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Direct Numerical Simulations of turbulent convection in a large aspect-ratiobox are carried out in the range of Rayleigh number $7 \times 10^4 \le Ra \le 2\times 10^6$ at Prandtl number Pr=0.71. A strong correlation between thevertical velocity and temperature is observed in the turbulent regime at almostall the length scales. Frequency spectra of all the velocities and temperatureshow a $-5/3$ law for a wide band of frequencies. The variances of horizontalvelocities at different points in the flow yield a single power-law.Probability density functions of velocities and temperature are close toGaussian only at higher Rayleigh numbers. The mean and variance of temperatureclearly show boundary layers, surface layers and a near-homogeneous bulkregion. The boundary layer thickness decreases and bulk-homogeneity is enhancedon increasing the Rayleigh numbers. The wave number spectra of the turbulentkinetic energy exhibit Kolmogorov like ($E(k)\sim k^{-5/3}$) andBolginao-Obukhov like ($E(k)\sim k^{-11/5}$) behaviour respectively in thecentral and near-wall regions of the container. An approximate balance betweenthe production due to buoyancy and the dissipation is found in the turbulentkinetic energy budget. Taylor's approximate equation of the production due toturbulent stretching and the dissipation of turbulent enstrophy is modified bythe inclusion of buoyancy production in the enstrophy budget. The presentresults support the previously proposed $2/7$ power-law dependence of theaverage Nusselt number on the Rayleigh number by yielding an exponent of 0.272,but do not necessarily support the proposed classification of "soft" and "hard"turbulence on the basis of this exponent.

Scalings of heat transport and energy spectra of turbulent Rayleigh-Benard convection in a large-aspect-ratio box