Interactive Control in Turbulent Shear Layers
Annual rept. Feb 91-Jan 92,
ILLINOIS INST OF TECH CHICAGO FLUID DYNAMICS RESEARCH CENTER
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Using Particle Image Velocimetry in a turbulent pipe flow, instantaneous large-scale structures were observed, which are not seen in low Reynolds number direct numerical simulations of bounded turbulent shear flow. A probable explanation for this discrepancy is the much larger experimental Reynolds number as compared with the DNS results. Further support of this Reynolds number influence was found when quantifying the relative role of the outer-layer structures and wall-layer structures on the spanwise correlation coefficient between the wall-shear stress and streamwise velocity. That is, the results suggest that the influence of the outer flow on the streamwise velocity fluctuations at y 10, increases with increasing Reynolds number. This outer-layer effect was then further examined in terms of the boundary layer intermittencywall-layer dynamics coupling. Although the outer layer is directly influencing the wall-layer region, it was found that the alternating passages of laminar and turbulent regions in the intermittent part o the boundary layer were not directly influencing the buffer layer statistics. The mechanisms of this influence are currently being investigated.
- Fluid Mechanics