A computational Preston tube method

A computational Preston tube method to determine local wall friction forces is presented, which unlike the conventional Preston tube method offers a greater scope of application. The method is based on measuring the dynamic pressures of two wall-Pitot tubes of different diameters and determining the local wall shear stress by applying a mathematical boundary-layer law to the flow velocities corresponding to the measured dynamic pressures. The method is verified experimentally in a laminar-turbulent transition flow of a flat plate, in a pipe entrance flow, in a turbulent pipe flow with sudden enlargement, in strongly non-adiabatic turbulent boundary-layer flows and in turbulent boundary-layer flows with adverse pressure gradient.