پیش‌بینی محدوده عدد پرانتل آشفته در احتراق متان-هوا با استفاده از مدل‌های مرتبه دوم شار اسکالر آشفته

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکترا-دانشکده مهندسی مکانیک-دانشگاه سمنان

2 استادیار دانشکده مهندسی مکانیک، دانشگاه سمنان

10.22034/jfnc.2019.92713

چکیده


هدف اصلی در تحقیق پیش­رو تخمین عدد پرانتل آشفته در احتراق غیرپیش­مخلوط متان-هواست. در این راستا، یک جریان احتراقی آشفته غیرپیش­مخلوط در شرایط استوکیومتریک، با استفاده از معادلات متوسط­گیری­شده رینولدز (RANS)، به­صورت عددی مورد تحلیل قرار گرفته ­است. برای مدل­ سازی تشعشع و آشفتگی جریان به­ترتیب مدل­ های جهات گسسته (DO) و k−ε ریلایزبل اعمال شده­اند. همچنین، برای مدل­ سازی احتراق آشفته از سه مدل اضمحلال گرداب ه­ای (EDM)، اضمحلال گرداب ه­ای مفهومی (EDC) و تابع چگالی احتمال (PDF) استفاده شده­ است. به ­همراه مدل EDM و EDC، مدل مرتبه دوم جبری GGDH و مرتبه بالای آن، یعنی HOGGDH، به­ همراه مدل پخش گرداب ه­ای ساده برای جمله شار حرارتی آشفته در معادله انرژی اعمال شده­ است. مقایسه نتایج عددی مدل SED با فرض پرانتل آشفته 85/0و مدل ­های مرتبه دوم با مقادیر تجربی موجود نشان می دهد که اعمال مدل­های مرتبه دوم شار حرارتی آشفته به­طور محسوسی منجر به اصلاح پیش­بینی توزیع دما در محفظه احتراق می­ شود. همچنین، توزیع NO    به­ دست­ آمده از مدل­ های مرتبه دوم مطابقت خوبی با مقادیر تجربی موجود دارد. براساس نتایج به ­دست آمده، در جریان احتراقی مقاله حاضر، مدل GGDH دارای دقت بالاتری نسبت به مدل HOGGDH در پیش­بینی دما و NO است. محاسبه عدد پرانتل آشفته در محفظه احتراق مورد بررسی نشان می­دهد که فرض عدد پرانتل 85/0 دور از واقعیت بوده و براساس مدل GGDH،  عدد پرانتل آشفته در نواحی مختلف از 25/0 تا 3/1 متغیر است. در نهایت عدد پرانتل آشفته 45/0 برای جریان احتراقی این پژوهش پیشنهاد شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Prediction of turbulent Prandtl number in the methane-air combustion using a second-order turbulent scalar flux model

نویسندگان [English]

  • Ali Ershadi 1
  • Mehran Rajabi Zargarabadi 2
1 Semnan University
2 Department of Mechanical Engineering, Semnan University
چکیده [English]

The main objective of the present study is to estimate the turbulent Prandtl number in non-premixed combustion of methane-air. In this regard, a turbulent stream of non-premixed combustion in a stoichiometric condition, is numerically analyzed using the (Reynolds averaged Navier-Stokes) (RANS). For modeling the combustion, the Eddy Dissipation Model (EDM), Eddy Dissipation Concept (EDC) and Probability Density Function (PDF) have been applied. The k-ε Realizable model and Discreet Ordinate (DO) also was used for the turbulence modeling and radiation modeling, respectively. To the turbulent heat flux in the energy equation, second order algebraic model (GGDH and HOGGDH) with simple eddy diffusivity model has been applied. Comparing the results of the numerical model SED (with the turbulent Prandtl 0.85) and second order models with available experimental data show that applying the SO Models significantly led to the modification of predicting the temperature distribution in the combustion chamber. Moreover the NO derived from SO models distribution model has a good agreement with available experimental data. Calculation of Prandtl number turbulence in the combustion chamber shows that the assumption of Prandtl number of 0.85 is far from reality and based on GGDH model, Prt in different areas varies from 0.2 to 1.3.  Finally, the Prandtl number of 0.45 has been proposed for the non-premixed combustion of methane-air.

کلیدواژه‌ها [English]

  • Combustion modeling
  • turbulent Prandtl number
  • algebraic turbulent flux models
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