Escort Tug at large Yaw Angle: Comparison of CFD Predictions with Experimental data
Molyneux, D and Bose, N, Escort Tug at large Yaw Angle: Comparison of CFD Predictions with Experimental data, International Journal of Small Craft Technology , 150, (B1) pp. 45-60. ISSN 1740-0694 (2008) [Refereed Article]
Escort tugs operate at high yaw angles in order to produce forces to steer and stop the
vessel they are escorting in an emergency. In this paper, RANS predictions of forces and
flow patterns around the hull of an escort tug model are compared with experimental data.
Two alternative meshing strategies were used, one using tetrahedral elements with
triangular faces and one using hexahedral elements with quadrilateral faces.
Experiments were carried out with and without the low aspect ratio tin that is typical of
many escort tugs. Lift and drag forces were measured experimentally for yaw angles from
15 to 45 degrees. Flow measurements around the tug at 45 degrees yaw were obtained
using a stereoscopic particle image velocimetry (PIV) system.
The results from each CFD simulation were compared to the measured flow patterns
using a numerical procedure that led to a quantitative measure of the accuracy of the
predicted results. The analysis of the flow patterns indicated that the main features of the
flow were predicted, and that on average, the predicted velocity magnitudes were within
10% of the measured values. Neither mesh approach had a significant effect on the
accuracy of the flow pattern predictions. The hexahedral mesh gave more accurate force
predictions that the tetrahedral mesh. Forces were predicted by the CFD code with this
mesh to within 5 % of the experimentally obtained values.