THE CYLINDER WAKE IN A MAGNETIC-FIELD ALIGNED WITH THE VELOCITY

We investigate experimentally the up- and downstream flow around an insulating cylinder in a conducting fluid subjected to an aligned magnetic field for low values of the magnetic Reynolds number R(m). For high values of the Alfven number alpha = B0/U0(rhomu0)1/2 the upstream flow is characterized by magnetic and kinematic wakes. In this configuration we have measured, for the first time, the local values of the induced magnetic field. The results were analysed in a confined situation and show that the Oseen number k = 1/2R(m)(1 - alpha2) is the main parameter that characterizes the perturbation. In the downstream flow the two fields of perturbations (magnetic and kinetic) are characterized by von Karman eddies. Our experiments were focused on the evolution of these eddies and show in particular that the critical Reynolds number increases strongly with the intensity of the magnetic field.