Turbulent Boundary Layers on Wire-Screen Roughnesses

抄録

Experiments were carried out on the boundary layer along plates artificially roughened by both wire-screens and also by sand. The flow was incompressible with zero pressure gradient, in the range of 2.3×10³<Uθ/v<1.2×10⁴ and 3.0×10<ku_*/v<2.0×10², where k is the height of roughness element. The velocity defect profiles (U-u)/u_* vs. yu_*/δ_*U for all types of walls were on a single curve within the experimental scatter but the logarithmic line for the rough plate lied slightly above that for the smooth plate. The effect of wire-screen roughness depends only on the pitch to diameter ratio, t/d. Experimental formula for equivalent sand roughness is given as a function of t/d. It is found that the experimental values of wall shearing stress and boundary layer thickness agree well with the present theories.