Active fluids are intrinsically out-of-equilibrium systems due to the internal energy injection of the active constituents. We show here that a transition from a motion-less isotropic state towards a flowing polar one can be possibly driven by the sole active injection through the action of polar-hydrodynamic interactions in absence of an ad hoc free energy which favors the development of an ordered phase. In particular, we propose an analytical argument and we perform lattice Boltzmann simulations where the appearance of large temporal fluctuations in the polar fraction of the system is observed at the transition point. We show that elastic absorption plays a relevant role in energy transfer dynamics, contrary to the case of the usual active gel theory where this term can be factually neglected.

由于活性成分的内部能量注入，活性流体本质上是不平衡的系统。我们在这里表明，从无运动的各向同性状态到流动的极性状态的转变可能是由唯一的主动注入通过极性 - 流体动力学相互作用的作用驱动的，而没有特别的自由能，这有利于有序的发展阶段。特别是，我们提出了一个分析论点，并进行了晶格玻尔兹曼模拟，其中在过渡点观察到系统极性部分出现大的时间波动。我们表明弹性吸收在能量转移动力学中起着相关作用，这与通常的活性凝胶理论的情况相反，该理论实际上可以忽略该术语。