DNS and LES of turbulent flow in a closed channel featuring a pattern of hemispherical roughness elements

Journal Article · Fri Mar 06 00:00:00 EST 2015 · International Journal of Heat and Fluid Flow

DOI:https://doi.org/10.1016/j.ijheatfluidflow.2015.01.002· OSTI ID:1565297

Chatzikyriakou, D. ^[1]; Buongiorno, J. ^[1]; Caviezel, D. ^[2]; Lakehal, D. ^[3]

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1. Massachusetts Inst. of Technology, Cambridge, MA (United States)
2. ASCOMP, Zurich (Switzerland)
3. Massachusetts Inst. of Technology, Cambridge, MA (United States); ASCOMP, Zurich (Switzerland)

Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) were performed for fully-developed turbulent flow in channels with smooth walls and walls featuring hemispherical roughness elements at shear Reynolds numbers Re$$_τ$$ = 180 and 400, with the goal of studying the effect of these roughness elements on the wall-layer structure and on the friction factor. The LES and DNS approaches were verified first by comparison with existing DNS databases for smooth walls. Then, a parametric study for the hemispherical roughness elements was conducted, including the effects of shear Reynolds number, normalized roughness height (k⁺ = 10–20) and relative roughness spacing (s⁺/k⁺ = 2–6). The sensitivity study also included the effect of distribution pattern (regular square lattice vs. random pattern) of the roughness elements on the walls. The hemispherical roughness elements generate turbulence, thus increasing the friction factor with respect to the smooth-wall case, and causing a downward shift in the mean velocity profiles. The simulations revealed that the friction factor decreases with increasing Reynolds number and roughness spacing, and increases strongly with increasing roughness height. The effect of random element distribution on friction factor and mean velocities is however weak. In all cases, there is a clear cut between the inner layer near the wall, which is affected by the presence of the roughness elements, and the outer layer, which remains relatively unaffected. The study reveals that the presence of roughness elements of this shape promotes locally the instantaneous flow motion in the lateral direction in the wall layer, causing a transfer of energy from the streamwise Reynolds stress to the lateral component. Finally, the study indicates also that the coherent structures developing in the wall layer are rather similar to the smooth case but are lifted up by almost a constant wall-unit shift y⁺ (~10–15), which, interestingly, corresponds to the relative roughness k⁺ = 10.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF)
• Sponsoring Organization: USDOE Office of Science (SC)
• OSTI ID: 1565297
• Alternate ID(s): OSTI ID: 22460127; OSTI ID: 1365591; OSTI ID: 1565296
• Journal Information: International Journal of Heat and Fluid Flow, Journal Name: International Journal of Heat and Fluid Flow Journal Issue: C Vol. 53; ISSN 0142-727X
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
DNS
LES
engineering
mechanics
roughness elements
thermodynamics
turbulent flow