The invention relates to a turbine blade having improved structural and cooling properties.
The turbine blades in a gas turbine engine operate in a harsh environment: a high G-field applies significant stress to the blades, and the blades operate under high-temperature conditions.
The size of the G-field can be illustrated by a simple example. Centrifugal acceleration is given by the expression
a=(w-squared)xc3x97r,
wherein
a is the centrifugal acceleration,
w is the rotational velocity in radians per second, and
r is the radius at which the acceleration is computed.
If a shaft of radius one foot rotates at 10,000 rpm, which corresponds to 167 revolutions per second, then the centrifugal acceleration a is computed as
a=(167xc3x972xc3x97PI)(1/sec)xc3x97(167xc3x972xc3x97PI)(1/sec)xc3x971 foot,
or about 1.1 million feet/second-squared. To convert this acceleration into units of G""s, wherein one G is the earth""s acceleration-due-to-gravity, one divides by 32.2, to obtain about 34,000 G""s.
Clearly, this high G-field applies significant stress to the blade: a blade which weighs one pound under static conditions will weigh 34,000 pounds in operation. In addition, the gas loading applies additional stresses to the blades, in different directions from the G-field.
In addition to stresses due to G-fields, the temperature of the gas to which the turbine blade is subject is high. For example, turbine inlet temperatures of 2,500 F. are common. High temperatures weaken many metals. To combat the high temperature, some turbine blades are actively cooled, as by passing cooling air through passages contained in the blades.
The Inventors have developed a new structure for a turbine blade, to reduce the deleterious effects of the stresses and temperatures.
In one form of the invention, a turbine blade is equipped with a specific tilt, specific lean, and a specific set of columns of cooling holes, wherein the hole distributions in many of the columns are non-uniform. The invention reduces a specific thermal gradient and mechanical loading in the blade, thereby reducing bowing of the blade.