考虑不可凝结气体的空化流模型及数值模拟

Cavitation model with non-condensable gas effect and its numerical simulation

以均相流假设为基础建立了一种基于输运方程的空化流模型,该模型在质量传输方程中不仅考虑了蒸发和凝结的机理,而且考虑了不可凝结气体的影响.采用RNG k-ε湍流模型,并引入与混合密度相关的修正函数对湍流涡黏性系数进行修正.应用文中的空化流模型,对NA-CA66翼型进行了定常空化流动数值模拟,翼型吸力面的压力系数分布曲线与试验结果吻合很好.在此基础上,进一步研究了模型中不可凝结气体质量分数以及不同进口湍动能和湍流耗散率对空泡形成和发展的影响,确定了模型中不可凝结气体质量分数、进口湍动能和湍流耗散率的合理取值.应用空化流模型对非定常空化流动进行了数值模拟,数值模拟结果清晰地反映了翼型表面空化云的初生、成长、脱落和溃灭的全过程,并指出反向射流是引起空化云脱落的重要原因.非定常计算得到的斯特劳哈数与试验相吻合,进一步验证了该模型在空化流数值计算中的可靠性.

A transport equation-based cavitation model was developed according to the homogeneous assumption in this paper. The mechanism of evaporation and condensation was considered in the model. The non-condensable gas was also taken into account in cavity formation and development. The RNG turbulence model was employed with a modified turbulent viscosity according to the mixed density. The proposed model was implemented to simulate the steady eavitating flow around a NACA66 airfoil. The pressure coefficient distributions on the suction side of the foil agreed well with the experiment results. Furthermore, the effects of non-condensable gas, inlet turbulent kinetic energy and turbulence dissipa- tion rate on the cavity length were evaluated. The proper values of non-condensable gas,inlet turbulent kinetic energy and turbulence dissipation were selected. Then, the proposed model was applied to an unsteady cavitating flow. The numerical results clearly reflected the whole process of the cavitation- cloud generation, growth, dispersion and collapse. The simulation showed re-entrant jet is one of the main reasons for the break-off process. The Strouhal number obtained agreed well with the experiment results. The overall results prove the reliability of the proposed model in cavitating flow simulations.