Theoretical and numerical study of hydraulic characteristics of orifice energy dissipator

Different factors affecting the efficiency of the orifice energy dissipator were investigated based on a series of theoretical analyses and numerical simulations.The main factors investigated by dimension analysis were identified,including the Reynolds number(Re),the ratio of the orifice diameter to the inner diameter of the pipe(d/D),and the ratio of distances between orifices to the inner diameter of the pipe(L/D).Then,numerical simulations were conducted with a k-ε two-equation turbulence model.The calculation results show the following:Hydraulic characteristics change dramatically as flow passes through the orifice,with abruptly increasing velocity and turbulent energy,and decreasing pressure.The turbulent energy appears to be low in the middle and high near the pipe wall.For the energy dissipation setup with only one orifice,when Re is smaller than 105,the orifice energy dissipation coefficient K increases rapidly with the increase of Re.When Re is larger than 105,K gradually stabilizes.As d/D increases,K and the length of the recirculation region L1 show similar variation patterns,which inversely vary with d/D.The function curves can be approximated as straight lines.For the energy dissipation model with two orifices,because of different incoming flows at different orifices,the energy dissipation coefficient of the second orifice(K2)is smaller than that of the first.If L/D is less than 5,the K value of the L/D model,depending on the variation of K2,increases with the spacing between two orifices L,and an orifice cannot fulfill its energy dissipation function.If L/D is greater than 5,K2 tends to be steady; thus,the K value of the L/D model gradually stabilizes.Then,the flow fully develops,and L has almost no impact on the value of K.