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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/110220


    Title: SIMULATIONS OF THE SHOCK WAVES AND CAVITATION BUBBLES DURING A HIGH-SPEED DROPLET IMPINGEMENT
    Authors: Niu, Yang-Yao
    Keywords: Compressible liquid;Shock wave;cavitation;Two-fluid model;AUSMD
    Date: 2016-02-15
    Issue Date: 2017-04-20 02:10:14 (UTC+8)
    Publisher: Tokyo Institute of Technology, Japan
    Abstract: 1. Background
    The thermo-fluids of high-speed liquids impact onto a rigid surface is important to the industry applications such as spray coating and cooling, steam turbine blade operation, metal cutting of materials. During the process of the liquid droplet impingement, we can observe some physical phenomena, such as the interaction of propagating shock, interface, rarefaction waves, the formation and collapse of cavitation bubbles and the eruption of jets.

    2. Method
    We investigate the aerodynamic characteristics inside a droplet impingement using a compressible two-fluid model. A MUSCL type hybrid type Riemann solver is proposed to compute numerical fluxes across the interfaces of gas-gas, liquid-liquid and gas-liquid flows in the considered flowfields. Here, the compressible liquid flows with high Reynolds number value allow us to use an inviscid approach and neglect the surface tension effect under the assumption of high Weber number.
       
    3. Results
    Numerical results demonstrate the evolution of shock-front, rarefaction, cavitation inside the droplet seen in Fig. 1-3 and the contact periphery expands very quickly and liquid compressibility plays an important role in the initial formation of flow physics inside the liquid droplet. Grid independence study is performed. Finally, we perform three-dimensional numerical simulations against the problem of a water droplet impact the wall based on the same initial and boundary conditions as the 2D cases. Here, we consider the velocities of 200, 300 500m/s. The grid independence studies are performed on (100x100x100), (125x125x125) and ( 140x140x140) points. The droplet moves perpendicular to the rigid surface without deformation. After the instant contact, the compressed region is generated, the propagating wave can be seen obviously and the cavitation zone in Fig.4 exists near the top inside droplet like the two-dimensional simulations we have observed. We also found that the growth rate of the cavitation zone is independent of the impact flow velocity. The estimated maximum wall pressure against the incoming Mach number is shown to be closer to the theoretical data than any other previous analysis.
    4. Conclusions

    In this work, a hybrid numerical flux combing AUSMD and linearized approximated solver is proposed to solve the compressible two-fluid six-equation model. The interaction of shock and rarefaction waves, the free surface and the formation and collapse of cavitation bubbles are captured clearly no matter in the 2D and 3D cases. It is noted that the formation of the impact pressure maximum and the size of cavitation zone is found to directly relate to the initial impact velocities. Also, the maximum pressure computed in the 2D case is bigger than the 3D case. The growth rate of cavitation zone is found to be independent to the magnitude of the impact velocity. Finally, the numerical cavitation is not seen in the simulation of the case with larger initial gas VOF value in the droplet.
    Relation: proceeding of The 8th Japan-Taiwan Workshop on Mechanical Engineering and Aerospace
    Appears in Collections:[航空太空工程學系暨研究所] 會議論文

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