Large Eddy Simulations of Cavitating Flow in a Step Nozzle With Injection Into Gas

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 break-up, 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 break-up. Moreover, the implosion of detached vapor structures induces pressure peaks that on the one hand amplify turbulent fluctuations and subsequently can enhance jet break-up 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.

Investigation of condensation shocks and re-entrant jet dynamics in a cavitating nozzle flow by Large-Eddy Simulation

“…The cavity-length jump can also be seen in other experimental measurements (Saito and Sato, 2003;Sou et al, 2007). In this strongly cavitating regime, the shed clouds can be transported to the nozzle outlet and generate a pressure gradient from the low-pressure vapor region to the outflow, which results in gas being ingested by the nozzle (Örley et al, 2015;Trummler et al, 2018). Further increase of the cavitation length can result in a complete flow detachment from the nozzle wall and the so-called hydraulic flip (Sou et al, 2007;Stanley et al, 2011).…”

“…In this work, the implicit LES approach for compact stencils recently proposed by Egerer et al (2016) is used, which is specially designed for compressible, cavitating flows. Additionally, an extension for the additional gas phase (Trummler et al, 2018) for multiphase application is included.…”

“…For wall-bounded turbulent flows, the dimensionless wall normal resolution y + is a parameter to evaluate the grid resolution. The analysis of y + for this configuration can be found in Trummler et al (2018): y + ≈ 1 within the nozzle, i.e. the near-wall cell is within the viscous sublayer.…”

Numerical investigation of non-condensable gas effect on vapor bubble collapse

“…We adopt a multi-component homogeneous mixture model ( Örley et al, 2015;Trummler et al, 2018b) to be applicable to vapor bubbles containing gas. In the employed modeling approach, the cavitating liquid (lv) and the non-condensable gas (g) are described by a substitute mixture fluid.…”

“…In this work, we present an adaptation of the multi-component model of Örley et al (2015) and Trummler et al (2018b) to be applicable to vapor bubbles containing gas. Preliminary studies to this work were presented in Trummler et al (2018aTrummler et al ( , 2019.…”