Small-scale turbulent fluctuations beyond Taylor's frozen flow hypothesis*

The space-time cross-correlation function C(r,t) of local temperature fluctuations in turbulent Rayleigh-Benard convection is obtained from simultaneous two-point time series measurements. The obtained C(r,t) is found to have the scaling form C(r,t) = C(R,0) with R$^2$ = [(r-Ut)$^2$ +(Vt)$^2$], where U and V are two characteristic velocities associated with the mean and rms velocities of the flow. The experiment verifies the theory and demonstrates its applications to a class of turbulent flows in which the requirement of Taylor's frozen flow hypothesis is not met.