Relative dispersion and Richardsonís constant
Seminar Room 1, Newton Institute
This talk will describe some very recent analysis of Direct Numerical Simulation results for turbulent relative dispersion over a wide range of Reynolds numbers. We will start with some background discussion of the nature and significance of relative dispersion and of the role of Kolmogorovís similarity theory, leading to the introduction of Richardsonís constant as a fundamental parameter of relative dispersion. Although it is of great fundamental and practical significance, Richardsonís constant has not been well-quantified, and model estimates for it range from 0.01 to 4.
We will describe first a traditional analysis of relative dispersion data, concluding that this approach does not yield a good estimate for Richardsonís constant even at the highest Reynolds number currently available. We then use a modified version of a new approach developed by Ott & Mann (JFM, 422, 207, (2000)) to show that a well-defined Richardson scaling range exists in our data. We estimate Richardsonís constant over a range of Reynolds numbers showing that it decreases weakly with Reynolds number to an asymptotic value at large Reynolds number of 0.55 - 0.57.