بررسي آزمايشگاهي تاثير ايجاد دندانه، روزنه و هوادهنده در سرريز كنگره اي مثلثي

Experimental study of the effect of dentate, orifice and aerator on a triangular labyrinth weir

ﺳﺮرﯾﺰ ﺳﺪﻫﺎ ﺟﻬﺖ ﺗﻨﻈﯿﻢ ﺳﻄﺢ آب اﺳﺘﻔﺎده ﻣﯽ ﺷﻮﻧﺪ. در ﺣﺪود 33 درﺻﺪ از ﺷﮑﺴﺖ ﺳﺪﻫﺎ ﺑﻪ دﻟﯿﻞ ﻋﺪم ﻇﺮﻓﯿﺖ ﮐﺎﻓﯽ ﺳﺮرﯾﺰﻫﺎ رخ داده اﺳﺖ. ﯾﮑـﯽ از راﻫﮑﺎرﻫﺎ، اﺳﺘﻔﺎده از ﺳﺮرﯾﺰﻫﺎي ﺑﺎ ﺗﺎج ﻏﯿﺮﺧﻄﯽ اﺳﺖ ﮐﻪ از ﺟﻤﻠﻪ اﯾﻦ ﺳﺮرﯾﺰﻫﺎ ﻣﯽ ﺗﻮان ﺑﻪ ﺳﺮرﯾﺰ ﮐﻨﮕﺮه اي اﺷﺎره ﻧﻤﻮد. در اﯾﻦ ﭘﮋوﻫﺶ ﺑﻪ ﺑﺮرﺳﯽ ﺗﺎﺛﯿﺮ اﯾﺠﺎد دﻧﺪاﻧﻪ و روزﻧﻪ و ﻫﻤﭽﻨﯿﻦ ﺣﺎﻟﺘﯽ ﺗﺮﮐﯿﺒﯽ از ﻫﺮ دو در ﺳـﺮرﯾﺰ و در ﺳـﻪ ﻧﺴـﺒﺖ ﺑـﺰرگ ﻧﻤـﺎﯾﯽ 3 ،2 و 4 ﭘﺮداﺧﺘـﻪ ﺷـﺪ. آزﻣـﺎﯾﺶ ﻫـﺎ در ﯾـﮏ ﮐﺎﻧـﺎل آزﻣﺎﯾﺸﮕﺎﻫﯽ ﻣﺴﺘﻄﯿﻠﯽ ﺑﻪ ﻃﻮل 15 ﻣﺘﺮ، ﻋﺮض 0/8 ﻣﺘﺮ و ارﺗﻔﺎع 0/8 ﻣﺘﺮ ﺑﺎ ﻣﺤﺪوده دﺑﯽ 10 ﺗﺎ 90 ﻟﯿﺘﺮ در ﺛﺎﻧﯿﻪ اﺟﺮا ﺷﺪﻧﺪ. 9 ﻣﺪل ﻓﯿﺰﯾﮑﯽ ﺳﺮرﯾﺰ، در اﯾﻦ ﭘﮋوﻫﺶ ﻣﻮرد اﺳﺘﻔﺎده ﻗﺮار ﮔﺮﻓﺖ ﮐﻪ ﺿﺨﺎﻣﺖ 3 ﻣﯿﻠﯽ ﻣﺘﺮ، ارﺗﻔﺎع 15 ﺳﺎﻧﺘﯽ ﻣﺘﺮ و ﻃﻮل 60،40 و 80 ﺳﺎﻧﺘﯽ ﻣﺘﺮ داﺷﺘﻨﺪ. ﻫﻤﭽﻨﯿﻦ رﺑﻊ اﺳﺘﻮاﻧﻪ ﻫﺎﯾﯽ ﺑﺎ ﺷﻌﺎع 1/5 ﺳﺎﻧﺘﯽ ﻣﺘﺮ ﺑﻪ ﻋﻨﻮان ﻫﻮاده روي ﺑﺎل ﻣﺪل ﻫﺎي ﺳﺎده ﺳﺮرﯾﺰ ﻧﺼﺐ ﺷﺪﻧﺪ. ﻧﺘﺎﯾﺞ ﭘﮋوﻫﺶ ﻧﺸﺎن داد ﮐﻪ ﻫﻮاده ﻫﺎ ﺣﺪاﮐﺜﺮ ﺗﺎ 13 درﺻﺪ ﺳﺒﺐ اﻓﺰاﯾﺶ ﺿﺮﯾﺐ دﺑﯽ ﻧﺴﺒﺖ ﺑﻪ ﺳﺮرﯾﺰ ﮐﻨﮕﺮه اي ﺳﺎده ﻣﯽ ﺷﻮﻧﺪ. اﻣﺎ ﺑﺎ اﻓﺰاﯾﺶ دﺑﯽ و ﻫﻤﭽﻨﯿﻦ اﻓﺰاﯾﺶ ﺑﺰرﮔﻨﻤﺎﯾﯽ ﺳﺮرﯾﺰ، اﯾﻦ ﺗﺎﺛﯿﺮ ﺑﺴﯿﺎر ﻧﺎﭼﯿﺰ ﺧﻮاﻫﺪ ﺷﺪ. ﺑﺮرﺳﯽ ﻫﺎ ﻧﺸـﺎن داد ﺑﺮاي 2 = L/W و 0.2 = H/P ، ﺿﺮﯾﺐ دﺑﯽ ﺳﺮرﯾﺰ دﻧﺪاﻧﻪ-روزﻧﻪ دار و ﺳﺮرﯾﺰ دﻧﺪاﻧﻪ دار ﺑﻪ ﺗﺮﺗﯿﺐ 75/6 و 17/5 درﺻـﺪ ﺑﯿﺸـﺘﺮ از ﺳـﺮرﯾﺰ ﮐﻨﮕـﺮه اي ﺳﺎده اﺳﺖ. ﺑﺎ اﯾﻦ ﺣﺎل ، دﻧﺪاﻧﻪ و روزﻧﻪ ﮐﺎراﯾﯽ ﺧﻮد را در ﻫﺪﻫﺎي ﺑﺎﻻ از دﺳﺖ ﻣﯽ دﻫﻨﺪ و ﺿﺮﯾﺐ دﺑﯽ ﻧﺰدﯾﮏ ﺑﻪ ﺳﺮرﯾﺰ ﮐﻨﮕﺮه اي ﺳﺎده ﺧﻮاﻫﺪ ﺷﺪ. دﻟﯿـﻞ اﯾﻦ ﺗﻐﯿﯿﺮات ﺗﺪاﺧﻞ ﺟﺮﯾﺎن در ﭘﺎﯾﯿﻦ دﺳﺖ ﺳﺮرﯾﺰ ﻣﯽ ﺑﺎﺷﺪ ﮐﻪ ﺑﺎ اﯾﺠﺎد دﻧﺪاﻧﻪ و روزﻧﻪ ﺑﯿﺸﺘﺮ ﻧﯿﺰ ﺧﻮاﻫـﺪ ﺷـﺪ . ﻫﻤﭽﻨـﯿﻦ اﻓـﺰاﯾﺶ ﺑﺰرﮔﻨﻤـﺎﯾﯽ ﺳـﺮرﯾﺰ ﻫـﺎي ﮐﻨﮕﺮه اي ﺳﺒﺐ ﮐﺎﻫﺶ ﺿﺮﯾﺐ دﺑﯽ ﻣﯽ ﺷﻮد اﻣﺎ اﯾﻦ ﮐﺎﻫﺶ در ﺳﺮرﯾﺰ ﮐﻨﮕﺮه اي دﻧﺪاﻧﻪ-روزﻧﻪ دار ﺑﺴﯿﺎر ﺑﯿﺸﺘﺮ از دو ﻧﻮع ﺳﺮرﯾﺰ دﯾﮕﺮ ﺑﻮده و ﺗﺎ 40 درﺻﺪ ﻧﯿﺰ ﻣﯽ رﺳﺪ. ﺑﻨﺎﺑﺮاﯾﻦ ﻋﻤﻠﮑﺮد ﺳﺮرﯾﺰ ﮐﻨﮕﺮه اي دﻧﺪاﻧﻪ-روزﻧﻪ دار در ﻧﺴﺒﺖ ﺑﺰرﮔﻨﻤﺎﯾﯽ ﺑﺎﻻ ﻣﻨﺎﺳﺐ ﺑﻨﻈﺮ ﻧﻤﯽ رﺳﺪ.

Dam Weirs are used to regulate the water level. About 33 percent of dam failures have occurred due to insufficient capacity of weirs. One way to prevent is to use weir with nonlinear crest, such as labyrinth weir. In this study, the effect of dentate and orifice as well as a combination of both in the weir and in three magnification ratios of 2, 3 and 4 were investigated. The experiments were performed in a rectangular laboratory channel 15 meters long, 0.8 meters wide and 1 meter high with a flow rate of 10 to 90 liters per second. Nine physical models of weirs were used in this study, which were 3 mm thick, 15 cm high and 40, 60 and 80 cm long. Also, quarter cylinders with a radius of 1.5 cm were installed as aerators on the simple weir models. The results showed that aerators increase the discharge coefficient up to 13% compared to simple labyrinth weir. But with the increase in flow as well as the magnification of the labyrinth weir, this effect will be very small. Studies showed for L/W= 2 and H/P= 0.2, the discharge coefficient of orifice-dentate weir and dentate weir are 75.6 and 17.5 percent, respectively, more than the simple labyrinth weir. However, dent and orifice may lose their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes is the flow interference in downstream of weir which will be more by creating dentate and orifices. Also, increasing the magnification of labyrinth weir reduces the discharge coefficient, but this reduction in orifice-dentate labyrinth weir is much greater than the other two types of weirs and reaches up to 40%. Therefore, the orifice-dentate labyrinth weir performance at high magnification ratios does not seem appropriate.