بررسی عددی اغتشاشات صوتی ایرفویل نوسانی NACA0012 مجهز به دندانه مثلثی

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی هوافضا، دانشگاه صنعتی امیرکبیر، تهران، ایران.

چکیده

نویز آیرودینامیکیِ ناشی از ایرفویل‌ها به دلیل آثار مخرب بر شنوایی و کارآیی وسایل نقلیه و توربین‌های باد، مسئله‌ای جدی برای صنعت است. این نویز، که از تغییرات هندسی، گردابه‌ها و جدایش جریان سرچشمه می‌گیرد، می‌تواند با افزودن دندانه‌های مثلثی به لبه‌ فرار کاهش یابد. در این پژوهش رفتار ایرفویل نوسانی ناکا 0012 با دامنه 10 درجه و بسامد 5 تا 25 هرتز حول مرکز آیرودینامیکی به روش عددی ارزیابی شد. میدان جریان با معادلات ناویر-استوکس میانگین‌گیری‌شده‌ی رینولدز و مدل آشفتگی kω SST حل شد. همچنین میدان صوتی پیرامون ایرفویل با الگوریتم فاکس-ویلیامز و هاوکینگز استخراج گردید؛ ویژگی‌های هواصوتی نظیر سطح فشار صوت و چگالی توان صوتی در فواصل مختلف از انتهای لبه فرار ایرفویل ثبت شدند. نتایج نشان داد که دندانه‌های مثلثی، با شکستن گردابه‌های بزرگ جریان و تبدیل آن‌ها به گردابه‌های کوچک‌تر، به‌طور میانگین 4/58 دسی‌بل از 51/18 دسی‌بل، یعنی 8/95درصد نویز ناشی از گردابه‌ها را کاهش دادند. این افت با تضعیف گردابه‌های غالب، کاهش نوسانات سرعت و القای اختلاف فاز در تابش امواج صوتی همراه بود و در نهایت، با تغییر ساختار آشفتگی دنباله، انتشار انرژی صوتی را محدود کرده و عملکرد آیرواکوستیکی را بهبود بخشیده‌ است. تأثیر کاهش نویز وابسته به فرکانس نوسان ایرفویل است، به‌طوری‌که دندانه در فرکانس‌های پایین‌ کارایی بیشتری داشته اما در فرکانس‌های بالاتر به دلیل ناپایداری‌های شدیدتر جریان، اثربخشی آن کاهش می‌یابد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

A Numerical Study on Pitching NACA0012 Airfoils with Saw-Tooth Serration

نویسندگان [English]

  • Mohammad Mostofi
  • Rojin Shokri Khanghah
  • Sahar Noori
Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran
چکیده [English]

Aerodynamic noise generated by airfoils poses a serious industrial challenge because of its detrimental impact on human hearing and on the performance of vehicles and wind turbines. This noise rooted in geometric parameters, vortex shedding and flow separation can be mitigated by mounting triangular serrations on the trailing edge. In the present study, the aeroacoustic behaviour of an oscillating NACA 0012 airfoil with a ±10° pitching amplitude and oscillation frequencies between 5 and 25 Hz about its aerodynamic centre was evaluated numerically. The flow field was solved with the Unsteady Reynolds-averaged Navier–Stokes equations with the k-ω SST turbulence model, while the surrounding acoustic field was predicted through the Ffowcs Williams–Hawkings (FW-H) acoustic analogy. Acoustic metrics, including sound pressure level and power spectral density, were recorded at several downstream positions from the trailing edge. Results demonstrate that the serrations fragmented large-scale vortices into smaller structures and, on average, lowered vortex-induced noise by 4.58 dB from 51.18 dB, equivalent to a 8.95% reduction. This attenuation is attributed to weakened dominant vortices, reduced velocity fluctuations, and creating phase shifts in acoustic wave propagation, which collectively suppress wake turbulence and limit acoustic energy propagation, thereby enhancing aeroacoustic performance. The effectiveness of serrations was frequency dependent, exhibiting greater efficacy at lower oscillation frequencies and reduced effectiveness at higher frequencies due to intensified flow instabilities.

کلیدواژه‌ها [English]

  • Oscillating Pitching Airfoil
  • Aeroacoustic Noise
  • Triangular Serrations
  • Frequency Analysis

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نشریه مهندسی مکانیک امیرکبیر
دوره 57، شماره 3
خرداد 1404
صفحه 303-332

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