基于分离涡模拟的旋转射流流场结构特征分析

Detached eddy simulation on the structure of swirling jet flow field

采用改进的分离涡模拟方法配合剪应力输运模型分析旋转射流涡结构、速度场、压力场的演化过程,探索喷嘴压降对大涡结构发展和湍流脉动波动的影响规律。研究结果表明:射流涡结构的发展可划分为Kelvin-Helmholtz不稳定性阶段、过渡阶段和旋转不稳定性阶段;旋流作用能够显著增强径向湍流脉动、增大射流扩散角,湍流脉动耗散是下游射流速度衰减的主要原因;随压降增大,射流速度和脉动幅度都相应增大,速度分布的对称性增强,沿轴线方向的压力脉动特征和涡旋输运强度显著增加,但当喷射距离超过约9倍无因次喷距后,提升压降并不能提高旋转射流的有效冲击距离,但可以增大旋流强度和射流扩散角。旋转射流更适用于需求大孔径的径向水平井钻孔、煤层气水平井造穴和煤矿巷道钻孔卸压等工程场景。

The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.