### Abstract

The three-dimensional turbulent field of a passive scalar has been mapped quantitatively by obtaining, effectively instantaneously, several closely spaced parallel two-dimensional images; the two-dimensional images themselves have been obtained by laser-induced fluorescence. Turbulent jets and wakes at moderate Reynolds numbers are used as examples. The working fluid is water. The spatial resolution of the measurements is about four Kolmogorov scales. The first contribution of this work concerns the three-dimensional nature of the boundary of the scalar-marked regions (the 'scalar interface'). It is concluded that interface regions detached from the main body are exceptional occurrences (if at all), and that in spite of the large structure, the randomness associated with small-scale convolutions of the interface are strong enough that any two intersections of it by parallel planes are essentially uncorrelated even if the separation distances are no more than a few Kolmogorov scales. The fractal dimension of the interface is determined directly by box-counting in three dimensions, and the value of 2.35±0.04 is shown to be in good agreement with that previously inferred from two-dimensional sections. This justifies the use of the method of intersections. The second contribution involves the joint statistics of the scalar field and the quantity X^{*} (or its components), X^{*} being the appropriate approximation to the scalar 'dissipation' field in the inertial-convective range of scales. The third aspect relates to the multifractal scaling properties of the spatial intermittency of X^{*}; since all three components of X^{*} have been obtained effectively simultaneously, inferences concerning the scaling properties of the individual components and their sum have been possible.

Original language | English (US) |
---|---|

Pages (from-to) | 1-34 |

Number of pages | 34 |

Journal | Journal of Fluid Mechanics |

Volume | 216 |

State | Published - Jul 1990 |

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### ASJC Scopus subject areas

- Computational Mechanics
- Mechanics of Materials
- Physics and Astronomy(all)
- Condensed Matter Physics

### Cite this

**Quantitative three-dimensional imaging and the structure of passive scalar fields in fully turbulent flows.** / Prasad, Rahul R.; Sreenivasan, K. R.

Research output: Contribution to journal › Article

*Journal of Fluid Mechanics*, vol. 216, pp. 1-34.

}

TY - JOUR

T1 - Quantitative three-dimensional imaging and the structure of passive scalar fields in fully turbulent flows

AU - Prasad, Rahul R.

AU - Sreenivasan, K. R.

PY - 1990/7

Y1 - 1990/7

N2 - The three-dimensional turbulent field of a passive scalar has been mapped quantitatively by obtaining, effectively instantaneously, several closely spaced parallel two-dimensional images; the two-dimensional images themselves have been obtained by laser-induced fluorescence. Turbulent jets and wakes at moderate Reynolds numbers are used as examples. The working fluid is water. The spatial resolution of the measurements is about four Kolmogorov scales. The first contribution of this work concerns the three-dimensional nature of the boundary of the scalar-marked regions (the 'scalar interface'). It is concluded that interface regions detached from the main body are exceptional occurrences (if at all), and that in spite of the large structure, the randomness associated with small-scale convolutions of the interface are strong enough that any two intersections of it by parallel planes are essentially uncorrelated even if the separation distances are no more than a few Kolmogorov scales. The fractal dimension of the interface is determined directly by box-counting in three dimensions, and the value of 2.35±0.04 is shown to be in good agreement with that previously inferred from two-dimensional sections. This justifies the use of the method of intersections. The second contribution involves the joint statistics of the scalar field and the quantity X* (or its components), X* being the appropriate approximation to the scalar 'dissipation' field in the inertial-convective range of scales. The third aspect relates to the multifractal scaling properties of the spatial intermittency of X*; since all three components of X* have been obtained effectively simultaneously, inferences concerning the scaling properties of the individual components and their sum have been possible.

AB - The three-dimensional turbulent field of a passive scalar has been mapped quantitatively by obtaining, effectively instantaneously, several closely spaced parallel two-dimensional images; the two-dimensional images themselves have been obtained by laser-induced fluorescence. Turbulent jets and wakes at moderate Reynolds numbers are used as examples. The working fluid is water. The spatial resolution of the measurements is about four Kolmogorov scales. The first contribution of this work concerns the three-dimensional nature of the boundary of the scalar-marked regions (the 'scalar interface'). It is concluded that interface regions detached from the main body are exceptional occurrences (if at all), and that in spite of the large structure, the randomness associated with small-scale convolutions of the interface are strong enough that any two intersections of it by parallel planes are essentially uncorrelated even if the separation distances are no more than a few Kolmogorov scales. The fractal dimension of the interface is determined directly by box-counting in three dimensions, and the value of 2.35±0.04 is shown to be in good agreement with that previously inferred from two-dimensional sections. This justifies the use of the method of intersections. The second contribution involves the joint statistics of the scalar field and the quantity X* (or its components), X* being the appropriate approximation to the scalar 'dissipation' field in the inertial-convective range of scales. The third aspect relates to the multifractal scaling properties of the spatial intermittency of X*; since all three components of X* have been obtained effectively simultaneously, inferences concerning the scaling properties of the individual components and their sum have been possible.

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M3 - Article

VL - 216

SP - 1

EP - 34

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -