可压缩喷流的温度混合层及近场压力POD分析

Temperature Mixing Layers and Proper Orthogonal Decomposition of Near Pressure Field in Compressible Jets

本文采用大涡模拟计算马赫数Ma=0.75.温度比T_(j)/T_(∞)=0.7、1和2的圆口喷流,着重研究了温度混合层与速度混合层发展规律的差异。同时采用近场压力的本征正交分解,研究温度对相干结构产生的影响,突出当喷流温度高于和低于环境温度时的声源的变化趋势。流场结果表明,温度混合层的增长速率高于速度混合层,且两种剪切层半值宽随温度比改变而呈现不同的变化趋势。声场结果显示非等温喷流的远声场均高于等温喷流,是由于压力脉动中声传播分量增强。随着温度比升高,相干结构不稳定性开始发生位置向上游移动,导致速度脉动水平的提前增长。湍流结构相干性的增强,使得速度脉动峰值水平升高。

Large eddy simulations are carried out for round jets at Ma=0.75 and temperature ratio T_(j)/T_(∞)=0.7,1 and 2,to study the difference between the temperature and velocity mixing layers.The pressure in near-field is analyzed by proper orthogonal decomposition so as to the study effects of temperature on the coherent structures.The changing trends of the sound source for the hot and cold jets are highlighted.The flow field results show that the growth rate of the temperature mixing layer is higher than that of velocity mixing layer.The developments of two half-width with the increase of temperature ratio are different.The far-field sounds for non-isothermal jets are higher than that of the isothermal jet,which is due to the increase of the acoustic component in pressure fluctuation.With the increase of temperature ratio,the starting location of the instability in coherent structure moves to upstream,leading to a faster rise of velocity fluctuation.The enhanced coherence of the turbulent structures results in the increase of peak velocity fluctuation.