| The deformation and breakup of droplets induced by shock waves is a classic multiphase fluid mechanics phenomenon that is widely present in the fields of hypersonic dynamics and detonation.The spatial,temporal characteristics and breakup modes of hundred-micron droplets,which occupy a large volume fraction in engineering fluids,directly affect subsequent mixing,evaporation,and combustion processes,and thereby affect the performance of the device or equipment.The mechanics involved covers multiple fields such as compressible gas dynamics,interface instability mechanics,and two-phase flow.In view of the importance of hundred-micron droplet breakup under the action of a shock wave in engineering applications,and the urgency of extracting key action mechanisms from various related fluid mechanics mechanisms,this paper conducted a study on the breakup process of hundred-micron water droplets under the action of a shock wave.Firstly,based on the horizontal shock tube platform and using dual-pulsed laser holography technology,high-resolution experimental data on the deformation and breakup modes of micrometer-sized droplets under different loads were obtained under shock Mach numbers Ma=1.09～1.63.Morphological and dynamic analysis of droplet breakup was carried out,with emphasis on the influence of Weber number(We)and initial droplet diameter on the deformation and breakup of micrometer-sized droplets.Secondly,using the pressure-based implicit solver method,the PISO algorithm to achieve pressurevelocity coupling,and coupling the VOF multiphase flow model and the RNG k-εturbulence model,a numerical calculation model suitable for predicting and analyzing hundred-micron droplet breakup was constructed.On the basis of verifying the effectiveness of the model,the evolution characteristics of hundred-micron droplets on the windward/leeward sides at high We numbers,which are difficult to achieve in experimental verification,were analyzed.The specific conclusions are as follows:(1)Under the same initial droplet diameter,increasing the Weber number will accelerate and promote the deformation and breakup process of droplets.Under the premise of the same Weber number,reducing the droplet diameter will increase the difficulty of droplet breakup and prolong the deformation time,allowing the droplet to undergo more deformation behaviors.Moreover,under low Weber number conditions within the critical range,the droplet deformation time is not only prolonged but also leads to a change in the droplet breakup mode.(2)The dimensionless windward displacement of droplets grows in a curve manner with the dimensionless time,and gradually decreases with the increase of the Weber number.Under low Weber number conditions,the acceleration of the dimensionless windward displacement changes with the deformation and breakup mode of the droplet.There is little difference in the dimensionless windward displacement of hundred-micron droplets under high Weber numbers.In terms of hydrodynamic surface instability,the Rayleigh-Taylor/Kelvin-Helmholtz instability(R-T/K-H instability)waves growth rate of the droplet surface shows an overall increasing trend with the change of the wave number,but the maximum growth rate and the wave number of the maximum growth rate of the two instabilities differ with the increase of the Weber number.(3)During the deformation and breakup process of droplets,a complex and dense small-scale instability appears on the windward side,but the front end remains smooth.After the airflow passes through the droplet,a small vortex flow is formed on the leeward side of the droplet,which is constantly developing,causing the leeward side of the droplet to be continuously squeezed into a concave shape.During the droplet breakup process,the windward and leeward sides will continuously generate surface waves under the action of post-shock airflow aerodynamics and eddy currents,causing almost all small droplets to fall off from the equator.The velocity of the leeward side of the droplet shows a flame tail and extends towards the direction of the airflow,and under the action of the eddy current,a U-shaped low-speed region appears on the leeward side of the droplet.This paper presents two innovative points.(1)An experimental method is developed by combining shock tube facilities and holographic testing techniques to systematically investigate the deformation and breakup characteristics of hundred-micron droplet.(2)Secondly,a numerical model is constructed for predicting and analyzing the breakup of hundred-micron droplets in high Weber number conditions,which are difficult to verify experimentally.The model analyzes the evolution characteristics of the leading and trailing edges of the droplets. |
PDF Full Text Request