High Reynolds Number Channel Flows Research Articles

Prediction of the phase difference between large-scale velocity and Reynolds stress fluctuations in wall turbulence

A resolvent-based model was used to predict the phase-difference profile between velocity and stress coherent motions measured in a high Reynolds number channel flow as a proxy for predicting large- and small-scale turbulent interactions. The resolvent model is based on the transfer-function approach for scale interactions in wall turbulence proposed in Jacobiet al.(J. Fluid Mech., vol 914, 2021, pp. 1–27), but incorporates a quasi-empirical weighting scheme to construct composite mode shapes that represent the realistic dispersion of convection velocities associated with the large scales of turbulence. The weighting scheme was derived from the observed similarity between the spectral region where the resolvent operator is low rank and the streamwise spectral energy density of wall-bounded turbulence, and was found to be superior to both single-convection velocity models and models based on linearly weighted modes, when compared with cross-spectral phase calculations from a channel flow computation. The ability to predict the phase relationship between large-scale coherent motions and their associated stress fluctuations allows for refining and extending resolvent-based models of turbulence to describe small-scale features of wall-bounded flows.

Effects of the quiescent core in turbulent channel flow on transport and clustering of inertial particles

The existence of a quiescent core (QC) in the center of turbulent channel flows was demonstrated in recent experimental and numerical studies. The QC-region, which is characterized by relatively uniform velocity magnitude and weak turbulence levels, occupies about 40% of the cross-section at Reynolds numbers Reτ ranging from 1000 to 4000. The influence of the QC region and its boundaries on transport and accumulation of inertial particles has never been investigated before. Here, we first demonstrate that a QC is unidentifiable at Reτ=180, before an in-depth exploration of particle-laden turbulent channel flow at Reτ=600 is performed. The inertial spheres exhibited a tendency to accumulate preferentially in high-speed regions within the QC, i.e. contrary to the well-known concentration in low-speed streaks in the near-wall region. The particle wall-normal distribution, quantified by means of Voronoï volumes and particle number concentrations, varied abruptly across the QC-boundary and vortical flow structures appeared as void areas due to the centrifugal mechanism. The QC-boundary, characterized by a localized strong shear layer, appeared as a barrier, across which transport of inertial particles is hindered. Nevertheless, the statistics conditioned in the QC-frame show that the mean velocity of particles outside of the QC was towards the core, whereas particles within the QC tended to migrate towards the wall. Such upward and downward particle motions are driven by similar motions of fluid parcels. The present results show that the QC exerts a substantial influence on transport and accumulation of inertial particles, which is of practical relevance in high-Reynolds number channel flow.

Numerical Study of Turbulent Channel Flow over Surfaces with Variable Spanwise Heterogeneities: Topographically-driven Secondary Flows Affect Outer-layer Similarity of Turbulent Length Scales

Wall-bounded turbulent flows over surfaces with spanwise heterogeneous surface roughness – that is, spanwise-adjacent patches of relatively high and low roughness – exhibit mean flow phenomena entirely different to what would otherwise exist in the absence of spanwise heterogeneity. In the outer layer, mean counter-rotating rolls occupy the depth of the flow, and are positioned such that “upwelling” and “downwelling” occurs above the low and high roughness, respectively. It has been comprehensively shown that these secondary flows are Prandtl’s secondary flow of the second kind (Anderson et al., J. Fluid Mech. 768, 316–347 2015). This behaviour indicates that spanwise spacing, s y , between adjacent patches of high and low roughness is, itself, a problem parameter; in this study, we have systematically assessed how s y affects turbulence structure in high Reynolds number channel flows via two-point correlations. “High roughness” is imposed with streamwise-aligned pyramid elements with height, h, selected to be ≈ 5% of the channel half height, H. For $s_{y}/H \gtrsim 1$ , we find that the aforementioned domain-scale mean circulations exist and the surface may be regarded as a topography. For s y /H ≲ 0.2, turbulence statistics show characteristics very similar to a homogeneous roughness and thus the surface may be regarded as a roughness. For 0.2 ≲ s y /H ≲ 2, the spatial extent of the counter-rotating rolls is controlled by proximity to adjacent rows, and we define such surfaces as being intermediate. We refer to such surfaces as intermediate state.

Recent progress in the development of the Elliptic Blending Reynolds-stress model

The Elliptic Blending Reynolds Stress Model (EB-RSM), originally proposed by Manceau and Hanjalić (2002) to extend standard, weakly inhomogeneous Reynolds stress models to the near-wall region, has been subject to various modifications by several authors during the last decade, mainly for numerical robustness reasons. The present work revisits all these modifications from the theoretical standpoint and investigates in detail their influence on the reproduction of the physical mechanisms at the origin of the influence of the wall on turbulence. The analysis exploits recent DNS databases for high-Reynolds number channel flows, spanwise rotating channel flows with strong rotation rates, up to complete laminarization, and the separated flow after a sudden expansion without and with system rotation. Theoretical arguments and comparison with DNS results lead to the selection of a recommended formulation for the EB-RSM model. This formulation shows satisfactory predictions for the configurations described above, in particular as regards the modification of the mean flow and turbulent anisotropy on the anticyclonic or pressure side.

Prandtl number effect on near wall temperature profile in high-Reynolds number channel flows

Prandtl number (Pr) effects on characteristics of the thermal boundary layer were investigated by means of Direct Numerical Simulations (DNS) in high-Reynolds number turbulent channel flows. The molecular Pr conditions were changed from 0.71 to 25.0, and the Reynolds number based on the friction velocity and channel half-width was kept to 1000 in all cases. The mean temperature profiles were good agreements with Kader's empirical equations except for the case of Pr = 25.0. The thicknesses of thermal conduction sub-layer became thinner in proportion to a one third power of Pr. On the other hands, the peak wall-normal heights in temperature intensity became thinner in proportion to a one half power of Pr. In both thermal layers of the conduction and logarithmic, results of quadrant and Kullback-Leibler Divergence (KLD) analyses were shown analogous characteristics in all Pr cases. On the other hand, in the buffer layer, the contributions of sweep and ejection events on wall-normal turbulent heat flux and distribution of KLD were shown the different distributions between in cases of Pr = 0.71 and Pr = 5.0, 25.0.

Discussion on Direct Numerical Simulation of Large-Scale Structures in High-Reynolds Number Channel Flow by Means of High-Order Accurate Finite Difference Method for Wall-Parallel Directions

Discussion on Direct Numerical Simulation of Large-Scale Structures in High-Reynolds Number Channel Flow by Means of High-Order Accurate Finite Difference Method for Wall-Parallel Directions

252 高レイノルズ数乱流熱輸送におけるプラントル数効果に関する4象限解析(流体工学III,学術講演)

252 高レイノルズ数乱流熱輸送におけるプラントル数効果に関する4象限解析(流体工学III,学術講演)

Quadrant and Joint Probability Density Function Analyses of High-Prandtl Number Turbulent Heat Transfer in High-Reynolds Number Channel Flows

Quadrant and Joint Probability Density Function Analyses of High-Prandtl Number Turbulent Heat Transfer in High-Reynolds Number Channel Flows

Discussion of High-Prandtl Number Effect on Inner Layer Turbulent Heat Flux in High-Reynolds Number Channel Flows

Discussion of High-Prandtl Number Effect on Inner Layer Turbulent Heat Flux in High-Reynolds Number Channel Flows

257 DNSデータベースを用いたLESによる高レイノルズ数大規模構造の精度検証(流体工学IV,学術講演)

257 DNSデータベースを用いたLESによる高レイノルズ数大規模構造の精度検証(流体工学IV,学術講演)

256 高レイノルズ数乱流場における大規模構造の影響(流体工学III,学術講演)

256 高レイノルズ数乱流場における大規模構造の影響(流体工学III,学術講演)

Solid particle acceleration in a high Reynolds number channel flow: DNS and LES with stochastic modelling of subgrid acceleration

Inertial particle acceleration statistics are analyzed using DNS in the case of a turbulent channel flow. Along with effects recognized in homogeneous isotropic turbulence, an additional effect is observed due to high and low speed vortical structures aligned with the channel wall. In response to those structures, the inertial particles experience strong streamwise acceleration variations. DNS is also used in order to assess LES-SSAM (Subgrid Stochastic Acceleration Model), in which an approximation to the instantaneous non-filtered velocity field is given by simulation of both, filtered and residual, accelerations. Advantages of this approach in predicting particle dynamics in the channel flow at a high Reynolds number are shown.

Nonlinear aspects of high Reynolds number channel flows

This paper considers the flow in a two-dimensional channel at high Reynolds number, with wall deformations which can lead to flow separation. An asymptotic model is proposed by using the successive complementary expansion method with generalized asymptotic expansions. In particular, the model emphasizes the asymmetry of the channel geometry by introducing a change of variables. It is shown that the model is more general than the models developed with the method of matched asymptotic expansions. Comparisons with Navier–Stokes solutions show that the model is well founded and enables us to treat original problems.

Modeling dilute sediment suspension using large-eddy simulation with a dynamic mixed model

Transport of suspended sediment in high Reynolds number channel flows [Re=O(600 000)] is simulated using large-eddy simulation along with a dynamic-mixed model (DMM). Because the modeled sediment concentration is low and the bulk Stokes’ number (Stb) is small during the simulation, the sediment concentration is calculated through the use of the Eulerian approach. In order to employ the DMM for the suspended sediment, we formulate a generalized bottom boundary condition in a finite-volume formulation that accounts for sediment flux from the bed without requiring specific details of the underlying turbulence model. This enables the use of the pickup function without requiring any assumptions about the behavior of the eddy viscosity. Using our new boundary condition, simulations indicate that the resolved component of the vertical flux is one order of magnitude greater than the resolved subfilter-scale flux, which is in turn one order of magnitude greater than the eddy-diffusive flux. Analysis of the behavior of the suspended sediment above the bed indicates the existence of three basic time scales that arise due to varying degrees of competition between the upward turbulent flux and downward settling flux. Instantaneous sediment concentration and velocity fields indicate that streamwise vortices account for a bulk of the resolved flux of sediment from the bed.

Large-Eddy Simulation of High Reynolds Number Cannel Flow applying Explicit Filtering

Correct representation of the effects of the turbulence structure near solid boundaries is very important for successful large-eddy simulation (LES). In the present work, this so-called wall-layer modeling is done on commutation error terms near solid boundaries obtained by explicit filtering. These terms are ignored in conventional LES, but in the present work, these error terms are modeled using a dynamic procedure, making use of the scale-similarity of the modeled terms. It is found, by applying the procedure in LES of a high Reynolds number channel flow, that the dynamic modeling of these error terms makes it possible to gain the roughly same velocity profile as DNS results statistically, and moreover, to simulate the features of large-scale structures instantaneously.

Wall modeling for LES of high Reynolds number channel flows: What turbulence information is retained?

A novel near-wall eddy-viscosity formulation for Large-eddy simulation (LES) has been used to compute high Reynolds number channel flows up to Re τ = 1,000,000. These computations allow an insight into what turbulence information is retained when LES with a wall model is applied to such high Reynolds numbers. Detailed results are presented for the mean and rms velocities, as well as energy spectra. It is observed that, when an appropriate scaling is used, the rms velocities, energy spectra and the production of turbulence kinetic energy are weakly Reynolds number dependent at these high Reynolds numbers.

Parallelization and scalability of a spectral element channel flow solver for incompressible Navier–Stokes equations

AbstractDirect numerical simulation (DNS) of turbulent flows is widely recognized to demand fine spatial meshes, small timesteps, and very long runtimes to properly resolve the flow field. To overcome these limitations, most DNS is performed on supercomputing machines. With the rapid development of terascale (and, eventually, petascale) computing on thousands of processors, it has become imperative to consider the development of DNS algorithms and parallelization methods that are capable of fully exploiting these massively parallel machines. A highly parallelizable algorithm for the simulation of turbulent channel flow that allows for efficient scaling on several thousand processors is presented. A model that accurately predicts the performance of the algorithm is developed and compared with experimental data. The results demonstrate that the proposed numerical algorithm is capable of scaling well on petascale computing machines and thus will allow for the development and analysis of high Reynolds number channel flows. Copyright © 2007 John Wiley & Sons, Ltd.

Large-Eddy Simulation With Simplified Collisional Microdynamics in a High Reynolds Number Particle-Laden Channel Flow

Computing high Reynolds number channel flows laden by heavy solid particles requires excessive CPU resources to calculate interparticle collisions. Since the frequency of these collisions is high, the kinematic details of each elementary collision may not be essential when calculating particle statistics. In this paper, the dynamics of a particle with a phase trajectory that is discontinuous (due to collisions) is simulated using a hypothetical “noncolliding” particle moving along a trajectory smoothed over interparticle collisions. The statistical temperature of this particle is assumed to be in equilibrium with the statistical “temperature” of the resolved turbulence. This simplified microdynamic is introduced into ballistic calculations of particles within the framework of the “two-way” LES approach. The simulation was conducted specifically to compare the velocity statistics of the hypothetical particle with statistics yielded by measurements in the gas∕particle channel flow and by the LES∕particle approach where binary collisions were simulated. This paper shows that, by assuming the universality of collisional microdynamics, one may predict the experimental observation and the results of detailed simulations without requiring supplementary CPU resources to compute the binary collisions.

Test Filter 너비의 추정을 통한 난류 채널 유동의 Large Eddy Simulation

The suitable estimation of the filter width in the dynamic eddy viscosity model were investigated in high Reynolds number channel flow. In this study, the improvement on matters by optimizing the test filter shape was attempted through the numerical experiment. The way that select optimum test filter width is recommended. Some test filters, one is based on a discrete representation of the top-hat filter and another are based on a high-order filtering operation, are evaluated in simulations of the turbulent channel flow at Reynolds number 1020, based on friction velocity and channel half width. It appears that the estimation of test filter width practically can decrease the dissipative nature of dynamic eddy viscosity model with explicit test filter. It shows that the value of the filter width ratio used in the dynamic procedure must match the properties of the test filter actually used in the calculation.<br/>

On the Large-scale Structure of Flow in Far Layer of Wall Turbulence

Comparatively high Reynolds number channel flows up to Reτ=640 are simulated by DNS. Noticeable property of the high Reynolds number flow is large-scale streaks which are larger not only in scale but also in their spanwise separation than those well-known in the buffer layer. It is revealed that the low-speed streaks are the region of high turbulent activity and accordingly of high turbulent shear stress with densely populated elementary vortices. These properties are little influenced by wall condition, such as drag controlled or not. LSE (Linear Stochastic Estimation) technique is applied to extract elementary vortex pairs. Time evolution of these vortices submerged in a laminar flow but having velocity distribution of turbulent one reveals the process of generation of large-scale streaks and accompanying densely populated elementary vortices. The formation of large-scale streaks by the model simulation is also little influenced by the wall condition and this modeled process is expected to mimic that taking place in the near-wall layer of practical channel flow. The existence of the low-speed streaks itself is the key for the formation of the structure, thus suggesting the self-sustenance of turbulence by both large-scale streaks and vortices concentrated area.