Design method of low-pollution central staged combustor

Abstract

The present invention discloses a design method for a low-pollution central staged combustor, belonging to the technical field of staged combustors. Since separation phenomena occur when a pre-diffuser is designed with a symmetric annular straight-wall expansion angle, separation vortices appear near the outer-ring sudden-expansion angle on the upper wall of the pre-diffuser, which in turn leads to an increase in the total pressure loss of the diffuser and a significant increase in the air intake of the inner ring cavity. The reason is considered that it is difficult to ensure that the central streamline of the pre-diffuser is consistent with the incoming flow direction of the combustor inlet and the air intake direction of the cap simultaneously by using a symmetric annular straight-wall expansion angle design. Therefore, on the basis of ensuring the area ratio and the length L of the pre-diffuser in the x direction pre d , the pre-diffuser is redesigned. The two-dimensional geometric structure is composed of straight-line segments and arc segments, which is convenient for machining. At the same time, it is ensured that the central streamlines at the inlet and outlet of the pre-diffuser are consistent with the incoming flow direction of the combustor inlet and the central axis of the combustor, and no separation vortices appear in the pre-diffuser section, with a low total pressure loss coefficient and a high static pressure recovery coefficient.

Description

Technical Field

[0001] The present invention relates to the technical field of staged combustors, and particularly to a low-pollution central staged combustor. Background Art

[0002] Due to the dual requirements of low fuel consumption and low emissions for advanced civil aeroengines, especially the increasingly stringent emission requirements for NOx emissions in new emission standards, a leaner combustion mode needs to be adopted at the head of advanced civil aeroengines. A large amount of air enters from the head of the flame tube, reducing or canceling the intake air volume of the large holes on the flame tube wall, significantly reducing the acoustic damping effect of the flame tube. Therefore, combustion instability is likely to occur. The strong pressure pulsation may cause the vibration of the combustor and even the entire engine to intensify, generating huge combustion noise, increasing the heat load, affecting the overall performance of the engine, and even damaging engine components seriously in severe cases.

[0003] Therefore, the demand for research on dynamic combustion characteristics for the design and performance improvement of low-emission combustors is very strong. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies in the prior art and propose a design method for a low-pollution central staged combustor.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A design method for a low-pollution central staged combustor includes the following design steps:

[0007] S1: Optimize the design of the diffuser and statistically calculate each data in the diffuser;

[0008] S2: Design the inner and outer annular cavity channels, and calculate the area at each cross-section by referring to the prototype engine, so as to obtain the threshold values of various indexes inside the device;

[0009] S3: Design the converging section of the flame tube. The cooling of the flame tube wall adopts a dense multi-inclined hole cooling form, and the opening area and arrangement of the cooling holes on the inner and outer annular cavity walls of the flame tube are obtained through design calculation;

[0010] S4: Design the structural parameters of the swirler, calculate the geometric flow path area, and finally determine the windward area and other structural parameters of each stage of the swirler through multiple iterative calculations, and design and calculate various numerical values of the cap;

[0011] S5: Design the head cooling holes, and finally determine the key parameters such as the number and diameter of the cooling holes and their arrangement through multiple iterative calculations;

[0012] S6: Design a 3D model for the overall structure of the main combustion chamber, partition the grid, analyze the final research results, and explore the feasibility of technical indicators.

[0013] Preferably, in the step S1, the various data in the diffuser are the diffuser inlet area, diffuser inlet air density, inlet air velocity, diffuser inlet Mach number, pre-diffuser area ratio, axial length, and diffuser sudden expansion angle.

[0014] Preferably, in the step S2, the size of the middle section of the flame tube is designed according to the middle diameter constant m k = 1 (that is, the areas of the upper and lower annular cavities divided by the center streamline are equal).

[0015] Preferably, in the step S3, the dense multi-oblique holes on the flame tube wall are designed according to the long rhombus opening rule, that is, the flow direction hole pitch s = the transverse hole row pitch p.

[0016] Preferably, in the step S5, the head cooling air volume is calculated according to the flow formula to obtain the cooling hole diameter, and the two rows are distributed concentrically and circumferentially in a cross pattern.

[0017] Preferably, in the step S6, when designing the 3D model of the overall structure of the main combustion chamber, the upper and lower wall surfaces of the converging section of the flame tube are respectively approximated by arcs, and the upper and lower wall surfaces of the converging section of the casing are replaced by arcs and straight line segments.

[0018] Preferably, in the step S6, the grid is partitioned and unstructured grids are used, and the number of grids is about 11.94 million.

[0019] Preferably, in the step S6, in the analysis of the final research results, a relatively stable central recirculation zone is formed in the main combustion zone, and small recirculation zones with similar degrees are also formed on both radial sides of the central recirculation zone.

[0020] Preferably, in the step S6, the cooling air volume of the dense multi-oblique holes on the flame tube wall forms a layer of protective gas film at the flame tube wall, and the air volume entering from the head accounts for more than 80% of the available air volume, resulting in the fact that the main stream of combustion in the flame tube is composed of the air volume at the head, and thus the high-temperature region is mainly concentrated in the middle region of the flame tube.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. Since the pre - diffuser with a symmetric design of annular straight - wall expansion angle will have a separation phenomenon, that is, separation vortices appear near the outer - ring sudden - expansion angle on the upper wall of the pre - diffuser, which will lead to an increase in the total - pressure loss of the diffuser and a significant increase in the air intake volume of the inner - ring cavity. The reason is that it is very difficult to ensure that the center streamline of the pre - diffuser is consistent with the incoming flow direction of the combustion chamber inlet and the air - intake direction of the hood at the same time when using the "symmetric design of annular straight - wall expansion angle". Therefore, on the basis of ensuring the area ratio and the length L pre d in the x - direction of the pre - diffuser, the pre - diffuser is redesigned. The two - dimensional geometric structure is composed of straight - line segments and arc segments, which is convenient for processing. At the same time, it ensures that the center streamlines at the inlet and outlet of the pre - diffuser are consistent with the incoming flow direction of the combustion chamber inlet and the central axis of the combustion chamber, and no separation vortices will appear in the pre - diffuser section, with a low total - pressure loss coefficient and a high static - pressure recovery coefficient.

[0023] 2. The converging section of the flame tube calculated according to the equal - velocity - gradient law is more in line with the design law required by the invention. Then, for the convenience of processing, the fitting curve of the converging section of the flame tube is approximately simulated and replaced by an arc - line segment.

[0024] 3. The present invention adopts the long - diamond - shaped hole - opening rule for the first - round design, that is, the flow - direction hole spacing s = the transverse hole row spacing p. This design idea is to make the collective arrangement of the holes on the cylinder body more regular. Compared with the regular diamond, under the same hole - opening rate per unit area, the interference between columns in the long - diamond - shaped arrangement is stronger, the air - film coverage uniformity is better, and the heat transfer of the cooling air flow to the wall surface is stronger.

[0025] 4. The function of the hood is to guide the compressor incoming flow to flow into the flame tube and the secondary - air passage with a small pressure loss, generate a small pressure loss in the hood to increase the head pressure drop, and is not sensitive to the inlet - air flow distortion. Therefore, the average radius of the hood inlet generally falls on the extension line of the center streamline of the pre - diffuser to ensure smooth air intake. If the opening area of the hood is too large, overflow is likely to occur; if the area is too small, flow contraction occurs, the static pressure recovery of the air flow decreases, and separation appears at the hood lip. Both situations will increase the loss.

[0026] 5. The NOx, Soot, and UHC emissions at the outlet section of the designed low - pollution center - staged combustion chamber are measured. Therefore, the pollutant emissions of the designed low - pollution center - staged combustion chamber of the present invention are much lower than the emission levels of the existing single - ring - cavity combustion chamber and double - ring - cavity combustion chamber under the same fuel - air ratio conditions. Brief Description of the Drawings

[0027] Figure 1 It is the design drawing of the aspect ratio of the diffuser

[0028] Figure 2 It is the velocity - distribution vector diagram of the pre - diffuser

[0029] Figure 3Optimized design drawing of the front diffuser

[0030] Figure 4 Design drawing of the converging section of the flame tube

[0031] Figure 5 Arrangement drawing of the cooling holes on the wall of the flame tube

[0032] Figure 6 Structural diagram of the low-pollution central staged swirler

[0033] Figure 7 Structural design drawing of the combustion chamber

[0034] Figure 8 Structural partition drawing of the low-pollution central staged combustion chamber

[0035] Figure 9 Mesh drawing of the low-pollution central staged combustion chamber

[0036] Figure 10 Contour map of the velocity distribution at the central cross-section under the design condition

[0037] Figure 11 Vector diagram of the velocity distribution at the central cross-section under the design condition

[0038] Figure 12 Contour map of the temperature distribution at the central cross-section under the design condition

[0039] Figure 13 Contour map of the temperature distribution at the outlet cross-section under the design condition

[0040] Figure 14 Distribution diagram of RTDF at the outlet cross-section of the low-pollution central staged combustion chamber

[0041] Figure 15 Screenshot of the Excel table "ε=f(AR)"

[0042] Figure 16 Screenshot of the Excel table "Inner and outer diameter values of the converging section of the flame tube (Witrosinski's law)"

[0043] Figure 17 Screenshot of the Excel table "Inner and outer diameter values of the converging section of the flame tube (constant velocity gradient law)" Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0045] Refer to Figures 1 - 17 ,

[0046] Table 1 Design requirements of the overall performance scheme

[0047]

[0048]

[0049] Table 2 Research Conditions of the Overall Performance Scheme

[0050]

[0051] Table 3 Structural Limiting Dimensions of the Overall Performance Scheme

[0052]

[0053] Table 4 Intake Air Distribution of the Overall Layout of the Combustor

[0054]

[0055] Calculate the inclination angle of the combustor:

[0056]

[0057] Since 20% of the turbine cooling air volume does not participate in combustion, the available air volume q m3.1 = 2.12625 × 80% = 1.701 kg / s.

[0058] Table 5 Proportion of Each Air Volume in the Flame Tube to the Available Air Volume

[0059]

[0060]

[0061] The average Ma number of the unburned mixture in the flame tube is selected to be 0.023, and this Ma number determines the cross-sectional area of the flame tube.

[0062] To calculate the average velocity of the unburned mixture in the flame tube, its flow rate is the air flow rate at the head: 2.12625 × 64.8% = 1.37781 kg / s

[0063] The air density is calculated based on Pt3.1 and T3, then

[0064]

[0065] The speed of sound is calculated based on T3, then

[0066] Rg is the gas constant, and the adiabatic index is obtained from the table as K = 1.3553.

[0067] Then the average velocity of the unburned mixture in the flame tube is: v = Ma × c = 0.023 × 559.8599 m / s = 12.8768 m / s.

[0068] According to the flow formula m = ρvA, that is

[0069] 1.37781 kg / s = 7.3903 kg / m 3 × 12.8768 m / s × A L ,

[0070] the cross-sectional area A of the single-head flame tube is obtained L = 14478.3580 mm 2

[0071] Calculate the effective area of the flame tube:

[0072]

[0073] In the formula, q m3.1 = 1.701 kg / s, ΔP L -- The pressure drop of the flame tube, which is the total pressure P t3.1 at the inlet of the flame tube minus the static pressure P4 at the outlet of the flame tube;

[0074] ΔP L = 1752990 Pa × 3.5% = 61354.65 Pa

[0075]

[0076] The effective area of the head inlet = 1786.2183 mm 2 × 81% = 1446.8368 mm 2

[0077] There is an empirical criterion: divide the cross-sectional area of the flame tube by the effective area of the head inlet: 14478.3580 mm 2 / 1446.8368 mm 2 = 10.0069. For an aeroengine combustion chamber, this ratio is 10 - 12. Its lower limit is applicable to large-flow combustion chambers, and its upper limit is applicable to small-flow combustion chambers. The cross-sectional area A of the flame tube = 14478.3580 mm² = 2πRd × Hd / 20, that is, Rd × Hd = 46086.0449 mm 2

[0078] Here, refer to the length L of the flame tube in the prototype f (excluding the swirler) = 169 mm, take it as the initial value and determine it by iteration.

[0079] Then set the head in the middle of the combustion chamber, and thus the radius Rd of the head position is obtained as 336.3011 mm, and Hd = 137.0380 mm.

[0080] The width B of the head:

[0081] Head width-to-height ratio: For large engines, the parameter θ is between 0.7 and 1.0.

[0082] The pre-combustion stage is used from startup to the transition point, and then the main combustion stage and the pre-combustion stage work together until the maximum fuel-air ratio. Under design conditions, from the perspective of NOx emissions, it is generally desired that the equivalence ratio of the main combustion stage is in the lean combustion range of 0.6 - 0.8, while from the perspective of combustion stability, it is desired that the equivalence ratio of lean-premixed combustion in the main combustion stage is greater than 0.5.

[0083] When the fuel distribution ratio between the main and pre-combustion stages is 90% and 10%, the equivalence ratio of the main combustion stage is:

[0084] When the fuel distribution ratio between the main and pre-combustion stages is 80% and 20%, the equivalence ratio of the main combustion stage is:

[0085] Therefore, the fuel distribution ratio between the main and pre-combustion stages is selected as 90% and 10%.

[0086] Example 1

[0087] The various data in the diffuser of the low-pollution center-staged combustor are the diffuser inlet area, diffuser inlet gas flow density, inlet air velocity, diffuser inlet Mach number, pre-diffuser area ratio, axial length, and diffuser sudden-expansion angle.

[0088] Diffuser inlet area:

[0089] A 3.0 = π(316.04 2 - 295.18 2 ) / 20 = 2002.7730 mm 2

[0090] Diffuser inlet gas flow density:

[0091]

[0092] Inlet air velocity:

[0093]

[0094] Diffuser inlet Mach number:

[0095] That is, the outlet velocity of the high-pressure compressor is 140.0635 m / s, making the pressure ratio about 7, and reducing the gas flow velocity to about 20 m / s. The pressure ratio is relatively large, and a sudden-expansion diffuser is selected.

[0096] From existing research, it is known that for every 1% increase in the total pressure loss coefficient, the specific fuel consumption rate increases by 0.5%. The overall total pressure loss coefficient of the combustion chamber is 6%, and the total pressure loss of the diffuser is approximately 30% of the total loss. If the flow of the gas in the pre-diffuser does not separate, then the total pressure loss coefficient of the diffuser is 6% × 30% = 2%.

[0097] The function of the diffuser is to reduce the speed and increase the pressure, while minimizing the total pressure loss as much as possible when increasing the static pressure. Generally, the loss is required to be within 2%. A longer pre-diffuser will lead to an increase in the loss caused by friction, while a shorter pre-diffuser with a larger divergence angle will result in an increase in the separation loss.

[0098] Figure 1 in which the abscissa is the dimensionless length The ordinate is the area ratio AR.

[0099] Empirical formula (corresponding to Figure 1 the dotted line):

[0100]

[0101] In the formula, h is the inlet height of the pre-diffuser, and L pre d is the length of the pre-diffuser in the x direction.

[0102] The outer diameter of the combustion chamber inlet R3.0 (= 316.04 mm) - the inner diameter of the combustion chamber inlet r3.0 (= 295.18 mm) = h = 20.86 mm

[0103] There is an optimal value for the sudden expansion gap ratio, which makes the static pressure recovery coefficient of the diffuser the largest and the total pressure loss coefficient the smallest. An Excel table ε = f(AR) is formulated for comparative analysis. As Figure 15 shown, finally, the value of AR is determined to be AR = 1.84, then

[0104]

[0105] The inlet height of the pre-diffuser h = 20.86 mm, the ratio of the outlet area to the inlet area of the pre-diffuser is AR = 1.84, and the length of the pre-diffuser L pre d = 84.2520 mm, and the divergence angle of the pre-diffuser According to the existing geometric conditions, check It should be within the range of 4° to 8°, meeting the requirements.

[0106] The ideal static pressure recovery coefficient is

[0107] The actual static pressure recovery coefficient is

[0108]

[0109] Diffuser efficiency

[0110] Under the conditions of 806.65K and 1752.99KPa, γ = 1.3553.

[0111] Total pressure loss of the pre - diffuser:

[0112]

[0113] Outlet velocity of the pre - diffuser

[0114] Total pressure loss of the sudden - expansion section: A3.0 = 2002.7730mm 2 , Aref = 14478.3580mm 2

[0115]

[0116] Total pressure loss of the entire diffuser section:

[0117] ε t = 1 - (1 - ε pd )(1 - ε dd ) = 1 - (1 - 0.004945)×(1 - 0.01161) = 0.01650

[0118] Generally speaking, the loss of the diffuser should be less than 2% of the total pressure at the compressor outlet.

[0119] Due to the use of a symmetric design of the annular straight - wall expansion angle for the pre - diffuser, separation phenomena will occur as Figure 2 shown, that is, separation vortices appear near the sudden - expansion angle of the outer ring on the upper wall of the pre - diffuser, which further leads to a significant increase in the intake air volume of the inner ring cavity. The reason is considered to be that the flow direction at the combustion chamber inlet section is not parallel to the center line of the pre - diffuser, that is, the pre - diffuser with a symmetric design of the annular straight - wall expansion angle is not compliant with the oncoming flow at the combustion chamber inlet. Therefore, on the basis of ensuring the area ratio and the length Lpred of the pre - diffuser in the x - direction, the design is as Figure 3The pre-stage diffuser shown, i.e., adopting the design of "ring-shaped curved wall expansion angle facing the flow", not only adapts to the incoming flow direction at the inlet of the combustion chamber, but also makes the outlet air flow direction of the pre-stage diffuser consistent with the central axis of the combustion chamber, that is, the central streamline at the head of the flame tube is on the extension line of the central streamline of the outlet air flow of the pre-stage diffuser, thus ensuring smooth air intake at the head of the flame tube. The "ring-shaped curved wall expansion angle facing the flow" design enables the pre-stage diffuser not only to avoid the generation of separated vortices, but also to greatly reduce its total pressure loss coefficient, which is 0.43%, far lower than the design standard of 2% during design. Therefore, under the condition that the total pressure loss index of the combustion chamber design remains unchanged, sufficient space is left for the total pressure loss of the flame tube design.

[0120] Example 2

[0121] Area A at the reference section of the combustion chamber ref , area A at the reference section of the flame tube L , referring to the prototype here, the initial value Then

[0122] Aref = 14478.3580mm 2 / 0.7295 = 19846.9609mm 2 ,

[0123] Then the flow area Apassage of the inner and outer ring cavities = Aref - AL = 5368.6029mm 2 ,

[0124] Air ratio m of the air flow channels in the inner and outer ring cavities passage : 35.2%,

[0125] Then from the flow formula W t3 ·m passage = ρ·V passage A passage ,

[0126] That is, 2.12625kg / s × 35.2% = 7.3903kg / m 3 ×V passage × 5368.6029mm 2 , calculating the average air flow velocity V in the air flow channels of the inner and outer ring cavities passage = 18.8640m / s.

[0127] The dimensions of the middle section of the flame tube are designed according to the scheme with the middle diameter constant m k = 1 (i.e., the areas of the upper and lower two ring cavities divided by the central streamline are equal).

[0128]

[0129] Among them, the combustion chamber inclination angle α = 9.1758°, Rd = 336.3011 mm, the head height Hd = 137.0380 mm. Substituting these values, we get: the outer ring cavity channel height Hpo = 20.4370 mm, and the inner ring cavity channel height Hpi = 34.5404 mm.

[0130] Given that the length of the flame tube Lf = 169 mm, and the area at the reference section of the flame tube AL = 14478.3580 mm 2 .

[0131] Volume of the flame tube:

[0132] V = L f ·A L = 169 × 14478.3580 = 2446842.502 mm 3

[0133] Volume flow rate of the flame tube:

[0134]

[0135] Residence time of the gas:

[0136]

[0137] Example 3

[0138] Length of the middle section L R Take the empirical value as:

[0139] L R = (0.6 - 0.7)H d == (82.22 - 95.93) mm = 85 mm.

[0140] Length of the contraction section of the flame tube:

[0141] L L = L f - L R = 169 mm - 85 mm = 84 mm

[0142] Inlet cross-sectional area of the converging section:

[0143]

[0144] Outlet cross-sectional area of the converging section:

[0145]

[0146] Design the center streamline of the flame tube - double arc line:

[0147] H = 0.5(D2 - D1) = R2 - R1 = 363.6 - 350.0313 = 13.5687 mm,

[0148] When X = 84,

[0149]

[0150] m k = 1.09. Therefore, the mean diameter constant m k = 1.09, that is, A1x = 0.5219Ax, A2x = 0.4781Ax,

[0151]

[0152] Vitosinski's law (empirical formula):

[0153]

[0154] Create an Excel sheet "Inner and Outer Diameter Values of the Flame Tube Convergence Section (Vitosinski's Law)", as Figure 16 shown.

[0155] Equal velocity gradient law:

[0156]

[0157] Create an Excel sheet "Inner and Outer Diameter Values of the Flame Tube Convergence Section (Equal Velocity Gradient Law), as Figure 17 shown.

[0158] By comparing the two, it is found that the flame tube convergence section calculated according to the equal velocity gradient law is more in line with the design law required by the invention. After that, for the convenience of processing, an arc line segment is used to approximately simulate and replace the fitting curve of the flame tube convergence section, as Figure 4 shown.

[0159] Example 4

[0160] The wall surface of the flame tube adopts a cooling form with dense multi-inclined holes. The discharge coefficient Cd is taken between 0.7 and 0.8, and the initial value is 0.75; the diameter of the cooling holes of the flame tube is limited between 0.6 and 0.7 mm, and the value is 0.7 mm; the inclination angle is selected as 22° (within the range of 20° - 30°) according to the shape of the flame tube.

[0161] Given that the proportion m c of the cooling air volume of the flame tube is 15.2%, according to the flow formula Calculated through multiple iterative calculations, the discharge coefficient Cd is finally determined to be 0.78, that is:

[0162] 2.12625 kg / s × 15.2% = 0.78 × 952.2912 × Acool,

[0163] Calculated: Acool = 437.3106 mm 2 ,

[0164] The number of cooling holes in the combustion chamber liner is 437.3106÷(π×0.35²) = 1136 holes.

[0165] Measured:

[0166] The upper wall area of the combustion chamber liner is 25978.8704 mm 2 ,

[0167] The lower wall area of the combustion chamber liner is 17572.0897 mm 2 ,

[0168] Then: 25978.8704 mm 2 / 17572.0897 mm 2 = 1.4784.

[0169] It is known that the cooling air volume of the combustion chamber liner accounts for 15.2% of the total inlet air volume of the combustion chamber. Let the proportion of the cooling air volume of the inner ring cavity wall of the combustion chamber liner be x, then x + 1.4784x = 15.2%, and calculated: x = 6.1330. Then: the proportion of the cooling air volume of the outer ring cavity wall of the combustion chamber liner is 9.0670%, and the proportion of the cooling air volume of the inner ring cavity wall of the combustion chamber liner is 6.1330%.

[0170] It is known that the proportion of the cooling air volume of the turbine is 20%. Suppose there are 2 outlets for the turbine cooling air extraction, which are connected to the inner and outer ring cavity channels respectively, and the air volume proportions are 8% for the outer ring cavity and 12% for the inner ring cavity.

[0171] Therefore, the air volume flowing through the outer ring cavity is:

[0172] 2.12625 kg / s×(8% + 9.0670%) = 0.36289 kg / s

[0173] The air volume flowing through the inner ring cavity is:

[0174] 2.12625 kg / s×(12% + 6.1330%) = 0.38555 kg / s

[0175] And Apassage = 5368.6029 mm 2 , Apassage / 2 = 2684.30145 mm 2

[0176] Therefore, the air volume flow rate in the outer ring cavity:

[0177] 0.36289 kg / s = 2684.30145 mm 2 ×7.3903 kg / m 3Vpassage,out

[0178] It is obtained that: Vpassage,out = 18.2929 m / s

[0179] Inner annulus gas flow rate:

[0180] 0.38555 kg / s = 2684.30145 mm 2 ×7.3903 kg / m 3 Vpassage,in

[0181] It is obtained that: Vpassage,in = 19.4351 m / s

[0182] From the ratio of the upper and lower wall areas of the flame tube = the ratio of the number of cooling holes on the upper and lower wall surfaces of the flame tube. Let the number of cooling holes on the inner annulus wall surface of the flame tube be x, then the number of cooling holes on the outer annulus wall surface of the flame tube is 1.4784x, that is, x + 1.4784x = 1136. Calculating gives x = 458. Therefore, there are 458 cooling holes on the lower wall surface of the flame tube and 678 cooling holes on the upper wall surface.

[0183] Example 5

[0184] The present invention adopts a long rhombus hole-opening rule for the first-round design, that is, the flow direction hole pitch s = the transverse hole row pitch p, as Figure 5 shown. This design idea is to make the collective arrangement of the holes on the cylinder body more regular. Compared with a regular rhombus, under the same unit area hole-opening rate, the interference between columns in the long rhombus arrangement is stronger, the gas film coverage uniformity is better, and the heat transfer of the cooling air flow to the wall surface is stronger.

[0185] After multiple iterative calculations, it is finally determined that:

[0186] There are 38 rows of holes on the upper wall surface, with 18 cooling holes in each row, s = 4.7 mm, p = 7.1 mm;

[0187] There are 38 rows of holes on the lower wall surface, with 12 cooling holes in each row, s = 4.5 mm, p = 7.0 mm.

[0188] Hole-opening rate Ap per unit area of the upper wall surface:

[0189]

[0190] Hole-opening rate Ap per unit area of the lower wall surface:

[0191]

[0192] Example 6

[0193] Let the total pressure loss of the designed combustion chamber flame tube be 3.5%

[0194]

[0195] The function of the hood is to guide the compressor inflow to flow into the combustor and the secondary air passage with a small pressure loss, generate a small pressure loss inside the hood to increase the head pressure drop, and be insensitive to the inlet air flow distortion. Therefore, the average radius of the hood inlet generally falls on the extension line of the central streamline of the pre-diffuser to ensure smooth air intake.

[0196] If the opening area of the hood is too large, overflow is likely to occur; if the area is too small, the flow will contract, the static pressure recovery of the air flow will decrease, and separation will occur at the hood lip. Both situations will increase the loss.

[0197] Generally, Acoin:Aain:Aaou≈Aoh:Aoin:Aoou

[0198] Where: Acoin -- the inlet area of the hood; Aain -- the area of the inner-ring secondary air passage; Aaou -- the area of the outer-ring secondary air passage; Aoh -- the area of the head holes; Aoin -- the area of the inner-ring inlet holes; Aoou -- the area of the outer-ring inlet holes.

[0199] Then Acoin:2684.30145:2684.30145≈

[0200] 2.12625×64.8% / 1.701:2.12625×(8% + 9.0670%) / 1.701:2.12625×(12% + 6.1330%) / 1.701 = 64.8%:8% + 9.0670%:12% + 6.1330%

[0201] = 64.8%:17.0670%:18.1330%

[0202] (17.0670% + 18.1330%) / 2 = 17.6%

[0203] It is obtained that: Acoin = 2684.30145×64.8% / 17.6% = 9883.1099mm 2

[0204] Acoin = π[(R + x) 2 -(R - x) 2 / 20 = 4πRx / 20, where R is the average radius of the cap inlet, and x is the distance in the y direction between the inner and outer diameters and the average radius of the cap inlet. R = 327.9421 mm, and by calculation, x = 47.9641 mm. Since the cap can reduce pressure loss, Acoin can be appropriately enlarged. Therefore, when designing, x is taken as 50 mm. However, considering the limitation of the head height Hd = 137.0380 mm, the design is based on the reference of the main oil point (26.7729 mm). That is, x is taken as 30 mm.

[0205] Cap inlet area: (2π×327.9421 / 20)×30×2 = 6181.5630 mm 2

[0206] Gas flow rate at the cap inlet:

[0207] 1.701 kg / s×(58% + 5% + 7% + 3.5% + 7.5%) = 1.37781 kg / s

[0208] According to the flow formula 1.37781 kg / s = 7.3903 kg / m 3 ×Vd×6181.5630 mm 2 , the gas flow velocity Vd at the cap inlet = 30.1598 m / s

[0209] Example 7

[0210] The designed low-pollution central staged swirler is as Figure 6 shown, and it consists of two-stage fuel injection and three-stage axial swirlers. The two-stage fuel nozzles are respectively a dual-fuel centrifugal nozzle and a lean-fuel direct-injection nozzle from the inside to the outside; looking from the side of the swirler outlet towards the oncoming flow direction, the swirl directions of the three-stage swirlers are clockwise rotation, counterclockwise rotation, and counterclockwise rotation in sequence from the inside to the outside.

[0211] Example 8

[0212] The generation of the central recirculation zone in the traditional swirl cup is borne by all the gas flow of the first-stage swirl and 80% of the gas flow of the second-stage swirl; the remaining gas flow of the second-stage swirl, all the gas flow of the third-stage swirl, and the inter-stage cooling gas flow jointly strengthen the atomization and fuel-air mixing of the main combustion stage fuel. On this basis, an inter-stage cooling ring cavity structure is designed to facilitate the cooling of the structure between the main and pre-combustion stage swirlers.

[0213] The swirl numbers of the axial vane type swirlers are as follows:

[0214]

[0215] The swirl intensity is characterized by the swirl number. The swirl number of the swirler directly affects the size and flow pattern of the recirculation zone at the head of the flame tube, and directly affects the combustion performance. When the swirl number is greater than 0.6, it is called strong swirl, and a recirculation zone will appear. The existence of the recirculation zone plays an important role in flame stabilization and fuel mixing.

[0216] For the pre-combustion stage two-stage swirler, the inner swirler air flow is mainly responsible for atomization, and the outer swirler air flow is mainly responsible for generating the recirculation zone. Therefore, it is determined that the swirl number of the outer swirler should be greater than that of the inner swirler. For the main combustion stage swirler, since the main combustion stage air flow needs to mix a large amount of fuel to achieve the purpose of premixing and pre-evaporation, a larger swirl intensity is required. The reference structural parameters of the given central staging swirler are shown in Table 6.

[0217] Table 6 Structural parameters of the central staging swirler

[0218]

[0219] Example 9

[0220] One of the basic design principles of the swirler is that there should be no light transmissibility, that is, when viewed from the front to the back, no light can be seen. This criterion is:

[0221] In the formula: n - the number of blades; L - the axial length of the swirler; θ - the blade outlet angle;

[0222] D - the outer diameter of the swirler flow path.

[0223] The chord length c of the blade:

[0224] The ratio of the swirler blade height h to the chord length c Determines the maximum diameter of the head air swirler. In addition, the length L will affect the fuel injection and the length of fuel-air mixing.

[0225] The blade inlet area formula: A sw =π(R o 2 -R i 2 )-nt(R o -R i ) / cosθ

[0226] In the case where there is no extension at the swirler outlet, its outlet geometric flow path area is:

[0227] A s =A sw ·cosθ

[0228] After calculating the geometric flow path area, the remaining task is to select the flow coefficient Cd. For axial cyclones, it is roughly between 0.84 and 0.88. For curved blades and polished blades, a higher value can be taken; for straight blades (due to air flow separation) and unpolished blades, a lower value can be taken. Therefore, the initial value of Cd is 0.84.

[0229] Since the swirl numbers and blade angles of the cyclones at all levels of the low-pollution center staged combustor are known, it is designed by the following method:

[0230]

[0231] (1 - x)(1 + x + x 2 ) = 1 - x 3 = a(1 - x 2 ) = a(1 - x)(1 + x),

[0232] 1 + x + x 2 = a(1 + x)

[0233] x 2 +(1 - a)x + 1 - a = 0

[0234] The solution is:

[0235] Ro = Ri / x

[0236] The inner radius value of the first-stage cyclone in the pre-combustion stage refers to the original cyclone design and takes the value of 7.5 mm.

[0237] However, it is found in the design that if the swirl number of the first-stage cyclone in the pre-combustion stage is given as 0.5, it will cause the cyclone to exceed the two-side boundaries of the single head, that is, the half-height of the cyclone should be ≤ 52.5206 mm. In addition, there should also be a design space for the head cooling holes, that is, the half-height of the cyclone should be ≤ 47 mm.

[0238] Example 10

[0239] According to the existing design experience, the blade swirl angle is generally between 30° and 60°, the blade thickness t is usually between 0.7 - 1.5 mm, and the number of blades n is usually between 8 - 16. The blade thickness refers to the center-staged cyclone of the high-temperature-rise combustor, and the blade swirl angle is given. It is found during the design process that adjusting the number of blades has little impact on the flow rate of the cyclones at all levels. Therefore, the design method adopted in this paper is to first make large adjustments to the inner and outer diameters of the cyclones at all levels, and then make small adjustments to the number of blades of the cyclones at all levels.

[0240] After multiple iterative calculations, the windward area and other structural parameters of the cyclones at all levels are finally determined as shown in Table 7.

[0241] Table 7 Structural parameters of the cyclones at all levels

[0242]

[0243]

[0244] Swirl number of the first-stage swirler in the pre-combustion stage:

[0245]

[0246] Swirl number of the second-stage swirler in the pre-combustion stage:

[0247]

[0248] Swirl number of the swirler in the main combustion stage:

[0249]

[0250] From the above calculation results, it can be seen that the swirl numbers of each stage of the finally determined low-pollution central staged swirler fully meet the given design parameters.

[0251] When designing the inter-stage cooling ring cavity structure, the initial value of the inter-stage cooling air intake flow coefficient is 0.7, then

[0252] 1786.2183×3.5% = 62.5176mm 2 = 0.7×Ain

[0253] We get Ain = 89.3109mm 2

[0254] The mean diameter R of the inter-stage cooling air intake is 18.4624mm

[0255] 2πRh = 89.3109mm 2 , we get the height h of the inter-stage air intake ring gap is 0.769904mm

[0256] After multiple iterations, the finally determined flow coefficient Cd = 0.6281, Ain = 99.5299mm 2

[0257] 2πRh = 99.5299mm 2 , h = 0.857996mm

[0258] It is known that the proportion of the inter-stage cooling air volume in the available air volume is 3.5%. Among them, the air flow is divided into two streams after entering the ring cavity. One stream is arranged around the main combustion stage nozzle, and the air volume proportion is 1%, which is called the inter-stage premixed air volume. The other stream is arranged at the expansion section on the outer diameter side of the second-stage swirler, that is, at the sleeve position, and the air volume proportion is 2.5%, which is called the inter-stage cooling air volume. Then:

[0259] The calculation of the inter-stage premixed air volume is as follows:

[0260] 1786.2183 × 1% = 17.8622 mm 2 = 0.7 × Ac

[0261] Ac = 25.5174 mm 2

[0262] The two rows of cooling holes are arranged in a cross pattern, with 54 holes per row.

[0263] 25.5174 mm 2 ÷ 0.2376 mm 2 = 108

[0264] 0.2376 mm 2 = πr 2 , r = 0.275 mm, d = 0.55 mm

[0265] The calculation of the inter-stage cooling air volume is as follows:

[0266] 1786.2183 × 2.5% = 44.6555 mm 2 = 0.70 × Ac

[0267] Ac = 63.7936 mm 2

[0268] 63.7936 mm 2 ÷ 0.2376 mm 2 = 270

[0269] The three rows of cooling holes are arranged in a cross pattern, with 90 holes per row.

[0270] 0.2376 mm 2 = πr 2 , r = 0.275 mm, d = 0.55 m

[0271] Example 11

[0272] In the combustion chamber application, there is often an extension section at the outlet of the swirler. At this time, the effective flow path area of the component with the extension section needs to be calculated, depending on the following situations: whether the outlet of the extension section is the minimum flow path area (if the outlet area of the extension section ≥ the effective flow path area, the influence is ignored); the length of the extension section (this influence is generally not significant, mainly the influence of friction); whether the outlet of the extension section is convergent (it should be so).

[0273] If the outlet area of the extension section < the effective flow path area and (the effective flow path area - the outlet area of the extension section) is large, then adopt:

[0274]

[0275] A 总--Total flow area of the cyclone;

[0276] A 有效 --Effective area of the cyclone;

[0277] A o --Minimum area of the converging section.

[0278] There is an extension section at the outlet of the third-stage cyclone, and the outlet of the extension section is converging. Therefore, it is necessary to calculate whether the outlet of the extension section is the minimum flow path area, that is, if the outlet area of the extension section ≥ effective flow path area, the influence is ignored. As can be seen from Table 7, the effective area of the third-stage cyclone is 1036.0066 mm 2 ; and the inner diameter at the minimum outlet area of the extension converging section of the third-stage cyclone is 22.6712 mm, and the outer diameter is 33.4562 mm. Then the minimum outlet area of the extension converging section is π×(33.4562 2 -22.6712 2 ) = 1901.7129 mm 2 >1036.0066 mm 2 , so the influence is ignored.

[0279] Example 12

[0280] The cooling air volume of the head is calculated according to the flow formula to obtain the cooling hole diameter, and the two rows are distributed concentrically and circumferentially in a cross pattern; it is known that the proportion m dc of the cooling air volume of the head is 6%. According to the flow formula calculate, where the flow coefficient Cd generally takes a value of 0.7 in most designs. Therefore, the initial value of the flow coefficient Cd is 0.7. After multiple iterative calculations, the final determined flow coefficient Cd is 0.94. That is, 2.12625 kg / s×6% = 0.94×952.2912×Adome, and Adome = 143.2392 mm 2 is calculated. The number of head cooling holes is designed to be 240 = 120 per row×2 rows, and the two rows are distributed concentrically and circumferentially in a cross pattern. The cooling hole diameter (limited between 0.8 - 1.0 mm) is 0.871726705 mm, and the straight hole impingement cooling method is used for design.

[0281] Example 13

[0282] The design of the reference combustion chamber includes a diffuser, a casing, the wall surface of the flame tube, the cooling holes of the flame tube, a cap, the head cooling holes, a cyclone, etc. Considering the processing difficulty, the upper and lower wall surfaces of the converging section area of the flame tube are approximated by arcs respectively, and the upper and lower wall surfaces of the converging section area of the casing are replaced by arcs and straight segments. At the same time, considering the installation and assembly problems of the test piece during the test, the outlet height of the lower wall surface of the converging section area of the casing is adjusted to be slightly lower than the lowest height of the lower wall surface of the flame tube, such as Figure 7as shown

[0283] Example 14

[0284] The low-pollution central staged combustor is designed with 20 heads. For the sake of simplicity in calculation, a single-head fan-shaped region is selected as the computational domain in this paper. The computational domain of this single-head combustor includes a swirler, a pre-diffuser, inner and outer secondary channels, a flame tube, etc. Since the cooling holes in the flame tube of the invention are designed in the way of dense multi-inclined holes, if structured grids are used, it will be too time-consuming and laborious. Therefore, unstructured grids are used in this invention, and the number of grids is about 11.94 million, as Figure 9 shown. Among them, considering the large number of grids, the complexity of the combustor structure and the performance of the working computer, when performing grid division, the overall structure of the combustor is partitioned for easy search and error correction, as Figure 8 shown

[0285] Example 15

[0286] In this invention, by comparing the axial velocity distribution along the radial direction at the center of the recirculation zone under different numbers of grids, when the velocity distribution no longer changes significantly with the number of grids, it is considered that the grids are independent, and finally the total number of grids is determined to be 11.94 million.

[0287] The inlet section adopts a flow inlet boundary condition, the outlet of the flame tube and the outlets of 2 turbine cooling air inlets are set as outflow boundary conditions, and the casing is set as an adiabatic wall. The swirling air volume of each stage of the swirler, the air volume entering the head cooling holes and the air flow rate entering the film cooling holes of the flame tube are obtained through flow coupling calculation. The side walls of the entire fluid domain of the single-head annular combustor are all set as rotating periodic boundary conditions.

[0288] A hollow conical spray model is set at the two-stage fuel nozzles, and the structure and aerodynamic parameters of the conical spray are set.

[0289] Example 16

[0290] From Figure 10 it can be seen that a relatively stable central recirculation zone is formed in the main combustion zone, and small recirculation zones with similar degrees are also formed on both radial sides of the central recirculation zone. The high-temperature regions at the outlet section of the flame tube are basically distributed at the center position in the radial direction of the outlet section. This situation is in line with the RTDF in Figure 14

[0291] From Figure 12 ​It can be seen that the main combustion level flame is in the shape of "wings", the pre-combustion level flame is in the shape of "flowers blooming", and the overall combustion in the flame tube is in the shape of "birds flying". This is because the special geometric structure of the designed central staged combustion chamber causes combustion stratification under the design conditions, where the outer layer of the flame is the main combustion level flame, and the inner layer is the duty level flame. It should be noted that the outer layer of the main combustion level flame and the inner layer of the duty level flame do not cross-propagate with each other, and the boundaries between the layers can be clearly seen. Therefore, when designing the air flow and fuel flow distribution scheme of the combustion chamber, it is necessary to take into account the characteristics of the combustion chamber flow field structure zoning, that is, it is necessary to comprehensively consider the low pollution and stable combustion oil-gas ratio requirements of each sub-combustion zone under different working conditions.

[0292] According to the simulation results, the temperature and pressure values are as follows:

[0293] Table 8 Numerical simulation results of low-pollution central staged combustion chamber

[0294]

[0295]

[0296] The outlet temperature distribution coefficient of the low-pollution central staged combustion chamber under the design condition is:

[0297] The design requirement of OTDF value < 0.286 is met.

[0298] The RTDF value obtained by simulation calculation under the design condition is 0.19. Figure 14 shown.

[0299] from Figure 14 It can be seen that under the design condition, the average radial temperature distribution of the flame tube outlet cross section has a "single peak", which appears roughly at a height of 20%-70%, that is, in the middle area of the outlet cross section. Figure 12 It can be seen that the combustion in the upper and lower areas of the flame tube is relatively uniform and symmetrical, the convergent section area in the flame tube has a "parabolic" outline, and the high-temperature combustion is mainly concentrated in the middle area. The reason is that the flame tube wall has dense and multi-slant hole cooling air, which forms a protective air film on the flame tube wall, and the air entering from the head accounts for more than 80% of the available air, resulting in the mainstream combustion in the flame tube being composed of the head air, and the high-temperature area is mainly concentrated in the middle area of the flame tube.

[0300] Total pressure loss coefficient of combustion chamber under design conditions: Meet the requirement that the total pressure loss coefficient is less than 6%.

[0301] The design operating condition combustion efficiency is 99.99%, which meets the requirement that the design operating condition combustion efficiency is greater than 99.90%.

[0302] Example 17

[0303] The pollutants emitted by aero-engines include nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC), soot particles (soot), and sulfur dioxide (SO2), among which NOx poses the greatest harm to the environment and human health. The Committee for Aviation Environmental Protection (CAEP), a subordinate body of the International Civil Aviation Organization (ICAO), has been committed to reducing the emissions of pollutants such as NOx.

[0304] The measured emissions of NOx, Soot, and UHC at the outlet section of the designed low-pollution central staged combustor are shown in Table 9. Therefore, the pollutant emissions of the designed low-pollution central staged combustor of the present invention are far lower than the emission levels of existing single-annular combustors and double-annular combustors under the same fuel-air ratio conditions.

[0305] Table 9 Numerical simulation results of the low-pollution central staged combustor

[0306]

[0307] From the analysis of the above research results, it can be obtained that under the condition of canceling the intake of large holes on the flame tube wall, the designed benchmark model of the low-pollution central staged combustor meets the design indicators, has a low total pressure loss coefficient, a high combustion efficiency, and a good temperature distribution at the outlet section of the flame tube, providing a benchmark scheme for the next research on the flow and combustion dynamic characteristics of the low-pollution central staged combustor.

[0308] The design condition of this project is the cruise condition. Under the design condition, the pilot flame ignites the main combustion stage, making the ignition of the main combustion stage rapid and reliable, and at the same time, a relatively uniform combustion temperature can be obtained.

Claims

1. Design method of a low-pollution central staged combustor, characterized in that It includes the following design steps: S1: Conduct the design optimization of the diffuser and perform statistical calculations on various data in the diffuser; S2: Design the inner and outer annular cavity channels, and calculate the area at each cross-section by referring to the prototype machine, so as to obtain the threshold values of various indicators inside the device; S3: Design the converging section of the flame tube. The cooling of the flame tube wall adopts the form of dense multi-oblique holes. Through design calculations, the opening area and arrangement of the cooling holes on the inner and outer annular cavity walls of the flame tube are obtained; The dense multi-oblique holes on the flame tube wall are designed according to the long diamond-shaped opening rule, and the flow direction hole spacing s = the transverse hole row spacing p; S4: Design the structural parameters of the swirler, calculate the geometric flow path area, and through multiple iterative calculations, finally determine the windward area and other structural parameters of each stage of the swirler, and design and calculate various numerical values of the cap; S5: Design the head cooling holes, and through multiple iterative calculations, finally determine the key parameters of the number and diameter of the cooling holes and the arrangement; S6: Conduct a three-dimensional model design of the overall structure of the main combustion chamber, partition the grid, analyze the final research results, and explore the feasibility of technical indicators; When conducting a three-dimensional model design of the overall structure of the main combustion chamber, the upper and lower wall surfaces of the converging section area of the flame tube are respectively approximated by arcs, and the upper and lower wall surfaces of the converging section area of the casing are replaced by arcs and straight line segments.

2. The design method of the low-pollution central staged combustor according to claim 1, wherein In step S1, the various data in the diffuser are the diffuser inlet area, diffuser inlet gas density, inlet air velocity, diffuser inlet Mach number, pre-diffuser area ratio, axial length, and diffuser sudden expansion angle.

3. The design method of the low-pollution central staged combustor according to claim 1, characterized in that In step S2, the size of the middle section of the flame tube is designed according to the middle diameter constant mk = 1, and the scheme with equal areas of the upper and lower two annular cavities divided by the center streamline.

4. The design method of the low-pollution central staged combustor according to claim 1, characterized in that, In step S5, the amount of head cooling air is calculated according to the flow formula to obtain the diameter of the cooling holes, and the two rows are distributed concentrically and circumferentially in a cross pattern.

5. The design method of the low-pollution central staged combustor according to claim 1, characterized in that, In step S6, the grid is partitioned, and unstructured grids are used, and the number of grids is 11.94 million.

6. The design method of the low-pollution central staged combustor according to claim 1, characterized in that, In step S6, the analysis of the final research results forms a relatively stable central recirculation zone in the main combustion zone, and small recirculation zones with similar degrees are also formed on the radial sides of the central recirculation zone.

7. The design method of the low-pollution center-staged combustor according to claim 1, wherein In step S6, the cooling air volume of the dense multi-oblique holes on the flame tube wall forms a layer of protective gas film at the flame tube wall, and the air volume entering from the head accounts for more than 80% of the available air volume, resulting in the main flow of combustion in the flame tube being composed of the air volume from the head, and thus the high-temperature region is mainly concentrated in the middle region inside the flame tube.

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