The energy dissipation in the flow region in front of the orifice is one of the important components which contribute to total energy loss in orifice discharge.The concept of the contributing flow region in front of the orifice is proposed in this paper

which may help to explain the flow mechanism for orifice discharge.The range and main affecting factors of the contributing flow region in front of the vertical sharp-edged orifice were investigated experimentally by using the suspended tracer particles method.The orifice flow was simulated with computational fluid dynamics (CFD) software Fluent 6.2.The calculated ranges of the contributing flow region in front of the orifice were basically in agreement with the experimental data.Moreover

the simulated orifice discharge coefficients were compared with the initial experimental data

which verified the reliability of simulation for their consistency.Correspondingly

velocity distribution

pressure distribution

flow pattern

and the range of the contributing flow region in front of the orifice were discussed under different operating conditions and orifice configurations.The characteristics of the energy dissipation in front of the orifice was compared between “small orifice” and “large orifice”.