In the turbulent boundary layer above a flat plate, the velocity profile is known to have the form v =v0[(1/κ)ln z+const]. The distance from the wall in dimensionless units is z and v0 is a uniquely defined velocity scale. The number κ is universal, and measurements over several decades have shown that it is nearly 0.42. We use a randomly stirred model of turbulence to derive the above law and find κ=√108/125π≃0.52
