Method for testing the burn-through strength of an aeroengine combustion chamber casing

Abstract

The application provides a kind of aero-engine combustion chamber casing burn-through strength test method, it includes the following steps: S1, with the measured data of aero-engine industry casing burn-through event occurs as the basis, determine the conservative casing burn-through damage size hypothesis;S2, with the structure strength verification thinking, determine the easy to be burnt position;S3, combined with the theory of fracture mechanics, obtain the structure strength verification method and judging criterion of casing with burn-through hole damage.The application is around the strength verification research direction of casing rupture after burn-through, based on the theory of fracture mechanics, gives the structure strength verification method of casing with burn-through hole damage, provides support for casing burn-through compliance verification from the angle of structure integrity verification, fills the gap of this research direction.The test method has a pioneering and guiding significance for the strength verification work under the condition of aero-engine combustion chamber casing burn-through.

Description

Technical Field

[0001] This invention relates to the field of aero-engine combustion chambers, and in particular to a method for testing the burn-through strength of an aero-engine combustion chamber casing. Background Technology

[0002] At present, the design and development of domestic aero-turbine engines is developing rapidly, but there are still many technical difficulties that need to be overcome. For example, the method for verifying the airworthiness compliance of the combustion chamber casing after burn-through is still a difficult problem that has not been solved.

[0003] The airworthiness compliance verification method for engine combustion chamber casing burn-through includes several research directions, such as determining the locations of the combustion chamber casing that are easily burned through, verifying the strength of the casing fracture after burn-through, and determining the jet flame pattern after casing burn-through, etc.

[0004] However, the existing technology only provides the verification of the static strength and stability of the structure under the condition of the combustion chamber casing in its intact state, taking into account the internal and external pressure difference, but does not mention the verification of casing burn-through.

[0005] In view of this, the inventors of this application have designed a test method for the burn-through strength of the combustion chamber casing of an aero-engine in order to overcome the above-mentioned technical problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiency in the prior art that there is no research on the verification of burn-through of the combustion chamber casing of aero-engines, and to provide a test method for the burn-through strength of the combustion chamber casing of aero-engines.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution: A method for testing the burn-through strength of an aero-engine combustion chamber casing, characterized in that the method includes the following steps: S1. Based on the measured data of casing burn-through incidents that have occurred in the aero-engine industry, a conservative assumption is made regarding the size of the casing burn-through damage. S2. Use structural strength verification to determine the locations that are easily burned through; S3. Combining fracture mechanics theory, a structural strength verification method and judgment criteria for casings with burn-through damage are obtained.

[0008] According to an embodiment of the present invention, step S1 specifically includes: assuming the burn-through location of the combustion chamber casing, from the perspective of structural strength, based on specific geometric characteristics, conservatively selecting the part with the most dangerous structural strength, wherein the part with the most dangerous structural strength is the place where the burn-through damage has the greatest impact on the structure.

[0009] According to one embodiment of the present invention, step S2 specifically includes: selecting multiple dangerous locations on the combustion chamber casing as assumed burn-through locations.

[0010] According to one embodiment of the present invention, the dangerous location includes a first location and a second location, which are respectively located in open areas without openings on the rear and front casings of the combustion chamber; The dangerous locations also include a third and a fourth location, which are located on the rear of the combustion chamber and the front casing, respectively, near the largest opening.

[0011] According to one embodiment of the present invention, the dangerous position includes a fifth position, located at the position where the distance between the two openings on the combustion chamber casing is the smallest.

[0012] According to one embodiment of the present invention, step S3 specifically includes: calculating the far-field circumferential stress generated by the pressure load acting on the front casing cone of the combustion chamber. ; Calculate the far-field circumferential stress generated by the pressure load acting on the cylindrical casing of the combustion chamber: ; Where R represents the maximum diameter of the casing, and ΔP represents the pressure difference acting on the casing. Indicates the minimum permissible thickness of the casing; This indicates the half-angle of the conical tube.

[0013] According to an embodiment of the present invention, step S3 further includes: obtaining the critical crack length corresponding to the critical stress intensity factor of the combustion chamber casing material based on the stress intensity factor definition formula. ; but,

[0014] in, This represents 1 / 2 of the critical crack length. This indicates the critical stress intensity factor of the material used in the combustion chamber casing. This indicates the far-field circumferential stress of the casing. This indicates the critical crack length of the rear casing of the combustion chamber. This indicates the critical crack length of the front casing of the combustion chamber.

[0015] According to one embodiment of the present invention, for the first position and the second position, the fracture safety margin of the front and rear casings is:

[0016] L1 represents the initial damage crack length in the open area of ​​the casing.

[0017] According to one embodiment of the present invention, for the third position and the fourth position, the safety margin for fracture on the front and rear casings is:

[0018] Where L2 represents the initial crack length, which is the sum of the initial burn-through damage size and the axial dimensions of the adjacent largest openings on the combustion chamber and the front casing.

[0019] According to an embodiment of the present invention, step S3 specifically includes: establishing a three-dimensional elastoplastic finite element model to simulate the situation where the axial ligament region between two closely spaced openings on the casing is burned out, and applying a normal operating pressure load. A complete, crack-free three-dimensional elastoplastic finite element model of the casing was also established, and the maximum working pressure load was applied.

[0020] According to one embodiment of the present invention, when using a three-dimensional elastoplastic finite element model to analyze the structural strength safety margin of the casing under extreme conditions, the applied pressure load usually needs to take into account the amplification factors K1, K2, K3, and K4. Among them, K1 is used to consider the impact of the minimum thickness manufacturing deviation of the casing on the structural analysis; K2 is used to consider the load factor specified in the engine static bearing component clause; K3 is used to consider the impact of the minimum stress-strain curve on the structural analysis; K4 is used to consider the impact of the deviation between the normal operating pressure or maximum possible pressure and the cavity pressure load at the end of takeoff on the strength verification.

[0021] The positive and progressive effects of this invention are as follows: This invention presents a test method for the burn-through strength of aero-engine combustor casings. Focusing on the research direction of strength verification of casing fracture after burn-through, and based on fracture mechanics theory, it provides a method for verifying the structural strength of casings with burn-through damage. From the perspective of structural integrity verification, it provides support for the conformity verification of casing burn-through, filling a gap in this research direction. The test method is pioneering and instructive for strength verification work under burn-through conditions of aero-engine combustor casings. Attached Figure Description

[0022] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, in which the same reference numerals always denote the same features, wherein: Figure 1 This is a flowchart of the test method for the burn-through strength of the combustion chamber casing of an aero-engine according to the present invention.

[0023] Figure 2 This is a schematic diagram illustrating the selection of the burn-through location in the burn-through strength test method for the combustion chamber casing of an aero-engine according to the present invention. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Embodiments of the invention will now be described in detail with reference to the accompanying drawings. Preferred embodiments of the invention will now be described in detail, examples of which are shown in the drawings. Wherever possible, the same reference numerals will be used in all the drawings to denote the same or similar parts.

[0026] Furthermore, although the terminology used in this invention is selected from commonly known and used terms, some terms mentioned in this specification may have been selected by the applicant in his or her judgment, and their detailed meanings are explained in the relevant sections of the description herein.

[0027] Furthermore, the invention should be understood not only through the actual terminology used, but also through the meaning implied by each term.

[0028] Figure 1 This is a flowchart of the test method for the burn-through strength of the combustion chamber casing of an aero-engine according to the present invention.

[0029] like Figure 1 As shown, this invention discloses a method for testing the burn-through strength of an aero-engine combustion chamber casing, which includes the following steps: Step S1: Based on the measured data of casing burn-through incidents that have occurred in the aero-engine industry, determine a conservative assumption for the size of the casing burn-through damage.

[0030] Preferably, step S1 includes: assuming the burn-through location of the combustion chamber casing, from the perspective of structural strength, conservatively selecting the part with the most dangerous structural strength based on the specific geometric characteristics, wherein the part with the most dangerous structural strength is the place where the burn-through damage has the greatest impact on the structure.

[0031] Step S2: Use structural strength verification to determine the locations that are easily burned through.

[0032] Preferably, step S2 includes selecting multiple dangerous locations on the combustion chamber casing as assumed burn-through locations.

[0033] For example, such as Figure 2 As shown, the dangerous location may preferably include a first location A1 and a second location A2, which are respectively located in open areas without openings on the rear and front casing bodies of the combustion chamber.

[0034] Alternatively, the dangerous locations may also include a third location A3 and a fourth location A4, located on the rear and front casing of the combustion chamber, respectively, near the largest opening.

[0035] Alternatively, the dangerous location may also include a fifth location A5, located at the position where the distance between the two openings on the combustion chamber casing is the smallest.

[0036] Step S3: Combining fracture mechanics theory, obtain the structural strength verification method and judgment criteria for the casing with burn-through damage.

[0037] Preferably, step S3 may include: calculating the far-field circumferential stress generated by the pressure load acting on the front casing cone of the combustion chamber. ; Calculate the far-field circumferential stress generated by the pressure load acting on the cylindrical casing of the combustion chamber: ; Where R represents the maximum diameter of the casing, and ΔP represents the pressure difference acting on the casing. Indicates the minimum permissible thickness of the casing; This indicates the half-angle of the conical tube.

[0038] Furthermore, step S3 specifically includes: according to the definition formula of stress intensity factor, the critical crack length corresponding to the critical stress intensity factor of the combustion chamber casing material can be obtained: ; but,

[0039] in, This represents 1 / 2 of the critical crack length. This indicates the critical stress intensity factor of the material used in the combustion chamber casing. This indicates the far-field circumferential stress of the casing. This indicates the critical crack length of the rear casing of the combustion chamber. This indicates the critical crack length of the front casing of the combustion chamber.

[0040] For the first position A1 and the second position A2, the fracture safety margin of the front and rear casings is:

[0041] L1 represents the initial damage crack length in the open area of ​​the casing.

[0042] For positions A3 and A4, the safety margin for fractures occurring on the front and rear casings is:

[0043] Where L2 represents the initial crack length, which is the sum of the initial burn-through damage size and the axial dimensions of the adjacent largest openings on the combustion chamber and the front casing.

[0044] In addition, for the fifth position A5, step S3 specifically includes: establishing a three-dimensional elastic-plastic finite element model to simulate the situation where the axial ligament region between two closely spaced openings on the casing is burned off, and applying normal operating pressure load. A complete, crack-free three-dimensional elastoplastic finite element model of the casing was also established, and the maximum working pressure load was applied.

[0045] When using a three-dimensional elastoplastic finite element model to analyze the structural strength safety margin of the casing under extreme conditions, the applied pressure load usually needs to consider the amplification factors K1, K2, K3, and K4. Among them, K1 is used to consider the impact of the minimum thickness manufacturing deviation of the casing on the structural analysis; K2 is used to consider the load factor specified in the engine static bearing component clause; K3 is used to consider the impact of the minimum stress-strain curve on the structural analysis; K4 is used to consider the impact of the deviation between the normal operating pressure or maximum possible pressure and the cavity pressure load at the end of takeoff on the strength verification.

[0046] Based on the above description, the following specific examples further illustrate the test method for burn-through strength of the aero-engine combustion chamber casing of the present invention: for example, First, select the location of the burn-through in the combustion chamber casing: Based on a real combustion chamber casing burn-through incident that occurred in the engine's service history, a foreign engine manufacturer assumed the shape and height of the jet flame, as well as the location and diameter of the burn-through hole. However, to verify the structural integrity of the casing with burn-through damage, the assumed location of the burn-through can be conservatively selected from a structural strength perspective, based on specific geometric characteristics, at the point where the structural strength is most vulnerable, i.e., the location where the burn-through damage has the greatest impact on the structure.

[0047] like Figure 2 As shown, five critical locations on the combustion chamber casing are selected as hypothetical burn-through locations. Location A1 and location A2 are respectively located in open areas without openings on the rear and front casing bodies of the combustion chamber. These areas are far from other features and are also where the maximum circumferential stress occurs.

[0048] Positions A3 and A4 are located on the rear and front casings, respectively, near the largest openings, i.e., near the fuel injector interfaces. The presence of these openings causes stress concentration in the circumferential direction.

[0049] Position A5 is assumed to be the location where the distance between two openings on the casing is smallest, such as the location between the bleed port and the fuel injector interface on the casing. The area between two adjacent openings may be joined together due to casing burn-through, so this area is called the "dangerous ligament".

[0050] II. Assumptions on the initial damage size of the casing burn-through

[0051] The largest jet flame burn-through diameter observed on the GE CF6 and CFM56 engines that experienced combustion chamber casing burn-through incidents was 1.1 inches. In contrast, flame analysis of the GE90 engine predicted a maximum burn-through diameter of 0.7 inches. A heat-affected zone exists around the burn-through, where cracking could also occur due to tensile overload and severe degradation of material properties, as temperatures here can exceed 2000 degrees Celsius. Therefore, when assessing the structural strength of the combustion chamber casing with burn-through damage, the assumed initial damage is a 2.5 in diameter through-hole, which includes a 1.1 in diameter jet flame burn-through hole and a surrounding annular heat-affected zone (considering the severe degradation of material properties).

[0052] III. Strength Verification of Combustion Chamber Casing with Burn-Through Damage

[0053] A structural strength assessment was conducted on the combustion chamber casing with assumed burn-through damage to demonstrate that it would not fracture and that structural integrity would be guaranteed. The material properties (temperature effects already considered), geometric dimensions, and pressure loads of the combustion chamber casing are assumed to be as shown in Table 1 below.

[0054] Table 1: Assuming material properties, geometric dimensions, and pressure loads of the casing

[0055] IV. Burn-through in the open area of ​​the combustion chamber casing

[0056] If the combustion chamber casing shows Figure 2 In the case of burn-through holes at the first position A1 or the second position A2 described above, the damage (hole or axial crack) caused by the jet flame is located on the pressure-bearing thin wall of the casing.

[0057] Based on the data in Table 1 above, the far-field circumferential stress generated by the pressure load acting on the conical cylinder of the combustion chamber front casing can be calculated using the following formula:

[0058] Similarly, the far-field circumferential stress generated by the pressure load acting on the cylindrical casing of the combustion chamber can be calculated using the following formula:

[0059] Where R represents the maximum diameter of the casing; ΔP represents the pressure difference acting on the casing, %P3-Pamb; t represents the minimum allowable thickness of the casing; and α represents the half-angle of the conical cylinder.

[0060] Based on the definition of the stress intensity factor, the critical crack length corresponding to the critical stress intensity factor of the combustion chamber casing material can be obtained:

[0061] but

[0062] in, This indicates 1 / 2 of the critical crack length; This indicates the critical stress intensity factor of the material used in the combustion chamber casing; This indicates the far-field circumferential stress of the casing. This indicates the critical crack length of the rear casing of the combustion chamber. This indicates the critical crack length of the front casing of the combustion chamber.

[0063] The initial damage crack length in the open area of ​​the casing is 2.5 inches, and the fracture safety margin for the front and rear casing cylinders is:

[0064] 5. Burn-through in the area adjacent to the largest opening of the combustion chamber casing.

[0065] If the combustion chamber casing shows Figure 2 For the burn-through cases described above, namely the third position A3 or the fourth position A4, which occur next to the fuel injector opening, the structural impact of the burn-through is evaluated using the same method described above.

[0066] The axial dimension of the fuel nozzle orifice on the casing is 2.1 inches, and the assumed initial burn-through damage size is 2.5 inches. Therefore, the initial crack length in this case is the sum of these two dimensions, 4.6 inches. For this initial crack, the safety margins for fracture on the front and rear casings are as follows:

[0067] VI. Burn-through of the "dangerous ligament" area of ​​the combustion chamber casing

[0068] If the combustion chamber casing shows signs of... Figure 2 This relates to the burn-through situation described above for position A5, where the ligament connection area between two adjacent openings on the casing is burned through and severed. For example, the axial ligament area between the bleed air opening and the fuel nozzle interface on the combustion chamber casing is burned through, severing the ability of this area on the casing to transmit circumferential stress.

[0069] A three-dimensional elastoplastic finite element model was established to simulate the situation where the axial ligament region between the bleed air opening and the fuel nozzle interface on the casing was burned off, and normal operating pressure load was applied.

[0070] Similarly, a complete, crack-free three-dimensional elastoplastic finite element model of the casing is established, and the maximum working pressure load is applied. When using the three-dimensional elastoplastic finite element model to analyze the structural strength safety margin of the casing under extreme conditions, the applied pressure load usually needs to consider four amplification factors: K1, K2, K3, and K4.

[0071] Among them, K1 is used to consider the impact of manufacturing deviations in the minimum thickness of the casing on structural analysis; K2 is used to consider the load factor specified in the CCAR33.64 engine static pressure component clause; K3 is used to consider the impact of the minimum stress-strain curve on structural analysis; and K4 is used to consider the impact of the deviation between the normal operating pressure or maximum possible pressure and the intracavity pressure load at the end of takeoff on strength verification.

[0072] For cases where the narrow ligament connection area on the casing is burned through, in order to be conservative, in addition to considering the above four pressure load amplification factors, all pressure loads should be amplified by an additional 1.5 times.

[0073] Three-dimensional elastoplastic finite element analysis revealed that the maximum equivalent plastic strain at the air intake opening and fuel nozzle interface on the casing was 0.07% and 0.08%, respectively, while the maximum equivalent plastic strain at the lead connector interface was 1.12%, all of which are far lower than the elongation of 9.5% at room temperature.

[0074] Therefore, it was proven that the casing would not rupture even with burn-through damage, thus ensuring structural integrity.

[0075] This invention presents a method for testing the burn-through strength of an aero-engine combustor casing. First, based on measured data from actual burn-through incidents in the aero-engine industry, a conservative assumption is made regarding the burn-through damage size. Then, using structural strength verification principles, the method identifies locations susceptible to burn-through by considering factors such as weak points in the combustor casing, unique geometric features, and the impact of changes in geometry after burn-through. Finally, combining fracture mechanics theory, a method and criteria for verifying the structural strength of the casing with burn-through damage are provided, along with specific calculation examples. This is the first description of a method for verifying the strength of a combustor casing after burn-through.

[0076] In summary, this invention, a test method for the burn-through strength of an aero-engine combustor casing, focuses on the strength verification research direction of casing fracture after burn-through. Based on fracture mechanics theory, it provides a structural strength verification method for casings with burn-through damage, providing support for the burn-through compliance verification of the casing from the perspective of structural integrity verification, thus filling a gap in this research direction. The test method is pioneering and instructive for strength verification work under burn-through conditions of aero-engine combustor casings.

[0077] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for testing the burn-through strength of an aero-engine combustion chamber casing, characterized in that, The method for testing the burn-through strength of the aero-engine combustion chamber casing includes the following steps: S1. Based on the measured data of casing burn-through incidents that have occurred in the aero-engine industry, a conservative assumption is made regarding the size of the casing burn-through damage. S2. Use structural strength verification to determine the locations that are easily burned through; S3. Combining fracture mechanics theory, obtain the structural strength verification method and judgment criteria for the casing with burn-through damage; Step S3 specifically includes: calculating the far-field circumferential stress generated by the pressure load acting on the conical cylinder of the combustion chamber front casing. ; Calculate the far-field circumferential stress generated by the pressure load acting on the cylindrical casing of the combustion chamber: ; Where R represents the maximum diameter of the casing, and ΔP represents the pressure difference acting on the casing. Indicates the minimum permissible thickness of the casing; Indicates the half-angle of the conical tube; Step S3 further includes: according to the definition formula of stress intensity factor, the critical crack length corresponding to the critical stress intensity factor of the combustion chamber casing material can be obtained: ; but, in, This represents 1 / 2 of the critical crack length. This indicates the critical stress intensity factor of the material used in the combustion chamber casing. This indicates the far-field circumferential stress of the casing. This indicates the critical crack length of the rear casing of the combustion chamber. This indicates the critical crack length of the front casing of the combustion chamber.

2. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 1, characterized in that, Step S1 specifically includes: assuming the burn-through location of the combustion chamber casing, from the perspective of structural strength, based on the specific geometric characteristics, conservatively selecting the part with the most dangerous structural strength, which is the place where the burn-through damage has the greatest impact on the structure.

3. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 2, characterized in that, Step S2 specifically includes: selecting multiple dangerous locations on the combustion chamber casing as assumed burn-through locations.

4. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 3, characterized in that, The dangerous locations include a first location and a second location, which are respectively located in open areas without openings on the rear and front casings of the combustion chamber. The dangerous locations also include a third and a fourth location, which are located on the rear of the combustion chamber and the front casing, respectively, near the largest opening.

5. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 4, characterized in that, The dangerous location includes the fifth location, which is located at the position where the distance between the two openings on the combustion chamber casing is the smallest.

6. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 4, characterized in that, For the first position and the second position, the fracture safety margin of the front and rear casings is: L1 represents the initial damage crack length in the open area of ​​the casing.

7. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 6, characterized in that, For the third and fourth positions, the safety margin for breakage on the front and rear casings is: Where L2 represents the initial crack length, which is the sum of the initial burn-through damage size and the axial dimensions of the adjacent largest openings on the combustion chamber and the front casing.

8. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 5, characterized in that, Step S3 specifically includes: establishing a three-dimensional elastoplastic finite element model to simulate the situation where the axial ligament region between two closely spaced openings on the casing is burned out, and applying normal operating pressure load. A complete, crack-free three-dimensional elastoplastic finite element model of the casing was also established, and the maximum working pressure load was applied.

9. The test method for burn-through strength of aero-engine combustion chamber casing as described in claim 5, characterized in that, When using a three-dimensional elastoplastic finite element model to analyze the structural strength safety margin of the casing under extreme conditions, the applied pressure load usually needs to consider the amplification factors K1, K2, K3, and K4. Among them, K1 is used to consider the impact of the minimum thickness manufacturing deviation of the casing on the structural analysis; K2 is used to consider the load factor specified in the engine static bearing component clause; K3 is used to consider the impact of the minimum stress-strain curve on the structural analysis; K4 is used to consider the impact of the deviation between the normal operating pressure or maximum possible pressure and the cavity pressure load at the end of takeoff on the strength verification.

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