The decay of the flow in the end region of a suddenly blocked pipe

We consider the decay to rest of initially laminar flow within the end region of a suddenly blocked pipe. Here the flow is dominated by two temporally developing boundary layers, one on the pipe wall and one located at the blockage. The evolution and interaction of these boundary layers contributes to the creation and annihilation of toroidal vortices in the end-region flow, the number and extent growing with increasing Reynolds numbers. For larger Reynolds numbers, these nonlinear vortices delay the decay process within the end region, decaying at a slower rate than flow far downstream of the blockage. Our numerical simulations for pre-blockage Reynolds numbers up to 3000 indicate that the flow in this end region is stable to axisymmetric disturbances.