DNS of turbulent flow in a rod-roughened channel

Ashrafian, Alireza; Andersson, Helge I.; Manhart, Michael

doi:10.1016/j.ijheatfluidflow.2004.02.004

Cited by 120 publications

(72 citation statements)

References 28 publications

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“…In extremely rough cases spanwise structures emerge near the wall and the turbulent state resembles a mixing layer. A direct comparison with the study of Ashrafian et al (2004) shows a good quantitative agreement of the mean flow and Reynolds stresses everywhere except in the immediate vicinity of the rough wall. The proposed roughness force term may be of benefit as a wall model for direct and large-eddy numerical simulations in cases where the exact details of the flow over a rough wall can be neglected.…”

mentioning

confidence: 63%

“…To this end the case of Ashrafian et al (2004) has been chosen, which considered channel flow over a rod-roughened wall by direct numerical simulations. There are several reasons for this choice: DNS data provides a high accuracy close to the wall where experimental measurements are difficult.…”

Section: Example For a Direct Comparisonmentioning

confidence: 99%

“…Also, a similar domain size was used 6.528δ × πδ × 2δ, which is close to the domain size of 7δ × 3.5δ × 2δ used in this paper. The DNS data of Ashrafian et al (2004) will be referred to as AAM in the following.…”

Section: Example For a Direct Comparisonmentioning

confidence: 99%

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Parametric forcing approach to rough-wall turbulent channel flow

Busse

Sandham

2012

J. Fluid Mech.

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The effects of rough surfaces on turbulent channel flow are modelled by an extra force term in the Navier-Stokes equations. This force terms contains two parameters, related to the density and the height of the roughness elements, and a shape function, which regulates the influence of the force term with respect to the distance from the channel wall. This permits a more flexible specification of a rough surface than a single parameter such as the equivalent sand grain roughness. The effects of the roughness force term on turbulent channel flow have been investigated for a large number of parameter combinations and several shape functions by direct numerical simulations. It is possible to cover the full spectrum of rough flows ranging from hydraulically smooth through transitionally rough to fully rough cases. By using different parameter combinations and shape functions it is possible to match the effects of different types of rough surfaces. Mean flow and standard turbulence statistics have been used to compare the results to recent experimental and numerical studies and a good qualitative agreement has been found. Outer scaling is preserved for the streamwise velocity both for the mean profile as well as its mean square fluctuations in all but extremely rough cases. The structure of the turbulent flow shows a trend towards more isotropic turbulent states within the roughness layer. In extremely rough cases spanwise structures emerge near the wall and the turbulent state resembles a mixing layer. A direct comparison with the study of Ashrafian et al. (2004) shows a good quantitative agreement of the mean flow and Reynolds stresses everywhere except in the immediate vicinity of the rough wall. The proposed roughness force term may be of benefit as a wall model for direct and large-eddy numerical simulations in cases where the exact details of the flow over a rough wall can be neglected.

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confidence: 63%

Section: Example For a Direct Comparisonmentioning

confidence: 99%

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Parametric forcing approach to rough-wall turbulent channel flow

Busse

Sandham

2012

J. Fluid Mech.

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“…The first DNS of fully developed channel flow was performed by Kim et al ͑1987͒. Since then, it has been applied to channel flows of increasing physical and geometrical complexities, including flows with free surface ͑Lam and Banerjee 1992͒, transpiration ͑Sumitani and Kasagi 1995͒, riblets ͑Choi et al 1993͒, etc. Recently, DNS has also been applied to the turbulent flows over two-dimensional roughness elements ͑Miy-ake et al 2000; Leonardi et al 2003;Ashrafian et al 2004͒. The present study and a similar one by Bhaganagar and Kim ͑2002͒ represent the DNS of the fully rough flow over three-dimensional ͑3D͒ roughness elements.…”

Section: Introductionmentioning

confidence: 78%

Numerical Simulation of Flow over a Rough Bed

2007

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This paper presents results of a direct numerical simulation ͑DNS͒ of turbulent flow over the rough bed of an open channel. We consider a hexagonal arrangement of spheres on the channel bed. The depth of flow has been taken as four times the diameter of the spheres and the Reynolds number has been chosen so that the roughness Reynolds number is greater than 70, thus ensuring a fully rough flow. A parallel code based on finite difference, domain decomposition, and multigrid methods has been used for the DNS. Computed results are compared with available experimental data. We report the first-and second-order statistics, variation of lift/drag and exchange coefficients. Good agreement with experimental results is seen for the mean velocity, turbulence intensities, and Reynolds stress. Further, the DNS results provide accurate quantitative statistics for rough bed flow. Detailed analysis of the DNS data confirms the streaky nature of the flow near the effective bed and the existence of a hierarchy of vortices aligned with the streamwise direction, and supports the wall similarity hypothesis. The computed exchange coefficients indicate a large degree of mixing between the fluid trapped below the midplane of the roughness elements and that above it.

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“…(0.015), spacing in streamwise-and spanwise-directions 1.8mm (0.035), and for three different roughness heights 0.3mm (0.00755), 0.6 mm (0.015) and 1.2 mm (0.025). More recently, two-dimensional roughness has been investigated by Ashrafian and Andersson [10] using direct numerical simulations (DNS) at Reynolds number based on the mean pressure-gradient of 400. Two-dimensional square rods, periodically arranged in the streamwise direction, with a roughness height of 0.0345, where 5 is the half-channel width, were introduced on both walls of the channel.…”

Section: Introductionmentioning

confidence: 99%

Rough-Wall Turbulent Boundary Layers

Kim¹

2004

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of intonnatlon, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Ariington, VA 22202-4302, and The objective of this project is to improve our fundamental knowledge of turbulent flows over rough surfaces. Specifically, we hope to investigate the manner in which roughness affects the near-wall drag-producing turbulent structures, and to what extent surface roughness affects the outer part of rough-wall boundary layers. Ultimately we hope to use this knowledge to propose control strategies to reduce momentum loss in rough-wall boundary layers. Technical Approach:We have developed a numerical tool to simulate flow over a complex boundary while retaining the simplicity and efficiency of computation in a Cartesian system. This was done using, an immersed boundary method (IBM). We used this method to simulate turbulent channel flow between a smooth wall and one covered with regular three-dimensional roughness elements. Our code uses a fourth-order compact finite-difference scheme in the wall-normal direction and Fourier in the streamwise and spanwise directions. The serial code has been successfully parallehzed using MPI. The parallelization strategy is based on the domain decomposition technique, since the IBM approach requires communication between the processors, which contain the interpolating velocity grid points, and those with the grid points where the body force needs to be applied. The communication among these processors has been obtained using an elegant MPI broadcasting and bookkeeping strategy. This code exhibits excellent scalability. Summairy:Direct numerical simulations of a turbulent channel flow between a smooth and rough wall have been performed in order to investigate the effects of surface roughness on wall-bounded turbulence. To get a clearer picture of the impact of roughness in turbulent boundary layers, we have investigated the effects of 3D roughness arranged in an "egg carton" pattern. We performed a statistical analysis of the large-and small-scale features of the flow. When normalized by the wall-shear velocity, Ur, at the smooth-wall side, the root-mean-square velocity fluctuations at the rough-wall side are higher than the smooth-wall side. A similar effect is seen for the vorticity fluctuations. But when normalized by the local Uj, the u and w fluctuations are smaller and the V fluctuation is higher for the rough-wafl side in the inner layer, indicating arnore isotropic state. In the outer layer all three velocity fluctuations are a smaller fraction of Ur on the roughwall side. The velocity f...

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DNS of turbulent flow in a rod-roughened channel

Cited by 120 publications

References 28 publications

Parametric forcing approach to rough-wall turbulent channel flow

Parametric forcing approach to rough-wall turbulent channel flow

Numerical Simulation of Flow over a Rough Bed

Rough-Wall Turbulent Boundary Layers

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