71th Annual Meeting of the APS Division of Fluid Dynamics (November 18, 2018 — November 20, 2018)

V0042: Simulations of the acoustically-driven growth and collapse of a cavitation bubble near a wall

Authors
  • Bradley Boyd, University of Canterbury, New Zealand
  • Sid Becker, University of Canterbury, New Zealand

We show the growth and collapse of a cavitation bubble in water exposed to an ultrasound field. The ultrasound input is simulated using an immersed moving reflective boundary that oscillates through a fixed grid of finite-volume cells.  The bubble dynamics are modeled using a compressible, inviscid, multiphase model. The numerical scheme consists of a conservative interface capturing scheme which uses the fifth-order WENO reconstruction with a maximum-principle-satisfying and positivity-preserving limiter, and the HLLC approximate Riemann flux.

For the case presented, the immersed moving boundary oscillates sinusoidally at a frequency of 30 kHz (the ultrasound frequency) with a displacement amplitude of 0.6956 μm which results in an ultrasound pressure amplitude of 200 kPa at the wall. The growth phase of the simulation shows the rapid non-spherical growth of the near-wall bubble. After the bubble reaches its maximum size and the collapse phase begins, the simulation shows the formation of a jet which penetrates the bubble towards the wall at the later stages of the collapse. For a bubble with an initial radius of 50 μm and a standoff distance (distance from the center of the bubble to the near-wall) of 117 μm, the pressure experienced by the wall increased rapidly nearing the end of the collapse, reaching a peak pressure of approximately 14 MPa.

We then compare the acoustically-driven bubble growth and collapse for various standoff distances. The change in standoff distance is seen to influence the bubble growth shape and the subsequent collapse. The maximum pressure experienced by the wall for the various standoff distances is presented.

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