Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-10-05
2002-06-11
Verdier, Christopher (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C415S115000
Reexamination Certificate
active
06402470
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.
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 local 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 ineffective cooling.
One cause of ineffective 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.
Another cause of ineffective cooling stems from the inability of some current designs to get cooling air where it is needed. Referring to
FIG. 6
, in a conventional airfoil the trailing edge cooling apertures typically extend between an upstream first cavity and to the pressure side exterior surface. The trailing edge cooling apertures generally include a meter portion and diffuser downstream of the meter portion. The diffuser has a surface profile that includes an upstream edge and a downstream edge. Under typical operating conditions: the static pressure (P
1
) at the upstream edge is greater than the static pressure (P
2
) at the exit of the meter portion; the static pressure (P
3
) at the entrance to the meter portion is equal to or less than the static pressure (P
2
) at the exit of the meter portion; and the static pressure (P
3
) at the entrance to the meter portion is equal to that within the cavity (P
4
). The relative static pressure values may be expressed as follows: P
1
>P
2
, P
2
≧P
3
, and P
3
=P
4
. Note that these pressures reflect the static pressure of the flow, which may not equal the total pressure at any particular position. Total pressure is the sum of the dynamic pressure and the static pressure of the flow at any particular position. The dynamic pressure reflects the kinetic energy of the flow by considering the flow's velocity at that particular position.
In those applications where the above pressure profile exists, cooling apertures (shown in phantom for explanation purposes) cannot be disposed between the first cavity and the outer surface of the airfoil because of the pressure difference across the apertures. Specifically, the static pressure P
1
at the outer surface, which is greater than the static pressure P
4
in the first cavity (i.e., P
1
>P
4
), would cause undesirable hot gas inflow through the apertures. Cooling apertures upstream of the trailing edge must tap into a second cavity upstream of the first cavity that contains cooling air having a static pressure P
5
) greater than the static pressure at the trailing edge (P
1
; P
5
>P
1
). For practical reasons, cooling apertures tapped into the second cavity are spaced a relatively long distance from the trailing edge cooling apertures. Cooling air exiting from those apertures is often ineffective at cooling the region upstream of the trailing edge cooling apertures located on the pressure side.
Hence, what is needed is a cooling apparatus and method that uses less cooling air and provides greater cooling effectiveness than conventional cooling schemes, one that helps create a uniform film of cooling air, and one that permits versatility in the positioning of cooling apertures.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of the present invention to provide an apparatus and method for cooling a wall that provides convective cooling within the wall.
It is another object of the present invention to provide an apparatus and a method for initiating film cooling along a wall.
According to the present invention, a cooling circuit is provided disposed between a first wall portion and a second wall portion that includes one or more inlet apertures and one or more exit apertures. The inlet aperture(s) provides a cooling airflow path into the cooling circuit and the exit aperture(s) provides a cooling airflow path out of the cooling circuit. The cooling circuit includes a plurality of first pedestals extending between the first wall portion and the second wall portion. The first pedestals are arranged in one or more rows. According to one aspect of the present invention, adjacent first pedestals in any particular row are separated from one another by an intra-row distance, and adjacent first pedestals in adjacent rows are separated by an inter-row distance. The intra-row distance is greater than inter-row distance.
According to another aspect of the present invention, the passages formed between adjacent first pedestals in adjacent rows include a diffuser to diffuse cooling air flowing through the passage and a pair of throats to accelerate cooling air flow.
An advantage of the present cooling circuit is that it promotes uniformity in the film cooling layer aft of the cooling
Hayes Douglas A.
Joe Christopher R.
Kvasnak William S.
LaFleur Ronald S.
Moroso Joe
United Technologies Corporation
Verdier Christopher
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