On transition to turbulence in boundary layers

The differences between the processes of transition to turbulence in open systems (such as boundary layers, jets, and wakes) and closed systems (like Taylor-Couette flow) are discussed. Experimental measurements of the evolution of excited periodic wave trains in a boundary layer are shown to exhibit extreme sensitivity to broad-band noise, either arising naturally from the free-stream turbulence or introduced artificially with the main sinusoidal signal. This property of the nonlinear systems provides one mechanism for the onset of chaos.