US Patent 8177496 Tone noise reduction in turbomachines

A blade for a turbomachine extends in use, in a radial direction relative to the axis of the turbomachine. The turbomachine has at least one operating condition which generates supersonic fluid flow at the blade. The blade is adapted to provide, at the supersonic operating condition, a leading edge sweep angle which varies such that successive radial positions (i) to (iii) along the leading edge are at respective sweep angle turning points. Position (i) is the radially inner and position (iii) the radially outer of the positions. Position (i) is at or radially outward of the 30% span position, where 0% span is the radially innermost point of the leading edge and 100% span is the radially outermost point of the leading edge.