S. Hijazi - School of Engineering, Emirates Aviation University, Dubai, United Arab Emirates
E. Tolouei - School of Engineering, Emirates Aviation University, Dubai, United Arab Emirates

Skin friction drag can be reduced through the application of bio-inspired riblet surfaces. Numerical simulations were performed using Large Eddy Simulation (LES) to investigate the effect of using riblets on reducing skin friction drag. In this study, three different riblet configurations were used; scalloped, sawtooth and a new design, hybrid, riblet. To validate the effect of using the proposed hybrid riblet design compared with other riblets used in the literature; before applying to complex geometries, they were initially applied to a flat plate in parallel arrangement. Results showed skin friction coefficient reduction of ۱۴% using the proposed hybrid riblet. This reduction was ۹.۲ times and ۱.۲ times more compared to sawtooth and scalloped configurations, respectively. The hybrid riblet was then applied partially and fully to NACA ۰۰۱۲ airfoil. Skin friction coefficient reduction of ۳۴.۵% was obtained when the hybrid riblet fully applied on the airfoil surface. Furthermore, the Convergent-Divergent (C-D) arrangement was studied, where the riblets were placed fully on the NACA ۰۰۱۲ and aligned with a yaw angle with respect to the flow direction. The convergent lines are inspired by the sensory part of the shark skin, whereas the divergent lines or herringbone are found on the bird feather. The two different riblet configurations, sawtooth and hybrid were modeled with the C-D arrangement and the hybrid riblet with C-D arrangement contributed to higher skin friction coefficient reduction, ۳۴.۵%, than the sawtooth riblet shape, ۲۶.۷۵%. Moreover, the C-D arrangement was compared to the parallel arrangement and shown that the C-D arrangement increased the lift coefficient (cl) of the airfoil, the flow separation was delayed and the overall performance of the airfoil was enhanced.

Computational fluid dynamics, Large eddy simulation, Riblets, Drag reduction, Aerodynamic efficiency NACA۰۰۱۲