Transition mechanisms of pulsatile flow in a constricted channel

Physical mechanisms based on the energy variation of two-dimensional modes are proposed for a pulsatile flow in a constricted channel with 50% occlusion. Floquet stability analysis and direct numerical simulations are carried out to explain the transition mechanisms observed in this system. This system is characterized by two distinct states; the first state lies in a two-dimensional space and the second in a three-dimensional space. When a three-dimensional nonlinear simulation is seeded with a two-dimensional base flow and an infinitesimal perturbation, there is energy transfer from the three-dimensional modes to the two-dimensional mode, such that the energy of the latter slightly increases and the three-dimensional modes go to zero, leading the system to its unconstrained state. In addition, the base flow behaviour follows the energy variation of the two-dimensional modes with Reynolds number. Thus, base flow changes occur when the Reynolds number is increased, even after the primary instability. Besides that, the two-dimensional modes go through an energy minimum in this process which lead the system to a different dynamic.