Space-time pressure-velocity correlations in a turbulent boundary layer

Yoshitsugu Naka, Michel Stanislas, Jean Marc Foucaut, Sebastien Coudert, Jean Philippe Laval, Shinnosuke Obi

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The spatio-temporal 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 set-up 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 Re<inf>θ</inf>=7300, 10 000, 18 000. The spatio-temporal three-dimensional structures of the pressure-velocity correlations, R<inf>pu</inf>, R<inf>pv</inf> and R<inf>pw</inf>, are evaluated. The wall pressure fluctuations are closely coupled with coherent structures which occupy a large region of the boundary layer in the wall-normal and spanwise directions and up to 10δ/U<inf>e</inf> in time, where δ and U<inf>e</inf> 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 large-scale motion and very-large-scale motion previously observed by different authors and seem to organize in a scheme analogous to the near-wall cycle, but at a much larger scale.

Original languageEnglish
Pages (from-to)624-675
Number of pages52
JournalJournal of Fluid Mechanics
Volume771
DOIs
Publication statusPublished - 2015 May 1

Fingerprint

turbulent boundary layer
Boundary layers
wall pressure
ejection
Reynolds number
boundary layer thickness
free flow
particle image velocimetry
conditioning
leading edges
upstream
boundary layers
velocity distribution
spatial resolution
Velocity measurement

Keywords

  • boundary layer structure
  • turbulent boundary layers

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Condensed Matter Physics

Cite this

Space-time pressure-velocity correlations in a turbulent boundary layer. / Naka, Yoshitsugu; Stanislas, Michel; Foucaut, Jean Marc; Coudert, Sebastien; Laval, Jean Philippe; Obi, Shinnosuke.

In: Journal of Fluid Mechanics, Vol. 771, 01.05.2015, p. 624-675.

Research output: Contribution to journalArticle

Naka, Yoshitsugu ; Stanislas, Michel ; Foucaut, Jean Marc ; Coudert, Sebastien ; Laval, Jean Philippe ; Obi, Shinnosuke. / Space-time pressure-velocity correlations in a turbulent boundary layer. In: Journal of Fluid Mechanics. 2015 ; Vol. 771. pp. 624-675.
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