A Review on the Effect of Sound Waves upon the Coalescence of Aerosol and Cloud and Fog Particles

Abstract

The effect of sound waves on the coalescence of aerosol particles and cloud and fog droplets is a frontier scientific problem in the field of cloud physics and weather modification. The technology of acoustic coalescence has attracted much attention due to its relatively simple experimental device, strong adaptability, and short operation time. These advantages make it a potential new technology of aerosol coalescence. The research progress of acoustic coalescence of aerosol particles and cloud and fog droplets is reviewed from the aspects of theory, experiment, and numerical simulation. The mechanisms of acoustic coalescence mainly include orthokinetic interaction, hydrodynamic interaction (including acoustic wake effect, mutual radiation pressure effect, and mutual scattering effect), and acoustic-induced turbulence effect. The coalescence of aerosol particles in the sound field appears under the combined action. The low-frequency strong sound wave can increase the relative motion between cloud and fog droplets and promote the process of collision and coalescence, which has a significant impact on cloud and fog growth and precipitation. Finally, the existing problems and improvement direction of the research on the theory, experimental observation, and numerical simulation of acoustic coalescence are discussed. The complexity of the acoustic coalescence process, the diversity of experimental conditions, and the limitations of the theory, the optimal experimental conditions and parameter configuration for high efficiency of acoustic coalescence are still imperfect, which requires further experimental studies and numerical simulations. In addition, the research on the coalescence effect of sound waves on fog and cloud particles is not deep enough, and the similarities and differences of acoustic coalescence mechanisms between cloud and fog particles and ordinary aerosols are not clear enough. It is emphasized that the cloud chamber and numerical simulation research on the effect of acoustic coalescence on cloud and fog particles should be strengthened, and a large number of field comprehensive observation experiments should be carried out, which is of great scientific significance for the development of new weather modification technologies.

Keywords

• acoustic coalescence
• aerosol particles
• cloud and fog droplets
• artificial fog dissipation and precipitation enhancement