Direct numerical simulation of turbulent duct flow with inclined or V-shaped ribs mounted on one wall

Abstract

In this research, highly disturbed turbulent flow of distinct three-dimensional characteristics in a square duct with inclined or V-shaped ribs mounted on one wall is investigated using direct numerical simulation. The turbulence field is highly sensitive to not only the rib geometry but also the boundary layers developed over the side and top walls. In a cross-stream plane secondary flows appear as large longitudinal vortices in both inclined and V-shaped rib cases due to the confinement of four sidewalls of the square duct. However, owing to the difference in the pattern of cross-stream secondary flow motions, the flow physics is significantly different in these two ribbed duct cases. It is observed that the mean flow structures in the cross-stream directions are asymmetrical in the inclined rib case but symmetrical in the V-shaped rib case, causing substantial differences in the momentum transfer across the spanwise direction. The impacts of rib geometry on near-wall turbulence structures are investigated using vortex identifiers, joint probability density functions between the streamwise and vertical velocity fluctuations, statistical moments of different orders, spatial two-point autocorrelations and velocity spectra. It is found that near the leeward and windward rib faces, the mean inclination angle of turbulence structures in the V-shaped rib case is greater than that of the inclined rib case, which subsequently enhances momentum transport between the ribbed bottom wall and the smooth top wall.

Direct Numerical Simulation of Thermal Turbulent Boundary Layer Flow over Multiple V-Shaped Ribs at Different Angles

“…Much attention has been devoted to conventional roughness, such as 2D rib-roughened surfaces. Mahmoodi and Wang [13] studied the turbulence on V-shaped and inclined ribs in a square duct and observed distinct mean and secondary flow structures. The pressure drag in the V-shaped rib case was nearly twice that of the inclined rib at a matched Reynolds number.…”

“…Additional parameters, such as wavelength and rib angle, also have significant impacts. Previous studies on V-shaped ribbed walls have primarily focused on the spatial distribution of mean and high-order flow statistics [13,14]. To the best of the authors' knowledge, less attention has been paid to secondary motion and its influence on the drag coefficient and Stanton number, as well as its influence on the local Reynolds analogy factor in thermal turbulent boundary layer flow.…”