بررسی تأثیر فشردگی جانبی روی ضریب دبی سرریزهای استوانه‌ای

نویسندگان

چکیده

از انواع سازه‌های اندازه‌گیری جریان در کانال‌های باز سرریزهای استوانه‌ای بوده که شکل مقطع کانال و هزینه‌های اقتصادی تعیین کننده طول تاج آن‌ها است. این پژوهش آزمایشگاهی تأثیر فشردگی تاج سرریزهای استوانه‌ای را بر خصوصیات جریان از جمله ضریب دبی بررسی می‌کند. آزمایش‌ها روی فلومی با ابعاد 460×300×7500 میلی‌متر،‏ با استفاده از مدل‌های سرریز استوانه‌ای با قطر 160? ?75 میلی‌متر،‏ درصدهای فشردگی (طول تاج سرریز به عرض کانال) تاج سرریز 1? ?2‎/0 و ترکیبات مختلف دبی و عمق جریان برای جریان آزاد انجام شد. نتایج نشان داد با افزایش عمق آب بالادست به ارتفاع سرریز ضریب دبی تمام سرریزها افزایش یافته ولی با کاهش نسبت b/B شیب تغییرات ضریب دبی در مقابل H/P کاهش می‌یابد. همچنین برای هر قطر و ثابت،‏ با افزایش b/B ضریب دبی افزایش می‌یابد. ضریب فشردگی جریان روی تاج چنین سرریزهایی با به کارگیری تئوری سرریزها و همچنین داده‌‌های آزمایشگاهی به دست آمده که در محدوده 4‎/2 2‎/1 از 71‎/0 تا 98‎/0 تغییر می‌کند. نتایج نشان می‌دهد با افزایش H/P ضریب فشردگی تمامی سرریزها کم می‌شود. از طرفی برای هر H/P ثابت،‏ با کاهش نسبت b/B،‏ ضریب فشردگی جریان روی تاج سرریز کوچک‌تر می‌شود.

کلیدواژه‌ها


عنوان مقاله [English]

Investigating the effect of side contraction on the discharge coefficient of Cylindrical weirs

نویسندگان [English]

  • fateme nadery
  • mohsen masoudian
  • Klaus Roettcher
چکیده [English]

Cylindrical weirs are a kind of flow measurement structures in open channels whose crest length is affected by the channel cross section and economical expenses. The current experimental research investigates the effect of side contracting on flow characteristics such as discharge coefficient of cylindrical weirs. The experiments were done on a laboratory flume with dimensions of 7500*300*460 mm, using various diameters of cylindrical weir models in the range of 75?P?160 mm, contraction ratios of 0.2?b/B?1, and various combinations of discharge and flow depth for free flow. The results show that an increase in the ratio of upstream water depth to the weir height (H/P), leads to an increase in the discharge coefficient for all weirs, but when b/B decreases, the gradient of Cd vs. H/P, will decrease too. On the other hand, for any given P and H, the discharge coefficient will increase with increasing the b/B ratio. The contraction coefficient (Cc) for such weirs, determined by using weir theory and experimental data, varies in the range of 0.71 to 0.98 for 1.2?H/P?2.4. These results also show when H/P increases, Cc will increase for all weirs too. Besides, for any given H/P ratio, the flow contraction coefficient over the weir crest will decrease with a decrease in the b/B ratio.
Cylindrical weirs are a kind of flow measurement structures in open channels whose crest length is affected by the channel cross section and economical expenses. The current experimental research investigates the effect of side contracting on flow characteristics such as discharge coefficient of cylindrical weirs. The experiments were done on a laboratory flume with dimensions of 7500*300*460 mm, using various diameters of cylindrical weir models in the range of 75?P?160 mm, contraction ratios of 0.2?b/B?1, and various combinations of discharge and flow depth for free flow. The results show that an increase in the ratio of upstream water depth to the weir height (H/P), leads to an increase in the discharge coefficient for all weirs, but when b/B decreases, the gradient of Cd vs. H/P, will decrease too. On the other hand, for any given P and H, the discharge coefficient will increase with increasing the b/B ratio. The contraction coefficient (Cc) for such weirs, determined by using weir theory and experimental data, varies in the range of 0.71 to 0.98 for 1.2?H/P?2.4. These results also show when H/P increases, Cc will increase for all weirs too. Besides, for any given H/P ratio, the flow contraction coefficient over the weir crest will decrease with a decrease in the b/B ratio.
Cylindrical weirs are a kind of flow measurement structures in open channels whose crest length is affected by the channel cross section and economical expenses. The current experimental research investigates the effect of side contracting on flow characteristics such as discharge coefficient of cylindrical weirs. The experiments were done on a laboratory flume with dimensions of 7500*300*460 mm, using various diameters of cylindrical weir models in the range of 75?P?160 mm, contraction ratios of 0.2?b/B?1, and various combinations of discharge and flow depth for free flow. The results show that an increase in the ratio of upstream water depth to the weir height (H/P), leads to an increase in the discharge coefficient for all weirs, but when b/B decreases, the gradient of Cd vs. H/P, will decrease too. On the other hand, for any given P and H, the discharge coefficient will increase with increasing the b/B ratio. The contraction coefficient (Cc) for such weirs, determined by using weir theory and experimental data, varies in the range of 0.71 to 0.98 for 1.2?H/P?2.4. These results also show when H/P increases, Cc will increase for all weirs too. Besides, for any given H/P ratio, the flow contraction coefficient over the weir crest will decrease with a decrease in the b/B ratio.
Cylindrical weirs are a kind of flow measurement structures in open channels whose crest length is affected by the channel cross section and economical expenses. The current experimental research investigates the effect of side contracting on flow characteristics such as discharge coefficient of cylindrical weirs. The experiments were done on a laboratory flume with dimensions of 7500*300*460 mm, using various diameters of cylindrical weir models in the range of 75?P?160 mm, contraction ratios of 0.2?b/B?1, and various combinations of discharge and flow depth for free flow. The results show that an increase in the ratio of upstream water depth to the weir height (H/P), leads to an increase in the discharge coefficient for all weirs, but when b/B decreases, the gradient of Cd vs. H/P, will decrease too. On the other hand, for any given P and H, the discharge coefficient will increase with increasing the b/B ratio. The contraction coefficient (Cc) for such weirs, determined by using weir theory and experimental data, varies in the range of 0.71 to 0.98 for 1.2?H/P?2.4. These results also show when H/P increases, Cc will increase for all weirs too. Besides, for any given H/P ratio, the flow contraction coefficient over the weir crest will decrease with a decrease in the b/B ratio.

کلیدواژه‌ها [English]

  • Contraction coefficient-Discharge coefficient-Cylindrical weir-Side contraction.-