孔壁通透率对平面附壁射流的影响

本文研究了不同壁面通透率对平面附壁射流动态特性的影响。实验结果表明孔壁减弱、甚至消除了流场中的低频摆动现象。随着孔壁通透率的增加,射流时均附壁点向下游逐渐移动,射流和壁面之间的回流区长度逐渐增大,而射流内侧剪切层内的涡旋与壁面之间的相互作用减小,壁面压强脉动强度变小,附壁射流的动态特性逐渐向自由射流转化。当孔壁通透率为40%左右时,射流与二维平面自由射流类似。距离射流出口不同位置上的壁面脉动压强之间的互谱表明,当孔壁通透率增大以后,射流内侧剪切层中的旋涡向下游传播距离变得更长,传播速度加快,这说明低孔壁通透率情况下的附壁射流中存在的低频摆动现象阻碍了剪切层高频旋涡向下游的发展。

Passive control of an offset attaching j et using a perforated plate

The effect of porous wall on the dynamic motions of an offset attaching planar j et was studied using experimental methods.The offset jets developed along perforated walls with different open area ratios (OAR)from 0% (solid wall)to approximately 40%.The fluctuating pressure on the bottom wall was measured using an array of microphones embedded in the wall a-long the centerline of the facility.The flow fields were also visualized using the smoke wire tech-nique.It was found that the root-mean-square values of the fluctuating wall pressure decreased when the wall porosity increased,while the average length of the recirculation region increased at the same time.The cross-spectra of the fluctuating wall pressure measured at different down-stream locations showed that the low frequency flapping motion disappeared when the open area ratio was more than 20% of the total area of the wall.The attaching jet behaved like a two-di-mensional free j et when the open area ratio of the wall was more than 40%.The spectra of the wall pressure also showed that the large scale vortices in the inner shear layer of the attaching j et propagated a longer distance in the flow with a larger porosity,which indicated the low-frequency flapping motions in the j ets with small open area ratio hindered the development of higher-fre-quency shear layer vortices.