Numerical investigation on the gas entrainment of ventilated partial cavity based on a multiscale modelling approach

Ventilated cavitation which is acknowledged as an efficient drag reduction technology for underwater vehicle is characterised by the very disparate length and time scales, posing great difficulty in the application of this technology. A multiscale numerical approach which integrates a sub-grid air entrainment model into the two-fluid framework is proposed in this paper to resolve the complex flow field created by ventilated cavity. Simulations have been carried out for the partially ventilated cavity underneath flat plate, with special efforts putting on understanding the gas entrainment at the cavity tail and the bubble dispersion process downstream. The flow parameters including the void fraction, the bubble velocity and the bubble size distributions in and downstream of the ventilated cavity are fully investigated. Comparisons between the numerical results with the experimental data are in satisfactory agreement, demonstrating the potential of the proposed methodology. The ventilation rate effect on the cavity shape and bubbly flow parameters are further investigated, obtaining the law of bubble dispersion and the bubble size evolution. This research not only provide a useful method for the investigation on the multiscale multiphase flow, but also give insight on understanding the combined drag reduction mechanism resulted from large-scale cavity and microbubbles.

[1]  D. Michaelis,et al.  Tomographic PIV measurements in a turbulent lifted jet flame , 2013 .

[2]  Th. Frank,et al.  VALIDATION OF CFD MODELS FOR MONO- AND POLYDISPERSE AIR-WATER TWO-PHASE FLOWS IN PIPES , 2008 .

[3]  H. Svendsen,et al.  Theoretical model for drop and bubble breakup in turbulent dispersions , 1996 .

[4]  Djamel Lakehal,et al.  Direct Numerical Simulation of Condensing Stratified Flow , 2008 .

[5]  S. Ceccio.  Friction Drag Reduction of External Flows with Bubble and Gas Injection , 2010 .

[6]  D. Drew,et al.  Application of general constitutive principles to the derivation of multidimensional two-phase flow equations , 1979 .

[7]  Hubert Chanson,et al.  Air Bubble Entrainment in Free-Surface Turbulent Shear Flows , 1996 .

[8]  Rex B. Thorpe,et al.  Liquid recirculation and bubble breakup beneath ventilated gas cavities in downward pipe flow , 2001 .

[9]  Jiyuan Tu,et al.  Numerical simulation of micro-bubble drag reduction using population balance model , 2009 .

[10]  G. Evans,et al.  Bubble breakup from ventilated cavities in multiphase reactors , 1997 .

[11]  Simo A. Mäkiharju.  The Dynamics of Ventilated Partial Cavities over a Wide Range of Reynolds Numbers and Quantitative 2D X-ray Densitometry for Multiphase Flow , 2012 .

[12]  Chul H. Song,et al.  The dependence of wall lubrication force on liquid velocity in turbulent bubbly two-phase flows , 2013 .

[13]  Simo A. Mäkiharju,et al.  Time-resolved two-dimensional X-ray densitometry of a two-phase flow downstream of a ventilated cavity , 2013 .

[14]  J. Flaherty,et al.  Analysis of phase distribution in fully developed laminar bubbly two-phase flow , 1991 .

[15]  H. Blanch,et al.  Bubble coalescence and break‐up in air‐sparged bubble columns , 1990 .

[16]  K. Yan,et al.  A coupled model for simulation of the gas–liquid two-phase flow with complex flow patterns , 2010 .

[17]  R. Kunz,et al.  A Level-Set Approach for Compressible, Multiphase Fluid Flows with Mass Transfer , 2009 .

[18]  Jiyuan Tu,et al.  A multi-fluid modelling approach for the air entrainment and internal bubbly flow region in hydraulic jumps , 2014 .

[19]  A. Dukler,et al.  Hydrodynamic model for gas‐liquid slug flow in vertical tubes , 1983 .

[20]  Xinyu Fu,et al.  Interfacial area measurement and transport modeling in air -water two -phase flow , 2001 .

[21]  Jiyuan Tu,et al.  On the numerical study of isothermal vertical bubbly flow using two population balance approaches , 2007 .

[22]  Eckhard Krepper,et al.  A multi-field two-fluid concept for transitions between different scales of interfacial structures , 2012 .

[23]  Assad A. Oberai,et al.  A Comprehensive Sub-Grid Air Entrainment Model for RaNS Modeling of Free-Surface Bubbly Flows , 2011 .

[25]  D. Ramkrishna,et al.  On the solution of population balance equations by discretization—II. A moving pivot technique , 1996 .

[26]  Timothy J. Barth,et al.  The design and application of upwind schemes on unstructured meshes , 1989 .

[27]  N. Zuber,et al.  Drag coefficient and relative velocity in bubbly, droplet or particulate flows , 1979 .