Investigation of flow through multi-stage restricting orifices

In this study, the characteristics of flow through a serial arrangement of two similar bevel-edged orifice plates fitted in a horizontal pipe of 25.4 mm internal diameter has been investigated. Computational fluid dynamics calculations were performed using the realizable k-ε eddy viscosity model to predict the flow features. The effects of various parameters such as pipe flow velocity in the range 1−4 m/s, orifice spacing of 1D and 2D, and orifice plate diameter ratios of 0.5, 0.63 and 0.77 on axial velocity and pressure distributions were obtained. The flow is always turbulent with Reynolds number ranging from R_e = 2.54 × 10⁴ to 1.02 × 10⁵. The location of vena contracta associated with the first orifice was found to be independent of addition of second orifice but varies with orifice diameter ratios while the presence of vena contracta downstream of the second orifice was found to depend on the orifice spacing. Also, the flow features downstream the second orifice is qualitatively similar to single orifice flow in terms of presence of recirculation, reattachment and shear layer regions but the flow features in the spacing between the two orifices are quite different having a donut-shaped vortex near the wall and jet-like flow in the core region. Not only the flow structure between the two orifices and downstream the second orifice was found to depend on the orifice spacing but also the total pressure drop and hydraulic losses. Orifice spacing of 1 and 2 pipe diameters gave the highest and lowest pressure recovery respectively compared to single orifice arrangement. The current study provides an insight into methods of pressure control without redesigning the complete flow system.