Laboratory study of orifice jets from a pressurized pipe

Orifice jet through a small opening or orifice into a surrounding fluid exhibits intricate fluid dynamics, encompassing the interaction of the jet with the fluid. Although the dynamics of simple jets has been extensively studied, there are still unresolved issues that need to be addressed. In this study, we experimentally investigated the characteristics of non-buoyant jets emerging from a sharp-edged orifice located in the wall of a pipe with a constant flow rate. Specifically, we examined how the ratio between the variable jet flow rate to the constant pipe flow rate upstream of the orifice influences not only the jet trajectory but (for the first time to the authors' knowledge) also the jet velocity-related features. Particle image velocimetry measurements were performed to explore the velocity fields in the near and intermediate regions of the jet and data were analyzed in terms of fields of time-averaged velocity components, turbulent intensities, Reynolds shear stresses, vorticity, and Q-criterion. The transversal velocity profiles were shown and their Gaussianity investigated via skewness and kurtosis. Thus, second-order statistics of turbulence of the velocity fluctuations were carried out. Moreover, a spectral analysis was performed after the Taylor hypothesis verification was proved and a net scale separation was guaranteed to develop the inertial sub-range. The influence of variable jet flow rate and the constant pipe flow rate on the jet behavior is shown and, in particular, how, as this parameter decreases, the jet moves away from the typical axisymmetric features of a round simple jet. In addition, the spectra analysis is used to identify the jet potential core and the large-scale organization zones, highlighting the effect of variable jet flow rate and the constant pipe flow rate on the extension of the potential core region and on the mixing layer.