Turbine blade dimple
A blade for mounting in an annular array about a rotary hub, the blade having: a blade root; an airfoil profile with a concave pressure side surface; a chord line extending between a leading edge and a trailing edge; and a blade tip, where the blade has a recess in the pressure side surface with an outer periphery disposed radially inwardly from the blade tip, and inwardly along the chord line from the leading edge and from the trailing edge.
1. A gas turbine blade for mounting in an annular array about a rotary hub, the blade having: a blade root; an airfoil profile with a concave pressure side surface; a chord line extending between a leading edge and a trailing edge; and a blade tip, the blade comprising:
a single recess in the pressure side surface with an outer periphery disposed radially inwardly from the blade tip, and inwardly along the chord line from the leading edge and from the trailing edge, the recess being open during use of the gas turbine engine, wherein the recess has base surface substantially parallel to and spaced inwardly from the pressure side surface.
2. A blade according to claim 1 wherein the outer periphery is substantially rectangular.
3. A blade according to claim 1 wherein the blade has a radial height defined between the blade platform and the blade tip, and wherein a top portion of the outer periphery is disposed radially inwardly from the blade tip a distance in the range of 2–20 per cent of the height.
4. A blade according to claim 3 wherein a bottom portion of the outer periphery is disposed radially inwardly from the blade tip a distance in the range of 10–50 per cent of the height.
5. A blade according to claim 1 wherein the blade has a chord length defined between the leading edge and the trailing edge, and wherein a leading portion of the outer periphery is disposed inwardly along the chord line from the leading edge a distance in the range of 10–40 per cent of the chord length.
6. A blade according to claim 5 wherein a trailing portion of the outer periphery is disposed inwardly along the chord line from the leading edge a distance in the range of 40–85 per cent of the chord length.
7. A blade according to claim 1 wherein the blade is selected from the group consisting of: a turbine blade; a compressor blade; and a fan blade.
8. A gas turbine engine having a plurality of blades extending radially in an annular array from a rotor hub, each blade having a natural frequency and having: an airfoil profile with a concave pressure side surface; a chord line extending from a leading edge to a trailing edge; and a blade tip; and
means for modifying the natural frequency of the airfoil comprising a hollow recess open to the pressure side surface with an outer periphery disposed radially inwardly from the blade tip, and inwardly along the chord line from the leading edge and from the trailing edge.
9. A method of increasing a natural frequency of a blade extending radially in an annular array from a rotor of a gas turbine engine, each blade having: an airfoil profile with a concave pressure side surface; a chord line extending from a leading edge to a trailing edge; and, a blade tip, the method comprising:
forming a recess open to the pressure side surface with an outer periphery disposed radially inwardly from the blade tip, and inwardly along the chord line from the leading edge and from the trailing edge, wherein the recess has base surface substantially parallel to and spaced inwardly from the pressure side surface; and
operating the gas turbine with the recess in an empty condition.
10. A method according to claim 9 wherein the base surface, periphery and pressure side surface merge smoothly together.
11. A method according to claim 9 wherein the outer periphery is substantially rectangular.
12. A method according to claim 9 wherein the blade has a radial height defined between the blade platform and the blade tip, and wherein a top portion of the outer periphery is disposed radially inwardly from the blade tip a distance in the range of 2–20 per cent of the height.
13. A method according to claim 12 wherein a bottom portion of the outer periphery is disposed radially inwardly from the blade tip a distance in the range of 10–50 per cent of the height.
14. A method according to claim 9 wherein the blade has a chord length along the chord line defined between the leading edge and the trailing edge, and wherein a leading portion of the periphery is disposed inwardly along the chord line from the leading edge a distance in the range of 10–40 per cent of the chord length.
15. A blade according to claim 14 wherein a trailing portion of the periphery is disposed inwardly along the chord line from the leading edge a distance in the range of 40–85 per cent of the chord length.