Numerical Simulation Research On The Flow Structure Of Hydraulic Flashboard Permeable Spur Dike

Hydraulic flashboard permeable spur dike is a new type of river and channel course improvement building.Its effect of embankment protection and slow flow is remarkable in heavily silt-carrying rivers.The arrangement of the permeable spur causes the change of the flow structure near the dam and the river bed readjustment.The study on the flow structure of permeable spur dikes is of great significance to the design and application.The three dimensional numerical simulations were carried out on the flow field of hydraulic flashboard permeable spur dike under different pervious passes,permeable rates,oriented angles,the effective length of spur dikes,flow rates and the spacing between spur dikes based on the numerical simulation method.Thus the variation characteristics of flow fields near the hydraulic flashboard permeable spur dike under different body type parameters were obtained,and the main conclusions were as follows:(1)Under different pervious passes,the law of velocity variation was same at the same upstream section of hydraulic flashboard permeable spur dike,while there was an obvious difference in velocity distribution at the same downstream section.The variation of flow velocity in the main stream was similar,and the values were same when the velocity tended to be constant.Compared with other permeable passes,the effect of reduce velocity and bank protection of the double-layer rectangular pervious hole was the best.(2)The change rule of flow structure around hydraulic flashboard permeable spur dike under different body type parameters: With the increase of water permeable rates,the flow velocity in the main stream dipped,while the flow velocity in the area behind the dike rose gradually.The intensity of circumfluence decreased gradually with increasing water permeable rates,and the circumfluence disappeared wh en the water permeable rate reached 40%;the backwater and water drop values between the front and back of the spur dike both tended to decrease.With the increase of oriented angle,both the flow velocity in the mainstream area and the backwater in the fr ont of the dam increased gradually;the water drop value in the vicinity of the dam head and the downstream section increased at first and then decreased slightly.When the oriented angle was 90 degrees,the water drop value reached the maximum.With the i ncrease of the effective length of spur dike,the flow velocity in the mainstream area increased gradually;the backwater and water drop values between the front and back of the spur dike both tended to increase.With the increase of flow rate,the velocit y of all the points on the section increased gradually,and the backwater and water drop values between the front and back of the spur dike both tended to increase.(3)The reasonable range of body type parameters for hydraulic flashboard permeable spur dike: The permeable rate was about 30%;the oriented angle was between 45 and 75 degrees;the effective length of spur dike was between 0.2 B and 0.3B,and the spacing between spur dikes was between 2 l and 4l.(4)The velocity at the dam head of the first spur dike in the hydraulic flashboard permeable spur dike group was the largest,where the flow rate was greater than the main flow velocity.While the velocity at other dam heads were smaller than the main flow velocity.With the increase of the spur dikes number,the cumulative effect of spur dikes increased,and along the downstream side,the flow velocity in the post dam area of the spur dikes decreased gradually.