The interface between the turbulent and non turbulent regions in a two dimensional turbulent jet is investigated by the simultaneous measurement of the velocity and pressure. The measurement is performed by using a combined probe comprising an X-type hot-wire and a static pressure tube. The measurement data are analyzed by the conditional sampling technique and an ensemble averaged technique on the basis of the intermittency function for the turbulent/non turbulent decision. The experimental data at the cross-streamwise edge of the turbulent region show that there is a thin interfacial layer with a sharp jump of physical quantities (such as mean streamwise velocity) at the cross-streamwise edge of the turbulent region, and the thickness of the interfacial layer is 0.08 times the half-width of the cross-streamwise profile of the mean streamwise velocity. The turbulent diffusion term in the turbulent energy transport equation near the interfacial layer is examined. It is also found that the turbulent energy is transported from the inside of the interfacial layer to both the inner side (the side of the turbulent fluid) and the outer side (the side of the non turbulent fluid) by the diffusion term. Furthermore, the components of the diffusion term are separately estimated. It is found that the turbulent diffusion term shows the gain of the turbulent energy at the inner side of the interfacial layer, and the pressure diffusion term transports the turbulent energy to the non turbulent fluid. Moreover, small scale vortices are found in the interfacial layer. From these results, there is a possibility that the existence of the interfacial layer (existence of the vortices) contributes to the transport of the turbulent energy to the non turbulent fluid since the velocity and the pressure field that determine the pressure diffusion is greatly influenced by the existence of the interfacial layer. This hypothesis indicates that the outward propagation from a turbulent fluid can be attributed to the presence of vortices in the interfacial layer.

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