Numerical Investigation of Instability and Transition in an Obstructed Channel Flow

Instability and transition in an obstructed channel are investigated using direct numerical simulation. Flow geometry under consideration is a plane channel with two-dimensional thin obstacles ("baffles") mounted symmetrically in the vertical direction and periodically in the streamwise direction. The flow undergoes a Hopf bifurcation as the Reynolds number increases, leading to an unsteady periodic solution. At high Reynolds numbers, the unsteady flow exhibits a symmetry-breaking bifurcation. A secondary instability is also observed at high Reynolds numbers, which is believed to be responsible for subsequent chaotic breakdown of the flow. To study the secondary instability, we consider an unsteady periodic solution which results from the Hopf bifurcation as a basic flow. Depending on the Reynolds number, the basic flow becomes unstable to three-dimensi onal disturbances, which results in a chaotic flow. Numerical results obtained are consistent with experimental findings currently available.