Bifurcation phenomena in the flow through a sudden expansion in a circular pipe

We report the results of an experimental investigation of laminar and time-dependent flows through a sudden expansion in a circular pipe. The flow state was investigated using high resolution MRI imaging techniques which have allowed us to settle a long standing debate on the first instability that occurs. As \textit{Re} is increased, the flow passes through a steady symmetry breaking bifurcation such that the position of the recirculating eddy becomes asymmetric within the pipe. This in turn gives way to simple periodic motion via a Hopf bifurcation with further increase in \textit{Re}.