Effects of Hook, Interceptor, and Water Jets on LCS Resistance/Power, Sinkage, and Trim

Abstract

Verification and validation of computational fluid dynamic simulations are performed at model and full scales for the high-speed littoral combat ship (LCS) surface combatant, including the effects of hook, interceptors, and water-jet propulsion. Predictions of the body force thrust, sinkage, and trim use a speed controller for attaining self-propulsion. Two methods for water-jet performance are used: 1) evaluation of forces based on integration of the stress over the wetted area of the hull and water-jet duct, pump casing, and nozzle (integral method) and 2) ITTC (2005) water-jet test procedure (control volume method). The comparison errors at model (resistance, sinkage, and trim) and full (power and trim) scales are satisfactory using both Froude (Fr) scaled model- and full-scale trial data, including the effects of the interceptors and water jets (WJ) on resistance/power, sinkage, and trim. For the model-scale model without WJs, the negative bottom hydrodynamic pressure near the water-jet inlets are observed without and with the hook simulations, and experiments with the hook. The negative bottom vertical force near the water-jet inlets for the simulations without the hook supports Savitsky’s (2014) assertion that semi-displacement monohulls do not exhibit hydrodynamic lift and disproves Giles’ (1992) assertion to the contrary. The hook and interceptors do not affect the pressure distribution significantly near the water-jet inlets. For the full scale model, the WJs induce bow up trim for the simulations and interpolated (between conditions)- and Fr scaled model-scale experiments. The negative bottom pressure and vertical force near the water-jet inlet for the simulations disprove Giles’ (1992) assertion that the WJs provide additional hydrodynamic lift. This is further supported by the comparisons of the vertical force % thrust vs. inlet velocity ratio for the LCS, with results shown in Bulten (2005) for a high-speed motor yacht. Bulten (2005) shows positive vertical force for inlet velocity ratios ≥ 1.25. However, LCS operates in the regime of an inlet velocity ≤ 1.2; thus, consistent with Bulten (2005), the vertical force is negative. The nonlinear effects between the interceptors and WJs are small such that a linear combination can provide a reasonable approximation.