Abstract
With the use of the ultrasonic velocimetry, we measured the velocity profiles in thermal turbulence in mercury. The measurement, which is different from the traditional measurement of time series of the local velocity, has brought about some intriguing results. We observed the inversion of the flow direction near the boundary plate, which seems the appearance of the velocity boundary layer.We also elucidated the nature of the fluctuation in thermal turbulence through the principal component analysis. The macroscopic flow structure and its vertical movement were observed. In addition, the energy spectrum and the velocity structure functions were calculated without employing Taylor's frozen-flow hypothesis for the first time in thermal turbulence, which appeared to be consistent with the Bolgiano-Obukhov theory.
