## Abstract

This note provides some explanation of the fact that, contrary to the requirements of local isotropy, the skewness S of the streamwise temperature derivative ∂θ/∂x_{1} has been observed to be a non-zero constant of magnitude of about unity in high-Reynolds-number and high-Péclet-number turbulent shear flows. Measurements in slightly heated homogeneous shear flows and in unsheared grid turbulence suggest that S is non-zero only when the mean shear dU_{1}/dx_{2} and the mean temperature gradient dT/dx_{2} are both non-zero. The sign of S is given by –sgn (dU_{1}/dx_{2}).sgn (dT/dx_{2}). For fixed dU_{1}/dx_{2}, S is of the form tanh (αdT/dx_{2}), α being a constant, while for fixed dT/dx_{2}, it is of the form S/S* = 1 − β_{1} exp (− β_{2}τ), where S* is a characteristic value of S, β_{1} and β_{2} are positive constants, and τ can be interpreted as a ‘total strain’. The derivative skewness data in other (inhomogeneous) shear flows are also compatible with the latter relation. Predictions from a simplified transport equation for [formula omitted], derived in the light of the present experimental observations, are in reasonable agreement with the measured values of S. A possible physical mechanism maintaining S is discussed.

Original language | English (US) |
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Pages (from-to) | 783-795 |

Number of pages | 13 |

Journal | Journal of Fluid Mechanics |

Volume | 101 |

Issue number | 4 |

DOIs | |

State | Published - Dec 1980 |

## ASJC Scopus subject areas

- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering