Numerical Simulation of Blade-Shaped Riblets Using LES-Based Methods

Abstract

Passive flow control techniques are widely implemented in many areas of fluid mechanics and aerodynamics, aiming at permanently altering the flow field to suppress undesired phenomena or enhance performance. Among many passive flow control techniques proposed for aeronautical applications, the microgroove geometries called riblets are especially promising in reducing an aircraft’s skin friction drag by altering the boundary layer characteristics in the near-the-wall region. In the present study, various blade-shaped riblets designed for application on an Unmanned Aerial Vehicle (UAV), are examined and evaluated through both Large Eddy Simulations (LES), as well as hybrid Embedded LES (ELES) computations. The different riblet geometries are simulated at zero-pressure gradient flow, their drag-reducing potential is identified, and their near-wall behaviour is examined. The use of ELES as a simulation method for riblet simulation is also evaluated. Concludingly, the riblets with equal width-to-height ratio ( ?? h =1) demonstrate the best drag reducing results, while those with the largest width ( ?? h =2) exhibit very poor performance and exceptionally high wall shear stresses. Finally, the hybrid ELES simulations are quantitatively similar with those performed using purely LES but result in higher absolute drag force values, due to the RANS-LES interface interference with the flow development.