Numerical and Experimental Investigation of the Aero-Hydrodynamic Effect on the Behavior of a High-Speed Catamaran in Calm Water

In this paper, the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods. Experiments were conducted in a towing tank over the Froude number range of 0.49-2.9 with two degrees of freedom. The model vessel displacement of 5.3 kg was implemented in experimental tests. Craft behavior was evaluated at the displacements of 5.3, 4.6, and 4 kg by using the numerical method. The numerical simulation results for the hull's resistance force were validated with similar experimental data. The fluid volume model was applied to simulate two-phase flow. The SST k-omega turbulence model was used to investigate the effect of turbulence on the catamaran. The results showed that in the planing mode, the contribution of air to pressure resistance increased by 55%, 40%, and 60% at the mentioned displacements, whereas the contribution of air to friction resistance was less than 15% on average. The contribution of the air to the total lift force at the abovementioned displacements exceeded 70%, 60%, and 50% in the planing mode but was less than 10% in the displacement mode. At the displacements of 5.3 and 4 kg, the area under the effect of maximum pressure moved around the center of gravity and caused porpoising longitudinal instability at the Froude numbers of 2.9 and 2.4, respectively. However, at the displacement of 4.6 kg, this effect did not occur, and the vessel maintained its stability.