### Abstract

A quasi-isotropic, quasi-homogeneous turbulence generated by an oscillating-grid, spatially decays according to power law of u ∝Z-n_{u}, where u is the root mean square (rms) horizontal velocity, Z is the vertical distance from the grid and n_{u} = 1. However, the findings of Nokes and Yi indicate that as the stroke of oscillation increases, the power law n_{u} ≠ 1 and does not follow the established decay law equation of Hopfinger. This paper investigates the characteristics of the turbulence that are generated using larger strokes S/M 1.6 and 2 and compares with that obtained using a S/M = 0.8, which is the stroke used when the equation was developed. Measurements of the grid-generated turbulence in a water tank were taken using particle image velocimetry (PIV). The results showed that the homogeneity occurred at distance beyond 2.5 mesh spacings away from the grid midplane, independent of the stroke and the frequency of oscillation. Within this region, the turbulent kinetic energy distribution was quasi-homogeneous, and the secondary mean flow is negligible. The statistical characteristics of the measured turbulence confirmed that although n_{u} decreases as stroke increases, the grid-turbulence generated at S/M 1.6 and 2 obeys the universal decay law.

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

Pages (from-to) | 473-481 |

Number of pages | 9 |

Journal | Journal of Hydrodynamics |

Volume | 28 |

Issue number | 3 |

DOIs | |

Publication status | Published - 1 Jun 2016 |

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### Keywords

- decay power law
- large strokes
- oscillating-grid turbulence

### ASJC Scopus subject areas

- Condensed Matter Physics
- Mechanical Engineering
- Mechanics of Materials
- Modelling and Simulation

### Cite this

**Oscillating-grid turbulence at large strokes : Revisiting the equation of Hopfinger and Toly.** / Wan Mohtar, Wan Hanna Melini.

Research output: Contribution to journal › Article

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TY - JOUR

T1 - Oscillating-grid turbulence at large strokes

T2 - Revisiting the equation of Hopfinger and Toly

AU - Wan Mohtar, Wan Hanna Melini

PY - 2016/6/1

Y1 - 2016/6/1

N2 - A quasi-isotropic, quasi-homogeneous turbulence generated by an oscillating-grid, spatially decays according to power law of u ∝Z-nu, where u is the root mean square (rms) horizontal velocity, Z is the vertical distance from the grid and nu = 1. However, the findings of Nokes and Yi indicate that as the stroke of oscillation increases, the power law nu ≠ 1 and does not follow the established decay law equation of Hopfinger. This paper investigates the characteristics of the turbulence that are generated using larger strokes S/M 1.6 and 2 and compares with that obtained using a S/M = 0.8, which is the stroke used when the equation was developed. Measurements of the grid-generated turbulence in a water tank were taken using particle image velocimetry (PIV). The results showed that the homogeneity occurred at distance beyond 2.5 mesh spacings away from the grid midplane, independent of the stroke and the frequency of oscillation. Within this region, the turbulent kinetic energy distribution was quasi-homogeneous, and the secondary mean flow is negligible. The statistical characteristics of the measured turbulence confirmed that although nu decreases as stroke increases, the grid-turbulence generated at S/M 1.6 and 2 obeys the universal decay law.

AB - A quasi-isotropic, quasi-homogeneous turbulence generated by an oscillating-grid, spatially decays according to power law of u ∝Z-nu, where u is the root mean square (rms) horizontal velocity, Z is the vertical distance from the grid and nu = 1. However, the findings of Nokes and Yi indicate that as the stroke of oscillation increases, the power law nu ≠ 1 and does not follow the established decay law equation of Hopfinger. This paper investigates the characteristics of the turbulence that are generated using larger strokes S/M 1.6 and 2 and compares with that obtained using a S/M = 0.8, which is the stroke used when the equation was developed. Measurements of the grid-generated turbulence in a water tank were taken using particle image velocimetry (PIV). The results showed that the homogeneity occurred at distance beyond 2.5 mesh spacings away from the grid midplane, independent of the stroke and the frequency of oscillation. Within this region, the turbulent kinetic energy distribution was quasi-homogeneous, and the secondary mean flow is negligible. The statistical characteristics of the measured turbulence confirmed that although nu decreases as stroke increases, the grid-turbulence generated at S/M 1.6 and 2 obeys the universal decay law.

KW - decay power law

KW - large strokes

KW - oscillating-grid turbulence

UR - http://www.scopus.com/inward/record.url?scp=84976523314&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84976523314&partnerID=8YFLogxK

U2 - 10.1016/S1001-6058(16)60651-0

DO - 10.1016/S1001-6058(16)60651-0

M3 - Article

AN - SCOPUS:84976523314

VL - 28

SP - 473

EP - 481

JO - Journal of Hydrodynamics

JF - Journal of Hydrodynamics

SN - 1001-6058

IS - 3

ER -