Conclusions

Predictions of the flow around an appended geometry have been obtained for a range of Reynolds’ numbers for different turbulence models. To obtain meaningful comparisons between the turbulence models for the range of Reynolds’ number it was necessary to increase the resolution and accuracy of all stages of the CFD process. The reliability of such comparison depends on how well the flow features are resolved. This imposes an increased level of rigour and control of factors such as grid resolution, computational accuracy and numerical precision. This also extends to the critical assessment of the predicted flow field, and its level of convergence.

The RNG turbulence model in conjunction with wall functions and the Menter turbulence model can make predictions from model to full scale for appended and unappended bodies. For the AFF1 configuration, there is some consistency in the scaling of their predictions. This is not yet the case for the more complex AFF4 configuration. As a whole, the predictions point to an increased sensitivity of the Menter model to changes in Reynolds number. However, insufficient numerical implementations have been used to come to definitive conclusion on this matter.

The performance of the particular solution algorithm appears to reduce somewhat when applied to appended geometries, especially when using the ‘down-to-the-wall’ turbulence models. There are some difficulties with the reliability of the solution algorithm, associated with the multi-block nature of the method.

Further work is required to clarify the requirements for grid resolution and numerical stability for the more complex ‘down-to-the wall’ turbulence models, especially for fully appended geometries.

1. Bull P., “The Validation of CFD Prediction of Nominal Wake for the SUBOFF Fully Appended Geometry”, Proceedings of 21st Symposium of Naval Hydrodynamics, Trondheim, Norway 1996.

2. Eça L and Hoekstra M., “Numerical Calculations of Ship Stern Flows at Full Scale Reynolds’ Numbers”, Proceedings of 21st Symposium of Naval Hydrodynamics, Trondheim, Norway 1996.

3. Ju S., “Numerical Study of Ship Stern and Wake Flows at Model Scale and Full-Scale Reynolds; Numbers”, IIHR Report no 323, 1991

4. Watson S.J.P. and Bull P.W., “The Scaling of High Reynolds’ Number Viscous Flow Predictions using CFD Techniques”, Third Osaka Colloquium on Advanced CFD Applications to Ship Flow and Hull Form Design, Osaka, Japan, 1998.

5. Sotiropoulos F. and Patel V.C., “Second moment modelling for ship-stern and wake flows”, Proceedings of CFD Workshop for Improvement of Hull Form Designs, Toyko, 1994.

6. Deng G., Visonneau M., “Evaluation of Eddy Viscosity and Second-Moment Turbulence Closures for Steady Flows Around Ships”. Proceedings of 21st Symposium on Naval Hydrodynamics, Trondheim, Norway, June 1996.

7. Larsson L., Patel V.C. and Dyne G., (ed), Proceedings of 1990 SSPA-CTH-IIHR Workshop on Ship Viscous Flow, 1990.

8. Wilcox D.C, “Turbulence Modelling for CFD” 1994, DCW Industries.

9. Menter F.R., “Influence of freestream values on k-ω turbulence model prediction”, AIAA Journal 30.6, 1992.

10 “CFX4.2 User Guide”, 1997, CFX International, Harwell Laboratory, Oxfordshire, OX11 0RA, United Kingdom

11 “SAUNA Release 3.0 Volume 1 User Guide”, 1998, ARA Limited, Manton Lane, Bedford MK41 7PF, United Kingdom.



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