Friction drag measurements in turbulent wall flows

Results of an experimental investigation devoted to the assessment of methodologies aimed at the friction drag measurement in turbulent wall flows are presented. Two techniques for local measurements have been developed. Namely, different versions of the velocity profile method have been used for a turbulent boundary layer developing on a flat plate. The oil flow interferometer has been arranged and results related with measurements performed in a fully developed turbulent channel flow and in the turbulent boundary layer are presented. Moreover a balance based on a floating-buoyancy system finalized to the integral measurement of the friction force acting on the flat plate is presented. The results of the three techniques are compared considering as a reference a well assessed empirical law. Good level of measurement accuracy using the balance has been evidenced highlighting the capability of the balance or the characterization of micro-grooved surfaces addressed for friction drag reduction applications.