Simulating bubbles and their role in shockwave and ultrasound therapies

High-intensity acoustic waves are increasingly used to manipulate matter in biological settings, with applications ranging from kidney stone fragmentation (lithotripsy) and noninvasive tissue ablation (histotripsy) to targeted drug delivery and cell-scale mechanobiology. In each case, the therapeutic effect can be mediated by the expansion and violent collapse of bubbles—either preexisting or nucleated in situ—which generate highly localized stresses, strains, and microjets. These same processes, however, can also produce unintended damage, and the central challenge is therefore one of control: predicting and shaping bubble dynamics across a wide range of spatial and temporal scales in complex, heterogeneous media. This challenge has exposed clear limitations in existing modeling and simulation tools. The relevant flows involve moving phase boundaries, strong compressibility effects, and tightly coupled multiscale interactions spanning micron-scale bubble dynamics and macroscopic wave propagation. In this talk, I will review recent progress in numerical methods for bubbly and cavitating flows, including both interface-resolving approaches and reduced models that treat the mixture as either a continuum or a dispersed population of bubbles. I will emphasize how these methods are being used to simulate single-bubble collapse and collective dynamics in bubble clouds, with the goal of quantifying the resulting mechanical fields. Looking forward, these capabilities point toward feedback-controlled acoustic treatments, in which waveforms are adapted in response to evolving conditions to achieve desired effects while minimizing damage, and toward the development of patient-specific “digital twins” that provide clinicians with predictive information about treatment progress that is currently inaccessible.

Professor Tim Colonius is the Frank and Ora Lee Marble Professor of Mechanical Engineering at the California Institute of Technology.  He received his B.S. from the University of Michigan in 1987 and M.S and Ph.D. in Mechanical Engineering from Stanford University in 1988 and 1994, respectively.   He and his research team use numerical simulations to study a range of problems in fluid dynamics, including aeroacoustics, flow control, instabilities, shock waves, and bubble dynamics.   Prof. Colonius also investigates medical applications of ultrasound and is a member of the Medical Engineering faculty at Caltech.  He is a Fellow of the American Physical Society and the Acoustical Society of America.  He is the recipient of the AIAA Aeroacoustics Award, the APS Stanley Corrsin Award, and the ASME Freeman Scholar Award.