A square-to-circular air inlet with continuous curvature and multiple arc sections and its design method

Abstract

The present invention discloses a square-to-circular air inlet with a continuous curvature multi-arc cross-section and a design method thereof, comprising adding a plurality of intermediate control cross-sections surrounded by multi-arc curves between the inlet and the outlet of each air inlet; the design method of each intermediate control cross-section comprises: establishing a function of the area change law of each intermediate control cross-section; and obtaining the area of ​​the central area and the area of ​​the four sides; according to the central area of ​​each intermediate control cross-section, respectively obtaining the width and height of the inscribed square central area of ​​each intermediate control cross-section; respectively obtaining the radius and central angle of each arc segment of each intermediate control cross-section; using the arcs corresponding to the segments of the inscribed square central area of ​​each intermediate control cross-section as the shape lines of each intermediate control cross-section, the square-to-circular air inlet with a continuous curvature multi-arc cross-section can be generated by sweeping the shape lines of each intermediate control cross-section. The present invention realizes the uniform transition of the curvature of the curved surface along the process, the continuity of the lip and the inlet curved surface, improves the flow in the inlet, and reduces the total pressure loss.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed propulsion systems, and in particular to a square-to-circular air inlet with a continuous curvature multi-arc cross-section and a design method thereof. Background Art

[0002] Green aviation's pursuit of environmental protection, energy, and sustainable development has garnered widespread attention on energy-saving and emission-reduction technologies for civil aircraft. The development of aviation propulsion system technology is a key approach to improving propulsion efficiency and reducing fuel consumption. Over the past few decades, increasing the bypass ratio of turbofan engines by increasing fan diameter has been widely used to enhance propulsion efficiency. However, excessive fan size not only increases the design complexity but also makes it difficult to meet installation requirements, particularly ground clearance constraints. Therefore, the method of continuously increasing fan diameter to improve bypass ratio will reach its limits, restricting further development of aviation propulsion system technology.

[0003] Distributed propulsion systems are a viable solution to these problems. Distributed propulsion systems replace the two or four turbofan engines typically mounted under the wings of conventional aircraft with a number of independently operated ducted fans. Depending on the energy management scheme, the aircraft provides a centralized energy supply, either through a turbine generator or batteries, which transmits mechanical or electrical energy to drive each ducted fan to generate thrust. This layout significantly improves the propulsion system's generalized bypass ratio, thereby enhancing the aircraft's fuel efficiency. For example, NASA's N3-X concept aircraft utilizes a turboelectric distributed propulsion system. Power is provided by two turboshaft engines mounted on the wingtips of the fuselage, which drive superconducting generators that generate electricity and, in turn, drive 16 ducted fans to generate thrust. Compared to the Boeing 777-200LR, the N3-X concept aircraft is expected to reduce specific fuel consumption by 70%, a significant contribution from the introduction of a distributed propulsion system.

[0004] Since the distributed propulsion system consists of several transversely arranged ducted fans, whether it is installed in an embedded manner in a wing-body blended aircraft (such as the NASAN3-X concept aircraft) or directly on the wing of a traditional tube-wing layout aircraft (such as the NASA SUSAN aircraft and the ESAero ECO150 aircraft), the air inlet of the propulsion system is no longer independent and is shared by multiple fans. At the same time, considering the integration with the fuselage or wing surface and making full use of the boundary layer suction effect, the air inlet of the distributed propulsion system is usually square. The transition from the square air inlet to the annular inlet of several ducted fans forms the unique air inlet form of the distributed propulsion system. Therefore, it is necessary to develop a square-to-circular air inlet design method to improve the flow state of the transition section and thereby improve the efficiency of the distributed propulsion system. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art and to provide a square-to-circular air inlet with a continuous curvature multi-arc cross-section and a design method.

[0006] One of the objectives of the present invention is to provide a method for designing a square-to-circular inlet with a continuous curvature multi-arc cross-section, comprising adding a plurality of intermediate control sections formed by multiple arc curves between the inlet square section and the outlet circular section of each inlet; the arc curvatures of the arc curves of the same intermediate control section are equal, and the design method of each intermediate control section includes:

[0007] Calculate the inlet square cross-sectional area of ​​the intake duct corresponding to a single ducted fan based on the area expansion ratio given in the design requirements and the area of ​​the intake cross-sectional area of ​​a single ducted fan;

[0008] Establish a function to describe the area variation of the middle control section;

[0009] The circular cross-section of the inlet duct outlet is divided into five regions: the central region of the inscribed square and the four-sided region surrounded by the arc and the line segment of the inscribed square. Under the premise of ensuring that the area change pattern of the four-sided region of the intermediate control section is consistent with the area change pattern of all intermediate control sections, the area of ​​the four-sided region of each intermediate control section is obtained, and then the area of ​​the central region of each intermediate control section is calculated;

[0010] Determine the inscribed square center area of ​​the intermediate control section: the width of the inscribed square center area varies linearly along the process. According to the area of ​​the center area of ​​each intermediate control section, the width and height of the inscribed square center area of ​​each intermediate control section are obtained respectively.

[0011] Determine the arcs corresponding to the line segments in the inscribed square center area of ​​the intermediate control section: ensure that the width of the inscribed square center area of ​​each intermediate control section is always equal, and obtain the arc radius and center angle corresponding to each segment of each intermediate control section;

[0012] The shape lines of each intermediate control section are formed by using multiple arc curves formed by the arcs corresponding to the segments of the inscribed square central area of ​​each intermediate control section. By sweeping the shape lines of each intermediate control section, a square-to-circular air inlet with continuous curvature and multiple arc sections can be generated.

[0013] As a preferred embodiment, the function of the variation rule of the area A(x) of each intermediate control cross section is:

[0014] A(x)=A1+(A2-A1)·δ(x);

[0015] Among them, A1 is the inlet area of ​​the air intake corresponding to a single ducted fan, A2 is the area of ​​the air intake cross section of a single ducted fan, δ(x) is the function that controls the change law of the air intake area, x is the dimensionless coordinate from the inlet to the outlet of the air intake, and a j (j=1, 2, 3, 4) is a constant, and different values ​​thereof will change the speed of change of the area from the inlet to the outlet of the intake duct.

[0016] As a preferred embodiment, the width C of the square center area inscribed in each intermediate control section is W (x) and height C H (x) is determined as follows:

[0017]

[0018] Where W is the width of the square section at the inlet, D is the fan diameter, x is the dimensionless coordinate from the inlet to the outlet, and AC(x) is the area of ​​the center region of any intermediate control section.

[0019] As a preferred method, the arc radius R and the center angle θ of each intermediate control section are W and θ H The method for determining is as follows:

[0020]

[0021] Among them, a and b are coefficients, respectively: C W is the width of the central area corresponding to the arc; C H is the height of the central area corresponding to the arc segment, and D is the fan diameter.

[0022] As a preferred method, an inlet array is generated according to the inlet lateral spacing b and sweep angle γ given by design requirements, and the translational lateral distance ΔX and axial distance ΔZ are: ΔX=D+b; ΔZ=ΔX·sinγ.

[0023] As an optimal method, multiple designed square-to-circular air inlets with continuous curvature and multi-arc sections are laterally combined, and segmented Bezier curves are used to generate transverse and longitudinal lip lines to ensure the continuity of the lip and the air inlet surface.

[0024] The second object of the present invention is to provide a square-to-circular air inlet with a continuous multi-arc cross-section of curvature designed by the above method, including an air inlet inlet and an air inlet outlet and several intermediate control sections located between the air inlet and the air inlet outlet, each intermediate control section being surrounded by several multi-arc curves, and each intermediate control section being determined by the above-mentioned design method of the intermediate control section.

[0025] As a preferred embodiment, it further comprises a lip continuously connected to the air inlet, wherein the lip shape line is generated by using a segmented Bezier curve to generate transverse and longitudinal lip shape lines.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention adds a number of control sections surrounded by multiple circular arc curves before the inlet square section and the outlet circular section. The curvature of each arc segment of each section is equal, thereby achieving a uniform transition of the curvature of the curved surface along the way. The present invention can complete the design of a square-to-circular air inlet of a distributed propulsion system containing any number of ducted fans through the design method of each intermediate control section, ensure the curvature continuity of several intermediate control sections, reduce the flow loss in the air inlet, and thus improve the overall performance of the distributed propulsion system.

[0028] The present invention combines multiple air inlets laterally and uses segmented Bezier curves to generate transverse and longitudinal lip lines, thereby ensuring the continuity of the lip and the air inlet surface, suppressing flow separation, improving the flow in the air inlet, and reducing total pressure loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the circular cross-section of the square-to-circular inlet outlet of a single ducted fan according to an embodiment of the present invention.

[0030] Figure 2 Schematic diagram of the middle control section of the square-to-circular air inlet of a single ducted fan according to an embodiment of the present invention.

[0031] Figure 3 This is a square-to-circular air inlet duct of a single ducted fan according to an embodiment of the present invention.

[0032] Figure 4 Schematic diagram of the air intake lip shaping method according to an embodiment of the present invention Figure 1 ;

[0033] Figure 5 Schematic diagram of the air intake lip shaping method according to an embodiment of the present invention Figure 2 ;

[0034] Figure 6 Schematic diagram of the ducted fan inlet duct model of Example 5 of the present invention Figure 1

[0035] Figure 7 Schematic diagram of the ducted fan inlet duct model of Example 5 of the present invention Figure 2 .

[0036] Figure 8 is the total pressure recovery coefficient of the inlet duct under different outlet Ma numbers in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0038] Unless otherwise defined, the technical or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present disclosure pertains. The terms "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are merely used to distinguish between different components. The terms "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" encompass the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0039] One of the objectives of the present invention is to provide a method for designing a square-to-circular inlet with a continuous curvature multi-arc cross-section. A plurality of intermediate control sections surrounded by multiple arc curves are added between the inlet square section and the outlet circular section of each inlet. The arc curvatures of the various arc curves of each intermediate control section are equal. The design method of the intermediate control sections surrounded by multiple arc curves includes:

[0040] Calculate the inlet square cross-sectional area A1 of the intake duct corresponding to a single ducted fan based on the area expansion ratio σ given by the design requirements and the area A2 of the intake cross-sectional area of ​​a single ducted fan;

[0041] Establish a function to describe the area variation of the middle control section;

[0042] The circular cross section of the inlet duct outlet is divided into five regions: the central region of the inscribed square and the four-sided region surrounded by the arc and the line segment of the inscribed square. Under the premise of ensuring that the area change pattern of the four-sided region of the intermediate control section is consistent with the area change pattern of all intermediate control sections, the central region area and the four-sided region area of ​​each intermediate control section are obtained;

[0043] Determine the inscribed square center area of ​​the intermediate control section: the width of the inscribed square center area varies linearly along the process, and according to the center area of ​​each intermediate control section, the width and height of the inscribed square center area of ​​each intermediate control section are obtained respectively;

[0044] Determine the arcs corresponding to the line segments in the inscribed square center area of ​​the intermediate control section: ensure that the width of the inscribed square center area of ​​each intermediate control section is always equal, and obtain the radius and central angle of each arc segment of each intermediate control section;

[0045] The shape lines of each intermediate control section are formed by splicing together multiple arc curves corresponding to the arcs in the inscribed square center area of ​​each intermediate control section. By sweeping the shape lines of each intermediate control section, a square-to-circular air inlet with continuous curvature and multiple arc sections can be generated.

[0046] As a preferred embodiment, the function of the variation law of the area A(x) of the intermediate control cross section is:

[0047] A(x)=A1+(A2-A1)·δ(x);

[0048] Among them, A1 is the inlet area corresponding to a single ducted fan, A2 is the inlet area corresponding to a single ducted fan, δ(x) is the function that controls the change law of the inlet area, x is the dimensionless coordinate from the inlet to the outlet of the inlet, a j (j=1, 2, 3, 4) is a constant, and different values ​​thereof will change the speed of change of the area from the inlet to the outlet of the inlet duct.

[0049] As a preferred embodiment, the width C of the square center area inscribed in each intermediate control section is W (x) and height C H (x) is determined as follows:

[0050]

[0051] Where W is the width of the square section at the inlet, D is the fan diameter, x is the dimensionless coordinate from the inlet to the outlet, and AC(x) is the center area of ​​any intermediate control section.

[0052] As a preferred method, the arc radius R and the center angle θ of each intermediate control section are W and θ H The method for determining is as follows:

[0053]

[0054] Among them, a and b are coefficients: C W is the width of the central area corresponding to the arc; CH is the height of the central area corresponding to the arc segment, and D is the fan diameter.

[0055] As a preferred method, an inlet array is generated according to the inlet lateral spacing b and sweep angle γ given by design requirements, and the translational lateral distance ΔX and axial distance ΔZ are: ΔX=D+b; ΔZ=ΔX·sinγ.

[0056] As an optimal method, multiple designed square-to-circular air inlets with continuous curvature and multi-arc sections are laterally combined, and segmented Bezier curves are used to generate transverse and longitudinal lip lines to ensure the continuity of the lip and the air inlet surface.

[0057] The second object of the present invention is to provide a square-to-circular air inlet with a continuous curvature multi-arc cross-section designed by the above method, including an air inlet inlet and an air inlet outlet, and a curvature continuous multi-arc cross-section located between the air inlet and the air inlet outlet. The shape line of each of the said continuous curvature multi-arc cross-sections is determined by the above-mentioned design method of the square-to-circular air inlet with a continuous curvature multi-arc cross-section.

[0058] As a preferred embodiment, it further comprises a lip continuously connected to the air inlet, wherein the lip shape line is generated by using a segmented Bezier curve to generate transverse and longitudinal lip shape lines.

[0059] Example

[0060] Step 1: Determine the inlet area and shape

[0061] First, calculate the inlet square cross-sectional area A1 of the corresponding single ducted fan inlet based on the given area expansion ratio σ and the inlet cross-sectional area A2 of the single ducted fan. To ensure flow quality, the inlet square cross-sectional width W is equal to the fan diameter D, and the inlet square cross-sectional height H is determined.

[0062] A1=σA2;

[0063]

[0064] Step 2: Determine the shape and position of the intermediate control section

[0065] Step 2.1 Determine the area change from the square cross-section at the inlet to the circular cross-section at the outlet;

[0066] The area of ​​the middle control section at any position is calculated using the following formula:

[0067] A(x)=A1+(A2-A1)·δ(x);

[0068]

[0069] Among them, δ(x) is the function that controls the change of the intake duct area, x is the dimensionless coordinate from the inlet to the outlet of the intake duct, and a j (j = 1, 2, 3, 4) are constants. Different values ​​of these constants will change the speed of area change from the inlet to the outlet of the inlet. For example, we can set a1 = 0, a2 = 3, a3 = -2, and a4 = 0 to make the area change speed consistent along the entire inlet.

[0070] Step 2.2 Determine the shape and position of each section;

[0071] Each cross section including the outlet circular cross section is divided into five regions, namely the inscribed square center region and the four-sided region surrounded by four circular arcs and the four line segments of the inscribed square, as shown in Figure 1 shown.

[0072] For the circular cross-section of the inlet duct outlet, the central area of ​​the inscribed square is a square, and the central area AC2 and the area of ​​the four sides AS2 can be calculated by the following formula:

[0073]

[0074] By ensuring that the area change pattern of each part of the intermediate control section is consistent with the area change pattern of all intermediate control sections, the central area and the four side areas of any intermediate control section can be obtained:

[0075] AC(x)=AC1+(AC2-AC1)·δ(x);

[0076] AS(x)=AS2δ(x);

[0077] For the inscribed square center area, its width and height are C W and C H , it is clear that for the inlet square cross section and outlet circular cross section, we have:

[0078] C W,1 =W, C H,1 =H;

[0079]

[0080] Taking the width of the inscribed square center area as a linear change along the process, the C of the middle control section can be obtained W and C H :

[0081]

[0082] During modeling, ensure that the width of each intermediate control section is always equal to avoid the inverted curvature of the intake duct wall. The radius and center angle of each arc of the intermediate control section can be calculated:

[0083]

[0084] Where a and b are coefficients:

[0085]

[0086] At this point, the shape lines of each intermediate control section can be obtained, and the intake duct surface can be generated by sweeping each section line.

[0087] Step 3: Generate the Inlet Array

[0088] According to the given inlet lateral spacing b and sweep angle γ required by the design, the inlet array can be generated. The lateral distance ΔX and axial distance ΔZ of the translation are:

[0089] ΔX=D+b;

[0090] ΔZ=ΔX·sinγ;

[0091] Step 4: Construct the Inlet Lip

[0092] Use two Bezier curves to generate the lip shape line, such as Figure 4 As shown in Figure 1, the two Bezier curves coincide at the stagnation point of the lip leading edge (points P4 and P5). Points P3 and P6 are collinear with point P4 to ensure continuity at the stagnation point. Points P2 and P7 move along the straight line along the axis of P1 and P8, respectively, to ensure continuity between the lip shape line and the inlet. For the lip above or below the inlet, continuity with the rear nacelle shape line must also be ensured, as shown in Figure 1. Figure 5 shown.

[0093] The resulting intake duct with five ducted fans is as follows: Figure 6 and Figure 7 As shown:

[0094] By adopting the method proposed in the present invention, the design of the square-to-circular air inlet of a distributed propulsion system containing any number of ducted fans can be completed, the curvature continuity of the intermediate control section can be ensured, the flow loss in the air inlet can be reduced, and the overall performance of the distributed propulsion system can be improved. Figure 8 As shown, this embodiment also compares the total pressure recovery coefficient of the distributed propulsion system square-to-circular inlet designed by adding a multi-arc intermediate control section with that without adding a multi-arc intermediate control section. The total pressure recovery coefficient is defined as the average total pressure at the inlet outlet. Ratio to the average total pressure at the inlet Right now:

[0095]

[0096] It can be seen that under the working conditions of different Ma numbers of the intake duct outlet, the total pressure recovery coefficient of the intake duct designed by this embodiment is higher than that of the intake duct not designed by this embodiment, and the difference between the two is even greater at high Ma numbers, indicating that this method better controls the flow state in the intake duct and reduces flow losses.

[0097] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A design method for a square-to-circular air inlet with a continuous curvature multi-arc cross section, characterized in that: Between the inlet square section and the outlet circular section of each inlet duct, a plurality of intermediate control sections formed by multiple arc curves are added; the arc curvatures of the arc curves of the same intermediate control section are equal. The design method of each intermediate control section includes: Calculate the inlet square cross-sectional area of ​​the intake duct corresponding to a single ducted fan based on the area expansion ratio given in the design requirements and the area of ​​the intake cross-sectional area of ​​a single ducted fan; Establish a function to describe the area variation of the middle control section; The circular cross-section of the inlet duct outlet is divided into five regions: the central region of the inscribed square and the four-sided region surrounded by the arc and the line segment of the inscribed square. Under the premise of ensuring that the area change pattern of the four-sided region of the intermediate control section is consistent with the area change pattern of all intermediate control sections, the area of ​​the four-sided region of each intermediate control section is obtained, and then the area of ​​the central region of each intermediate control section is calculated; Determine the inscribed square center area of ​​the intermediate control section: the width of the inscribed square center area varies linearly along the process. According to the area of ​​the center area of ​​each intermediate control section, the width and height of the inscribed square center area of ​​each intermediate control section are obtained respectively. Determine the arcs corresponding to the line segments in the inscribed square center area of ​​the intermediate control section: ensure that the width of the inscribed square center area of ​​each intermediate control section is always equal, and obtain the arc radius and center angle corresponding to each segment of each intermediate control section; A square-to-circular inlet with a continuous curvature and multiple arc sections can be generated by sweeping the shape lines of each intermediate control section, using multiple arc curves formed by arcs corresponding to the segments of the inscribed square center area of ​​each intermediate control section as the shape lines of each intermediate control section. The area of ​​each intermediate control section The function of the change law is: ； ;in, A 1 The inlet area of ​​a single ducted fan ，A 2 is the area of ​​the air intake cross section of a single ducted fan ， δ(x) is the function that controls the change of the intake duct area. x is the dimensionless coordinate of the inlet from the inlet to the outlet, a j (j=1, 2, 3, 4) is a constant, and different values ​​will change the speed of area change from the inlet to the outlet of the inlet.

2. The method for designing a square-to-circular air inlet with a continuous curvature multi-arc cross section according to claim 1, characterized in that: The width of the square center area inscribed in each intermediate control section and height The method for determining is as follows: ； ； in, W is the square cross-section width of the inlet duct, D is the fan diameter; x is the dimensionless coordinate of the inlet from the inlet to the outlet, is the central area of ​​any intermediate control section.

3. The method for designing a square-to-circular air inlet with a continuous curvature multi-arc cross section according to claim 1, characterized in that: The radius of each arc segment of each intermediate control section and the central angle and The method for determining is as follows: ； ， ； Among them, a and b are coefficients, respectively: ; ; is the width of the central area corresponding to the arc; is the height of the central area corresponding to the arc segment, D is the fan diameter.

4. The method for designing a square-to-circular air inlet with a continuous curvature multi-arc cross section according to claim 3, characterized in that: The lateral spacing of the air inlet duct is given according to design requirements b and sweep angle γ , generate the inlet array, the lateral distance of translation Δ X and axial distance Δ Z They are: ; .

5. The method for designing a square-to-circular air inlet with a continuous curvature multi-arc cross section according to claim 4, characterized in that: The designed multiple square-to-circular air inlets with continuous curvature and multi-arc sections are combined laterally, and the transverse and longitudinal lip lines are generated using segmented Bezier curves to ensure the continuity between the lip and the air inlet surface.

6. A square-to-circular air inlet with a continuous curvature multi-arc cross section, characterized in that: The invention comprises an air intake duct inlet and an air intake duct outlet and several intermediate control sections located between the air intake duct inlet and the air intake duct outlet, each intermediate control section is surrounded by several multi-arc curves, and each intermediate control section adopts the curvature continuous multi-arc section square-to-circular air intake design method according to claim 1.

7. The square-to-circular air inlet with a continuous curvature multi-arc cross section according to claim 6, characterized in that: The invention also comprises a lip continuously connected to the air inlet, wherein the shape line of the lip is generated by using a segmented Bezier curve to generate transverse and longitudinal lip shape lines.

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