### Abstract

Flow in the separation bubble formed along the sides of a blunt flat plate with right angled corners has been studied in terms of extensive single and two point measurements of velocity and surface pressure fluctuations. The cross correlations between the surface pressure and velocity fluctuations are found to be useful for the study of large scale vortex structure in the bubble. Large scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U_{∞}/x_{R}where U_{∞}is the approaching velocity and x_{R}is the time mean length of the bubble. On top of this regular vortex shedding, there exists a large scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U_{∞}/x_{R}. The large scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7-0.8) x_{R}and their convection velocity is about 0.5U_{∞}near the reattachment line. The cross correlations also suggest the existence of a longitudinal counter rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6x_{R}. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.

Original language | English |
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Pages (from-to) | 83-113 |

Number of pages | 31 |

Journal | Journal of Fluid Mechanics |

Volume | 137 |

DOIs | |

Publication status | Published - Jan 1 1983 |

Externally published | Yes |

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### All Science Journal Classification (ASJC) codes

- Fluid Flow and Transfer Processes
- Engineering(all)

### Cite this

*Journal of Fluid Mechanics*,

*137*, 83-113. https://doi.org/10.1017/S002211208300230X

**Structure of a turbulent sevaration bubble.** / Kiya, Masaru; Sasaki, Kyuro.

Research output: Contribution to journal › Article

*Journal of Fluid Mechanics*, vol. 137, pp. 83-113. https://doi.org/10.1017/S002211208300230X

}

TY - JOUR

T1 - Structure of a turbulent sevaration bubble

AU - Kiya, Masaru

AU - Sasaki, Kyuro

PY - 1983/1/1

Y1 - 1983/1/1

N2 - Flow in the separation bubble formed along the sides of a blunt flat plate with right angled corners has been studied in terms of extensive single and two point measurements of velocity and surface pressure fluctuations. The cross correlations between the surface pressure and velocity fluctuations are found to be useful for the study of large scale vortex structure in the bubble. Large scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xRwhere U∞is the approaching velocity and xRis the time mean length of the bubble. On top of this regular vortex shedding, there exists a large scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7-0.8) xRand their convection velocity is about 0.5U∞near the reattachment line. The cross correlations also suggest the existence of a longitudinal counter rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.

AB - Flow in the separation bubble formed along the sides of a blunt flat plate with right angled corners has been studied in terms of extensive single and two point measurements of velocity and surface pressure fluctuations. The cross correlations between the surface pressure and velocity fluctuations are found to be useful for the study of large scale vortex structure in the bubble. Large scale vortices are shed downstream from the separation bubble with a frequency of about 0.6U∞/xRwhere U∞is the approaching velocity and xRis the time mean length of the bubble. On top of this regular vortex shedding, there exists a large scale unsteadiness in the bubble. Vortices which are much larger than the regular vortices are shed with frequencies less than about 0.2U∞/xR. The large scale unsteadiness is accompanied by enlargement and shrinkage of the bubble and also by a flapping motion of the shear layer near the separation line. The intermittent nature of the flow in the bubble is clarified in some detail. The distributions of the cross correlations between the pressure and velocity fluctuations demonstrate the vortex structure in the reattaching zone. The longitudinal distance between the vortices is estimated to be (0.7-0.8) xRand their convection velocity is about 0.5U∞near the reattachment line. The cross correlations also suggest the existence of a longitudinal counter rotating system in the bubble. The distance between the axes of the rotation is of the order of 0.6xR. Variations of timescales, lengthscales and phase velocities of the vortices are presented and discussed.

UR - http://www.scopus.com/inward/record.url?scp=0020865261&partnerID=8YFLogxK

UR - https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/structure-of-a-turbulent-separation-bubble/BA70A16D4DD59766334F7CF28E71F581

U2 - 10.1017/S002211208300230X

DO - 10.1017/S002211208300230X

M3 - Article

VL - 137

SP - 83

EP - 113

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -