### 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 language | English |
---|---|

Pages (from-to) | 624-675 |

Number of pages | 52 |

Journal | Journal of Fluid Mechanics |

Volume | 771 |

DOIs | |

Publication status | Published - 2015 May 1 |

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### Keywords

- boundary layer structure
- turbulent boundary layers

### ASJC Scopus subject areas

- Mechanical Engineering
- Mechanics of Materials
- Condensed Matter Physics

### Cite this

*Journal of Fluid Mechanics*,

*771*, 624-675. https://doi.org/10.1017/jfm.2015.158

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

Research output: Contribution to journal › Article

*Journal of Fluid Mechanics*, vol. 771, pp. 624-675. https://doi.org/10.1017/jfm.2015.158

}

TY - JOUR

T1 - Space-time pressure-velocity correlations in a turbulent boundary layer

AU - Naka, Yoshitsugu

AU - Stanislas, Michel

AU - Foucaut, Jean Marc

AU - Coudert, Sebastien

AU - Laval, Jean Philippe

AU - Obi, Shinnosuke

PY - 2015/5/1

Y1 - 2015/5/1

N2 - 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 Reθ=7300, 10 000, 18 000. The spatio-temporal three-dimensional 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 wall-normal 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 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.

AB - 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 Reθ=7300, 10 000, 18 000. The spatio-temporal three-dimensional 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 wall-normal 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 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.

KW - boundary layer structure

KW - turbulent boundary layers

UR - http://www.scopus.com/inward/record.url?scp=84928641750&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84928641750&partnerID=8YFLogxK

U2 - 10.1017/jfm.2015.158

DO - 10.1017/jfm.2015.158

M3 - Article

VL - 771

SP - 624

EP - 675

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -