Identifying the pattern of breakdown in a laminar-turbulent transition via binary sequence statistics and cellular-automaton simulations

: The laminar-turbulent transition induced by two-dimensional steplike roughness is investigated focusing on the pattern of breakdown. The statistics of the turbulent burst rate is found to be significantly different from the prediction of the classical theory. A systematic investigation of the pattern of breakdown is motivated by this phenomenon. It is identified with heuristic analysis that a pattern of distributed breakdown is responsible for the deviation, in contrast to the concentrated breakdown hypothesis in the classical theory. The pattern indicates that the steps probably induced a bypass transition in present experimental setup, which is different from the current understanding about the step-induced transition. Cellular-automaton simulations are carried out to validate the heuristic analysis. The influences of quasiconcentration and non-Poisson process in spot generation on the breakdown statistics are also discussed based on the simulation results.