دانش و فناوری هوافضا

دانش و فناوری هوافضا

مدل‌سازی عددی رفتار ناپایای جت پالسی در محدوده نزدیک خروجی نازل

نوع مقاله : مقاله پژوهشی

نویسنده
استادیار، پژوهشگاه هوافضا، وزارت علوم، تحقیقات و فناوری، تهران، ایران
چکیده
در این پژوهش رفتار ناپایای یک جت هوای پالسی در محیط ساکن، با استفاده از شبیه‌سازی عددی دوبعدی بررسی شده است. در گام نخست، برای صحه‌گذاری مدل عددی، جریان جت پایا در شرایط مشابه آزمایشگاهی شبیه‌سازی و نتایج با داده‌های تجربی مقایسه شده است. اختلاف کم حدود 7% میان نتایج نشان می‌دهد که مدل آشفتگی k-ε RNG و حلگر تراکم‌پذیر، جریان جت آزاد را با دقت خوبی بازتولید می‌نماید. در ادامه، جت پالسی با فرکانس ۱۰۰ هرتز تحلیل شده است. نتایج کانتورهای سرعت و ورتیسیته در فازهای روشن و خاموش سیکل نشان می‌دهد که جبهه هوای پرانرژی اولیه منجر به تشکیل گردابه‌های پیشرو می‌شود و اندرکنش گردابه‌ها با هوای محیط، فرآیند اختلاط و گسترش عرضی جریان را تسریع می‌کند. برای بررسی تأثیر دما بر شکل‌گیری سازوکارهای ناپایا و تکامل گردابه‌ها، دو دمای هوای ورودی ۳۰۰ و ۴۰۰ کلوین مدنظر قرار گرفت. نتایج بیانگر آن بود که افزایش دمای هوای ورودی، موجب افزایش حدود 16% در سرعت اوج گردابه پیشرو و کاهش حدود 12% در سرعت گردابه دنباله‌ای می‌شود. همچنین مقدار بیشینه انرژی جنبشی آشفتگی در جت گرم حدود 34% بیشتر از حالت مرجع است که بیانگر تشدید نوسانات سرعت و افزایش شدت درون‌آمیختگی در میدان نزدیک می‌باشد.
کلیدواژه‌ها

عنوان مقاله English

Numerical Modeling of the Unsteady Behavior of a Pulsed Jet in the Near-Nozzle Region

نویسنده English

Soheila Abdolahi
Assistant Professor, Ministry of Science, Research and Technology, Iran
چکیده English

In this study, the unsteady behavior of a pulsed air jet in a quiescent environment was investigated using two-dimensional numerical simulations. First, to verify the accuracy of the numerical model, a steady jet flow was simulated under laboratory-like conditions, and the results were compared with experimental data. The results confirmed that the RNG k–ε turbulence model combined with a compressible solver can accurately reproduce the main characteristics of a free jet flow. Subsequently, a pulsed jet with a frequency of 100 Hz was analyzed. The contours of velocity and vorticity during the on and off phases of the pulse cycle revealed that the initial high-energy air front leads to the formation of leading vortices, and their interaction with the ambient air enhances the mixing process and lateral jet spreading. To examine the effect of inlet air temperature on the formation of unsteady flow structures and vortex evolution, two inlet temperatures of 300 K and 400 K were considered. The results showed that increasing the inlet air temperature led to approximately a 16% increase in the peak velocity of the leading vortex and about a 12% reduction in the trailing vortex velocity. Moreover, the maximum turbulent kinetic energy in the hot jet was about 34% higher than that in the reference case, indicating intensified velocity fluctuations and enhanced mixing intensity in the near-field region.

کلیدواژه‌ها English

Pulsed Jet
Numerical Modeling
Unsteady Turbulent Flow
Entrainment
Temperature Effects
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