Effect of gap flow on the shallow wake of a sharp-edged bluff body –mean velocity fields
This is an Accepted Manuscript of an article published by Taylor & Francis Group in JOURNAL OF TURBULENCE on 08/17/2015, available online: http://dx.doi.org/10.1080/14685248.2015.1088155
The support of the Natural Sciences and Engineering Research Council (NSERC) of Canada is gratefully acknowledged. The authors thank Arindam Singha for his role in carrying out some of the PIV measurements.
This experimental study was carried out to investigate the turbulent shallow wake generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The objective of this study is to understand the effect of the gap flow on the wake by studying two different gap heights between the channel bed and the bottom edge of the bluff body. These two cases will be compared to the no-gap case which is considered as a reference case. Themaximumflowvelocity was 0.45m/s and the Reynolds number based on the water depthwas 45,000. Extensivemeasurements of the flowfield in the verticalmid-plane and in the horizontal near-bed, mid-depth, and near-surface planes weremade using particle image velocimetry. This paper is part of an extensive study to characterise the gap-flow effects and is primarily concerned with the mean velocity fields, while a companion paper discusses the turbulence characteristics. The size of the wake identified in the horizontal planes is found to vary in the three planes, where the gap flow enhances the entrainment in the near-wake region in the near-bed velocity field. The results also revealed that, if the gap flow is weak, it is engulfed by the recirculation zone formed just behind the bluff body whose axis is perpendicular to the vertical mid-plane. On the other hand, if the gap flow is relatively strong, it penetrates in the downstream direction and only a portion of it is diverted upward to feed the recirculation zone.