Periodic turbulent strips and calmed regions in a transitional boundary layer

The evolution of the spot calmed region and its erosion in a turbulent boundary layer is discussed. Results of experiments simulating wake boundary layer interactions in turbomachines are presented. A train of turbulent strips generated upstream of a steady flow transition region can reduce the average intermittency to about half its value downstream of the steady transition location. Periods of laminar flow were maintained in an otherwise turbulent environment. The calm region is eroded inside the turbulent boundary layer, probably by the generation of its new spots inside it. Simple kinematics modeling of the described phenomena is capable of reproducing most of the measured events that are relevant to transition delay in turbomachines.