We report an experimental investigation of the longitudinal space–time cross-correlation function of the velocity field, , in a cylindrical turbulent Rayleigh–Bénard convection cell using the particle image velocimetry (PIV) technique. We show that while Taylor’s frozen-flow hypothesis does not hold in turbulent thermal convection, the recent elliptic model advanced for turbulent shear flows (He & Zhang, Phys. Rev. E, vol. 73, 055303) is valid for the present velocity field for all over the cell, i.e. the isocorrelation contours of the measured have an elliptical curve shape and hence can be related to via with and being two characteristic velocities. We further show that the fitted is proportional to the mean velocity of the flow, but the values of are larger than the theoretical predictions. Specifically, we focus on two representative regions in the cell: the region near the cell sidewall and the cell’s central region. It is found that and are approximately the same near the sidewall, while at the cell centre.