Validation of the CFD approach for modelling roughness effect on ship resistance

Abstract

Recently, there have been active efforts to investigate the effect of hull roughness on ship resistance using Computational Fluid Dynamics (CFD). Although, several studies demonstrated that the roughness modelling in the CFD simulations can precisely predict the increase in frictional resistance due to the surface roughness, the experimental validations have been made only for flat plates which have zero pressure gradient. This means that the validations cannot necessarily guarantee the validity of this method for other ship resistance components besides the frictional resistance. Therefore, it is worth to demonstrate the validity of the roughness modelling in CFD on the total resistance of a 3D hull. In this study, CFD models of a towed flat plate and a KRISO Container Ship (KCS) model were developed. In order to simulate the roughness effect in the turbulent boundary layer, a previously determined roughness function of a sand-grain surface was employed in the wall-function of the CFD model. Then the result of the CFD simulations was compared with the experimental data. The result showed a good agreement suggesting that the CFD approach can precisely predict the roughness effect on the total resistance of the 3D hull. Finally, the roughness effects on the individual ship resistance components were investigated. Recently, the use of Computational Fluid Dynamics (CFD) is considered as an effective alternative to improve these shortcomings [17]. The merit of using CFD is that the distribution of the local friction velocity, , is dynamically computed for each discretised cell, and therefore the dynamically varying roughness Reynolds number, + , and corresponding roughness function, + , can be considered in the computation. The 3D effects can also be taken into account, and the simulations are free from the scale effects if they are modelled in full-scale. Correspondingly, there have been increasing number of studies utilising CFD modelling to predict the effect of surface roughness on ship resistance [16, 18-20] and propeller performance [21, 22], as well as ship self-propulsion characteristics [23]. These recent studies suggest that the hull roughness does not only increase the ship frictional resistance but also affects the viscous pressure resistance and the wave making resistance.

Investigating the Effect of Heterogeneous Hull Roughness on Ship Resistance Using CFD

“…Song et al [24] evaluated the roughness function of the sand grit (60/80 grit aluminium oxide abrasive powder) from the results of flat plate towing tests. Later on, a mathematical model of the roughness function (i.e., roughness function model) was proposed by Song et al [25] to be used in CFD simulations.…”

“…Recently, Song et al [24,25] validated Granville's method and the CFD method by comparing the predictions against a ship model test with a rough surface.…”

“…In this study, CFD simulations of the Wigley hull were developed with different hull roughness conditions using the modified wall-function approach with the roughness function model of the sand-grain surface, which were determined from previous studies [24,25]. The CFD simulations of the Wigley hull model were performed with different hull conditions.…”

“…An Unsteady Reynolds Averaged Navier-Stokes (URANS)-based CFD model was developed to replicate the physical Wigley hull model test of Song et al [27]. The different hull roughness conditions were modelled using the modified wall-function approach with the roughness function model ( + ) of Song et al [25]. The CFD simulations were performed with different hull conditions and compared with the towing test results [27].…”

Investigate the Drag Resistance of Antifouling Self-Adhesive Film

“…Flat plate simulations have good agreement with towing test results of ship models with rough surfaces [19]. A simple 2D model can be used for the flat plate simulation using CFD to numerically calculate the frictional resistance of a surface with certain roughness by neglecting wave generation and end effects [20].…”