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.

Drag Reduction by Microvortexes in Transverse Microgrooves

“…For some complex problems, it is difficult to present the analytical solutions and numerical simulation is a kind of effective method [15,16]. Here, the numerical simulation was chosen to study the boundary layer structure when liquid flows over the transverse microgrooved surface.…”

“…The grid spacing increased from the walls by aspect ratio of less than 1.1 to get a structured mesh. A renormalized group (RNG) -model, which had an additional term in its equation that significantly improves the accuracy [15], was used for turbulence modeling [15,16]. An implicit solution scheme was used in combination with an algebraic multigrid method to achieve faster convergence.…”

Analysis of the influence of transverse groove structure on the flow of a flat-plate surface based on Liutex parameters

“…Lang et al (2017) reported the same mechanism and stated that the variation in the boundary layer in the trench basin weakened the low-velocity band and delayed the flow separation. Moreover, Ranjan et al (2011) suggested that reducing the distance between the two grooves reduces the overall effect of the grooves and impacts the overshoot and undershoot of the fluid. In the laminar sublayer, the average velocity and turbulence intensity does not significantly differ between the smooth and groove walls.…”