The effect of turbulent diffusion on transit-time determination by cross correlation of temperature fluctuations

At high Reynolds numbers heat transport by turbulent diffusion can have a significant effect on the correlation of temperature fluctuations in a flowing fluid. In such a case the conventional methods for transit-time estimation by noise correlation, which are based on the (,(,F or on the phase of the (,PSD, give too low values. This paper provides a theoretical basis for the (ʹCF and the CPSD of temperature fluctuations in the case of turbulent diffusion and drift. Theoretical findings are supported by experimental results. It is shown that more sophisticated methods for transit-time determination give accurate results in the case with and without diffusion. The differences found in estimated transit times are in the range of 5-8 %.