CN110552786A - Supersonic axisymmetric air inlet with serrated lip and design method - Google Patents

Abstract

The invention discloses a supersonic axisymmetric air inlet with a serrated lip and a design method thereof. Under the action of the zigzag lip, when the Mach number of incoming flow is low, the air inlet channel is easy to realize self-starting; when the Mach number of incoming flow is high, redundant flow can be overflowed by using the sawtooth-shaped cuts, and the flow separation phenomenon caused by the fact that precursor shock waves are incident into the lip under an over-rated state is effectively improved. The design scheme can effectively reduce the self-starting Mach number of the air inlet, improve the total pressure recovery coefficient and widen the working Mach number range of the air inlet. The invention has simple structure, does not introduce a movable mechanism and is easy to realize.

Description

Supersonic axisymmetric inlet with serrated lip and design method

technical field

The invention relates to the design field of an air-breathing supersonic/hypersonic aircraft, in particular to a supersonic axisymmetric inlet.

Background technique

Supersonic/hypersonic vehicles fly in the atmosphere, mainly using ramjet engines as power. As an important part of ramjet engines, the air inlet is responsible for introducing sufficient flow of air for the engine from the atmosphere, and also plays the role of bringing low-pressure supersonic air into the atmosphere. The flow is pre-compressed, decelerated and pressurized to make the air flow velocity entering the combustion chamber adapt to the flame propagation velocity. Its performance and the quality of the flow field it provides have an important impact on the performance of the engine and the entire aircraft. Therefore, the design of the intake port is very critical to the performance improvement of the ramjet engine.

The axisymmetric inlet is a typical configuration of the ramjet. It has the advantages of simple structure, high utilization of the windward side, easy manufacture, portability and launching. The lip of the existing axisymmetric inlet generally adopts the unit flat Lips are widely used in missile weapons and aircraft. Supersonic/hypersonic vehicles require the inlet to have good starting characteristics, high total pressure recovery coefficient and flow coefficient, low drag coefficient, anti-backpressure capability and good The quality of the outlet flow field, the existing flat-lip inlet of the common unit will have difficulty in starting at a low flight Mach number, resulting in a large-area flow separation phenomenon inside, resulting in insufficient engine thrust or even flameout; on the other hand , at a high Mach number, because the precursor shock wave is incident on the inside of the lip, it is easy to cause flow separation in the boundary layer near the lip cover, resulting in a decrease in the total pressure recovery coefficient of the inlet, and even destroying the flow of the entire inlet in severe cases. field. In order to broaden the working Mach number range of the inlet and improve the working performance of the inlet, many scholars have adopted variable geometry schemes to improve the inlet lip, such as stretching and rotating the lip. However, the variable geometry design scheme will increase the complexity of the intake port processing technology and the weight and complexity of the engine to a certain extent, and at the same time cause structural connection, sealing, cooling, control and other problems, and the reliability is poor.

Contents of the invention

Purpose of the invention: The present invention provides a supersonic axisymmetric inlet with a serrated lip, which can reduce the self-starting Mach number of the inlet, increase the total pressure recovery coefficient of the inlet, improve the quality of the flow field, and broaden the intake scope of work.

Technical solution: In order to realize the purpose of the above invention, the present invention adopts the following technical solution.

A supersonic axisymmetric air intake with a serrated lip, comprising an axisymmetric air intake main body, an air intake lip cover installed outside the air intake main body, the lip cover is coaxial with the air intake main body and the same It is axisymmetrically arranged, and between the main body of the air intake channel and the lip cover of the air intake channel, the front edge of the channel lip cover in the air intake channel is a serrated lip; the serrated lip includes several serrated incisions, and the incisions Distributed in a continuous array at equal intervals along the lip on the lip.

Beneficial effects: the present invention, on the basis of other basic configuration parameters and geometric features of the designed original air inlet unchanged, forms a number of zigzag incisions arranged in the circumferential direction on the front end of the lip, and acts on the lip. When the incoming flow Mach number is low, the intake port is easy to realize self-starting; when the incoming flow Mach number is high, the excess flow can be overflowed by using the sawtooth cut, which can effectively improve the impact of the precursor shock wave incident into the lip under the over-rated state. caused by flow separation. This design scheme can reduce the shock wave intensity of the inlet channel during the deceleration and diffusion process through the increased overflow at the lip, thereby effectively improving the total pressure recovery coefficient and reducing the total pressure loss.

Further, the zigzag incision and the lips at the same distance on both sides together form a module, and 16 modules are distributed throughout the circumference, and each module occupies 22.5°.

Further, the air inlet is an axisymmetric structure with three-stage compression cones, and the sawtooth cuts on the lip are arranged at equal intervals around the axis of rotation.

The present invention also provides a design method for the supersonic axisymmetric inlet, including the following solutions:

A design method of the supersonic axisymmetric air inlet, the zigzag incision is by drawing a quasi-isosceles curved surface triangle with two waist lengths of 13.1cm and an interior angle of 54° along the surface of revolution on the edge of the original air inlet lip. To the normal plane of the lower lip mask, a quasi-isosceles plane triangle with a waist length of 13cm, an inner angle of 54.5°, and a top angle rounded R=1cm is obtained. After stretching and drafting 70° toward the lip mask direction, a Boolean difference operation is performed with the lip mask main body. owned.

Further, the zigzag cut forms a slope based on an isosceles triangle by cutting a part of the original air inlet lip, and the normal vector of the lip section obtained after cutting and the normal vector of the lower lip are on the left and right sides and The three orientations at the top form an included angle of 25°, 25°, and 26° respectively, which is smaller than the corresponding shock angle at the starting Mach number of the original inlet.

The present invention is easy to realize by carrying out shear modification on the lip of the designed original air inlet while other basic configuration parameters and geometric features remain unchanged, without introducing a new movable mechanism.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a three-dimensional structure diagram of an air inlet with a serrated lip.

Fig. 2 is a plan view of the original air intake according to the present invention.

Fig. 3 is a top view of the air inlet with serrated lip according to the present invention.

Fig. 4(a) is the flow field structure diagram of any symmetrical section of the original inlet when the incoming flow Mach number is Ma6.0.

Figure 4(b) is a cross-sectional flow field structure diagram of the inlet with a serrated lip passing through the serrated cut when the Mach number of the incoming flow is Ma6.0.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figures 1 and 3 below, the present invention discloses a supersonic axisymmetric air intake with a serrated lip, which includes an air intake main body 1 and an air intake lip cover installed outside the main air intake main body 1 2. The lip cover includes a serrated lip 3 . Between the air inlet main body 1 and the air inlet lip cover 2 is an air inlet channel 4 . The serrated lip 3 includes several serrated cutouts 5 . As shown in Figures 1 and 3, the air inlet is an axisymmetric structure with three-stage compression cones, and the sawtooth cuts 5 on the lip 3 are evenly spaced on the lip around the axis of rotation.

The air inlet is formed by constructing a zigzag cut 5 at the front end of the lip after completing the design of the original air inlet while keeping other basic configuration parameters and geometric features unchanged. As shown in Figure 2, the original inlet is an axisymmetric structure with three-stage compression cones, the three-stage half-cone angles are 10°, 7.4°, and 12.6° respectively, and the flight Mach number is Ma3.5, based on the aerodynamic relationship type, the wave system is designed according to the seal, and its starting Mach number is Ma3.2. The zigzag incision 5 draws a quasi-isosceles curved triangle with a waist length of 13.1 cm and an interior angle of 54° on the edge of the original air intake lip along the surface of revolution, and projects it to the normal plane of the lower lip mask to obtain a waist length of 13 cm and an interior angle of 54.5°. °, vertex angle rounded R = 1cm isosceles plane triangle, stretch the triangle plane to the direction of the lip mask for 70°, and then perform Boolean difference operation with the lip mask surface to obtain the zigzag incision 5.

The cross-section of the zigzag cut 5 is a slope surface at a certain angle, and the normal vector of the slope surface and the normal vector of the lower lip surface form a clip of 25°, 25°, and 26° on the left and right sides and the top three directions respectively. Angle, the included angle is smaller than the shock angle corresponding to the starting Mach number of the original inlet, so as to avoid the occurrence of detached shock waves on the three sections and affect the normal operation of the inlet. The zigzag cut 5 and the lips at the same distance on both sides together form a module, 16 modules are distributed around the entire circumference, and each module occupies 22.5°.

Under the action of the saw-toothed notch 5, the inlet can effectively reduce the starting Mach number through the extra overflow at the notch during the starting process; when the flight Mach number is higher than the design Mach number, the precursor shock wave is incident on the lip cover 2 The boundary layer interference between the inner and lower lip causes flow separation, while the evenly distributed zigzag cuts along the lip swivel array can make the incident shock wave overflow to a certain extent, and can reduce the separation packet caused by the shock wave/boundary layer interference. Therefore, at low incoming flow Mach number, it is easy to realize the self-starting of the intake port, and at high incoming flow Mach number, the phenomenon of flow separation in the lip cover of the intake port under the over-rated state can be improved. On the other hand, the increased overflow at the serrated lip 3 reduces the shock wave intensity of the intake port during deceleration and diffusion, thereby effectively increasing the total pressure recovery coefficient and reducing total pressure loss.

Applications

(1) The flight Mach number in the working state of the design inlet is Ma3.5, and the flight Mach number in the over-rated state is Ma6.0.

(2) Program introduction:

A supersonic axisymmetric inlet with three-stage compression cones is designed, the three half-cone angles are 10°, 7.4°, and 12.6° respectively, and the Mach number of the throat is Ma1 when the Mach number of the incoming flow is Ma3.5. 58. According to the aerodynamic relation, the precursor shock wave meets exactly at the lip. As mentioned above, the supersonic axisymmetric inlet with serrated lip is obtained by cutting the inlet lip. Through numerical simulation, the comparative analysis of the starting ability, the total pressure recovery coefficient and the flow field under the over-rated state of the original inlet and the inlet with serrated lip is obtained.

(3) Comparison of starting ability

As shown in Table 1, when the incoming flow Mach number is Ma3.5, the original inlet starts at Ma3.2, while the inlet with serrated lip starts at Ma2.7, and the starting Mach number decreases by 15.63% . It can be seen that due to the change of the shape of the lip, that is, the reduction of the area of the lip, the extra overflow of the lip portion increases, which effectively improves the starting ability of the intake port, and the range of the operating Mach number of the intake port is significantly expanded.

original intake Inlet with serrated lip Self-starting Mach number 3.2 2.7

Table 1 Comparison of self-starting Mach number of inlet port (4) Comparison of total pressure recovery coefficient

As shown in Table 2, when the incoming flow Mach number is Ma3.5, the total pressure recovery coefficient at the throat of the inlet with serrated lip is 2.49% higher than that of the original inlet, and the total pressure recovery coefficient at the outlet is An increase of 2.15%. This shows that the increased overflow at the lip reduces the shock wave intensity of the inlet during the deceleration and diffusion process, reducing the loss caused by flow separation, thereby effectively increasing the total pressure recovery coefficient and reducing the total pressure loss.

Throat Export original intake 0.6571 0.5989 Inlet with serrated lip 0.6735 0.6118

Table 2 Comparison of the total pressure recovery coefficient of the inlet port (5) Comparison of the flow field when the Mach number of the incoming flow is Ma6.0

When the Mach number of the incoming flow reaches Ma6.0, the flight Mach number is higher than the design Mach number, the precursor shock wave is incident into the lip cover, and the air inlet is in an over-rated working state. As shown in Fig. 4(a) and 4(b), the interference between the shock wave and the boundary layer of the lower lip causes flow separation, and the zigzag cuts evenly distributed along the lip rotary array can make the incident shock wave overflow to a certain extent, and It can reduce the separation packet caused by the shock wave/boundary layer interference, thereby improving the flow separation caused by the shock wave/boundary layer interference and improving the quality of the flow field.

In summary, the inlet with serrated lip can reduce the self-starting Mach number of the inlet, increase the total pressure recovery coefficient of the inlet, improve the quality of the flow field, and broaden the working range of the inlet, so the design The solution is feasible.

The above is only the preferred implementation of the present invention, it should be pointed out that without departing from the concept of the present invention, some deduction or substitution can also be made, and these deduction or substitution should be regarded as the protection scope of the present invention.

Claims (5)

1. A supersonic speed axisymmetric air inlet with a serrated lip comprises an axisymmetric air inlet main body and an air inlet lip cover arranged on the outer side of the air inlet main body, wherein the lip cover is coaxial with the air inlet main body and is also axisymmetric, and an air inlet inner channel is arranged between the air inlet main body and the air inlet lip cover; the serrated lip comprises a plurality of serrated notches, and the notches are distributed on the lip along the lip in an equidistant and continuous array.

2. The supersonic axisymmetric intake duct of claim 1, characterized in that: the serrated cut-out, together with the lips on both sides at the same distance, forms a module with 16 modules distributed over the circumference, each module occupying 22.5 °.

3. The supersonic axisymmetric intake duct of claim 1, characterized in that: the air inlet is of an axisymmetric structure with a three-stage compression conical surface, the front end of a main body of the air inlet is of an axisymmetric cone, and saw-tooth notches on a lip are uniformly distributed around a rotating shaft at equal intervals.

4. A method of designing a supersonic axisymmetric intake duct according to any of claims 1-3, characterized in that: the zigzag incision is obtained by drawing an isosceles-curved-surface-like triangle with the waist length of 13.1cm and the inner angle of 54 degrees along a revolution surface at the edge of an original inlet lip, projecting the isosceles-curved-surface-like triangle to a lower lip normal plane to obtain an isosceles-curved-surface-like triangle with the waist length of 13cm, the inner angle of 54.5 degrees and the apex angle radius R of 1cm, stretching and drawing the die in the direction of the lip cover for 70 degrees, and then performing Boolean difference calculation with the lip cover main body.

5. The design method according to claim 4, wherein: the serrated notch forms a slope surface based on an isosceles triangle by shearing a part of the lip of the original air inlet channel, and the normal vector of the cross section of the lip obtained after shearing and the normal vector of the lower lip form included angles of 25 degrees, 25 degrees and 26 degrees respectively in the left side, the right side and the top, and the included angles are smaller than the corresponding shock wave angle of the original air inlet channel under the starting Mach number.