The dust travels through the bleed system and can melt and block the exit holes... blade gets too hot and is damaged
This is the key to the whole set of issues around engine damage caused by LOW levels of VA.
(Forget, for a moment, accurate detection of areas of HIGH VA concentration in bad visibility and especially at night, and the specific risks from this. Forget also the possibility of blocked pitot heads and other critical features of the aircraft that might be affected by LOW VA .)
A VA particle passing through a combustion chamber will probably be melted, so may solidify onto a turbine blade. Yup - Very Bad Thing, especially if the build-up of glassy material blocks the exit(s) of cooling duct(s).
VA particles going through the cooling bleed and then through the inside of a (hot) blade might also melt and would then presumably be more likely to re-solidify in a clump where the temperature was lower and block some ducts. Another Very Bad Thing.
BUT what is the temperature of the cooling air inside a blade or other potential hot-spot? As low as possible, obviously, so as to give maximum cooling effect - engine manufacturers have a design trade-off between larger volume of hotter air versus smaller, cooler volume to achieve a given cooling effect. So given that it costs thrust to divert air into the cooling bleeds, the air temperature is going to be minimised by design. The
big question: can the turbine cooling air temperature ever exceed the melting point of VA? If so, under what circumstances and where?
Anyone know this? I don't know and can't find any reference myself....