Effects of adverse pressure gradient on quasi-coherent structures in turbulent boundary layer

✍ Scribed by Tomoya Houra; Toshihiro Tsuji; Yasutaka Nagano

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 651 KB
• Volume: 21
• Category: Article
• ISSN: 0142-727X
• DOI: 10.1016/s0142-727x(00)00014-x

✦ Synopsis

Statistical and kinematic characteristics of turbulent boundary layer ¯ows subjected to adverse pressure gradients are found to dier signi®cantly from those of zero-pressure-gradient ordinary boundary layers. The turbulent energy and shear stress transport vu 2 and vuv occurs in the direction toward the wall from the regions away from the wall, as the pressure gradient parameter P increases. This event is completely opposite to that in zero-pressure-gradient cases. The instantaneous waveforms of third-order moments are markedly altered in the near-wall region. The quadrant splitting and trajectory analyses reveal that obvious changes do occur in large-amplitude sweep motions (Q4) and outward interactions (Q1). On the other hand, the contributions from other coherent motions, especially the ejection motions (Q2), signi®cantly decrease and their durations become longer, i.e., these motions are dull and less active. Moreover, multi-point simultaneous measurements with ®ve X-probes are made to depict the kinematic pictures of the eects of the adverse pressure gradient on the eddy structures.