The Thermal Structure of Turbulent Convection

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Abstract
An experimental study of the vertical distribution of instantaneous local vertical temperature gradient and local temperature in terms of their first three moments and spectral properties is reported. These experiments were performed in air (Pr = 0.71) over the range 1.0 × 106 < Ra < 1 × 107. An approximate measure of the heat flux yielded the dependence Nu ≈ 0.21 Ra0.26. The shape of the vertical profiles of each variable and its moments is invarient with Ra (except at the level of inverse symmetry located at the mid-level in the fluid) when the vertical scale Z* = Nu Z/D is used. Based on the statistical properties observed, three vertical layers may be defined: 1) a conduction layer in which at least ½ of the heat flux is by conduction 0 ≲ Z* ≲ 0.5; 2) a transition or “power law” layer in which the nondimensional temperature gradient (β) ≈ Z−2, and 3) an interior region in which β ap; 0.0 and σT ∝ Z−⅓. Spectral data in the frequency domain for both gradient and temperature show a much stronger... Abstract An experimental study of the vertical distribution of instantaneous local vertical temperature gradient and local temperature in terms of their first three moments and spectral properties is reported. These experiments were performed in air (Pr = 0.71) over the range 1.0 × 106 < Ra < 1 × 107. An approximate measure of the heat flux yielded the dependence Nu ≈ 0.21 Ra0.26. The shape of the vertical profiles of each variable and its moments is invarient with Ra (except at the level of inverse symmetry located at the mid-level in the fluid) when the vertical scale Z* = Nu Z/D is used. Based on the statistical properties observed, three vertical layers may be defined: 1) a conduction layer in which at least ½ of the heat flux is by conduction 0 ≲ Z* ≲ 0.5; 2) a transition or “power law” layer in which the nondimensional temperature gradient (β) ≈ Z−2, and 3) an interior region in which β ap; 0.0 and σT ∝ Z−⅓. Spectral data in the frequency domain for both gradient and temperature show a much stronger...

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