Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1999-10-05
2001-07-03
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
C416S09700R
Reexamination Certificate
active
06254334
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to gas turbine engines in general, and to cooling passages disposed within a wall inside of a gas turbine engine in particular.
2. Background Information
A typical gas turbine engine includes a fan, compressor, combustor, and turbine disposed along a common longitudinal axis. The fan and compressor sections work the air drawn into the engine, increasing the pressure and temperature of the air. Fuel is added to the worked air and the mixture is burned within the combustor. The combustion products and any unburned air, hereinafter collectively referred to as core gas, subsequently powers the turbine and exits the engine producing thrust. The turbine comprises a plurality of stages each having a rotor assembly and a stationary vane assembly. The core gas passing through the turbine causes the turbine rotors to rotate, thereby enabling the rotors to do work elsewhere in the engine. The stationary vane assemblies located forward and/or aft of the rotor assemblies guide the core gas flow entering and/or exiting the rotor assemblies. Liners, which include blade outer air seals, maintain the core gas within the core gas path that extends through the engine.
The extremely high temperature of the core gas flow passing through the combustor, turbine, and nozzle necessitates cooling in those sections. Combustor and turbine components are cooled by air bled off a compressor stage at a temperature lower and a pressure greater than that of the core gas. The nozzle (and augmentor in some applications) is sometimes cooled using air bled off of the fan rather than off of a compressor stage. There is a trade-off using compressor (or fan) worked air for cooling purposes. On the one hand, the lower temperature of the bled compressor air provides beneficial cooling that increases the durability of the engine. On the other hand, air bled off of the compressor does not do as much work as it might otherwise within the core gas path and consequently decreases the efficiency of the engine. This is particularly true when excessive bled air is used for cooling purposes because of inefficient cooling.
One cause of inefficient cooling can be found in cooling air that exits the wall with unspent cooling potential. A person of skill in the art will recognize that cooling air past through a conventional cooling aperture typically contains cooling potential that is subsequently wasted within the core gas flow. The present invention provides convective cooling means that can be tailored to remove an increased amount of cooling potential from the cooling air prior to its exit thereby favorably affecting the cooling effectiveness of the wall.
Another cause of inefficient cooling can be found in poor film characteristics in those applications utilizing a cooling air film to cool a wall. In many cases, it is desirable to establish film cooling along a wall surface. A film of cooling air traveling along the surface of the wall increases the uniformity of the cooling and insulates the wall from the passing hot core gas. A person of skill in the art will recognize, however, that film cooling is difficult to establish and maintain in the turbulent environment of a gas turbine. In most cases, air for film cooling is bled out of cooling apertures extending through the wall. The term “bled” reflects the small difference in pressure motivating the cooling air out of the internal cavity of the airfoil. One of the problems associated with using apertures to establish a cooling air film is the film's sensitivity to pressure difference across the apertures. Too great a pressure difference across an aperture will cause the air to jet out into the passing core gas rather than aid in the formation of a film of cooling air. Too small a pressure difference will result in negligible cooling airflow through the aperture, or worse, an in-flow of hot core gas. Both cases adversely affect film cooling effectiveness. Another problem associated with using apertures to establish film cooling is that cooling air is dispensed from discrete points, rather than along a continuous line. The gaps between the apertures and areas immediately downstream of those gaps are exposed to less cooling air than are the apertures and the spaces immediately downstream of the apertures, and are therefore more susceptible to thermal degradation.
Hence, what is needed is an apparatus and a method for cooling a wall that can be tailored to provide a heat transfer profile that matches a thermal load profile, one that effectively removes cooling potential from cooling air, and one that facilitates film cooling.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of the present invention to provide an apparatus and method for cooling a wall having a selectively adjustable heat transfer profile that can be adjusted to substantially match a thermal load profile.
According to the present invention, a cooling circuit is disposed within a wall inside a gas turbine engine. The cooling circuit includes a forward end, an aft end, a first wall portion, a second wall portion, and a plurality of pedestals. The first and second wall portions extend lengthwise between the forward and aft ends of the cooling circuit, and are separated a distance from one another. The pedestals extend between the first and second wall portions. The characteristics and array of the pedestals within the cooling circuit are chosen to provide a heat transfer cooling profile within the cooling circuit that substantially offsets the profile of the thermal load applied to the wall portion containing the cooling circuit. At least one inlet aperture extends through the first wall portion to provide a cooling airflow path into the forward portion of the cooling circuit from the cavity. A plurality of exit apertures extend through the second wall portion to provide a cooling airflow path out of the aft portion of the cooling circuit and into the core gas path outside the wall.
The present cooling circuits are designed to accommodate non-uniform thermal profiles. The temperature of cooling air traveling through a passage, for example, increases exponentially as a function of the distance traveled within the passage. The exit of a cooling aperture is consequently exposed to higher temperature, and therefore less effective, cooling air than is the inlet. In addition, the wall portion containing the passage is often externally cooled by a film of cooling air. The film of cooling air increases in temperature and degrades as it travels aft, both of which result in a decrease in cooling and consequent higher wall temperature traveling in the aft direction. To ensure adequate cooling across such a non-uniform thermal profile (typically present in a conventional cooling passage) it is necessary to base the cooling scheme on the cooling requirements of the wall where the thermal load is the greatest, which is typically just upstream of the exit of the cooling passage. As a result, the wall adjacent the inlet of the cooling passage (i.e., where the cooling air within the passage and the film cooling along the outer surface of the wall are the most effective) is often overcooled. The present invention cooling circuit advantageously avoids undesirable overcooling by providing a method and an apparatus capable of creating a heat transfer cooling profile that substantially offsets the profile of the thermal load applied to the wall portion along the length of the cooling circuit.
Another advantage of the present cooling circuits is a decrease in thermal stress within the component wall. Thermal stress often results from temperature gradients within the wall; the steeper the gradient, the more likely it will induce undesirable stress within the wall. The ability of the present cooling circuit to produce a heat transfer profile that substantially offsets the local thermal load profile of the wall decreases the possibility that thermal stress will grow within the wall.
Another advantage of the present cooling circuit is that it decreases the possi
Getz Richard D.
Look Edward K.
McAleenan James M.
United Technologies Corporation
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