مطالعه آزمایشگاهی شاخص سرعت (نسبت سرعت متوسط به سرعت سطحی) و الگوهای سطحی جریان فوق‌بحرانی روی شیب تند با استفاده از LSPIV

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه سازه های آبی، دانشکده مهندسی علوم آب، دانشگاه شهید چمران اهواز

2 دانشگاه شهید چمران اهواز- استاد دانشکده مهندسی علوم آب

3 دانشیار، انستیتو مهندسی هیدرولیک و مدیریت منابع آب، دانشگاه صنعتی گراتز، اتریش

4 گروه سازه های آبی، دانشکده مهندسی علوم آب، دانشگاه شهید چمران اهواز.

چکیده

اندازه‌گیری دبی جریان در آبراهه‌های روباز همواره یکی از مهم‌ترین دغدغه‌های متخصصین حوزه آب بوده است. رویکردی که اخیراً به‌عنوان یک گزینه غیرتماسی برای اندازه‌گیری جریان در مجاری روباز موردتوجه قرارگرفته است استفاده از روش‌های سرعت‌سنجی مبتنی بر تصویربرداری از سطح جریان می‌باشد. ازجمله این روش‌ها گونه‌ای از روش سرعت‌سنجی تصویری ذرات (PIV) موسوم به سرعت‌سنجی بزرگ‌مقیاس تصویری ذرات (LSPIV) است که به دلیل حذف ضرورت استفاده از لیزر طرفداران زیادی پیداکرده است. در این مطالعه برای اندازه‌گیری میدان دوبعدی سرعت بر روی سطح جریان فوق‌بحرانی روی شیب تند از LSPIV بهره‌گیری شد. بدین ترتیب که تعداد 24 آزمایش برای سه شیب مختلف (2، 6 و 10 درصد) و هشت مقدار مختلف نسبت ابعاد (7 تا 5/20) انجام و در هر آزمایش به مدت 60 ثانیه با فرکانس 125 فریم بر ثانیه تصویربرداری از سطح جریان صورت گرفت. از داده‌های سرعت حاصله برای محاسبه شاخص سرعت (VI) استفاده گردید. این شاخص برای تبدیل سرعت سطحی به ‌سرعت متوسط مقطع و نهایتاً اندازه‌گیری دبی جریان بکار می‌رود. تأثیر تغییرات نسبت ابعاد روی این شاخص مورد بررسی قرار گرفت. مقدار متوسط بدست آمده برای شاخص سرعت معادل 701/0 می‌باشد که با مقدار متداول 85/0 حدود 17 درصد اختلاف دارد. بعلاوه الگوهای سرعت متوسط زمانی سطح جریان برای حالات مختلف به‌صورت کمی مقایسه شد. با توجه به‌اینکه تاکنون شاخص سرعت غالباً برای شرایط زیربحرانی مطالعه شده است، نتایج این تحقیق می‌تواند برای اندازه‌گیری جریان‌های فوق‌بحرانی راهگشا باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental Study of Velocity Index and Supercritical Flow Surface Patterns on Steep Ship Using LSPIV

نویسندگان [English]

  • Farhad Akbarpour 1
  • Manoochehr Fathi-Moghadam 2
  • Josef Schneider 3
  • Ahmad Fathi 4
1 Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Iran
2 Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Iran
3 Institute of Hydraulic Engineering and Water Resource Management, Graz University of Technology, Austria
4 Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Iran
چکیده [English]

Measuring flow discharge in open waterways has always been one of the most important concerns for water experts. Flow surface image velocimetry method as a non-contact option has recently been widely utilized to measure discharge in open channels. One of these methods is a type of PIV method named LSPIV which has been paied more attention due to the elimination of laser application. In this study, LSPIV was used to measure 2D velocity field over the surface of a steep supercritical flow. Totally 24 experiments including three different slopes (2, 6 and 10 percent) and eight different dimension ratios (7 to 20.5) were conducted and in each experiment the flow surface was recorded with a frequency of 125 fps for 60 seconds. The Velocity Index was calculated bt the obtained velocity data. This index is used for convering the surface velocity to average velocity of the cross section and subsequently for determination of flow discharge. The effect of different dimention ratios on VI was investigated. The average value for VI was obtained to be 0.701 which is differ from the established value (0.85) by about 17%. Moreover, the flow surface time-averaged velocity patterns were quantitavely compared for different flow conditions. Since, the velocity index has been so far studied for subcritical conditions, the results of this study may be helpfull for measuring supercritical flows.

کلیدواژه‌ها [English]

  • LSPIV
  • Steep Channels
  • Velocity Index (VI)
  • Flow pattern
  • Supercritical Flow
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