ANumerical Analysis of the Growth of Unstable Waves fir High-speed Liquid Jet Atomization

• Main Authors: Wang Charng-Jyh, 王長志
• Other Authors: S. G. Chuech
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/13943476180565598536

碩士 === 國立海洋大學 === 機械與輪機工程學系 === 87 === The high-speed jet atomization is a topic of practical applications, such as gas-turbine combustors, diesel engines, rocket thrust chambers, and spray coatings of protective materials on surface, etc. The liquid jet atomization is related with the unstable waves on the jet surface. The unstable growth rate of the surface wave is affected by initial jet velocity, liquid viscosity, liquid surface tension, liquid/gas density ratio, the difference between liquid and gas velocity, and the initial disturbance on the jet surface. In the present study, a cylindrical liquid jet issued from a nozzle at a constant velocity was considered in the cylindrical coordinate. The dispersion equations governing the temporal growth rates of the jet surface were derived from the continuity equation and the momentum equations with the small perturbation theory. The approximate and general solutions of the temporal dispersion equations were solved numerically. In the present numerical analyses, the jet parameters, such as liquid velocity, nozzle diameter, liquid viscosity, surface tension, liquid/gas density ratio and the difference between liquid and gas velocity, were varied to study their influences on the unstable wave growth rate. The present models were applied to several low-speed and high-speed jets. The numerical results showed that the trend of variations of the drop sizes and size distributions is in good agreement with the observation of past experimental studies. The present model also predicted that the surface wave growth rate is increased with increasing the jet velocity, and the wavelength of the surface wave with a maximum growth rate becomes shorter. This indicates that the higher the jet velocity the finer droplets are produced in the high-speed atomization process.