scholarly journals High-Reynolds-number effects on turbulent scalings in compressible channel flow

PAMM ◽  
2015 ◽  
Vol 15 (1) ◽  
pp. 489-490
Author(s):  
Davide Modesti ◽  
Matteo Bernardini ◽  
Sergio Pirozzoli
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
High Reynolds Number ◽  
Reynolds Number Effects ◽  
High Reynolds

scholarly journals Passive scalars in turbulent channel flow at high Reynolds number

2016 ◽  
Vol 788 ◽  
pp. 614-639 ◽  
Author(s):  
Sergio Pirozzoli ◽  
Matteo Bernardini ◽  
Paolo Orlandi
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
High Reynolds Number ◽  
Correction Term ◽  
Scalar Dissipation ◽  
Channel Height ◽  
Passive Scalars ◽  
The Core ◽  
The Mean ◽  
High Reynolds

We study passive scalars in turbulent plane channels at computationally high Reynolds number, thus allowing us to observe previously unnoticed effects. The mean scalar profiles are found to obey a generalized logarithmic law which includes a linear correction term in the whole lower half-channel, and they follow a universal parabolic defect profile in the core region. This is consistent with recent findings regarding the mean velocity profiles in channel flow. The scalar variances also exhibit a near universal parabolic distribution in the core flow and hints of a sizeable log layer, unlike the velocity variances. The energy spectra highlight the formation of large scalar-bearing eddies with size proportional to the channel height which are caused by a local production excess over dissipation, and which are clearly visible in the flow visualizations. Close correspondence of the momentum and scalar eddies is observed, with the main difference being that the latter tend to form sharper gradients, which translates into higher scalar dissipation. Another notable Reynolds number effect is the decreased correlation of the passive scalar field with the vertical velocity field, which is traced to the reduced effectiveness of ejection events.

Statistical structure of high-Reynolds-number turbulence close to the free surface of an open-channel flow

2003 ◽  
Vol 474 ◽  
pp. 355-378 ◽  
Author(s):  
ISABELLE CALMET ◽  
JACQUES MAGNAUDET
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
High Reynolds Number ◽  
Open Channel ◽  
Open Channel Flow ◽  
Surface Region ◽  
Scale Model ◽  
Normal Velocity ◽  
Near Surface ◽  
High Reynolds

Statistical characteristics of turbulence in the near-surface region of a steady open- channel flow are examined using new data obtained in a high-Reynolds-number large-eddy simulation using a dynamic subgrid-scale model. These data, which correspond to a Reynolds number Re* = 1280 based on the total depth and shear velocity at the bottom wall, are systematically compared with those found in available direct numerical simulations in which Re* is typically one order of magnitude smaller. Emphasis is put on terms involved in the turbulent kinetic energy budget (dominated by dissipation and turbulent transport), and on the intercomponent transfer process by which energy is exchanged between the normal velocity component and the tangential ones. It is shown that the relative magnitude of the pressure–strain correlations depends directly on the anisotropy of the turbulence near the bottom of the surface-influenced layer, and that this anisotropy is a strongly decreasing function of Re*. This comparison also reveals the Re*-scaling laws of some of the statistical moments in the near-surface region, especially those involving vorticity fluctuations. Velocity variances, length scales and one-dimensional spectra are then compared with predictions of the rapid distortion theory elaborated by Hunt & Graham (1978) to predict the effect of the sudden insertion of a flat surface on a shearless turbulence. A very good agreement is found, both qualitatively and quantitatively, outside the thin viscous sublayer attached to the surface. As the present high-Reynolds-number statistics have been obtained after a significant number of turnover periods, this agreement strongly suggests that the validity of the Hunt & Graham theory is not restricted to short times after surface insertion.

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