Turbulent channel flow with large-amplitude velocity oscillations

Measurements in turbulent channel flow with forced oscillations covering a wide range of frequencies (ω + =0.03-0.0005) and amplitudes (10-70% of centreline velocity) are presented and discussed. Phase averages of the velocity across the flow, and of the wall shear stress , as well as the turbulent fluctuations and are obtained with LDA and hot-film techniques. The time-mean quantities, except u' 2 , are only slightly affected by the imposed oscillations whatever their frequency and amplitude. It is shown that the appropriate similarity parameter for the oscillating quantities u and τ is the non-dimensional Stokes length l g + (or the frequency ω + =2/l g +2 )