-
Electrostatic Discharge
Simulation of electrostatic discharge during in-flight refuelling
We have substantial capability and experience in the modelling of lightning strike to aircraft using an in-house finite-difference time-domain solver. Both direct and indirect phenomena (including electromagnetic pulse) can be modelled such as the flow of currents through a sheet of composite material such as a wing panel or tail fin and the ingress of fields inside the aicraft with subsequent coupling to avionics and wiring looms.
The ATC has also successfully demonstrated the simulation of electrostatic discharge during in-flight refuelling. This scenario typically occurs when a military aircraft attaches to the trailing fuel pipe from a much larger tanker aircraft. The subsequent discharge due to static charge build up generates large surface currents flowing on the airframe which has been computed successfully by ATC scientists.
The finite-difference time-domain (FDTD) technique is a well established numerical method of solving Maxwell's equations for time-varying phenomena. The ATC has developed the technique further by incorporating a 'reduced light velocity' capability for handling diffusion analysis where the conduction currents dominate the displacement currents. This has been deployed successfully in the solution of current flow through resistive carbon fibre composite sheets in the form of wing panels and also for the modelling of magnetic diffusion through metallic enclosures. Another important development has been the conformal correction for curved metallic surfaces which permits the much more accurate representation of curved metallic interfaces than the standard FDTD scheme which uses staircasing. This technique has been well validated on a wide range of objects including almond and ogive bodies and complex structures such as engine ducts with associated compressor assemblies. The results of the code agree well with other solution techniques such as method of moments and also with measurement data.
What is believed to be a novel application of the FDTD technique initiated by BAE SYSTEMS consists of the simulation of inflight refuelling. During flight, aircraft become electrically charged due to frictional mechanisms with the subsequent development of a high voltage potential relative to ground. When two charged aircraft couple together for refuelling purposes, severe electrostatic discharging can take place causing unwanted electromagnetic pulses and other hazards to occur. The FDTD solver can simulate these processes and estimate the currents flowing - see picture (right). This technique also finds application in the civil aviation sector in the guise of ground refuelling where internal sparking can occur inside aircraft fuel tanks as kerosene is pumped aboard. Very recently, a charged particle module used for tracking of lightning attachment to air frames and the subsequent motion of the sweeping phase has been developed. This permits the initialization and subsequent motion of the arc channel to be simulated.
