Characterization of a Superheated Water Jet Released Into Water Using Proper Orthogonal Decomposition Method

Abstract

The external characteristics of a superheated water jet released into water at ambient conditions are dominated by the vapor bubble formation, which results in an unsteady flow dynamics. This hinders the use of classical methods to assess the mean flow and the turbulence characteristics. Here, the proper orthogonal decomposition (POD) technique was employed on the velocity measurements obtained using particle image velocimetry (PIV) to quantify the external characteristics of a superheated water jet released into water. This was done at three different inlet pressure ratios. From the energy modes obtained using the POD technique, it was observed that the first mode well represents the mean flow, while subsequent higher modes show the fluctuating nature. The phase-averaged properties were calculated by considering only the first mode. Unlike a canonical jet, the maximum value of the mean centerline velocity for a superheated jet occurs far downstream from the nozzle, at x/D ≈ 15, due to the thermal nonequilibrium in the jet attributed to the formation of vapor bubbles. The turbulent kinetic energy (TKE), size of the coherent structures (CS), and swirling strength showed a nonmonotonic decrease in the downstream direction, indicating that the vapor formation has significant influence on the jet dynamics. The novel aspect of this work is the use of POD technique for phase averaging, using which dynamics of a superheated jet have been quantified. The distribution of vapor bubbles in the flow field was also measured using the Shadowgraphy technique to substantiate the above observations.