The phase-locked mean impulse response of a turbulent channel flow
  We describe the first DNS-based measurement of the complete mean response of a turbulent channel flow to small external disturbances. Space-time impulsive perturbations are applied at one channel wall, and the linear response describes their mean effect on the flow field as a function of spatial and temporal separations. The turbulent response is shown to differ from the response a laminar flow with the turbulent mean velocity profile as base flow. 
Paolo Luchini, Maurizio Quadrio and Simone Zuccher