Experiments with Fluid Friction in Roughened Pipes

摘要: Nikuradse (1933; Prandtl 1933), experimenting with pipes roughened internally by a uniform layer of sand, found that such were indistinguishable from perfectly smooth ones, provided the pressure gradient was less than given pV*k / μ = 4, where V √( T p ), shear stress at wall, density fluid, , —- viscosity k diameter roughness grains. With lesser flows neither resistance nor distribution velocity measurably influenced size grains, and observed law satisfactorily type required Karman-Prandtl theory for surfaces. This is usually expressed in following form: