Method for designing subsonic s-shaped short inlet

Abstract

A method for designing a subsonic S-shaped short inlet. The subsonic S-shaped short inlet comprises a lip and a diffuser section, which are connected to each other. For the design of the centerline of the diffuser section of the inlet, the form of a new centerline with a controllable front-to-rear steepness variation is used. The front and the rear of the centerline separately use a circular arc having a radius of curvature, and the center of the centerline is a line segment tangential to the front and rear circular arcs. By means of adjusting the radius of curvature r1 of the first circular arc and the radius of curvature r2 of the second circular arc, a centerline having the highest total pressure recovery coefficient is selected. The area variation pattern of the diffuser section of the inlet uses the centerline that has the highest total pressure recovery coefficient between a "steeper front, gentler rear" area variation pattern and a "balanced steepness" area variation pattern.

Description

A subsonic S-bend short inlet design method

[0001] The present application claims priority to the Chinese patent application No. 202410848700X, filed on June 27, 2024, and entitled "A subsonic S-bend short inlet design method", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to a subsonic S-bend short inlet design method, belonging to the field of aerodynamic design of subsonic aircraft. BACKGROUND

[0003] As an important part of the aircraft power system, the inlet functions to slow down and pressurize the high-speed incoming flow in the channel to provide sufficient high-quality airflow for the engine thermodynamic cycle. In order to realize the stable and efficient work of the compressor and combustion chamber in the engine, the total pressure, temperature, velocity, turbulence intensity, distortion, etc. of the inlet outlet flow should be controlled within a certain range. The S-bend inlet is widely used in aircraft due to its compact geometric shape and strong universality.

[0004] Common S-bend inlets are designed based on previous empirical formulas of centerline variation law and cross-sectional area variation law, wherein the centerline variation law determines the flow cross-sectional pressure distribution, and the streamline pressure gradient distribution is mainly affected by the cross-sectional area variation law. With the development of aircraft functional diversification and structural complexity, the design difficulty of S-bend short inlet with a length-diameter ratio less than 5 is greatly improved due to the overall space limitation. The existing design experience formulas such as "first rapid and then slow", "slow and rapid", and "first slow and then rapid" obviously cannot meet the current design requirements.

[0005] SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and improve the flow separation and turbulence intensity in the S-bend short inlet.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] In a first aspect, the present application provides a subsonic S-bend short inlet design method, comprising:

[0009] The inlet layout is selected as an abdominal inlet layout;

[0010] The inlet shape is matched with the aerodynamic shape of the aircraft;

[0011] The center line of the diffuser section of the air inlet passage adopts a front circular arc-line segment-a rear circular arc, and the line segment is tangent to the front circular arc and the rear circular arc at two ends respectively; r1 and r2 are the curvature radii of the front circular arc and the rear circular arc respectively, and the value range of r1 / r2 is 1 to 1.5;

[0012] The area variation law of the diffuser section of the air inlet passage is determined according to the following equation:

[0013] A represents the cross-sectional area of the diffuser section of the air inlet passage, A1 represents the inlet cross-sectional area of the diffuser section of the air inlet passage, A2 represents the outlet cross-sectional area of the diffuser section of the air inlet passage, X represents the axial coordinate of the center line of the diffuser section of the air inlet passage, and L represents the axial length of the diffuser section of the air inlet passage;

[0014] A subsonic S-bend short inlet passage with an abdominal air inlet layout is formed by using software modeling.

[0015] Based on the first aspect, in an embodiment of the present application, the length-diameter ratio of the subsonic S-bend short inlet passage is limited to less than 5.

[0016] Based on the first aspect, in an embodiment of the present application, the total pressure recovery coefficient of the center line is selected by adjusting the front circular arc curvature radius r1 and the rear circular arc curvature radius r2 of the center line of the diffuser section of the air inlet passage.

[0017] Based on the first aspect, in an embodiment of the present application, the inner and outer profile shapes of the lip profile of the subsonic S-bend short inlet passage adopt NACA-1 airfoils.

[0018] Based on the first aspect, in an embodiment of the present application, the inlet shape adopts a semicircular shape.

[0019] The second aspect of the present application provides a subsonic S-bend short inlet passage, which comprises a lip and a diffuser section connected with each other, and the diffuser section is determined by using the design method of the subsonic S-bend short inlet passage described in the first aspect; the inner and outer profile shapes of the lip profile adopt NACA-1 airfoils.

[0020] Based on the second aspect, in an embodiment of the present application, the length-diameter ratio of the subsonic S-bend short inlet passage is limited to less than 5.

[0021] Based on the second aspect, in an embodiment of the present application, the total pressure recovery coefficient of the center line is selected by adjusting the front circular arc curvature radius r1 and the rear circular arc curvature radius r2 of the center line of the diffuser section of the air inlet passage.

[0022] Based on the second aspect, in an embodiment of the present application, the inlet shape adopts a semicircular shape.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The S-bend air inlet channel of the present application can control the distribution of pressure load, can intuitively distribute the pressure gradient "load" of the two bending positions of the S-bend air inlet channel, avoid introducing unnecessary center line bending and the flow distortion interference caused thereby, and, starting from the design experience of "expanding first and then bending" of the S-bend air inlet channel, the area change law of the diffuser section of the air inlet channel adopts an area change curve with higher total pressure recovery coefficient between the area change law of "fast in front and slow in back" and the area change law of "slow in front and fast in back".

[0025] (2) The method of the present application is suitable for S-bend air inlet channels with controllable "load" of short diffuser and flow direction change of front and back half course, improves the state that the design method of S-bend air inlet channel is too dependent on experience and has poor adaptability, and can take into account the performance of total pressure recovery coefficient and pressure distortion index of the air inlet channel.

[0026] (3) The S-bend short air inlet channel designed by the method of the present application has been verified to have good aerodynamic characteristics, can significantly reduce the flow turbulence in the air inlet channel and improve the total pressure recovery coefficient at the outlet of the air inlet channel, and significantly improves the engineering use effect.

[0027] (4) The optimized center line change law design method in the present application can reasonably distribute the "load" distribution of the upstream and downstream bends, while avoiding introducing unnecessary center line deformation, and can significantly suppress the flow separation of the airflow at the S-bend.

[0028] (5) The optimized cross-sectional area change law design method in the present application avoids the transverse secondary flow caused by too fast expansion of the upstream, and can effectively improve the aerodynamic performance of the airflow in the air channel.

[0029] (6) The present application has good aerodynamic performance, the total pressure recovery coefficient is significantly improved compared with the conventional method, and the flow separation in the air inlet channel is also significantly suppressed. By reasonably distributing the "load" distribution of the fairing and diffuser in the S-bend short air inlet channel, the flow characteristics of the airflow in the S-bend short air inlet channel are effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] Fig. 1 is a schematic diagram of the center line change law design method of the present application;

[0031] Fig. 2 is a comparison diagram of the center line change law of the S-bend air inlet channel;

[0032] Fig. 3 is a comparison diagram of the cross-sectional area change law of the S-bend air inlet channel;

[0033] Fig. 4 is a schematic diagram (cross-sectional view) of the design and shaping of the S-bend air inlet channel. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application clearer, the embodiments of the present application will be described in further detail below with reference to the drawings.

[0035] The application discloses a subsonic S-bend short inlet design method, which can effectively improve flow separation of an inlet and reduce an outlet pressure distortion index. The subsonic S-bend short inlet is mainly composed of a lip and a diffuser section. After overall parameters such as the length of the inlet, the longitudinal offset and the outlet diameter are determined, the flow condition in the S-bend short inlet with a length-diameter ratio less than 5 is mainly affected by factors such as the center line of the diffuser section and the area variation law. The center line variation law directly determines the coherence of the wall surface transition of the inlet, and the area variation law plays a key role in the reverse pressure distribution of the S-bend short inlet channel. In the application, the center line of the diffuser section of the inlet is designed in a new center line form with controllable front and rear abrupt changes. The front and rear of the center line are respectively provided with a curvature radius arc, and the middle is provided with a line segment tangent to the front and rear arcs. The first arc (the front arc) curvature radius r1 and the second arc (the rear arc) curvature radius r2 are adjusted to select a center line with the highest total pressure recovery coefficient. The area variation law of the diffuser section of the inlet is designed in a center line with the highest total pressure recovery coefficient between the area variation law with front abrupt and rear gradual changes and the area variation law with gradual and abrupt changes.

[0036] The application discloses a subsonic S-bend short inlet design method, which can effectively improve flow separation of an inlet and reduce an outlet pressure distortion index. The subsonic S-bend short inlet is mainly composed of a lip and a diffuser section. After overall parameters such as the length of the inlet, the longitudinal offset and the outlet diameter are determined, the flow condition in the S-bend short inlet with a length-diameter ratio less than 5 is mainly affected by factors such as the center line of the diffuser section and the area variation law. The center line variation law directly determines the coherence of the wall surface transition of the inlet, and the area variation law plays a key role in the reverse pressure distribution of the S-bend short inlet channel. In the application, the center line of the diffuser section of the inlet is designed in a new center line form with controllable front and rear abrupt changes. The front and rear of the center line are respectively provided with a curvature radius arc, and the middle is provided with a line segment tangent to the front and rear arcs. The first arc (the front arc) curvature radius r1 and the second arc (the rear arc) curvature radius r2 are adjusted to select a center line with the highest total pressure recovery coefficient. The area variation law of the diffuser section of the inlet is designed in a center line with the highest total pressure recovery coefficient between the area variation law with front abrupt and rear gradual changes and the area variation law with gradual and abrupt changes.

[0037] The inlet layout is selected as the abdominal inlet layout mode.

[0038] The inlet shape should be as close as possible to the aerodynamic shape of the aircraft, so as to avoid introducing additional spillage drag. The inlet shape is selected as a semicircle with rounded corners, and the outlet shape is circular. The inner and outer profile shapes of the lip profile are designed by using NACA-1 airfoils.

[0039] The center line is designed by using a design method with controllable front and rear half-course abrupt change "load" distribution. Specifically, the front and rear of the center line are respectively provided with a section of equal curvature radius arc, and the middle is provided with a line segment tangent to the front and rear arcs. The front and rear arcs are tangent to the design flow direction of the upstream and downstream. The method can select a center line with the optimal aerodynamic performance of the inlet by adjusting the first arc curvature radius r1 and the second arc curvature radius r2. The center line diagram of the inlet is shown in FIG. 1. According to the design experience and simulation verification of the S-bend inlet, when r1 / r2 is greater than 1, the total pressure recovery coefficient is relatively high and tends to be constant; when r1 / r2 is less than 1.5, the pressure distortion index is relatively low and tends to be constant. Therefore, the value range of r1 / r2 is 1 to 1.5, and the S-bend inlet has better comprehensive performance. The comparison between the optimization method and the common center line variation laws with front abrupt and rear gradual changes, gradual and abrupt changes and front gradual and rear abrupt changes is shown in FIG. 2. The reference equation of the front abrupt and rear gradual change law is:

[0040] The reference equation of the gradual and abrupt change law is:

[0041] The reference equation of the front slow and rear rapid change law is:

[0042] In the formula, Y is the longitudinal coordinate of the center line of the diffuser, △Y is the longitudinal offset of the center line of the diffuser, X is the axial coordinate of the center line of the diffuser, and L is the axial length of the diffuser.

[0043] In the embodiment, the center line of the diffuser is designed by using a circular arc-line segment-circular arc method, r1 / r2=1.5 is selected according to experience, wherein r1 and r2 are the curvature radii of the first and second circular arcs respectively, and are 150 mm and 100 mm respectively according to the geometric size and the commonly used design law.

[0044] According to the design experience of the S-shaped inlet that “expands first and then turns”, a more effective design method is extracted from the traditional design method for the area change law of the diffuser, that is, a center line with a higher total pressure recovery coefficient between the front rapid and rear slow area change law and the slow and rapid area change law is adopted, wherein the reference equation of the front rapid and rear slow area change law is:

[0045] The reference equation of the slow and rapid area change law is:

[0046] The reference equation of the front slow and rear rapid area change law is:

[0047] The reference equation of the improved area change law is:

[0048] In the formula, A represents the cross-sectional area of the diffuser, A1 represents the inlet cross-sectional area of the diffuser, A2 represents the outlet cross-sectional area of the diffuser, X represents the axial coordinate of the center line of the diffuser, and L represents the axial length of the diffuser. The comparison of the front rapid and rear slow area change law, the slow and rapid area change law and the optimized area change law of the diffuser is shown in FIG. 3.

[0049] The area change law of the diffuser adopts the optimized design, and the reference equation is as follows:

[0050] An integrally formed S-shaped short inlet with an abdominal air inlet layout is formed by using software modeling.

[0051] Embodiment:

[0052] A subsonic S-shaped short inlet design method, comprising:

[0053] The geometric size constraints are as follows: the inlet diameter D is 126 mm, the axial length L of the diffuser section is 3.2D, and the longitudinal offset is 1.46D.

[0054] The inlet shape adopts a commonly used semicircular inlet, and the inlet area is 0.01 m2.

[0055] The lip of the inlet is designed by a conventional method, the inner and outer profiles adopt NACA-1 airfoil shapes, and the lip thickness is 9 mm, which is an integrally formed uniform thickness lip.

[0056] The center line variation law of the diffuser section is designed according to experience, r1 / r2=1.5, wherein r1 and r2 are the first and second arc radii respectively, and are finally 150 mm and 100 mm respectively according to the geometric size and the commonly used design law.

[0057] The area variation law of the diffuser section adopts an optimized design variation law, which satisfies the equation:

[0058] In the equation, A represents the cross-sectional area of the diffuser section, A1 represents the inlet cross-sectional area of the diffuser section, A2 represents the outlet cross-sectional area of the diffuser section, X represents the axial coordinate of the center line of the diffuser section, and L represents the axial length of the diffuser section.

[0059] Through the above geometric shape design method, a one-piece S-bend inlet with an abdominal inlet is formed by software modeling, as shown in FIG. 4. According to the calculation of the CFD fluid simulation software, the total pressure recovery coefficient of the inlet at the design condition is above 97.7%, and the pressure distortion index is below 10.8%, which is better than the conventional design method and meets the design requirements.

[0060] The contents not described in detail in the specification of the present application are known to those skilled in the art.

[0061] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not depart from the technical solutions of the present application, belongs to the protection scope of the technical solutions of the present application.

Claims

1. A method of designing a subsonic S-bend short inlet, characterized in that, The application relates to a subsonic S-curved short inlet. The air inlet layout is selected as an abdominal air inlet layout mode; The inlet shape is matched with the aerodynamic shape of the aircraft; The center line of the diffuser section of the air inlet is composed of a front circular arc, a line segment and a rear circular arc, the line segment is tangent to the front circular arc and the rear circular arc at two ends, r1 and r2 are the radii of curvature of the front circular arc and the rear circular arc respectively, and the value range of r1 / r2 is 1 to 1.5; The area variation law of the diffuser section of the inlet passage is determined according to the following equation: A represents the cross-sectional area of the diffuser section of the air inlet, A1 represents the inlet cross-sectional area of the diffuser section of the air inlet, A2 represents the outlet cross-sectional area of the diffuser section of the air inlet, X represents the axial coordinate of the center line of the diffuser section of the air inlet, and L represents the axial length of the diffuser section of the air inlet; The subsonic S-curved short inlet is formed by software modeling.

2. The subsonic S-bend short inlet design method of claim 1, wherein The length-diameter ratio of the subsonic S-curved short inlet is less than 5.

3. The subsonic S-bend short inlet design method of claim 1, wherein The center line with the highest total pressure recovery coefficient is selected by adjusting the front circular arc radius r1 and the rear circular arc radius r2 of the center line of the diffuser section of the air inlet.

4. The subsonic S-bend short inlet design method of claim 1, wherein The inner and outer profile shapes of the lip profile of the subsonic S-curved short inlet are both NACA-1 airfoils.

5. The subsonic S-bend short inlet design method of claim 1, wherein The inlet shape is semicircular.

6. A subsonic S-bend short inlet characterized in that, The application relates to an air inlet comprising a lip and a diffuser section connected to each other, wherein the diffuser section is determined by the design method of the subsonic S-curved short inlet according to claim 1, and the inner and outer profile shapes of the lip profile are both NACA-1 airfoils.

7. The subsonic S-bend short intake of claim 6, wherein The length-diameter ratio of the subsonic S-curved short inlet is less than 5.

8. The subsonic S-bend short inlet according to claim 6, characterized in that The center line with the highest total pressure recovery coefficient is selected by adjusting the front circular arc radius r1 and the rear circular arc radius r2 of the center line of the diffuser section of the air inlet.

9. The subsonic S-bend short inlet according to claim 6, characterized in that The inlet shape is semicircular.

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