Abstract
Abradable seals are used at the interface between blade tips and compressor casings in modern gas turbine engines. These materials wear in preference to the blade tips leaving a track which perfectly fits the blades, thus improving sealing at the blade tip an increasing both efficiency and stall margin of the compressor.The wear mechanisms occurring at this interface have been characterised for two common abradable materials. Changes to these mechanisms with blade speed, incursion rate and abradable hardness have been investigated and described statistically. The wear mechanisms proposed in this work and previously suggested have been used as the foundation for linear models which have been fitted to the results. These models have been used to test the quality of the mechanisms and indicate which processes are poorly understood.The models were well correlated to results for forces with normally distributed residuals indicating rubbing force systems are well represented by the proposed mechanisms. Temperature and blade length change results were less well correlated indicating these processes are more poorly understood. This work shows that simple linear models based on a mechanistic understanding of underlying processes can be used for describing forces.
Highlights
Abradable materials are used in gas turbine engines to maintain seals at the compressor blade tips
Behaviours observed with the AlSi polyester abradable are very different to those of the NiCrAl bentonite abradable
Substantial differences between batches were observed and it clear that future work in this field should not focus on single spray batches as if they are representative of all batches as found previously for the AlSi hBN abradable [6]
Summary
Abradable materials are used in gas turbine engines to maintain seals at the compressor blade tips. In the high pressure compressor temperatures are prohibitively high for both titanium blades and the AlSi alloy used in these abradables [3]. For these stages Inconel 718 blades are run against a NiCrAl bentonite abradable [4]. Research on these rubbing systems is largely carried out on scaled test rigs which aim to recreate the conditions present in service. Research on the AlSi polyester abradable [5] has consistently shown adhesion from the abradable to the blade tip with some blade wear at low incursion rates as seen in service. Cutting behaviour is observed at high incursion rates, similar to turning or milling of the abradable
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