### Abstract

The effects of explicit flow modulation on the dispersion of a passive scalar field are studied. Broadband forcing is applied to homogeneous isotropic turbulence to modulate the energy cascading and alter the kinetic energy spectrum. Consequently, a manipulation of turbulent flow can be achieved over an extended range of scales beyond the directly forced ones. This modifies transport processes and influences the physical-space turbulent mixing of a passive scalar field. We investigate by direct numerical simulation the stirring-efficiency associated with turbulence modified by forcing. This is quantified by monitoring the surface-area and wrinkling of a level-set of the passive scalar field. We consider different forcing to manipulate the quality and rate of mixing. The instantaneous mixing efficiency measured in terms of surface-area or wrinkling is found to increase when additional energy is introduced at the smaller scales. The increased intensity of small scales significantly influences the small-scale mixing characteristics depicted by wrinkling, while the forcing of large scales primarily affects the surface-area. Evaluation of geometrical statistics in broadband-forced turbulence indicates that the self-amplification process of vorticity and strain is diminished. This leads generally to smaller extremal values of the velocity gradients but higher average values as a result of the competition between the natural cascading processes and the explicit small-scales forcing.

Original language | Undefined |
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Title of host publication | IUTAM symposium on computational physics and new perspectives in turbulence |

Place of Publication | Netherlands |

Publisher | Springer |

Pages | 131-136 |

Number of pages | 6 |

ISBN (Print) | 978-1-4020-6472-2 |

DOIs | |

Publication status | Published - 2008 |

### Publication series

Name | IUTAM Bookseries |
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Publisher | Springer Verlag |

Number | 11 |

Volume | 4 |

ISSN (Print) | 1875-3507 |

ISSN (Electronic) | 1875-3493 |

### Keywords

- EWI-14732
- IR-65255
- METIS-238752

## Cite this

Kuczaj, A. K., & Geurts, B. J. (2008). Control over multiscale mixing in broadband-forced turbulence. In

*IUTAM symposium on computational physics and new perspectives in turbulence*(pp. 131-136). [10.1007/978-1-4020-6472-2_20] (IUTAM Bookseries; Vol. 4, No. 11). Netherlands: Springer. https://doi.org/10.1007/978-1-4020-6472-2_20