Large eddy simulation is performed to investigate the mixing characteristics between the hot and cold fluids in a T-junction with different amplitudes and periods of inlet velocity. The distributions of temperature field and velocity field as well as the properties of vortex structures are focused in the present study. In addition, the wavelet power spectrum density (WPSD) of both temperature and velocity fluctuations are investigated by wavelet transform. The results show that the instantaneous temperature and velocity in the mixing area vary periodically, while the variation period is the same as that of inlet velocity. A typical phenomenon is observed near the moment of lowest inlet velocity, the backflow occurs near the upstream of the opposite wall of the jet entrance. Moreover, the WPSD results show that both mixing velocity and temperature fluctuations have the identical prominent frequency which is equal to that of inlet velocity. The period of inlet velocity has a large effect on the WPSDs of velocity and temperature fluctuations in the low frequency region, while does the amplitude of inlet velocity in the high frequency region. In addition, the effect of either period or amplitude on velocity fluctuations is not synchronized with that of temperature fluctuations.

进行了大涡模拟，以研究T形结中热流体和冷流体之间的混合特性，其入口速度的幅度和周期不同。本文重点研究了温度场和速度场的分布以及涡结构的性质。另外，通过小波变换研究了温度和速度波动的小波功率谱密度（WPSD）。结果表明，混合区的瞬时温度和速度呈周期性变化，而变化周期与进口速度相同。在最低进气速度的瞬间观察到典型现象，回流发生在射流入口相对壁的上游附近。此外，WPSD结果表明，混合速度和温度波动具有相同的显着频率，与进口速度相同。入口速度的周期对低频区域的速度和温度波动的WPSD都有很大的影响，而入口频率的幅度在高频区域则有很大的影响。另外，周期或幅度对速度波动的影响与温度波动的影响不同步。