We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulen...We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulences in two or threedimensional geometries. The heterogeneity arises from a gradient of bacterial activity due to oxygen depletion along the droplet’s radial direction. Motile bacteria inject energy at individual scales, resulting in local anisotropic energy fluctuations that collectively give rise to isotropic turbulence. We find that the total kinetic energy and enstrophy decrease as distance from the drop contact line increases, due to the weakening of bacterial activity caused by oxygen depletion. While the balance between kinetic energy and enstrophy establishes a characteristic vortex scale depending on the contact angle of the sessile drop. The energy spectrum exhibits diverse scaling behaviors at large wavenumber, ranging from k-1/5to k-1,depending on the geometric confinement. Our findings demonstrate how spatial regulation of turbulence can be achieved by tuning the activity of driving units, offering insights into the dynamic behavior of living systems and the potential for controlling turbulence through gradient confinements.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12174306 and 12004308)the Natural Science Basic Research Program of Shaanxi (Grant No. 2023-JC-JQ-02)。
文摘We investigate a novel form of non-uniform living turbulence at an extremely low Reynolds number using a bacterial suspension confined within a sessile droplet. This turbulence differs from homogeneous active turbulences in two or threedimensional geometries. The heterogeneity arises from a gradient of bacterial activity due to oxygen depletion along the droplet’s radial direction. Motile bacteria inject energy at individual scales, resulting in local anisotropic energy fluctuations that collectively give rise to isotropic turbulence. We find that the total kinetic energy and enstrophy decrease as distance from the drop contact line increases, due to the weakening of bacterial activity caused by oxygen depletion. While the balance between kinetic energy and enstrophy establishes a characteristic vortex scale depending on the contact angle of the sessile drop. The energy spectrum exhibits diverse scaling behaviors at large wavenumber, ranging from k-1/5to k-1,depending on the geometric confinement. Our findings demonstrate how spatial regulation of turbulence can be achieved by tuning the activity of driving units, offering insights into the dynamic behavior of living systems and the potential for controlling turbulence through gradient confinements.
