Frictional drag measurements of large-scale plates in an enhanced plane channel flowcell.

This paper describes the design of an enhanced, plane channel, flowcell and its use for testing large-scale coated plates (0.6 m × 0.22 m) in fully developed flow, over a wide range of Reynolds numbers, with low uncertainty. Two identical, hydraulically smooth plates were experimentally tested. Uniform biofilms were grown on clean surfaces to test skin friction changes resulting from different biofilm thickness and densities. A velocity survey of the flowcell measurement section, using laser Doppler anemometry, showed a consistent velocity profile and low turbulence intensity in the central flow channel. The skin friction coefficient was experimentally determined using a pressure drop method. Results correlate closely to previously published regression data, particularly at higher speeds. Repeated measurements indicated very low uncertainty. This study demonstrates this flowcell's applicability for representing consistent frictional drag of ship hull surfaces, enabling comparability of hydrodynamic drag caused by surface roughness to the reference surface measurements.

An investigation into the effects of marine biofilm on the roughness and drag characteristics of surfaces coated with different sized cuprous oxide (Cu2O) particles.

Biofilms typically increase surface roughness and consequently the drag penalties on marine vessels. However, there is a lack of data regarding the time-dependent influence of biofilms on antifouling surface characteristics and frictional drag, especially for surface coatings with different sizes of cuprous oxide (Cu2O). In this study, a series of pressure drop measurements was carried out using flat plates coated with different sizes of Cu2O. The cuprous oxide-containing surfaces were deployed at sea for a period of six months to allow biofilm to develop. Surface microstructure and roughness analyses were carried out every six weeks using scanning electron microscopy and laser roughness surface profilometry. From the data, the added frictional drag caused by biofilm on ships was predicted, based on roughness function using Granville extrapolations. The analyses indicated that biofilms had significant impacts by altering the surface microstructure, resulting in higher frictional drag. However, due to the interaction between the biofilm and the physico-chemical properties of the substratum for panels coated with larger Cu2O, the roughness and drag measurement results were both found to have fluctuating increments.