Abstract
Direct Numerical Simulations have been performed for turbulent flow in circular pipes with smooth and corrugated walls. The numerical method, based on second-order finite discretization together with the immersed boundary technique, was validated and applied to various types of flows. The analysis is focused on the turbulence kinetic energy and its budget. Large differences have been found in the near-wall region at low Reynolds number. The change in the near-wall turbulent structures is responsible for increase of drag and turbulence kinetic energy. To investigatselinae the effects of wall corrugations, the velocity fields have been decomposed so as to isolate coherent and incoherent motions. For corrugated walls, we find that coherent motions are strongest for walls covered with square bars aligned with the flow direction. In particular, the coherent contribution is substantial when the bars are spaced apart by a distance larger than their height. Detailed analysis of the turbulence kinetic energy budget shows for this set-up a very different behavior than for the other types of corrugations.
Highlights
Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza University of Rome, Via Eudossiana 16, Abstract: Direct Numerical Simulations have been performed for turbulent flow in circular pipes with smooth and corrugated walls
We focus on the near-wall coherent structures, which affect the azimuthal distribution of the turbulence statistics, and as a consequence each term in the turbulence kinetic energy budgets
Large efforts were directed to studying similar corrugations in channels, where spanwise confinement may have an influence on the large structures residing away from the wall
Summary
DNS of flows at bulk Reynolds number Re = 2UB Rc /ν = 6534 (where UB is the bulk velocity, and ν the fluid kinematic viscosity) past different deterministic roughness geometries (corrugations) have been performed to investigate differences with respect to the case of a smooth wall (SM). Triangular bars have been considered, either with s/h ≈ 1 with h+ ≈ 49 (TL, see Figure 1d), and with s/h ≈ 2 with h+ ≈ 47 (TLS, see Figure 1e), modifying the flow intensity below the plane of the crests. The friction velocity is defined as uτ = τW 1/2 R E /RC , and the friction Reynolds number in Table 1 is defined as Reτ = uτ RC /ν In these expressions, the overline denotes averages in time and in the homogeneous directions, limited to the region above the plane of the crests, and v′ i = Vi − Vi
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