L. Chan

A fast direct numerical simulation method for characterising hydraulic roughness

We describe a fast direct numerical simulation (DNS) method that promises to directly characterise the hydraulic roughness of any given rough surface, from the hydraulically smooth to the fully rough regime. The method circumvents the unfavourable computational cost associated with simulating high-Reynolds-number flows by employing minimal-span channels (Jimenez & Moin 1991). Proof-of-concept simulations demonstrate that flows in minimal-span channels are sufficient for capturing the downward velocity shift, that is, the Hama roughness function, predicted by flows in full-span channels. We consider two sets of simulations, first with modelled roughness imposed by body forces, and second with explicit roughness described by roughness-conforming grids. Owing to the minimal cost, we are able to conduct DNSs with increasing roughness Reynolds numbers while maintaining a fixed blockage ratio, as is typical in full-scale applications. The present method promises a practical, fast and accurate tool for characterising hydraulic resistance directly from profilometry data of rough surfaces.

Turbulent flow over transitionally rough surfaces with varying roughness densities

We investigate rough-wall turbulent flows through direct numerical simulations of flow over three-dimensional transitionally rough sinusoidal surfaces. The roughness Reynolds number is fixed at

The minimal-span channel for rough-wall turbulent flows

k^+=10

The minimal channel: a fast and direct method for characterising roughness

, where

A systematic investigation of roughness height and wavelength in turbulent pipe flow in the transitionally rough regime

k

Investigation of the Flow Structures in Supersonic Free and Impinging Jet Flows

is the sinusoidal semi-amplitude, and the sinusoidal wavelength is varied, resulting in the roughness solidity,

Large eddy simulation and Reynolds-averaged Navier-Stokes calculations of supersonic impinging jets at varying nozzle-to-wall distances and impinging angles

\Lambda

Numerical simulation of a rough-wall pipe from the transitionally rough regime to the fully rough regime

(frontal area divided by plan area) ranging from 0.05 to 0.54. The high cost of resolving both the flow around the dense roughness elements and the bulk flow is circumvented by the use of the minimal-span channel technique, recently demonstrated by Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) to accurately determine the Hama roughness function,

Numerical simulation of supersonic impinging jet flows using Reynolds averaged Navier-Stokes and Large Eddy Simulation

\Delta U^+

Direct numerical simulation of pulsatile flow in pipes

. Good agreement of the second-order statistics in the near-wall roughness-affected region between minimal- and full-span rough-wall channels is observed. In the sparse regime of roughness (