A Time-Periodic Bifurcation Theorem and its Application to Navier-Stokes Flow Past an Obstacle

We show an abstract time-periodic bifurcation theorem in Banach spaces. The key point as well as the novelty of the method is to split the original evolution equation into two different coupled equations, one for the time-average of the sought solution and the other for the "purely periodic" component. This approach may be particularly useful in studying physical phenomena occurring in unbounded spatial regions. Actually, we furnish a significant application of the theorem, by providing sufficient conditions for time-periodic bifurcation from a steady-state flow of a Navier-Stokes liquid past a three-dimensional obstacle.