بررسی آزمایشگاهی اثر تغییر عرض ناگهانی بر هیدرودینامیک جبهه جریان غلیظ و اندرکنش نیروهای مؤثر

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه سازه‌های آبی، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید چمران اهواز، اهواز، ایران.

10.22059/jwim.2025.387490.1196

چکیده

در این پژوهش، ۱۸ آزمایش جهت بررسی اثر تنگ‌شدگی و باز‌شدگی ناگهانی، بر هیدرودینامیک پیشانی انجام شد. دبی جریان ۱/۱ لیتر بر ثانیه و متغیرها شامل غلظت‌های ۵ و ۱۰ گرم بر لیتر، شیب‌های صفر، ۵/۱ و ۳ درصد و نسبت‌های عرض ۳۹/۰، ۶۴/۰ و ۹۲/۰ بودند. رژیم جریان شامل هر سه حالت زیر بحرانی، بحرانی و فوق بحرانی بود. در تنگ‌شدگی با نسبت‌های ۳۹/۰ و ۶۴/۰، سرعت پیشانی ابتدا، به دلیل افزایش شار شناوری تا یک نقطه افزایش یافته و سپس تحت تأثیر اختلاط کاهش می‌یابد. افزایش شدت تنگ‌شدگی و شیب، سرعت بیشینه را بیشتر و محل وقوع آن را دورتر می‌کند؛ به نحویکه، در شیب ۳ درصد، سرعت بیشینه در نسبت ۳۹/۰ در مقایسه با نسبت ۶۴/۰، برای غلظت‌های ۵ و ۱۰ گرم بر لیتر به ترتیب ۲۹/۲۰ و ۴۹/۲۴ درصد افزایش یافت. در باز‌شدگی با دو نسبت مزبور، روند تغییرات سرعت با فاصله، به دلیل تشدید ناپایداری‌های تلاطمی کاهشی بود؛ که شدت آن برای نسبت ۳۹/۰ بیشتر بود. در نسبت ۹۲/۰، تنگ‌شدگی و باز‌شدگی تأثیر خاصی نداشته و تغییرات سرعت با فاصله، مشابه کانال با عرض ثابت، برای شیب صفر، نزولی و در کانال شیبدار، صعودی بود. تغییرات ارتفاع پیشانی با فاصله، در تنگ‌شدگی و بازشدگی، برای تمام نسبت‌ها، صعودی بود؛ که شدت آن برای نسبت کمتر، بیشتر بود. عملکرد تنگ‌شدگی به نفع نیروی رانش جریان است؛ که با افزایش شیب تقویت و با افزایش غلظت تضعیف ‌می‌شود. در باز‌شدگی، مقاومت ناشی از اختلاط غلبه دارد؛ که با افزایش غلظت تقویت و با افزایش شیب تضعیف می‌گردد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Experimental investigation of the effects of sudden width changes on the hydrodynamics of density current front and the interaction of the effective forces

نویسندگان [English]

  • Pouya Ehdaei
  • Mehdi Ghomeshi
  • Mehdi Daryaee
  • Mohammad Reza Zayri
Department of Hydraulic Structures, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
چکیده [English]

In this research, 18 experiments were conducted to investigate the effects of sudden constriction and expansion on frontal hydrodynamics. The flow rate was set at 1.1 l/s, with variables including concentrations of 5 and 10 gr/l, slopes of zero, 1.5, and 3 percent, and width ratios of 0.39, 0.64, and 0.92. The flow regime encompassed all three states: subcritical, critical, and supercritical. In constrictions with ratios of 0.39 and 0.64, the front velocity initially increases up to a point due to buoyancy flux but then decreases under the influence of mixing. Increasing the constriction intensity and slope raises the maximum velocity and delays its occurrence. Specifically, at a 3 percent slope, the maximum velocity for the 0.39 ratio compared to 0.64 increased by 20.29 percent and 24.49 percent for concentrations of 5 and 10 gr/l, respectively. In expansions with these two ratios, the velocity decreases with distance due to intensified turbulent instabilities, with a more pronounced effect at the 0.39 ratio. At the 0.92 ratio, constriction and expansion had no significant impact, and the velocity trend resembled that of a constant-width channel: decreasing at zero slope and increasing in sloped channels. The front height increased with distance in both constriction and expansion regions for all width ratios, with greater intensity at smaller ratios. The effect of constriction is in support of flow driving force, strengthened by slope but weakened by concentration. In expansion, mixing-induced resistance prevailed, strengthened by concentration but weakened by slope.

کلیدواژه‌ها [English]

  • Sudden Constriction
  • Sudden Expansion
  • Driving Force
  • Mixing-Induced Resistance
  • Kelvin-Helmholtz Instabilities

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مدیریت آب و آبیاری
دوره 15، شماره 2
شهریور 1404
صفحه 233-252

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