Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
2000-12-20
2002-08-06
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
With safety device
C244S13400A
Reexamination Certificate
active
06427434
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the deicing of air inlet cowls of jet engines, particularly aircraft engines.
It is known that, if necessary (as a preventative measure against the formation of ice or to eliminate ice already formed), the leading edge of the air inlet cowl of such engines is deiced by heating it with pressurized hot air tapped from said engine and supplied to said leading edge by a hot air circulation circuit.
To this end, an air inlet cowl such as this comprises:
a hollow leading edge delimiting an internal peripheral chamber closed by an internal partition (or frame) and equipped with orifices placing said internal chamber in communication with the outside; and
a pipe which can be connected, at its rear end which is the opposite end to said leading edge, to said hot air circulation circuit and, at its front end toward the leading edge, to an injector injecting said hot air into said internal chamber.
Thus, the pressurized hot air injected by said injector sweeps through said internal peripheral chamber, heating it up, and is discharged through said orifices.
DESCRIPTION OF THE PRIOR ART
U.S. Pat. No. 5,365,731 already discloses an air inlet cowl of this type comprising a number of such hot air discharge orifices made directly in the leading edge of said cowl, the rate of flow of the deicing hot air being controlled by the cross section of said orifices. A known air inlet cowl such as this has the major drawbacks of weakening the leading edge of said cowl (which happens to be the most vulnerable part of an engine nacelle, because it is located at the front, and to be difficult to repair because of its large size) and of substantially degrading the aerodynamic performance of said cowl. Specifically, as far as the latter drawback is concerned, this is because said orifices are located in a shape of leading edge that encourages scooping — and therefore makes the ejection of hot air difficult — this being true throughout all the phases of flight of the aircraft when the deicing is not in operation. In addition, the ejection orifices produce a large ejection area, which leads to drag over a high proportion of the leading edge, this drag being accentuated by the fact that the surface of the nacelle immediately downstream of this aerodynamically polluted surface, is also generally very disturbed, which means that it generates additional drag. Furthermore, in a known air inlet cowl such as this, it is difficult to correct the ejection cross section during flight trials, because this section consists of orifices made in a very large part (the leading edge).
Another source, document EP-A-0 205 283, discloses an air inlet cowl in which said pressurized hot air supply pipe is surrounded by an enveloping metallic structure comprising pipework, the free end of which forms an orifice used for ejecting deicing air to the rear of the leading edge of said cowl. This then avoids the aforementioned drawbacks but, in this known device, the rate of flow of hot air is controlled by the cross section of said ejection pipework, as well as by the orientation of fins located at the free end thereof. This results in poor control over the ejection rate and in layers of hot air on the outside. In addition, the ejection of the hot air is highly concentrated, which may damage nearby structures which are sensitive to heat. In any case, a device such as this is the source of significant thermal radiation, also with the risk of damaging said structures. Finally, the device is expensive because it consists of many parts which have to be assembled using joints whose life is limited because they are subjected to high temperatures.
Also known, for example from document GB-A-2 259 679 , is an air inlet cowl in which the deicing hot air is discharged to the outside by bent pipework passing through said internal partition to eject the hot air at the rear of said leading edge. Here again, the rate of flow of hot air is controlled by the cross section of the pipework and by the orientation of fins arranged therein. This air inlet cowl therefore again encounters the same drawbacks as those mentioned hereinabove with regard to document EP-A-0 205 283.
Finally, document EP-A-0 536 089 discloses an air inlet cowl in which said internal partition is equipped with a trough-shaped duct directed toward the rear of the leading edge and open toward the periphery of said air inlet cowl. The trough-shaped duct is closed off by a plate pierced with a multitude of identical rectangular orifices, whose direction is orthogonal to the leading edge, said orifices being aligned parallel to the latter.
By virtue of this arrangement, said orifices, which serve to discharge to the outside the pressurized hot air which has heated up said leading edge, may be in the part of said cowl that is located just behind said leading edge. This therefore means that the leading edge, which is a part which is sensitive from the aerodynamic point of view in terms of engine performance and from the maintenance point of view because it is exposed to various impacts, is not weakened by said orifices. However, an arrangement such as this does not make it possible to optimize the ejection of the deicing hot air either aerodynamically or thermally or acoustically, particularly because:
the jets of hot air passing through said rectangular orifices tend to group together downstream of said plate, which gives rise to significant aerodynamic drag and detracts from the cooling of said jets (the thermal radiation of which thus runs a risk of burning the outer surface — generally made of composite material — of said cowl downstream of said plate); and
the jets of hot air passing through the lateral rectangular orifices widen laterally and burn the lateral surface, also made of composite material, of said cowl, which surface is located laterally to said plate.
Furthermore, such orifices give rise to aerodynamic noise, whistling, etc.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome these drawbacks.
To this end, according to the invention, the air inlet cowl for a jet engine, particularly for an aircraft, said air inlet cowl being equipped, at the front, with means for deicing its leading edge and for this purpose comprising:
a hollow leading edge delimiting an internal peripheral chamber which is closed by an internal partition, said internal partition being equipped with a trough-shaped duct directed toward the rear of said leading edge and open toward the periphery of said air inlet cowl;
a pipe which can be connected, at its rear end which is the opposite end to said leading edge, to a pressurized hot air circuit and, at its front end toward said leading edge, to an injector injecting said pressurized hot air into said internal chamber; and
a calibration piece made of a material resistant to high temperatures and forming part of the external surface of said cowl, to the rear of said leading edge, said piece closing off said trough-shaped duct and being pierced with orifices to place said internal chamber in communication with the outside, said orifices being distributed at least roughly parallel to said leading edge and serving to calibrate the flow of pressurized hot air ejected by said trough-shaped duct, while deflecting away from said cowl the pressurized hot air jets resulting from the passage of said flow of hot air through said orifices, is noteworthy in that said orifices form an arrangement such that at least two pressurized hot air jets passing through two adjacent orifices have, downstream of said calibration piece, different inclinations with respect to said calibration piece, and in that said calibration piece extends longitudinally in said external surface of said cowl, toward the rear thereof, to act as thermal protection for said cowl with respect to said hot air jets passing through said orifices.
Thus, said orifices allow control over the rate of ejection and, also, make it possible to obtain favorable heat exchange between the ejected hot air and the external ambient air whil
Porte Alain
Viala Stephane
Aerospatiale Matra Airbus
Koczo Michael
Stevens Davis Miller & Mosher LLP
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