Large-Eddy Simulation of Particle Diffusion in a Particle-laden Swirling Jet

武信, 道岡; 良一, 黒瀬

doi:10.1299/kikaib.73.30

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“…円筒型サイクロンセパレータの粒子分離メカニズム(第 2 報) © 2012 The Japan Society of Mechanical Engineers 旋回流中の粒子追跡に関しては，Park らが，粒子が噴流の発達を遅らせる影響を Direct Numerical Simulation (DNS)により明らかにしている (8) ．道岡らは，Dynamic Smagorinsky モデルを適用した LES により，旋回流中の渦運動のスケールが粒子の拡散挙動に及ぼす影響を粒径や旋回強度を変えて詳細に検討した (9) ■Control Volume V inside :…”

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Mechanism of Particle Separation in a Cylindrical Cyclone Separator (2nd Report, Validation of Lagrangian Particle Tracking Method and Investigation on Detailed Particle Behaviour)

Akiyama

2012

Trans.JSME, Ser.B

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Mechanism of particle separation in a cylindrical cyclone separator has been fully clarified by a combined numerical method of large eddy simulation and a particle tracking method. The former resolves all the important vortical structures in the separator while the latter inputs the instantaneous flow fields computed by the LES and computes trajectory of each particle by considering Stokes drag as well as gravity force. Particle collection efficiency predicted by the proposed method has been compared with the experimental data measured for two cylindrical cyclone separators with several sets of particle diameters. The results showed that the collection efficiency has been quantitatively predicted by the proposed method, which confirms that the method can be used for the engineering design of such a cyclone separator. Detailed investigation of the particle trajectories predicted by the present method has clarified the mechanism of particle separation of a cylindrical cyclone separator. Those particles that are successfully collected by the separator move outward in the swirl flow and are collected when the swirl flow changes its direction at the bottom of the separator. The essential mechanism of this particle separation is due to the centrifugal forces acting on the particles. Three types of particle trajectories have been identified for those particles that are exhausted from the cyclone separator together with the swirl flow. More than half of the uncollected particles are trapped by longitudinal vortexes. The unsteady longitudinal vortexes and vortex rope drastically decrease collection efficiency. 1. 緒言サイクロンの最初の特許が出願された 1885 年以降，粒子の捕集効率(collection efficiency) の向上を目的とした，速度場や捕集効率の実験結果が数多く報告されている (1)(2) ．出口管 (vortex finder)や入口部の幾何形状 (3) ，円筒部における軸長の効果 (4) ，らせん渦 (vortex rope，サイクロンの文献では vortex core とよばれる)の壁面付着による不安定な現象 (5) などに関して，製品開発に有用な知見が蓄積されている．流体解析が実用的になった 1990 年代以降は，流体解析と粒子追跡とを組み合わせて，粒子の経路や捕集効率の予測が行われている．サイクロンに関わる研究では，Derksen が標準 Smagorinsky モデルを適用した Large-Eddy Simulation (LES)の基礎方程式を格子ボルツマン法で離散化し，粒子追跡を実施した．この手法により，粒子の捕集効率が精度良く予測されている (6) ．さらに， Derksen らは粒子と空気の質量比が 0.2 と濃厚な系を対象として双方向連成解析に研究を発展させている (7) ．円筒型サイクロンセパレータの粒子分離メカニズム＊ (第 2 報，粒子追跡の精度検証と粒子運動の詳細検討)

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Mechanism of Particle Separation in a Cylindrical Cyclone Separator (2nd Report, Validation of Lagrangian Particle Tracking Method and Investigation on Detailed Particle Behaviour)

Akiyama

2012

Trans.JSME, Ser.B

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Large-Eddy Simulation of Particle Diffusion in a Particle-laden Swirling Jet

Cited by 1 publication

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Mechanism of Particle Separation in a Cylindrical Cyclone Separator (2nd Report, Validation of Lagrangian Particle Tracking Method and Investigation on Detailed Particle Behaviour)

Mechanism of Particle Separation in a Cylindrical Cyclone Separator (2nd Report, Validation of Lagrangian Particle Tracking Method and Investigation on Detailed Particle Behaviour)

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