Evolution of wall shear stress with Reynolds number in fully developed turbulent channel flow experiments

The Reynolds-number-dependence of wall shear stress (tau(w)) in fully developed, high-aspect-ratio turbulent channel flow is experimentally studied over the range of 230 Re-tau <= 950. The principal conclusion of the present work is that beyond Re-tau similar to 600, the wall shear stress evolves to an asymptotic state in which the statistical moments, probability density function, and power spectra of tau(w) become independent of Reynolds number. In this state, the turbulent intensity, skewness and kurtosis of the wall shear stress take on values that are slightly larger than those previously measured, because prior estimates of these quantities did not resolve the full range of wall shear stress fluctuations, which extended beyond 10 standard deviations above the mean. For Re-tau greater than or similar to 600, the spectra of tau(w) were found to collapse very well when using a wall-unit-based normalization, providing further evidence of an asymptotic state of the wall shear stress at large Reynolds numbers.