['The', 'accuracy', 'and', 'usefulness', 'of', 'the', 'multiple', 'scales', 'approach', 'has', 'been', 'validated', 'against', 'finite', '-', 'element', 'methods', '\xa0', '[', '6', ']', 'for', 'realistic', 'aeroengine', 'configurations', 'and', 'acoustic', 'frequencies', '\xa0', '[', '7,8', ']', '.']