### Abstract

To study the mixing of a passive scalar in nearly isotropic turbulence, experiments have been made in isotropically mixed thermal fields with thermal mesh size M_{θ} (a) equal to the momentum mesh size M, (b) larger than M (obtained by heating only alternate rods of the turbulence generating grid), and (c) smaller than M. This last condition was achieved by inserting a fine heating screen with M_{θ} <M, at locations downstream of the turbulence grid. The heating screen was designed to produce negligible statistical change in the velocity field a short distance downstream. In all the heated grid experiments, for a given initial configuration of the thermal field, the intensity of temperature fluctuations θ normalized by the mean temperature rise ΔT, and the decay rate of [formula omitted] were both independent of the temperature of the grid. The principal effect of having M_{θ} > M was an increase in the relative intensity of temperature fluctuations compared with the M_{θ} = M case, and a marginal increase in their decay rate; contrary to expectation, the ratio R of temperature to velocity integral scales in the region of approximate homogeneity did not differ from that corresponding to M_{θ} = M. In heated screen experiments, the relative decay rate was independent of M_{θ}/M and ΔT. For the three locations of the heating screen used in these experiments, the decay rate was also independent of the relative distance x_{s} of the heating screen from the turbulence generating grid; however, larger x_{s} was associated with larger relative intensity of fluctuations. To a first approximation, the ratio R approached unity according to the empirical relation R = 1 − A exp [− αx_{θ}/(UT_{0})], where x_{θ} is downstream distance measured from the heating screen, and T_{0} is a characteristic turbulence decay time scale at x_{0} = 0. It was also verified that the skewness of the streamwise temperature derivative is approximately zero sufficiently downstream of the heating screen. Where the present study overlaps with previous measurements, an extensive comparison reveals several points of agreement as well as departure.

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

Pages (from-to) | 597-621 |

Number of pages | 25 |

Journal | Journal of Fluid Mechanics |

Volume | 100 |

Issue number | 3 |

DOIs | |

State | Published - 1980 |

### Fingerprint

### ASJC Scopus subject areas

- Mechanical Engineering
- Mechanics of Materials
- Condensed Matter Physics

### Cite this

*Journal of Fluid Mechanics*,

*100*(3), 597-621. https://doi.org/10.1017/S0022112080001309

**Temperature fluctuations and scales in grid-generated turbulence.** / Sreenivasan, K. R.; Tavoularis, S.; Henry, R.; Corrsin, S.

Research output: Contribution to journal › Article

*Journal of Fluid Mechanics*, vol. 100, no. 3, pp. 597-621. https://doi.org/10.1017/S0022112080001309

}

TY - JOUR

T1 - Temperature fluctuations and scales in grid-generated turbulence

AU - Sreenivasan, K. R.

AU - Tavoularis, S.

AU - Henry, R.

AU - Corrsin, S.

PY - 1980

Y1 - 1980

N2 - To study the mixing of a passive scalar in nearly isotropic turbulence, experiments have been made in isotropically mixed thermal fields with thermal mesh size Mθ (a) equal to the momentum mesh size M, (b) larger than M (obtained by heating only alternate rods of the turbulence generating grid), and (c) smaller than M. This last condition was achieved by inserting a fine heating screen with Mθ <M, at locations downstream of the turbulence grid. The heating screen was designed to produce negligible statistical change in the velocity field a short distance downstream. In all the heated grid experiments, for a given initial configuration of the thermal field, the intensity of temperature fluctuations θ normalized by the mean temperature rise ΔT, and the decay rate of [formula omitted] were both independent of the temperature of the grid. The principal effect of having Mθ > M was an increase in the relative intensity of temperature fluctuations compared with the Mθ = M case, and a marginal increase in their decay rate; contrary to expectation, the ratio R of temperature to velocity integral scales in the region of approximate homogeneity did not differ from that corresponding to Mθ = M. In heated screen experiments, the relative decay rate was independent of Mθ/M and ΔT. For the three locations of the heating screen used in these experiments, the decay rate was also independent of the relative distance xs of the heating screen from the turbulence generating grid; however, larger xs was associated with larger relative intensity of fluctuations. To a first approximation, the ratio R approached unity according to the empirical relation R = 1 − A exp [− αxθ/(UT0)], where xθ is downstream distance measured from the heating screen, and T0 is a characteristic turbulence decay time scale at x0 = 0. It was also verified that the skewness of the streamwise temperature derivative is approximately zero sufficiently downstream of the heating screen. Where the present study overlaps with previous measurements, an extensive comparison reveals several points of agreement as well as departure.

AB - To study the mixing of a passive scalar in nearly isotropic turbulence, experiments have been made in isotropically mixed thermal fields with thermal mesh size Mθ (a) equal to the momentum mesh size M, (b) larger than M (obtained by heating only alternate rods of the turbulence generating grid), and (c) smaller than M. This last condition was achieved by inserting a fine heating screen with Mθ <M, at locations downstream of the turbulence grid. The heating screen was designed to produce negligible statistical change in the velocity field a short distance downstream. In all the heated grid experiments, for a given initial configuration of the thermal field, the intensity of temperature fluctuations θ normalized by the mean temperature rise ΔT, and the decay rate of [formula omitted] were both independent of the temperature of the grid. The principal effect of having Mθ > M was an increase in the relative intensity of temperature fluctuations compared with the Mθ = M case, and a marginal increase in their decay rate; contrary to expectation, the ratio R of temperature to velocity integral scales in the region of approximate homogeneity did not differ from that corresponding to Mθ = M. In heated screen experiments, the relative decay rate was independent of Mθ/M and ΔT. For the three locations of the heating screen used in these experiments, the decay rate was also independent of the relative distance xs of the heating screen from the turbulence generating grid; however, larger xs was associated with larger relative intensity of fluctuations. To a first approximation, the ratio R approached unity according to the empirical relation R = 1 − A exp [− αxθ/(UT0)], where xθ is downstream distance measured from the heating screen, and T0 is a characteristic turbulence decay time scale at x0 = 0. It was also verified that the skewness of the streamwise temperature derivative is approximately zero sufficiently downstream of the heating screen. Where the present study overlaps with previous measurements, an extensive comparison reveals several points of agreement as well as departure.

UR - http://www.scopus.com/inward/record.url?scp=77950919622&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77950919622&partnerID=8YFLogxK

U2 - 10.1017/S0022112080001309

DO - 10.1017/S0022112080001309

M3 - Article

AN - SCOPUS:77950919622

VL - 100

SP - 597

EP - 621

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

IS - 3

ER -