Electromagnetic flow control of a bifurcated jet in a rectangular cavity

• Self-sustained oscillations in a thin cavity with submerged nozzle were observed.
• The self-sustained oscillations were influenced by applying a Lorentz force.
• A POD was applied to study the distribution of kinetic energy.
• The large scale fluctuations can be enhanced or suppressed by the Lorentz force.
• The turbulence fluctuations are not affected by the Lorentz force.

The effect of Lorentz forcing on self-sustained oscillations of turbulent jets (Re = 3.1 × 103) issuing from a submerged bifurcated nozzle into a thin rectangular liquid filled cavity was investigated using free surface visualization and time-resolved particle image velocimetry (PIV). A Lorentz force is produced by applying an electrical current across the width of the cavity in conjunction with a magnetic field. As a working fluid a saline solution is used. The Lorentz force can be directed downward (FL<0)(FL<0) or upward (FL>0)(FL>0), to weaken or strengthen the self-sustained jet oscillations. The low frequency self-sustained jet oscillations induce a free surface oscillation. When FL<0FL<0 the amplitude of the free surface oscillation is reduced by a factor of 6 and when FL>0FL>0 the free surface oscillation amplitude is enhanced by a factor of 1.5.A large fraction of the turbulence kinetic energy k=12ui′ui′‾ is due to the self-sustained jet oscillations. A triple decomposition of the instantaneous velocity was used to divide the turbulence kinetic energy into a part originating from the self-sustained jet oscillation kosckosc and a part originating from the higher frequency turbulent fluctuations kturbkturb. It follows that the Lorentz force does not influence kturbkturb in the measurement plane, but the distribution of kosckosc can be altered significantly. The amount of energy contained in the self-sustained oscillation is three times lower when FL<0FL<0 compared to the situation with FL>0FL>0.