Abstract
This study assessed two cavitation models for compressible cavitating flows within a single hole nozzle. The models evaluated were SS (Schnerr and Sauer) and ZGB (Zwart-Gerber-Belamri) using realizable k-epsilon turbulent model, which was found to be the most appropriate model to use for this flow. The liquid compressibility was modeled using the Tait equation, and the vapor compressibility was modeled using the ideal gas law. Compressible flow simulation results showed that the SS model failed to capture the flow physics with a weak agreement with experimental data, while the ZGB model predicted the flow much better. Modeling vapor compressibility improved the distribution of the cavitating vapor across the nozzle with an increase in vapor volume compared to that of the incompressible assumption, particularly in the core region which resulted in a much better quantitative and qualitative agreement with the experimental data. The results also showed the prediction of a normal shockwave downstream of the cavitation region where the local flow transforms from supersonic to subsonic because of an increase in the local pressure.
Highlights
Cavitation in confined flows is a highly complex phenomenon observed in many applications and can affect their performance considerably; the occurrence of cavitation in fuel supply systems of aircraft and automobiles, cryogenic pipelines and pipelines of nuclear power plants can lead to unexpected degradation in the system performance and damage to the components
Similar dispersion of the vapor can be seen with realizable k-epsilon model, the vapor never reaches the nozzle axis, and that the cavitation structure extends beyond the exit of the nozzle, Figure 7c. These features are further confirmed when the cavitation contours for both models are plotted outside the orifice by [48], where the results clearly show the extension of cavitation into the circular expansion region of the orifice for the realizable k-epsilon model, while it terminates at the exit of the orifice for the standard k-epsilon model
A cavitating flow in a submerged orifice was used to evaluate the predictive capability of different cavitation models for compressible flows
Summary
Cavitation in confined flows is a highly complex phenomenon observed in many applications and can affect their performance considerably; the occurrence of cavitation in fuel supply systems of aircraft and automobiles, cryogenic pipelines and pipelines of nuclear power plants can lead to unexpected degradation in the system performance and damage to the components. The bubbly cavitating fluid behaves like a compressible fluid and has an unusual characteristic; the presence of even a small fraction of gas/vapor can considerably reduce the local sonic speed of liquid–gas mixture compared to the sonic speed within its constituents [1,2,3,4]. This unusual phenomenon occurs because the mixture phase is compressed owing to the compressibility of gas bubbles, it remains dense due to the dominant mass of the liquid [5]. The model predicted a sharp rise in pressure or “shock” just downstream of the cavitation clouds where vapor transforms to liquid because of higher local pressure
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