Flame tube design method

Abstract

The application provides a flame tube design method and relates to the technical field of aero-engines.The flame tube design method comprises the following steps: step 1, dividing a thermal load level area based on a temperature field of a uniformly distributed cooling hole scheme; step 2, dynamically configuring hole diameter and inclination angle parameters of the cooling hole for different thermal load level areas; step 3, dynamically designing a cooling hole spacing for different thermal load level areas; step 4, setting a hole diameter gradual change buffer zone at the junction of axial and circumferential partitions, and realizing continuous and gradual change of the hole diameter by setting the gradual change buffer zone; step 5, verifying the continuity of the air film formed by the cooling hole; and step 6, simulating and calculating the wall temperature of the flame tube by using simulation software, and evaluating whether the comprehensive wall temperature gradient index meets the requirements.The application can solve the problems of large wall temperature gradient and local wall temperature over-temperature of the main combustion chamber of a high-performance engine, make the wall temperature tend to be uniformly distributed, and greatly prolong the service life of the flame tube.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and more specifically to a flame tube design method. Background Technology

[0002] With the improvement of aero-engine performance, the inlet temperature and temperature rise of the combustion chamber have increased further. More air is used for combustion, and the amount of air used for cooling has decreased. The working environment of the flame tube has become more severe, which puts forward higher requirements for cooling design.

[0003] Traditional multi-hole flame tube cooling designs employ a fixed inclination angle, equal spacing, and uniform orifice diameter arrangement, resulting in a uniform airflow distribution across the flame tube wall. However, the distribution of high-temperature combustion gases within the flame tube is non-uniform, directly influencing the flame tube wall temperature distribution. The area near the main combustion orifice is a high-heat-load zone with higher wall temperatures and a larger cooling gas demand, while the area near the outlet is a low-heat-load zone with lower wall temperatures and a smaller cooling gas demand. This traditional cooling arrangement leads to excessive cooling airflow in the low-heat-load zone and insufficient cooling in the high-heat-load zone, resulting in low cooling air utilization. This can easily lead to large localized wall temperature gradients and thermal stress concentration, posing a risk of tube deformation and ablation, negatively impacting the reliability and service life of the flame tube. Summary of the Invention

[0004] In view of this, the present invention provides a flame tube design method to effectively improve the utilization efficiency of cooling air, reduce the wall temperature gradient, and extend the life of the flame tube.

[0005] This invention provides the following technical solution: a flame tube design method, comprising: Step 1, dividing the temperature field of a uniformly distributed cooling hole scheme into heat load level regions; Step 2, dynamically configuring the aperture and inclination angle parameters of the cooling holes for different heat load level regions; Step 3, dynamically designing the spacing between cooling holes for different heat load level regions; Step 4, setting a gradual aperture buffer zone at the boundary of the axial and circumferential zones, and achieving continuous gradual aperture change by setting the gradual buffer zone; Step 5, verifying the continuity of the gas film formed by the cooling holes; Step 6, using simulation software to simulate and calculate the flame tube wall temperature, and evaluating whether the comprehensive wall temperature gradient index meets the requirements.

[0006] Compared with the prior art, the beneficial effects that the at least one technical solution adopted by the present invention can achieve include at least the following:

[0007] Breaking away from the traditional approach of uniformly arranging cooling holes, this method establishes a dynamic matching design approach for heat load and cooling distribution. Based on the actual heat load, it designs cooling hole diameters and spacing with gradient variations. This addresses the issues of large temperature gradients and localized overheating in the main combustion chamber flame tube of high-performance engines, resulting in a more uniform wall temperature distribution and significantly extending flame tube life. It can guide the cooling design of high-temperature combustion chamber flame tubes, shortening the design cycle and reducing flame tube operating costs.

[0008] This invention can effectively support model engineering design and has been applied and verified in the combustion chamber of a certain type of gas turbine. It has high versatility and operability, can be promoted and applied in the industry, and has good economic benefits and great practical engineering application value. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a flowchart of an embodiment of the present invention;

[0011] Figure 2 This is a schematic diagram of axial heat load zoning;

[0012] Figure 3 This is a schematic diagram of the circumferential heat load zoning;

[0013] Figure 4 This is a schematic diagram of the gradient hole arrangement. Detailed Implementation

[0014] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0015] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] like Figures 1 to 4 As shown, this embodiment of the invention provides a flame tube design method, specifically including the following steps:

[0017] Step 1: Divide the temperature field into heat load level regions based on the uniformly distributed cooling hole scheme.

[0018] Based on the design input, the cooling flow rate of the flame tube is determined to be W. hole Calculate the opening area of ​​the gas film in the flame tube:

[0019] (1)

[0020] Among them, A film W represents the opening area of ​​the air film pores. hole C is the air film pore flow rate. d ρ is the air film orifice flow coefficient, ρ is the air density, and ΔP is the pressure difference between the inlet and outlet of the air film orifice.

[0021] Calculation of cooling opening area for the inner and outer rings of the flame tube:

[0022] (2)

[0023] (3)

[0024] Among them, A film,in A film,o These are the film gas pore areas of the inner and outer rings of the flame tube, respectively. in A o These are the surface areas of the inner and outer rings of the flame tube, respectively.

[0025] Calculate the number of cooling holes based on the opening area of ​​the air film vents:

[0026] (4)

[0027] Where, N hole d represents the number of cooling holes. hole This is the diameter of the cooling hole.

[0028] Based on the preliminary obtained number and diameter of cooling holes, the cooling design of the multi-hole flame tube is completed. The cooling holes are evenly distributed, and the ratio of the circumferential spacing to the axial spacing of the cooling holes should be between 0.6 and 0.9. The inclination angle of the cooling holes is between 20° and 45°.

[0029] The flame tube was simulated and evaluated to obtain the flame tube wall temperature distribution. The flame tube was divided into three-dimensional partitions according to the heat load. Along the axial direction, it was divided into the head zone (Ⅰ), the main combustion zone (Ⅱ), the transition zone (Ⅲ), and the outlet zone (Ⅳ). The area directly opposite the fuel nozzle along the circumference was the high heat load arc segment (A), and the area between the fuel nozzles was the secondary heat load arc segment (B).

[0030] Step 2: Dynamically configure the cooling hole diameter and tilt angle parameters for different areas.

[0031] Calculate the cooling hole diameter along the engine axial direction according to the heat load zones:

[0032] Main combustion zone:

[0033] (5)

[0034] (6)

[0035] Head area:

[0036] (7)

[0037] (8)

[0038] Transition zone:

[0039] (9)

[0040] (10)

[0041] Export area:

[0042] (11)

[0043] (12)

[0044] Wherein, α is the descent rate in the high-temperature region, ranging from 0 to 1.4; λ is the descent rate in the low-temperature region, ranging from 0.2 to 0.7; k is the pore size variation factor in the high-temperature region, ranging from 1 to 1.5; and β is the pore size scaling factor, ranging from 1.0 to 1.5.

[0045] Step 3: Dynamically design the spacing of cooling holes for different temperature zones.

[0046] The axial hole spacing is calculated based on the wall temperature level and the design of the cooling hole spacing.

[0047] (13)

[0048] Where: x is the axial coordinate, T(x) is the wall temperature at the current hole row position, and T max T is the highest wall temperature in the axial region. min S is the lowest wall temperature in the region. min δ is the minimum axial hole spacing. s is the hole spacing expansion coefficient (1~5), and q is the gradient morphology index.

[0049] The calculation method for the circumferential hole spacing is as follows:

[0050] (14)

[0051] Where: θ is the circumferential angle with the nozzle centerline as 0°; T(θ) is the wall temperature at angle θ, T zmax T represents the highest wall temperature in region A. zmin P is the lowest wall temperature in region B. min γ is the minimum circumferential hole spacing, γ is the circumferential hole spacing expansion coefficient (0.15~0.6), N is the number of nozzles, and p is the angle index (2.0~5.0).

[0052] The hole spacing designed using this method has the characteristics of densely arranged cooling holes in areas with higher wall temperatures and sparsely arranged cooling holes in areas with relatively lower wall temperatures.

[0053] Step 4: Transition Zone Design

[0054] A gradual aperture buffer zone is set at the junction of the axial and circumferential zones. The aperture is continuously gradually changed by setting the zone transition buffer zone. The width of the buffer zone is ≥3 rows of cooling holes.

[0055] Step 5: Verification of air-supported membrane continuity

[0056] After completing the preliminary design, the effectiveness of the air-supported membrane structure was verified using the following formula:

[0057] (15)

[0058] Where θ is the tilt angle of the cooling hole.

[0059] When η≥0.1, the requirement is met. When η<0.1, step 2 needs to be repeated, and the hole spacing S or the cooling hole inclination angle θ needs to be increased on the basis of the previous step until the requirement for effective air film coverage is met.

[0060] Step 6: Wall Temperature Gradient Assessment

[0061] Simulation software is used to simulate and calculate the flame tube wall temperature to evaluate whether the comprehensive wall temperature gradient index meets the requirements. If it does, the flame tube cooling design meets the requirements; otherwise, the cooling structure parameters need to be readjusted.

[0062] Among them, C is calculated in the initial calculation of the cooling holes. d The value range is 0.6~0.8, and the diameter d of the cooling hole is... hole The value range is 0.5~1.2mm.

[0063] Furthermore, the aperture change ratio between the high heat load zone and the low heat load zone must meet the following requirements:

[0064] 1.2≤d h / d c≤1.8 (16)

[0065] In step 3, the value of the gradient morphology index n is related to the degree of wall temperature change. The region with linear wall temperature change is q=1, the region with accelerated wall temperature change is q=2, and the region with steep drop and slow rise in wall temperature change is q=3.

[0066] The rate of change of axial hole spacing must meet the following requirements:

[0067] The difference in axial spacing between the first and last rows in the head area and the main combustion zone ;

[0068] The difference in axial spacing between the first and last rows in the transition zone and the exit zone .

[0069] It should be noted that the head zone and main combustion zone are areas where wall temperature rises, and the axial spacing decreases, so it is the first row minus the last row. The purpose of being greater than 0.8 is to ensure that as the temperature rises, the reduction in the spacing of the holes is large enough, and the cooling air volume increases. The transition zone and outlet zone are areas where the temperature drops, and the trend is opposite, so it is the last row minus the first row.

[0070] In step 4, the change in the transition buffer aperture adopts an exponentially decaying function:

[0071] Transition from high temperature zone to low temperature zone:

[0072] (17)

[0073] Transition from low temperature zone to high temperature zone:

[0074] (18)

[0075] Where, d h For the aperture in the high-temperature region, d c The aperture is in the low-temperature zone, and x is the current axial position. h x is the axial coordinate at the end of the high-temperature zone. c θ represents the initial axial coordinate of the low-temperature region, and β is the attenuation intensity coefficient.

[0076] β is adjusted according to different engine sizes, with a value range of 3.0 to 8.0. The larger the β value, the faster the aperture decay rate.

[0077] The aperture change designed using an exponential decay function has the characteristics of a steep drop in the first part and a gradual drop in the second part. The aperture shrinks rapidly near the high temperature region and the aperture change is gradual near the low temperature region.

[0078] In step 6, the method for calculating the overall wall temperature gradient exponent is as follows:

[0079] First, calculate the axial temperature gradient evaluation index G. axial And circumferential temperature gradient evaluation index U circ :

[0080] (19)

[0081] Where n is the number of holes, S i The axial spacing of the i-th row of holes, S avg Δx represents the axial spacing of the i-th row, and Δx represents the axial spacing between adjacent holes.

[0082] Circumferential temperature gradient evaluation index U circ The calculation method is as follows:

[0083] (20)

[0084] Wherein, P(θ) is the circumferential hole spacing at angle θ, P min T is the minimum circumferential hole spacing. avg The circumferential average temperature.

[0085] The method for calculating the overall wall temperature gradient index is as follows:

[0086] (twenty one)

[0087] When G axial ≤1℃ / mm, axial gradient is considered acceptable, U circ If E ≤ 0.5, the circumferential gradient is considered acceptable; if E ≤ 5, the overall wall temperature gradient is considered acceptable.

[0088] The following description uses a specific embodiment:

[0089] Step 1: Divide the temperature field into heat load level regions based on the uniformly distributed cooling hole scheme.

[0090] Based on the design inputs, the combustion chamber parameters were determined as follows: inlet temperature 750K, inlet pressure 2.1 MPa, inlet flow rate 50kg / s, and flame tube cooling flow rate accounting for 25%. Based on the above parameters, a uniform arrangement scheme was designed: cooling hole diameter 0.8mm, hole row spacing 10mm, circumferential spacing 7mm, hole inclination angle 30°, and a flame tube model was established.

[0091] Commercial software was used to perform fluid-structure interaction simulation calculations of the main combustion chamber to obtain the flame tube wall temperature distribution. The highest wall temperature was 850℃ and the lowest was 500℃. Based on the wall temperature distribution, the flame tube was divided into three-dimensional partitions according to the heat load. Along the axial direction, it was divided into the head zone (Ⅰ), the main combustion zone (Ⅱ), the transition zone (Ⅲ), and the outlet zone (Ⅳ). The area directly opposite the fuel nozzle along the circumference was the high heat load arc segment (A), and the area between the fuel nozzles was the secondary heat load arc segment (B).

[0092] Step 2: Dynamically configure the cooling hole diameter and tilt angle parameters for different areas.

[0093] Based on the wall temperature distribution obtained in step 1, the diameter and inclination angle of the cooling holes along the flow path are calculated. The diameters of the cooling holes in the head zone, main combustion zone, transition zone, and outlet zone are 0.7 mm, 1.0 mm, 0.8 mm, and 0.7 mm, respectively, and the inclination angles are 30°, 25°, 30°, and 40°, respectively. The ratio of the hole diameter change between the high heat load zone and the low heat load zone is 1.67, satisfying 1.2 ≤ d. h / d l The requirement is ≤1.8.

[0094] Step 3: Dynamically design the spacing of cooling hole rows for different temperature zones.

[0095] Based on the wall temperature distribution obtained in step 1, the axial spacing S(x) and circumferential spacing S(θ) of the cooling holes related to the wall temperature are calculated using formulas (13) and (14), respectively. The hole spacing in the high-temperature section approaches the minimum value, enhancing local cooling in the high-temperature zone. The calculation results are as follows:

[0096] Table 1 Calculation results of hole spacing

[0097]

[0098] Table 2 Calculation results of circumferential spacing

[0099]

[0100] After the design is completed, the rationality of the aperture distribution needs to be checked. The final design result meets the requirement that the cooling holes are densely arranged in areas with higher wall temperatures and sparsely arranged in areas with relatively lower wall temperatures.

[0101] Step 4: Transition Zone Design

[0102] A gradual aperture transition buffer zone is set at the boundary of the axial and circumferential zones, with a width of ≥3 rows of cooling holes. The aperture d(x) of the cooling holes in the transition buffer zone is calculated using an exponential decay function. The aperture decreases rapidly near the high-temperature zone and changes gradually near the low-temperature zone. This calculation method ensures a continuous and gradual aperture transition, avoiding areas of discontinuity in the cooling gas film. For example, the aperture calculation results for the transition zone from the head zone to the main combustion zone are as follows:

[0103]

[0104] Step 5: Verification of air-supported membrane continuity

[0105] After completing the preliminary design, the effectiveness of the air film coverage needs to be verified to determine its effectiveness. The effective air film coverage index η is calculated, and the calculated η value for this scheme is 0.12~0.3. When the design requirements are met, the cooling design of the flame tube is reasonable.

[0106] Step 6: Wall Temperature Gradient Assessment

[0107] The wall temperature of the flame tube was simulated and calculated using simulation software. The axial temperature gradient evaluation index G was obtained from the calculation results. axial= 0.8, circumferential temperature gradient evaluation index U circ =0.3, and the comprehensive wall temperature gradient index E=3.2, proving that the low wall temperature cooling structure has a low wall temperature gradient and the cooling design meets the requirements.

[0108] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A flame tube design method, characterized in that, include: Step 1: Divide the temperature field into heat load level regions based on the uniformly distributed cooling hole scheme; Step 2: Dynamically configure the aperture and tilt angle parameters of the cooling holes for different heat load levels. Step 3: Dynamically design the spacing of cooling holes for different heat load levels. Step 4: Set a aperture gradient buffer zone at the junction of the axial and circumferential zones to achieve continuous aperture gradient. Step 5: Verify the continuity of the air film formed by the cooling holes; Step 6: Use simulation software to simulate and calculate the flame tube wall temperature, and evaluate whether the comprehensive wall temperature gradient index meets the requirements. Step 1 specifically involves: The flame tube is divided into three-dimensional zones according to the heat load, and along the axis, it is divided into the head zone, main combustion zone, transition zone and outlet zone; The area directly opposite the fuel nozzle in the circumference is divided into high heat load arc segments, and the area between the fuel nozzles is divided into secondary heat load arc segments. Step 2 specifically involves: Through formula The aperture of the main combustion zone is calculated using the formula. Calculate the tilt angle of the main combustion zone, where ; Through formula The aperture of the head region is calculated using the formula. Calculate the tilt angle of the head region, where ; Through formula The aperture of the transition zone is calculated using the formula. Calculate the tilt angle of the transition region, where ; Through formula The aperture of the outlet region is calculated using the formula. Calculate the inclination angle of the outlet region, where ; Where α is the lapse rate in the high-temperature zone; λ is the lapse rate in the low-temperature zone; k is the aperture variation factor in the high-temperature zone; β is the aperture scaling factor; T is the temperature corresponding to the x-axis coordinate at the designed aperture position; T3 is the combustion chamber inlet air temperature; T max This is the highest wall temperature within the axial region; Step 3 specifically involves designing the spacing of the cooling hole rows based on the wall temperature level. The calculation method for axial hole spacing is as follows: Where x is the axial coordinate, T(x) is the wall temperature at the current hole row position, and T min S represents the lowest wall temperature in the axial region. min δ is the minimum axial hole spacing. s is the hole spacing expansion coefficient, and q is the gradient morphology index; The calculation method for the circumferential hole spacing is as follows: Where: θ is the circumferential angle with the nozzle centerline as 0°; T(θ) is the wall temperature at angle θ, T zmax The highest wall temperature within the high heat load arc segment, T zmin P is the lowest wall temperature within the secondary heat load arc segment. min γ is the minimum circumferential hole spacing, N is the number of nozzles, and p is the angle index.

2. The flame tube design method according to claim 1, characterized in that, Step 4 specifically involves: The design method for a gradual buffer zone when transitioning from a high-temperature zone to a low-temperature zone is as follows: ; The design method for a gradual buffer zone when transitioning from a low-temperature region to a high-temperature region is as follows: ; Where d(x) is the aperture of the gradient buffer band, d h For the aperture in the high-temperature region, d c The aperture is in the low-temperature zone, and x is the current axial position. h x is the axial coordinate at the end of the high-temperature zone. c θ represents the initial axial coordinate of the low-temperature region, and β is the attenuation intensity coefficient.

3. The flame tube design method according to claim 2, characterized in that, Step 5 specifically involves: using the formula The effectiveness of the air film coverage is verified; where η is the verification coefficient of the air film coverage effectiveness, d is the diameter of the cooling holes, S is the axial spacing of the cooling holes, and θ is the inclination angle of the cooling holes.

4. The flame tube design method according to claim 3, characterized in that, When η≥0.1, the air film continuity meets the requirements; When η < 0.1, step 2 needs to be repeated.

5. The flame tube design method according to claim 1, characterized in that, In step 3: The difference in axial spacing between the first and last rows in the head zone and the main combustion zone meets the requirements. S1 is the first row of the area corresponding to the head area and the main combustion area, S n This refers to the last row of the area corresponding to the head zone and the main combustion zone, where n is the row number of the area corresponding to the head zone and the main combustion zone.

6. The flame tube design method according to claim 1, characterized in that, In step 3: The difference in axial spacing between the first and last rows in the transition zone and the exit zone meets the requirements. S1 is the first row of the corresponding area between the transition zone and the exit zone. m This represents the last row of the area corresponding to the transition zone and the exit zone, where m is the row number of the area corresponding to the transition zone and the exit zone.

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