Electro-magnetic control of hydrofoil wake

An actuator, consisting of a specific array ofalternating stripwise electrodes and permanent magnets, will generate awall-parallel Lorentz force as submerged in a weakly conducting fluid, whichinfluences the flow in the boundary layer. The experiments have beenconducted in a rotating annular tank filled with a copper sulphate(CuSO_4)electrolyte, to investigate the flow around a hydrofoil and itselectromagnetic control. To reveal the transient behavior of controlled flowfrom the initial to the final steady state, the flow fields are visualizedby potassium permanganate (KMnO_4) used as a marker and record by a camera.To verify the influence of flow control on the lift and the drag of ahydrofoil, force measurements have been carried out by strain gages attachedto a fixed beam to which the hydrofoil is suspended.It has been shown from the experimental results that, for the absence of theLorentz force, there exist two kinds of vortex, i.e. shedding on the leadingedge and the trailing edge respectively, which affect each other and finallyleave the leeward surface of the hydrofoil periodically to form a wake. Theinfluences of the Lorentz force on the flow around the hydrofoil are justsomething like the variations of the attack angle. The Lorentz force instreamwise direction can suppress the flow separation and the wake, ashappened in the cases with a small or zero attack angles. In contradiction,for the reversed Lorentz force, the vortex street on the leeward surface ofhydrofoil is introduced, as happened in the cases with a big attack angle.