Titre/Title : Non-equilibrium turbulent axisymmetric wakes
Contact : Nicolas Mordant (équipe EDT)
Résumé/Abstract : Recently, flow regions with non-equilibrium high Reynolds number turbulence at odds with usual Richardson-Kolmogorov phenomenology have been discovered in a number of turbulent flows, in particular axisymmetric and self-preserving turbulent wakes of plates with irregular (fractal-like/multiscale) edges. These regions are characterised by streamwise scalings of the mean centreline velocity deficit and wake width which have only recently been documented. In this study, we perform a study of turbulent axisymmetric wakes generated by a set of bluff bodies (with different peripheries and thicknesses) in a wind tunnel using how-wire anemometry.
This work is divided in two parts. On the first part we study the presence of non-equilibrium turbulence in the turbulent wake of one axisymmetric plate. For that purpose, we revisit the classical theory of axisymmetric wakes. We show that the non-equilibrium scalings are not the preserve of irregular plates, but appear universal as they also hold for regular plates over a very substantial downstream distance.
On the second part of the seminar, we apply the revisited theory to the study of the interaction of two bluff bodies. Our results show that non-equilibrium scalings properly describe the interaction of the turbulent wakes of the two bluff bodies, predicting both at which distance the wakes meet on average and the velocity fluctuation intensity at that point. Moreover, the streamwise evolution of the turbulence dissipation rate, estimated between both plates seems to follow the non-equilibrium law.