بررسی خصوصیات نوسانات سطحی جریان عبوری از موانع با استفاده از اعداد بی‌بعد روشکو و اورسل

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانش آموخته/دانشگاه شهید چمران اهواز

2 عضو هیئت علمی گروه عمران دانشگاه اراک

چکیده

در اثر برخورد جریان با موانع موجود در مسیر خود، پدیده گردابه ایجاد می‌شود. در صورت برابری بسامد گردابه‌های ایجادشده با بسامد نوسانات طبیعی، پدیده‌ی تشدید رخ‌داده و نوسانات سطحی عمود بر جریان با بیشترین دامنه موج به وجود می‌آید. در این تحقیق به‌منظور بررسی خصوصیات موج عرضی حاصل از گردابه منتشرشده از موانع، 135 مانع استوانه‌ای به قطر ۲۰ میلی‌متر در 5 حالت مختلف در فلوم آزمایشگاهی چیده شدند. در مجموع 900 آزمایش انجام‌شد که متغیرهایآن دبی جریان،عمق متوسط جریان، شیب کانال وفواصل طولی وعرضی موانع بود.درهرآزمایش پس از تشکیل نوسانات عرضی، خصوصیات مربوط به آنها شامل دامنه و بسامد موج ضبط گردید. سپس متغیرهای مؤثر بر خصوصیات امواج عرضی و تأثیرات آن‌ها براعدادبی‌بعد دخیل بررسی شد. نتایج حاکی از آن بودبا افزایش دبی جریان، حداکثر دامنه موج در اثر تشدید در عمق متوسط جریان بزرگتری رخ می‌دهد و مقدار آن نیز افزایش می‌یابد. همچنین در اکثر حالت‌ها با تغییر فاصله طولی بین موانع، روند تغییرات روشکو نسبت به افزایش اورسل در ابتدا صعودی و پس از رسیدن به یک محدوده‌ی خاص از عدد اورسل حالت معکوس به خود می‌گرفت؛ ضمن آنکه هرچه دبی جریان بیشتر می‌شد، سرعت تغییرات اورسل نسبت به روشکو کاهش می‌یافت. در نهایت با استفاده از آنالیز ابعادی و نرم‌افزار آماری، ُعد روشکو با اورسل و فرود جریان برای هر یک از مدهای I و II پیشنهاد شد و صحت روابط با رابطه‌ای ‌با مجذور ضریب همبستگی بیش از 92/0 موردتایید قرارگرفت.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigating the characteristics of surface oscillations of flow through obstacles using Roshko and Ursell dimensionless numbers

نویسندگان [English]

  • Ehsan Moghaddasi 1
  • Nazanin Shahkarami 2
1 Master's graduates of Civil_River Engineering, Shahid Chamran university of Ahvaz, Iran
2 Assistant Professor, Faculty of Engineering, Arak University, Arak, Iran
چکیده [English]

Vortex is shed by flow collision with obstacles in its path. If the frequency of vortex shedding equals the frequency of natural oscillations of flow, resonance will be created and transverse oscillation perpendicular to flow with greatest wave amplitude will occur. In this study, in order to investigate the characteristics of the transverse wave caused by the vortex shedding of the obstacles, 135 cylinder barriers with a diameter of 20 mm in 5 different configurations were arranged in the laboratory flume. In total, 900 tests were carried out which variables were flow discharge, average flow depth, channel slope, longitudinal and transverse distance between obstacles. In each test, after the formation of transverse oscillations, their characteristics including amplitude and frequency of wave were recorded. Then, the effective variables on transverse wave characteristics and their effects on the involved dimensionless numbers were investigated. The results indicated whatever the flow discharge is increased, the maximum wave amplitude due to resonance occurs in larger average flow depth, which has more amount. Also by changing the longitudinal distance of obstacles, Roshko’s changes relative to increasing of Ursell were ascending at the beginning and they were reversed after reaching a certain range of Ursell number; moreover, by increasing the flow discharge, the rate of Ursell changes relative to Roshko decreased. Finally, by using dimensional analysis and statistical software, the equations between Roshko with Ursell and Froude numbers were proposed for each of the modes I and II and the validation of equations were approved (R2= 0.92).

کلیدواژه‌ها [English]

  • Resonance
  • Wave amplitude
  • Vortex
  • Cylindrical barrier
  • Transverse wave
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