以VIC方法探討紊流態混合層流重粒子的彌散

An Investigation on Heavy Particle Dispersion in Turbulent Plane Mixing Layer by Vortex-in-Cell Technique

許掙強(Cheng-Chiang Hsu)

《航空太空及民航學刊.系列B》 41卷2期 (2009/10) Pp. 67-76

https://doi.org/10.6124/JAAA.200910_41(2).01

摘要

氣固二相流雙向計算方式被提出研究粒子彌散特性及相關之統計特性。流體速度場以Vortex-in-Cell模式計算，固體粒子之運動軌跡以Lagrangian方式求算，並以粒子存在會對流場渦量造成改變之觀點，求算粒子對流場影響。藉實驗與本數值結果比較，驗證了本數值運算模式之可信度。由結果發現混合層流中Stoke數呈階梯遞減方式往下游演變，故無法以單一的粒子彌散形態，描述整個流場渦結構與粒子之交互作用；由於固體粒子之慣性作用，在上游粒子速度於高速區低於流體速度，於低速區則高於流體速度，並使低速區粒子會較高速區粒子先調至和流體具一致速度；粒子擾動速度均方根值均比流體擾動速度均方根值小，且粒子對流向擾動感受力較橫向擾動?高。下游處能量頻譜被求出，明顯觀察到於對數尺度下具斜率－3之二維紊流場enstrophy串級區域。

關鍵字

固氣雙相流 ； 渦流 ； 混合層流 ； 史托克數

並列摘要

Particle dispersion in mixing layer was investigated by numerical approach. Vortex-in-Cell technique was adopted to calculate velocity field, Lagrangian approach was used to find particle trajectories, and vorticity modified algorithm was introduced to present the interaction between flow and particles. By comparing numerical and experimental results, excellent agreement was found and the reliability of the present numerical procedure was verified. In the present results, we also observed that Stoke number descended downstream in mixing layer, so not just a single particle dispersive style existed in flow field; because the inertia of particle was larger than that of flow, particle streamwise mean velocity was smaller than flow streamwise mean velocity at the high speed side and was larger than that at the low speed side in the upstream, and particle streamwise mean velocity at the low speed side approached to flow streamwise mean velocity more faster than that at the high speed side; particle was more sensitive to streamwise velocity fluctuation than to transverse velocity fluctuation. Energy spectrum at downstream was calculated and the enstrophy cascade region with slope -3 at log scale was observed.

並列關鍵字

Gas-particle multiphase flow ； Vortex ； Mixing layer ； Stoke number