入口速度比对射流拟序结构的影响

Influences of inlet velocity ratio on coherent structures in planar jets

为了深入了解湍流流动机理以及湍流拟序结构发展过程的影响因素,本文采用大涡模拟方法对不同入口射流伴流速度比的平面湍射流流动进行了数值模拟。采用分步投影法求解动量方程,亚格子项采用标准Smagorinsky亚格子模式模拟,压力泊松方程采用修正的循环消去法快速求解,空间方向采用二阶精度的差分格式,在时间方向上采用二阶精度的显式差分格式。模拟结果给出了平面射流中湍流拟序结构的瞬态发展演变过程,分析了入口速度比对射流拟序结构发展演化过程及宏观流场形态的影响,为进一步研究射流拟序结构及其在湍流流动中的作用提供了基础。

Turbulent jet flow is the most widely used flow type in engineering applications. Most proportion of energy transportation and conversion processes is dominated by the transient evolution of the large-scale structures, or the coherent structures, in turbulent jets. Two-dimensional spatial developing turbulent planar jets with different velocity ratios of jet fluid to co-flow fluid at the inlet section are simulated with the large eddy simulation approach in order to give the detailed information of transient behaviors of coherent structures in turbulent jets and to explain how the velocity ratios affect the evolution of coherent structures. Transient distributions of velocity are obtained at different evolution periods of turbulent jets, and evolutions of coherent structures in flow field are also given. Filtered nondimensionalized governing equations are solved with the standard Smagorinsky sub-grid scale model, and the transport equation of passive scalar is solved in order to perform the numerical visualization of flow field. The numerical simulation is performed by the Chorin's fractional step method. The Buneman variant of the cyclic odd-even reduction algorithm is adopted for solving the pressure correction Poisson equation. Simulation results show the structures of flow field at different velocity ratios and the transient evolution process of coherent structures in planar jets as well as the interaction between velocity ratio and coherent structures, and they explain the existence of the potential core region in turbulent jets. Results of this paper may provide the basis for the control and optimization of engineering applications associated with turbulent jet flows.