Featured Case Study

The Ingestion and Deposition of Volcanic Ash inside Gas Turbine Aeroengines

The eruption of Eyjafjallajokull in Iceland in 2010 cost the airline industry tens of millions of pounds when the Civil Aviation Authority imposed a blanket ban on flights across Europe. These costs stimulated a renewed interest into the effects of volcanic ash deposition in gas turbine aeroengines. An international consortium of industrial and academic partners including Double Precision Consultancy, Easyjet, Rolls Royce and Cambridge University has since been established. More details on this consortium can be found at the following web address:

http://www.ccg.msm.cam.ac.uk/initiatives/provida

 

One of the main objectives of the project is to identify the parameters that promote the deposition of volcanic ash on both static and rotating components inside aeroengines. These include the particle size distribution, the relative proportion of crystalline and amorphous phases, glass transition temperatures, particle trajectories, particle velocities and particle temperature histories. These parameters and their importance are being assessed using a combination of experimental techniques, computational fluid dynamics modelling and full-scale engine tests.

The ingestion of volcanic ash inside gas turbine aeroengines can have serious implications for the safety of the aircraft and its passengers. There are also serious economic consequences for airline operators.

As part of the experimental programme, a novel set-up for the study of the high temperature, high speed impact behaviour of volcanic ashes was devised and commissioned. It involved the manufacture of compressed spherical pellets of volcanic ash (which were ~6 mm in diameter), and their subsequent heating within the barrel of a pressurised gas-gun. The heated pellets of ash were then fired at static targets at high speed (~100 m/s) while still hot (~1000 degrees Centigrade). Some of the high speed video footage that was captured is shown below. It demonstrates an important point which is that, even at very high temperatures, some volcanic ashes are unlikely to stick, with the likelihood of sticking have a strong dependence on composition (particularly Si content). These experiments, along with relevant others, are more thoroughly documented in the published papers that have so far emerged from this work (available for download below).

High speed video footage of a high Si content volcanic ash pellet striking a stationary target at ~100 m/s and ~1000 degrees Centigrade

High speed video footage of a low Si content volcanic ash pellet striking a stationary target at ~100 m/s and ~1000 degrees Centigrade

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