Reduction in Flow Parameter Resulting from Volcanic Ash Deposition in Engine Representative Cooling Passages

Internal cooling passages of turbine blades have long been at risk to blockage through the deposition of sand and dust during fleet service life. An additional difficulty is that these cooling system are frequently impossible to inspect in order to assess the level of deposition. The ingestion of high volumes of volcanic ash therefore poses a real risk to engine operability. This paper reports results from experiments carried out at typical HP turbine blade metal temperatures (1163K to 1293K) and coolant inlet temperatures (800K to 900K) in engine scale models of a turbine cooling passage with film-cooling offtakes. The experimental rig allows the metered delivery of volcanic ash through the coolant system at the start of a test. The key metric indicating blockage is the flow parameter, with visual inspection used to determine the deposition location. Volcanic ash samples from the 2010 Eyjafjallajökull eruption were used for the majority of the experiments conducted. A further ash sample from the 2008 Chaiten eruption allowed the effect of ash composition to be investigated. Experimental results have characterised the reduction of flow parameter with changing particle size distribution, blade metal temperature, ash sample composition, film-cooling hole configuration, ash dosage, and pressure ratio across the holes. There is qualitative evidence that hole geometry can be manipulated to decrease the likelihood of blockage. A discrete phase CFD model implemented in Fluent has allowed the trajectory of the ash particles within the coolant passages to be modelled, to help explain the behaviour observed