FULLY-DEVELOPED TURBULENT PIPE-FLOW - A COMPARISON BETWEEN DIRECT NUMERICAL-SIMULATION AND EXPERIMENT

Direct numerical simulations (DNS) and experiments are carried out to study fully developed turbulent pipe flow at Reynolds number Re(c) alm ost-equal-to 7000 based on centreline velocity and pipe diameter. The agreement between numerical and experimental results is excellent for the lower-order statistics (mean flow and turbulence intensities) and reasonably good for the higher-order statistics (skewness and flatness factors). To investigate the differences between fully developed turb ulent flow in an axisymmetric pipe and a plane channel geometry, the p resent DNS results are compared to those obtained from a channel flow simulation. Beside the mean flow properties and turbulence statistics up to fourth order, the energy budgets of the Reynolds-stress componen ts are computed and compared. The present results show that the mean v elocity profile in the pipe fails to conform to the accepted law of th e wall, in contrast to the channel flow. This confirms earlier observa tions reported in the literature. The statistics on fluctuating veloci ties, including the energy budgets of the Reynolds stresses, appear to be less affected by the axisymmetric pipe geometry. Only the skewness factor of the normal-to-the-wall velocity fluctuations differs in the pipe flow compared to the channel flow. The energy budgets illustrate that the normal-to-the-wall velocity fluctuations in the pipe are alt ered owing to a different 'impingement' or 'splatting' mechanism close to the curved wall.