caa a22 4500 606198725 CHVBK 20210128100935.0 cr unu---uuuuu 210128e20150501xx s 000 0 eng 10.1007/s00348-015-1978-7 doi (NATIONALLICENCE)springer-10.1007/s00348-015-1978-7 Turbulent Taylor-Couette flow over riblets: drag reduction and the effect of bulk fluid rotation [Elektronische Daten] [A. Greidanus, R. Delfos, S. Tokgoz, J. Westerweel] A Taylor-Couette facility was used to measure the drag reduction of a riblet surface on the inner cylinder. The drag on the surfaces of the inner and outer cylinders is determined from the measured torque when the cylinders are in exact counter-rotation. The three velocity components in the instantaneous flow field were obtained by tomographic PIV and indicate that the friction coefficients are strongly influenced by the flow regimes and structures. The riblet surface changes the friction at the inner-cylinder wall, which generates an average bulk fluid rotation. A simple model is proposed to distinguish drag changes due to the rotation effect and the riblet effect, as a function of the measured drag change $$\Delta \tau _w/\tau _{w,0}$$ Δ τ w / τ w , 0 and shear Reynolds number $$Re_{\rm s}$$ R e s . An uncorrected maximum drag reduction of 5.3% was found at $$Re_{\rm s}=4.7 \times 10^4$$ R e s = 4.7 × 10 4 that corresponds to riblet spacing Reynolds number $$s^+=14$$ s + = 14 . For these conditions, the model predicts an azimuthal bulk velocity shift of 1.4%, which is confirmed by PIV measurements. This shift indicates a drag change due to a rotation effect of −1.9%, resulting in a net maximum drag reduction of 3.4%. The results correspond well with earlier reported results and demonstrate that the Taylor-Couette facility is a suitable and accurate measurement tool to characterize the drag performance of surfaces. The Author(s), 2015 Greidanus A. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut Delfos R. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut Tokgoz S. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut Westerweel J. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut Experiments in Fluids Springer Berlin Heidelberg 56/5(2015-05-01), 1-13 0723-4864 56:5<1 2015 56 348 https://doi.org/10.1007/s00348-015-1978-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-1978-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Greidanus A. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut NATIONALLICENCE 700 1- Delfos R. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut NATIONALLICENCE 700 1- Tokgoz S. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut NATIONALLICENCE 700 1- Westerweel J. Laboratory for Aero and Hydrodynamics, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/5(2015-05-01), 1-13 0723-4864 56:5<1 2015 56 348