Turbulent boundary layers over rod- and cube-roughened walls

Statistics of the turbulent boundary layers over 3D cube-roughened walls

“…The properties of the near-wall statistics for the 2D rod were consistent with previous studies of turbulent channel flows involving 2D transverse square bars (Cui et al, 2003;Leonardi et al, 2003;Orlandi and Leonardi, 2008). Lee et al (2012) inferred that because the actual streamwise spacing was identical in the surfaces with 2D and 3D roughness due to the staggered array of the cube roughness, the important parameter affecting the near-wall friction statistics was the streamwise spacing; however, the 3D cube study performed by Lee et al (2012) provided results that differed from the results reported in previous study of the 3D cube-roughened channel flow (Leonardi and Castro, 2010). Leonardi and Castro (2010) performed direct numerical simulations (DNSs) of channel flows with large cube roughness (k/h = 0.125) to examine the dependence of the turbulent statistics on the area density.…”

“…Lee et al (2011) presumed that the failure of the wall-similarity could be attributed to the regularized roughness array with a square-shaped plane and a long streamwise spacing, which would be sufficient to significantly disrupt the structures, although the roughness effects of the 3D cube were less significant than those of the 2D rod. Lee et al (2012) recently attempted to observe the effects of the streamwise spacing on the turbulence statistics, both in the nearwall region and in the outer layer, for 2D rods and 3D cubes. They varied the streamwise spacing over the values p x /k = 2, 3, 4, 6, 8, and 10, while holding the spanwise spacing fixed, at the value used in the previous study (p z /k = 2).…”

Effect of upstream flow regime on street canyon flow mean turbulence statistics

“…Similarly, the friction velocity and shear stress (normalized by the freestream velocity) were found to increase from 2D to 3D configurations throughout the boundary layer by Volino et al [35]. Lee et al [17] found a similar trend when the streamwise spacing of roughness elements was smaller than 5h but the opposite when the spacing increases. No clear information about the influence of λp was given.…”

“…The influence of varying the roughness geometry on the turbulence integral length scales was also investigated. Volino et al [35] and Lee et al [16,17] found that this change of geometry has a strong influence, with larger length scales above the roughness for 2D cases than 3D cases [35], but Takimoto et al [34] show no consistent variation of integral length scales between the 2D and 3D cases. Of the studies presented here, Volino et al [35] makes the most definitive conclusions concerning integral length scales.…”

Transition of Turbulent Boundary Layer with a Step Change from Smooth to Rough Surface

“…3) 새로운 표면조도를 만난 유동은 천이 과정을 거치면 서 평형상태에 도달하게 되는데, 새로운 평형상태에 도달 하기 위해서는 유동이 주 유동 방향으로 충분히 발달 할 수 있도록 긴 도메인이 필요하며, 필요한 도메인 길이는 하류의 표면조도에 의해 영향을 받는다 (6,7) .…”