Coupling of acoustic cavitation with DEM-based particle solvers for modeling de-agglomeration of particle clusters in liquid metals

The aerospace and automotive industries are seeking advanced materials with low weight yet high strength and durability. Aluminum and magnesium-based metal matrix composites with ceramic micro- and nano-reinforcements promise the desirable properties. However, larger surface-area-to-volume ratio in micro- and especially nanoparticles gives rise to van der Waals and adhesion forces that cause the particles to agglomerate in clusters. Such clusters lead to adverse effects on final properties, no longer acting as dislocation anchors but instead becoming defects. Also, agglomeration causes the particle distribution to become uneven, leading to inconsistent properties. To break up clusters, ultrasonic processing may be used via an immersed sonotrode, or alternatively via electromagnetic vibration. This paper combines a fundamental study of acoustic cavitation in liquid aluminum with a study of the interaction forces causing particles to agglomerate, as well as mechanisms of cluster breakup. A non-linear acoustic cavitation model utilizing pressure waves produced by an immersed horn is presented, and then applied to cavitation in liquid aluminum. Physical quantities related to fluid flow and quantities specific to the cavitation solver are passed to a discrete element method particles model. The coupled system is then used for a detailed study of clusters’ breakup by cavitation

Experimental observation of nonlinear self-focusing in the cavitation field

Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.25.Yw.The nonlinear self-focusing of the pressure field with onset of cavitation is experimentally and theoretically analysed in the kHz range. Self-focusing in the cavitation field has already been reported above 500 kHz and it was attributed to the non-uniformity of bubble density. In this case, bubble density remains small, non-linearity is weak and focal distance remains much larger than the acoustic wavelength in the liquid.In this work, inertial cavitation field radiated by a 20 kHz sonotrode-type transducer is considered. A cone like bubble structure is established. This structure is very repetitive and selfconstructs in any container when a piston like emitter is used. The acoustic field is directly evaluated by using a BR&K. hydrophone and averaged pressure waveforms are analysed. The number of chosen samples is high enough to have stable measured pressure results (including nonlinear distortion). A self-focusing effect is observed with a focal distance comparable to the acoustic wavelength in the liquid. Models accounting for the high bubble density and strong non-linear effects are proposed. Theoretical predictions are compared to experiments and discussed.Peer reviewe

Numerical modeling of the ultrasonic cavitation field and experimental evaluation of bubble density

6 pages.-- PACS nr.: 43.35 Ei.-- Communication presented at: Forum Acusticum Sevilla 2002 (Sevilla, Spain, 16-20 Sep 2002), comprising: 3rd European Congress on Acoustics; XXXIII Spanish Congress on Acoustics (TecniAcústica 2002); European and Japanese Symposium on Acoustics; 3rd Iberian Congress on Acoustics.-- Special issue of the journal Revista de Acústica, Vol. XXXIII, year 2002.A numerical model of ultrasonic cavitation field is described. It is based on a phenomenological description of a cavitating fluid as a non linear fluid whose characteristics (sound speed, density) depend upon the bubble density. To obtain the constitutive relationship between bubble density and acoustic pressure, a real-time measurement method of the bubble density, relying upon the variation of the electrical resistance of the medium, is proposed. The finite element formulation of the model is derived and implemented in the ATILA code. Computational results on the cavitation field created by a cylindrical concentrator are presented.This work was supported by CNRS and CSIC (French-Spanish cooperation project #7967) and by the European Union (Feder-Retex II).Peer reviewe

Numerical Study of Air-Borne Acoustic Field of Stepped-Plate High-Power Ultrasonic Transducers

International audienceA numerical-experimentalstudy of the displacementsdistribution and the radiated field of various (directiona]and focusing)f1exura] plate transducersis presented.The numericalmethodbasicallyconsistsof calculatingthe distribution of displacementsof the transducersby the finite element method by using the code ATILAwhile the corresponding radiated field is calculated by the boundary element method by means of the code EQI. In this way the near and far field of the transducersis calculatedas well as their directivitypattern and vibrationdistribution.The obtainedresults are compared with experimentaldata. The good agreement obtained indicatesthat the numericalmethod used in this paper is a very useful too] for calculatingthe fieldof transducersand for the optimisationof their design

Transductores macrosónicos tipo placa vibrante escalonada Fundamentos, desarrollos, estado actual

PACS: 43.25.Vt, 43.40.Dx.-- Publicado en el Vol. XXXI, núm. 3-4, tercer y cuarto trimestre 2000 de la Revista de Acústica: Número especial dedicado al XXV Aniversario del Instituto de Acústica del C.S.I.C.[ES] En este artículo se describen muy brevemente los fundamentos y desarrollo de un nuevo tipo de transductor macrosónico. El estudio y desarrollo de diferentes aspectos de este dispositivo ha constituido una línea de investigación original y permanente del Departamento de Sistemas, Señales y Tecnologías Ultrasónicos del Instituto de Acústica, que ha permitido generar y utilizar en forma eficiente y novedosa ondas acústicas de alta intensidad.[EN] This paper deals with brief review about of the fundamentals and development of a new type of high power acoustic transducer. The study and development of the different aspects of this device have constituted an original and permanent research topic in the Ultrasonic Department of the Instituto de Acústica, giving rise to the efficient generation of high intensity acoustic waves and their use in new applications.Peer reviewe