Separation control at hydrofoils using Lorentz forces

Lorentz forces originating from surface-mounted actuators of permanent magnets and electrodes in weakly conducting fluids like seawater can be used to control flow separation at hydrofoils. The numerical results presented here are based on direct numerical simulation in the laminar flow regime, limited to Reynolds numbers of O(500). Control by steady forcing at the suction side and by oscillatory forcing near the leading edge of the foil is investigated in the post-stall regime.By applying a strong enough steady control, separation can be completely suppressed. Oscillatory forcing always has to compete with the natural shedding process, lock-in behavior may occur. Lift-optimum control for strong amplitudes is found in a frequency band around the natural shedding frequency. In terms of the momentum coefficient describing the control effort, appropriate excitation frequencies in relation to the natural vortex shedding frequency allow for a more effective lift control than steady forcing.