مطالعه آزمايشگاهي الگوي جريان پيرامون آبشكن‌هاي سري ساده در كانال پيچان رودي با جداره شيب‌دار فرسايش‌پذير

Experimental study of the flow pattern around simple series spur dikes in meandering channel with erodible sloping wall

آﺑﺸﮑﻦ ﺑﻪﻋﻨﻮان ﯾﮑﯽ از ﻣﺮﺳﻮمﺗﺮﯾﻦ ﺳﺎزهﻫاي ﺳﺎﻣﺎﻧﺪﻫﯽ رودﺧﺎﻧﻪ ﺑﻪﻣﻨﻈﻮر ﮐﺎﻫﺶ ﻓﺮﺳﺎﯾﺶ ﺳﻮاﺣﻞ و ﮐﻨﺎرهﻫﺎي رودﺧﺎﻧﻪ ﺷﻨﺎﺧﺘﻪ ﺷﺪه اﺳﺖ. اﯾﻦ ﺳﺎزهﻫﺎ ﺑﺎ ﻃﻮل و زاوﯾﻪ ﻣﻨﺎﺳﺐ ﻧﺴﺒﺖ ﺑﻪ راﺳﺘﺎي ﺟﺮﯾﺎن از دﯾﻮاره ﻃﺒﯿﻌﯽ رودﺧﺎﻧﻪ ﺗﻮﺳﻌﻪ ﯾﺎﻓﺘﻪ، ﺳﺒﺐ اﻧﺤﺮاف ﺟﺮﯾﺎن از ﮐﻨﺎرهﻫﺎ و ﻫﺪاﯾﺖ آن ﺑﻪ ﺳﻤﺖ ﻣﺤﻮر ﻣﺮﮐﺰي رودﺧﺎﻧﻪ ﻣﯽ ﺷﻮﻧﺪ. در اﯾﻦ ﭘﮋوﻫﺶ آزﻣﺎﯾﺸﮕﺎﻫﯽ، اﻟﮕﻮي ﺟﺮﯾﺎن ﭘﯿﺮاﻣﻮن آﺑﺸﮑﻦﻫﺎي ﺳﺮي ﺳﺎده درﮐﺎﻧﺎل ﭘﯿﭽﺎن رودي ﺑﺎ ﺟﺪاره ﺷﯿﺐ دار ﻓﺮﺳﺎﯾﺶﭘﺬﯾﺮ ﻣﺘﺸﮑﻞ از ﺳﻪ ﻗﻮس ﻣﺘﻮاﻟﯽ ﺑﺎ زواﯾﺎي 90 ،45 و 45 درﺟﻪ، ﺑﺮاي دﺑﯽﻫﺎي 35 ،40 و 30 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ ﻣﻄﺎﻟﻌﻪ ﺷﺪه اﺳﺖ. ﻧﺘﺎﯾﺞ ﺑﯿﺎﻧﮕﺮ اﯾﻦ اﺳﺖ ﮐﻪ ﻣﻮﻗﻌﯿﺖ ﺑﺮﺧﻮرد اوﻟﯿﻦ ﺧﻂ ﺟﺮﯾﺎن در ﺗﺮاز ﻧﺰدﯾﮏ ﺑﺴﺘﺮ ﺑﻪ ﺟﺪاره داﺧﻠﯽ ﻗﻮس ﺷﻤﺎره 2 در دﺑﯽ 40 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ زودﺗﺮ از دﺑﯽ 35 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ و در دﺑﯽ 35 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ زودﺗﺮ از دﺑﯽ 30 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ ﺻﻮرت ﮔﺮﻓﺘﻪ اﺳﺖ. ﺑﻪ-ﻃﻮريﮐﻪ ﻣﻮﻗﻌﯿﺖ ﺑﺮﺧﻮرد اوﻟﯿﻦ ﺧﻂ ﺟﺮﯾﺎن در ﺗﺮاز ﻧﺰدﯾﮏ ﺑﺴﺘﺮ ﺑﻪ ﺟﺪاره داﺧﻠﯽ ﻗﻮس ﺷﻤﺎره 2 در دﺑﯽﻫﺎي 35 ،40 و 30 ﻟﯿﺘﺮ ﺑﺮ ﺛﺎﻧﯿﻪ ﺑﻪ ﺗﺮﺗﯿﺐ در زواﯾﺎي 15 ،-18- و 10- درﺟﻪ ﻧﺴﺒﺖ ﺑﻪ ﻣﺤﻮر ﻣﺮﮐﺰي ﻗﻮس ﻣﺬﮐﻮر ﺻﻮرت ﮔﺮﻓﺘﻪ اﺳﺖ. در ﺷﺮاﯾﻂ ﺣﻀﻮر آﺑﺸﮑﻦ ﻫﺎ، اﺑﻌﺎد ﮔﺮداﺑﻪﻫﺎ ﺑﺎ ﺣﺮﮐﺖ در ﻋﻤﻖ ﺗﻐﯿﯿﺮ ﻣﯽ ﮐﻨﻨﺪ، ﺑﻪ اﯾﻦ ﺻﻮرت ﮐﻪ ﺑﺎ ﺣﺮﮐﺖ ﺑﻪ ﺳﻤﺖ ﺳﻄﺢ آب در ﯾﮏ دﺑﯽ ﺛﺎﺑﺖ، ﺑﻪدﻟﯿﻞ ﺗﻤﺎﯾﻞ ﺟﺮﯾﺎن ﺑﻪ ﺟﺪاره ﺧﺎرﺟﯽ، ﺷﯿﺐدار ﺑﻮدن ﺟﺪاره ﻗﻮس و اﻓﺰاﯾﺶ ﺳﻄﺢ ﺗﻤﺎس ﻃﻮل آﺑﺸﮑﻦ، اﺑﻌﺎد ﮔﺮداﺑﻪ اﻓﺰاﯾﺶ ﯾﺎﻓﺘﻪ اﺳﺖ.

The spur dike has been known as one of the most common organizing constructs of the river to reduce the erosion of coasts and river banks. These structures are developed with the right lengths and angles towards the flow of the natural walls of the river that cause flow deviation from the sides and lead it toward the central river axis. In this experimental study, the flow pattern around the simple series spur dike in the meandering channel with a sloped erodible wall consisting of three consecutive arches with angles of 45, 90 and 45 degrees, has been studied for 40, 35 and 30 liter/sec rates. The results indicate that the collision position of the first line of flow in the near bed to the inner wall of bend no. 2 in discharge 40 liters per second earlier than discharge 35 liters per second and in discharge 35 liters per second earlier than the discharge 30 liter per second. So that the collision position of the first line of flow in the near bed to the inner wall of bend no. 2 in discharge, 40, 35 and 30 liters per second, respectively, in the -18, -15 and -10 degree sections compared to the central arc of the mentioned bend. In conditions of the presence of spur dikes, the vortex dimensions change with the depth of movement, so that moving towards the surface of the water in a fixed discharge, due to the tendency of flow to the outer wall, the slope of the bend wall and increasing the level of contact surface of the spur dike length, the vortex dimensions are increased.