Simulation of head-tail biofilm streamer growth based on immersed boundary method.

Biofilms are subjected to various forces in the fluid field, as a result, the biofilm forms a head-tail structure known as a streamer to reduce pressure differential resistance. To characterize biofilm growth in fluid, we establish a head-tail biofilm streamer growth model based on the immersed boundary method using MATLAB software, and simulate streamer growth in various environmental conditions to explore the factors affecting its growth. Firstly, we found that a higher flow velocity makes the streamer grow faster and thereby produce more biomass. Secondly, we explored the effect of the position of nutrient source on the streamer growth, found that when the nutrient source overlaps with the streamer, its length is longer than when the nutrient source and the streamer are mismatched. Further we found that the Young's modulus of the streamer also influences its growth length. Streamers with small Young's modulus were more likely to deform, making them grow longer than the streamers with large Young's modulus. Finally, we determined the relationship between the tail length and the head diameter of the streamer through mechanical analysis, and found that there is an optimal ratio of the tail length to the head diameter which exposes the streamer to the minimum drag in the fluid field.