['The', 'propagation', 'of', 'unsteady', 'disturbances', 'in', 'ducts', 'of', 'slowly', '-', 'varying', 'geometry', ',', 'such', 'as', 'those', 'typical', 'of', 'an', 'aeroengine', ',', 'can', 'be', 'successfully', 'modelled', 'using', 'a', 'multiple', 'scales', 'approach', '.']