Numerical investigation on acoustic-induced particle agglomeration and atmospheric acoustic attenuation

Abstract

As a result of global warming and rapid population growth, various extreme climates have resulted in a significant crisis for future water supply security. With the advancement of science and technology, acoustic-stimulated precipitation technology is promising to revolutionize the usage of atmospheric water resources. Therefore, it is necessary to have an integrated understanding of acoustic agglomeration mechanisms and acoustic rainfall evaluation. To this end, this study explores the acoustic agglomeration of liquid aerosol particles in a standing wave sound field and provides a platform for evaluating acoustic rainfall and its influencing factors based on several acoustic atmospheric attenuation experiments. First of all, a three-dimensional CFD–DEM model is developed to model the acoustic agglomeration of liquid aerosol particles in a standing acoustic wave field. The flow field and acoustic field propagation are solved based on the Eulerian method, and the movement of atomized particles is solved based on the Lagrangian method. The model not only includes the fluid-particle interaction in the form of a momentum source term, but also considers the interaction between two particles using a linear elastic collision model. A comprehensive investigation is concentrated on the agglomeration characteristics of the liquid aerosol particles under the action of a standing wave field with different acoustic frequencies and acoustic power. It is found that an acoustic field with a larger acoustic power and higher ambient temperature to some extent have good agglomeration performances. Secondly, based on the air-modulated fluidic acoustic system and the large-scale field acoustic atmospheric attenuation experiments, a fully automatic evaluation platform was developed. The platform can be used for evaluating the actual acoustic effective area in precipitable clouds. The acoustic model simulations revealed the law of atmospheric acoustic wave attenuation, and the field experiments confirmed the model results. Besides, the effective area and influential area of the characteristic sound pressure level (SPL) value at a certain height can be used to describe the effect of acoustic waves on cloud particles. In this study, the directional propagation and energy concentration of acoustic waves are achieved in combination with the air-modulated fluidic acoustic system equipped with a cluster acoustic source, which appears to be favorable for realizing intelligent assessment and further comprehensive applications of the emerging technologies of acoustic-stimulated precipitation. Lastly, the attenuation factor G, derived by multiplying the transmission distance by the absorption coefficient, can be used to describe the continuous attenuation of acoustic intensity. Besides, the influencing factors affecting the attenuation of acoustic waves in the atmosphere are quantitatively analyzed. To promote the transmission efficiency of acoustic intensity economically, three characteristic frequencies are used to evaluate the optimized design of a multi-acoustic source combination layout. This is of guiding significance for the efficiency improvement of implementations of the acoustic-induced precipitation technology. Overall, the thesis contributes to improvements in the theoretical mechanisms and evaluation methods of acoustic-induced precipitation technology. This paves the way for future research on the influence of outdoor acoustic waves on particle motion.