Measurement and modeling of surface erosion in acoustic cavitation

该项目的主题是声空化：液体中强烈的超声场产生并激活经历强烈体积振荡的气泡。对于应用来说，最相关的效应是气泡的强烈坍塌(内爆)，在那里可能会发生冲击波、化学和发光。一个关键的现象是任何固体材料都会被气蚀侵蚀。它与强烈气泡在接近物体时破裂时的强烈条件有关，即高压峰和高温峰直接出现在材料表面。该项目是前人关于声空化气泡种群测量和建模的工作的扩展，该工作研究了简单几何形状的块状液体中的空化现象。现在，实验和数值技术将扩展到声空化的实际应用条件，其中固体物体被淹没，使用更复杂的液体。特别的目标应用是固体表面清洁和用于回收的酸中的金属腐蚀。该项目的实验部分在格奥尔格-奥古斯特-哥廷根大学进行，数值工作在TU Clausthal进行。这些实验包括利用高速成像、声场、发光和腐蚀测量，对主频范围从20到50 kHz的空化以及在变表面张力和高粘度的液体中的空化进行了研究。研究的核心是研究固体存在时的空化行为，这些固体的尺度大约从声波波长的1/15到1/15。为此，在改变几何形状和液体参数的情况下，实验实现了人工气泡源和受控气泡与固体的相互作用。对固定床和流态化条件下的多目标情况进行了研究，对声波在固体中的穿透和散射、空化扩展和结构以及气泡在固体上的活动进行了评估和优化。数值工作扩展了以前开发的空化液体中声场传播和消散的程序。包括气泡-气泡和气泡-固体相互作用，以便更真实地描述物体存在时的声空化。在单气泡数值研究的基础上，进一步发展和调整了表面侵蚀预测模型。模拟扩展到在固定和浮动条件下浸入液体中的多个固体对象。数值计算结果和实验结果不断比较，以确保模型能够捕捉到本质，旨在对相关的液、固和空化三相系统进行一致的描述。

The topic of the project is acoustic cavitation: Intense ultrasonic fields in liquids generate and activate bubbles that undergo strong volume oscillations. The most relevant effect for applications is the strong collapse (implosion) of bubbles where shock waves, chemistry, and luminescence can occur. A key phenomenon is the erosion of any solid material by cavitation. It is linked with the intense conditions during the strong bubble collapse when it appears close to objects, i.e. high pressure and temperature peaks directly at the material surface.The project is an extension of the previous work on “Measurement and modeling of acoustic cavitation bubble populations” where cavitation in the bulk liquid in simple geometries was investigated. Now the experimental and numerical techniques will be expanded to realistic application conditions of acoustic cavitation where solid objects are submerged and more complex liquids are employed. Particular target applications are solid surface cleaning and metal erosion in acids for recycling.The experimental part of the project is conducted at Georg-August-University Göttingen, and the numerical work is done at TU Clausthal. The experiments comprise studies on cavitation in the main frequency range from 20 to 50 kHz and in liquids of variable surface tension and of high viscosity, employing high-speed imaging, sound field, luminescence, and erosion measurements. The core of the investigations is concerned with the behavior of cavitation in the presence of solid objects that scale approximately from the acoustic wavelength to 1/15th thereof.For this purpose, artificial bubble sources and controlled bubble interaction with solids are experimentally realized under variation of geometry and liquid parameters. The case of multiple objects is studied in fixed bed and in fluidized bed conditions, and sound wave penetration and scattering, cavitation extension and structures, and bubble activity at the solids are assessed and optimized. The numerical work extends previously developed codes for sound field propagation and dissipation in cavitating liquids. Bubble-bubble and bubble-solid interactions are included to reach more realistic descriptions of acoustic cavitation in the presence of objects. Surface erosion prediction models are further developed and adjusted on basis of single-bubble numerical studies. Simulations are extended to multiple solid objects submerged in the liquid, both in fixed and floating conditions. Numerical and experimental results are continuously compared to ensure that the essentials are captured by the model, aiming at a coherent description of the relevant three-phase systems of liquid, solid and cavitation bubbles.