Computational analysis of frictional drag over transverse grooved flat plates

Abstract

Skin-friction coefficient of turbulent boundary layer flow over a smooth-wall with transverse square grooves is investigated for four grooved-wall cases. The four grooved-wall configurations is like‘d’ type rough wall, which is characterized by regularly spaced two-dimensional square cavities (grooves) placed normal to the flow. This is made up of 5 mm square grooved-wall, where square grooves are spaced 10, 20 and 40 element widths apart in the streamwise direction. A commercial CFD code-‘Fluent 6.3’ is used for the mean velocity and turbulence intensity calculation. Hexahedral meshing is used to mesh the domain, with the first grid point placed at a height of 0.001 mm till the dimensionless wall distance, y+ = 10 and afterwards the grid spacing was increased by aspect ratio of 1.1 to get a structured mesh. A steady state renormalized group (RNG) k-ε model is used for turbulence modeling with non-equilibrium wall functions for near wall treatment. CFD code is validated against the experimental data reported by Stuardi and Ching. The skin-friction coefficient determined from the velocity profile increases sharply just downstream of the groove. This overshoot is followed by an undershoot and then relaxation back to the smooth-wall value. This behavior is observed in most grooved-wall cases. Integrating the skin-friction coefficient in the streamwise direction indicates that there is an increase in the overall drag with maximum to be 3.54% for the single groove case.

Keywords: Turbulent boundary layer, transverse groove, skin-friction, drag reduction, computational fluid dynamics (CFD).