Turbine dovetail slot heat shield

Gas turbine engine turbine blade assembly includes a hollow airfoil joined to blade root, dovetail slot heat shield bonded or attached to a bottom surface of the root, and a shield outlet from heat shield open to inlet apertures extending radially through a radially inner root end of the root. Heat shield may have body with legs extending upwardly from heat shield bottom, slanted open upstream end, and free ends of the legs longer than the heat shield bottom. Flanges may be located along free ends and bonded to bottom surface. Body, heat shield bottom and/or the legs may be rounded. Disk includes a plurality of dovetail slots formed in a rim, complimentary plurality of turbine blades removably retained in dovetail slots by the roots, slot bottoms of the dovetail slots extending circumferentially between disk posts in rim. Heat shield bottoms may be radially spaced apart the slot bottoms.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates generally to gas turbine engine turbine blade cooling and, more specifically, cooled turbine blades and slots for mounting the blades.

Background Information

Turbine blades in gas turbine engine turbines and, particularly, high pressure turbine blades are often cooled by a portion of pressurized air from a compressor of the engine. Each turbine stage includes a row of turbine rotor blades extending radially outwardly from a supporting rotor disk with the radially outer tips of the blades being mounted inside a surrounding turbine shroud. Typically, turbine rotor blades of at least the first turbine stage are cooled by the bled portion of the pressurized air from the compressor. The blades include roots slid into and secured by axial slots in a turbine disk.

The blades are typically cooled using a portion of high pressure compressor discharge air bled (also known as compressor discharge pressure or CDP air) from the last stage of the compressor. The air is suitably channeled through internal cooling channels inside the hollow blades and discharged through the blades in various rows of film cooling holes from the leading edge and aft therefrom, and also typically including a row of trailing edge outlet holes or slots on the airfoil pressure side.

Blade cooling air is gathered and transferred from static portions of the engine to the rotating disk supporting the blades. The cooling air passes through the slot and into the blade root from where it is distributed through a cooling circuit having cooling passages in an airfoil of the blade.

The typical turbofan aircraft engine initially operates at a low power, idle mode and then undergoes an increase in power for takeoff and climb operation. Upon reaching cruise at the desired altitude of flight, the engine is operated at lower or intermediate power setting. The engine is also operated at lower power as the aircraft descends from altitude and lands on the runway, following which thrust reverse operation is typically employed with the engine again operated at high power. In the various transient modes of operation of the engine where the power increases or decreases, the turbine blades heat up and cool down respectively.

A slot bottom of the disk is exposed to blade cooling air during engine operation. The cooling air increases the thermal response of the slot bottom creating a large thermal gradient between the slot bottom and bore of the disk. This gradient creates large thermal stresses in both the acceleration and deceleration of the engine. These large thermal stresses reduces the low cycle fatigue life of the disk.

Accordingly, it is desired to provide a gas turbine engine having turbine blade cooling with a design which reduces a thermal gradient in a bottom of a root mounting slot. It is further desired to reduce large thermal stresses in the bottom of the root mounting slot caused by the thermal gradient. It is also desired to increase the low cycle fatigue life of the disk by reducing these thermal stresses.

BRIEF DESCRIPTION OF THE INVENTION

A gas turbine engine turbine blade assembly includes a hollow airfoil integrally joined to a blade root, a dovetail slot heat shield attached to a bottom surface of the root, and a shield outlet from the dovetail slot heat shield open to at least one inlet aperture extending radially through a radially inner root end of the root. The heat shield may be bonded to the bottom surface.

The heat shield may include a body with a heat shield bottom and sides or legs extending upwardly or radially outwardly from the heat shield bottom. The heat shield may have a slanted open forward or upstream end and free ends of the legs may be longer than the heat shield bottom.

An axially extending straight flange may be located along a free end of each of the legs and the flanges may be bonded to the bottom surface. The heat shield may have a slanted open forward or upstream end of the heat shield and the flanges and the free ends of the legs may be longer than the heat shield bottom. The body may be rounded. The heat shield bottom and/or the legs may be rounded.

A gas turbine engine turbine disk assembly may include a disk including a web extending radially outwardly from a hub to a rim; a plurality of dovetail slots in the rim; a complimentary plurality of turbine blades removably retained in the plurality of dovetail slots; slot bottoms of the dovetail slots and the dovetail slots extending circumferentially between disk posts in the rim on the disk assembly, and each of the turbine blades including a hollow airfoil integrally joined to a blade root, a dovetail slot heat shield attached to a bottom surface of the root, and a shield outlet from the dovetail slot heat shield open to at least one inlet aperture extending radially through a radially inner root end of the root.

The gas turbine engine turbine disk assembly may include a clearance between the heat shield bottoms of the heat shields and respective ones of the slot bottoms. The heat shield bottoms may be radially spaced apart from respective ones of the slot bottoms and the heat shields may be bonded to the bottom surfaces.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated schematically inFIG. 1is an exemplary gas turbine engine high pressure turbine (HPT) section22circumscribed about a longitudinal or axial centerline axis12. The high pressure turbine section22includes a turbine nozzle20having a circumferential row of stator vanes38suitably mounted between outer and inner bands21,23. Following the turbine nozzle20is a single row of exemplary turbine blades10removably mounted to the perimeter or rim24of a first stage HP rotor disk30. The rotor disk30includes a web25extending radially outwardly from a hub28to the rim24.

Referring toFIGS. 1-3, each of the turbine blades10includes a hollow airfoil16integrally joined to an axial-entry dovetail root18at a platform27of the turbine blade10. As illustrated inFIGS. 2 and 4, the preferred embodiment of the blade dovetail root18includes an upper pair of laterally or circumferentially opposite lobes or tangs19and a lower pair of lobes or tangs26. The tangs are configured in a typical fir tree configuration for supporting and radially retaining the individual blade in a complementary axial dovetail slot29formed in the rim24of the rotor disk30as illustrated inFIGS. 1-4.

Referring toFIG. 3, a plurality of inlet apertures50extend radially through a radially inner root end35of the dovetail root18. The inlet apertures50allow turbine blade cooling air11to flow from the dovetail slot29into a cooling air circuit52in the airfoil16as illustrated inFIGS. 1-2. Referring toFIGS. 1-2, an annular flow inducer84injects the turbine blade cooling air11into the rotating rotor disk30as is well known in the field. The flow inducer84typically includes a row of vanes86which tangentially accelerates, meters, and/or pressurizes the cooling air11and injects the cooling air11into the dovetail slot29of the rotating first stage rotor disk30.

The cooling air11flows into the dovetail slot29, through the root end35, and then radially outwardly through cooling channels70in the cooling air circuit52in the airfoil16. The cooling air11is then discharged through rows of outlet holes in the pressure and suction sides of the blade airfoil in a conventional manner. Further referring toFIG. 3, a slot bottom60and the dovetail slot29extend circumferentially between disk posts62in the rim24on the rotor disk30. The dovetail slot29extends axially between a dovetail slot inlet32and a dovetail slot aft end36. The dovetail roots18are axially retained in the dovetail slots29by forward and aft retaining plates46,48mounted to the rotor disk30as illustrated inFIGS. 1 and 2.

Referring toFIGS. 1-3, a dovetail slot cooling air chamber or manifold44is radially located between the root end35of the dovetail root18and the slot bottom60of the dovetail slot29in the rim24on the rotor disk30. The root end35of the dovetail root18demarks a top39or radially outer boundary of the dovetail slot cooling air chamber or manifold44. The root end35of the dovetail root18is longer than an axially extending width W of the rim24along the dovetail slot29and axially longer than the slot bottom60. A notch or cutback42in an axially forward end45of the rim24accommodates the root end35of the dovetail root18being axially longer than the slot bottom60.

Referring toFIGS. 1-3, a dovetail slot heat shield40is attached to a bottom surface37of the dovetail root18and disposed within the dovetail slot cooling air chamber or manifold44. The heat shield40may be bonded to the bottom surface37such as by brazing or welding. The heat shield40is designed to shield a slot bottom60from the cooling air11. The heat shield40is designed to reduce the ability of the cooling air11to substantially impact the thermal response of the slot bottom60and to reduce a rim to bore thermal gradient as well as the thermal stresses.

Referring toFIGS. 4-7, the exemplary embodiment of the dovetail slot heat shield40illustrated herein has a preferably rounded body88including a rounded heat shield bottom90. Sides or legs92extending radially outwardly or upwardly from the heat shield bottom90. The legs may be rounded as illustrated inFIGS. 4, 5, and 8. An axially extending straight flange96is located along a free end98of each of the legs92. The flanges96are attached or bonded to the bottom surface37of the dovetail root18such as by brazing. The heat shield bottom90may be radially spaced apart from the slot bottom60to help protect the slot bottom60from being directly exposed to the cooling air11.

An open forward or upstream end100of the heat shield40is bevelled or slanted upstream indicated by a bevel102on the upstream end100. The upstream end100is bevelled or slanted such that the flanges96and the free ends98of the legs92are longer than the heat shield bottom90of the heat shield40. The bevelled or slanted upstream end100of the heat shield40helps direct the cooling air11into a hollow interior89of the body88of the heat shield40. The cooling air11exits the hollow interior89through a shield outlet93between the flanges96and the free ends98of the legs92and through the plurality of inlet apertures50. The cooling air11flows through the dovetail slot and through the inner root end35of the dovetail root18with minimal contact of the slot bottom60disposed along the rim24on the rotor disk30.

Illustrated inFIG. 8is a clearance C between at least the heat shield bottom90of the heat shield40and the slot bottom60to help protect the slot bottom60from being directly exposed to the cooling air11. The clearance C in some embodiments of the heat shield, root, and slot may be about 0.04 inches along a substantial portion of the heat shield and slot. The body88including the heat shield bottom90and legs92may be rounded in order to have the body88closely conform to the rim24along the slot cooling air chamber or manifold44between the root end35of the dovetail root18and the slot bottom60of the dovetail slot29in the rim24on the disk30.

While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims.