## DIRECT NUMERICAL SIMULATIONS OF TURBULENT BOUNDARY LAYERS OVER SQUARE-EDGED 2-D AND 3-D ROUGH WALLS
## ResumoDirect numerical simulations (DNSs) of spatially
developing turbulent boundary layers (TBLs) over two-dimensional
(2-D) rod- and three-dimensional (3-D) cube-roughened
walls were performed to see the roughness
effects on the properties of TBL. The 2-D and 3-D
roughness were periodically arranged in the downstream
direction with pitches of p = 2 with
staggered array, where _{z}/kp and _{x}p are the streamwise and
spanwise spacings of the roughness and_{z} k is the roughness
height. Inspection of the Reynolds stresses showed that
except for p = 2 and 3 over the 2-D rough walls, the effects
of the surface roughness extend to the outer layer over the
2-D and 3-D rough walls and the magnitude of the Reynolds
stresses in the outer layer is increased in proportion to _{x}/kp.
The consistent results were observed in the behavior of
wall-normal fluctuations ( _{x}/kν_{w}^{+} ) on the crest of the roughness
suggested by Orlandi & Leonardi (2008), indicating that ν_{w}^{+}
might be a suitable parameter to predict the influence of the
surface roughness in the outer layer over the square-edged
rough walls. However, such results are contrary to the
trends of the form drag, roughness function and roughness
length against p, which showed the maximum values at
_{x}/kp = 8 and 4 over the 2-D and 3-D rough walls respectively._{x}/k |

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