Immediate and Near Wake Flow Patterns Behind Slotted Disks

Abstract

The effect of spacing ratio on the near-wake regions immediately behind porous disks that consisted of multiple annular elements is investigated experimentally. Annular jets through individual slots merge into groups of highmomentum regions that displace a global recirculating region downstream. Multiple wake patterns result from the same overall conditions. Once the pattern forms, it remains nearly unchanged unless the e ow is disturbed. Compared to the e ow behind a solid disk, three-dimensional large-scale motions are suppressed downstream and the wake motions are more axisymmetric. The patterns of jet mergings are also axisymmetric and persistent. The mean and time-dependent large- and small-scale velocity e uctuations are characteristic of individual spacing ratios and e ow patterns, and they are analyzed and compared with e ow visualizations. The process of how the wake settles into a certain e ow pattern also is addressed.