T. Watanabe, Y. Sakai, K. Nagata, Y. Ito, T. Hayase
Reactive scalar field near the turbulent/non-turbulent interface in a planar jet with a second-order chemical reaction
Physics of Fluids 26 105111 2014
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Abstract
The reactive scalar field near the turbulent/non-turbulent (T/NT) interface is analyzed using a direct numerical simulation (DNS) of a planar jet with an isothermal second-order chemical reaction A + B → P. Reactants A and B are supplied from the jet and ambient flows, respectively. The DNS of the reactive jet is performed for Damköhler numbers Da = 0.1, 1, and 10. A visualization of the T/NT interface shows that most of the product P is contained in the turbulent region. The conditional mean concentrations of the reactive species change sharply near the T/NT interface. The width of the jump in the conditional mean concentration is almost independent of the chemical species and the Damköhler number. For the slow reaction (Da = 0.1), the conditional average of the chemical production rate gradually increases from the non-turbulent region toward the turbulent region. In contrast, the conditional average of the production rate for Da = 1 and 10 has a large peak value slightly inside the T/NT interface. The chemical reaction near the T/NT interface strongly depends on the interface orientation. The reactant A is deficient near the T/NT interface. The production rate is large near the interface toward which the deficient reactant A is frequently transported by the velocity fields. The transport due to the velocity relative to the interface movement strongly depends on the relationship between the interface geometry and the mean flow field. The dependence of the chemical reaction on the interface orientation becomes strong as Da increases. When the interface propagates toward the non-turbulent region, the reactant A and product P are contained in the turbulent region although the molecular diffusion and reaction contribute to the increase in the concentrations of A (non-reactive case) and P in the non-turbulent region. In contrast, the interface propagation toward the turbulent region leaves the fluids containing A and P in the non-turbulent region.
日本語訳 (DeepL翻訳)
二次の化学反応を伴う平面噴流の乱流・非乱流界面近傍における反応性スカラー場
乱流/非乱流界面近傍の反応スカラー場を、恒温二次化学反応A + B → Pを伴う平面噴流の直接数値シミュレーション(DNS)を用いて解析した。反応噴流のDNSは、Damköhler数Da = 0.1, 1, 10に対して行われた。T/NT界面の可視化により、生成物Pのほとんどが乱流領域に含まれることがわかった。反応種の条件付き平均濃度は、T/NT界面付近で急激に変化する。条件付き平均濃度のジャンプの幅は、化学種やダムケーラー数にほとんど依存しない。遅い反応(Da = 0.1)では、化学生成速度の条件付き平均値は非乱流領域から乱流領域に向かって徐々に増加する。一方、Da = 1 と 10 の条件付き平均値は、T/NT 界面のやや内側で大きなピークを持つ。T/NT 界面近傍の化学反応は、界面の向きに強く依存する。反応物 A は T/NT 界面近傍で不足する。反応物AはT/NT界面近傍で不足し、界面近傍で生成率が大きく、不足した反応物Aは速度場によって頻繁に輸送される。界面移動に対する速度による輸送は、界面形状と平均流場の関係に強く依存する。化学反応の界面配向への依存性は、Daが大きくなるほど強くなる。界面が非乱流領域に向かって伝播する場合、分子拡散と反応により非乱流領域でのA（非反応の場合）とPの濃度上昇に寄与するものの、反応物Aと生成物Pは乱流領域に含まれることになる。一方、乱流領域に向かって界面が伝播することで、AやPを含む流体が非乱流領域に残される。