幂律流体气流雾化射流不稳定性分析

Instability Analysis of a Gas Jet Ejected into a Power-Law Stream

基于射流不稳定性理论系统研究了一个圆柱形可压缩气流喷入有限厚度的幂律流体的时间模式不稳定性.在对幂律流体本构方程线性近似的基础上,推导了表征轴对称模式幂律流体气流雾化射流不稳定性的色散方程.通过数值计算,分析了液相雷诺数、韦伯数、气/液密度比和速度比、气流马赫数以及幂律指数对于剪切变稀流体与剪切变稠流体两种情形气流雾化射流的不稳定性影响.结果表明:无论是剪切变稀情形还是剪切变稠情形,液体的黏性力总是抑制其不稳定性,减小幂律指数均可促进幂律流体气流雾化射流的不稳定性.随着气流速度的不断增大,由气/液相互运动导致的剪切波逐渐主导幂律流体气流雾化射流的不稳定性与破碎过程.当液相的参数保持不变,增大气流密度、气流速度以及气流可压缩性均可有效地促进幂律流体气流射流的破碎.空气动力是促进幂律流体射流破碎的有效措施.同时,对于一个小韦伯数,表面张力促进气体射流不稳定性;而随着韦伯数增大到临界值后,表面张力将会逐渐抑制其不稳定性.

Based on the jet perturbation theory,the instability of a compressible gas jet ejected into the limited thickness power-law stream was investigated in detail.The effects of the liquid Reynolds number,the Weber number,the gas-liquid density ratio,the gas-liquid velocity ratio,the gas Mach number,and the power-law exponent on the instability of gas jets into the power-law stream were analyzed.The numerical results show that the liquid viscous force always dampens the instability of gas jets.A lower power-law exponent will trigger a more unstable gas jet in the power-law stream.Meanwhile,with the gas stream velocity increasing,the interface instability of gas jets ejected into the power-law stream is gradually dominated by the shear wave,resulted from the gas-liquid relative motion.To increase the gas stream density,the gas stream velocity and the gas compressible all quickly amplify the gas jet instability and promote the breakup of power-law stream.Finally,for a low Weber number,the liquid surface tension will promote the gas jet instability,while the liquid surface tension will restrain the gas jet when the Weber number exceeds the critical Weber number.