A new method is presented for obtaining full-scale resistance predictions from model-scale submarine resistance tests. Traditionally, model-scale submarine resistance data is scaled using Froude’s Hypothesis, where the resistance is decomposed into frictional resistance and residual resistance. The frictional resistance is computed from a flat plate friction line formula at both model- and full-scale. The residual resistance coefficient is measured model-scale and is assumed to be independent of Reynolds number. Since the flow is assumed to be turbulent at fullscale, turbulence stimulators are placed at about 5% x/L to trip the flow in the model tests. The parasitic drag from the turbulence stimulators must be measured and subtracted from the model-scale resistance.
In the new approach a momentum thickness simulator is used in place of a traditional turbulence stimulator. The purpose of the momentum thickness simulator is to achieve similarity for model-scale and full-scale normalized momentum thickness of the boundary layer at the stern of the vessel as momentum thickness is directly related to ship resistance. The size and location of the momentum thickness simulator is computed to assure the flow is turbulent downstream of the simulator and to produce similar momentum thickness on the body downstream of the simulator. With this approach the total resistance is scaled from model-scale to full-scale without decomposing the resistance into frictional resistance and residual resistance. The parasitic drag is not measured and subtracted, as the additional drag from the momentum simulator is computed to produce the correctly scaled momentum thickness. In the new approach the physics associated with resistance is more clearly expressed and improved accuracy of resistance predictions is expected.