Ship bow wave breaking phenomenon is still a challenge for CFD simulation, due to unsteady mixture flow and the lack of detailed experimental validation data. As a new wave breaking study case, a scaled KRISO container ship (KCS) model of 1/52.6667 is selected. To determine the appropriate detailed wave breaking measurement case conditions for future CFD validation, experimental and computational investigations are conducted with trim and sinkage variation. The trim and sinkage have significant effects on wave breaking phenomenon. Spilling and plunging wave breaking are observed.
Wave breaking is a quite common flow phenomenon at sea for ships. The breaking waves around ship bow region can produce sprays, mixture of air – water mixture flow and will extend to the far field of ship's downstream, which will affect the performance of the hull & propulsion systems and increase the ship wake signatures.
The 3D breaking wave and the flow field due to the breaking waves are quite challenging for CFD solvers. Wilson et al. (2006) investigated the breaking waves for the high-speed transom stern ship (R/V Athena I) by using the URANS solver in CFDSHIP-IOWA. One low Fr 0.25 and two high Fr 0.43 and 0.62 were selected. The single-phase level set method for the free surface and structured overset grids for refining the local regions were used. The plunging breaker and multiple free surface scars were shown at higher speed cases in the results. The velocity measurement data due to the breaking waves was not available for CFD validation. Wilson et al. (2007) used the unsteady RANS single-phase level set method with local overset grid refinement to predict the 3D breaking waves of the DTMB 5415 surface combatant ship model mainly at Fr 0.35. Detailed velocity and free surface measurement for the breaking waves were used for CFD validation. The experimentally observed weak spilling shoulder wave was not captured by CFD. The wake of low axial velocity and vertical cross flow was accurately predicted. Wang et al. (2020) compared the URANS and DDES approaches for simulating the KCS model wave breaking using photo observation results. The VOF technique in OpenFOAM is used to capture the free surface. The DDES approach was found to be more appropriate for simulating the breaking wave profile and the vorticity field. Noblesse et al. (2013) reviewed the ship bow waves' practical results and presented mechanism in an analytical method. The boundary between two basic bow wave regimes – steady overturning with fast fine bow ship and unsteady breaking with slow blunt bow ship - was shown in association with Bernoulli relation. Pistani (2005) investigated the scale effects of bow wave breaking by using three different scales of the same benchmark model DTMB 5415. Three models of 9.916m, 5.720m, 3.048m in length with speed range of Froude numbers from 0.05 to 0.41 were tested in INSEAN towing tank. Froude numbers and scale effects on wave breaking were discussed. The wave breaking has significant scale effects due to surface tension. The weak wave breaking was observed for the small and middle model, and the largest model had similar wave breaking phenomenon to the full-scale case. Olivieri et al. (2007) investigated the ship bow and shoulder wave breaking by detailed EFD and complementary CFD (CFDSHIP-IOWA RANS code v.4) mainly for the DTMB 5415 model of 5.72m at Fr 0.35. The mean & RMS value of wave height, mean velocity, scars, vortices were compared between EFD and CFD. The satisfactory agreement was achieved. Wang et al. (2014) used a multiphase incompressible flow server Gerris and the Octree mesh type of 8M grids to calculate the drag and free surface elevation for a ship at Fr 0.316. Good agreements were claimed to be achieved although no details were shown in the paper. Yu et al. (2020) performed ship bow wave breaking for a 6.07m KCS model at Fr 0.35 and Fr 0.40 by using in-house CFD solver naoe-FOAM-SJTU. The numerical calculation results were compared with wave observation by photo study.
