Propulsors
Structured grid Structured grid
General information
ReFRESCO is the viscous-flow CFD code used to compute the flow around propellers, open or ducted, pump-jets or thrusters. For open-water conditions, CFD calculations have significant added value when compared with traditional approaches: 1) modelling accuracy is higher than potential flow approaches; 2) provides substantially more insight in the physics than model-testing; 3) permits to check scale effects. The often referred drawback “it is too CPU-time expensive” is nowadays mitigated at MARIN by the use of smart numerical algorithms, steady calculations, and HPC clusters; a standard calculation for a propeller in open-water condition can be done in a couple of hours. When talking about propulsors (and propulsion), accuracy is a hot topic, since 1% of increase of efficiency may lead to significant amounts of savings (fuel and costs). Therefore numerical verification and validation of ReFRESCO for propeller flows is crucial, and is continuously done at MARIN since 2008.

Unstructured grid Unstructured grid
Numerical Issues
Since very high accuracies are needed for the analysis of propulsors, small details do play a role. Therefore proper geometry definition, high quality grids and higher-order numerical schemes have to be used in order to reach low numerical uncertainties. On the geometry side, MARIN has now the tools to correctly define propeller tip region, leading and trailing edges, hub-blade root connections, fillets. And on the grid-generation side MARIN can now produce both structured grids around simple to moderately complex blade geometries, and unstructured grids for complex blade geometries and propulsor arrangements. Combination of both is also possible.

Example 1: open propeller
Numerical studies, numerical verification and validation have been done for the well-known INSEAN E779A propeller benchmark test-case. The pictures below illustrate (top-left) the velocity field at the slip-stream of the propeller, together with an iso-surface of the Q, which is a quantity used to identify vortical structures. The picture (top-right) illustrates the comparison between experimental data, PROCAL calculations and ReFRESCO calculations for the complete open-water advanced coefficient range.

E779A case. (left) Flow field;
E779A case. (right) Open-water diagram results vs experiments.
Example 2: ducted propeller
For a ducted propeller, the flow is more complex due to the interaction of duct and blades (see picture below). Conventional approaches are difficult for these cases, and standard model-tests do not easily provide insight in the flow physics. After numerical verification and validation, scale effects have been studied using ReFRESCO. The different flow vorticity fields, for model scale and full scale for two different Js (left J=0.30, right J=1.0) can be visualized in the next picture.

Ducted-propeller scale-effects study.(left) J=0.3; (right) J=1.0 Ducted-propeller scale-effects study.(left) J=0.3; (right) J=1.0
Most recent papers on CFD for propulsors presented by MARIN
(complete overview of publications can be found under Publications)

On the Use of the γ-Reθ Transition Model for the Prediction of the Propeller Performance at Model-Scale
Baltazar, J., Rijpkema, D. and Falcão de Campos, J.A.C., Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017

Computational fluid dynamics prediction of marine propeller cavitation including solution verification
Lloyd, T., Vaz, G., Rijpkema, D.R. and Reverberi, A., Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017

Prediction of the Open-Water Performance of Ducted Propellers With a Panel Method
Baltazar, J., Rijpkema, D.R., Falcão de Campos, J.A.C. and Bosschers, J., Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017

Towards cavitation modelling accounting for transition effects
Reverberi, A., Lloyd, T. and Vaz, G., 19th Numerical Towing Tank Symposium (NuTTS), St. Pierre d'Oléron, France, 2016

Comparison of uRANS and BEM-BEM for propeller pressure pulse prediction: E779A propeller in a cavitation tunnel
Perali, P., Lloyd, T. and Vaz, G., 19th Numerical Towing Tank Symposium (NuTTS), St. Pierre d'Oléron, France, 2016

Using the FW-H equation for hydroacoustics of propellers
Lloyd, T.P., Lidtke, A.K., Rijpkema, D.R., Wijngaarden, H.C.J. van, Turnock, S.R. and Humphrey, V.F., 18th Numerical Towing Tank Symposium (NuTTS), Cortona, Italy, 2015

Influence Of Local And Adaptive Mesh Refinement On The Tip Vortex Characteristics Of A Wing And Propeller
Windt, J. and Bosschers, J., VI International Conference on Computational Methods in Marine Engineering (MARINE2015), Rome, Italy, 2015

Numerical Studies For Verification And Validation Of Open-Water Propeller RANS Computations
Baltazar, J.M., Rijpkema, D.R., and Falcão de Campos, J.A., VI International Conference on Computational Methods in Marine Engineering (MARINE2015), Rome, Italy, 2015

The Potsdam propeller test case in oblique flow: prediction of cavitation patterns and pressure pulses
Lloyd, T., Vaz, G., Rijpkema, D.R. and Schuiling, B., Second International Workshop on Cavitating Propeller Performance, Austin, Texas, 2015

Viscous flow simulations of propellers in different Reynolds number regimes
Rijpkema, D.R., Baltazar, J., and Falcão de Campos, J., Fourth International Symposium on Marine Propulsors (SMP), Austin, Texas, 2015

Contact
For more information on how MARIN can help your organisation with CFD for Propulsors, please contact the Ships Department.

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