Computational Analysis of Spray Deflector Designs

Abstract: Planing hull is a common hull design concept which decreases the resistance while speed is increasing for a specific speed range. It is also suitable for hull modifications to achieve higher efficiency. Spray deflector is a promising hull modification which offers extra resistance decreasing and less vertical acceleration for planing hulls. Spray deflector technology can decrease the resistance up to 28% compared to the bare hull. However, the information on spray deflector design is strongly limited. In this study, there are two different types of spray deflector designs compared via CFD to achieve better design. Star CCM+ software was used to create CFD models with given numerical settings: 3-Dimensional, implicit unsteady, multiphase VOF, RANS based SST K-Omega turbulences model, all y+ Hybrid Wall Treatment while only considering heave and trim. Froude Number of the simulations ranges from 2 to 2.6. To improve the value of CFD models, mesh sensitivity study, time step study, y+ study, and alteration of prism layer number were conducted. The experimental base of this thesis is Molchanov’s “Experimental validation of spray deflectors' impact on the performance of high-speed planing” study from 2018. All CFD outcomes were evaluated according to these experiments.  There is a problem named numerical ventilation which downgrades the value of outcomes. Thus, three different methods were evaluated against numerical ventilation additionally to the spray deflector comparison. These methods are “Phase Replacement”, “Modified High-Resolution Interface Capturing Scheme”, and “Volume Fraction Source Term”. Application of Volume Fraction Source Term method gave the best achievements for the calculation of resistance with 0.35% error ratio, and trim angle 17% error ratio while causing 16% error ratio for heave. The modified HRIC scheme achieved a 1.4% error ratio for heave, 12.5% error ratio for resistance, and 20.4% error ratio for trim angle. The restrictions of these methods and their application ways are specified in this thesis.