scholarly journals Direct numerical simulation of turbulent channel flow over porous walls

2015 ◽  
Vol 784 ◽  
pp. 396-442 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Cortelezzi ◽  
Maurizio Quadrio
Keyword(s):  
Porous Material ◽  
Momentum Transfer ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Volume Averaging ◽  
Wall Turbulence ◽  
Navier Stokes ◽  
Parameter Study ◽  
Detailed Knowledge ◽  
Porous Walls

We perform direct numerical simulations (DNS) of a turbulent channel flow over porous walls. In the fluid region the flow is governed by the incompressible Navier–Stokes (NS) equations, while in the porous layers the volume-averaged Navier–Stokes (VANS) equations are used, which are obtained by volume-averaging the microscopic flow field over a small volume that is larger than the typical dimensions of the pores. In this way the porous medium has a continuum description, and can be specified without the need of a detailed knowledge of the pore microstructure by independently assigning permeability and porosity. At the interface between the porous material and the fluid region, momentum-transfer conditions are applied, in which an available coefficient related to the unknown structure of the interface can be used as an error estimate. To set up the numerical problem, the velocity–vorticity formulation of the coupled NS and VANS equations is derived and implemented in a pseudo-spectral DNS solver. Most of the simulations are carried out at $Re_{{\it\tau}}=180$ and consider low-permeability materials; a parameter study is used to describe the role played by permeability, porosity, thickness of the porous material, and the coefficient of the momentum-transfer interface conditions. Among them permeability, even when very small, is shown to play a major role in determining the response of the channel flow to the permeable wall. Turbulence statistics and instantaneous flow fields, in comparative form to the flow over a smooth impermeable wall, are used to understand the main changes introduced by the porous material. A simulation at higher Reynolds number is used to illustrate the main scaling quantities.

Burgers turbulence model for a channel flow

1971 ◽  
Vol 47 (2) ◽  
pp. 321-335 ◽  
Author(s):  
Jon Lee
Keyword(s):  
Channel Flow ◽  
Stokes Equations ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Amplitude Equations ◽  
Fourier Amplitude ◽  
Navier Stokes Equations ◽  
Burgers Model ◽  
Model Dynamics

The truncated Burgers models have a unique equilibrium state which is defined continuously for all the Reynolds numbers and attainable from a realizable class of initial disturbances. Hence, they represent a sequence of convergent approximations to the original (untruncated) Burgers problem. We have pointed out that consideration of certain degenerate equilibrium states can lead to the successive turbulence-turbulence transitions and finite-jump transitions that were suggested by Case & Chiu. As a prototype of the Navier–Stokes equations, Burgers model can simulate the initial-value type of numerical integration of the Fourier amplitude equations for a turbulent channel flow. Thus, the Burgers model dynamics display certain idiosyncrasies of the actual channel flow problem described by a truncated set of Fourier amplitude equations, which includes only a modest number of modes due to the limited capability of the computer at hand.

scholarly journals Turbulent channel flow over an anisotropic porous wall – drag increase and reduction

2018 ◽  
Vol 842 ◽  
pp. 381-394 ◽  
Author(s):  
Marco E. Rosti ◽  
Luca Brandt ◽  
Alfredo Pinelli
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
High Speed ◽  
Vertical Direction ◽  
Porous Wall ◽  
Turbulent Channel Flow ◽  
Spanwise Direction ◽  
Normal Velocity ◽  
Porous Walls ◽  
The One

The effect of the variations of the permeability tensor on the close-to-the-wall behaviour of a turbulent channel flow bounded by porous walls is explored using a set of direct numerical simulations. It is found that the total drag can be either reduced or increased by more than 20 % by adjusting the permeability directional properties. Drag reduction is achieved for the case of materials with permeability in the vertical direction lower than the one in the wall-parallel planes. This configuration limits the wall-normal velocity at the interface while promoting an increase of the tangential slip velocity leading to an almost ‘one-component’ turbulence where the low- and high-speed streak coherence is strongly enhanced. On the other hand, strong drag increase is found when high wall-normal and low wall-parallel permeabilities are prescribed. In this condition, the enhancement of the wall-normal fluctuations due to the reduced wall-blocking effect triggers the onset of structures which are strongly correlated in the spanwise direction, a phenomenon observed by other authors in flows over isotropic porous layers or over ribletted walls with large protrusion heights. The use of anisotropic porous walls for drag reduction is particularly attractive since equal gains can be achieved at different Reynolds numbers by rescaling the magnitude of the permeability only.

scholarly journals Numerical investigation of particles turbulent dispersion in channel flow

2012 ◽  
Vol 16 (5) ◽  
pp. 1510-1514
Author(s):  
Tian Li ◽  
Li-Hao Zhao ◽  
Xiao-Ke Ku ◽  
Helge Andersson ◽  
Terese Lovas
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Numerical Investigation ◽  
Channel Flow ◽  
Particle Distribution ◽  
Turbulent Dispersion ◽  
Wall Turbulence ◽  
Navier Stokes ◽  
Reynolds Averaged Navier Stokes ◽  
Over Time

This paper investigates the performance of Reynolds-averaged Navier-Stokes model on dispersion of particles in wall turbulence. A direct numerical simulation of wall-bounded channel flow with particles suspensions was set as a benchmark. The standard k-? model coupled with two different eddy interaction models was used in Reynolds-averaged Navier-Stokes model and compared to the direct numerical simulation. Detailed comparisons between direct numerical simulation and Reynolds-averaged Navier-Stokes model on particle distribution evolving over time were carried out.

An Approach for the Scanning and Construction of Biofouled Surfaces to be used for Drag Measurements

2017 ◽  
Author(s):  
Christina Dehn ◽  
Eric Holm ◽  
Peter Chang ◽  
Abel Vargas ◽  
Scott Storms
Keyword(s):  
Channel Flow ◽  
Laser Scanning ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Surface Preparation ◽  
Turbulent Channel Flow ◽  
Geometric Parameters ◽  
Navier Stokes ◽  
Ship Hulls ◽  
Cfd Method

A methodology for digitizing and processing calcareous biofouling typically found on US Navy ship hulls has been developed. Panels that were immersed in seawater and allowed to grow biofouling were captured using 3-D laser scanning. The advantage of these digital replicas over real biofouled rough surfaces are many-fold: the surfaces can be manipulated to meet channel flow and large eddy simulation (LES) viscous size constraints; 3-D printing can then be used to build scaled rough surfaces that can be used in the fully developed turbulent channel flow; complex statistical and geometric parameters that encapsulate drag-producing physics can be computed; subregions of the surfaces can be tiled together to create composite surfaces that can span various parameter spaces. This paper describes, in detail, the digitizing, surface preparation, and 3-D printing methodologies. In addition, it describes the surface characterization software. Data from nine scanned surfaces, with biofouling from coastal Florida and Pearl Harbor, Hawaii are shown with preliminary correlations between pierside data and more complex geometric parameters. The work described herein is part of a larger project to develop a fast and accurate ReynoldsAveraged Navier Stokes (RANS) computational fluid dynamics (CFD) method to predict the drag penalty of fouled ships based on data obtained from pierside underwater surveys.

scholarly journals Identifying eigenmodes of averaged small-amplitude perturbations to turbulent channel flow

2019 ◽  
Vol 875 ◽  
pp. 758-780
Author(s):  
A. S. Iyer ◽  
F. D. Witherden ◽  
S. I. Chernyshenko ◽  
P. E. Vincent
Keyword(s):  
Channel Flow ◽  
Small Amplitude ◽  
Direct Evidence ◽  
Graphics Processing Unit ◽  
Turbulence Models ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Processing Unit ◽  
Graphics Processing ◽  
First Time

Eigenmodes of averaged small-amplitude perturbations to a turbulent channel flow – which is one of the most fundamental canonical flows – are identified for the first time via an extensive set of high-fidelity graphics processing unit accelerated direct numerical simulations. While the system governing averaged small-amplitude perturbations to turbulent channel flow remains unknown, the fact such eigenmodes can be identified constitutes direct evidence that it is linear. Moreover, while the eigenvalue associated with the slowest-decaying anti-symmetric eigenmode mode is found to be real, the eigenvalue associated with the slowest-decaying symmetric eigenmode mode is found to be complex. This indicates that the unknown linear system governing the evolution of averaged small-amplitude perturbations cannot be self-adjoint, even for the case of a uni-directional flow. In addition to elucidating aspects of the flow physics, the findings provide guidance for development of new unsteady Reynolds-averaged Navier–Stokes turbulence models, and constitute a new and accessible benchmark problem for assessing the performance of existing models, which are used widely throughout industry.

The Effect of the Earth’s Rotation on Channel Flow

1986 ◽  
Vol 53 (1) ◽  
pp. 198-202 ◽  
Author(s):  
C. G. Speziale
Keyword(s):  
Channel Flow ◽  
Stokes Equations ◽  
Rectangular Channel ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Earth’S Rotation ◽  
Earth's Rotation ◽  
The Earth ◽  
Laminar Channel Flow ◽  
Rotation Of The Earth

The influence that the rotation of the earth has on laminar channel flow is investigated theoretically. The full nonlinear Navier-Stokes equations relative to a reference frame rotating with the earth are solved numerically for laminar flow in a rectangular channel whose axis is aligned east-west: the orientation which yields the most drastic effect. It is demonstrated that for channels of moderate width (less than 1 ft for the flow of most liquids), the rotation of the earth can give rise to a roll instability which has a severe distortional effect on the classical parabolic velocity profile. Consequently, the usual assumption made of neglecting the effect of the earth’s rotation in the calculation of channel flow can lead to serious errors unless the channel is substantially smaller than this size. It is briefly shown that similar effects would be expected for turbulent channel flow when the channel width is approximately an order of magnitude larger.

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