TED-AJ03-543 LARGE EDDY SIMULATIONS OF PARTICLE DISPERSION BY TURBULENCE DRIVEN SECONDARY FLOWS IN A SQUARE DUCT

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概要

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• Particle transport in complex geometries has applications ranging from combustion to industrial sprays. It is well known that preferential concentration of particles occurs in turbulent flows, with the degree of particles occurs in turbulent flows, with the degree of preferential concentration varying with the value of the ratio of the particle response time to the fluid response time. Since locally non-uniform particle concentrations in a flow can substantially change the combustion or reaction rates, it is desirable to understand the mechanisms which cause particles to disperse non-uniformly. Previous works in complex geometries have predominantly relied on Reynolds Averaged Navier-Stokes (RANS) methods to predict the particle dispersion. In the square duct geometry, which is representative of many typical applications in heating/ventilation, combustion and materials processing, turbulence driven secondary flows are known to exist which cannot be predicted accurately by RANS methods. The instantaneous secondary flows can significantly contribute to the particle dispersion, and advanced methods such as Large Eddy Simulations (LES) are needed to capture the transient flow structures. In the present work, the dispersion of solid particles in a vertical downward square duct flow at Re_τ=360 is studied using large eddy simulations. The particle equation of motion includes the drag force, the lift forces in the wall directions, and the gravitational force in the streamwise direction. Results indicate that the swirling strength, trace of the velocity gradient tensor squared, strain-rate, and vorticity magnitude are all good indicators of preferential concentration. The degree of preferential concentration is seen to vary with the particle response time and location in the cross-section. Instantaneous pictures of particle positions, such as in Fig.1,as well as probability density functions of the indicators of preferential concentration are reported. Variation of vorticity magnitude, swirling strength, strain-rate, and ∇u : ∇u, and their probability distribution functions (PDF), with particle response time and location is shown to demonstrate preferential concentration. Particles are seen to accumulate in regions of high ∇u : ∇u and strain-rate and in regions of low swirling strength. In general, particles accumulate in regions of low vorticity magnitude. However, near the wall, large particles accumulate in regions of high vorticity magnitude. The preferential accumulation effect is strongest near the wall and weakest near the duct center. In addition, instantaneous contours of the above statistics and scatter plots of particle positions in a near-wall plane are presented to visually illustrate preferential concentration in a square duct.[figure]

• 一般社団法人日本機械学会の論文

著者

• Vanka S.

  University Of Illinois At Urbana

• Winkler C.

  University of Illinois at Urbana

• Rani S.

  University of Illinois at Urbana

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• TED-AJ03-543 LARGE EDDY SIMULATIONS OF PARTICLE DISPERSION BY TURBULENCE DRIVEN SECONDARY FLOWS IN A SQUARE DUCT
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