J Mar Sci Technol (2003) 8:68–75 DOI 10.1007/s00773-003-0155-5 Breaking wave at the bow of a fast displacement ship model Angelo Olivieri, Fabrizio Pistani, and Andrea Di Mascio INSEAN, Italian Ship Model Basin, Via di Vallerano 139, 00128 Rome, Italy At present, the available models for wave breaking simulations cannot describe three-dimensional flows, although they reproduce two-dimensional classical ex- periments very well. 1,2 Colagrossi et al. 3 recently pro- posed a “2D + t meshless model” in order to simulate breaking waves around a ship, and their computed flows qualitatively match the breaking scenario. Intensive experimental work has been carried out in order to obtain data on ships breaking waves. Dong et al. 4 studied the flow under the bow wave of the DTMB 4817 model by measuring the flow in a plane orthogonal to the wave crest by the PIV system. Similarly, Roth et al. 5 measured the velocity components in the earlier stages of the bow wave breaking development. The work by Dong et al. 4 was carried out for a small model (3.05 m), and the wave breaking was dominated by sur- face tension. 6 Furthermore, the small Reynolds number of the experiment did not allow the production of a fully developed turbulent flow. The experiment by Roth et al. 5 was characterized by higher Weber and Reynolds numbers, and these were of the same order of magni- tude as those in the present experiment. Neither the Dong or Roth experiments gave information on the velocity component normal to their measurement areas. We studied the breaking bow wave generated by a large model (L PP = 5.72 m) at a relatively high Froude number (Fr = 0.35). The velocity measurements were carried out by means of a 5-hole Pitot probe in two planes normal to the hull motion. All three mean veloc- ity components (axial, transverse, and vertical) were measured. The model INSEAN 2340 used for the test is an iden- tical geosym of the DTMB 5415 model that has been adopted by the International Towing Tank Conference (ITTC) as a recommended benchmark for CFD valida- tion for resistance and propulsion. 7 A previous experi- mental study of far-field wave elevation was performed for Froude numbers Fr = 0.28 and Fr = 0.41. 8 With Fr = 0.28, the wave breaking was too gentle and was affected Abstract We investigated the flow structures under the bow wave generated by a fast displacement ship model (INSEAN model 2340) in the presence of wave breaking. The data acquired were also used for a detailed database for CFD validation. The mean and r.m.s. point-wise values of the wave height were measured by means of a finger probe. The inten- sity of the breaking wave was taken as the r.m.s value of the wave height. The mean velocity field under the free surface was measured at 0.15 L PP and 0.2 L PP downstream of the fore perpendicular by means of a 5-hole Pitot probe. Uncertainty assessment of the wave height and velocity field results was performed following the AIAA Standards S-071-1995. Pre- liminary CFD results from a RANSE code with a breaking model are shown in comparison with the measured data. Key words Bow breaking waves · Free surface flow · CFD validation Introduction Although wave-breaking phenomena are frequently present in naval hydrodynamics applications, they are far from being completely understood. From the physi- cal point of view, it is crucial to understand how break- ing waves are generated, and how they modify the flow field. Furthermore, it is important to have a physical model in order to take into account the effects of the wave breaking in the CFD. Nonetheless, all models need calibration, and this can be performed only if the relevant experimental data are available. Address correspondence to: A. Olivieri (e-mail: a.olivieri@insean.it) Received: October 4, 2002 / Accepted: May 2, 2003