Streamwise turbulence intensity formulation for flat-plate boundary layers

A similarity formulation is proposed to describe the streamwise turbulence intensity across the entire smooth-wall zero-pressure-gradient turbulent boundary layer. The formulation is an extension of the Marusic, Uddin, and Perry [Phys. Fluids 9, 3718 (1997)] formulation that was restricted to the outer region of the boundary layer, including the logarithmic region. The new formulation is found to agree very well with experimental data over a large range of Reynolds numbers varying from laboratory to atmospheric flows. The formulation is founded on physical arguments based on the attached eddy hypothesis, and suggests that the boundary layer changes significantly with Reynolds number, with an outer flow influence felt all the way down to the viscous sublayer. The formulation may also be used to explain why the empirical mixed scaling of DeGraaff and Eaton [J. Fluid Mech. 422, 319 (2000)] appears to work.