Riblet Performance Evaluation Using Diameter-Adapted Reference Models in Pipe Flow

This paper presents the Riblet benefit evaluation in pipe flow using a diameter-adaptable test bench setup. The aim is to quantify drag reduction of trapezoidal Riblets by comparing measurements against validated smooth pipe references. Smooth pipe measurements across multiple diameters have been used to generate a generalized approximation curve, enabling the comparison of riblet measurements against a reference of any desired diameter. This capability allows precise evaluation of the riblet benefit in terms of drag reduction and the s⁺ value. Both foil and laser-manufactured riblet structures were tested and show promising reductions in friction, highlighting the influence of manufacturing technique and the importance of diameter-specific reference corrections.