| Project/Area Number |
15560150
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Fluid engineering
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| Research Institution | Osaka Prefecture University |
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Principal Investigator |
TAKAHARA Hiroyuki Osaka Prefecture Univ., Dept.of Energy Systems Eng., Prof., 工学研究科, 教授 (80206870)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2003: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Keywords | Toroidal Bubble / Real Gas Effect / Boundary Element Method / Shock Wave / Ghost Fluid Method / Level Set Method / Focusing Ultrasonic Oscillator / Surface Tension / 気泡変形 / 熱移動 / 気体拡散 |
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| Research Abstract |
We calculated the collapse of toroidal bubbles using the boundary element method combined with the finite volume method by considering the van der Waals equation of state for the internal gas. It was shown that the thermal boundary layer becomes thin and the maximum internal pressure becomes higher than that of ideal gas due to the real gas effect. We also showed the physical meaning of the pressure terms in the Rayleigh-Plesset equation that is used to calculate the radial motion of bubbles in an averaged equation for cavitating flows. Also, we have improved the Ghost Fluid Method(GFM) by correcting velocities, pressure and density at boundary nodes using the Riemann solutions to avoid numerical oscillations near the gas-liquid interface. We have succeeded in capturing the sharp interface for the shock-air bubble interaction in water by using the improved GFM coupling with the hybrid particle level set method. The results showed that the correction of boundary nodes improves the numerical stability of the GFM for compressible gas-liquid flows. It is effective to give the tangential velocity, which is not obtained from the Riemann solution, by the velocity at the nearest real node to the interface.
Small focusing ultrasonic oscillators were devised. We tested two kinds of piezoelectric ceramics whose radius of curvature were 8 mm and 5.77 mm. It was shown that the better focusing is realized by the ceramics with the long radius of curvature. The experimental and numerical results showed that the position of focusing is moved toward the ceramics due to the influence of the edge of the ceramics. We also investigated the influence of gas diffusion on the stability of microbubbles. It was shown that the decrease of the surface tension due to the compression of the surface area at the maximum surfactant concentration stabilize the microbubbles.
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