Unducted aeroengines

Abstract

The unducted aeroengines comprise a propeller extending around a main axis and comprising at least one rotor blade having a variable pitch around a rotor pitch axis. For each variable pitch rotor blade, the maximum thickness relative position (x°_EPmax) decreases from a first relative height (R1) comprised between 20% and 40% to a second relative height (R2) comprised between 55% and 100%, wherein the maximum thickness relative position (x°_EPmax) is comprised between 15% and 35%, preferably between 20% and 30%.

Description

Technical Field

[0001] This invention relates to a ductless aero-engine for aircraft. Background Technology

[0002] The blades of a ductless aircraft engine propeller (also known as an "open fan" or "open rotor") can be subjected to upstream flow that is neither uniform nor parallel to the engine axis; this is called "incident" flight, and it occurs particularly during the takeoff or landing phase of the aircraft and / or in crosswinds. For example, when an aircraft engine is mounted under a wing, the presence of the wing can induce an upward flow at the propeller height, which increases the incident flow experienced by the propeller blades. In this case, increased forces and moments are generated in the propeller plane. These forces and moments are called "1P loads" (or "p-factors") and can be determined from a mechanical engineering perspective in the design.

[0003] At incidence, the propeller not only provides thrust; it also generates vertical and lateral loads and moments, which in some cases can be as large as the thrust itself. These loads are non-stationary and depend on the azimuth position relative to the main axis of the blade in question. When an aircraft engine is mounted under the wing, the downward-facing propeller blades (the blades at the 3 o'clock position when viewed from the front, with the propeller rotating clockwise) experience increased incidence and therefore bear greater loads, unlike the upward-facing blades (the blades at the 9 o'clock position when viewed from the front, with the propeller rotating clockwise), to which a smaller load is applied. Therefore, during one rotation of the engine, a single propeller blade bears different loads depending on its azimuth position.

[0004] An aircraft engine may also include a stator (or propeller) located downstream of the propeller, and its blades may have variable incidence depending on their azimuth position.

[0005] USF (upstream propeller-downstream stator) or CROR (upstream propeller-downstream propeller) applications can also be considered. High-speed propellers (without a downstream row of blades) also fall within the scope of this invention. A high-speed propeller is defined as a propeller capable of flying at a speed greater than M=0.7 in CR mode.

[0006] The advantage of a downstream stator or downstream propeller is that it utilizes the yaw of the flow caused by the upstream propeller, thereby improving the efficiency of the aircraft engine. It should also be noted that upstream incident radiation (from the aircraft or from devices such as wings, masts, etc.) is not completely filtered out by the upstream propeller. In addition to variations in IP load, the downstream stator or downstream propeller may experience different incident radiation (due to the aircraft's incident radiation) depending on its azimuth position.

[0007] However, at high incidence, there is a risk of airflow separation, meaning there is a risk that the airflow may separate from the suction or pressure side. For example, this separation can occur on the suction side of propeller blades and between the mid-span and free end, where the propeller blades are subjected to high aerodynamic loads during takeoff and / or during flight phases characterized by high incidence or high thrust. Airflow separation at the height of the propeller blades and / or stator can impair the performance of both the aero-engine and the aircraft (e.g., when the aircraft's wings or lifting surfaces are exposed to separated airflow originating from the aero-engine blades).

[0008] Therefore, it may be desirable to evaluate the performance of propeller blades (and / or stator blades) under various incident conditions from mechanical, aerodynamic and acoustic perspectives. Summary of the Invention

[0009] Therefore, a ductless aero-engine is proposed, the ductless aero-engine comprising a propeller extending about a main axis and including at least one rotor blade, the rotor blade having a variable pitch about a rotor pitch axis, each variable pitch rotor blade comprising: -front edge; - trailing edge; - The inner radius at the leading edge relative to the principal axis; -Outer radius relative to the principal axis at the leading edge; - The inner radius relative to the principal axis at the trailing edge; -Outer radius relative to the principal axis at the trailing edge; -At each relative height relative to the principal axis, from the inner radius to the outer radius, at the leading edge and / or at the trailing edge: • A chord, which extends in a cross-sectional plane perpendicular to the rotor pitch axis or the radial component of the pitch axis, passes through the relative height and connects the leading edge to the trailing edge, and • The thickness in the cross-sectional plane, which varies according to the relative position along the chord from the leading edge to the trailing edge, and reaches its maximum value at a relative position known as the maximum thickness relative position; The feature is that, for each variable pitch rotor blade, the maximum thickness relative position decreases from a first relative height between 20% and 40% to a second relative height between 55% and 100%, wherein the maximum thickness relative position is between 15% and 35%, preferably between 20% and 30%.

[0010] The present invention may also include one or more of the following optional features in any technically possible combination.

[0011] Optionally, the activity factor of the variable pitch rotor blade is between 145 and 230, preferably between 155 and 205, and its maximum thickness relative position reaches a maximum at a relative height of less than 40%, preferably less than 30%, more preferably less than 20%.

[0012] Optionally, for each variable pitch rotor blade, the maximum thickness relative position reaches its maximum value at the relative height closest to 0%.

[0013] Optionally, for each variable pitch rotor blade, there is at least one relative height, said at least one relative height having a maximum thickness relative position greater than 20%, preferably greater than 25%, more preferably greater than 30%.

[0014] Optionally, for each variable pitch rotor blade, at the first relative height, the maximum thickness relative position is between 20% and 40%, preferably between 25% and 35%, and more preferably between 26% and 32%.

[0015] Optionally, for each variable pitch rotor blade, the variation of the maximum thickness relative position between the relative height closest to 0% and the first relative height is less than the variation between the first relative height and the second relative height.

[0016] Optionally, for each variable pitch rotor blade, for all relative heights, the maximum thickness relative position is maintained between 10% and 40%, preferably between 15% and 35%, and more preferably between 20% and 34%.

[0017] Optionally, for each variable pitch rotor blade, the maximum thickness relative position is strictly reduced from 0% of the relative height to 100% of the relative height.

[0018] Optionally, for each variable pitch rotor blade, the maximum thickness relative position has at least one local maximum and / or one local minimum in relative height.

[0019] Optionally, at each relative height, each variable pitch rotor blade also has, on the one hand, a chord length defined as the distance along the chord separating the leading edge from the trailing edge, and on the other hand, a normalized maximum thickness defined as the maximum thickness at the relative height divided by the chord length, the normalized maximum thickness decreasing strictly from the relative height closest to 0% to 60% of the relative height, preferably to 70% of the relative height.

[0020] Optionally, for each variable pitch rotor blade, the normalized maximum thickness at the relative height closest to 0% is between 0.1 and 0.25, preferably between 0.13 and 0.2.

[0021] Optionally, for each variable pitch rotor blade, the normalized maximum thickness at the relative height closest to 100% is between 0.02 and 0.048, preferably between 0.03 and 0.06.

[0022] Optionally, for each variable pitch rotor blade, the normalized maximum thickness decreases from the relative height closest to 0% until, at a relative height between 25% and 50%, the normalized maximum thickness reaches one-quarter of the normalized maximum thickness at the relative height closest to 0%.

[0023] Optionally, for each variable pitch rotor blade, the normalized maximum thickness is strictly reduced from the relative height closest to 0% to the relative height closest to 100%.

[0024] Optionally, for each variable pitch rotor blade, the normalized maximum thickness increases from 70% of the relative height, preferably from 80% of the relative height, to 100% of the relative height.

[0025] Optionally, for each variable pitch rotor blade, the normalized maximum thickness at the closest relative height to 100% is less than or equal to 3 times, preferably 2.5 times, and more preferably 2 times, the normalized maximum thickness at 70% relative height.

[0026] Alternatively, the aircraft engine may also include a housing and fixed, ductless stator blades mounted on the housing.

[0027] An aircraft is also proposed, which includes a ductless aero-engine according to the invention. Attached Figure Description

[0028] The invention will be better understood through the following description, given only by way of example and with reference to the accompanying drawings, in which: - Figure 1 This is a cross-sectional view of an aircraft engine from which the present invention can be implemented. - Figure 2 As shown Figure 1 The image shown is a side view of the rotor blades of an aircraft engine propeller. - Figure 3 yes Figure 2 A cross-sectional view of the rotor blades. - Figure 4 It shows Figure 2 Another cross-sectional view of the rotor blade is shown, along with a graph illustrating the variation in the thickness of the rotor blade's cross-section from the leading edge to the trailing edge. - Figure 5 It is a graph showing the change in the relative position of the maximum thickness as a function of the relative height along the rotor blades. - Figure 6 This is a graph showing the normalized maximum thickness as a function of the relative height along the rotor blades. - Figure 7 The cross-section of the rotor blade is shown, with its maximum thickness located at a certain distance from the leading edge, and... - Figure 8 The cross-section of the rotor blade is shown, with its maximum thickness near the leading edge. Detailed Implementation

[0029] refer to Figure 1 The aircraft engine 100 that embodies the present invention will now be described.

[0030] Aircraft engine 100 is ductless (e.g., "ductless single fan" type, also referred to by the abbreviation USF) and is designed to aid in aircraft propulsion. At this stage, it should be clear from the outset that the solution of this invention is applicable to any ductless aircraft engine and / or "counter-rotor open rotor" (also referred to by the abbreviation CROR) or "open fan" type aircraft engine (turbine, turbojet, turboprop engine with high-speed propeller, etc.), as some of the aforementioned problems are not necessarily specific to the aforementioned types of aircraft engines.

[0031] First, the aircraft engine 100 includes a housing 102 and a hub 104, which is mounted to pivot about a main axis X relative to the housing 102.

[0032] In the following text, the terms “upstream” and “downstream” will be used to specify the relative positions of the components of the aircraft engine 100 along the main axis X in the direction of airflow PHI from the front to the rear of the aircraft engine 100 and / or the aircraft.

[0033] For example, hub 104 is located upstream of housing 102.

[0034] The aircraft engine 100 also includes a propeller 106, which is a propulsive, ductless rotor mounted on a hub 104, allowing it to pivot relative to the outer casing 102 about a main axis X. The propeller 106 is designed to drive a downstream airflow PHI to propel the aircraft forward. For this purpose, the propeller 106 includes rotor blades 108 (e.g., between 3 and 25, preferably between 10 and 16), arranged, for example, in a single annular row around the main axis X. For example, the rotor blades 108 may all be identical and spaced at a regular angular spacing around the main axis X. Alternatively, irregular angular spacing is conceivable.

[0035] The rotor blades 108 can have variable pitch, with each blade rotating about its own corresponding radial rotor pitch axis Y. The described solution can cover the following cases: - The rotor pitch axis Y is perpendicular to the main axis X, meaning that the rotor pitch axis Y can form a right angle with the main axis X; for example... Figure 1 As shown, the rotor pitch axis Y and the main axis X are projected onto the plane or cross-section of the aero-engine containing the main axis X. - The rotor pitch axis Y is not perpendicular to the main axis X; in other words, the rotor pitch axis Y is inclined; for example, when the rotor pitch axis Y has a longitudinal component (along the direction of the main axis X) and a component perpendicular to the main axis X.

[0036] The aircraft engine 100 also includes an engine 110 for driving a hub 104 and thus driving a propeller 106 via the hub 104. For example, the engine 110 extends into a housing 102. For example, the engine 110 is located downstream of the propeller 106. This arrangement is referred to as a “tractioner.” The engine 110 includes, for example, a turbine, and / or (at least) a turbojet engine, and / or (at least) a turbofan engine, and / or (at least) a turboshaft engine, including, for example, a gas generator that typically includes, from upstream to downstream, at least one compressor, at least one combustion chamber, and at least one power turbine configured to drive the propeller 106. Alternatively, the engine 110 may include, for example, an electric motor and / or (at least) a hydrogen engine and / or (at least) a hybrid power engine: internal combustion and / or electric and / or hydrogen.

[0037] The aircraft engine 100 also includes fixed, ductless stator blades 112 mounted on the housing 102 and downstream of the propeller 106. The fixed stator blades 112 form a stator attached to the housing 102, extending about a main axis X, but not rotatable about the main axis X. The fixed stator blades 112 include stator blades 114, which are arranged, for example, in a single annular row around the main axis X. For example, between 3 and 25 stator blades 114 are provided, preferably between 8 and 14. Preferably, the number of stator blades 114 differs from the number of rotor blades 108 to reduce the noise of the aircraft engine 100. In particular, the number of rotor blades 108 is greater than the number of stator blades 114. In fact, if the number of rotor blades 108 equals the number of stator blades 114, all the wake of the propeller 106 can interact with the stator blades 114 simultaneously, which will increase the noise level. For example, the stator blades 114 may all be identical and spaced at a regular angular interval around the main axis X. Alternatively, the stator blades may be different and / or spaced at an irregular interval around the main axis X in the azimuth direction.

[0038] The fixed stator blades 112 are designed to straighten at least a portion of the airflow PHI passing through the propeller 106 to improve the performance of the aero engine 100. More specifically, the fixed stator blades 112 are intended to counteract the yaw caused by the propeller 106 to improve the performance of the ductless configuration. However, the presence of the fixed stator blades introduces a major noise source from their interaction with the wake of the propeller 106 (and the blade tip vortices when the stator blades 114 are not sufficiently trunculated). Therefore, it is necessary to reduce the noise generated by the fixed stator blades 114 and their interaction with the wake of the propeller 106 while maintaining good aerodynamic performance, as reducing noise emissions and fuel consumption are major challenges for ductless engine configurations.

[0039] At least one stator blade 114 has a variable pitch, with each stator blade revolving around a corresponding radial axis Y'. Ideally, all stator blades 114 should have variable pitch. This allows the flow configuration upstream of the stator blades 114 to be adjusted according to the operating point, thereby improving aerodynamic performance and reducing noise generated by the interaction between the wake of the upstream propeller 106 and the stationary stator blades. In effect, changing the pitch of the stator blades 114 allows for alteration of sound directionality and reduction of pure-tone interference noise.

[0040] For example, the aircraft engine 100 also includes an air inlet 116 for supplying the mains air to the engine 110. The air inlet 116 is located, for example, between the propeller 106 and the fixed stator blades 112.

[0041] refer to Figure 2Each rotor blade 108 first comprises a leading edge BA impacted by the airflow PHI and a trailing edge BF away from the airflow PHI. The leading edge BA extends from the root BA_P (the point on the leading edge BA closest to the main axis X) to the tip BA_T (the point on the leading edge BA furthest from the main axis X). Between the root BA_P and the tip BA_T, the leading edge BA can have curvature in a constant direction (i.e., without any inflection points) and can also be continuous (i.e., without any discontinuities).

[0042] Similarly, the trailing edge BF extends from the root BF_P (the point on the trailing edge BF closest to the principal axis X) to the tip BF_T (the point on the trailing edge BF furthest from the principal axis X). Between the root BF_P and the tip BF_T, the trailing edge BF can have curvature in a constant direction (i.e., without inflection points), and the trailing edge BF can also have smooth curvature (i.e., without any discontinuities).

[0043] Each rotor blade 108 can also be truncated at its free end, as in the example shown, i.e., there is a truncated portion 202 connecting the tips BA_T and BF_T, which is, for example, straight. In this case, there is a curvature discontinuity at the tip BA_T between the leading edge BA and the truncated portion 202, and another curvature discontinuity at the tip BF_T between the truncated portion 202 and the trailing edge BF. Alternatively, the rotor blade 108 can be untruncated, in which case the tips BA_T and BF_T will be identical.

[0044] Each rotor blade 108 has an inner radius Ri_BA (defined as the distance between the main axis X and the root BA_P) at its leading edge BA and an inner radius Ri_BF (defined as the distance between the main axis X and the root BF_P) at its trailing edge BF. Similarly, each rotor blade 108 has an outer radius Re_BA (defined as the distance between the main axis X and the tip BA_T) at its leading edge BA and an outer radius Re_BF (defined as the distance between the main axis X and the tip BF_T) at its trailing edge BF. The inner radii Ri_BA, Ri_BF and the outer radii Re_BA, Re_BF can be measured when the rotor blade 108 is at any pitch angle that allows the aero-engine 100 to operate at its nominal performance, i.e., when the pitch angle of the rotor blade 108 will allow the airflow PHI to be guided from the front to the rear of the aero-engine 100 and / or the aircraft. For example, when the rotor blades 108 are set to the optimal pitch angle for cruise operation (i.e., for a medium-range aircraft, at a Mach number greater than 0.7), the inner radius Ri_BA, Ri_BF and the outer radius Re_BA, Re_BF can be measured.

[0045] To determine the height h_BA between the inner radius Ri_BA and the outer radius Re_BA, the formula can be used. Let h°_BA be the relative height (which can be expressed as a percentage). Therefore, the relative height h°_BA varies between 0% at the inner radius Ri_BA and 100% at the outer radius Re_BA. To determine the height h_BF between the inner radius Ri_BF and the outer radius Re_BF, the formula can be used. Let h°_BF be the relative height (which can be expressed as a percentage). Therefore, the relative height h°_BF varies between 0% at the inner radius Ri_BF and 100% at the outer radius Re_BF. Given relative heights h°_BA and h°_BF, due to the height differences between the roots BA_P and BF_P and / or the tips BA_T and BF_T, for relative heights close to 0% or close to 100%, there may be no leading or trailing edge.

[0046] Therefore, to avoid this problem, a formula can also be used. Define the higher of the two roots BA_P and BF_P ( Figure 2 The example shown is BF_P) and the lower of the two tips BA_T and BF_T ( Figure 2 The example shown represents the so-called "complete" relative height h°_C between BF_T). Therefore, utilizing this definition of complete relative height, for each relative height h°_C between 0% and 100%, there exists a leading edge and a trailing edge. This allows for the definition of a complete cross-section (i.e., including both the leading and trailing edges) for any relative height h°_C, as will be referenced later. Figure 3 Explanation.

[0047] Therefore, h° can represent h°_BA and / or h°_BF and / or the complete relative height h°_C, since the invention can be implemented using relative heights measured at the leading and / or trailing edges.

[0048] Figure 3 The cross-section or aerodynamic profile of the rotor blade 108 along the cross-sectional plane is shown. This cross-sectional plane can be defined in several ways: - When the pitch axis Y is perpendicular to the principal axis X, the cross-sectional plane can be perpendicular to the pitch axis Y and pass through it at a certain relative height h°. - When the pitch axis Y is inclined relative to the main axis X, the cross-sectional plane can be perpendicular to the radial component of the pitch axis Y and pass through at a certain relative height h°.

[0049] As can be seen, the rotor blade 108 has a concave pressure side 302 and a convex suction side 304 connected to each other by the leading edge BA and the trailing edge BF, respectively. For example, the trailing edge BF can be characterized by a truncation to simplify the manufacturing process, as shown in the second small figure in the figure.

[0050] The leading edge BA and trailing edge BF are connected by a chord 306 extending in the cross-sectional plane and separated by a distance (referred to as chord length c) along this chord 306. The orientation of the chord 306 and chord length c can vary depending on the relative height h° considered. The angle between the chord 306 and the axis P perpendicular to the principal axis X defines the pitch angle in the cross-sectional plane. .

[0051] One parameter that provides an initial estimate of the chord length distribution 5 along the span or radial direction of the rotor blade 108 is its activity factor FA, which is defined as follows: Where Ri corresponds to the inner radius Ri_BA of the rotor blade 108 at the leading edge BA, or the inner radius Ri_BF of the rotor blade 108 at the trailing edge BF; Re corresponds to the outer radius Re_BA of the rotor blade 108 at the leading edge BA, or the outer radius Re_BF of the rotor blade 108 at the trailing edge BF (see [reference]). Figure 2 ); Represents the radial distance from the principal axis X divided by the outer radius Re,c. ) represents the radial distance The chord length between the leading edge BA and the trailing edge BF of the aerodynamic section or profile at the location.

[0052] The activity factor FA of the rotor blade 108 is preferably between 145 and 230, more preferably between 155 and 205. Using such a value ensures a sufficient distribution of the chord length c on the rotor blade 108 to guarantee blade balance and mechanical integrity, and, combined with an appropriate thickness distribution optimized to withstand the loads acting on the rotor blade 108 during the flight phase at incident, as proposed in this invention.

[0053] Furthermore, the (average) mid-curve or skeleton line 308 of the cross-section of the rotor blade 108 can be defined. For the cross-section of the blade, the mid-curve or skeleton line 308 is defined as the midline between the pressure side and the suction side. For example, this mid-curve or skeleton line 308 can be obtained by drawing inscribed circles in the cross-section such that the center of these inscribed circles (see dashed circles) defines the mid-curve or skeleton line 308.

[0054] refer to Figure 4 The rotor blade 108 has a thickness EP that varies from the leading edge BA to the trailing edge BF in the cross-sectional plane. For example, the thickness EP is defined as the distance between the pressure side 302 and the suction side 304 of the rotor blade 108, perpendicular to the mid-arc line or frame line 308.

[0055] The thickness EP can be scaled according to the relative position x° from the leading edge BA to the trailing edge BF along the chord 306.

[0056] Therefore, the thickness EP of the blade's cross-section varies according to the relative position x° along the chord 306 from the leading edge BA to the trailing edge BF. The relative position x° is defined as... , where x is the distance from the leading edge along chord 306. Therefore, the relative position x° is 0% at the leading edge BA and 100% at the trailing edge BF. The thickness EP has a maximum value EPmax at a relative position (called the maximum thickness relative position x°_EPmax).

[0057] refer to Figure 5 and Figure 6 Four examples, 502, 504, and 506, will be used to describe the determination of the dimensions of the rotor blade 108.

[0058] It should be noted that when the relative height h° is the relative height at the leading edge or the relative height at the trailing edge, Figure 5 and Figure 6 The curve in the curve may not precisely start at h°=0% and end at h°=100%. Therefore, when we subsequently refer to the relative height h° as "closest to 0%" or "closest to 100%", this would mean the relative height at which the complete cross-section still exists. Figure 2 In the example shown, the relative height h°_BA closest to 0% is therefore the relative height h°_BA at the root BF_P, and the relative height h°_BA closest to 100% is therefore the relative height h°_BA at the tip BF_T. When the relative height h° is the full relative height h°_C, the phrase "closest to 0%" should mean "0%", and "closest to 100%" should mean "100%".

[0059] Special reference Figure 5Preferably, as in the cases of the four examples 502, 504, 506, and 508, the maximum thickness relative position x°_EPmax reaches its maximum at a relative height h° of less than 40%, preferably less than 30%, and more preferably less than 20%. Specifically, for the three examples 502, 504, and 506, the maximum thickness relative position x°_EPmax reaches its maximum at a relative height h° closest to 0% (i.e., at the cross-section at the blade root). This contributes to the mechanical strength of the blade under 1P load during the incident flight phase, and helps limit the flow acceleration and / or impact intensity that may form near the hub 104 or housing 102 during cruise flight, which could increase aerodynamic losses. For example, the maximum thickness relative position x°_EPmax is greater than 20%, preferably greater than 25%, and more preferably greater than 30%. This allows for control of the velocity gradient across the root cross-section, where the transition cross-section between two adjacent blades along the azimuth direction is minimized, particularly when the number of rotor blades 108 is large (e.g., 10 or more, preferably 12 or more).

[0060] Preferably, as in the four examples 502, 504, 506, and 508, at the first relative height R1, the maximum thickness relative position x°_EPmax is between 20% and 40%, preferably between 24% and 35%, and more preferably between 26% and 32%. This ensures that the maximum thickness position in the lower part of the rotor blade 108 is located relatively downstream (and close to the center of gravity of the rotor blade 108), particularly relative to the maximum thickness position in the upper part of the rotor blade 108, thereby ensuring good balance and mechanical stability of the rotor blade 108. This will also allow for increased thickness of the cross-section near the root of the rotor blade 108 and at the spars and / or other structural elements within the rotor blade 108, enabling loads to be transferred below the hub 104.

[0061] In addition, for Figure 5 In most examples, the maximum thickness relative position x°_EPmax decreases in a strictly monotonically decreasing manner from a first relative height R1 to a second relative height R2, which is between 55% and 100%, wherein the maximum thickness relative position x°_EPmax is between 15% and 35%, preferably between 22% and 30%.

[0062] In fact, for high relative heights h°, the thickness EP decreases, such as from Figure 6As can be seen in the three examples 502, 504, and 506. However, in the case of rotor blades 108 with thin thickness, separation may be more likely to occur on the suction side, particularly in the upper part of the blade and at the leading edge, which leads to aerodynamic losses and increased noise. By positioning the maximum thickness EPmax close to the leading edge BA (i.e., with a low maximum thickness relative position x°_EPmax), airflow separation is mitigated or prevented, especially under high incidence conditions, such as during the aircraft's landing and / or takeoff phases (which are particularly important flight phases for certifying aircraft noise levels according to international standards). (Refer to...) Figure 7 and Figure 8 Explain this effect.

[0063] Preferably, as in the cases of the four examples 502, 504, 506, and 508, the variation of the maximum thickness relative position x°_EPmax between 0% of the relative height h° and the first relative height R1 is less than the variation between the first relative height R1 and the second relative height R2. Specifically, for the three examples 502, 504, and 506, the maximum {x°_EPmax} – minimum {x°_EPmax} when h° varies between 0% and 20% is less than the maximum {x°_EPmax} – minimum {x°_EPmax} when h° varies between 40% and 55%.

[0064] This ensures that the maximum thickness relative position x°_EPmax does not vary excessively at the root of rotor blade 108, which is beneficial to the balance and mechanical integrity of rotor blade 108 and helps to maintain the 1P load at the blade root during the flight phase involving incident.

[0065] Preferably, as in the cases of the four examples 502, 504, 506, and 508, for all relative heights h°, the maximum thickness relative position x°_EPmax is maintained between 10% and 40%, preferably between 15% and 35%, and more preferably between 20% and 34%.

[0066] Preferably, as in the three examples 502, 504, and 506, the maximum thickness relative position x°_EPmax decreases strictly from 0% of the relative height h° to 100% of the relative height h°. This means that the position of the maximum thickness moves towards the leading edge BA of the rotor blade 108 between the root and tip, thereby limiting or preventing separation and thus improving efficiency while reducing noise.

[0067] In an alternative embodiment, the maximum thickness relative position x°_EPmax has at least one local maximum and / or minimum value between 0% of the relative height h° and 100% of the relative height h°. Specifically, as... Figure 5As shown in Example 508, a local minimum exists in the second relative height R2 (preferably when the relative height h° varies between 80% and 100%), allowing the maximum thickness relative position x°_EPmax to locally shift away from the leading edge. This allows aerodynamic loads to be distributed more evenly across the tip cross-section of the rotor blade 108, thereby reducing local flow velocity and / or eddy intensity during cruise flight, and consequently reducing noise perceived by passengers in the cabin. Reduced cabin noise contributes to improved passenger comfort during flight.

[0068] refer to Figure 6 The rotor blade 108 has a normalized maximum thickness EPmax°, which is defined as the maximum thickness EPmax at the relative height in question divided by the chord length c at the relative height in question.

[0069] Preferably, the normalized maximum thickness EPmax° decreases strictly from 0% of the relative height h° to at least 60%, preferably to 70% of the relative height h°.

[0070] For example, in examples 504 and 506, the normalized maximum thickness EPmax° decreases monotonically from 0% of the relative height h° to 100% of the relative height. This allows for a thinner profile at the top portion, thereby reducing the mass and weight of the rotor blade 108.

[0071] In contrast, for Examples 506 and 508, the normalized maximum thickness EPmax° increases from approximately 70%, preferably 80%, of the relative height h° towards the closest to 100% of the relative height h°. In this case, the normalized maximum thickness EPmax° at the closest to 100% of the relative height h° is preferably less than or equal to three times the normalized maximum thickness EPmax° at 70% of the relative height h°, or preferably less than or equal to 2.5 times the normalized maximum thickness EPmax° at 70% of the relative height h°, or preferably less than or equal to twice the normalized maximum thickness EPmax° at 70% of the relative height h°. This increase in the maximum thickness near the blade tip allows control over the frequency of the blade's first bending mode, which may be necessary to withstand 1P loads. This increase in the maximum thickness near the blade tip can also benefit structural integrity when increasing the sweep angle and / or dihedral angle to reduce noise. From an aeroacoustic perspective, the increased thickness of the tip cross-section helps control incidence and prevent any potential separation.

[0072] Preferably, the normalized maximum thickness EPmax° at the relative height h° closest to 0% is between 0.1 and 0.25, and more preferably between 0.13 and 0.20. This ensures that the thickness of the profile near the blade root is sufficient to withstand and transmit the aerodynamic and mechanical loads acting on the rotor blade 108.

[0073] Preferably, the normalized maximum thickness EPmax° at the relative height h° closest to 100% is between 0.02 and 0.08, more preferably between 0.03 and 0.06. Limiting the thickness at the tip helps reduce the mass near the free end of the rotor blade 108, thereby limiting any torque transmitted to the rotor blade 108. Furthermore, this is necessary to limit the mass released in the event of a portion of the blade being lost following a bird strike.

[0074] Preferably, the normalized maximum thickness EPmax° decreases from the relative height h° closest to 0% until it reaches one-quarter of the normalized maximum thickness EPmax° at the relative height h° closest to 0% at a relative height h° between 25% and 50%. Reducing the thickness toward the free end helps to reduce the mass near the free end of the rotor blade 108, thereby limiting any torque transmitted to the rotor blade 108. Furthermore, this is necessary to limit the mass released in the event of a portion of the blade being lost after a bird strike.

[0075] refer to Figure 7 When the maximum thickness is too far from the leading edge, the airflow that impacts the leading edge with a high incident rate I is difficult to stick to the suction side (i.e., it is difficult to stay close to the suction side) and moves away from the suction side, causing separation and thus generating turbulence T.

[0076] However, reference Figure 8 When the maximum thickness EPmax is closer to the leading edge BA, the leading edge BA becomes more convex or more rounded. This allows for more effective capture of airflow under high incidence conditions.

[0077] In conclusion, it is clear that the aero-engine described above provides the optimal operating range under high incident conditions at the leading edge.

[0078] It should also be noted that the present invention is not limited to the embodiments described above. In fact, it will be apparent to those skilled in the art that various modifications can be made to the embodiments described above based on the teachings just disclosed.

[0079] In the foregoing detailed presentation of the invention, the terminology used should not be construed as limiting the invention to the embodiments set forth in this specification, but should be interpreted to include all equivalents that a person skilled in the art could anticipate by applying his common sense to the implementation of the teachings that have just been disclosed.

Claims

1. A ductless aero-engine (100) comprising a propeller (106) extending about a main axis (X) and including at least one rotor blade (108) having a variable pitch about a rotor pitch axis (Y), each variable pitch rotor blade (108) comprising: - Leading edge (BA); - Trailing edge (BF); - The inner radius (Ri_BA) at the leading edge (BA) relative to the main axis (X); - The outer radius (Re_BA) at the leading edge (BA) relative to the main axis (X); - The inner radius (Ri_BF) at the trailing edge (BF) relative to the principal axis (X); - The outer radius (Re_BF) at the trailing edge (BF) relative to the principal axis (X); - At each relative height (h°) relative to the principal axis (X), from the inner radius (Ri_BA, Ri_BF) to the outer radius (Re_BA, Re_BF), at the leading edge (BA) and / or at the trailing edge (BF): • A chord (306), which extends in a cross-sectional plane perpendicular to the rotor pitch axis (Y) or to the radial component of the pitch axis (Y), passes through the relative height (h°) and connects the leading edge (BA) to the trailing edge (BF), and • The thickness (EP) in the cross-sectional plane varies according to the relative position (x°_EP) from the leading edge (BA) to the trailing edge (BF) along the chord (306), and the thickness (EP) reaches a maximum value (EPmax) at a relative position referred to as the maximum thickness relative position (x°_EPmax). The feature is that, for each variable pitch rotor blade (108), the maximum thickness relative position (x°_EPmax) decreases from a first relative height (R1) between 20% and 40% to a second relative height (R2) between 55% and 100%, wherein the maximum thickness relative position (x°_EPmax) is between 15% and 35%, preferably between 20% and 30%.

2. The ductless aero-engine (100) according to claim 1, wherein, The activity factor (FA) of at least one variable pitch rotor blade (108) is between 145 and 230, preferably between 155 and 205, and the maximum thickness relative position (x°_EPmax) of the variable pitch rotor blade reaches a maximum at a relative height (h°) of less than 40%, preferably less than 30%, more preferably less than 20%.

3. The ductless aero-engine (100) according to claim 1 or 2, wherein, For each variable pitch rotor blade (108), the maximum thickness relative position (x°_EPmax) reaches its maximum value at the relative height (h°) closest to 0%.

4. The ductless aero-engine (100) according to any one of claims 1 to 3, wherein, For each variable pitch rotor blade (108), there is at least one relative height (h°), which has a maximum thickness relative position (x°_EPmax) greater than 20%, preferably greater than 25%, more preferably greater than 30%.

5. The ductless aero-engine (100) according to any one of claims 1 to 4, wherein, For each variable pitch rotor blade (108), at the first relative height (R1), the maximum thickness relative position (x°_EPmax) is between 20% and 40%, preferably between 25% and 35%, and more preferably between 26% and 32%.

6. The ductless aero-engine (100) according to any one of claims 1 to 5, wherein, For each variable pitch rotor blade (108), the variation of the maximum thickness relative position (x°_EPmax) between the relative height (h°) closest to 0% and the first relative height (R1) is less than the variation between the first relative height (R1) and the second relative height (R2).

7. The ductless aero-engine (100) according to any one of claims 1 to 6, wherein, For each variable pitch rotor blade (108), for all relative heights (h°), the maximum thickness relative position (x°_EPmax) is maintained between 10% and 40%, preferably between 15% and 35%, and more preferably between 20% and 34%.

8. The ductless aero-engine (100) according to any one of claims 1 to 7, wherein, For each variable pitch rotor blade (108), the maximum thickness relative position (x°_EPmax) strictly decreases from 0% of the relative height (h°) to 100% of the relative height (h°).

9. The ductless aero-engine (100) according to any one of claims 1 to 7, wherein, For each variable pitch rotor blade (108), the maximum thickness relative position (x°_EPmax) has at least one local maximum and / or one local minimum at the relative height (h°).

10. The ductless aero-engine (100) according to any one of claims 1 to 9, wherein, At each relative height (h°), each variable pitch rotor blade (108) has, on the one hand, a chord length (c), defined as the distance along the chord (306) separating the leading edge (BA) from the trailing edge (BF), and on the other hand, a normalized maximum thickness (EPmax°), defined as the maximum thickness at the relative height (h°) divided by the chord length (c), the normalized maximum thickness (EPmax°) decreasing strictly from the relative height (h°) closest to 0% to 60% of the relative height (h°), preferably to 70% of the relative height (h°).

11. The ductless aero-engine (100) according to claim 10, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) at the relative height (h°) closest to 0% is between 0.1 and 0.25, preferably between 0.13 and 0.

2.

12. The ductless aero-engine (100) according to claim 10 or 11, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) at the relative height (h°) closest to 100% is between 0.02 and 0.048, preferably between 0.03 and 0.

06.

13. The ductless aero-engine (100) according to any one of claims 10 to 12, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) decreases from the relative height (h°) closest to 0% until, at a relative height (h°) between 25% and 50%, the normalized maximum thickness reaches one-quarter of the normalized maximum thickness (EPmax°) at the relative height (h°) closest to 0%.

14. The ductless aero-engine (100) according to any one of claims 10 to 13, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) is strictly reduced from the relative height (h°) closest to 0% to the relative height (h°) closest to 100%.

15. The ductless aero-engine (100) according to any one of claims 10 to 13, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) increases from 70% of the relative height (h°), preferably from 80% of the relative height (h°) to 100% of the relative height (h°).

16. The ductless aero-engine (100) according to claim 15, wherein, For each variable pitch rotor blade (108), the normalized maximum thickness (EPmax°) at the closest relative height (h°) to 100% is less than or equal to 3 times, preferably 2.5 times, and more preferably 2 times, the normalized maximum thickness (EPmax°) at 70% relative height (h°).

17. The ductless aero-engine (100) according to any one of claims 1 to 16 further includes a housing (102) and fixed ductless stator blades (112) mounted on the housing (102).

18. An aircraft comprising a ductless aero-engine (100) according to any one of claims 1 to 17.

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