بررسی تجربی نویز جریان پیرامون استوانه با مقطع دایره‌ای با اندازه‌گیری نوسانات فشار ناپایای سطح

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی مکانیک ، دانشگاه یزد، یزد، ایران

چکیده

در مطالعه حاضر نویز منتشر شده از یک مدل استوانه ای با مقطع دایر های به قطر 22 میلی متر و طول 500 میلی متر بطور تجربی بررسی شده است. برای این منظور نوسانات فشار سطحی با استفاده از میکروفون‌های کندانسوری کوچک Pa‑WM‑61A هم در جهت دهانه مدل و هم در جهت محیطی اندازه گیری شده است. کلیه آزمایش‌ها در تونل باد مادو نصوت با سطح آشفتگی 3/0 درصد و حداکثر سرعت 25 متر برثانیه انجام گرفته است. نتایج نشان دادند که نویز باریک باند به ترتیب برای سرعت‌های 10 و 15 و 20 متر بر ثانیه در بسامدهای ریزش گردابه 98 و 142 و 186 هرتز رخ می‌دهد که تقریبا متناظر با عدد استروهال 2/0 است. علاوه براین هارمونیک‌های اول و دوم آن به ترتیب در بسامدهایی دو و سه برابر بسامد ریزش گردابه رخ می‌دهند. در این مطالعه بهترین اجتماع داده‌های طیف فشار سطح در محدوده بسامدهای پایین و میانی به ازای استفاده از مقیاس‌های جریان بالادست )مرتبط باساختارهای بزرگ( و در بسامدهای بالا به دلیل استفاده از پارامترهای مرتبط با جریان پایین دست مدل )مرتبط باساختارهای کوچک( در محل شکل‌گیری گردابه حاصل شده است. توابع همدوسی عرضی و محیطی، نشان می‌دهند که ابعاد فیزیکی و طول عمر )زمان فروپاشی( گردابه‌های بزرگ بیشتر است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Experimental Investigation of Flow Induced Noise Around Circular Cylinder by Measuring Unsteady Surface Pressures

نویسندگان [English]

  • R. Maryami
  • A.A. Dehghan
  • A. Afshari
Department of Mechanical Engineering, Yazd University, Yazd, Iran
چکیده [English]

In the present study, noise emission from a circular cylinder model with 22 mm diameterand 500 mm length has been experimentally investigated. For this purpose, the surface pressurefluctuations have been measured both in spanwise and azimuthal directions by employing miniaturecondenser microphones, Pa-WM-61A. All the experiments are carried out in a subsonic wind tunnel withthe turbulence intensity of 0.3% and maximum upstream velocity of 25 m/s. The results show that tonalnoise for velocities of 10, 15 and 20 m/s takes place at vortex shedding frequencies of 98, 142 and 186Hz respectively which correspond to typical Strouhal number of 0.2. Moreover, frequency of the firstand second harmonic occurs at two and three times of the vortex shedding frequency respectively. In thisstudy, the best collapses of the surface pressure spectra at low and middle frequencies can be obtainedusing the upstream flow scales whereas at high frequencies data are collapsed by employing downstreamscales at vortex formation location. Furthermore, the longitudinal and lateral coherences can provideadequate information about the lifespan (or, inversely, the decay) of eddies and their physical size.

کلیدواژه‌ها [English]

  • Tonal noise
  • Circular cylinder model
  • Surface pressure spectra
  • Eddy convection velocity
  • Spanwise length scale

مراجع

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نشریه مهندسی مکانیک امیرکبیر
دوره 51، شماره 2
خرداد و تیر 1398
صفحه 329-346

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