AN EXPERIMENTAL-OBSERVATION OF LOW-DIMENSIONAL DYNAMICS IN AN OPEN-CHANNEL FLOW

We present the results of an experimental study of dynamical phenomena in the fluid flow through a symmetric nominally two-dimensional chann el expansion. The particular phenomena of interest are observed as a r esult of modulating the flow rate through the system. In the absence o f modulation, the flow downstream of the expansion is found to be stea dy at low Reynolds numbers. It then loses stability to a high-dimensio nal dynamical state for Reynolds numbers above a critical value. Howev er, when a small periodic modulation is added to the flow rate new low -dimensional dynamical phenomena emerge. In some parameter ranges this novel temporal behavior arises at Reynolds numbers below those at whi ch the transition to irregular fluid flow occurs in the unforced syste m. In other regions of parameter space the low-dimensional dynamics su ppress the irregular flow of the unforced system. Moreover, the dynami cs are organized by the underlying solution structure and show evidenc e for a subharmonic resonance, quasiperiodicity, and homoclinicity. (C ) 1995 American Institute of Physics.