Videos of decaying turbulent secondary motions

We produce videos of turbulent secondary motions of different sizes as they decay starting from a statistically steady condition. The secondary motions are generated by adding some strip-type roughness to the walls of a channel flow; strip type roughness consists in spanwise-alternating streamwise-elongated strips of smooth and rough wall. The size of the induced motions can be controlled by adjusting the width s shared by smooth and rough strips. Once the secondary motions reach a statistically-steady state, the strip-type roughness is removed; the system evolves towards a spanwise-homogeneous statistically-steady state and the secondary motions decay. The procedure is repeated several times for each value of s to enable the calculation of the ensemble-averaged decay.