Scaling of the velocity power spectra in turbulent thermal convection.

We report measurements of the local velocity in a convection cell filled with water. In the buoyancy subrange (the scales between the Bolgiano scale f(B) and the integral scale f(o)), two scaling regions of the velocity frequency power spectra, separated by the peak frequency f(p) of the dissipation spectra, are found. For f(p)<f<f(B), we observe a power law with the Bolgiano-Obukhov scaling exponent -11/5. For f(o)<f<f(p), an unexpected scaling with an exponent -1.35 is observed. We also found that the velocity power spectra are universal functions with respect to the characteristic scales f(p). and f(B).