High-speed exhaust nozzle

Abstract

The invention relates to a high-speed exhaust nozzle, in particular of a fan or a jet engine, with a characteristic cross-sectional shape that forms a closed contour formed by six continuously connected segments, these segments comprising alternating rectilinear and arcuate segments, shaped symmetrically relative to the axis passing through the centre of the cross-section. Preferably, the cross-sectional shape is defined by a mathematical function that determines the form of an area of even distribution of pressures exerted by a stream of gases flowing through the nozzle according to the invention. The nozzle is characterised by the fact that its cross-section has a shape defined by the following relationships: (I) where the functions γk, k=1,2,3,4,5,6 have the following form (II) for t∈[0;1]. Preferably, at the midpoint of the segments defined by the function (I) for γ2; γ4; γ6, there are gas jet guide vanes pointing towards the centre of the nozzle.

Description

High-speed exhaust nozzle

[0001] The invention relates to a high-speed exhaust nozzle, in particular of a fan or a jet engine, with a characteristic cross-sectional shape defined by a mathematical function that determines the form of an area of even distribution of pressures exerted by a stream of gases flowing through the nozzle according to the invention.

[0002] From patent application EP2239420A2, there are known jet engine exhaust nozzles comprising jet guide vanes used to reduce noise and increase heat exchange.

[0003] A structural solution for guide vanes in an exhaust nozzle presented in document US3092205A is known, wherein the exhaust nozzle is provided with longitudinal wavy outlet jet guide vanes located over the entire perimeter of the nozzle, resulting in a significant noise reduction.

[0004] The solution presented in patent application US3174282A presents a structural solution for shaping an exhaust nozzle that reduces noise. The solution uses asymmetrical ducts that cause the cold and hot streams to mix in the lower part, restricting the flow very slightly and causing a minor drop in efficiency. The nozzle is shaped in such a way that the decreased stream velocity in the lower part is compensated for by increased flow rate.

[0005] Patents US6360528B1 and US6532729B2 present structural solutions for shaping an exhaust nozzle in the form of so-called chevrons (triangular tips located on the perimeter of the exhaust nozzle). These solutions enable noise and thermal signature to be reduced with a low level of mixing of cold and hot flows and minor losses in efficiency.

[0006] From patent application WO2014200401A1, there is known a variable exhaust nozzle for a jet engine. The nozzle comprises an upstream portion, flap means being pivotally connected to the jet engine via the upstream portion. The flap means comprise a downstream portion forming a downstream linear edge. Actuator means are arranged to actuate said flap means for variation of the cross-sectional area of the nozzles between two possible positions. The flap means are skewed. The nozzle comprises shape forming flap means for forming the cross-sectional area, and adjacent flap means having sliding surfaces in continuous contact during said variation.

[0007] From patent application EP3032032A1, there is known an outlet guide grate having an outer wall, inner wall for forming an annular channel and for guiding the hot gas stream, and having at least one guide blade that is arranged between the outer wall and the inner wall. At least one cross-section reducing constriction is arranged between the front edge of the guide blade and the downstream end of the outer wall. At least one absolute constriction is arranged in an area between the leading edge and the downstream end located closer to the trailing edge of the guide blade than to the end.

[0008] From patent application US2005060984A1, there is known a convergent-divergent turbojet nozzle comprising driven divergent flaps, follower divergent flaps interposed between the driven flaps, and means for supplying cooling air to the follower flaps. Said follower flaps have a box structure and have lateral openings for delivering cooling air towards the inner face of said driven flaps, in such a way as to limit the heating up of these flaps when the turbojet is in operation.

[0009] From patent applicationUS4989406A, there is known a turbine assembly that includes an annular fairing and strut subassembly that provides mechanical strength to the turbine assembly and support for the rotor aft bearing. A readily demountable annular outlet guide vane assembly is mounted to the aft of the fairing and strut assembly for deswirling the exhaust gasses which exit the turbine assembly. The aft mounting of the outlet guide vanes allows for an axially shorter and lighter turbine engine design which removes greater inlet swirl than prior designs, with equal or less pressure loss.

[0010] The article titled "The Schwarz type inequality for harmonic mappings of the unit disc with boundary normalization" by Dariusz Partyka and Jozef Zajac presents a series of results for class H harmonic mappings F defined in a unit disk D and with values in this disk. These mappings additionally satisfy the normalisation condition stating that for every k = 0, 1, 2, and almost every z ∈ Tk := {eiθ : 2kπ / 3 ≤ θ ≤ 2(k + 1)π / 3} the radial limit of the function F at point z belongs to an angular sector determined by a convex set spanned by the origin of the coordinate system and the arc Tk, k = 0, 1, 2. The main result presented in the article is a theorem providing a sharp estimation of the magnitude of |F(z)| for z∈D and for all F∈H. Extremal functions yielding the equality in this estimation are given. Further development of this research resulted in the determination of the variability range of the zero for the class H, that is, the set , which was used to determine the cross-sectional shape of a nozzle with three symmetrically arranged longitudinal guides. The validity of using such a nozzle shape has been positively verified empirically.

[0011] The invention is a continuation of work on reducing flow resistance, flow stabilising and reducing noise generated in exhaust nozzles, which is presented in patent PL239213B1: Exhaust nozzle of a turbofan engine. The nozzle presented in this solution is characterised by the fact that its cross-section has a shape defined by the following relationships:

[0012] ,

[0013] where is the radius of the circumcircle of the nozzle cross-section, whereas is a function defined by the formula:

[0014]

[0015] and

[0016] , when for .

[0017] The technical problem to be solved is to achieve as uniform a pressure distribution as possible inside the exhaust nozzle.

[0018] The object of the invention is a high-speed exhaust nozzle. Its essence lies in the fact that its cross-section forms a closed contour formed by six continuously connected segments, these segments comprising alternating rectilinear and arcuate segments, shaped symmetrically relative to the axis passing through the centre of the cross-section.

[0019] In a variant, gas jet guide vanes pointing towards the centre of the cross-section arearrangedalong three rectilinear segments of the cross-section.

[0020] Preferably, the cross-section has a shape defined by the following relationships:

[0021]

[0022] where the functions have the following form for

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] Optionally, at the midpoint of the segments defined by the function

[0030] for , there are gas jet guide vanes pointing towards the centre of the nozzle.

[0031] The object of the invention is presented in an embodiment in the drawing, where the individual figures present:

[0032] Fig. 1—a cross-sectional outline of the exhaust nozzle described by the function ,

[0033] Fig. 2—a cross-sectional outline of the exhaust nozzle with stream guide vanes described by the function .Description of Embodiments

[0034] The main advantage resulting from the use of the present invention is that the given shape of the exhaust nozzle provides a fairly uniform pressure distribution within the jet. This translates into reduced losses related to turbulences resulting from a non-uniform pressure distribution within the jet and at its edge, as is the case with a classic nozzle. A particular improvement in these properties is noticeable at high gas flow rates. The conditions that are considered in the mathematical model are satisfied by gas flows at supersonic speeds. The performed tests proved the formation of air areas in the corners and against the walls where the thrust is significantly reduced in relation to the central part of the nozzle.Examples

[0035] In the example shown in the drawing, the exhaust nozzle of the hot gas path of the jet engine has a cross-section with a shape defined by the following relationships:

[0036]

[0037] where is a function satisfying the conditions:

[0038]

[0039] and

[0040]

[0041] The conversion of a formula defining a closed curve in polar coordinates results in equivalent equations in the Cartesian coordinate system:

[0042] The equation results in

[0043]

[0044]

[0045] Consider the following cases:

[0046] Case 1.

[0047] If is assumed for ,

[0048] then and for , hence

[0049]

[0050] therefore, the equations

[0051]

[0052] describe the set .

[0053] Case 2.

[0054] If is assumed for , then and for , hence

[0055]

[0056]

[0057]

[0058]

[0059] Therefore, the equations

[0060]

[0061] describe the set .

[0062] Case 3.

[0063] The equation , substituted into case 1,

[0064] where , gives

[0065]

[0066]

[0067]

[0068]

[0069]

[0070] Therefore, the equations

[0071]

[0072] describe the set .

[0073] Case 4.

[0074] The equation , substituted into case 2, where , gives

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084] Therefore, the equations

[0085]

[0086] describe the set .

[0087] Case 5.

[0088] The equation , substituted into case 3, where , gives

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] Therefore, the equations

[0097]

[0098] describe the set .

[0099] Case 6.

[0100] The equation , substituted into case 4, where , gives

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] Therefore, the equations

[0111]

[0112] describe the set .

[0113] In particular, the object of the invention has been adapted to be mounted on a twin-flow turbofan engine.

Claims

A high-speed exhaust nozzlecharacterisedin thatits cross-section forms a closed contour formed by six continuously connected segments, these segments comprising alternating rectilinear and arcuate segments, shaped symmetrically relative to the axis passing through the centre of the cross-section.The nozzle according to claim 1,characterisedin thatgas jet guide vanes pointing towards the centre of the cross-section are arranged along three rectilinear segments of the cross-section.The nozzle according to claim 1,characterisedin thatits cross-section has a shape defined by the following relationships:where the functionshave the following form forThe nozzle according to claim 3, characterised in that at the midpoint of the segments defined by the functionfor, there are gas jet guide vanes pointing towards the centre of the nozzle.

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