بررسی عددی رفتار دینامیکی شعله پیش‌آمیخته هیدروژن-هوا در عبور ازخم 90 درجه‌ای

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشگاه آزاد اسلامی، وحد نجف آباد

2 هیات علمی دانشگاه آزاد اسلامی واحد نجف آباد

چکیده

شعله پیش‌آمیخته منتشر شده در یک کانال به­‌طور ذاتی ناپایدار است. این ناپایداری خود را به‌صورت وارونگی شعله و نهایتاً شعله لاله‌ای خود را نشان می‌دهد. در کار حاضر، به مطالعه تأثیر خم 90 درجه‌ای بر انتشار شعله لاله‌ای پرداخته شده است. در این شبیه‌سازی عددی، که به‌صورت سه­بعدی انجام گرفته، از رویکرد اغتشاشی شبیه‌سازی گردابه‌های بزرگ (LES) و مدل احتراقی شعله ضخیم­شده مصنوعی (ATF) به‌همراه سینتیک شیمیایی 7 مرحله‌ای استفاده شده است. نتایج حاضر نشان می‌دهند که با شروع تغییر شکل شعله در قسمت افقی کانال، که هم‌زمان با کاهش رشد فشار و سرعت پیشروی جبهه شعله است، وارونگی در جبهه شعله روی می‌دهد. در این لحظات، شکل‌گیری یک جفت گردابه بزرگ­مقیاس در گاز سوخته و در مجاورت شعله باعث تغییر میدان جریان اطراف جبهه شعله می‌شود. در بخش افقی کانال، نمای سه­بعدی شعله به شکل یک شعله لاله‌ای با چهار زبانه کاملاً مشابه است. با ورود شعله به خم، زبانه‌های پایینی شعله سرعت پیشروی بیشتری داشته، به‌طوری‌که پس از مدتی زبانه‌های بالایی کاملاً محو شده و زبانه‌های پایینی کل عرض کانال را اشغال می‌کنند. اگر چه وجود خم تغییر قابل توجه‌ای بر روند افزایشی فشار محفظه نداشته، اما دامنه نوسانات سرعت را تا حدی کاهش داده است.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical study of the dynamic behavior of premixed hydrogen-air flame in a 90-degree bend duct

نویسندگان [English]

  • Ahmad Mosallanejad 1
  • SOBHAN EMAMI 2
1 دانشگاه آزاد اسلامی، وحد نجف آباد
2 هیات علمی دانشگاه آزاد اسلامی واحد نجف آباد
چکیده [English]

The dynamics of premixed flame propagating in a channel is inherently unstable. This instability shows itself as a flame inversion and finally tulip flame. The present study is investigated the effect of a 90° bend on the propagation of the tulip flame. The three-dimensional (3-D) large eddy simulation (LES) approach is performed utilizing the artificially thickened flame (ATF) combustion model with a 7-step chemical mechanism. The present results show that the onset of the flame deformation at the horizontal portion of the channel that coincides with the decreasing in the pressure growth and the flame front propagation speed, the flame inversion occurs. At this moment, the formation of a pair of large-scale vortex in the burned gas near the flame causes a change in the flow field around the flame front. In the horizontal section of the channel, the 3-D tulip flame forms with four tongues. After entering the bend, the lower tongues speed up and dominate the flame propagation. Hence, after a while, the upper tongues completely fade and the lower tongues occupy the entire width of the channel. Although the bend has not a significant change on the increasing trend of the chamber pressure, the amplitude of the flame speed oscillation decreases to some extent.

کلیدواژه‌ها [English]

  • Flame dynamics
  • : Flame dynamics
  • Tulip flame
  • Distorted Tulip flame
  • hydrogen-air mixture
  • Large Eddy Simulation
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