Large eddy simulations of cavitating flow in a step nozzle with injection into gas

TL;DR

This paper uses large eddy simulations to study cavitating flow in a step nozzle with gas injection, revealing how cavitation, gas entrainment, and vapor structure implosions influence jet breakup, flow rates, and erosion.

Contribution

It introduces a high-order implicit large eddy simulation approach for cavitating flows with gas, capturing vapor collapse effects and analyzing their impact on flow dynamics.

Findings

Detached vapor structures reach the nozzle outlet during cavitation.

Gas entrainment affects cavitation dynamics and jet breakup.

Vapor implosions induce pressure peaks that influence turbulence and erosion.

Abstract

We present results of large eddy simulations of a cavitating nozzle flow and injection into gas, investigating the interactions of cavitation in the nozzle, primary jet breakup, mass-flow rates, and gas entrainment. During strong cavitation, detached vapor structures can reach the nozzle outlet, leading to partial entrainment of gas from the outflow region into the nozzle. The gas entrainment can affect cavitation dynamics, mass-flow rates, and jet breakup. Moreover, the implosion of detached vapor structures induces pressure peaks that on the one hand amplify turbulent fluctuations and subsequently can enhance jet breakup and on the other hand can damage walls in the proximity and thus lead to cavitation erosion. Our numerical setup is based on a reference experiment, in which liquid water is discharged into ambient air through a step nozzle. The cavitating liquid and the non-condensable gas phase are modeled with a barotropic homogeneous mixture model while for the numerical model a high-order implicit large eddy approach is employed. Full compressibility of all components is taken into account, enabling us to capture the effects of collapsing vapor structures. Two operating points covering different cavitation regimes and jet characteristics are investigated. Special emphasis is placed on studying the effects of cavitation on the mass flow and the jet as well as the impact of partial gas entrainment. Therefore, frequency analyses of the recorded time-resolved signals are performed. Furthermore, the dynamics and intensities of imploding vapor structures are assessed.