Towards inferring drag produced by patchy, heterogeneous soft biofilms

Unlike hard biofilms, the mechanisms of drag produced by soft biofilms are not completely understood, resulting in the lack of availability of models and parameters to predict drag at full scale. Several factors, such as types and distributions of species, the growth duration, the nature of the resulting fouling morphology (presence of streamers, compliance, etc.), their distributions (coverage), and sloughing with time, play a significant role in skewing laboratory measurements. In this study, we develop synthetic materials aimed at replicating alive biofouling in a controlled manner. The effect of patchy, heterogeneous coverage on the measured drag, and its relationship to parameters such as equivalent sand grain roughness, roughness function, etc., is investigated in a turbulent channel flow. Specifically, the effect of protrusion height, location, and coverage extent is explored for a range of rough and compliant surfaces with a range of mechanical properties. Observed results are then compared with live biofilm drag measurements of various growth durations.