Turbulent convection over a heated horizontal surface

Detailed measurements have been made of the temperature field in natural convection above a heated horizontal surface in air, with and without a cold upper boudary. The object was to provide experimental material for the testing of existing theories of convection and the development of new ones. Using a variety of experimental techniques, it was possible to measure the heat transfer, the mean temperature profiles, mean squares of the temperature fluctuations and the autocorrelation functions of the temperature fluctuations. These results are considered in relation with the ‘similarity’ theory of Priestley and the ‘neutral stability’ theory of Malkus. Both these theories lead to the conclusion that, for convection between parallel planes at high Rayleigh numbers, nearly the whole of the mean temperature variation occurs in comparatively thin surface layers whose mutual interaction is small. The present experiments confirm this in some detail, but the exact form of the variation of mean temperature cannot be completely reconciled with either of the theories.