Underwater Radiated Noise by Cavitating Tip Vortices
Bosschers, J., Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017