SECONDARY INSTABILITY IN PLANE CHANNEL FLOW WITH SPATIALLY PERIODIC PERTURBATIONS

Laboratory experiments on plane channel flow with a streamwise-periodic array of cylinders reveal a bifurcation from two-dimensional traveling waves to three-dimensional spanwise standing waves. The standing waves select a wave number that is independent of the wave number imposed initially by time-periodic disturbances. The stable tertiary flow stands in contrast with most open flows where instability develops directly to turbulence.