Experimental study on discharge coefficient of a gear-shaped weir

摘要

This study focused on hydraulic characteristics around a gear-shaped weir in a straight channel.Systematic experiments were carried out for weirs with two different gear heights and eight groups of geometrical parameters.The impacts of various geometrical parameters of gear-shaped weirs on the discharge capacity were investigated.The following conclusions are drawn from the experimental study:(1)The discharge coefficient(mc)was influenced by the size of the gear:at a constant discharge,the weir with larger values of a/b(a is the width of the gear,and b is the width between the two neighboring gears)and a/c(c is the height of the gear)had a smaller value of mc.The discharge capacity of the gear-shaped weir was influenced by the water depth in the weir.(2)For type C1 with a gear height of 0.01 m,when the discharge was less than 60 m3/h and H1/P<1.0(H1 is the water depth at the low weir crest,and P is the weir height),mc significantly increased with the discharge and H1/P;with further increases of the discharge and H1=P,mc showed insignificant decreases and fluctuated within small ranges.For type C2 with a gear height of 0.02 m,when the discharge was less than 60 m3/h and H1/P<1.0,mc significantly increased with the discharge and H1/P;when the discharge was larger than 60 m3/h and H1/P>1.0,mc slowly decreased with the increases of the discharge and H1/P for a/b<1.0 and a/c<1.0,and slowly increased with the discharge and H1/P for a/b>1.0 and a/c>1.0.(3)A formula of mc for gear-shaped weirs was established based on the principle of weir flow,with consideration of the water depth in the weir,the weir height and width,and the height of the gear.