Particle image velocimetry measurements of flow field behind a circular square-edged orifice in a round pipe

In this paper, we use a planar particle image velocimetry system to measure the flow field downstream of a circular square-edged orifice plate in a round pipe. The flow field is a fully developed pipe flow well upstream of the orifice plate. The Reynolds number based on pipe diameter and cross-sectional mean velocity is in the range of 25,000–55,000. We present detailed mean and turbulent fields and investigate similarities and differences with other separated flows. A noteworthy difference is the formation of a vena contracta behind the orifice at a distance of approximately one pipe radius. Upstream of the vena contracta, the properties of the shear layers in the orifice flow are quite similar to those of other separated flows. However, because the shear layer in the orifice flow begins to merge at a distance of approximately one pipe diameter, it is significantly different from the shear layers in other separated flows. Finally, we assess the reliability of the Reynolds stress model to represent orifice flows by comparing numerical results with experimental results.