PIV measurements of a thruster wake in open water conditions


was not possible before. This data is extremely valuable for the validation of CFD calculations.


The model test programme also included measurements with the thruster built into a barge model. Here, the deflection of the thruster wake, due to the presence of the hull and its rounded bilge (Coanda effect), could be captured (see example alongside).


These first PIV measurements will be used as validation material for CFD calculations. A key issue in these calculations is the correct representation of the shape of the thruster wake.


PIV measurements of the wake of an azimuthing thruster under a barge


often only become available relatively late in the design process, making it difficult to incorporate the results in the design.


CFD calculations could be an alternative method but there is little experience in the application of CFD as an engineering tool for thrust degradation effects. With the rapidly increasing capabilities of CFD models and computer hardware, the time is right for the development of new tools to analyse thrust- er interaction.


New measuring techniques In the summer of 2009, MARIN received its new stereo-PIV measurement system which has


a powerful Class 4 laser with two digital cameras built into a single underwater housing (see Report 98). A research project was carried out to evaluate the possibilities of using the PIV system for measuring the flow velocities in the wake of an azimuthing thruster. Model tests were carried out in MARIN’s Deepwater Towing Tank. An exam- ple of the measured wake velocities in open water conditions, showing both cross sections and velocities in the longitudinal plane, is shown above.


Results show that the new PIV system is capable of recording the velocity field in the propeller wake, with a level of detail that


Research efforts In the coming years, CFD calculations will increasingly be used as an engineering tool for application in offshore hydrodynamics. Examples are the calculation of current and wind loads, viscous effects in wave loads, VIM and the analysis of thruster interaction. MARIN’s research plans for CFD have been documented in a “roadmap”, in a bid to streamline R&D.


Currently, MARIN is starting a Joint Industry Project on the hydrodynamics of thruster interaction, called the Thrust Hydro- dynamics JIP (TRUST JIP). The TRUST JIP aims to gain insight into physical pheno- mena, quantifying thruster interaction effects and investigating possibilities for improvement. In the TRUST JIP model test data, CFD calculations and full-scale meas- urements will be combined to provide the


report 11


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