An embedded inlet applicable to a stealth cruise vehicle

Abstract

The present invention provides an embedded inlet applicable to a stealth cruise vehicle. The main implementation formulas of the present invention are the formula for the variation law of the new centerline and the range of the outer inclination angle of the inlet entrance is 0° to 12°, and the equivalent aspect ratio range is 2 to 3. When the present invention is actually applied to the design of the embedded inlet of a stealth cruise vehicle, an inlet with excellent stealth effect and qualified aerodynamic performance of the inlet can be obtained. The total pressure recovery coefficient is above 92%, and the forward RCS value is reduced by 30% compared with that of a common inlet.

Description

Technical Field

[0001] The invention relates to a buried air inlet suitable for a stealth patrol aircraft, and belongs to the field of air inlet design. Background Art

[0002] In the design of aircraft air inlets, in response to the high stealth requirements of patrol aircraft, the problem of the inability to balance the high stealth performance and air intake performance of the embedded air inlet was solved.

[0003] The primary function of an inlet is to supply the required air to the jet engine and decelerate the incoming high-speed airflow, converting the airflow's kinetic energy into pressure energy, pre-compressing the air, and adjusting the inlet outlet flow rate to meet the requirements of the compressor (or fan) or combustion chamber. The inlet layout has always been a crucial component of the aerodynamic design of a patrol vehicle, as it not only influences the vehicle's external flow field but is also closely linked to the engine's internal flow field. The interaction between the vehicle's external flow field and the inlet's internal flow has a significant impact on the vehicle's overall performance. As a crucial component of an aircraft engine, the inlet's aerodynamic performance impacts engine operation and directly influences the engine's thrust. Engineering experience generally suggests that for every 1% decrease in the inlet's total pressure recovery coefficient, engine thrust decreases by 1.2% to 1.5%.

[0004] However, due to the lack of stealth capabilities inherent in patrol aircraft and the limitations of their combat missions, they suffer a high battlefield loss rate. Therefore, in future warfare dominated by "non-contact" methods, it is imperative to address the stealth performance issues of patrol aircraft as soon as possible. Stealth-based patrol aircraft have become an inevitable development trend. Due to the cavity-like structure of the air inlet itself, the air inlet is one of the main sources of scattering on the patrol aircraft. The RCS (radar cross-section) of a conventional air inlet typically accounts for more than 50% of the patrol aircraft's overall radar cross section. Therefore, the size of the air inlet RCS will greatly affect the patrol aircraft's battlefield survivability. Therefore, a rational air inlet design with good air intake performance and stealth performance is a key component of patrol aircraft design.

[0005] At present, the air intake design of conventional aircraft usually adopts an exposed type, which is commonly seen in the form of air intake on both sides, under the wings, under the ribs or on the abdomen. This type of design has a significant impact on electromagnetic stealth performance due to the presence of parts protruding from the surface. For example, the US F22 stealth fighter uses air intake on both sides, the main purpose of which is to ensure excellent aerodynamic performance. In order to improve stealth performance, an internal type can be used. Compared with the conventional layout, this form will reduce the exposed area, thereby improving stealth performance. However, some typical flying wing layout drones such as the X-45A, "Thor", "Neuron", etc., considering the need for air intake, the air intake design still uses air intakes protruding from the fuselage surface, which will still affect the overall stealth performance to a certain extent.

[0006] At present, the main design method of the embedded inlet is to set a virtual throat outside the airframe, design it according to the design method of the ordinary S-bend inlet, and then delete the part outside the airframe. It is very difficult for the stealth performance and aerodynamic performance of the embedded inlet designed by this method to meet the requirements of the cruise vehicle. Summary of the Invention

[0007] The embedded inlet proposed by the present invention does not protrude from the original fuselage surface at all, has excellent stealth performance, and at the same time the intake performance reaches an acceptable level.

[0008] Technical solution of the present invention:

[0009] An embedded inlet applicable to a stealth cruise vehicle is as follows:

[0010] Step 1: According to the engine speed-altitude characteristics and the overall flight envelope, substitute into the following formula to obtain the throat area.

[0011]

[0012] In the above formula, A is the throat area; ε is a coefficient multiplied to consider the required flow rate for engine cooling, etc. For subsonic flight, ε is about 1.03 - 1.05; σ BX is the total pressure recovery coefficient of the inlet; G np is the reduced flow rate of the engine; q(λ0) is the flow function; Φ is the flow coefficient of the inlet.

[0013] Step 2: Set the throat at a suitable position, design the centerline using the new centerline change law formula, and complete the design of the S-bend inlet.

[0014] The new centerline change law formula is as follows:

[0015]

[0016] Among them, b1 - b8 are empirical coefficients, X and Y are the two elements of the binary equation, L represents the length of the inlet, and ΔY represents the eccentricity.

[0017] Step 3: Delete the front part of the inlet from the 50% position inside the inlet, design a suitable inlet entrance, the shape of the entrance plane is a rounded trapezoid, the outer inclination angle ranges from 0° to 12°, and the equivalent aspect ratio (height divided by the mean of the upper and lower bases) ranges from 2 to 3. As shown in [[ID=B]] Figure 1 . The actual inlet angle of attack of the inlet air is between 0° and 5°.

[0018] Advantages of the present invention: The present invention provides a design method for an embedded inlet applicable to a stealth cruise vehicle. The main implementation formulas of the present invention are the new centerline variation law formula, i.e., formula (1), and the outer inclination angle range of the inlet is 0° to 12°, and the equivalent aspect ratio range is 2 to 3. When the present invention is actually applied to the design of the embedded inlet of a stealth cruise vehicle, an inlet with excellent stealth effect and qualified aerodynamic performance of the inlet can be obtained. The total pressure recovery coefficient is above 92%, and the forward RCS value is reduced by 30% compared with that of a conventional inlet. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the inlet design.

[0020] Figure 2 It is a schematic diagram of the virtual throat design method.

[0021] Figure 3 It is a schematic diagram of the brand-new embedded inlet design method.

[0022] Figure 4 It is a process diagram of the S-bend inlet design.

[0023] Figure 5 It is a process diagram of the modification design of the embedded inlet. Detailed Implementation Manner

[0024] 1. S-bend inlet design

[0025] The design process of the S-bend inlet is as Figure 4 shown. Determine the throat area according to the flight conditions and engine parameters. Determine the throat shape and position according to the overall aerodynamic shape design to make the overall resistance and stealth performance reach the optimum. After determining the throat area, obtain the total length of the diffuser section and the eccentricity, and select the appropriate centerline variation law and area variation law. Finally, draw the S-bend inlet according to the above parameters.

[0026] 2. Modify it into an embedded inlet

[0027] First, remove the first 50% part of the S-bend inlet, then design the embedded inlet entrance, and finally design the transition section profile.

[0028] Usually, the design of the embedded inlet adopts the virtual throat design method, that is, a throat is set at a certain place, and the S-bend inlet design is made between it and the inlet outlet, and then the part of the S-bend inlet protruding from the airframe is removed. The aerodynamic performance and stealth performance of the inlet designed by this method cannot meet the standards. At the same time, the actual inlet entrance shape, entrance angle and other parameters cannot be effectively controlled.

[0029] The present invention will adopt a new centerline change law and a new design method for the buried inlet. The implementation scheme is as follows: (1) According to the engine speed-altitude characteristics and the overall aircraft flight envelope, substitute into the following formula to obtain the throat area.

[0030]

[0031] In the above formula, A is the throat area; ε is a coefficient multiplied to account for the required flow rate for engine cooling, etc. For subsonic flight, ε is approximately 1.03 - 1.05; σ BX is the total pressure recovery coefficient of the inlet; G np is the reduced flow rate of the engine; q(λ0) is the flow function; Φ is the flow coefficient of the inlet.

[0032] (2) Set the throat at an appropriate position, and use the new centerline change law formula to design the centerline to complete the design of the S-bend inlet.

[0033] The new centerline change law formula is as follows:

[0034]

[0035] where b1 - b8 are empirical coefficients.

[0036] (3) Delete the front part of the inlet from about 50% inside the inlet, and design an appropriate inlet entrance. The shape of the entrance plane is a rounded trapezoid, with the outer inclination angle ranging from 0° to 12°, and the equivalent aspect ratio (height divided by the average of the upper and lower bases) ranging from 2 to 3. As shown in Figure 1 . The actual incident angle of the inlet air flow at the entrance is between 0° and 5°.

Claims

1. An embedded air inlet applicable to a stealth cruise vehicle, characterized in that, The details are as follows: Step 1: According to the engine speed-height characteristics and the overall aircraft flight envelope, substitute into the following formula to obtain the throat area; In the above formula, A is the throat area; ε is the coefficient considering the required flow rate for engine cooling; σ BX is the total pressure recovery coefficient of the intake duct; G np is the reduced flow rate of the engine; q(λ0) is the flow function; Φ is the flow coefficient of the intake duct; Step 2: Set the throat at an appropriate position, design the centerline using the new centerline change law formula, and complete the design of the S-bend inlet; The new centerline change law formula is as follows: where b1 to b8 are empirical coefficients, X and Y are the two elements of the binary equation, L represents the inlet length, and ΔY represents the eccentricity; Step 3: Delete the front part of the inlet from the 50% position inside the inlet, design a suitable inlet entrance, the entrance plane shape is a rounded trapezoid, the outer inclination angle ranges from 0° to 12°, and the equivalent aspect ratio ranges from 2 to 3; the actual inlet air inflow angle of the inlet is between 0° and 5°.

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