Direct numerical simulation and analysis of instability enhancing parameters in liquid sheets at moderate Reynolds numbers

2008 ◽  
Vol 20 (5) ◽  
pp. 053301 ◽  
Author(s):  
Wolfgang Sander ◽  
Bernhard Weigand
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Reynolds Numbers ◽  
Liquid Sheets

scholarly journals Direct Numerical Simulation of Particle-laden Flow Around an Obstacle at Different Reynolds Numbers

2021 ◽  
Vol 1877 (1) ◽  
pp. 012035
Author(s):  
Shengxiang Lin ◽  
Huanxiong Xia ◽  
Zhenyu Zhang ◽  
Jianhua Liu ◽  
Honglei Wang
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Reynolds Numbers ◽  
Particle Laden Flow

Direct Numerical Simulation of Heat Transfer in Converging–Diverging Wavy Channels

2006 ◽  
Vol 129 (7) ◽  
pp. 769-777 ◽  
Author(s):  
E. Stalio ◽  
M. Piller
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
High Temperature ◽  
Direct Numerical Simulation ◽  
Reynolds Numbers ◽  
Temperature Fields ◽  
Second Order Statistics ◽  
Iterative Procedures ◽  
Wavy Channels ◽  
Unsteady Problems

Corrugated walls are widely used as passive devices for heat and mass transfer enhancement; they are most effective when operated at transitional and turbulent Reynolds numbers. In the present study, direct numerical simulation is used to investigate the unsteady forced convection in sinusoidal, symmetric wavy channels. A novel numerical method is employed for the simulations; it is meant for fully developed flows in periodic ducts of prescribed wall temperature. The algorithm is free of iterative procedures; it accounts for the effects of streamwise diffusion and can be used for unsteady problems. Results of two simulations in the transitional regime for Reynolds numbers based on average duct height and average velocity of Re=481 and Re=872 are reported. Time averaged and instantaneous velocity and temperature fields together with second-order statistics are interpreted in order to describe the mechanism associated with heat transfer augmentation. Heat flux distributions locate the most active areas in heat transfer and reveal the effects of convective mixing. Slanted traveling waves of high temperature are identified; peak values of Nusselt number are attained when the high-temperature fluid of the waves reaches the converging walls.

scholarly journals Clustering instabilities in sedimenting fluid–solid systems: critical assessment of kinetic-theory-based predictions using direct numerical simulation data

2017 ◽  
Vol 823 ◽  
pp. 433-469 ◽  
Author(s):  
William D. Fullmer ◽  
Guodong Liu ◽  
Xiaolong Yin ◽  
Christine M. Hrenya
Keyword(s):  
Numerical Simulation ◽  
Kinetic Theory ◽  
Direct Numerical Simulation ◽  
Parameter Space ◽  
Qualitative Agreement ◽  
Critical Density ◽  
Reynolds Numbers ◽  
Dynamic State ◽  
Mean Flow ◽  
Density Ratios

In this work the quantitative and qualitative ability of a kinetic-theory-based two-fluid model (KT-TFM) is assessed in a state of fully periodic sedimentation (fluidization), with a focus on statistically steady, unstable (clustered) states. The accuracy of KT-TFM predictions is evaluated via direct comparison to direct numerical simulation (DNS) data. The KT-TFM and DNS results span a rather wide parameter space: mean-flow Reynolds numbers on the order of 1 and 10, mean solid volume fractions from 0.1 to 0.4, solid-to-fluid density ratios from 10 to 1000 and elastic and moderately inelastic (restitution coefficient of 0.9) conditions. Data from both KT-TFM and DNS display a rich variety of statistically steady yet unstable structures (clusters). Instantaneous snapshots of KT-TFM and DNS demonstrate remarkable qualitative agreement. This qualitative agreement is quantified by calculating the critical density ratio at which the structure transitions from a chaotic, dynamic state to a regular, plug-flow state, with good overall comparisons. Further quantitative assessments of mean and fluctuating velocities show good agreement at high density ratios but weaker agreement at intermediate to low density ratios depending on the mean-flow Reynolds numbers and solid fractions. Deviations of the KT-TFM results from the DNS data were traced to a breakdown in one of the underlying assumptions of the kinetic theory derivation: high thermal Stokes number. Surprisingly, however, even though the low Knudsen number assumption, also associated with the kinetic theory derivation, is violated throughout most of the parameter space, it does not seem to affect the good quantitative accuracy of KT-TFM simulations.

scholarly journals A fast direct numerical simulation method for characterising hydraulic roughness

2015 ◽  
Vol 773 ◽  
pp. 418-431 ◽  
Author(s):  
D. Chung ◽  
L. Chan ◽  
M. MacDonald ◽  
N. Hutchins ◽  
A. Ooi
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Computational Cost ◽  
Simulation Method ◽  
Reynolds Numbers ◽  
Proof Of Concept ◽  
Hydraulic Roughness ◽  
Velocity Shift ◽  
High Reynolds ◽  
Reynolds Number Flows

We describe a fast direct numerical simulation (DNS) method that promises to directly characterise the hydraulic roughness of any given rough surface, from the hydraulically smooth to the fully rough regime. The method circumvents the unfavourable computational cost associated with simulating high-Reynolds-number flows by employing minimal-span channels (Jiménez & Moin, J. Fluid Mech., vol. 225, 1991, pp. 213–240). Proof-of-concept simulations demonstrate that flows in minimal-span channels are sufficient for capturing the downward velocity shift, that is, the Hama roughness function, predicted by flows in full-span channels. We consider two sets of simulations, first with modelled roughness imposed by body forces, and second with explicit roughness described by roughness-conforming grids. Owing to the minimal cost, we are able to conduct direct numerical simulations with increasing roughness Reynolds numbers while maintaining a fixed blockage ratio, as is typical in full-scale applications. The present method promises a practical, fast and accurate tool for characterising hydraulic resistance directly from profilometry data of rough surfaces.

Direct Numerical Simulation of Mass Transfer from Spherical Bubbles: the Effect of Interface Contamination at Low Reynolds Numbers

2006 ◽  
Vol 4 (1) ◽  
Author(s):  
Adil Dani ◽  
Arnaud Cockx ◽  
Pascal Guiraud
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Direct Numerical Simulation ◽  
Reynolds Numbers ◽  
Solid Sphere ◽  
Creeping Flow ◽  
Spherical Bubbles ◽  
Cap Model ◽  
Liquid Mass Transfer ◽  
Low Reynolds

The gas-liquid mass transfer from bubbles is estimated by Direct Numerical Simulation for fully contaminated bubbles behaving as solid spheres, partially contaminated spherical bubbles and clean spherical bubbles. Partial contamination of bubble interface is accounted by the Stagnant Cap Model to show the effect of the surfactant on hydrodynamic and mass transfer at low Reynolds number. Hydrodynamics results are validated by comparison with other works of the literature. The numerical mass transfer is then analysed in term of local and averaged Sherwood numbers. The comparison of DNS results with classical relations gives the good scaling of Sherwood with Pe1/3 and Pe1/2 respectively for solid sphere and clean bubble in creeping flow. For partially contaminated bubble and after validation of simulated drag coefficient, the effect of the contamination on mass transfer is shown for several Peclet numbers. A correlation for Sherwood number in function of contamination angle is then proposed in creeping flow.

Direct Numerical Simulation of a Fully Developed Turbulent Channel Flow With Respect to the Reynolds Number Dependence

2001 ◽  
Vol 123 (2) ◽  
pp. 382-393 ◽  
Author(s):  
Hiroyuki Abe ◽  
Hiroshi Kawamura ◽  
Yuichi Matsuo
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Channel Flow ◽  
Correlation Coefficients ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Reynolds Stresses ◽  
Point Correlation ◽  
Reynolds Number Dependence

Direct numerical simulation (DNS) of a fully developed turbulent channel flow for various Reynolds numbers has been carried out to investigate the Reynolds number dependence. The Reynolds number is set to be Reτ=180, 395, and 640, where Reτ is the Reynolds number based on the friction velocity and the channel half width. The computation has been executed with the use of the finite difference method. Various turbulence statistics such as turbulence intensities, vorticity fluctuations, Reynolds stresses, their budget terms, two-point correlation coefficients, and energy spectra are obtained and discussed. The present results are compared with the ones of the DNSs for the turbulent boundary layer and the plane turbulent Poiseuille flow and the experiments for the channel flow. The closure models are also tested using the present results for the dissipation rate of the Reynolds normal stresses. In addition, the instantaneous flow field is visualized in order to examine the Reynolds number dependence for the quasi-coherent structures such as the vortices and streaks.

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