圆湍射流的轴对称大涡模拟

对空间发展的不可压缩圆湍射流进行了大涡模拟研究。在流动轴对称假定下，对Re数等于11300的圆浩射流流动进行数值模拟。大涡模拟很好地再现了圆湍射流中拟序结构非定常演化的前期过程，成功地捕获到了射流中Kelvin～Helmholtz不稳定性的触发与初级涡环的卷起及其第一次和第二次配对合并现象。但在流动轴对称假设下，大涡模拟不能模拟出湍流拟序涡环结构的破碎过程。对圆湍射流的轴对称大涡模拟结果进行长时间统计平均，能够预报出圆湍射流的核心区特征，但与圆湍射流的理论分析解和经典的实验数据对比发现，核心区后大涡模拟预报的流向速度降低缓慢。从控制方程的数学本质和拟序结构的物理机制上对圆湍射流在轴对称假设下产生上述大涡模拟结果的原因进行了分析与探讨。

Large-Eddy Simulation of a Round Turbulent Jetunder the Flow AxisymmetricAssumption

Large-eddy simulation results are reported for an unforced,incompressible,spatially developing turbulent round jet at a moderate Reynolds number,Re=11 300,using the fractional-step projection method.Under the flow axisymmetric assumption,the unsteady evolution processes of the coherent structures have been successfully represented,as a result of the development of the Kelvin-Helmholtz instability of the shear layer in the proximal region of the jet flow.The roll-up of the primary vortex rings and succeeding vortex-pairing phenomena of the round jet have been numerically visualized.However,the tear-up of the large-scale structures could not be reproduced under the axisymmetric assumption.Detailed statistical properties of the round turbulent jet are also obtained through the present LES work.The potential core of the round turbulent jet predicted is coincident with the analytical results.But the further decrease of the time-averaged stream-wise velocity component is slow under the flow axisymmetric assumption compared to the experimental data.The possible causes for such phenomena have been suggested on the basis of coherent structure dynamics and through analyzing the intrinsic characteristic of governing equations.