A method for designing the profile of main combustion chamber cap

Abstract

The present invention relates to the field of aero-engine technology and discloses a method for designing a main combustion chamber cap profile. Based on the outlet position of the pre-diffuser and the inlet position of the flame tube, a three-segment arc design method is used to match the cap with the pre-diffuser, thereby achieving precise adjustment of the cap profile. This avoids the problems of existing hyperbolic cap designs that can only provide simple cap shaping and poor matching between the designed cap and the pre-diffuser, thereby solving the problems of cap separation and lip overflow, ensuring that no significant flow losses are generated, and meeting engineering requirements. Furthermore, the design process eliminates the need for extensive simulation and model testing, ensuring the accuracy of the cap profile design while avoiding the problems of large computational complexity and numerous tests required in the separate design and verification of the pre-diffuser, flame tube, and cap.

Description

Technical Field

[0001] The invention relates to the technical field of aviation engines and discloses a method for designing a main combustion chamber cap profile. Background Art

[0002] As the engine thrust-to-weight ratio continues to increase, the Mach number at the combustion chamber inlet is getting higher and higher, and the length of the combustion chamber is getting shorter and shorter. A higher inlet Mach number and a limited length can achieve lower total pressure loss. The combination of a sudden expansion diffuser and a flame tube cap is a commonly used structure in the main combustion chamber of an aircraft engine. This structure has high reliability, can use a shorter diffuser length to achieve dynamic stability of the diffuser flow field, and is insensitive to the distortion of the compressor outlet airflow field. It is the main solution currently used in the combustion chambers of major advanced engines.

[0003] In engineering, not only aerodynamic performance must be considered, but also the ease of assembly of head structures such as nozzles and vortex finders. Therefore, in actual design, it is necessary to consider the assembly of various components and reserve sufficient space between the front diffuser and the cap cover.

[0004] In actual engine operation, the functions of the pre-diffuser and the cap are that the pre-diffuser decelerates and pressurizes the high-speed airflow at the compressor outlet, and the cap guides the decelerated and pressurized airflow into the flame tube and the two-stream channel with a smaller pressure loss, and generates a smaller pressure loss in the cap to increase the head intake pressure, thereby improving the total pressure recovery coefficient and combustion stability of the combustion chamber. However, in actual design, due to the lack of engineering-applicable design methods, the design process is complicated, and the pre-diffuser and the cap are not well matched in the design, which may lead to airflow separation in the cap during the diversion process under high inlet Mach number conditions, overflow of the cap lip, and increase flow losses. Summary of the Invention

[0005] The purpose of the present invention is to provide a main combustion chamber cap surface design method, which has high cap surface design accuracy, simple design process and short time consumption; it can avoid the problem of poor matching between the cap and the front diffuser, thereby solving the problems of cap separation and lip overflow, ensuring that no large flow loss will be generated, and meeting engineering requirements.

[0006] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0007] A method for designing a main combustion chamber cap profile, comprising:

[0008] According to the position of the pre-diffuser outlet and the position of the flame tube inlet, a cap profile boundary line is set between the pre-diffuser outlet and the flame tube inlet;

[0009] Connecting the inlet and outlet of the inner profile of the front diffuser to obtain a first straight line, and extending the first straight line to intersect the boundary line of the cap profile at a first intersection point;

[0010] Select a first circle center in the flame tube, draw a first arc passing through the first intersection point and the starting point of the flame tube inner profile surface, and determine the inferior arc segment between the first intersection point on the first arc and the starting point of the flame tube inner profile surface as the inner profile surface of the cap;

[0011] Connecting the inlet and outlet of the front diffuser outer surface to obtain a second straight line, and extending the second straight line to intersect the cap surface boundary line at a second intersection point;

[0012] Select a second center of the circle in the flame tube, draw a second arc passing through the second intersection point and the starting point of the flame tube outer surface, and the inferior arc segment between the second intersection point on the second arc and the starting point of the flame tube outer surface is determined as the outer surface of the cap;

[0013] Select the third center in the flame tube and draw a third arc passing through the first intersection and the second intersection. The inferior arc segment between the first intersection and the second intersection on the third arc determines the middle profile of the cap.

[0014] Furthermore, the method for setting the boundary line of the cap profile includes: determining the relative sudden expansion gap that meets the assembly structure according to the outlet position of the pre-diffuser and the inlet position of the flame tube, and making the boundary line of the cap profile according to the relative sudden expansion gap, wherein the relative sudden expansion gap is the ratio of the distance between the outlet section of the pre-diffuser and the inlet section of the cap to the inlet height of the pre-diffuser.

[0015] Furthermore, the relative sudden expansion gap d / H=1.1-2.0, wherein d is the distance between the outlet cross section of the pre-diffuser and the inlet cross section of the cap, and H is the inlet height of the pre-diffuser.

[0016] Furthermore, the method for selecting the first center of the circle is: taking the intersection of the first perpendicular bisector of the connecting line segment between the first intersection point and the starting point of the inner profile of the flame tube and the center line of the profile of the front diffuser as the first center of the circle.

[0017] Furthermore, the method for selecting the second center of the circle is: determining the intersection of the first arc and the center line of the front diffuser profile as the third intersection point, and determining the center of the circle formed by the second intersection point, the third intersection point and the starting point of the outer profile of the flame tube as the second center of the circle.

[0018] Furthermore, the method for selecting the third center of the circle is: determining the second perpendicular bisector of the first intersection point and the second intersection point, and determining the intersection of the line connecting the first center of the circle and the second center of the circle and the second perpendicular bisector as the third center of the circle.

[0019] Compared with the prior art, the present invention has the following advantages: Based on the pre-diffuser outlet position and the flame tube inlet position, the present invention adopts a three-segment arc design method to match the cap and pre-diffuser, achieving precise adjustment of the cap profile. This avoids the existing hyperbolic cap design, which only allows for simple cap shaping and poor matching between the designed cap and the pre-diffuser. This solves the cap separation and lip overflow issues, ensures that no significant flow losses occur, and meets engineering requirements. Furthermore, the design process eliminates the need for extensive simulations and model testing, ensuring the accuracy of the cap profile design while avoiding the high computational effort and numerous tests required in the separate design and verification of the pre-diffuser, flame tube, and cap. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the inner surface design of the main combustion chamber cap in Example 1 or 2;

[0021] Figure 2 Schematic diagram of the outer surface design of the main combustion chamber cap in Example 1 or 2;

[0022] Figure 3 Schematic diagram of the design of the middle profile of the main combustion chamber cap in Example 1 or 2. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the present invention to the following embodiments, as all technologies implemented based on the present invention fall within the scope of the present invention.

[0024] Example 1

[0025] A method for designing a main combustion chamber cap profile, comprising:

[0026] According to the position of the pre-diffuser outlet and the flame tube inlet, a cap profile boundary line l1 is set between the pre-diffuser outlet and the flame tube inlet;

[0027] like Figure 1 , connected to the front diffuser inner surface inlet G i 、Pre-diffuser inner surface outlet F i Obtain a first straight line, and extend the first straight line to intersect the cap profile boundary line l1 at a first intersection point B;

[0028] Select the first center of the circle in the flame tube and draw a first arc passing through the first intersection point B and the starting point A of the inner profile of the flame tube. The inferior arc segment between the first intersection point B and the starting point A of the inner profile of the flame tube on the first arc is determined as the inner profile of the cap.

[0029] like Figure 2 , connected to the front diffuser outer surface inlet Go 、Pre-diffuser outer surface outlet F o Obtain a second straight line, and extend the second straight line to intersect with the cap profile boundary line l1 at a second intersection point E;

[0030] Select the second center of the circle in the flame tube, draw a second arc passing through the second intersection point E and the starting point D of the outer profile of the flame tube, and the inferior arc segment between the second intersection point E and the starting point D of the outer profile of the flame tube on the second arc is determined as the outer profile of the cap;

[0031] like Figure 3 , select the third center in the flame tube, draw a third arc passing through the first intersection B and the second intersection E, and the inferior arc segment between the first intersection B and the second intersection E on the third arc determines the middle profile of the cap.

[0032] In this embodiment, a three-segment arc design method is employed to match the hood to the pre-diffuser, based on the pre-diffuser outlet position and the liner inlet position. This allows for precise adjustment of the hood profile, avoiding the limitations of existing hyperbolic hood designs, which only allow for simple hood shaping and poor matching between the hood and the pre-diffuser. This solves the problems of hood separation and lip overflow, ensuring minimal flow losses and meeting engineering requirements. Furthermore, the design process eliminates the need for extensive simulations and model testing, ensuring the accuracy of the hood profile design while avoiding the computationally intensive and often arduous testing required to independently design and verify the pre-diffuser, liner, and hood.

[0033] Example 2

[0034] This embodiment takes the design of the main combustion chamber cap of an aircraft engine as an example to explain the method of the present invention in detail. The relevant design process is as follows:

[0035] Step 1: After determining the overall parameters of the engine's main combustion chamber, complete the design of the pre-diffuser and flame tube of the main combustion chamber. At the same time, make the pre-diffuser's profile centerline l2 based on the pre-diffuser's internal and external flow channel profiles. Generally, the profile centerline l2 is the midpoint line connecting the pre-diffuser's inlet and outlet heights.

[0036] Step 2: setting a cap surface boundary line l1 between the pre-diffuser outlet and the flame liner inlet according to the pre-diffuser outlet position and the flame liner inlet position;

[0037] In this embodiment, after determining the positions of the prediffuser and liner, a relative sudden-diffusion clearance is determined based on the assembly requirements. This clearance can be determined by referring to the design recommendations. The key principle is to select a clearance that meets the assembly requirements from the recommended values. An optimal relative sudden-diffusion clearance, d / H, has an optimal value for prediffuser performance, where d is the distance between the prediffuser outlet and the cap inlet, and H is the prediffuser inlet height. Furthermore, the combustion chamber's structural layout, such as nozzle assembly and disassembly, must be considered. Therefore, in this embodiment, the relative sudden-diffusion clearance, d / H, is set between 1.1 and 2.0.

[0038] like Figure 1 According to the selected relative expansion gap, the cap surface boundary line l1 is made. In this embodiment, the cap surface boundary line can be parallel to the straight line where the inner and outer surface outlets of the front diffuser are located. That is, the cap surface boundary line l1 is formed after the connecting line of the inner and outer surface outlets of the front diffuser is translated toward the flame tube by a distance D.

[0039] Step 3: Connect the inner surface inlet G of the pre-diffuser i 、Pre-diffuser inner surface outlet F i A first straight line is obtained and extended to intersect the cap profile boundary line l1 at a first intersection point B. A first center of a circle is selected within the flame tube. In this embodiment, the first center of a circle is selected by intersecting the first perpendicular bisector of the line segment connecting the first intersection point B and the starting point A of the flame tube inner profile with the centerline of the pre-diffuser profile at point O1. A first arc is constructed with O1 as the first center, passing through the first intersection point B and the starting point A of the flame tube inner profile. The inferior arc segment of the first arc between the first intersection point B and the starting point A of the flame tube inner profile is defined as the cap inner profile.

[0040] Step 4: Connect the front diffuser outer surface inlet G o 、Pre-diffuser outer surface outlet F o Get the second straight line, and extend the second straight line to intersect with the cap profile boundary line l1 at the second intersection point E; select the second center of the circle in the flame tube, such as Figure 2 In this embodiment, the method for selecting the second center of the circle is as follows: the intersection of the first arc and the center line l2 of the front diffuser is determined as the third intersection C, the center O2 of the circle formed by the second intersection E, the third intersection C, and the starting point D of the outer surface of the flame tube is determined as the second center of the circle, a second arc is drawn passing through the second intersection E and the starting point D of the outer surface of the flame tube, and the inferior arc segment between the second intersection E and the starting point D of the outer surface of the flame tube on the second arc is determined as the outer surface of the cap.

[0041] Step 5. Select the third center of the flame tube, such as Figure 3The method for selecting the third center of the circle in this embodiment is as follows: determine the second perpendicular bisector of the first intersection point B and the second intersection point E, and the intersection point O3 of the line connecting the first center of the circle and the second center of the circle and the second perpendicular bisector; with O3 as the third center of the circle, draw a third arc passing through the first intersection point B and the second intersection point E, and the inferior arc segment between the first intersection point B and the second intersection point E on the third arc determines the middle profile of the cap.

[0042] The main combustion chamber cap surface design method in this embodiment takes into account the actual assemblability, changes in the front diffuser and flame tube surfaces, and completes the precise adjustment of the cap surface. There is no need for a large number of simulations and model tests during the design process, which ensures the accuracy of the cap surface design while avoiding the problems of large amount of calculations and large number of tests in the design process; and can achieve the matching design of the front diffuser, flame tube and cap surface, especially solving the problem of poor matching between the front diffuser and the cap in engineering design, which leads to airflow separation and cap lip overflow during the diversion process of the cap under high inlet Mach number conditions, thereby avoiding the problem of large flow losses.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for designing the profile of a main combustion chamber cap, characterized in that: include: According to the position of the pre-diffuser outlet and the position of the flame tube inlet, a cap profile boundary line is set between the pre-diffuser outlet and the flame tube inlet; Connecting the inlet and outlet of the inner profile of the front diffuser to obtain a first straight line, and extending the first straight line to intersect the boundary line of the cap profile at a first intersection point; With the intersection of the first perpendicular bisector of the connecting line segment between the first intersection point and the starting point of the inner profile of the flame tube and the centerline of the profile of the pre-diffuser as the first circle center, a first arc is drawn passing through the first intersection point and the starting point of the inner profile of the flame tube. The inferior arc segment between the first intersection point and the starting point of the inner profile of the flame tube on the first arc is determined as the inner profile of the cap; Connecting the inlet and outlet of the front diffuser outer surface to obtain a second straight line, and extending the second straight line to intersect the cap surface boundary line at a second intersection point; Determine the intersection of the first arc and the centerline of the profile of the pre-diffuser as the third intersection point, determine the center of the circle formed by the second intersection point, the third intersection point, and the starting point of the outer profile of the flame tube as the second center point, draw a second arc passing through the second intersection point and the starting point of the outer profile of the flame tube, and determine the inferior arc segment between the second intersection point and the starting point of the outer profile of the flame tube on the second arc as the outer profile of the cap; Determine the second perpendicular bisector of the first intersection and the second intersection, determine the intersection of the line connecting the first center of the circle and the second center of the circle and the second perpendicular bisector as the third center of the circle, draw a third arc passing through the first intersection and the second intersection, and the inferior arc segment between the first intersection and the second intersection on the third arc determines the middle profile of the cap.

2. The main combustion chamber cap profile design method according to claim 1, characterized in that: The method for setting the boundary line of the cap surface includes: determining the relative sudden expansion gap that meets the assembly structure according to the outlet position of the pre-diffuser and the inlet position of the flame tube, and making the boundary line of the cap surface according to the relative sudden expansion gap. The relative sudden expansion gap is the ratio of the distance between the outlet section of the pre-diffuser and the inlet section of the cap to the inlet height of the pre-diffuser.

3. The main combustion chamber cap profile design method according to claim 2, characterized in that: Relative expansion gap ,in is the distance between the outlet section of the pre-diffuser and the inlet section of the cap, is the pre-diffuser inlet height.

Images