### Abstract

Original language | English |
---|---|

Pages (from-to) | 192-230 |

Number of pages | 39 |

Journal | Journal of Fluid Mechanics |

Volume | 849 |

Early online date | 18 Jun 2018 |

DOIs | |

Publication status | Published - 25 Aug 2018 |

### Fingerprint

### Keywords

- coastal engineering
- surface gravity waves
- turbulent boundary layers

### Cite this

*Journal of Fluid Mechanics*,

*849*, 192-230. https://doi.org/10.1017/jfm.2018.403

**Turbulence statistics in smooth wall oscillatory boundary layer flow.** / Van der A, Dominic A.; Scandura, Pietro; O'Donoghue, Thomas.

Research output: Contribution to journal › Article

*Journal of Fluid Mechanics*, vol. 849, pp. 192-230. https://doi.org/10.1017/jfm.2018.403

}

TY - JOUR

T1 - Turbulence statistics in smooth wall oscillatory boundary layer flow

AU - Van der A, Dominic A.

AU - Scandura, Pietro

AU - O'Donoghue, Thomas

N1 - This work has been carried out within the SINBAD project, funded through the UK’s Engineering and Physical Sciences Research Council (EPSRC grant EP/J00507X/1). PS acknowledges the funding from the University of Aberdeen to support his Honoray Research Fellowship and funding from the Ministero dell’Istruzione dell’Universit`a e della Ricerca through PRIN 2012 “Hydromorphodynamic and modeling of coastal processes for engineering purposes”. The authors acknowledge the support of the technical staff at the University of Aberdeen, especially Fluids Laboratory Technician Roy Gillanders. The experimental and numerical datasets presented in this paper are available on https://dx.doi.org/10.5281/zenodo.1095116.

PY - 2018/8/25

Y1 - 2018/8/25

N2 - Turbulence characteristics of an asymmetric oscillatory boundary layer flow are analysed through two-component laser-Doppler measurements carried out in a large oscillatory flow tunnel and direct numerical simulation (DNS). Five different Reynolds numbers, , in the range 846–2057 have been investigated experimentally, where with the maximum oscillatory velocity in the irrotational region, the Stokes length and the fluid kinematic viscosity. DNS has been carried out for the lowest three equal to 846, 1155 and 1475. Both experimental and numerical results show that the flow statistics increase during accelerating phases of the flow and especially at times of transition to turbulent flow. Once turbulence is fully developed, the near-wall statistics remain almost constant until the late half-cycle, with values close to those reported for steady wall-bounded flows. The higher-order statistics reach large values within a normalized wall distance of approximately at phases corresponding to the onset of low-speed streak breaking, because of the intermittency of the velocity fluctuations at these times. In particular, the flatness of the streamwise velocity fluctuations reaches values of the order of ten, while the flatness of the wall-normal velocity fluctuations reaches values of several hundreds. Far from the wall, at locations where the vertical gradient of the streamwise velocity is zero, the skewness is approximately zero and the flatness is approximately equal to 3, representative of a normal distribution. At lower elevations the distribution of the fluctuations deviate substantially from a normal distribution, but are found to be well described by other standard theoretical probability distributions.

AB - Turbulence characteristics of an asymmetric oscillatory boundary layer flow are analysed through two-component laser-Doppler measurements carried out in a large oscillatory flow tunnel and direct numerical simulation (DNS). Five different Reynolds numbers, , in the range 846–2057 have been investigated experimentally, where with the maximum oscillatory velocity in the irrotational region, the Stokes length and the fluid kinematic viscosity. DNS has been carried out for the lowest three equal to 846, 1155 and 1475. Both experimental and numerical results show that the flow statistics increase during accelerating phases of the flow and especially at times of transition to turbulent flow. Once turbulence is fully developed, the near-wall statistics remain almost constant until the late half-cycle, with values close to those reported for steady wall-bounded flows. The higher-order statistics reach large values within a normalized wall distance of approximately at phases corresponding to the onset of low-speed streak breaking, because of the intermittency of the velocity fluctuations at these times. In particular, the flatness of the streamwise velocity fluctuations reaches values of the order of ten, while the flatness of the wall-normal velocity fluctuations reaches values of several hundreds. Far from the wall, at locations where the vertical gradient of the streamwise velocity is zero, the skewness is approximately zero and the flatness is approximately equal to 3, representative of a normal distribution. At lower elevations the distribution of the fluctuations deviate substantially from a normal distribution, but are found to be well described by other standard theoretical probability distributions.

KW - coastal engineering

KW - surface gravity waves

KW - turbulent boundary layers

U2 - 10.1017/jfm.2018.403

DO - 10.1017/jfm.2018.403

M3 - Article

VL - 849

SP - 192

EP - 230

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -