中心体喷嘴自由水射流的波动与能量分布特性

Fluctuation and Energy Distribution in Free Water Jet Discharged From a Central-Body Nozzle

在15MPa射流压力条件下,对一中心体喷嘴进行自由水射流实验。用高速数码摄像技术捕捉喷嘴出口附近的瞬态流束界面波动特征;用相位多普勒粒子分析技术(PDPA)测量充分发展的射流场中的平均速度、均方根速度及液滴粒径分布。研究表明,中心体喷嘴射流流束的界面波动明显,远离喷嘴出口,流束界面波动频率降低,但波动幅值增大;射流轴心线附近的均方根速度较小,自射流轴心线向流束外缘,均方根速度出现明显的双峰分布;在距中心体喷嘴出口一定轴向距离的射流断面上,轴心线附近的液滴平均粒径小,沿径向向外出现液滴平均粒径峰值;大于此距离,液滴平均粒径分布与普通圆柱水射流的液滴平均粒径分布情况一致。

Under jet pressure of 15 MPa,free water jet discharged from a central-body nozzle was experimentally studied.High speed photography was used to capture the transient fluctuation of the jet interface.Phase Doppler Particle Anemometry（PDPA） was used to measure distributions of mean velocity,Root Mean Square（RMS） velocity and droplet diameter in the fully developed jet flow. Apparent fluctuation of jet interface is proved in the study.With the jet＇s advancing,fluctuation frequency of jet interface gets smaller,but fluctuation magnitude is enlarged.Just near the jet axis,there is a distribution of relatively small Root Mean Square（RMS） velocity.When the radial distance from jet axis increases,two symmetrical RMS velocity peaks appear.At those transverse sections within a certain axial distance from nozzle outlet,dual-peak distribution of average droplet diameter is the general case.However,when the axial distance from nozzle outlet gets further large, distribution of average droplet diameter becomes similar with that in the water jet discharged from common round nozzle.