Aerofoil

1. An aerofoil comprising

a trailing edge,

a leading edge, the leading edge comprising a plurality of peaks and every peak of the leading edge is generally aligned in a straight line in a spanwise direction, and

a plurality of slits extending toward the trailing edge, each slit defining a slit height from a respective peak of the plurality of peaks at the leading edge to a trough spaced from the leading edge, the troughs defining a repeating waveform pattern, such that the troughs define a plurality of mutually coherent noise sources to cause destructive interference of noise created by the troughs, wherein

the aerofoil is for a gas turbine engine, and

each slit comprises a side surface extending generally chordwise at each end of each peak, interconnecting each peak with an adjacent trough, and extending orthogonally to a generally spanwise extending upstream end surface.

2. The aerofoil according to claim 1 , wherein the repeating waveform pattern comprises one of a sawtooth waveform, a triangular waveform, and a sinusoidal waveform.

3. The aerofoil according to claim 1 , wherein a spanwise extending interconnecting portion extends at an angle of 30° relative to the chordal direction.

4. The aerofoil according to claim 1 , wherein each of the troughs respectively comprises a spanwise extending interconnecting portion extending across the trough interconnecting adjacent side surfaces and defining a spanwise extent.

5. The aerofoil according to claim 4 , wherein the spanwise extending upstream end surface has a spanwise extent between 2 and 5 times greater than the spanwise extent of the interconnecting portion.

6. The aerofoil according to claim 5 , wherein

a leading edge profile defines a waveform chordal extent between a nadir at a downstream end of the leading edge and the spanwise extending upstream end surface,

a ratio of the chordal extent to a spanwise extent of the interconnecting portion is between 30 and 100, and

a ratio between the chordal extent and the spanwise extent of the spanwise extending upstream end surface is between 10 and 25.

7. The aerofoil according to claim 6 wherein a ratio of a wavelength defined by a spanwise separation between adjacent nadirs to the spanwise extent of the spanwise extending upstream end surface is between 10 and 60.

8. The aerofoil according to claim 1 , wherein a leading edge profile comprises a nadir at a downstream end of the leading edge.

9. The aerofoil according to claim 8 , wherein the leading edge profile defines a waveform chordal extent between the nadir and the spanwise extending upstream end surface, and wherein a ratio of the chordal extent to a spanwise extent is between 30 and 100, wherein the spanwise extent is across the trough between adjacent side surfaces.

10. The aerofoil according to claim 8 ,

wherein the leading edge profile defines a waveform chordal extent between the nadir and the spanwise extending upstream end surface, the aerofoil includes a mean chord line defined as a line extending from a root to the tip of the aerofoil along an arithmetic mean of a chordal position of midpoints of chords between the leading edge and the trailing edge of the aerofoil, and includes a mean chord extent defined as a distance between the trailing edge and the mean chord line, and

wherein a ratio between the mean chord extent and the waveform chordal extent is between 20:1 and 10:1.

11. The aerofoil according to claim 1 , wherein a leading edge profile comprises a plurality of nadirs each at a downstream end of the leading edge, and a waveform wavelength is defined by a spanwise separation between adjacent ones of the plurality of nadirs, and wherein a ratio of the wavelength to a spanwise extent is between 10 and 60, wherein the spanwise extent is across the trough between adjacent side surfaces.

12. A gas turbine engine comprising the aerofoil in accordance with claim 1 .

13. The gas turbine engine according to claim 12 , wherein the aerofoil comprises an outlet guide vane.

14. An aircraft comprising the aerofoil according to claim 1 .