Computational characterization of plunging liquid jets

  • Xiaoliang Qu

Student thesis: Master's Thesis

Abstract

Plunging liquid jets are found in vast number of engineering applications and have received considerable attention in the past. The flow in such a configuration is unsteady, multiphase and turbulent and therefore presents a challenge to either experimental or numerical investigations. Most of the previous studies were laboratory investigations. Due to the complexity of the flow and sometimes computational resources required, numerical studies have been limited and the few studies conducted have focused on using complex and resource demanding two-fluid models to predict the flow behavior of two-phase flow field and volume fraction distributions. Interface tracking methods which are well capable of detecting the phases interface and catching the interface topology have not seen wider applications. This study focuses on two (axisymmetric) and three dimensional computational predictions of the flow characteristics of round vertical turbulent liquid jets plunging into a liquid bath partially filled with water. The simulations are conducted using the Reynolds averaged Navier-stokes equations combined with standard k − ϵ turbulence model. To take account of the multiphase nature of the flow, three multiphase models, the homogeneous Mixture model, Volume of Fluid (VOF) and level set models were employed. The main objective is a comparative and evaluation study of the used multiphase models in predicting the interface topology during the jet initial impact process, the flow field, phase volume fraction and jet penetration depth under continuous air entrainment regimes. The numerical results are contrasted with xiipublished experimental data and empirical results, as well as experiments conducted with intent to validate the numerically predicted jet initial impact process. Good agreements were found between experimental and numerical results and the three multiphase modelling approaches on the jet initial impact, penetration depths and entraining flow characteristics, with interface tracking rendering better predictions than the Mixture model. The VOF and level set models, based on the interface tracking technique successfully reproduced the jet initial impact process and the numerical results are validated by experiments in quantity. The Mixture model failed to capture this process but predicts the jet penetration depth reasonably well. VOF and level set were found to be capable of predicting the jet penetration depth quantitatively well and the entrained flow characteristics in the flow developing and developed regions were also estimated better by the interface tracking models than the Mixture model. Nevertheless, only the VOF method predicted the phase volume fraction in the near impingement regions with good acceptable accuracy while level set and the Mixture model failed in this region due to models limitations.
Date of AwardDec 2011
Original languageAmerican English
SupervisorLyes Khezzar (Supervisor)

Keywords

  • Applied sciences
  • Plunging liquid jets
  • Mechanical engineering
  • 0548:Mechanical engineering

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