Direct numerical simulation of turbulent mixing of a passive scalar in pipe flow

Turbulent mixing of a passive scalar in fully developed turbulent pipe flow has been investigated by means of a Direct Numerical Simulation (DNS). The scalar is released from a point source located on the centreline of the pi pe. The domain size of the concentration field has been chosen large enough to capture the different stages of turbulent mixing. Results are presented for mean concentration profiles, turbulent fluxes, concentration fluctuati ons, probability density functions and higher-order moments. To validate th e numerical simulations the results are compared with experimental data on mixing in grid-turbulence that have been reported in the literature. The ag reement between the experimental measurements and the computations is satis factory. We have also considered the Probability Density Function (PDF); Fo r small diffusion times and positions not on the plume centreline, our resu lts lead to a PDF of an exponential form with a large peak at zero concentr ation. When the diffusion time increases, the PDF shifts from a exponential to a more Gaussian form. (C) Elsevier, Paris.