Topological defects lead to energy transfer in active nematics

Active nematics are fluids in which the components have nematic symmetry and are driven out of equilibrium due to the microscopic generation of an active stress. When the active stress is high, it drives flows in the nematic and can lead to the proliferation of topological defects, a state we refer to as defect chaos. Using numerical simulations of active nematics at low Reynolds number, we observe energy transfer from long to short length scales during defect chaos. We demonstrate that this energy transfer is driven by the exchange between variations in the orientation and degree of order in the nematic that predominantly occurs during defect creation and annihilation. We then show that the primary features of energy transfer during defect chaos scale with the active length scale. Finally, we identify a second regime that forms extended bend walls instead of point like topological defects, which we refer to as bend wall chaos. The bend walls grow and extend over the whole system and result in an energy transfer from short to long length scales.