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SUMMARY:Adhesion of Volcanic Ashes in Gas Turbines and Potential Effects o
 n Thermal Barrier Coatings - Professor Bill Clyne\, Department of Material
 s Science &amp\; Metallurgy
DTSTART:20160205T140000Z
DTEND:20160205T150000Z
UID:TALK63283@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:Deposition of ingested volcanic ash (VA) within gas turbine ae
 roengines presents an increasing level of hazard as turbine entry temperat
 ures (TET) continue to be raised\, and can cause severe engine damage.  Th
 e key issue is whether ingested particulate adheres to surfaces inside the
  engine\, with the low softening temperature of many VAs making this more 
 likely.  Such adhesion has been studied in a small turbojet aeroengine (us
 ing a borescope)\, in a customized plasma torch-based set-up designed to s
 imulate a turbine combustion chamber and has also been explored for VA pel
 lets in a gas gun via high speed photography.  Deposition in the engine ma
 inly occurs on static components.  Numerical modelling has been used to pr
 edict particle flight histories in the customized set-up and correlations 
 established with observed rates of particle deposition.  Particle size is 
 important\, since the Stokes number of small (<~5 µm) particles is such t
 hat they do not impact solid surfaces\, whereas large (>~40 µm) particles
  remain relatively cool.  Unfortunately\, VA particles in the intermediate
  size range commonly reach the turbine.  The composition of VA\, which var
 ies significantly between different volcanoes\, is also important\, partic
 ularly insofar as it affects the glass transition temperature\, Tg\, and t
 he glass content.  Many VAs have very low softening temperatures (<~700˚C
 )\, particularly when compared with TET values of up to 1400˚C.  The visc
 osity (at high strain rates) is also important.  In this study\, four Icel
 andic VAs have been employed and correlations established between these fe
 atures and corresponding observed deposition characteristics.  Investigati
 ons have also been carried out into the effect of deposited VA on sinterin
 g-induced spallation of thermal barrier coatings\, which is of short term 
 concern even when deposition levels are insufficient to impair gas flow.  
 Establishing whether a particular VA cloud represents a serious hazard to 
 air traffic is likely to require in situ sampling\, probably using drones\
 , and some points are made concerning such measures.
LOCATION:Department of Engineering - LR4
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