## Abstract

All three components of the dissipation rate of the fluctuating temperature θ are measured simultaneously in the inner region of a fully developed turbulent boundary layer at a moderate Reynolds number. Measurements are made with a probe of four cold wires consisting of two closely spaced parallel vertical wires mounted a small distance upstream of two closely spaced parallel horizontal wires. In the inner region of the layer, local isotropy is not closely approximated [(∂θ/θz)
^{2}
_{>}(∂ θ/∂y)
^{2}
_{>}(∂θ/∂x)
^{2}]. The spectral density of the sum χ[ = (∂θ/∂x)
^{2} + (∂θ/∂y)
^{2} +(∂θ/∂z)
^{2}] is similar in shape to that of (∂θ/∂y)
^{2} or (∂θ/∂z)
^{2} , but not as rich in high frequency content as that of (∂θ/∂x)
^{2}. The probability density of χ has a lower skewness and flatness factor and is more closely log-normal than those of the individual components. This is true regardless of whether χ and its components are unaveraged or locally averaged over a linear dimension r. When averaging is applied, departures from log-normality are diminished but do not disappear entirely. The variance σ
^{2} of the logarithm of the locally averaged χ is proportional to 1n r over a wide range of r (r
_{max}/r
_{min}≃30), in contrast to the individual components where this ratio may be as small as 2. The value of the Kolmogoroff constant μ
_{θ}determined from the slope of σ
^{2} vs 1n r is about 0.35. This is consistent with the slope of the spectral density of χ and is also in agreement with previous best estimates of μ
_{θ}(and μ) obtained at high Reynolds numbers.

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

Pages (from-to) | 1238-1249 |

Number of pages | 12 |

Journal | Physics of Fluids |

Volume | 20 |

Issue number | 8 |

DOIs | |

State | Published - 1977 |

## ASJC Scopus subject areas

- Condensed Matter Physics
- General Physics and Astronomy
- Mechanics of Materials
- Computational Mechanics
- Fluid Flow and Transfer Processes