On the effects of surface texturing on turbulent flow and its impact on the early-stage of bio-fouling settlement
Peyvasteh Nejad, Amin
(2024)
On the effects of surface texturing on turbulent flow and its impact on the early-stage of bio-fouling settlement.
PhD thesis, Dublin City University.
Bio-fouling formation and growth can significantly alter the surfaces of most structures, systems, or equipment designed to operate in the marine environment. Many effective anti-fouling solutions have been developed over the years, but in the past, these have mainly relied on paints or coatings designed to leach biocides. Environmental concerns and regulatory changes have prompted research into alternative, non-toxic anti-fouling solutions. Bio-inspired micro-scale surface modifications have gained popularity as an anti-fouling solution. Surface textures typically rely on roughness ridges arranged in arrays with spacings smaller than the dimensions of fouling species to prevent organisms from forming secure attachments to the substrate. Although this has proven effective at limiting bio-fouling settlement under static conditions, below a certain spacing, narrow gaps can also be expected to prevent hydrodynamic stresses from reaching initial settlement sites on surfaces. This work attempts to examine how the size of texture gaps affects the turbulent flow above and within textures, with the implication of disrupting the early stage of fouling settlement, which could result in minimizing fouling settlement.
This research has relied on high-fidelity Large Eddy Simulations to model turbulent flow within and above five sets of bio-inspired texture models. The spacing scales were chosen to mimic spacing gaps observed on the growth rings of the brill fish Scophthalmus rhombus. Local and high-order turbulent correlations ranging from second to fourth order have been used to analyse the turbulent stresses forming within and above textures. Furthermore, A bio-fouling organism model placed at three locations within and above a candidate texture was used to assess the impact
of the textures on hydrodynamic forces acting on the organism. The arrangement of textures was observed to significantly affect turbulent flow by altering the distribution of Reynolds and dispersive stress within them, potentially leading to the disruption of fouling settlements. Furthermore, the analysis of hydrodynamically exerted forces on the organism at various locations of candidate textures showed that areas with elevated dispersive stress intensity, particularly at the rear side of textures, could lead to a 60% stream-wise force acting on the organism. Moreover, additional examination revealed that dispersive stresses primarily influence mean hydrodynamic forces, whereas the role of Reynolds stresses is to adjust the fluctuations in forces acting on an organism. This shows the importance of the textures arrangements to minimize biofouling settlements by maximizing the hydrodynamic forces exerted on organisms.