Space–time pressure–velocity correlations in a turbulent boundary layer
type de publication 
article dans une revue internationale avec comité de lecture 
date de publication 
2015 
auteur(s) 
Naka Yoshitsugu; Stanislas Michel; Foucaut JeanMarc; Coudert Sébastien; Laval JeanPhilippe; Obi Shinnosuke 
journal (abréviation) 
Journal of Fluid Mechanics (J Fluid Mech) 
volume (numéro) 
771 
 
pages 
624 – 675 
résumé 
The spatiotemporal pressure–velocity correlation in a turbulent boundary layer is investigated so as to understand the link between pressure fluctuations and turbulent coherent structures. A new experimental setup is developed to measure the pressure fluctuations at the wall and in the field and, simultaneously, the velocity field by stereoscopic particle image velocimetry. The present measurement area covers the whole boundary layer thickness, and the spatial resolution of the measurement is good enough to assess the representative length scales of the flow. The Reynolds number effect is quantified from the data at Reθ=7300, 10 000, 18 000. The spatiotemporal threedimensional structures of the pressure–velocity correlations, Rpu, Rpv and Rpw, are evaluated. The wall pressure fluctuations are closely coupled with coherent structures which occupy a large region of the boundary layer in the wallnormal and spanwise directions and up to 10δ/Ue in time, where δ and Ue denote the boundary layer thickness and the free stream velocity. Reynolds number effects are mainly observed on the size and intensity of the pressure–velocity correlations. Conditioning the correlations on the pressure signal sign shows different types of flow phenomena linked to the positive and negative pressure events. For the wall pressure, positive pressure fluctuations appear to be correlated with the leading edge of a large sweeping motion of splatting type followed by a large ejection. The negative pressure fluctuations are linked to a localized ejection upstream, followed by a large sweeping motion downstream. For the pressure fluctuations in the field, in addition to the structures observed with the wall pressure, the pressure–velocity correlations exhibit a significant correlation in a region very extended in time. Such long structures appear to be independent of the one observed at the wall and to grow significantly in time with the Reynolds number when scaling with external variables. When conditioned by the pressure sign, clear ejection and sweeping motions are observed with associated streamwise vortical structures at a scale of the order of 0.2δ. These structures can be linked to the largescale motion and verylargescale motion previously observed by different authors and seem to organize in a scheme analogous to the nearwall cycle, but at a much larger scale. 
mots clés 
boundary layer structure; turbulent boundary layers 
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