GB2144806A

GB2144806A - Turbine blades

Info

Publication number: GB2144806A
Application number: GB08420040A
Authority: GB
Inventors: William Richard Wagner
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1983-08-08
Filing date: 1984-08-07
Publication date: 1985-03-13
Also published as: DE3425402A1; FR2550579A1; GB8420040D0

Abstract

A blade 10 for a high-temperature turbine, such as that of a rocket engine, operating above 2000-2500 DEG R (827-1102 DEG C) is formed from beryllium and has internal passages 16 for forced- convection fluid cooling. The blade may also have radial passages 18 for film cooling of the surface of the blade. <IMAGE>

Description

SPECIFICATION Blades for high-temperature turbines This invention relates to blades for high-temperature turbines.

The current trend in high-efficiency rocket engines is in the direction of higher and higher operating temperatures and pressures, e.g., temperatures in the 2500-3000"R.

range (1102-1 377'C). Current technology employs turbine blades formed from Co-Nisteel alloys which are characterised by high strength but low conductivity. These blades are unsuitable for either internal convection cooling or external film cooling which are required at temperatures above 2000"R (827"C) and, therefore, provide short life before breaking down. Blade breakdown can result in destruction of the entire engine and, even when the engine is not destroyed, the expense of replacing blades is very high.

The use of high conductivity copper, gold or silver alloys is precluded for high-temperature operation by their low melting points. For rotating elements, the employment of refractory metals is prohibited by their high densities which contribute to excessive rotational stresses. Moreover, refractory materials, such as SiC and SiN, which have low density and moderate strength, are unsuitable due to their brittleness.

For cooled rotor blade elements in environments where internal and/or external convection cooling must be employed, the use of a material having high thermal conductivity, low density and high melting point is required.

Beryllium is a metal having these properties and, also, mechanical strength. However, beryllium has not been used, perhaps because it has not been possible heretofore to form beryllium into rotor blades with internal convection passages.

The invention, which is defined in the claims, is directed to an improved, practical blade for high-temperature turbines operating above about 2500"R (1102"C). In preferred embodiments, the blade is formed from the metal beryllium and has internal passages for the conveyance of a coolant fluid for convectively cooling the blade. Radial passages may also extend from the internal convection passages to the outer surface of the blade to provide film cooling of the surface.

The invention will now be further described by way of example with reference to the drawing, in which: The single figure is a cross-sectional view of a rotor blade of a turbine showing the internal and radial cooling-fluid passages.

The single figure shows a cross-section of a turbine blade 10, either rotor or stator, for use in a high-temperature generally above 2000-2500"R (827-1102"C) engine, e.g., a rocket engine. The blade 10 may, for example, typically be about 2 inches (50.8 mm) high and 1 inch (25.4 mm) from tip 1 2 to tail 14. The blade 10 is formed with internal fluid-coolant passages 1 6 for cooling the blade by convection and a few radial passages 1 8 for conveying fluid coolant to the outer surfaces 20 of the blade for film cooling of the surfaces.

The blade 10 is formed from beryllium by the recently-developed powder-metallurgy molding process. Fine micron beryllium powder is placed in a mold containing a core or cores for forming the passages 1 6 and 1 8.

The beryllium in the mold is then subjected to high temperature and pressure, at which levels the powder is sintered. The high pressure and temperatures are removed, the passage-forming core or cores are eliminated and the blade with its fluid-conducting passage is ready for machining processes such as surface-finishing. Each core may be made of evaporable plastics material in which case it evaporates during the sintering process. Alternatively, the core material could be aluminium or zirconium and leached out with acid after the sintering process.

The fluid used for cooling a forced internalconvection-cooled Be blade may, for example, be liquid hydrogen or liquid methane. As an example, with a liquid hydrogen forced-convection mass velocity of 19lbs/in2-sec., (1.33Kg/cm2-sec.), the following are typical conditions with a tip temperature of about 1000"R (277"C): T,= 2600"R (1157 C).

Tc = 100 R (-218'C).

hg = 0.05 BTU/in2-sec- R (14.8 Watts/cm2- C) hc =0.17 BTU/in2-sec-'R (50 Watts/cm2- C) where Tg is the temperature of the gas coming into the turbine, Tc is the temperature of the coolant fluid, h, is the average heat transfer coefficient on the gas sides of the blade wall, and hc is the average heat transfer co efficient on the coolant sides of the blade wall.

The blade thickness at its tip 1 2 might typically be about 0.035" (0.89 mm). The manufacture of the blade 10 could also be by a different process than the powder molding process described above.

Turbine blades for use in high-temperature turbines operating above 2000-2500"R (827-1102"C) should be made of a metal or alloy having high thermal conductivity, low density, a high melting point and, preferably, reasonable ductility, although the first three characteristics are the essential ones. Beryllium has the desired properties. For example, beryllium's thermal conductivity is about 100 BTU/hr-ft- R (1.74W/cm-"C) whereas steel's is 8-10(0.14 to 0.17W/cm- C). Copper's conductivity is better, being 200 (3.5), but copper has high density (8.9g/cm3) and a melting point (about 2440"R-1067"C) which is just on the border of the lower limit of the high-operating temperature range.Titanium has good properties except for its thermal conductivity, which is low; 4.3 (0.07). Its density is 4.44 gm/cm3. Beryllium's melting point is 2800'R (1267"C) and its density is very low, about 1.85 gms/cm3. It thus has the proper combination of properties for the intended use.

The terms "high thermal conductivity" and "low density" are taken relative to the constants of a steel alloy, MAR M246-cc, which is the criterion for turbine blade materials. The thermal conductivity of this steel is .03 Cal/ sec-cm- K (0.12 W/cm-"C) and its density is 8.45 gms/cm3. Thus, "high" thermal conductivity is about .03 Cal/sec-cm- K (0.12 W/cm- C) or more, and "low" density is about 8.45 or less. As previously stated, "high" melting point would be considered to be about 826"C or above.

Claims

1. A blade for the turbine of a hightemperature turbine engine wherein the blade is formed from a metal having the combination of properties of high thermal conductivity, low density and high melting point.

2. A blade for the turbine of a hightemperature turbine engine wherein the blade is formed from the metal beryllium.

3. A blade according to claim 2, wherein the blade is formed from a powder of beryllium particles.

4. A blade according to claim 2, wherein said blade is formed from powdered beryllium by compressing the powder in a mold under suitable conditions of temperature and pressure.

5. A blade according to any of the preceding claims formed with internal passages for the conveyance of convection-cooling fluid therethrough.

6. A blade according to claim 5 formed with passages extending from at least one of the internal passages radially outward to the outer surfaces of the blade.

7. A blade for the turbine of a hightemperature turbine engine substantially as described with reference to the drawing.