JP2015068264A - Reflected electromagnetic wave attenuation structure for aircraft-engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflected electromagnetic wave attenuation structure for an aircraft-engine capable of suppressing detection by an electromagnetic wave approaching from backward.SOLUTION: A reflected electromagnetic wave attenuation structure for an aircraft-engine includes: a plurality of guide vanes 13 arranged radially from a side surface 11a of a tail cone 11 provided backward of a central portion of a turbine 12 toward an inner surface 10a of an exhaust duct 10, and for rectifying combustion gas discharged from the turbine 12 in a direction of a rotary shaft 12a of the turbine 10; and an electromagnetic wave absorption section 15 formed on the side surface 11a of the tail cone 11 and for absorbing an electromagnetic wave. The guide vanes 13 are arranged curved in a circumferential direction of the turbine 12 so as to visually shield the turbine 12 and partially overlapped with one another if the turbine 12 is viewed from backward of the turbine 12 along the rotary shaft 12a of the turbine 12. The guide vanes 13 each include a rear end portion 13r forming a part of a paraboloid focusing on the electromagnetic wave absorption section 15 and for reflecting the electromagnetic wave approaching from backward of an aircraft engine intensively to the electromagnetic wave absorption section 15.

Description

  The present invention relates to a structure that is provided in an aircraft engine and suppresses detection of the aircraft engine by attenuating reflected waves of electromagnetic waves entering from behind.

  Military aircraft with stealth characteristics against radar generally use a unique aircraft that reflects radar waves arriving from one direction in another direction, and by using radio wave absorbers that contain components that absorb radar waves. Radar reflection cross section is reduced. Hereinafter, for convenience of explanation, the stealth property with respect to the radar is simply referred to as “stealth property”.

  This demand for stealth is no exception for aircraft engines (hereinafter simply referred to as engines). However, as is well known, the essential purpose of the engine is to obtain the thrust of the fuselage. Therefore, the engine configuration should be designed from an aerodynamic point of view, and stealth must be sacrificed to some extent. Here, the engine means a jet engine including at least a compressor, a combustor, and a turbine, and does not include a reciprocating engine.

  In spite of such circumstances, Patent Document 1 discloses a plurality of guide vanes provided at the rear of the turbine as a countermeasure for improving the stealth of the engine. Specifically, these guide vanes are installed behind the turbine rotor blades, and are arranged radially with the rotation axis of the turbine as the central axis. The rotor blades of the turbine can be regarded as a rotating body that irregularly reflects radar waves coming from behind. On the other hand, the airfoil (cross section) of the guide vane is curved in a substantially S shape, and the airfoil center line (camber line) is directed toward the turbine side and the exhaust port side in the direction of the rotation axis of the turbine. It extends in parallel with. Further, one turbine side portion of the adjacent guide vane and the other exhaust port side portion overlap each other when viewed from the rear of the engine. Accordingly, the plurality of guide vanes visually shields the turbine blades, and prevents radar waves coming from behind from being directly applied to the turbine blades. That is, direct reflection of radar waves to the rear of the engine is suppressed, and stealth is improved.

  In addition to the above function, the guide vane of Patent Document 1 rectifies the exhaust gas from the turbine in the engine in the discharge direction (that is, the direction opposite to the traveling direction of the airframe). That is, these guide vanes reduce the thrust by converting the component of the exhaust gas velocity component along the circumferential direction of the turbine (hereinafter referred to as the circumferential component) into the exhaust gas discharge direction. It is preventing.

US Pat. No. 7,195,456

  In order to suppress the reflection of the radar wave by the moving blades of the turbine, as in Patent Document 1, the guide vanes are curved in the arrangement direction (circumferential direction), and the adjacent guide vanes are partially connected from the rear. What is necessary is just to arrange | position so that it may overlap seeing.

  However, it is necessary to increase the number of guide vanes in order to visually shield the turbine from behind and to avoid interference with the exhaust gas flow as much as possible. As described above, the curved portion is formed in the guide vane. When the number of guide vanes is small, it is necessary to enlarge the curved portion in the circumferential direction in order to obtain visual shielding of the turbine rotor blades. This means that the above-described rectification cannot be sufficiently achieved because the circumferential component of the exhaust gas is temporarily increased. Therefore, it is necessary to increase the number of guide vanes in order to obtain appropriate visual shielding and appropriate rectification.

  However, when the number of guide vanes is increased, the number of guide vane rear ends is inevitably increased. In addition, the rear end portion is exposed when viewed from the rear of the engine. Accordingly, the radar wave entering from behind is reflected by the rear end portion in the direction opposite to the approach direction. The intensity of the reflected radar wave is proportional to the number of installed guide vanes. That is, if the number of guide vanes is increased, the possibility that radar waves are easily captured increases.

  In view of such circumstances, an object of the present invention is to provide a reflected electromagnetic wave attenuation structure for an aircraft engine that attenuates a reflected wave of an electromagnetic wave such as a radar wave entering from behind.

  One aspect of the present invention is an aircraft engine reflected electromagnetic wave attenuation structure, an exhaust duct provided at the rear of a turbine, a tail cone provided at the rear of a central portion of the turbine in the exhaust duct, and the tail cone A plurality of guide vanes installed radially from the side surface of the exhaust duct toward the inner surface of the exhaust duct and rectifying the combustion gas discharged from the turbine in the direction of the rotation axis of the turbine; Each of the guide vanes is configured to visually shield the turbine when viewed from the rear of the turbine along the rotation axis of the turbine. The guide vanes are focused on the electromagnetic wave absorber. And summarized in that a rear end portion that reflects intensively toward the electromagnetic wave entering to form part of the object surface from the rear of the aircraft engine to the electromagnetic wave absorber.

  The electromagnetic wave absorbing portion may be an electromagnetic wave absorbing member provided locally on the side surface of the tail cone.

  The electromagnetic wave absorber may be locally formed on the side surface as a recess opening on the side surface of the tail cone.

  The electromagnetic wave absorbing portion may include a flange portion that confines the electromagnetic wave in the concave portion in the opening portion of the concave portion.

  Each said guide vane is provided in the said rear end part, and reflects the electromagnetic wave which approachs from the back of the said aircraft engine in the state which shifted only half wavelength with respect to the electromagnetic wave reflected from the said rear end part May be included.

  ADVANTAGE OF THE INVENTION According to this invention, the reflected electromagnetic wave attenuation | damping structure of the aircraft engine which attenuates the reflected waves of electromagnetic waves, such as a radar wave which approachs from back, can be provided. That is, it is possible to provide an aircraft engine with improved stealth properties against electromagnetic waves.

It is a figure which shows an example of the aircraft engine provided with the reflected electromagnetic wave attenuation structure which concerns on embodiment of this invention. It is a schematic block diagram of the reflected electromagnetic wave attenuation structure which concerns on embodiment of this invention. It is a figure which shows the positional relationship of the guide vane and electromagnetic wave absorption part which concern on embodiment of this invention. It is a figure which shows the some example of the electromagnetic wave absorber which concerns on embodiment of this invention. It is an enlarged view which shows the modification of the rear-end part of the guide vane which concerns on embodiment of this invention.

  Hereinafter, a reflected electromagnetic wave attenuation structure for an aircraft engine according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted. In the following description, an aircraft engine is simply referred to as an engine. This engine means a jet engine such as a turbojet engine or a turbofan engine including at least a compressor, a combustor, and a turbine, and does not include a reciprocating engine.

  FIG. 1 is a diagram illustrating an example of an engine provided with a reflected electromagnetic wave attenuation structure according to the present embodiment. FIG. 2 is a schematic configuration diagram of the reflected electromagnetic wave attenuation structure according to the present embodiment. As shown in FIG. 1, this structure is provided in the rear part of the engine 1 in order to attenuate the reflected waves of electromagnetic waves such as radar waves entering from behind. The engine 1 is composed of known devices such as a compressor, a combustor, and a turbine, and detailed illustration in this paper is omitted.

  As shown in FIG. 2, the reflected electromagnetic wave attenuation structure includes an exhaust duct 10 and a tail cone 11. The exhaust duct 10 is formed in a cylindrical shape with the rotation axis (rotation center axis) 12 a of the turbine 12 as a central axis, and is provided at the rear of the turbine 12. The exhaust duct 10 is connected to the rear part of a case (not shown) that accommodates the turbine 12, and has an exhaust port (not shown) at the rear. That is, the exhaust duct 10, together with the tail cone 11 and the guide vane 13 described later, discharges exhaust gas from the turbine 12 in the discharge direction G (rear of the engine 1, that is, rightward in FIGS. 1 and 2). Define the flow path. The exhaust duct 10 is formed to extend rearward. Accordingly, electromagnetic waves other than the electromagnetic wave having the highest intensity entering from behind the engine 1 in parallel with the traveling direction of the aircraft (not shown) are diffusely reflected and attenuated by the exhaust duct 10. That is, the reflected electromagnetic wave attenuation structure of the present embodiment may be designed mainly for blocking electromagnetic waves that enter parallel to the traveling direction of the aircraft (not shown).

  The tail cone 11 is provided behind the central portion of the turbine 12 in the exhaust duct 10. The tail cone 11 is formed in a substantially conical shape with the bottom surface facing the turbine 12. That is, the side surface 11a of the tail cone 11 is axisymmetric with respect to the rotating shaft 12a of the turbine 12, and the distance between the side surface 11a and the rotating shaft 12a becomes shorter toward the rear of the engine 1 along the rotating shaft 12a. Yes.

  As shown in FIGS. 2 and 3, the reflected electromagnetic wave attenuation structure includes a plurality of guide vanes 13 provided between the inner surface 10 a of the exhaust duct 10 and the side surface 11 a of the tail cone 11. The plurality of guide vanes 13 are installed radially from the side surface 11 a of the tail cone 11 toward the inner surface 10 a of the exhaust duct 10. The plurality of guide vanes 13 rectify the exhaust gas flowing between the side surface 11 a of the tail cone 11 and the inner surface 10 a of the exhaust duct 10. Specifically, the plurality of guide vanes 13 rectify the combustion gas discharged from the turbine 12 in the direction of the rotation axis of the turbine 12 (in other words, the discharge direction G).

  The plurality of guide vanes 13 are curved in the circumferential direction of the turbine 12 so as to visually shield the turbine 12 when viewed from the rear of the turbine 12 along the rotation axis 12a of the turbine 12. Specifically, as shown in FIG. 3, the airfoil center line (camber line) 14 of the guide vane 13 is connected to the rotating shaft 12 a of the turbine 12 from the rear end portion 13 r to the front end portion 13 f of the guide vane 13. After extending substantially in parallel, it curves toward the rotational direction R of the turbine 12. Note that the airfoil center line 14 may be curved toward the rotation direction R of the turbine 12, and then again extend substantially parallel to the rotation shaft 12 a of the turbine 12. As shown in FIG. 3, the side surface of the rear end portion 13 r extends substantially parallel to the rotational axis direction of the turbine 12 in order to rectify the exhaust gas in the rotational axis direction of the turbine 12.

  As shown in FIG. 3, the plurality of guide vanes 13 overlap each other so as to visually shield the turbine 12 when viewed along the rotating shaft 12 a of the turbine 12 from the rear of the engine 1. Array. In other words, one front end (turbine side portion) 13f of the adjacent guide vane 13 and the other rear end (exhaust port side portion) 13r overlap each other when viewed from the rear of the turbine 12 (engine 1). Accordingly, the plurality of guide vanes 13 visually shield the moving blades 12r of the turbine 12, and block the direct entry of radar waves into the moving blades 12r of the turbine 12.

  As shown in FIG. 3, the guide vane 13 has a curved surface 13 a that faces the rear of the engine 1 and curves toward the adjacent guide vane. In the airfoil of the guide vane 13, the curvature of the curved surface 13 a is set so as to reflect the electromagnetic wave 30 as a radar wave entering from the rear of the engine 1 toward the turbine 12 side along the rotation axis 12 a of the turbine 12. Has been. Therefore, when the electromagnetic wave 30 enters between the two guide vanes 13, it is not reflected in the direction opposite to the entering direction, but is repeatedly irregularly reflected between the turbine 12 and the guide vane 13, and as a result, attenuates.

  As shown in FIG. 2, the rear end portion 13 r of the guide vane 13 is formed so as to form a part of a paraboloid 16 with a later-described electromagnetic wave absorbing portion 15 as a focal point. As described above, the electromagnetic wave 30 that has entered between the two guide vanes 13 is reflected toward the turbine 12 by the curved surface 13a and does not return. However, the rear end portion 13r of the guide vane 13 extends rearward of the engine 1 along the rotating shaft 12a of the turbine 12 in order to rectify the exhaust gas. Accordingly, the rear end portion 13r includes a contour having a tangent line orthogonal to the approaching direction of the electromagnetic wave 30 in the airfoil of the guide vane 13. When the rear end portion 13r extends in a direction orthogonal to the rotating shaft 12a of the turbine 12, the electromagnetic wave is reflected toward the generation source in the above contour.

  Therefore, the rear end portion 13r of the present embodiment is formed so as to form a part of the paraboloid 16 with the electromagnetic wave absorbing portion 15 (described later) as the focal point P. The axis of symmetry 16 a of the paraboloid 16 is parallel to the rotational axis 12 a of the turbine 12. Therefore, when the electromagnetic wave 30 enters the rear end portion 13r from the rear of the engine 1 in parallel with the rotating shaft 12a of the turbine 12, for example, the electromagnetic wave 30 is reflected toward the electromagnetic wave absorbing portion 15. That is, the rear end portion 13 r of the guide vane 13 reflects the electromagnetic wave 30 entering from the rear of the engine 1 toward the electromagnetic wave absorbing portion 15 in a concentrated manner. The electromagnetic wave absorber 15 has a finite size (spread). Therefore, even if the approach direction of the electromagnetic wave 30 is slightly inclined from the rotating shaft 12 a of the turbine 12, the electromagnetic wave 30 can be reflected toward the electromagnetic wave absorber 15.

  The electromagnetic wave absorber 15 absorbs the electromagnetic wave 30 reflected from the rear end 13r. As shown in FIG. 2, the electromagnetic wave absorber 15 is provided on the side surface 11 a of the tail cone 11. The electromagnetic wave absorber 15 is provided at least at the focal point P of the paraboloid 16 that forms the rear end portion 13r of the guide vane 13. For example, as shown in FIG. 3, the electromagnetic wave absorber 15 is located on an extension line 17 that extends from the rear end 13 r to the rear of the engine 1 along the rotation axis 12 a of the turbine 12. The electromagnetic wave absorber 15 may be provided on the entire side surface 11a, or the electromagnetic wave absorber 15 may be provided locally on the side surface 11a as shown in FIG. In the latter case, the installation location (formation location) of the electromagnetic wave absorber 15 includes the above-described focal point. The latter is more cost effective than the former.

  4A to 4C show specific forms of the electromagnetic wave absorber 15. The electromagnetic wave absorbing portion 15 shown in FIG. 4A is an electromagnetic wave absorbing member provided locally on the side surface 11 a of the tail cone 11. The electromagnetic wave absorbing member is formed of any one of a conductive electromagnetic wave absorbing material, a dielectric electromagnetic wave absorbing material, a magnetic electromagnetic wave absorbing material, or a combination of at least two of them. The thickness of this member is arbitrary as long as desired conditions such as electromagnetic wave absorption, heat resistance, and mechanical strength are satisfied. For example, the electromagnetic wave absorber 15 may be formed by applying the above-described radio wave absorber to the side surface 11a. Alternatively, a solid electromagnetic wave absorbing member may be prepared in advance and embedded in the side surface 11a. In addition, the shape of the electromagnetic wave absorbing member viewed from the side surface 11a is not limited to a rectangle, and may be another shape such as a circle. Moreover, you may employ | adopt V-shaped shape for the cross-sectional shape of an electromagnetic wave absorption part.

  The electromagnetic wave absorber 15 shown in FIG. 4B is locally formed on the side surface 11 a as a recess 18 that opens on the side surface 11 a of the tail cone 11. The electromagnetic wave 30 reflected from the rear end portion 13r enters the inside of the recess 18 and then repeatedly diffuses and attenuates in the recess 18. The inner surface of the recess 18 is formed of a flat surface, a curved surface, or a combination thereof. In addition, the depth and width of the recess 18 are set to such an extent that irregular reflection of the electromagnetic wave 30 occurs. The shape of the recess 18 viewed from the side surface 11a is not limited to a rectangle, but may be another shape such as a circle.

  As shown in FIG. 4C, the electromagnetic wave absorber 15 may include a flange 19 formed at the opening of the recess 18 in addition to the recess 18 in FIG. The size (diameter or width) of the opening formed by the collar portion 19 is set to a value that takes into account the cutoff frequency. This value is set to the same level as the wavelength of the electromagnetic wave 30, for example. When only the recess 18 shown in FIG. 4B is formed, the electromagnetic wave 30 that has entered the recess 18 may escape from the recess 18 due to subsequent reflection. The collar portion 19 confines the electromagnetic wave 30 in the recess 18. However, it is unlikely that the final traveling direction of the electromagnetic wave 30 that has escaped from the recess 18 is parallel to the initial approach direction. The shape of the opening as viewed from the side surface 11a is not limited to a rectangle, and may be another shape such as a circle.

  According to the present embodiment, the arrangement and curvature of the guide vanes 13 visually shield the turbine as viewed from the rear of the engine 1, and electromagnetic waves entering from the rear of the engine are directly incident on the turbine (blade). Prevent and diffusely reflect. Therefore, it is possible to suppress the turbine itself from being captured by the radar.

  Further, the rear end portion 13r of the guide vane 13 is formed so as to form a part of the paraboloid 16 with the electromagnetic wave absorbing portion 15 as a focal point. The electromagnetic wave absorber 15 is located at the focal point P of the paraboloid 16. Therefore, although the electromagnetic wave 30 incident on the rear end portion 13r is reflected rearward of the engine 1, the traveling direction thereof is concentrated toward the electromagnetic wave absorbing portion 15. The electromagnetic wave absorber 15 attenuates the electromagnetic wave 30 that has arrived by absorption or irregular reflection. As a result, the reflection of electromagnetic waves entering from behind the engine 1 in the direction opposite to the entering direction is suppressed. That is, it is possible to provide an aircraft engine in which reflected waves of electromagnetic waves such as radar waves entering from behind are attenuated to improve stealth property against electromagnetic waves.

  As shown in FIG. 5, the guide vane 13 may include a phase interference unit 20 provided at the rear end portion 13r. The phase interference unit 20 is provided on the surface of the rear end portion 13r, and reflects the electromagnetic wave 30 entering from the rear of the engine 1 with a phase shifted by half a wavelength with respect to the electromagnetic wave 30 reflected from the rear end portion 13r. The phase interference unit 20 is formed, for example, by applying an electromagnetic wave absorbing material to the surface of the rear end part 13r. In this case, the thickness T of the applied electromagnetic wave absorbing material is set to a value that allows the electromagnetic wave 30 to pass through the phase interference unit 20 by a distance of 1/4 of the wavelength. A part of the electromagnetic wave 30 is reflected on the surface of the phase interference unit 20, and the rest travels in the phase interference unit 20. The electromagnetic wave 30 traveling in the phase interference unit 20 is reflected by the surface of the rear end portion 13r and is emitted from the phase interference unit 20. However, the phase of the electromagnetic wave emitted from the phase interference unit 20 is shifted by a half wavelength from the phase of the electromagnetic wave reflected by the surface of the phase interference unit 20. Therefore, the sum of the intensities of the electromagnetic waves 30 reflected from the phase interference part 20 and the rear end part 13r is reduced due to mutual phase interference. Even when the rear end portion 13r is formed as a paraboloid, the reduction effect is slightly weakened, but such a reduction in strength can be obtained. Therefore, by combining with the electromagnetic wave absorber 15 described above, attenuation of the reflected wave of the electromagnetic wave can be promoted.

  In addition, this invention is not limited to embodiment mentioned above, is shown by description of a claim, and also includes all the changes within the meaning and range equivalent to description of a claim.

P Focus 1 engine (aircraft engine)
DESCRIPTION OF SYMBOLS 10 Exhaust duct 11 Tail cone 12 Turbine 13 Guide vane 13r Rear end part 15 Electromagnetic wave absorption part 16 Parabolic surface 18 Recessed part 19 Gutter part 20 Phase interference part 30 Electromagnetic wave

Claims (5)

A reflection electromagnetic wave attenuation structure of an aircraft engine,
An exhaust duct provided behind the turbine;
A tail cone provided behind the center of the turbine in the exhaust duct;
A plurality of guide vanes installed radially from the side surface of the tail cone toward the inner surface of the exhaust duct and rectifying the combustion gas discharged from the turbine in the direction of the rotation axis of the turbine;
Provided on the side surface of the tail cone, and comprising an electromagnetic wave absorbing portion for absorbing electromagnetic waves,
Each of the guide vanes is curved in the circumferential direction of the turbine so that the turbine is visually shielded when viewed from the rear of the turbine along the rotation axis of the turbine, and a part of each guide vane is mutually Arranged so that they overlap,
Each of the guide vanes has a rear end portion that forms a part of a paraboloid with the electromagnetic wave absorbing portion as a focal point and intensively reflects electromagnetic waves entering from the rear of the aircraft engine toward the electromagnetic wave absorbing portion. A reflected electromagnetic wave attenuation structure for an aircraft engine, comprising:   The reflected electromagnetic wave attenuation structure for an aircraft engine according to claim 1, wherein the electromagnetic wave absorbing portion is an electromagnetic wave absorbing member locally provided on the side surface of the tail cone.   The reflected electromagnetic wave attenuation structure for an aircraft engine according to claim 1, wherein the electromagnetic wave absorbing portion is locally formed on the side surface as a recess opening on the side surface of the tail cone.   4. The reflected electromagnetic wave attenuation structure for an aircraft engine according to claim 3, wherein the electromagnetic wave absorbing portion includes a flange portion for confining the electromagnetic wave in the concave portion at an opening portion of the concave portion.   Each said guide vane is provided in the said rear end part, and reflects the electromagnetic wave which approachs from the back of the said aircraft engine in the state which shifted only half wavelength with respect to the electromagnetic wave reflected from the said rear end part The reflected electromagnetic wave attenuation structure for an aircraft engine according to any one of claims 1 to 4, characterized by comprising:

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