TY  - CPAPER
AU  - MacDonald, M
AU  - Ooi, A
AU  - Hutchins, N
AU  - Chung, D
Y2  - 2020/12/07
Y1  - 2017/01/01
SN  - 9780000000002
SN  - 0022-1120
UR  - http://hdl.handle.net/11343/252860
AB  - We conduct minimal-channel direct numerical simulations of turbulent flow over two-dimensional rectangular bars aligned in the spanwise direction. This roughness has been often described as dtype, as the roughness function ΔU+ is thought to depend only on the outer-layer length scale (pipe diameter, channel half height or boundary layer thickness). This is in contrast to conventional engineering rough surfaces, named k-type, for which ΔU+ depends on the roughness height, k. The minimal-span rough-wall channel is used to circumvent the high cost of simulating high Reynolds number flows, enabling a range of bars with varying aspect ratios to be investigated. The present results show that increasing the trough-to-crest height (k) of the roughness while keeping the width between roughness bars, W, fixed in wall units, results in non-k-type behaviour. The roughness function appears to scale with W, suggesting that this is the only relevant parameter for very deep rough surfaces with k/W≥ 3. In these situations, the flow no longer has any information about how deep the roughness is and instead can only 'see' the width of the fluid gap between the bars.
T1  - Direct numerical simulation of high aspect ratio spanwise-aligned bars
DO  - 10.1017/jfm.2018.150
IS  - Journal of Fluid Mechanics
VL  - 3
SP  - 126-155
L1  - /bitstream/handle/11343/252860/139.pdf?sequence=2&isAllowed=y
ER  -