Sheared bioconvection in a horizontal tube.
Sheared bioconvection in a horizontal tube.
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水平管中的剪切生物对流。
DOI：
10.1088/1478-3975/7/4/046001
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发表时间：
2010
期刊：
影响因子：
2
通讯作者：
Croze OA
中科院分区：
文献类型：
--
作者：
Croze OA
最近的兴趣在使用微生物的生物燃料是动机足以研究生物对流和细胞分散管受强制流。为了优化光和营养吸收，许多微生物在环境线索（例如藻类的趋光性和细菌的趋化性）的偏向下游泳。这样的税收不可避免地导致细胞的积累，由于许多微生物具有与流体不同的密度，这可以引起流体动力学不稳定性。大规模的流体流动和壮观的模式出现被称为生物对流。然而，在何种程度上生物对流的影响或抑制所施加的流体流动和生物对流如何影响的平均流量分布和细胞运输是悬而未决的问题。这项实验研究是第一个解决这些问题的定量模式，由于悬浮液的重力和gyrotactic绿色双鞭藻Chlamyphora在水平管受到一个强加的流量。在没有流动的情况下，对于三种不同的管直径，建立了图案开始时的主导图案波长对细胞浓度的依赖性。对于小的强制流动，观察到的垂直羽流的细胞只是在流动的方向弓。对于足够高的流速，羽流逐渐分裂成分段线性对角羽流，意外地以恒定角度倾斜并以固定速度平移。图案波长通常随着流速而增长，其中临界速率处的转变取决于浓度。即使在高施加的流速下，生物对流也没有完全被抑制并且扰动流场。
The recent interest in using microorganisms for biofuels is motivation enough to study bioconvection and cell dispersion in tubes subject to imposed flow. To optimize light and nutrient uptake, many microorganisms swim in directions biased by environmental cues (eg phototaxis in algae and chemotaxis in bacteria). Such taxes inevitably lead to accumulations of cells, which, as many microorganisms have a density different to the fluid, can induce hydrodynamic instabilites. The large-scale fluid flow and spectacular patterns that arise are termed bioconvection. However, the extent to which bioconvection is affected or suppressed by an imposed fluid flow and how bioconvection influences the mean flow profile and cell transport are open questions. This experimental study is the first to address these issues by quantifying the patterns due to suspensions of the gravitactic and gyrotactic green biflagellate alga Chlamydomonas in horizontal tubes subject to an imposed flow. With no flow, the dependence of the dominant pattern wavelength at pattern onset on cell concentration is established for three different tube diameters. For small imposed flows, the vertical plumes of cells are observed merely to bow in the direction of flow. For sufficiently high flow rates, the plumes progressively fragment into piecewise linear diagonal plumes, unexpectedly inclined at constant angles and translating at fixed speeds. The pattern wavelength generally grows with flow rate, with transitions at critical rates that depend on concentration. Even at high imposed flow rates, bioconvection is not wholly suppressed and perturbs the flow field.