Direct Numerical Simulation of Turbulent Pipe Flow at Moderately High Reynolds Numbers

Khoury, George K. El; Schlatter, Philipp; Noorani, Azad; Fischer, Paul; Brethouwer, Geert; Johansson, A.

doi:10.1007/s10494-013-9482-8

Cited by 256 publications

(226 citation statements)

References 31 publications

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“…turbulence intensity u /U, skewness S and flatness F, of the streamwise velocity component, as a function of the Reynolds number, are shown in figure 3b, where the prime denotes the root mean square value (RMS). The Reynolds-number invariance found for the skewness and flatness at the centreline is in accordance with findings from the Superpipe [5] as well as low Re pipe flow DNSs, which 'show nearly constant values with S ≈ −0.48 and F ≈ 3.4' [42]. The inner-scaled streamwise RMS values are also almost Re independent for low Re DNSs [42], which, together with U + CL ∝ ln R + , result in a decrease in the turbulence intensity, which agrees qualitatively with the present as well as the Superpipe data.…”

Section: (A) Centreline Turbulence Quantitiessupporting

confidence: 89%

Reynolds stress scaling in pipe flow turbulence—first results from CICLoPE

Örlü

Fiorini

Segalini

et al. 2017

Phil. Trans. R. Soc. A.

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Section: (A) Centreline Turbulence Quantitiessupporting

confidence: 89%

Reynolds stress scaling in pipe flow turbulence—first results from CICLoPE

Örlü

Fiorini

Segalini

et al. 2017

Phil. Trans. R. Soc. A.

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“…The grid nearest the centerline contains a cylindrical region with a stretched Cartesian grid, similar to the grid used for a DNS of pipe flow in Nek5000 (El-Khoury et al 2013). In the present grid, this region contains 128 elements over the axial cross-section, and extends from r = 0 to the outer radius of the inner pipe at r = 0.14, where it attaches to an outer cylindrical grid.…”

Section: Nonlinear Simulations and Podmentioning

confidence: 99%

Coherent structures in a swirl injector at Re = 4800 by nonlinear simulations and linear global modes

2016

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The large-scale coherent motions in a realistic swirl fuel injector geometry are analysed by direct numerical simulations (DNS), proper orthogonal decomposition (POD), and linear global modes. The aim is to identify the origin of instability in this turbulent flow in a complex internal geometry.The flow field in the nonlinear simulation is highly turbulent, but with a distinguishable coherent structure: the precessing vortex core (a spiraling mode).The most energetic POD mode pair is identified as the precessing vortex core. By analysing the FFT of the time coefficients of the POD modes, we conclude that the first four POD modes contain the coherent fluctuations. The remaining POD modes (incoherent fluctuations) are used to form a turbulent viscosity field, using the Newtonian eddy model.The turbulence sets in from convective shear layer instabilities even before the nonlinear flow reaches the other end of the domain, indicating that equilibrium solutions of the Navier-Stokes are never observed. Linear global modes are computed around the mean flow from DNS, applying the turbulent viscosity extracted from POD modes. A slightly stable discrete m = 1 eigenmode is found, well separated from the continuous spectrum, in very good agreement with the POD mode shape and frequency. The structural sensitivity of the precessing vortex core is located upstream of the central recirculation zone, identifying it as a spiral vortex breakdown instability in the nozzle. Furthermore, the structural sensitivity indicates that the dominant instability mechanism is the KelvinHelmholtz instability at the inflection point forming near vortex breakdown. Adjoint modes are strong in the shear layer along the whole extent of the nozzle, showing that the optimal initial condition for the global mode is localized in the shear layer.We analyse the qualitative influence of turbulent dissipation in the stability problem (eddy viscosity) on the eigenmodes by comparing them to eigenmodes computed without eddy viscosity. The results show that the eddy viscosity improves the complex frequency and shape of global modes around the fuel injector mean flow, while a qualitative wavemaker position can be obtained with or without turbulent dissipation, in agreement with previous studies.This study shows how sensitivity analysis can identify which parts of the flow in a complex geometry need to be altered in order to change its hydrodynamic stability characteristics.Key Words: † Email address for correspondence: outi-leena.tammisola@nottingham.ac.uk , and the exit velocity from the swirler (U E ). The coordinate system is also defined: the origin is at the centerline at the swirler exit location. The relative dimensions of the geometry are the same as in the numerical simulation, except that the numerical domain is longer in the downstream direction.

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“…Thus, higher compression ratios imply smaller file sizes. Figure 3 illustrates the behavior of the DLT truncation on a test case, namely the turbulent flow through a straight pipe, which is further described in Section 4 and in [14]. In this figure we also show the compression-ratio results obtained by using the DCT, as in our previous work [19].…”

Section: Description Of the Compression Proceduresmentioning

confidence: 97%

“…The first case under consideration is the turbulent flow through a smooth straight pipe, obtained through a fully-resolved DNS by El Khoury et al [14]. Although this is one of the three main canonical flow cases in wall-bounded turbulence, it has not been investigated numerically as thoroughly as channels [21,22] or zero-pressure-gradient boundary layers [23,24], due to the numerical problems associated with the singularity at the pipe center.…”

Section: Summary Of Test Casesmentioning

confidence: 99%

See 1 more Smart Citation

Lossy Data Compression Effects on Wall-bounded Turbulence: Bounds on Data Reduction

Otero

Vinuesa

Marin

et al. 2018

Flow Turbulence Combust

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Postprocessing and storage of large data sets represent one of the main computational bottlenecks in computational fluid dynamics. We assume that the accuracy necessary for computation is higher than needed for postprocessing. Therefore, in the current work we assess thresholds for data reduction as required by the most common data analysis tools used in the study of fluid flow phenomena, specifically wall-bounded turbulence. These thresholds are imposed a priori by the user in L 2 -norm, and we assess a set of parameters to identify the minimum accuracy requirements. The method considered in the present work is the discrete Legendre transform (DLT), which we evaluate in the computation of turbulence statistics, spectral analysis and resilience for cases highly-sensitive to the initial conditions. Maximum acceptable compression ratios of the original data have been found to be around 97%, depending on the application purpose. The new method outperforms downsampling, as well as the previously explored data truncation method based on discrete Chebyshev transform (DCT).

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Direct Numerical Simulation of Turbulent Pipe Flow at Moderately High Reynolds Numbers

Cited by 256 publications

References 31 publications

Reynolds stress scaling in pipe flow turbulence—first results from CICLoPE

Reynolds stress scaling in pipe flow turbulence—first results from CICLoPE

Coherent structures in a swirl injector at Re = 4800 by nonlinear simulations and linear global modes

Lossy Data Compression Effects on Wall-bounded Turbulence: Bounds on Data Reduction

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