Direct numerical simulation on the effects of surface slope and skewness on rough-wall turbulence

The transport of passive scalars in turbulent flows over progressive water waves is studied using direct numerical simulation. A combined pseudo-spectral and finite-difference scheme on a wave-surface-fitted grid is used to simulate the flow and scalar fields above the wave surface. Three representative wave ages (i.e. wave-to-wind speed ratios) are considered, corresponding to slow, intermediate and fast wind-waves, respectively. For each wave condition, four Schmidt numbers are considered for the scalar transport. The presence of progressive surface waves is found to induce significant wave-phase-correlated variation to the scalar field, with the phase dependence varying with the wave age. The time- and plane-averaged profiles of the scalar over waves of various ages exhibit similar vertical structures as those found in turbulence over a flat wall, but with the von Kármán constant and effective wave surface roughness for the mean scalar profile exhibiting considerable variation with the wave age. The profiles of the root-mean-square scalar fluctuations and the horizontal scalar flux exhibit good scaling in the viscous sublayer that agrees with the scaling laws previously reported for flat-wall turbulence, but with noticeable wave-induced variation in the viscous wall region. The profiles of the vertical scalar flux in the viscous sublayer exhibit apparent discrepancies from the reported scaling law for flat-wall turbulence, due to a negative vertical flux region above the windward face of the wave crest. Direct observation and quadrant-based conditional averages indicate that the wave-dependent distributions of the scalar fluctuations and fluxes are highly correlated with the coherent vortical structures in the turbulence, which exhibit clear wave-dependent characteristics in terms of both shape and preferential location.

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Numerical investigation of particles turbulent dispersion in channel flow

Thermal Science ◽

10.2298/tsci1205510l ◽

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.

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0507 Peta-Scale Direct Numerical Simulation of Wall Turbulence at High Reynolds Number by K computer

The Proceedings of the Fluids engineering conference ◽

10.1299/jsmefed.2013._0507-01_ ◽

2013 ◽

Vol 2013 (0) ◽

pp. _0507-01_-_0507-02_

Author(s):

Naoya FUKUSHIMA ◽

Kazuaki TOKUMARU ◽

Hiroya MAMORI ◽

Kaoru IWAMOTO ◽

Koji FUKAGATA ◽

...

Keyword(s):

Numerical Simulation ◽

Reynolds Number ◽

Direct Numerical Simulation ◽

High Reynolds Number ◽

Wall Turbulence ◽

High Reynolds

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Instability of streaks in wall turbulence with adverse pressure gradient

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.193 ◽

2011 ◽

Vol 681 ◽

pp. 205-240 ◽

Cited By ~ 61

Author(s):

MATTHIEU MARQUILLIE ◽

UWE EHRENSTEIN ◽

JEAN-PHILIPPE LAVAL

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Pressure Gradient ◽

Gradient Flow ◽

Adverse Pressure Gradient ◽

Turbulent Channel Flow ◽

Streamwise Velocity ◽

Wall Turbulence ◽

Instability Modes ◽

Weak Pressure Gradient

A direct numerical simulation of a turbulent channel flow with a lower curved wall is performed at Reynolds number Reτ ≈ 600. Low-speed streak structures are extracted from the turbulent flow field using methods known as skeletonization in image processing. Individual streaks in the wall-normal plane averaged in time and superimposed to the mean streamwise velocity profile are used as basic states for a linear stability analysis. Instability modes are computed at positions along the lower and upper wall and the instability onset is shown to coincide with the strong production peaks of turbulent kinetic energy near the maximum of pressure gradient on both the curved and the flat walls. The instability modes are spanwise-symmetric (varicose) for the adverse pressure gradient streak base flows with wall-normal inflection points, when the total average of the detected streaks is considered. The size and shape of the counter-rotating streamwise vortices associated with the instability modes are shown to be reminiscent of the coherent vortices emerging from the streak skeletons in the direct numerical simulation. Conditional averages of streaks have also been computed and the distance of the streak's centre from the wall is shown to be an essential parameter. For the upper-wall weak pressure gradient flow, spanwise-antisymmetric (sinuous) instability modes become unstable when sets of highest streaks are considered, whereas varicose modes dominate for the streaks closest to the wall.

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Direct numerical simulation of turbulent duct flow with inclined or V-shaped ribs mounted on one wall

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.1028 ◽

2021 ◽

Vol 932 ◽

Author(s):

S.V. Mahmoodi-Jezeh ◽

Bing-Chen Wang

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Secondary Flows ◽

Wall Turbulence ◽

Spanwise Direction ◽

Duct Flow ◽

Mean Flow ◽

Square Duct ◽

Turbulence Structures ◽

The Mean

In this research, highly disturbed turbulent flow of distinct three-dimensional characteristics in a square duct with inclined or V-shaped ribs mounted on one wall is investigated using direct numerical simulation. The turbulence field is highly sensitive to not only the rib geometry but also the boundary layers developed over the side and top walls. In a cross-stream plane secondary flows appear as large longitudinal vortices in both inclined and V-shaped rib cases due to the confinement of four sidewalls of the square duct. However, owing to the difference in the pattern of cross-stream secondary flow motions, the flow physics is significantly different in these two ribbed duct cases. It is observed that the mean flow structures in the cross-stream directions are asymmetrical in the inclined rib case but symmetrical in the V-shaped rib case, causing substantial differences in the momentum transfer across the spanwise direction. The impacts of rib geometry on near-wall turbulence structures are investigated using vortex identifiers, joint probability density functions between the streamwise and vertical velocity fluctuations, statistical moments of different orders, spatial two-point autocorrelations and velocity spectra. It is found that near the leeward and windward rib faces, the mean inclination angle of turbulence structures in the V-shaped rib case is greater than that of the inclined rib case, which subsequently enhances momentum transport between the ribbed bottom wall and the smooth top wall.

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