Sharp bending special-shaped exhaust diffuser with concave surface on outlet surface

Abstract

The invention discloses a sharp-bending special-shaped exhaust diffuser with an inward concave surface on an outlet surface. The sharp-bending special-shaped exhaust diffuser comprises an exhaust diffuser main body, an air inlet, an air outlet and an exhaust flow channel for connecting the air inlet with the air outlet, the exhaust flow channel is bent, one wall face of the exhaust flow channel is concaved inwards to form an inwards-concave face used for discharging low-energy flow, the inwards-concave face comprises a plurality of curved faces which are smoothly connected, and the outer edge of the inwards-concave face forms a part of the edge of the air outlet. The front end of the inner concave surface is positioned on the connecting surface of the upper end of the air inlet and the air outlet, the rear end forms a part of the edge of the air outlet, and the width of the front end gradually expands towards the rear end. Low-energy flow at the outlet section of the front bent surface of the exhaust diffuser is discharged to the two sides through the inner concave surface, so that generation of a separation area near the wall surface is restrained, the flow speed of airflow near the wall surface is increased, and the ejection capacity of airflow at the sharp bent wall surface is improved.

Description

Technical Field

[0001] The invention relates to the technical field of engine and aircraft design, in particular to a sharply curved special-shaped exhaust diffuser with an outlet surface having an inner concave surface. Background Art

[0002] A high power-to-weight ratio is a key technical indicator pursued by the new generation of turboshaft engines. To achieve this, in addition to comprehensively improving the overall performance of core turboshaft engine components—the compressor, combustor, and turbine—it is also crucial to focus on enhancing the performance of the exhaust duct, the downstream component of the free turbine. Unlike turbojet engine exhaust ducts, the internal profile of a turboshaft engine's exhaust duct is essentially a subsonic diffuser. Its purpose is to reduce the pressure at the free turbine outlet and convert as much enthalpy as possible into shaft power. Clearly, the diffuser's pressure reduction capability significantly affects the free turbine's output shaft power. It is generally believed that for every 1% loss in total exhaust system pressure, the engine's maximum continuous power loss is 0.5-1.0%. Furthermore, during helicopter integration, the exhaust diffuser also serves to direct ventilation and cooling air within the engine compartment. Its performance is directly related to the temperature within the engine compartment, the engine oil temperature, and the temperature of external components and accessories. Under poor conditions, this capability can cause engine-related sensors to malfunction, leading to engine loss of control.

[0003] For turboshaft engines with rear output shafts, since the engine power output shaft needs to pass through the middle of the exhaust diffuser, the flow path inside the exhaust diffuser is an irregular shape and the exhaust direction is lateral exhaust, so the exhaust pipe of this type of turboshaft engine is mostly designed as a curved special-shaped exhaust diffuser. In recent years, the overall contour size constraints imposed by helicopter flight platforms on engines have become increasingly stringent, and the axial length of the exhaust diffuser needs to be as short as possible. In this context, the exhaust pipe of turboshaft engines with rear output shafts is mostly designed as a sharply curved special-shaped exhaust diffuser, and its basic structure is as follows: Figure 1 As shown, it includes an exhaust diffuser body 1, an air inlet 10', an air outlet 30', and an exhaust flow channel connecting the air inlet 10' and the air outlet 30'. This type of exhaust diffuser has a short axial distance, which leads to a large airflow separation area at the bend of the internal flow path. The existence of this separation area will not only lead to the unevenness of the exhaust outlet flow field, reduce the exhaust diffuser's ability to radiate the airflow in the engine compartment, and cause the cabin temperature to be high at a local position in the engine compartment; in an integrated working environment with a helicopter, it will also cause some high-temperature combustion gas to flow back into the engine compartment, causing the operating temperature of the accessories at a local position of the engine to rise sharply, and in severe cases, it will cause the failure of related sensors. Because the airflow completes the deflection of the flow direction in a short axial space, this increases the complexity of the flow control scheme to a certain extent. At present, there has been 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 in the separation zone of the sharp bend, which can increase the flow velocity of the airflow near the wall of the sharp bend without sacrificing the flow capacity of the exhaust diffuser and prevent the high-temperature gas from flowing back into the engine compartment. Summary of the Invention

[0005] Purpose of the invention: In order to address the shortcoming of existing sharply curved special-shaped exhaust diffusers that a large airflow separation area will be generated at the bend of the airflow, the present invention provides a sharply curved special-shaped exhaust diffuser with an inner concave surface on the outlet surface. The inner concave surface is used to discharge the low-energy flow at the outlet section of the front curved surface of the exhaust diffuser to both sides, effectively weakening the separation area.

[0006] Technical solution: To solve the above problems, the present invention adopts a sharply curved special-shaped exhaust diffuser with an inner concave surface on the outlet surface, comprising an exhaust diffuser 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, and one wall surface of the exhaust flow channel is concave inward to form an inner concave surface for discharging low-energy flow, the inner concave surface includes multiple smoothly connected curved surfaces, and the outer edge of the inner concave surface forms a part of the edge of the air outlet.

[0007] Furthermore, the axis of the air inlet is perpendicular to the axis of the air outlet.

[0008] Furthermore, the air inlet is in a circular ring shape.

[0009] Furthermore, the cross-section of the air outlet includes wide parts at both ends and a narrow part formed by the inward compression of the outer edge of the inner concave surface. The outer edge line of the inner concave surface forms an inward concave arc on one side of the narrow part, and the two ends of the inward concave arc are smoothly connected to the outer edge line of the wide part on this side.

[0010] Furthermore, the front end of the inner concave portion is located on the connecting surface between the upper end of the air inlet and the air outlet, the rear end forms a part of the edge of the air outlet, and the width gradually expands from the front end to the rear end.

[0011] Furthermore, the width of the inner concave surface on the surface where the air outlet is located is l1 = (0.74 ~ 0.76) * D, the height of the inner concave surface in the axial direction of the air outlet is H0 = (0.46 ~ 0.48) * d, and the distance between the front end of the inner concave surface and the plane where the air inlet is located is l0 = (0.22 ~ 0.24) * d, where d is the inner diameter of the air inlet ring, and D is the outer diameter of the air inlet ring.

[0012] Furthermore, the inner concave surface includes a first arc surface located in the middle and second arc surfaces symmetrically arranged on both sides of the first arc surface.

[0013] Furthermore, the radius of the first arc surface R0 = (0.41-0.43)*D, and the radius of the second arc surface R1 = (0.16-0.18)*D.

[0014] Furthermore, the projection width of the air outlet on the surface where the air inlet is located is L=(1.36-1.38)*D.

[0015] Beneficial effect: Compared with the prior art, the significant advantage of the present invention is that the low-energy flow at the outlet section of the front curved surface of the exhaust diffuser is discharged to both sides through the inner concave surface, thereby suppressing the formation of a separation zone near the wall surface, and increasing the flow velocity of the airflow near the wall surface, thereby improving the airflow ejection capability at the sharp bend wall surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of an existing sharply curved special-shaped exhaust diffuser;

[0017] Figure 2 This is a schematic diagram of the overall structure of the sharply curved special-shaped exhaust diffuser of the present invention;

[0018] Figure 3 This is a front view of the sharply curved special-shaped exhaust diffuser of the present invention;

[0019] Figure 4 A top view of the sharply curved special-shaped exhaust diffuser of the present invention;

[0020] Figure 5 This is a top-view dimensioned drawing of the sharply curved special-shaped exhaust diffuser of the present invention;

[0021] Figure 6 This is a cross-sectional view of the steeply curved special-shaped exhaust diffuser of the present invention;

[0022] Figure 7 Schematic diagram of the airflow direction of the sharply curved special-shaped exhaust diffuser of the present invention;

[0023] Figure 8 This is a schematic diagram of the airflow of the three-dimensional model of the sharply curved special-shaped exhaust diffuser of the present invention;

[0024] Figure 9 This is the velocity distribution cloud diagram of the benchmark prototype steeply curved special-shaped exhaust diffuser outlet surface;

[0025] Figure 10 This is a velocity distribution cloud diagram of the outlet surface of the sharply curved special-shaped exhaust diffuser of the present invention. DETAILED DESCRIPTION

[0026] like Figures 1 to 8As shown in the figure, a sharply curved, profiled exhaust diffuser with an inwardly concave outlet surface in this embodiment 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. The axis of the air inlet 10 is perpendicular to the axis of the air outlet 30, and the planes of the air inlet 10 and the air outlet 30 are also perpendicular to each other. The air inlet 10 is annular, and the upper side of the annular ring is connected to the air outlet 30 via the exhaust flow channel 20.

[0027] The exhaust flow channel 20 is curved, and its upper sidewall is inwardly concave, forming a concave surface for discharging low-energy flow. The outer edge of this concave surface forms part of the edge of the air outlet 30. The cross-section of the air outlet includes wide portions at both ends and a narrow portion formed by the inward compression of the outer edge of the concave surface. The outer edge of the concave surface forms an inwardly concave arc on one side of the narrow portion, and the two ends of this inwardly concave arc smoothly connect to the outer edge of the wide portion on that side.

[0028] The inner concave surface includes a first arcuate surface 31 located in the middle and second arcuate surfaces 32 symmetrically arranged on either side of the first arcuate surface 31. The front end of the inner concave surface is located at the connection between the upper end of the air inlet 10 and the air outlet 30, and the rear end forms part of the edge of the air outlet 30. The width of the inner concave surface on the plane where the air outlet 30 is located is l1 = (0.74-0.76) * D. The height of the inner concave surface along the axis of the air outlet 30 is H0 = (0.46-0.48) * d. The distance between the front end of the inner concave surface and the plane where the air inlet 10 is located is l0 = (0.22-0.24) * d, where d is the inner diameter of the air inlet 10 ring and D is the outer diameter of the air inlet 10 ring. The radius of the first arcuate surface 30 is R0 = (0.41-0.43) * D, and the radius of the second arcuate surface 32 is R1 = (0.16-0.18) * D. 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.

[0029] The purpose of setting the inner concave surface is to discharge the low-energy flow at the outlet section of the front curved surface of the exhaust diffuser to both sides through this surface, increase the flow velocity in the near-wall area of ​​the sharp bend wall to resist the local strong adverse pressure gradient, thereby effectively suppressing the formation of the separation zone near the wall, optimizing the flow field quality, and improving the airflow ejection ability at the sharp bend wall.

[0030] To verify whether the addition of an internal concave surface improves exhaust diffuser performance, a baseline prototype of a sharply curved, contoured exhaust diffuser without an internal concave surface and a sharply curved, contoured exhaust diffuser with an internal concave surface on the outlet surface were designed. Both models share the same basic shape: the inner diameter d of the inlet ring 10 is 209 mm, the outer diameter D of the inlet ring 10 is 409 mm, and the width L of the projection of the outlet 30 on the plane containing the inlet 10 is 560 mm. The internal concave surface parameters of the sharply curved, contoured exhaust diffuser with an internal concave surface are as follows: the width l1 of the internal concave surface on the plane containing the outlet 30 is 309 mm, the height H0 of the internal concave surface along the axis of the outlet 30 is 98 mm, the distance l0 between the front end of the internal concave surface and the plane containing the inlet 10 is 49 mm, the radius R0 of the first arc surface 31 is 173 mm, and the radius R1 of the second arc surface 32 is 70 mm.

[0031] The three-dimensional numerical simulation was used to compare and analyze the prototype sharp-bend special-shaped exhaust diffuser and the sharp-bend special-shaped exhaust diffuser with a bulge on the outlet surface. The inlet total pressure was set to 110kPa, the total temperature was 830K, the exhaust diffuser outlet ambient pressure was 101kPa, and the ambient temperature was 288.15K. The results are as follows: Figure 9 and Figure 10 As shown in the figure, the baseline prototype's steeply curved profiled exhaust diffuser exhibits a very large separation zone at the front curved surface, and the flow velocity near the wall of the front curved surface is low, indicating that this location has very weak ability to draw air from the surrounding air. However, the steeply curved profiled exhaust diffuser with an inwardly concave outlet surface significantly suppresses the separation zone near the wall near the front steeply curved surface, while significantly improving the separation zone at the front curved wall.

[0032] In addition, the average flow velocity and outlet flow rate at the sharp bend near the wall of the two models were measured. The average flow velocity near the wall of the sharp bend of the baseline prototype sharp bend special-shaped exhaust diffuser was -10m / s, indicating the presence of backflow in this area, and the outlet flow rate was 7.5kg / s. The average flow velocity near the wall of the sharp bend of the sharp bend special-shaped exhaust diffuser with an inner concave surface at the outlet was 85m / s, and the outlet flow rate was 8.0kg / s. Compared with the baseline prototype structure, the outlet flow rate of the sharp bend special-shaped exhaust diffuser with an inner concave surface increased, indicating that the flow capacity of the exhaust diffuser has been improved. The flow velocity near the wall of the sharp bend was greatly increased, the area of ​​the backflow zone was greatly reduced, and the airflow ejection capacity at the sharp bend wall was effectively improved.

Claims

1. A sharply curved special-shaped exhaust diffuser with an inner concave surface at the outlet, comprising 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 one wall surface of the exhaust flow channel (20) is concave inward to form an inner concave surface for discharging low-energy flow. The inner concave surface includes a plurality of smoothly connected curved surfaces, and the outer edge of the inner concave surface forms a part of the edge of the air outlet (30).

2. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 1, characterized in that: The axis of the air inlet (10) is perpendicular to the axis of the air outlet (30).

3. The sharply curved special-shaped exhaust diffuser with an inner concave surface at the outlet according to claim 2, characterized in that: The air inlet (10) is in the shape of a circular ring.

4. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 3, characterized in that: The cross section of the air outlet includes wide parts at both ends and a narrow part formed by the inward compression of the outer edge of the inner concave surface. The outer edge line of the inner concave surface forms an inward concave arc on one side of the narrow part, and the two ends of the inward concave arc are smoothly connected to the outer edge line of the wide part on this side.

5. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 4, characterized in that: The front end of the inner concave surface is located on the connecting surface between the upper end of the air inlet (10) and the air outlet (30), and the rear end forms a part of the edge of the air outlet (30), and the width of the front end gradually expands toward the rear end.

6. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 5, characterized in that: The width of the inner concave surface on the surface where the air outlet (30) is located is l1=(0.74-0.76)*D, the height of the inner concave surface in the axial direction of the air outlet (30) is H0=(0.46-0.48)*d, and the distance between the front end of the inner concave surface and the plane where the air inlet (10) is located is l0=(0.22-0.24)*d, wherein d is the inner diameter of the circular ring of the air inlet (10), and D is the outer diameter of the circular ring of the air inlet (10).

7. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 6, characterized in that: The inner concave surface comprises a first arc surface (31) located in the middle, and second arc surfaces (32) symmetrically arranged on both sides of the first arc surface (31).

8. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 7, characterized in that: The radius of the first arc surface (31) R0=(0.41-0.43)*D, and the radius of the second arc surface (32) R1=(0.16-0.18)*D.

9. The sharply curved special-shaped exhaust diffuser with an inner concave outlet surface according to claim 3, characterized in that: The projection width L of the air outlet (30) on the surface where the air inlet (10) is located is (1.36-1.38)*D.

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