Abstract
In an attempt to quantify the instantaneous pressure field in cavitating liquids at large forcing signals, pressures were measured in four different liquids contained in vessels with a frequency mode in resonance with the forcing signal. The pressure field in liquid metal was quantified for the first time, with maximum pressures of the order of 10–15 MPa measured in liquid aluminium. These high pressures are presumed to be responsible for deagglomeration and fragmentation of dendritic intermetallics and other inclusions. Numerical modelling showed that acoustic shielding attenuates pressure far from the sonotrode and it is prominent in the transparent liquids studied but less so in aluminium, suggesting that aluminium behaviour is different. Due to acoustic shielding, the numerical model presented cannot adequately capture the pressure field away from the intense cavitation zone, but gives a good qualitative description of the cavitation activity. The results obtained contribute to understanding the process of ultrasonic melt treatment (UST) of metal alloys, while facilitating further the guidelines formulation and reproducible protocols for controlling UST at industrial levels.
Highlights
Ultrasonic melt treatment (UST), and the resulting production of high-quality light alloys, is of great interest to the casting, automotive, and aerospace industries
The high-intensity ultrasonic waves that are introduced into liquid metal induce acoustic cavitation
For first time, proper quantification coupling the acoustic pressure field with the size of the cavitation bubbles is achieved within a sonicated liquid metal environment
Summary
Ultrasonic melt treatment (UST), and the resulting production of high-quality light alloys, is of great interest to the casting, automotive, and aerospace industries. The small spatial and large temporal scales that are involved in the process hinder clear visualization of the physical processes and, a deeper insight into the behaviour of cavitation bubbles This imposes restrictions on the validation of numerical models [16]. Modelling of acoustic cavitation is challenging: the temporal resolution that is required to solve the coupled flow and cavitation equations makes solving the acoustic cavitation models expensive These models are generally not accurate at high forcing pressures [20]. The experimental measurements of pressure are compared with predictions from the Caflisch equations The aim of this investigation is to quantify the pressure field in cavitating liquids at large forcing signals, facilitating further the guidelines formulation and reproducible protocols for controlling UST at industrial levels
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