圆形和矩形燃气射流在受限液体中扩展特性的对比研究

Comparative Study on Expansion Characteristics of Round and Rectangular Combustion-Gas Jets in Confined Liquid Medium

关键词:  水下燃气射流  扩展特性  湍流掺混  气液相互作用

Key words:  Submerged combustion-gas jet  Expansion characteristic  Turbulent mixing  Gas-liquid interactions

摘要:

为研究不同喷孔结构的燃气射流在受限液体工质空间的扩展特性，采用VOF(Volume of fluids)模型分别对圆柱形充液室中圆形射流和矩形射流扩展过程进行气水耦合数值求解。考虑了燃气可压缩性、流体粘性和热量交换因素对射流扩展特性的影响。通过数值模拟，获得圆形射流扩展形态及轴向速度计算值，与实验结果吻合较好。在此基础上，进一步对比分析了矩形射流和圆形射流的扩展特性，获得射流场中密度、压力、温度和速度的分布图以及涡的演化过程。计算结果表明:燃气自喷孔喷出，由于出口处压力较大，高温燃气继续膨胀产生膨胀波，膨胀波在气液界面反射形成压缩波，圆形射流的膨胀波和压缩波均比矩形射流强。燃气射流扩展过程中，由于周围液体惯性效应，气液卷吸掺混效应以及膨胀压缩波作用，圆形射流的压力场和温度场分布较矩形射流更加复杂，同时刻的圆形射流轴向扩展速度也比矩形射流小。从速度云图发现矩形射流的速度核心区比圆形射流速度核心区要短；同时从圆形射流和矩形射流不同截面流向速度分布图发现流向速度峰值均发生了偏移，但矩形射流发生偏移的区间更长，偏离距离更远。

Abstract:

To explore the expansion characteristics of combustion gas jet with different nozzle structures in confined liquid working medium，the coupling numerical value results for the expansion process of round jet and rectangular jet in cylindrical filling liquid chamber was obtained by means of Volume of Fluids model. The effects of jet compressibility，fluid viscosity and energy transfer between water and combustion gas on jet expansion characteristics were considered. The simulation results of jet shape and axial velocity of round jet are in good agreement with the experiments. On this basis，the expansion characteristics of rectangular jet and round jet are further comparatively analyzed. And the distribution maps of density，pressure，temperature，velocity and evolution processes of vortices were obtained. Results show that，the combustion-gas jet expands further as the pressure is great when the jet just out of the nozzle exit，and it forms a expansion wave in the Taylor cavity. The expansion wave is reflected in the gas-liquid interface and forms a shock wave. The intensities of both the expansion wave and the shock wave in round jet are stronger than those of rectangular jet. In the whole expansion process of combustion-gas jet，the pressure field and temperature field of round jet are more complicated than those of rectangular jet due to the influence of inertial effect of surround liquid，entrainment and mixing effect between gas and liquid，and the expansion wave and shock wave. Meanwhile the axial expansion velocity of round jet is smaller compared with rectangular jet. As seen from the distribution maps of velocity，the potential core of rectangular jet is shorter than that of round jet，meanwhile as shown from the streamwise velocity profiles of both round jet and rectangular jet，the peak of streamwise velocity deviate from central axis，but the deviation distance of rectangular jet is farther than that of round jet.