بررسی آزمایشگاهی اثر زبری کف بر تنش‌برشی و قدرت گردابه در قوس 90 درجه تند کانال مستطیلی

نویسندگان

چکیده

الگوی جریان در قوس‌ها به‌دلیل تغییر شرایط هیدرولیکی سبب فرایند فرسایش و رسوب‌گذاری می‌شود. در این مطالعه آزمایش‌هایی در قوس 90 درجه تند یک کانال مستطیلی با نسبت R/B=2 با عمق ثابت 17 سانتی‌متر در سه دبی 15،‏ 25 و 35 لیتر در ثانیه با اعداد فرود 17‎/0،‏ 28‎/0 و 4‎/0 انجام شد. در هر حالت،‏ کف فلوم توسط ذراتی با دانه‌بندی یکنواخت،‏ با سه زبری mm5‎/0،‏ mm2 و mm5 زبر شد. نتایج نشان می‌دهد با افزایش زبری،‏ تنش‌برشی کف افزایش یافته و موقعیت تنش‌برشی حداکثر در تمامی حالت‌ها از 10 تا 65 درجه،‏ نزدیک دیوار داخلی و از 90 درجه به بعد نزدیک دیوار خارجی است. همچنین،‏ تغییرات قدرت گردابه در طول کانال دارای یک حداکثر مطلق و یک حداکثر نسبی در موقعیت 50 درجه و 80 درجه است که افزایش زبری باعث می‌شود حداکثر مطلق در رأس قوس (50 درجه) تشکیل شود. علاوه بر آن،‏ نتایج نشان داد که شرایط هیدرولیکی بستر از نظر صاف و یا زبر بودن عامل مؤثر بر قدرت گردابه است. براساس تغییرات تنش‌برشی کف و قدرت گردابه،‏ مقطع 80-90 درجه قوس نزدیک دیوار خارجی،‏ به‌عنوان منطقه فرسایش‌پذیر تعیین شد.

کلیدواژه‌ها


عنوان مقاله [English]

Experimental Investigation of the Effects of Height of Bed Roughness on Shear stress and the Strength of Vortex in a 90 Degree Sharp Rectangular Bend

نویسندگان [English]

  • neda sheikh rezazadeh nikou
  • aziz sozepor
  • mahmmod shafai
چکیده [English]

Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

کلیدواژه‌ها [English]

  • Experimental model-Vortex strength.-Shear stress of bed-Height of bed roughness-?? degree bend-