scholarly journals Particle-resolved direct numerical simulation of homogeneous isotropic turbulence modified by small fixed spheres

2016 ◽  
Vol 796 ◽  
pp. 40-85 ◽  
Author(s):  
A. W. Vreman
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Velocity Gradient ◽  
Dissipation Rate ◽  
Point Particle ◽  
Turbulence Kinetic Energy ◽  
Spherical Particles ◽  
Particle Model ◽  
Particle Simulations

A statistically stationary homogeneous isotropic turbulent flow modified by 64 small fixed non-Stokesian spherical particles is considered. The particle diameter is approximately twice the Kolmogorov length scale, while the particle volume fraction is 0.001. The Taylor Reynolds number of the corresponding unladen flow is 32. The particle-laden flow has been obtained by a direct numerical simulation based on a discretization of the incompressible Navier–Stokes equations on 64 spherical grids overset on a Cartesian grid. The global (space- and time-averaged) turbulence kinetic energy is attenuated by approximately 9 %, which is less than expected. The turbulence dissipation rate on the surfaces of the particles is enhanced by two orders of magnitude. More than 5 % of the total dissipation occurs in only 0.1 % of the flow domain. The budget of the turbulence kinetic energy has been computed, as a function of the distance to the nearest particle centre. The budget illustrates how energy relatively far away from particles is transported towards the surfaces of the particles, where it is dissipated by the (locally enhanced) turbulence dissipation rate. The energy flux towards the particles is dominated by turbulent transport relatively far away from particles, by viscous diffusion very close to the particles, and by pressure diffusion in a significant region in between. The skewness and flatness factors of the pressure, velocity and velocity gradient have also been computed. The global flatness factor of the longitudinal velocity gradient, which characterizes the intermittency of small scales, is enhanced by a factor of six. In addition, several point-particle simulations based on the Schiller–Naumann drag correlation have been performed. A posteriori tests of the point-particle simulations, comparisons in which the particle-resolved results are regarded as the standard, show that, in this case, the point-particle model captures both the turbulence attenuation and the fraction of the turbulence dissipation rate due to particles reasonably well, provided the (arbitrary) size of the fluid volume over which each particle force is distributed is suitably chosen.

A direct comparison of particle-resolved and point-particle methods in decaying turbulence

2018 ◽  
Vol 850 ◽  
pp. 336-369 ◽  
Author(s):  
M. Mehrabadi ◽  
J. A. K. Horwitz ◽  
S. Subramaniam ◽  
A. Mani
Keyword(s):  
Numerical Simulation ◽  
Particle Acceleration ◽  
Direct Numerical Simulation ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Point Particle ◽  
Particle Methods ◽  
Particle Model ◽  
Second Moment ◽  
Acceleration Model

We use particle-resolved direct numerical simulation (PR-DNS) as a model-free physics-based numerical approach to validate particle acceleration modelling in gas-solid suspensions. To isolate the effect of the particle acceleration model, we focus on point-particle direct numerical simulation (PP-DNS) of a collision-free dilute suspension with solid-phase volume fraction $\unicode[STIX]{x1D719}=0.001$ in a decaying isotropic turbulent particle-laden flow. The particle diameter $d_{p}$ in the suspension is chosen to be the same as the initial Kolmogorov length scale $\unicode[STIX]{x1D702}_{0}$ ($d_{p}/\unicode[STIX]{x1D702}_{0}=1$) in order to overlap with the regime where PP-DNS is valid. We assess the point-particle acceleration model for two different particle Stokes numbers, $St_{\unicode[STIX]{x1D702}}=1$ and 100. For the high Stokes number case, the Stokes drag model for particle acceleration under-predicts the true particle acceleration. In addition, second moment quantities which play key roles in the physical evolution of the gas–solid suspension are not correctly captured. Considering finite Reynolds number corrections to the acceleration model improves the prediction of the particle acceleration probability density function and second moment statistics of the point-particle model compared with the particle-resolved simulation. We also find that accounting for the undisturbed fluid velocity in the acceleration model can be of greater importance than using the most appropriate acceleration model for a given physical problem.

Numerical Simulation of Flow Field in Burnt Lime Hydrator

2011 ◽  
Vol 383-390 ◽  
pp. 2206-2210
Author(s):  
Ming Hua Bai ◽  
Yu Zhang ◽  
Qiu Fang Wang
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Flow Field ◽  
Velocity Gradient ◽  
Rotational Speed ◽  
Fugitive Dust ◽  
Work Condition ◽  
Burnt Lime ◽  
Stirring Effect ◽  
Recirculation Zones

The flow field distribution in burnt lime hydrator has been investigated by a software FLUENT, with k-ε turbulence model and MRF method. The simulation result shows that when four blades deflect 30°, the whole velocity gradient of flow reduces and the recirculation zones also diminish; when the rotational speed is 75r/min, the turbulence kinetic energy of stir zone between two axes becomes larger, which can raise stirring effect and reduce fugitive dust, so it is easy to achieve the purpose of improving the environment of work condition.

The influence of entropy fluctuations on the interaction of turbulence with a shock wave

1997 ◽  
Vol 334 ◽  
pp. 353-379 ◽  
Author(s):  
KRISHNAN MAHESH ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Scaling Law ◽  
Linear Analysis ◽  
Turbulent Field ◽  
Bulk Compression ◽  
Baroclinic Torque

Direct numerical simulation and inviscid linear analysis are used to study the interaction of a normal shock wave with an isotropic turbulent field of vorticity and entropy fluctuations. The role of the upstream entropy fluctuations is emphasized. The upstream correlation between the vorticity and entropy fluctuations is shown to strongly influence the evolution of the turbulence across the shock. Negative upstream correlation between u′ and T′ is seen to enhance the amplification of the turbulence kinetic energy, vorticity and thermodynamic fluctuations across the shock wave. Positive upstream correlation has a suppressing effect. An explanation based on the relative effects of bulk compression and baroclinic torque is proposed, and a scaling law is derived for the evolution of vorticity fluctuations across the shock. The validity of Morkovin's hypothesis across a shock wave is examined. Linear analysis is used to suggest that shock-front oscillation would invalidate the relation between urms and Trms, as expressed by the hypothesis.

scholarly journals Shock interaction with a deformable particle: Direct numerical simulation and point-particle modeling

2013 ◽  
Vol 113 (1) ◽  
pp. 013504 ◽  
Author(s):  
Y. Ling ◽  
A. Haselbacher ◽  
S. Balachandar ◽  
F. M. Najjar ◽  
D. S. Stewart
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Point Particle ◽  
Shock Interaction ◽  
Particle Modeling ◽  
Deformable Particle
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