بررسی ارتعاشات ناشی از جریان حول استوانه با تکیه گاه الاستیک در مجاورت سطح آزاد سیّال: بسامد و مُدهای رهایش گردابه

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشگاه علم و صنعت ایران

چکیده

در این مقاله، شبیه سازی عددی ارتعاشات القائی ناشی از جدایش گردابه از سطح استوانه ی دایره ای دو درجه آزادی با تکیه گاه الاستیک در مجاورت سطح آزاد سیّال انجام شده است. جریان اطراف استوانه، آرام و در محدوده ی اعداد رینولدز 60 الی 130 در نظر گرفته شده است. اثر سطح آزاد با عدد فرود 0.2 با در نظرگیری دو نسبت فاصله ی 2.5 و 1.5 از آن بررسی می شود. فرکانس طبیعی سیستم جرم- فنر در هر نسبت فاصله بگونه ای انتخاب شده که با عدد استروهال جریان در رینولدز 100 حول استوانه ی ساکن برابر باشد. شبیه سازی های ارتعاشات ناشی از جریان و سطح آزاد سیّال بطور جداگانه تطابق خوبی با نتایج قبلی نشان داده اند. این مقاله بخش دوم تحقیق درباره تأثیر سطح آزاد سیّال بر پدیده ی ارتعاشات القایی ناشی از رهایش گردابه است. تأثیر سطح آزاد سیّال بر ناحیه ی قفل شدگی با استفاده از مقایسه ی مُدهای رهایش گردابه و نمودارهای تطابق فرکانسی در دو نسبت فاصله بررسی می شود که نتایج با نزدیک شدن استوانه به سطح آزاد، حاکی از تغییر نوع مُدهای رهایش گردابه، کاهش محدوده قفل شدگی و افزایش عدد استروهال و نسبت فرکانسی بی بعد جریان هستند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical Investigation of Vortex-Induced Vibrations of an elastically-mounted Circular Cylinder Beneath a Free Surface: Modes & Frequencies

نویسندگان [English]

  • Seyed Mostafa Hosseinalipoor
  • Navid Haji ghafoori boukani
Iran University of Science and Technology
چکیده [English]

In this paper, a two-dimensional numerical simulation is applied to study the Vortex[1]Induced Vibrations (VIV) of an elastically mounted rigid circular cylinder beneath a free surface of fluid. The effect of free surface in laminar flow (60 < Re < 130) with Fr=0.2 is investigated with considering two Gap-Ratios of 2.5, 1.5. The natural structural frequency of oscillator is assumed to match the vortex shedding frequency for a stationary cylinder at Re=100. Simulations of VIV and Free Surface of fluid flow have separately shown good agreement with previous results. User Defined Function (UDF) hooked in the Software is given to couple the motion of cylinder to flow motion. For simulation of free surface, Volume of fluid (VOF) method is used. This paper is the second part of an investigation about effects of Free Surface of fluid on VIV phenomena. The effects of Free Surface is investigated with using a comparison of vortex shedding modes and non-dimensional frequency diagrams for the two Gap-Ratios. With approaching cylinder to free surface, results shows changing type of vortex shedding modes, abatement in lock-in region, increasing Strouhal number and non[1]dimensional frequency ratio.

کلیدواژه‌ها [English]

  • Vortex Induced Vibration
  • free surface
  • Lock-in region
  • Vortex shedding modes
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