استفاده از نظریه‌ی خود تشابهی ناقص به منظور تخمین نسبت عمقهای مزدوج پرش آبی ایجاد شده در جریانهای غلیظ عبوری از روی بسترهای صاف و زبر

محورهای موضوعی : برگرفته از پایان نامه

نادر برهمند ¹

1 - گروه مهندسی عمران، واحد لارستان، ‌دانشگاه ‌آزاد ‌اسلامی، لارستان، ایران.

تاریخ دریافت : 1394/12/12 تاریخ پذیرش : 1394/12/12 تاریخ انتشار : 1394/12/01

کلید واژه: جریان غلیظ, پرش آبی در جریان غلیظ, نظریه‌ی خود تشابهی ناقص, نسبت عمقهای مزدوج, زبری بستر,

چکیده مقاله :

جریان غلیظ به علت تفاوت چگالی با سیال محیطی به وجود می­آید. این تفاوت جرم حجمی می تواند ناشی از ذرات جامد نامحلول، مواد محلول، تفاوتهای دمایی و ... باشد. پرشهای آبی ایجاد شده در جریانهای غلیظ، نقش مهمی در تغییرات خصوصیات کیفی جریان غلیظ، و همچنین سیال محیطی (همانند دریاچه­ها و مخازن سدها) دارند. در این تحقیق، با استفاده از تحلیل ابعادی و نظریه­ی خود تشابهی ناقص، چنین پرشهایی مورد مطالعه قرار گرفته، و معادله­ای جدید جهت محاسبه­ی نسبت عمقهای مزدوج پرش به دست آمده است. به منظور بررسی کارایی این معادله، از نتایج مجموعه­ای از آزمایشها، که جهت هر دو نوع بستر صاف و زبر صورت پذیرفته است، کمک گرفته شد. نتایج آزمایش، نشان دهنده­ی دقت و کارایی مناسب معادله­ی جدید به دست آمده نسبت به معادله سنتی می­باشند. به عبارت دیگر، نشان داده شده است که نمی­توان از تاثیر اختلاط سیال محیطی با جریان غلیظ، و همچنین از تاثیر زبری بستر بر مقدار نسبت عمقهای مزدج پرش، حتی در مقادیر کوچک، صرف­نظر کرد.

چکیده انگلیسی:

Density current is produced because of a density contrast with the ambient fluid. This density difference can result from dissolved solids, suspended materials, temperature, etc. Density jumps significantly influence the quality characteristics of the gravity currents and the ambient fluid (e.g., lakes and reservoirs). In this research, using dimensional analysis and incomplete self-similarity method, these jumps were studied and a new equation was obtained for calculating the sequent depth ratio. This equation was validated using experimental results. Therefore, these experiments were carried out on both smooth and rough beds. The results indicate that the new relationship is more accurate than the classical equation; it was shown that the effects of both the entrainment ratio and the bed roughness are not negligible, even for their small amount.

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