【摘要】 为研究入口扰动对矩形射流的影响,对不同扰动频率下的三维矩形射流进行了大涡模拟,用分布投影法求解动量方程,对压力泊松方程采用FACR直接解法。计算结果预报的速度在横向的单峰分布和速度半宽沿流向的近似线性增长与实验结果吻合良好。计算结果表明扰动频率为射流的本征频率fe=0.22时射流的卷吸作用最强,而高频扰动则抑制卷吸作用;激励频率接近本征频率时射流提前出现速度在展向的马鞍型双峰分布,更早趋于圆射流形态。进一步的流场二维和三维瞬态涡结构图谱表明:上述现象与f=0.1和f=0.22时射流近场更频繁卷起、更丰富的大涡结构存在密切关系,正是这些大涡运动不断地在横向卷吸入外界流体,实现射流在横向的迅速扩展。更多还原

【Abstract】 Large eddy simulations of three-dimensional rectangular jet flows were carried out to explore the effects of inlet disturbance frequency on jet flows.The projection scheme was used to solve the momentum equation,together with the Fourier Analysis-Cyclic Reduction(FACR)direct solver for the pressure Poisson equation derived from the projection scheme.The predicted single-peak profile of streamwise velocity distribution along transverse direction and the quasi-linear increasement of half-velocity width are in good agreements with experimental data.Simulation results indicate that the jet entrainment rate is mostly enhanced when the imposed frequency of the inlet disturbance is near the value of the characteristic frequency fe=0.22,while it’s greatly retarded when high frequency imposed.When f=0.22 and 0.1,the jets show spanwise double-peak saddle-backed velocity profiles at earlier streamwise positions and develop towards round jets at more upstream positions than when f=0,0.4 and 2.5.Further instantaneous 2D and 3D vortexes topologies of the flow field illustrate that the above effects of various frequencies are closely related to the existence of richer and earlier vortexes when f=0.22 and 0.1.It’s the rich vortexes that entrain more background fluid into the central jet,and expand the jet more quickly in radial directions.更多还原