Drag-topography correlations in biofouling roughness via Direct Numerical Simulations

Biofouling is the accumulation of marine organisms on the hull of naval vessels and can severely result in increased drag and fuel consumption. Given today's energy crisis, the need of minimizing fuel consumption is more urgent than ever. Thus, the development of predictive tools that can assess the impact of biofouling topographies on the frictional resistance of naval vessels is of great importance. Today most of these correlations are based on rough surfaces that are not representative of biofouling surfaces. Analyses of scanned biofouled surfaces indicate that they are characterized by high skewness (Sk>1) and low effective slope (ES<0.5) for example. In the current study will report Direct Numerical Simulations of turbulent boundary layers and/or channels-flows over biofouled surfaces synthesized using various fouling organisms (e.g., barnacles, tubeworms, oysters). To investigate the drag sensitivity to specific surface characteristics, a systematic parametric study is performed. A highly efficient, in-house, Navier-Stokes solver based on an immersed boundary formulation is utilized, alongside a sophisticated algorithm encharged with the surface creation. We will report correlations of various surface statistics with the resulting hydrodynamic forces and emphasis will be given to the surface characteristics which lead to increased roughness-function, ΔU+, values.