A design method for a backpack embedded air inlet for a stealth aircraft

Abstract

The present invention relates to the technical field of engine air inlet, and specifically to a design method for a backpack embedded air inlet of a stealth aircraft. According to the flight Mach number of the stealth aircraft, the required flow rate of the engine, the outlet area of ​​the embedded air inlet and the outlet Mach number, the centerline variation law of the inner flow channel of the embedded air inlet, the cross-sectional area variation law, the radius variation law of the rounded corner part of the rounded rectangle, the throat area of ​​the inner flow channel and the lip area of ​​the embedded air inlet are determined; by analyzing the vortex formed by the airflow near the lip of the embedded air inlet, the shape of the lip is designed and the variation law of the transition fillet radius between the lip and the aircraft fuselage along the arc length is determined. Compared with the prior art, the present invention provides the variation law of the centerline, cross-sectional area, radius of the rounded corner part of the rounded rectangle and the transition fillet radius between the lip and the air inlet inlet along the inner flow channel. The backpack embedded air inlet designed by the design method for stealth aircraft is convenient and fast, has excellent performance, and effectively improves the convenience and flexibility of the design of such air inlets.

Description

Technical Field

[0001] The invention relates to the technical field of engine air inlet ducts, and in particular to a design method for a backpack-type embedded air inlet duct of a stealth aircraft. Background Art

[0002] With the development of aviation technology, more and more scholars are paying attention to the high speed of aircraft while pursuing the stealth performance of aircraft to improve their survivability in modern warfare; and the characteristic of aircraft using embedded air inlets is high stealth performance. The embedded air inlet connects the inlet of the air inlet and the outer surface of the fuselage into one, and buries the entire inner flow channel in the fuselage. This design makes the fuselage surface free of any protrusions, which not only reduces the radar scattering area and improves its stealth performance, but also effectively reduces the wind resistance during flight.

[0003] However, the inlet of the embedded air inlet is completely placed on the surface of the fuselage, and it cannot directly use the incoming flow ram pressure to inlet air. It can only rely on the pressure gradient perpendicular to the incoming flow direction at the inlet and the vortex generated by the side edges to inlet air. At the same time, the fuselage forebody of the stealth aircraft is relatively long, and the boundary layer of the incoming flow naturally develops to the inlet position, which has become very thick, and when the airflow flows through the curved inner flow channel of the air inlet, flow separation may occur. The above situation leads to large total pressure loss and airflow mixing loss. A large amount of low-energy flow enters the embedded air inlet, which makes the total pressure recovery coefficient of the inlet outlet section low and the distortion index large. Due to the existence of these problems, the application of embedded air inlets in aircraft is greatly restricted.

[0004] Studies have shown that if the lip and inner flow channel profile of the backpack embedded inlet are reasonably designed, the total pressure recovery coefficient of the inlet can be greatly improved, while the distortion index of the outlet flow field is effectively reduced. Therefore, the design of the lip and inner flow channel profile is the key and difficulty in the design of the backpack embedded inlet. The curvature and tangent vector direction of each point on the surface of the embedded inlet lip change greatly from the leading edge point to the trailing edge point of the lip, and there are many variables, so it is difficult to summarize the change law of the lip surface. The shape of the centerline of the inner flow channel determines the deflection of the airflow in the inlet; in the curved channel, the airflow is unevenly distributed and distorted due to the centrifugal force. The distribution law of the cross-sectional area along the way determines the change of the flow pressure ratio in the tube. The inappropriate area distribution plus the centrifugal force will easily cause the flow in the inlet to separate. Therefore, the centerline shape and area distribution design largely determine the performance of the embedded inlet. Therefore, it is necessary to develop a new type of inlet. Summary of the invention

[0005] Purpose of the invention: To solve the above-mentioned problems, the present invention provides a design method for a stealth aircraft backpack embedded air inlet, and provides the law of along-the-way variation of the center line and cross-sectional area of ​​the inner flow channel, the radius of the rounded corner part of the rounded rectangle, and the radius of the transition fillet between the lip and the aircraft fuselage. The backpack embedded air inlet designed by this design method for stealth aircraft is convenient and fast, has superior performance, and effectively improves the convenience and flexibility of the design of such air inlets.

[0006] Technical solution: To achieve the above-mentioned purpose, the air inlet designed by the design method of the backpack embedded air inlet of the stealth aircraft described in the present invention includes an inner flow channel of the air inlet, an air inlet inlet formed by the opening of the aircraft fuselage, and an air inlet lip formed by the inward depression of the air inlet inlet; there is a transition chamfer between the air inlet inlet and the lip; the inner flow channel of the air inlet includes a transition section connected to the air inlet lip, a throat connected to the rear end of the transition section, a turning section connected to the rear end of the throat, and an outlet connected to the rear end of the turning section; the air inlet lip includes a leading edge, a trailing edge and side edges located on both sides, the side edges are two first straight lines gradually expanding from front to back and outward, and the leading edge is an arc line whose width gradually increases from front to back; the trailing edge includes two second straight lines inclined from the symmetry center of the lip, and the intersection of the two second straight lines forms an obtuse angle; the intersection of the two second straight lines is at a relatively forward position of the intersection of the trailing edge and the side edges, and the intersection of the side edges and the trailing edge is an arc chamfer; it is characterized in that the design method includes the following steps:

[0007] 1) Determine the centerline shape according to the main body size of the stealth aircraft and the engine inlet position, and obtain the distribution law of the centerline along the way;

[0008] 2) According to the flight Mach number of the stealth aircraft, the engine required flow rate, the buried inlet outlet area and the outlet Mach number, the inlet inlet cross-sectional area is calculated, the throat cross-sectional area is determined, and the internal flow channel cross-sectional area change curve function is constructed;

[0009] 3) According to the distribution law of the center line and the distribution law of the inner flow channel cross-sectional area along the way, the distribution law of the radius of the rounded corner part of the rounded rectangle, the variation law of the length, width and side length of the rounded rectangle along the way, and the distribution law of the radius of the semicircle along the way are determined to obtain the inner flow channel profile of the air inlet channel;

[0010] 4) According to the cross-sectional area of ​​the inlet, the leading edge radius of the lip, the length of the side edge and the deflection angle α2 from the center axis of the lip, the arc chamfer radius and the trailing edge length and the deflection angle are calculated, and the change law of the transition chamfer radius between the lip and the aircraft fuselage along the arc length is determined to obtain the shape of the inlet lip.

[0011] Furthermore, the centerline shape change rule is calculated by the following formula:

[0012] Z = f(X) = A·X2 +B·X 3 +C·X 4

[0013] Among them, the dimensionless variable Z = z / ΔZ, X = x / ΔX, ΔZ is the height of the embedded air intake, ΔX is the total length of the air intake, and the coefficients A, B, and C determine the shape of the centerline.

[0014] Furthermore, the coefficient A ranges from -6 to 4, the coefficient B ranges from -8 to 6, the coefficient C ranges from -3 to 3, and the coefficients A, B, and C satisfy A+B+C=1.

[0015] Furthermore, the inlet cross-sectional area of ​​the air inlet is determined by the following formula:

[0016]

[0017] in, The flow rate captured by the buried inlet, P * is the total pressure of the incoming flow, T * is the total temperature of the incoming flow, A i is the inlet cross-sectional area, q(λ) is the flow coefficient determined by the Mach number, and K is a constant.

[0018] Furthermore, the throat cross-sectional area A t Should meet A e =1.1~1.15A t , where A e is the given buried inlet duct outlet cross-sectional area.

[0019] Furthermore, the inlet cross-sectional area, throat cross-sectional area and outlet cross-sectional area of ​​the inlet duct establish a cross-sectional area function along the way, and the cross-sectional area variation law is calculated by the following formula:

[0020] A1=a·X 2 +b·X 3 +c·X 4

[0021] Among them, dimensionless variable A1=(AA t ) / (A e -A i ), X = x / ΔX, A is the cross-sectional area of ​​the flow channel along the submerged air intake duct, and the coefficients a, b, and c determine the expansion and contraction degree of the flow channel in the submerged air intake duct.

[0022] Furthermore, the coefficient a ranges from -4 to 4, the coefficient b ranges from -5 to 3, and the coefficient c ranges from -2 to 4.

[0023] Furthermore, the radius of the leading edge of the embedded air inlet lip is R1, the central angle is α1, the length of the side edge is l1, the angle between the side edge and the center line is α2, the radius of the arc chamfer is R2, and the angle between the trailing edge of the lip and the perpendicular direction of the center line is α3, satisfying 0.6D≤R1≤0.8D, 0.75D≤l1≤1.06D, 0.16D≤R2≤0.2D, α1 is preferably 60°~90°, α2 is preferably 3°~5°, and α3 is preferably 22°~30°, wherein D is the semicircular diameter of the embedded air inlet outlet cross-section.

[0024] Furthermore, the change rule of the transition fillet radius between the embedded air inlet lip and the aircraft fuselage is calculated by the following formula:

[0025] r=-0.0034S 3 +0.3698S 2 -0.7102S+0.3906

[0026] Among them, the dimensionless radius of the transition fillet between the lip and the inlet inlet r = R2 / R, the dimensionless arc length S = s / ΔS, R2 is the radius of the transition fillet between the lip and the inlet inlet, R is the radius of the inlet outlet cross-section circle, s is the arc length of the center point of the leading edge of the inlet lip moving along the side edges and the trailing edge of the lip on either side, and ΔS is the total arc length from the center point of the leading edge of the lip to the center point of the trailing edge of the lip.

[0027] Furthermore, the cross-sectional shape of the turning section is a semi-rounded rectangle at the upper part and a semicircle at the lower part; and the cross-sectional shape of the straight section such as the exit is a circle.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: according to the flight Mach number of the stealth aircraft, the engine required flow rate, the outlet area of ​​the embedded air inlet and the outlet Mach number, the centerline change law along the inner flow channel of the embedded air inlet, the cross-sectional area change law along the course, the radius change law of the rounded corner part of the rounded rectangle, the throat area of ​​the inner flow channel, and the lip area of ​​the embedded air inlet are determined; by analyzing the vortex formed by the airflow near the lip of the embedded air inlet, the lip shape is designed and the change law of the transition fillet radius between the lip and the aircraft fuselage along the arc length is determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the design of the back-mounted embedded air inlet of the stealth aircraft described in the present invention.

[0030] Figure 2 It is a schematic diagram of the design of the backpack-type embedded air inlet lip described in the present invention.

[0031] Figure 3 It is a schematic cross-sectional view of the turning section of the inner flow channel of the backpack-type embedded air inlet according to the present invention.

[0032] Figure 4 It is a schematic cross-sectional diagram of the straight section of the inner flow channel outlet of the backpack embedded air inlet according to the present invention.

[0033] Figure 5 It is a schematic diagram of the change pattern of the center line of the flow channel along the backpack embedded air inlet described in the present invention.

[0034] Figure 6 It is a schematic diagram of the variation law of the cross-sectional area of ​​the flow channel along the backpack embedded air inlet of the present invention.

[0035] Figure 7 This is a top view of the shape of the backpack-type embedded air inlet lip of the present invention.

[0036] Figure 8 It is a schematic diagram of the variation law of the transition fillet radius between the lip of the backpack embedded air inlet and the aircraft fuselage along the arc length according to the present invention. DETAILED DESCRIPTION

[0037] The present invention discloses a design method for a backpack-embedded air intake of a stealth aircraft. Figures 1 to 8 As shown, the design method of the backpack embedded air inlet of the stealth aircraft provided by the present invention is further described in detail below: The air inlet designed by the design method of the backpack embedded air inlet of the stealth aircraft includes an air inlet inner flow channel 3, an air inlet inlet formed by the opening of the aircraft fuselage 1, an air inlet lip 2 formed by the inward depression of the air inlet inlet, and an air inlet outlet 7; the air inlet inlet and the lip 2 are transitionally rounded; the air inlet inner flow channel 3 includes a transition section 4 connected to the air inlet lip 2, a throat 12 connected to the rear end of the transition section, and a throat 13 connected to the rear end of the throat. The inlet lip 2 includes a leading edge 8, a trailing edge 10 and side edges 9 on both sides, wherein the side edges 9 are two first straight lines that gradually expand outward from front to back, and the leading edge 8 is an arc line that gradually increases in width from front to back; the trailing edge 10 includes two second straight lines that are inclined from the symmetry center of the lip 2, and the intersection of the two second straight lines forms an obtuse angle; the intersection of the two second straight lines is at a relatively forward position of the intersection of the trailing edge 10 and the side edges 9, and the intersection of the side edges 9 and the trailing edge 10 is an arc chamfer 11. The design method includes the following steps: 1) Determine a suitable centerline shape according to the main body size of the stealth aircraft and the engine inlet position, so that the centerline shape is appropriate in terms of urgency to prevent the airflow from separating in the inner flow channel 3. The centerline shape change law is calculated by the following formula:

[0038] Z = f(X) = A·X 2 +B·X 3 +C·X 4

[0039] Taking coefficients A = -3.05, B = 4.98, C = -1.94, the distribution law of the center line along the path is obtained as follows Figure 5 shown.

[0040] 2) Set the aircraft's flight Mach number Ma = 0.8, and the engine's required flow rate The diameter of the section circle of the buried inlet duct outlet 7 is D = 130 mm, and the inlet duct inlet section area is determined by the following formula:

[0041]

[0042] in, The flow rate captured by the buried inlet, P * is the total pressure of the incoming flow, T * is the total temperature of the incoming flow, A i is the inlet cross-sectional area, q(λ) is the flow coefficient determined by the Mach number, and K is a constant, K=0.04042.

[0043] According to the given cross-sectional area A of the buried air inlet outlet 7 e Calculate the cross-sectional area A of the throat 12 t , let A e =1.1A t A curve function of the cross-sectional area change of the inner flow channel 3 with continuous first-order and second-order derivatives is established, and the change law of the cross-sectional area of ​​the inner flow channel 3 is calculated by the following formula:

[0044] A1=a·X 2 +b·X 3 +c·X 4

[0045] Taking coefficients a = 2.30, b = -2.28, c = 0.89, the distribution law of the cross-sectional area of ​​the inner flow channel 3 along the way is as follows Figure 6 shown.

[0046] 3) According to the distribution law of the cross-sectional area of ​​the inner flow channel 3 along the flow path, the radius of the fillet part of the fillet matrix is ​​determined by the following formula:

[0047] R1=X n

[0048] The index n is set to 0.5, and R1 changes first fast and then slows down with the change of the dimensionless parameter X, so that the transition section 4, the turning section 5 and the straight section 6 have smooth transitions, and the flow channel 3 profile of the inlet duct is obtained.

[0049] 4) The radius of the leading edge 8 of the buried inlet lip is R1, the central angle is α1, the length of the side edge 9 is l1, the angle between the side edge 9 and the center line is α2, the radius of the arc chamfer 11 is R2, and the angle between the trailing edge 10 of the lip and the center line in the vertical direction is α3. R1=50mm, l1=190mm, 0R2=13mm, α1=80°, α2=4°, α3=27° are set. The trailing edge 10 of the lip of the inlet is designed to extend forward from the center, and the whole is swept back in the top view. This shape can generate a pressure gradient perpendicular to the incoming flow direction, and move the low-energy flow caused by the long aircraft forebody and the vortex structure at the center of the inlet inlet to both sides to prevent it from entering the inlet and causing a decrease in the total pressure recovery coefficient.

[0050] The change rule of the transition fillet radius r between the embedded air inlet lip 2 and the aircraft fuselage 1 is calculated by the following formula:

[0051] r=-0.0034S 3 +0.3698S 2 -0.7102S+0.3906

[0052] The radius of the transition fillet between the lip and the aircraft fuselage 1 varies along the arc length as follows: Figure 8 As shown, the shape of the air inlet lip 2 is obtained. At this time, the transition surface of the lip 2 meets the shape constraints of the aircraft fuselage surface and the inner channel, and a smooth transition between the two is achieved.

[0053] The design method of the embedded air inlet on the back of a stealth aircraft provided by the present invention fully considers the smooth transition of each cross section, realizes the smoothness of the embedded air inlet profile, and provides the variation law of each variable that determines the inner flow channel profile and the lip shape along the way, which greatly simplifies the design process of the embedded air inlet, and the designed embedded air inlet has a smaller distortion index.

Claims

1. A method for designing a backpack-type embedded air inlet for a stealth aircraft, wherein the designed air inlet comprises an air inlet inner flow channel (3), an air inlet inlet formed by an opening of an aircraft fuselage (1), and an air inlet lip (2) formed by being recessed inward from the air inlet inlet; a transition chamfer is formed between the air inlet inlet and the lip (2); the air inlet inner flow channel (3) comprises a transition section (4) connected to the air inlet lip (2), a throat (12) connected to the rear end of the transition section, a turning section (5) connected to the rear end of the throat, and an outlet straight section (6) connected to the rear end of the turning section; the air inlet The airway lip (2) comprises a front edge (8), a rear edge (10) and side edges (9) on both sides, wherein the side edges (9) are two first straight lines gradually extending outward from front to back, and the front edge (8) is a circular arc line whose width gradually increases from front to back; the rear edge (10) comprises two second straight lines inclined from the symmetry center of the lip (2), and the intersection of the two second straight lines forms an obtuse angle; the intersection of the two second straight lines is at a position forward of the intersection of the rear edge (10) and the side edges (9), and the intersection of the side edges (9) and the rear edge (10) is a circular arc chamfer (11); characterized in that, The design method includes the following steps: 1) Determine the centerline shape according to the main body size of the stealth aircraft and the engine inlet position, and obtain the distribution law of the centerline along the way; 2) calculating the inlet cross-sectional area of ​​the air inlet according to the flight Mach number of the stealth aircraft, the engine required flow rate, the area of ​​the buried air inlet outlet (7) and the outlet Mach number, determining the cross-sectional area of ​​the throat (12), and constructing a curve function of the cross-sectional area change of the inner flow channel (3); 3) According to the distribution law of the center line along the path and the distribution law of the cross-sectional area of ​​the inner flow channel (3) along the path, the distribution law of the radius of the rounded corner part of the rounded rectangle along the path, the variation law of the length, width and side length of the rounded rectangle along the path, and the distribution law of the radius of the semicircle along the path are determined to obtain the profile of the inner flow channel (3) of the air inlet duct; 4) calculating the radius of the leading edge (8) of the lip, the length of the side edge (9) and the deflection angle α2 from the central axis of the lip, the radius of the arc chamfer (11) and the length and deflection angle of the trailing edge (10) according to the inlet cross-sectional area of ​​the air inlet, determining the variation rule of the transition chamfer radius between the lip (2) and the aircraft fuselage (1) along the arc length, and obtaining the shape of the air inlet lip (2); The radius of the leading edge (8) of the embedded air inlet lip is R1, the central angle is α1, the length of the side edge (9) is l1, the angle between the side edge (9) and the center line is α2, the radius of the arc chamfer (11) is R2, and the angle between the trailing edge (10) of the lip and the vertical direction of the center line is α3, satisfying 0.6D≤R1≤0.8D, 0.75D≤l1≤1.06D, 0.16D≤R2≤0.2D, α1 is preferably 60° to 90°, α2 is preferably 3° to 5°, and α3 is preferably 22° to 30°, wherein D is the semicircular diameter of the cross section of the embedded air inlet outlet (7); The variation rule of the transition rounding radius between the embedded air inlet lip (2) and the aircraft fuselage (1) is calculated by the following formula: r=-0.0034S 3 +0.3698S 2 -0.7102S+0.3906 Among them, the dimensionless fillet radius of the transition between the lip (2) and the inlet of the air inlet is r=R2 / R, the dimensionless arc length S=s / ΔS, R2 is the fillet radius of the transition between the lip (2) and the inlet of the air inlet, R is the radius of the cross-sectional circle of the air inlet outlet (7), s is the arc length of the center point of the leading edge (8) of the air inlet lip moving along the side edge (9) on any side and the trailing edge (10) of the lip, and ΔS is the total arc length from the center point of the leading edge (8) of the lip to the center point of the trailing edge (10) of the lip.

2. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 1 is characterized in that: The centerline shape change rule is calculated by the following formula: Z=f(X)=A·X 2 +B·X 3 +C·X 4 Among them, the dimensionless variable Z = z / ΔZ, X = x / ΔX, ΔZ is the height of the embedded air intake, ΔX is the total length of the air intake, and the coefficients A, B, and C determine the shape of the centerline.

3. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 2 is characterized in that: The coefficient A ranges from -6 to 4, the coefficient B ranges from -8 to 6, the coefficient C ranges from -3 to 3, and the coefficients A, B, and C satisfy A+B+C=1.

4. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 1 is characterized in that: The inlet cross-sectional area of ​​the air inlet is determined by the following formula: in, The flow rate captured by the buried inlet, P * is the total pressure of the incoming flow, T * is the total temperature of the incoming flow, A i is the inlet cross-sectional area, q(λ) is the flow coefficient determined by the Mach number, and K is a constant.

5. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 1 is characterized in that: The cross-sectional area A of the throat (12) t Should meet A e =1.1~1.15A t , where A e is the given buried inlet duct outlet cross-sectional area.

6. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 1 is characterized in that: The inlet cross-sectional area, throat (12) cross-sectional area and outlet cross-sectional area of ​​the air inlet duct establish a cross-sectional area function along the way, and the cross-sectional area variation rule is calculated by the following formula: A1=a·X 2 +b·X 3 +c·X 4 Among them, dimensionless variable A1=(AA t ) / (A e -A i ), X=x / ΔX, A is the cross-sectional area of ​​the flow channel (3) in the embedded air intake duct, and the coefficients a, b, and c determine the expansion and contraction degree of the flow channel (3) in the embedded air intake duct.

7. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 6 is characterized in that: The coefficient a ranges from -4 to 4, the coefficient b ranges from -5 to 3, and the coefficient c ranges from -2 to 4.

8. The design method of the backpack embedded air inlet of a stealth aircraft according to claim 1 is characterized in that: The cross-sectional shape of the turning section (5) is a semi-rounded rectangle at the upper part and a semi-circular at the lower part; the cross-sectional shape of the outlet straight section (6) is a circle.

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