Structures of the Intermittent Region of a Turbulent Thermal Boundary Layer

Turbulent structures in the outer intermittent region of a thermal boundary layer were experimentally investigated. To distinguish accurately two unique thermal states related to the inside or the outside of the thermal boundary layer, we have modified a previous method by simultaneous use of the instantaneous temperature and the time derivative of temperature fluctuation. The theoretical probability density function (p.d.f.) of an intermittent turbulent quantity, e.g., t and ∂t/∂x, has been obtained from the intermittency-factor-weighted sum of two p.d.f.s inside and outside the thermal boundary layer. The distributions of the p.d.f.s and statistical quantities remain similar in the thermal entrance region. The conditionally-sampled weighted p.d.f. of the wall-normal turbulent heat flux and the wavelet transform of velocity and temperature fluctuations clearly show that ejection-type fluid motion dominates the heat transport or thermal-field entrainment in the outer region of a thermal boundary layer.