External lightning protection system for wind turbine blades : preliminary aerodynamic results

In general, there are three components making up a lightning protection system for wind turbines. These are the receptors, the down conductor and the grounding grid. Receptors and down conductors are usually found in the more recent wind turbine blades and where the down conductors are normally installed on the internal side of the blade. Consequently, the blades are vulnerable to damage and burn resulting from lightning strikes. The authors believe that a system with an external down conductor is likely to reduce the risk of damage when compared to the system having an internal down conductor. One could envisage an external down conductor would look similar to the one installed on a building or an aircraft. However, external down conductors may compromise the aerodynamic performance of the turbine blades. This paper reports the effect of external down conductors on the pressure coefficient distribution around the turbine blade. The blade profile (aerofoil) used is according to NACA 4418. Numerical simulations, using computational fluid dynamics (CFD), were conducted on an aerofoil without and with external down conductors of 1mm thickness. The k-ɛ turbulence model that is incorporated in COMSOL Multiphysics (CFD Module) was used for the simulation and the wind speed and angle of attack used was 5 m/s and 5˚ respectively. The preliminary results show that the degradation on aerodynamic properties may not be too significant and these indicate that external down conductor arrangement could be considered