Corrections to Taylor's Approximation from Computed Turbulent Convection Velocities

A new method for estimating the convection velocity of individual Fourier modes in turbulent shear flows is applied to numerical channels in the range Re-tau = 180-1880. Smaller scales travel at the local mean velocity, while large 'global' modes travel at a more uniform speed proportional to the bulk velocity. The modifications introduced in the energy spectrum by the use of Taylor's approximation with a wavelength-independent convection velocity are then discussed. Near the wall, it not only displaces the large-scale end of experimental spectra to shorter apparent wavelengths, but it also modifies its shape, giving rise to spurious peaks similar to those observed in some experiments. This result suggests that some of the recent challenges to the k(x)(-1) energy spectrum may have to be reconsidered.