Experimental Characterization of Shocks, Stress Waves, Plasma, and Radicals Generated During Collapse of Vapor and Gas Bubbles Near Solid Boundaries
Abstract
The objective of this project is to characterize experimentally the interaction of isolated cavitation bubbles with a nearby solid boundary. The focus is on determining the time evolution of pressure and temperature inside the bubble, the flow and pressure fieldsaround the bubble, including the impact of shock propagating in the liquid, as well as the strain and stress fields inside the solid wall. The proposed experiments involve two types of bubbles: Vapor bubble will be generated using a focused pulsed (5-200 ns duration) laser beam. Controlled, mono-dispersed trains of 20-200 #m diameter gas microbubbles will be generated by a micro-pipette device, and excited by a high intensity (up to 400 W) focused ultrasonic (HIFU) beam operating at 250 and 500 kHz. The experiments will be performed in a specialized chamber at ambient mean pressure that can be varied from 0.3 to 30 bar. Ultra high-speed imaging (5 MHz) will be used for measuring the evolution of the bubble size and shape at high spatial and temporal resolution. The experiments will be performed for varying initial bubble size, dissolved gas type and concentration, ambient mean pressure, amplitude of the ultrasonic beam, intensity and duration of the laser pulse generating the vapor bubbles, ambient mean temperature, distance of the bubblefrom the wall, composition of the non-condensable gases, and surface tension.Stereo-PIV, holographic microscopy, and tomographic particle tracking (TPTV) will be used for measuring the 3D flow and acceleration around the collapsing and rebounding bubbles. To focus on the flow between the bubble and the wall, especially at small scales, some of the tests will be performed by matching the refractive index of the wall with that of the liquid. This approach will enable us to perform microscopic observation even if/when the interior wall is deformed. Fluorescent particles or droplets and proper filtering will alleviate the reflections from the bubble surface, allowing unobstructed measurements. The time evolution of pressure inside the collapsing bubbles will be assessed from the speedof shock waves propagating in the liquid using established relationships between the shock speed and pressure difference across it in liquids. Images will be acquired using a 5 MHz camera by recording two-four exposures per frame, and extrapolated to the origin of the shock. The pressure in the flow field, especially in the space between the bubbles and the wall, will be determined by integrating the material acceleration of the liquid, while accounting for compressibility effects using appropriate equations of state. Theluminescence from the collapsing bubbles, covering the UV to the infrared range, will be recorded by a spectrometer/photodiode. A comparison to blackbody radiation will be used for assessing the temperature inside the bubble during the period of luminescence, when the interior temperature is expected to exceed 5,000K. The spectral analysis will also be usedfor detecting the formation and duration of transient OH radicals. Finally, we also propose to characterize the dynamics of stress and strain fields inside the solid wall located near the bubble. Using transparent walls, where shock waves can be tracked optically, and if needed, seeding molded wallswith particles and tracking them, the deformation, and amplitudes of reflected and transmitted waves will be quantified simultaneously with the bubble size and shape. The measurements will be performed for walls having a Young modulus ranging from 100 kPa to 2.4 GPa. Approved for public release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412750
Entities
People
- Joseph Katz
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy