Measurements on the Development of Thermal Turbulence in Air between Horizontal Plates

The transition from steady to turbulent thermal convection in air between horizontal plates is inferred from temperature measurements. Spatial and temporal records of air temperature for Rayleigh numbers ranging from 5000 to 1.5 × 106 are presented along with spatial temperature spectra. A region of transition from nearly steady organized convection to irregular turbulent convection was found to exist between Rayleigh numbers of about 6300 and 10 000, although a dominant wavelength continues to exist at much larger Rayleigh numbers. Spatial scales of temperature are noted to extend to both larger and smaller wavelengths with increase in Rayleigh number.