The experiments on the characteristics of the fluid discharging through the streamlined contractive orifice and the vertical sharp-edged orifice with same diameter were carried out.The mechanical energy loss of the fluid flowing in front of vertical sharp-edged orifice was imitated by that of the fluid through the streamlined contractive orifice

which was compared with the mechanical energy consumed in the whole orifice discharge process through vertical sharp-edged orifice.Thus

the proportion of the upstream mechanical energy loss to total mechanical energy loss can be obtained quantitatively with respect to typical “large orifice” and “small one” at different operating conditions.The proportion reflects the difference of the mechanical energy consumed inside orifice between large orifice and small orifice

as well as the effects of the plate thickness.Moreover

the flow mechanism of orifice discharge proposed in the study before this work was verified.Afterwards

according to the physical model of the contributing flow region in front of orifice and the data of the flow field simulated with computational fluid dynamics (CFD) software Fluent 6.2 before this work

the basic mode of equation on the resistance coefficient of the contributing flow region in front of orifice was obtained.Therefore

the model of mechanical energy consumed upstream at fully developmental turbulent regime was founded by simulated the experimental data.