Turbine blade and corresponding method of servicing

1. A turbine blade comprising:

an airfoil comprising an outer wall formed by a pressure sidewall and a suction sidewall joined at a leading edge and at a trailing edge,

a blade tip at a first radial end and a root at a second radial end opposite the first radial end for supporting the blade and for coupling the blade to a disc,

wherein the blade tip comprises:

a tip cap extending between the pressure sidewall and the suction sidewall,

a squealer tip wall extending radially outward of the tip cap and extending along a direction from the leading edge to the trailing edge, the squealer tip wall comprising a forward surface that is continuous with an outer surface of the pressure sidewall, and

a plurality of cooling channels spaced apart along a contour of the squealer tip wall, each cooling channel comprising:

an inlet configured for receiving a coolant from airfoil internal cavity,

an upstream section comprising a closed channel extending from the inlet to the forward surface of the squealer tip wall,

a downstream section comprising an open channel formed by a slot on the forward surface of the squealer tip wall, the slot extending radially outward in a downstream direction so as to guide the coolant along the forward surface toward a radially outermost tip of the squealer tip wall,

wherein the slot extends through the radially outermost tip of the squealer tip wall, and

wherein a forward edge of a radially outward facing tip surface of the squealer tip wall is defined by alternating peaks and valleys.

2. The turbine blade according to claim 1 , wherein the slot has a diverging width in the radially outward direction.

3. The turbine blade according to claim 2 , wherein the slot is formed by a slot floor flanked on opposite sides by a pair of slot sidewalls, wherein the width of the slot floor defined by a distance between the slot sidewalls increases in the radially outward direction.

4. The turbine blade according to claim 3 , wherein the slot sidewalls are orthogonal to the slot floor.

5. The turbine blade according to claim 1 , wherein the slot has a depth that tapers off in the radially outward direction to a substantially zero depth at the radially outermost tip of the squealer tip wall.

6. The turbine blade according to claim 1 , wherein the closed channel forming the upstream section has a substantially constant flow cross-section.

7. The turbine blade according to claim 1 , wherein the inlet is formed on a radially inner surface of the tip cap facing the airfoil internal cavity.

8. The turbine blade according to claim 1 , wherein the slot extends at least up to the radially outermost tip of the squealer tip wall.

9. The turbine blade according to claim 1 , wherein the blade tip comprises a radially outward step at a pressure side edge of the tip cap, wherein the squealer tip wall extends radially outward from said step to said radially outermost tip.

10. The turbine blade according to claim 9 , wherein the blade tip further comprises a plurality of chord-wise spaced apart cooling holes formed through the step which are in fluid communication with an airfoil internal cooling system.

11. The turbine blade according to claim 1 , wherein the forward surface of the squealer tip wall is inclined with respect to a radial axis toward a blade pressure side.

12. The turbine blade according to claim 1 , wherein the squealer tip wall comprises an aft surface laterally opposite to the forward surface, wherein in relation to a radial axis, the aft surface and the forward surface are oriented at respective angles which vary independently along the chord-wise direction, such that the chord-wise variation of a first angle between the aft surface and the radial axis is different from the chord-wise variation of a second angle between the forward surface and the radial axis.

13. A method for servicing a turbine blade to improve blade tip cooling, the turbine blade comprising an airfoil comprising an outer wall formed by a pressure sidewall and a suction sidewall joined at a leading edge and at a trailing edge, a blade tip at a first radial end and a root at a second radial end opposite the first radial end for supporting the blade and for coupling the blade to a disc, wherein the blade tip comprises a tip cap extending between the pressure sidewall and the suction sidewall, and a squealer tip wall extending radially outward of the tip cap and extending along a direction from the leading edge to the trailing edge, the squealer tip wall comprising a forward surface that is continuous with an outer surface of the pressure sidewall,

the method comprising:

machining a plurality of cooling channels spaced apart along a contour of the squealer tip wall, wherein machining each cooling channel comprises:

machining a cooling channel inlet configured to be in fluid communication with airfoil internal cavity,

machining an upstream section comprising a closed channel extending from the inlet to the forward surface of the squealer tip wall,

machining a downstream section comprising an open channel formed by a slot on the forward surface of the squealer tip wall, the slot extending radially outward in a downstream direction toward a radially outermost tip of the squealer tip wall, the slot extending through the radially outermost tip of the squealer tip wall, and a forward edge of a radially outward facing tip surface of the squealer tip wall defined by alternating peaks and valleys.