بررسی آزمایشگاهی عملکرد هیدرولیکی سرریزهای پلکانی قوس محور متاثر از تغییرات شیب کانال تبدیل پایین‌دست

ﺳﺎﺑﻘﻪ و ﻫﺪف: ﺳﺮرﯾﺰ ﭘﻠﮑﺎﻧﯽ ﻧﻘﺶ ﻗﺎﺑﻞ ﻣﻼﺣﻈﻪ ای در اﺗﻼف ﻣﺆﺛﺮ اﻧﺮژی ﺟﺮﯾﺎن داﺷﺘﻪ و ﺑﻪﻋﻨﻮان ﻗﺪرﺗﻤﻨﺪﺗﺮﯾﻦ ﺳﺎزه ﻫﯿﺪروﻟﯿﮑﯽ ﻧﺴﺒﺖ ﺑﻪ ﺳﺮرﯾﺰ اوﺟﯽ ﺑﺮای ﻣﺴﺘﻬﻠﮏ ﮐﺮدن اﻧﺮژی ﺟﺮﯾﺎن ﺷﻨﺎﺧﺘﻪ ﻣﯽﺷﻮد. اﮔﺮﭼﻪ ﭘﮋوﻫﺶ ﻫﺎی ﻣﺘﻌﺪدی در اﯾﻦ زﻣﯿﻨﻪ اﻧﺠﺎم ﺷﺪه اﺳﺖ، اﻣﺎ ﺑﺮرﺳﯽﻫﺎ ﺑﯿﺎﻧﮕﺮ آن اﺳﺖ ﺑﺎوﺟﻮداﯾﻦ ﭘﮋوﻫﺶ ﻫﺎی ﻣﺘﻌﺪد، ﻫﯿﺪروﻟﯿﮏ ﺟﺮﯾﺎن ﺳﺮرﯾﺰﻫﺎی ﭘﻠﮑﺎﻧﯽ ﻗﻮس ﻣﺤﻮر ﻣﺘﺄﺛﺮ از ﺗﻐﯿﯿﺮات ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ ﭘﺎﯾﯿﻦدﺳﺖ ﺗﺎﮐﻨﻮن ﻣﻮردﺗﻮﺟﻪ ﻗﺮار ﻧﮕﺮﻓﺘﻪ و ﭘﮋوﻫﺸﯽ ﺑﺮ روی آن اﻧﺠﺎم ﻧﺸﺪه اﺳﺖ ﺑﻪ ﻫﻤﯿﻦ دﻟﯿﻞ ﻫﯿﺪروﻟﯿﮏ اﯾﻦ ﻧﻮع ﺧﺎص ﺳﺮرﯾﺰ ﺗﺎﮐﻨﻮن ﻧﺎﺷﻨﺎﺧﺘﻪ ﻣﺎﻧﺪه اﺳﺖ، ﺑﻨﺎﺑﺮاﯾﻦ در اﯾﻦ ﭘﮋوﻫﺶ ﺳﺮرﯾﺰ ﭘﻠﮑﺎﻧﯽ ﻗﻮس ﻣﺤﻮر ﺑﺎ دﯾﻮارهﻫﺎی ﻫﺎدی ﻣﺘﻘﺎرب ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﺗﻐﯿﯿﺮات ﺷﯿﺐ ﺗﺒﺪﯾﻞ ﻣﻮرد آزﻣﺎﯾﺶ واﻗﻊ ﺷﺪه اﺳﺖ. ﻣﻮاد و روش ﻫﺎ: اﯾﻦ ﭘﮋوﻫﺶ ﺑﺎ ﻫﺪف ﺑﺮرﺳﯽ آزﻣﺎﯾﺸﮕﺎﻫﯽ ﻋﻤﻠﮑﺮد ﻫﯿﺪروﻟﯿﮑﯽ ﺳﺮرﯾﺰﻫﺎی ﭘﻠﮑﺎﻧﯽ ﻗﻮس ﻣﺤﻮر ﺗﺤﺖ ﺗﺄﺛﯿﺮ ﺗﻐﯿﯿﺮات ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ اﻧﺠﺎم ﺷﺪه اﺳﺖ. آزﻣﺎﯾﺶ ﻫﺎ در ﯾﮏ ﻓﻠﻮم ﻣﺴﺘﻄﯿﻠﯽ ﺑﻪ ﻃﻮل 15 ﻣﺘﺮ، ارﺗﻔﺎع 1 ﻣﺘﺮ و ﻋﺮض 1 ﻣﺘﺮ اﻧﺠﺎم ﺷﺪ. آزﻣﺎﯾﺶﻫﺎ ﺑﻪ ازای دﺑﯽﻫﺎی ﻣﺨﺘﻠﻒ ﺑﯿﻦ 0/15 ﺗﺎ 2/01 ﺑﺮاﺑﺮ دﺑﯽ ﻃﺮاﺣﯽ ﺳﺮرﯾﺰ اﻧﺠﺎم ﮔﺮدﯾﺪ و ﻣﺪل ﻓﯿﺰﯾﮑﯽ ﺳﺎﺧﺘﻪ ﺷﺪه ﺗﺤﺖ 4 ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ ﭘﺎﯾﯿﻦدﺳﺖ (m) ﺷﺎﻣﻞ 1:27، 1:30، 1:33 و 0 ﻣﻮرد آزﻣﺎﯾﺶ ﻗﺮار ﮔﺮﻓﺖ. ﯾﺎﻓﺘﻪ ﻫﺎ: ﻧﺘﺎﯾﺞ آزﻣﺎﯾﺶ ﻫﺎ ﻧﺸﺎن داد ﮐﻪ در ﺳﺮرﯾﺰﻫﺎی ﭘﻠﮑﺎﻧﯽ ﻗﻮس ﻣﺤﻮر ﺗﺤﺖ اﺛﺮ ﺗﻐﯿﯿﺮات ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ ﭘﺎﯾﯿﻦ دﺳﺖ (𝑚) ﺑﺎ ﮐﺎﻫﺶ ﺷﯿﺐ ﺗﺒﺪﯾﻞ، ﻇﺮﻓﯿﺖ ﺗﺨﻠﯿﻪ ﺳﺮرﯾﺰ ﺑﻪ ازای ﺑﺎﻻﺗﺮﯾﻦ ﻫﺪ ﻣﺠﺎز ﺑﯿﺶ ﺗﺮ ﺧﻮاﻫﺪ ﺷﺪ. ﻫﻢ ﭼﻨﯿﻦ در ﺑﺎزه 0/7>𝐻/𝐻𝑑 )ﺑﺎر آﺑﯽ ﮐﻞ ﺑﺮ ﻫﺪ ﻃﺮاﺣﯽ( ﻣﻘﺪار ﺿﺮﯾﺐ دﺑﯽ در ﻣﺪل ﻓﯿﺰﯾﮑﯽ ﭘﻠﮑﺎﻧﯽ در ﻫﻤﻪ ﺷﯿﺐﻫﺎ ﮐﻢ ﺗﺮ از ﻣﺪل ﺻﺎف usbr ﻣﺸﺎﻫﺪه ﮔﺮدﯾﺪ. در ﺑﺎزه 𝐻/𝐻𝑑 >0/7<1/3 اﯾﻦ ﻣﻘﺪار ﺑﺎ ﺿﺮﯾﺐ آﺑﮕﺬری ﺳﺮرﯾﺰ usbr ﺗﻄﺎﺑﻖ دارد، اﻣﺎ ﺑﺎ اﻓﺰاﯾﺶ ﺑﺎر آﺑﯽ در ﺗﻤﺎﻣﯽ ﺷﯿﺐ ﺗﺒﺪﯾﻞﻫﺎ، ﺑﻪ دﻟﯿﻞ اﺳﺘﻐﺮاق ﺳﺮرﯾﺰ، ﻧﻤﻮدار ﺿﺮﯾﺐ دﺑﯽ روﻧﺪ ﮐﺎﻫﺸﯽ ﺑﻪ ﺧﻮد ﮔﺮﻓﺘﻪ و ﮐﺎﻫﺶ ﮐﺎراﯾﯽ ﺳﺮرﯾﺰ ﻧﺴﺒﺖ ﺑﻪ ﺳﺮرﯾﺰ اوﺟﯽ اﺳﺘﺎﻧﺪارد usbr ﻣﺸﺎﻫﺪه ﻣﯽﺷﻮد. ﻋﻼوه ﺑﺮ اﯾﻦ، آزﻣﺎﯾﺶ ﻫﺎ ﻧﺸﺎن داد، ﻣﺪلﻫﺎی ﺑﺎ ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ 0=m و 1:33=m، ﺗﻨﻬﺎ ﻣﺪلﻫﺎﯾﯽ ﻣﯽﺑﺎﺷﻨﺪ ﮐﻪ در ﻣﻘﯿﺎس واﻗﻌﯽ ﺗﻮان ﻋﺒﻮر ﺣﺪاﮐﺜﺮ دﺑﯽ ﺳﯿﻼب ﻣﺤﺘﻤﻞ را در ﺣﺪاﮐﺜﺮ ارﺗﻔﺎع ﻣﺠﺎز )5m( دارا اﺳﺖ و ازآﻧﺠﺎﯾﯽ ﮐﻪ ﺷﯿﺐ ﮐﺎﻧﺎل ﮔﺬار 1:33=m دارای اﺑﻌﺎد ﻫﻨﺪﺳﯽ ﮐﻮﭼﮏ ﺗﺮی در ﮐﺎﻧﺎل ﭘﺎﯾﯿﻦدﺳﺖ در ﻣﻘﺎﯾﺴﻪ ﺑﺎ ﺷﯿﺐ ﮐﺎﻧﺎل ﮔﺬار 0=m اﺳﺖ، ﺑﻨﺎﺑﺮاﯾﻦ اﯾﻦ ﺷﯿﺐ ﻣﯽﺗﻮاﻧﺪ ﺑﻪ ﻋﻨﻮان ﻣﻨﺎﺳﺐﺗﺮﯾﻦ ﺷﯿﺐ ﺗﺒﺪﯾﻞ در ﮐﺎﻧﺎل ﭘﺎﯾﯿﻦدﺳﺖ ﻣﻌﺮﻓﯽ ﮔﺮدد. ﻧﺘﯿﺠﻪﮔﯿﺮی: ﻧﺘﺎﯾﺞ ﮐﻤﯽ و ﮐﯿﻔﯽ ﭘﮋوﻫﺶ ﺣﺎﺿﺮ ﺑﻪ ﺻﻮرت زﯾﺮ ﺧﻼﺻﻪ ﻣﯽﮔﺮدد. 1- در ﺳﺮرﯾﺰﻫﺎی ﭘﻠﮑﺎﻧﯽ ﻗﻮس ﻣﺤﻮر ﺑﺎ اﻓﺰاﯾﺶ ﺑﺎر آﺑﯽ ﺑﺎﻻدﺳﺖ، ﺿﺮﯾﺐ دﺑﯽ ﺑﻪ ازای ﺗﻤﺎﻣﯽ ﺷﯿﺐ ﺗﺒﺪﯾﻞﻫﺎ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ و ﻧﯿﺰ ﺗﺎ ﻫﻨﮕﺎﻣﯽ ﮐﻪ ﺳﺮرﯾﺰ در ﻣﺤﺪوده ﺟﺮﯾﺎنﻫﺎی ﺑﺤﺮاﻧﯽ و ﻓﻮق ﺑﺤﺮاﻧﯽ ﻗﺮار دارد، ﺗﻐﯿﯿﺮات ﺷﯿﺐ ﺗﺒﺪﯾﻞ ﺗﺄﺛﯿﺮ ﻓﺮاواﻧﯽ ﺑﺮ ﺿﺮﯾﺐ دﺑﯽ ﻧﺪارد. ﻋﻠﯽرﻏﻢ اﯾﻦ، وﻗﺘﯽ ﺳﺮرﯾﺰ ﻣﺴﺘﻐﺮق ﻣﯽﮔﺮدد، ﺗﻔﺎوت در ﺿﺮﯾﺐ دﺑﯽ ﻧﻤﺎﯾﺎن ﻣﯽﺷﻮد ﮐﻪ ﻣﯽﺗﻮاﻧﺪ ﺑﻪ ﺧﺎﻃﺮ اﺳﺘﻐﺮاق ﻣﻮﺿﻌﯽ در ﭘﺎﯾﺎب ﺑﺎﺷﺪ. 2- اﺳﺘﻬﻼک اﻧﺮژی ﺑﺎ اﻓﺰاﯾﺶ دﺑﯽ ﮐﺎﻫﺶ ﻣﯽﯾﺎﺑﺪ، اﻣﺎ ﻣﺪلﻫﺎ ﺑﺎ ﻣﻘﺎدﯾﺮ ﺷﯿﺐ ﺗﺒﺪﯾﻞ ﮐﻮﭼﮏ ﺗﺮ اﻧﺮژی ﺑﯿﺶ ﺗﺮی را در دﺑﯽﻫﺎی ﺑﺎﻻﺗﺮ ﻣﺴﺘﻬﻠﮏ ﻣﯽﮐﻨﻨﺪ. 3- ﻣﺪل ﺑﺎ ﺷﯿﺐ ﮐﺎﻧﺎل ﺗﺒﺪﯾﻞ 1:33=m ﮐﻪ ﺗﻮان ﻋﺒﻮر ﺣﺪاﮐﺜﺮ دﺑﯽ ﺳﯿﻼب ﻣﺤﺘﻤﻞ را در ﺣﺪاﮐﺜﺮ ارﺗﻔﺎع ﻣﺠﺎز (5m) دارا اﺳﺖ ﻣﯽﺗﻮاﻧﺪ ﺑﻪ ﻋﻨﻮان ﻣﻨﺎﺳﺐﺗﺮﯾﻦ ﺷﯿﺐ ﺗﺒﺪﯾﻞ در ﮐﺎﻧﺎل ﭘﺎﯾﯿﻦدﺳﺖ ﻣﻌﺮﻓﯽ ﮔﺮدد.

Experimental Study of Hydraulic Performance of Stepped Spillway with a Curve Axis Affected by Downstream Transition Channel slope Changes

Background and Objectives: The purpose of the design of energy dissipaters is to dissipate part of the kinetic energy of the inflowing flow in order to return safely the flow to the downstream channel or river and prevent scour below spillways, chutes and sluices. However, surveys show that despite the numerous researches, there is a lack of research on the comprehensive study of hydraulic performance of stepped spillway with curve axis under downstream transition channel slope variation. Therefore, in this study, several physical models of curve axis stepped spillway with converging training walls were made and the impact of downstream transition channel slope variation on the hydraulic characteristics of this type spillway was assessed.Materials and Methods: This study was conducted with the aim of investigating the hydraulic performance of stepped spillway with curve axis under downstream transition channel slope variation. The experiments were carried out in a rectangular flume with length of 15 m, height of 1 m and width of 2 m. The experiments were performed at different discharge rates from 0.015 to 2.1 times the design discharge and the physical model was tested under four different transition channel slopes of m=0, m=1:33, m=1:30, and m=1:27.Results: The results of the experiments indicate that in the converging steeped spillway with downstream transition channel slope variation, by decreasing slope of transition channel, the discharge flood in the maximum head allowed will go up. Also, it is find that in the range of H/Hd = 0.7, the discharge coefficient in the stepped physical model for all transition slopes was less than the smooth USBR model and in the range of 0.7 < H/Hd < 1. 3 there was a good consistency with the USBR model. However, with increasing the total water head, due to the spillway submergence the discharge coefficient for all transition slopes showed a descending trend and the spillway efficiency decreased in compared with the standard USBR ogee spillway. Moreover, the results showed that the models with slope of 0 and 1:33 are two models which can pass the probable maximum flood discharge in the maximum allowable height successfully But, the model dimension of physical model with downstream transition Channel slope of m=1:33 is smaller than that of m=0.Therefore, model with slope of m=1:33 can be selected as the most efficient model.Conclusion: General qualitative and quantitative results of the present study are summarized as the fallowing:1 In the converging stepped spillway by increasing total upstream head, the discharge coefficient will go up for each of the transition Channel slope (m) and until the downstream flow is at either supercritical or critical stages, the discharge coefficient is independent of variation of transition Channel slope. By contrast, at the submergence stage for the spillway, the difference in the discharge coefficient can be due to tailwater submergence occurring in the spillway.2 Energy dissipation over converging stepped spillway decreases with increasing the discharge ratio, but model with smaller amount of transition slope (m) lead to decline more energy dissipation in higher discharge.3 The model with slope of m=1:33 can be selected as the best model due to it’s ability to pass the probable maximum flood in the Maximum allowable head.