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.

Keywords: Head-tail biofilm streamer; fluid field; fluid-structure interaction; immersed boundary method.

生物膜在流场中会受到各种力的作用，结果是生物膜形成了头尾结构，称为Streamer，以减少压力差阻力。为了描述流体环境中生物膜的生长情况，我们基于浸入边界法，在MATLAB软件上建立了一个头尾生物膜Streamer生长模型，并模拟了不同环境条件下Streamer的生长过程，探讨影响其生长的因素。首先，我们发现较高的流动速度使得Streamer生长更快并产生更多的生物质。其次，我们研究了营养源位置对Streamer生长的影响，发现当营养源与Streamer重叠时，其长度比不匹配时更长。进一步地，我们还发现了Streamer的杨氏模量也会影响其增长长度，杨氏模量较小的Streamer更容易变形，因此在流场中的长度会超过杨氏模量较大的Streamer。最后，通过机械分析确定了Streamer尾部长度与头部直径之间的关系，并发现存在一个最佳的比例使得Streamer在流场中所受阻力最小。

关键词： 头尾生物膜Streamer；流体域；流固耦合；浸入边界法。