The strength of the vorticity that is trailed into the wake from a rotor blade is largely dependant of the lift distribution across the span of the blade. At the tip (and the root in some cases) there is a large discontinuity in the lift distribution therefore a strong vortex is trailed.
We have shown recently using Computational Fluid Dynamics techniques that even the addition of a cap that is a simple revolution of the aerofoil shape will significantly reduce the strength of the vortex that is created. This in turn means that the blade vortex interactions that occur in the wake, will also be less severe and so the noise produced by the aircraft will be reduced.
It's exciting stuff really!
As to the effect of fuel injection on the engine.....well i'm not an engine person really, but I would guess that by using electronic fuel injection the nature of the combustion process in the cyclinder and the reacting fluid dynamics are significantly altered. I would expect that less fuel is injected into the cylinder for a given power output than would be required for the carb'd version of the engine by virtue of the well known improvements in combustion effeciency obtained using a good fuel injection system. Therefore this implies that less energy is available to create noise, vibration etc etc. More specifically, I would expect the pressure pulse created as the burning gas mixture expands to be smoother with fuel injection by virtue of a better atomised fuel spray. This is due to a smoother propagation of the flame front and may therefore be expected to have a reduced excitation effect on the engine struictural dynamics. Again a signicant noise source.
Hope this helps......right, back to work.
CRAN
