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Published byRegina Greene Modified over 8 years ago
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Dynamique du recollement turbulent pendant la crise de traînée du cylindre circulaire Olivier Cadot Sanjay Mittal Aditya Desai Charad Saxena Brajesh Chandra National Wind Tunnel Facility IIT Kanpur, India
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Oil print on the wall (Schewe 1986) Drag crisis (Roshko 1961) Bubbles transitions (Bearman 1969)
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10 m/s < U 0 < 75 m/s Turbulence intensity < 0.3% Pressure coefficient measurements Cp(t) = 2(p(t)-p 0 )/ U 0 2 Pressure scanner 32HD @ Measurement Specialties 32 ports, 500Hz per port NWTF
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U0U0 =12° 0 30 ports for C p ( ,t)
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Time response fc~150 Hz -2 Autopower spectrum C p (84°,t) subcritical régime (short time dynamics) bistable régime (long time dynamics) U Cp (84°,t) f (Hz) U=35 m/s U=59 m/s pressure scanner, sampling rate : 500Hz
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Sectional drag and lift vs. Reynolds number Analysis of C p ( ,t ) vs. Re first transition one side reattachment both sides reattachment
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Periodic dynamics tU/D~5
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Symmetric disturbances having long time dynamics tU/D~5000 #1 #2 #1 #2
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#1 #2 Symmetric perturbation #1 #2 Discrete transition leading to a bi- stable behavior. Larger adverse pressure gradient after the transition. Consistent with the symmetric reattachment of Higuchi et al. (1989).
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top bottom
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Conditionnal averaging over quadrants :
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50.5% 49% 0.5% 37% 1% 62%
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Statistics of changes of states kdt =320 d/U Consistent with binomial law : Slope -2
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Conclusion Reattachment is discrete and random : the mean pressure distribution is given by the time proportion of well defined states. Symetric and antisymmetric couplings are observable. AS coupling S coupling Re Due to reattachment somewhere else on the cylinder ? Dynamics along the span ?
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