Sharp bending special-shaped exhaust diffuser with beveled outlet

Abstract

The invention discloses a sharp-bending special-shaped exhaust diffuser with a beveled outlet. The sharp-bending special-shaped exhaust diffuser comprises an exhaust diffuser body, an air inlet, an air outlet and an exhaust flow channel connected with the air inlet and the air outlet. The exhaust runner is bent, the air outlet comprises a front edge, a rear edge and a side edge which are located on the same plane, the front edge is close to the air inlet, the rear edge is far away from the air inlet, and the projection of the front edge and the projection of the rear edge on the plane where the air inlet is located have a preset height difference. According to the exhaust diffuser, the height of the flow channel at the outlet of the front bent surface is shortened to form the beveled air outlet, so that the reattachment area of a separation area at a sharp bend is weakened, the separation area is greatly reduced, and meanwhile, the flow capacity of the exhaust diffuser is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of engine and aircraft design, and particularly relates to a curved profile exhaust diffuser with a bevelled outlet. BACKGROUND

[0002] High power-to-weight ratio is one of the key technical indicators pursued by the new generation of turboshaft engines. In order to improve the power-to-weight ratio, in addition to comprehensively improving the comprehensive performance of the core components of the turboshaft engine such as the compressor, the combustion chamber and the turbine, attention must also be paid to the performance improvement of the downstream component of the free turbine, i.e. the exhaust pipe. The exhaust pipe of the turboshaft engine is different from the exhaust pipe of the turbojet engine. The inner profile of the passage is essentially a subsonic diffuser, and its purpose is to reduce the pressure at the outlet of the free turbine and convert as much enthalpy as possible through the free turbine into shaft power. Obviously, the diffusing capacity will significantly affect the size of the shaft power output by the free turbine. It is generally believed that for every 1% loss of total pressure in the exhaust system, the maximum continuous power of the engine is lost by 0.5-1.0%. In addition, in the process of integration with the helicopter, the exhaust diffuser also undertakes the function of injecting the ventilation cooling airflow in the engine compartment. The injection capacity will directly affect the temperature in the engine compartment, the temperature of the engine oil and the temperature of the surface of the related external accessories of the engine. In severe cases, it may cause the failure of the related sensors of the engine, resulting in the loss of control of the engine.

[0003] For the turboshaft engine with a rear output shaft, the engine power output shaft needs to pass through the middle of the exhaust diffuser. The flow path inside the exhaust diffuser is of an irregular profile, and the exhaust direction is lateral. Therefore, the exhaust pipe of this type of turboshaft engine is usually designed as a curved profile exhaust diffuser. In recent years, the overall outline size constraint of the engine by the helicopter flight platform is becoming more and more stringent, and the axial length of the exhaust diffuser needs to be as short as possible. Under this background, the exhaust pipe of the turboshaft engine with a rear output shaft is usually designed as a curved profile exhaust diffuser. Due to the short axial distance, the curved profile exhaust diffuser of this type will cause a large airflow separation zone at the bending position of the internal flow path. The existence of the separation zone not only causes the non-uniformity of the flow field at the exhaust outlet, reduces the injection capacity of the exhaust diffuser to the airflow in the engine compartment, and causes the high temperature in the local position of the engine compartment; in the integrated working environment with the helicopter, it also causes the backflow of part of the high-temperature gas to the engine compartment, which causes the rapid increase of the working temperature of the accessories at the local position of the engine. In severe cases, it may cause the failure of the related sensors. Because the airflow completes the deflection of the flow direction in the short axial distance, this increases the complexity of the flow control scheme to some extent. At present, there is no research on the control of this type of flow phenomenon in China.

[0004] Therefore, it is of great significance to develop a simple and effective flow control structure of the separation zone at the sharp bend, which can avoid the backflow of high-temperature gas into the engine cabin without sacrificing the flow capacity of the exhaust diffuser. SUMMARY

[0005] The present application aims at solving the problem that the existing sharp-bend-shaped exhaust diffuser has a large airflow separation zone at the airflow bending position.

[0006] Technical Scheme: To solve the above problem, the present application adopts a sharp-bend-shaped exhaust diffuser with a beveled outlet, which comprises an exhaust diffuser main body, an air inlet, an air outlet, and an exhaust flow channel connecting the air inlet and the air outlet; the exhaust flow channel is curved, the air outlet comprises a leading edge, a trailing edge and a side edge located on the same plane, the leading edge is close to the air inlet, the trailing edge is away from the air inlet, and the projections of the leading edge and the trailing edge on the plane where the air inlet is located have a preset height difference.

[0007] Further, the air inlet is circular.

[0008] Further, the exhaust flow channel comprises a front curved surface and a rear curved surface, the end of the front curved surface extends to the leading edge, the end of the rear curved surface extends to the trailing edge, the front curved surface comprises a front curved section and a front straight section, the rear curved surface comprises a rear curved section and a rear straight section, the ends of the front curved section and the rear curved section are located on the same plane, and the plane is perpendicular to the plane where the air inlet is located; the length of the front straight section is less than the length of the rear straight section.

[0009] Further, the front straight section is perpendicular to the plane where the ends of the front curved section and the rear curved section are located, the length H2 of the front straight section is (0.018-0.022)*d, and d is the inner diameter of the circular air inlet.

[0010] Further, the rear straight section comprises a first rear straight section and a second rear straight section, the first rear straight section is perpendicular to the plane where the ends of the front curved section and the rear curved section are located, and the second rear straight section is inclined inward by an angle θ0 compared to the first rear straight section.

[0011] Further, the length H1 of the first rear straight section is (0.071-0.0.074)*D, the length H0 of the second rear straight section in the direction perpendicular to the plane where the ends of the front curved section and the rear curved section are located is (0.070-0.0.073)*D, and D is the outer diameter of the circular air inlet.

[0012] Further, θ0=(2.5-3.5)°.

[0013] Further, the plane where the air outlet (30) is located and the plane where the front straight section is perpendicular to the ends of the front curved section and the rear curved section are at an angle θ1, and θ1=(24-26)°.

[0014] Further, the exhaust flow channel (20) further comprises a side curved surface, the side curved surface extends to a side edge at an end, the side curved surface is inclined inwardly by an angle θ2, θ2=(2.5-3.5)°.

[0015] Further, a projection width L of the air outlet on a plane where the air inlet is located is (1.36-1.38)*D.

[0016] Advantages: compared with the prior art, the present application has the following advantages: (1) by shortening the height of the flow channel at the outlet of the front curved surface, a bevelled air outlet is formed, so that the reattachment area of the separation zone at the sharp bend is weakened, the separation zone is greatly reduced, and the flow capacity of the exhaust diffuser is enhanced; (2) the height of the rear curved surface is extended, and the outlet section of the rear curved surface is inclined forward by a certain angle, so that the air flow of the air outlet is inclined forward when discharged, and the side curved surface is also inclined inwardly by a certain angle, so that the air flow discharged at the outlet of the rear curved surface is not directly sprayed on the wall of the exhaust mixing pipe to form a high pressure zone, and the air flow injection capacity at the outlet is improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Fig. 1 is a schematic diagram of the overall structure of the sharp curved special-shaped exhaust diffuser with a bevelled outlet of the present application;

[0018] Figure 2 Fig. 2 is a front view of the sharp curved special-shaped exhaust diffuser with a bevelled outlet of the present application;

[0019] Figure 3 Fig. 3 is an A-A sectional view of the sharp curved special-shaped exhaust diffuser with a bevelled outlet of the present application;

[0020] Figure 4 Fig. 4 is a side view of the sharp curved special-shaped exhaust diffuser with a bevelled outlet of the present application;

[0021] Figure 5 Fig. 5 is a schematic diagram of the existing exhaust diffuser and exhaust mixing pipe lap joint;

[0022] Figure 6 Fig. 6 is a schematic diagram of the exhaust diffuser and exhaust mixing pipe lap joint of the present application;

[0023] Figure 7 Fig. 7 is a schematic diagram of the exhaust diffuser and exhaust mixing pipe lap joint section of the present application;

[0024] Figure 8 Fig. 8 is a cloud diagram of the outlet plane velocity distribution of the baseline prototype sharp curved special-shaped exhaust diffuser;

[0025] Figure 9 Fig. 9 is a cloud diagram of the outlet plane velocity distribution of the sharp curved special-shaped exhaust diffuser with a bevelled outlet of the present application;

[0026] Figure 10 Gas flow diagram of a prototype sharply curved irregular exhaust diffuser;

[0027] Figure 11 This is a gas simulation streamline diagram of the sharply curved irregular exhaust diffuser of the present invention. Detailed Implementation

[0028] like Figures 1 to 7 As shown, this embodiment of a sharply curved, irregularly shaped exhaust diffuser with a slanted outlet includes an exhaust diffuser body 1, an inlet 10, an outlet 30, and an exhaust flow channel 20 connecting the inlet 10 and the outlet 30. The inlet 10 is annular, and the outlet 30 includes a leading edge 31, a trailing edge 32, and two side edges 33 located on the same plane. The exhaust flow channel 20 is curved, including a front curved surface 3, a rear curved surface 2, and side curved surfaces. The end of the front curved surface 3 extends to the leading edge 31, the end of the rear curved surface 2 extends to the trailing edge 32, and the end of the side curved surface extends to the side edge 33. The leading edge 31 is on the side closer to the inlet 10, and the trailing edge 32 is on the side farther from the inlet 10.

[0029] The front curved surface 3 includes a front curved section and a front straight section, and the rear curved surface 2 includes a rear curved section and a rear straight section. The ends of the front and rear curved sections are located on the same plane, and this plane is perpendicular to the plane where the air inlet 10 is located. The plane where the air outlet 30 is located forms an angle θ1 with the front straight section perpendicular to the plane where the ends of the front and rear curved sections are located, where θ1 = (24~26)°. The projection width L of the air outlet 30 on the plane where the air inlet 10 is located is (1.36~1.38)*D. The length of the front straight section is shorter than the length of the rear straight section, making the air outlet obliquely shaped. Compared with the flat outlet of a traditional exhaust diffuser, the airflow tends to adhere at the front curved surface and generate a large separation zone. This invention shortens the height of the front curved surface to form an obliquely shaped air outlet, thereby weakening the area of ​​reattachment in the separation zone at sharp bends, greatly reducing the separation zone, and enhancing the flow capacity of the exhaust diffuser.

[0030] Specifically, the front straight line segment is perpendicular to the plane where the end of the front curved segment and the end of the back curved segment are located, and the length of the front straight line segment H2=(0.018-0.022)*d, d is the inner diameter of the circular ring of the air inlet 10. The back straight line segment includes a first back straight line segment and a second back straight line segment, the first back straight line segment is perpendicular to the plane where the end of the front curved segment and the end of the back curved segment are located, and the length of the first back straight line segment H1=(0.071-0.0.074)*D. The second back straight line segment is inclined inward by an angle θ0 compared to the first back straight line segment, θ0=(2.5-3.5)°; the length of the second back straight line segment in the direction perpendicular to the plane where the end of the front curved segment and the end of the back curved segment are located H0=(0.070-0.0.073)*D, D is the outer diameter of the circular ring of the air inlet 10. When the exhaust diffuser is working, the rear end of the air outlet 30 is overlapped with the exhaust mixing pipe 6, the side wall of the exhaust mixing pipe 6 is parallel to the first straight line segment, and the second straight line segment is inclined forward by a certain angle in the present application, so that the airflow of the air outlet is discharged in a forward inclined direction, avoiding the direct injection of the discharged airflow at the outlet of the back curved surface on the wall of the exhaust mixing pipe to form a local high pressure area, and the stagnation of the high pressure area will cause a local reverse pressure gradient, resulting in local backflow and gas backflow into the power cabin, and further affecting the airflow injection capacity.

[0031] The exhaust flow channel 20 further includes a side curved surface, the end of the side curved surface extends as a side edge 33, and the side curved surface is inclined inward by an angle θ2, θ2=(2.5-3.5)°. The same as the design principle of the second straight line segment, the side curved surface is inclined inward by a certain angle, avoiding the direct injection of the airflow on the wall of the exhaust mixing pipe, which helps to improve the airflow injection capacity.

[0032] In order to verify whether the performance of the exhaust diffuser is improved, a benchmark prototype sharp curved special-shaped exhaust diffuser and a sharp curved special-shaped exhaust diffuser with a beveled outlet are designed respectively. The basic shapes of the two are the same, the inner diameter of the circular ring of the air inlet 10 d=209mm, the outer diameter of the circular ring of the air inlet 10 D=409mm, and the projection width of the air outlet 30 on the plane where the air inlet 10 is located L=558mm. The structural parameters of the sharp curved special-shaped exhaust diffuser with a beveled outlet are as follows: the length of the front straight line segment H2=4.5mm, the length of the first back straight line segment H1=30mm, and the length of the second back straight line segment in the direction perpendicular to the plane where the end of the front curved segment and the end of the back curved segment are located H0=29.5mm. The second back straight line segment is inclined inward by an angle θ0=3° compared to the first back straight line segment, the side curved surface is inclined inward by an angle θ2=3°, and the plane where the air outlet 30 is located is perpendicular to the plane where the end of the front curved segment and the end of the back curved segment are located by an angle θ1=25°.

[0033] The benchmark prototype sharp curved special-shaped exhaust diffuser and the sharp curved special-shaped exhaust diffuser with a beveled outlet are compared and analyzed by three-dimensional numerical simulation, the total pressure of the inlet is set to 110kPa, the total temperature is set to 830K, the outlet environment pressure of the exhaust diffuser is set to 101kPa, and the environment temperature is set to 288.15K. As shown inFigure 8 As shown, the prototype exhaust diffuser exhibits a very large separation zone at the forward curved surface, with a low flow velocity near the wall of the forward curved surface. This indicates that the airflow entrainment capability at this location is very weak. Furthermore, it can be inferred that there is a potential risk of high-temperature exhaust gases being drawn into the engine compartment beneath the helicopter platform. Figure 10 As shown, the benchmark prototype's sharply curved, irregularly shaped exhaust diffuser may experience a situation where the outlet gas flows back into the engine compartment.

[0034] like Figure 9 As shown, the separation zone area near the wall surface of the sharply curved exhaust diffuser with a beveled outlet is significantly reduced, and the separation zone at the front curved wall surface is greatly improved. Figure 11 As shown, no gas flowed back into the engine compartment from the outlet of the sharply curved, irregularly shaped exhaust diffuser of this invention.

[0035] In addition, the outlet flow rate and ejection coefficient of the two models near the wall at sharp bends were measured. The outlet flow rate of the baseline prototype sharply bend irregular exhaust diffuser was 7.5 kg / s, and the ejection coefficient was 10%. The outlet flow rate of the sharply bend irregular exhaust diffuser with the oblique outlet of this invention was 7.7 kg / s, and the ejection coefficient was 15%. Compared with the baseline prototype structure, the outlet flow rate of the sharply bend irregular exhaust diffuser with the oblique outlet of this invention is increased, indicating that the flow capacity and ejection capacity of the exhaust diffuser are improved.

Claims

1. A sharply curved, irregularly shaped exhaust diffuser with a beveled outlet, characterized in that, The device includes an exhaust diffuser body (1), an air inlet (10), an air outlet (30), and an exhaust flow channel (20) connecting the air inlet (10) and the air outlet (30); characterized in that the exhaust flow channel (20) is curved, and the air outlet (30) includes a front edge (31), a rear edge (32), and a side edge (33) located on the same plane, the front edge (31) being the side closer to the air inlet (10), the rear edge (32) being the side farther away from the air inlet (10), and the projections of the front edge (31) and the rear edge (32) on the plane where the air inlet (10) is located have a preset height difference.

2. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 1, characterized in that, The air inlet (10) is annular.

3. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 2, characterized in that, The exhaust channel (20) includes a front curved surface (3) and a rear curved surface (2). The end of the front curved surface (3) extends to a leading edge (31), and the end of the rear curved surface (2) extends to a trailing edge (32). The front curved surface (3) includes a front curved section and a front straight section, and the rear curved surface (2) includes a rear curved section and a rear straight section. The ends of the front curved section and the rear curved section are located on the same plane, and this plane is perpendicular to the plane where the air inlet (10) is located. The length of the front straight section is less than the length of the rear straight section.

4. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 3, characterized in that, The front straight segment is perpendicular to the plane where the ends of the front and rear curved segments are located. The length of the front straight segment H2 = (0.018~0.022)*d, where d is the inner diameter of the air inlet (10) ring.

5. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 4, characterized in that, The rear straight segment includes a first rear straight segment and a second rear straight segment. The first rear straight segment is perpendicular to the plane where the ends of the front and rear curved segments are located. The second rear straight segment is inclined inward at an angle θ0 relative to the first rear straight segment.

6. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 5, characterized in that, The length of the first rear straight segment H1 = (0.071 ~ 0.074) * D, and the length of the second rear straight segment in the plane perpendicular to the ends of the front and rear curved segments H0 = (0.070 ~ 0.073) * D, where D is the outer diameter of the air inlet (10) ring.

7. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 6, characterized in that, The θ0 is (2.5~3.5)°.

8. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 7, characterized in that, The plane where the air outlet (30) is located forms an angle θ1 with the plane where the front straight segment is perpendicular to the plane where the ends of the front and rear curved segments are located, θ1 = (24~26)°.

9. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 8, characterized in that, The exhaust channel (20) also includes a side curved surface, the end of which extends into a side edge (33), the side curved surface being inclined inward at an angle θ2, θ2 = (2.5~3.5)°.

10. The sharply curved, irregularly shaped exhaust diffuser with a beveled outlet as described in claim 9, characterized in that, The projection width of the air outlet (30) on the surface where the air inlet (10) is located is L = (1.36~1.38)*D.

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