不同间距比下串列平板绕流尾迹的LDA试验研究

Experimental investigation of wake flow around two flat plates in tandem under different gap ratios by LDA measurements

本文以串列平板为研究对象,运用激光多普勒测速技术(LDA),研究了亚临界雷诺数Re D=3×104下,间距比T/D在1~6之间的上下游平板近尾迹区时均速度、脉动速度分布及其频谱特性,探讨了间距比变化对串列平板绕流尾迹的影响。试验结果表明:小间距比下(T/D<3),上游平板尾迹受下游平板抑制作用显著,无明显涡脱产生;随着间距比增大,这种抑制作用逐渐减弱,上游平板尾缘处出现明显涡脱。上游平板近尾缘区(x 1/D≤0.5),间距比对其尾迹影响较小;远离尾缘区(x 1/D>0.5、x 2/D>0.5),间距比对上游平板尾迹影响更为显著。间距比T/D≥3时,上下游平板均能形成稳定涡脱,且随着间距比增大两平板流动状态趋于一致,均趋向于单平板绕流。T/D=3可作为该雷诺数下,串列双平板绕流的临界间距比,此处St数有极小值。

A pair of flat plates in tandem is taken as the research object in this paper.The influence of gap ratio on wake flow around the plates was studied by the Laser Doppler Anemometry(LDA)technique under the subcritical Reynolds number Re D=3×104.The time-averaged velocity,and its fluctuations,frequency spectra characteristics in the near wake of upstream and downstream plate were analyzed when the gap ratio(T/D)varied from 1 to 6.The experimental results show that the wake of upstream plate is restrained significantly by the existence of downstream plate at the smaller gap ratios(T/D<3),where vortex shedding cannot be formed completely.With the increasing of gap ratio,the inhibitory effect becomes weak gradually and an obvious vortex shedding is formed at the tailing edge of the upstream plate.The gap ratio has less effect on the near wake region(x 1/D≤0.5)of the upstream plate.Far away from the tailing edge(x 1/D>0.5、x 2/D>0.5),the effect of gap ratio on wake of upstream plate is more significant.When the gap ratio T/D≥3,both upstream and downstream flat plates can form stable vortices,and the flow structures are tended to be consistent with the increase of the gap ratio,and both tended to flow around a single plate.It is found that the T/D=3 can be used as the critical gap ratio of flow around tandem double flat plates under this Reynolds number,where the Strohal number has a minimum value.