Low-emission gas turbine combustion chamber flow field simulation experiment test method

Abstract

The invention belongs to the technical field of measurement of a flow field in a combustion chamber, and particularly discloses a low-emission gas turbine combustion chamber flow field simulation experiment test method which is used for performing experiment test on the vertical direction of the central axis of a swirler so as to obtain flow field characteristics of an outlet of the swirler and a head of the combustion chamber. According to the invention, a PIV test system is adopted to perform experimental test on the flow field of the coaxial staged combustion chamber of the engine, and at present, related research reports at home and abroad are few; and 2, carrying out numerical calculation on the flow field characteristics of the coaxial staged combustion chamber of the engine by coupling the constructed simplified natural gas chemical reaction mechanism and the CFD calculation model. The research results can provide theoretical basis and technical support for revealing the flow field characteristics in the coaxial staged combustion chamber of the natural gas turbine and optimizing the structure and performance of the combustion chamber. And thirdly, a numerical calculation method for the flow field of the engine combustion chamber is newly explored.

Description

Technical Field

[0001] The invention relates to the technical field of flow field measurement in a combustion chamber, in particular to a flow field simulation experimental test method for a low-emission gas turbine combustion chamber. Background Art

[0002] Gas turbines are widely used in the fields of power generation and aviation propulsion. According to the design guiding ideology, design concept, machine parameter matching and component design method, gas turbines are divided into three categories: micro, light and heavy. Among them, micro and light gas turbines can be modified from aircraft engines (also known as "aero-to-fuel"), with a power usually within 50MW, and can be used in industrial power generation, ship power, pipeline boosting, tank locomotives, distributed power generation and combined heat and power. Heavy gas turbines have a power of more than 50MW and are mainly used as fixed generators on land, such as urban power grids. Gas turbines have the advantages of high thermal efficiency, small size, light weight, fast start-up and high reliability, and have become the main power equipment in the energy field. However, pollutants such as nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) generated during the combustion process of gas turbines have serious impacts on the environment and human health. Therefore, research on controlling gas turbine pollutant emissions has important practical significance.

[0003] At the same time, due to the restrictions of environmental protection regulations, the low-emission combustion technology of gas turbines has become the entry threshold for domestic and foreign markets. my country currently has several types of mass-produced light gas turbines, and also has the only R0110 heavy-duty gas turbine designed and put into operation. Due to substandard emissions and other problems, the light gas turbine market is almost completely occupied by multinational companies such as GE and RR, and the heavy-duty gas turbine market is almost completely occupied by companies such as GE, Siemens, Mitsubishi, and Ansaldo. At present, the staged combustion modes adopted by low-emission combustion chambers of gas turbines at home and abroad include circumferential staged, radial staged, axial staged, and coaxial staged combustion modes. Compared with the combustion modes such as circumferential staged, radial staged, and axial staged, the problems of cross-flame in the combustion chamber, uniformity of temperature distribution, organization of the combustion field, stable working boundary, and difficulty of pollutant control under the coaxial staged combustion mode are relatively easy to solve, and can better realize the transplantation design of low-emission combustion chambers of light gas turbines and heavy gas turbines. Therefore, the application prospect of the coaxial staged combustion mode is more promising and its application is more extensive. Since my country started the research on low NOx emission combustion technology for gas turbines relatively late, it lacked awareness of the huge challenges brought by the strict size restrictions of small-sized, high-volume heat-load combustion chambers, resulting in the lack of low-emission combustion technology available for gas turbines in my country. Therefore, conducting in-depth and systematic research on the flow field characteristics of gas turbine combustion chambers, which have not yet been effectively mastered, is the basis for breaking the foreign technology monopoly, opening up the market, and developing my country's independent gas turbine R&D capabilities. It is an urgent practical need to provide reliable basic technical support for engineering design units, and it is also the core technical problem to be solved.

[0004] Considering that there are certain differences in the combustion chamber structure and working parameter range of different types of gas turbines, the staged combustion modes adopted by various research institutions are not exactly the same. At present, the staged combustion modes adopted by low-emission combustion chambers of gas turbines at home and abroad include circumferential staged, radial staged, axial staged and coaxial staged combustion modes. Compared with the combustion modes such as circumferential staged, radial staged and axial staged, the problems of flame crossover, temperature distribution uniformity, combustion field organization, stable working boundary, and pollutant control difficulty in the coaxial staged combustion mode are relatively easy to solve, and can better realize the transplantation design of low-emission combustion chambers of light gas turbines and heavy gas turbines. Therefore, the application prospect of the coaxial staged combustion mode is more potential and its application is more extensive. Therefore, it is urgent to further study its internal flow field distribution based on the coaxial staged combustion chamber and the PIV test technology, so as to improve the combustion efficiency and solve the core problem of large pollutant emissions in the existing technology. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-emission gas turbine combustion chamber flow field simulation experimental test method.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] A low-emission gas turbine combustion chamber flow field simulation test method is used to test the vertical direction of the swirler center axis to obtain the flow field characteristics of the swirler outlet and the combustion chamber head; the single-head graded swirling model combustion chamber includes a combustion chamber and a swirler, the combustion chamber and the swirler are made of resin glass, the combustion chamber and the swirler are designed in 1:1 size according to the actual structure of the reflow combustion chamber and the swirler, the upper wall of the combustion chamber is a flat resin glass structure without air film holes, and the lower wall of the combustion chamber is provided with a complete air film cooling structure, and the flow field analysis mainly analyzes the position below the center line of the swirler; the swirler outlet diameter is 78mm; the following steps are included:

[0008] S1. Select a lens and measuring distance suitable for the field of view of the particle image velocimetry (PIV) system, so that the camera of the particle image velocimetry (PIV) system faces the measurement area of ​​the turntable, and the lens plane is parallel to the measurement plane; use a body laser to project onto the measurement surface to evenly illuminate the measurement area, and use the particle image velocimetry (PIV) system to control the camera and laser to trigger the acquisition synchronously;

[0009] S2. Use a typical two-dimensional calibration method to convert the pixel size corresponding to the known circumference width to obtain the image magnification ratio; use the particle image velocimetry PIV system to synchronously trigger the camera and laser to continuously collect 50 pairs of images of the measurement area and save them. According to the acquisition interval △t value, substitute the field of view size and camera resolution for calculation; select the calculation area, take the cross-correlation calculation window of 32×32 pixels, iterate once, and calculate the velocity field of each pair of images respectively. The experiment uses a high-frequency PIV system produced by a certain company, with a resolution of 1024×1024pixel, a maximum frequency of 3.6kHz, a minimum frame interval of <1μs, a dynamic range of 12bit, a laser wavelength of 527nm, and a laser energy of 2×100mJ@50Hz;

[0010] S3. Take the average of all the calculated results. Since the circumference of the rotating disk being measured is an arc surface, the velocity distribution in the entire area is not equal. Although the camera is facing the measurement area, its horizontality and inclination errors in all directions cannot be completely eliminated. Therefore, the maximum velocity distribution on any straight line in the longitudinal direction is taken as the final measurement result. The measurement result is compared with the theoretical value calculated using the formula v=ωr=2πnr / 60=πnd / 60 to verify the accuracy of the velocity measurement of the PIV test system.

[0011] S4. The particle image velocimetry (PIV) system uses the FLUENT computing software to construct the physical and computational model of the coaxial staged combustion chamber of a natural gas gas turbine, couples the simplified chemical reaction mechanism of natural gas, and performs numerical calculations on the flow field in the coaxial staged combustion chamber of a natural gas gas turbine under multiple operating conditions; analyzes the combustion chamber head structure, and determines the optimal combustion chamber head structure and aerodynamic matching scheme.

[0012] Furthermore, in step S4, the numerical calculation specifically includes:

[0013] (1) Law of Conservation of Mass

[0014] The law of conservation of mass is expressed as follows: the increase in mass in a fluid microelement per unit time is equal to the net mass flowing into the microelement during the same time interval, as shown in formula (1):

[0015]

[0016] Where: u j represents the velocity component in the j direction, j = 1, 2, 3…; ρ represents density; t represents time; j = x, y, z; t = 0, that is, Then we have:

[0017]

[0018] (2) Law of Conservation of Momentum

[0019] The law of conservation of momentum is expressed as follows: the rate of change of the momentum of the fluid in the microelement with respect to time is equal to the sum of various forces acting on the microelement from the outside, as shown in formula (3):

[0020]

[0021] Where:

[0022] Where: τ ij represents the stress tensor; μ represents the fluid viscosity coefficient; P represents the static pressure; g i Represents gravitational body force; F i represents other model-related source terms; F i =0;

[0023] (3) Law of Conservation of Energy

[0024] The law of conservation of energy is expressed as follows: the rate of increase of energy in a microelement is equal to the net heat flow entering the microelement plus the work done on the microelement by the volume force and the surface force, as shown in formula (4):

[0025]

[0026] Where: E is the total energy of the fluid microgroup, usually kinetic energy K = 1 / 2 (u 2 +v 2 +w 2 ), the sum of potential energy P and internal energy i; J i represents the diffusion flux of component i; h i represents the enthalpy value of i; k eff Represents the thermal conductivity; S h Source terms representing the heat of reaction and volume heat;

[0027] (4) Law of Conservation of Components

[0028] The law of conservation of components is expressed as follows: the rate of change of the mass of a chemical component in the system with respect to time is equal to the sum of the net diffusion through the system interface and the production rate of the component produced by chemical reaction, as shown in formula (5):

[0029]

[0030] Where: Y i Represents the quality score; R i It represents the net generation rate of the reactant; S i Represents the additional production rate of this reactant caused by other sources.

[0031] (5) Ideal gas state equation

[0032] P=ρRT (6)

[0033] Where: R represents the universal gas constant.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention selects an axially graded natural gas gas turbine combustion chamber with swirl premixing + head grading, first explores the gas distribution scheme of the combustion chamber, then conducts experimental tests on the combustion and emission characteristics of the combustion chamber, and analyzes the changing laws of the point-and-extinguish characteristics, outlet temperature distribution, temperature rise, main pollutant concentration, combustion efficiency, etc. of the model combustion chamber under various working conditions; finally, the reaction mechanism is coupled to simplify the reaction mechanism, and the combustion and emission process of a single flame tube of the model combustion chamber is calculated by reaction kinetics, and compared and analyzed with the experimental results, providing theoretical support for the research related to the combustion and emission characteristics of the natural gas gas turbine combustion chamber. At the same time, according to the structural characteristics of the coaxially graded single-head combustion chamber of the natural gas gas turbine, the flow field characteristics in the combustion chamber under different working parameters are tested, and compared and analyzed with the numerical calculation results, and finally the axial / radial average flow velocity, flow field cloud map and trace, Reynolds stress and turbulence intensity, recirculation zone position and other flow field characteristics of the single-head graded swirl model combustion chamber under different working conditions can be determined, as well as the changing laws of the key factors such as air temperature and flow rate on the flow field characteristics.

[0036] At the same time, the technical advantages of PIV testing are non-contact measurement of the velocity vector of a surface; high measurement accuracy; wide velocity measurement range: from 0 to supersonic range; simple measurement principle and little influence from the outside world; wide application, can be used for micro-scale flow measurement (micrometer level), can also be used for wind, water tunnel measurement, and multiphase flow measurement.

[0037] In terms of innovation, the present invention firstly adopts the PIV test system to experimentally test the flow field of the engine coaxial staged combustion chamber. Currently, there are few related research reports at home and abroad. Secondly, the simplified natural gas chemical reaction mechanism and CFD calculation model are coupled to numerically calculate the flow field characteristics of the engine coaxial staged combustion chamber. The research results will provide a theoretical basis and technical support for revealing the flow field characteristics in the coaxial staged combustion chamber of the natural gas gas turbine and the optimization of the combustion chamber structure and performance. Thirdly, new explorations have been made on the numerical calculation method of the engine combustion chamber flow field. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the flow field characteristics test area.

[0039] Figure 2 Velocity vector distribution in the center section of the combustion chamber: (a) is the velocity distribution of the axial velocity with the swirler height; (b) is the velocity distribution of the radial velocity with the swirler height.

[0040] Figure 3 The flow field cloud map and trajectory map of the central section of the combustion chamber.

[0041] Figure 4 The Reynolds stress cloud map and turbulence intensity cloud map of the central section of the combustion chamber: (a) is the Reynolds stress cloud map; (b) is the turbulence intensity cloud map.

[0042] Figure 5 It is the recirculation area in the center section of the combustion chamber.

[0043] Figure 6 Comparison of the vertical cross-section flow field in the center of the combustion chamber at different air temperatures: (a) is the velocity vector comparison; (b) is the recirculation zone comparison.

[0044] Figure 7 Comparison of the vertical cross-section flow field in the center of the combustion chamber with different air flow rates: (a) is the velocity vector comparison; (b) is the recirculation area comparison.

[0045] Figure 8 It is the axial velocity vector distribution at 50mm in the center section of the combustion chamber.

[0046] Fig. 9 These are the flow field cloud diagram and trajectory diagram of the central section of the combustion chamber.

[0047] Fig.10 Velocity vector distribution of the 50 mm center section of the combustion chamber: (a) is the axial velocity; (b) is the radial velocity.

[0048] Fig.11 Flow field cloud diagram and trajectory diagram of the central section: (a) is working condition 5; (b) is working condition 6; (c) is working condition 7; (d) is working condition 8.

[0049] Fig.12 Flow field cloud diagram and trajectory diagram of the central section: (a) is working condition 5; (b) is working condition 6; (c) is working condition 7; (d) is working condition 8.

[0050] Fig.13 It is the location of the recirculation zone in the central section.

[0051] Fig.14 Turbulence intensity cloud diagram of the central section: (a) is working condition 5; (b) is working condition 6; (c) is working condition 7; (d) is working condition 8. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0053] This embodiment exemplarily demonstrates a low-emission gas turbine combustion chamber flow field simulation experimental test method, which is used to perform experimental tests in the vertical direction of the swirler center axis to obtain the flow field characteristics of the swirler outlet and the combustion chamber head; Figure 1 As shown, the single-head graded swirl model combustion chamber includes a combustion chamber and a swirler, both of which are made of resin glass. The combustion chamber and the swirler are designed in 1:1 size according to the actual structure of the reflow combustion chamber and the swirler. The upper wall of the combustion chamber is a flat resin glass structure without air film holes. The lower wall of the combustion chamber is provided with a complete air film cooling structure. The flow field analysis mainly analyzes the position below the center line of the swirler; the outlet diameter of the swirler is 78 mm; the following steps are included:

[0054] S1. Select a lens and measurement distance suitable for the field of view of the particle image velocimetry PIV system, so that the camera of the particle image velocimetry PIV system faces the measurement area of ​​the turntable, and the lens plane is parallel to the measurement plane; use a body laser to project onto the measurement surface to evenly illuminate the measurement area, and use the particle image velocimetry PIV system to control the camera and laser to trigger the acquisition synchronously; the particle image velocimetry PIV system used in this embodiment is produced by TSI, USA, and its maximum measurement area is 300mm×300mm. Its basic components include: computer and related software, synchronous controller, double-pulse Nd:YAG laser and light guide arm, camera (Charge Coupled Device, CCD), optical components, etc. The measurement principle can be simply summarized as speed = displacement / time, that is, v = ds / dt. The double-pulse laser emits two pulses of laser at a fixed time interval dt (controllable). When the laser passes through the measured flow field, due to the addition of tracer particles, Mie scattering signals are generated (when the wavelength of the incident light ≈ particle diameter). At the same time, the CCD camera starts the exposure with an appropriate delay time and captures the Mie scattering signal generated by the first frame of laser, and completes the operation of cutting off the exposure and then starting the exposure between the first frame of laser and the second frame of laser to obtain the Mie scattering signal map under the second frame of laser. Then, the two Mie scattering signal maps are processed by autocorrelation or cross-correlation, and the displacement ds of the relevant particles are obtained one by one, and finally the flow field velocity distribution is calculated.

[0055] S2. Use a typical two-dimensional calibration method to convert the pixel size corresponding to the known circumference width to obtain the image magnification ratio; use the particle image velocimetry PIV system to synchronously trigger the camera and laser to continuously collect 50 pairs of images of the measurement area and save them. According to the acquisition interval △t value, substitute the field of view size and camera resolution for calculation; select the calculation area, take the cross-correlation calculation window of 32×32 pixels, iterate once, and calculate the velocity field of each pair of images respectively. The experiment uses a high-frequency PIV system produced by a certain company, with a resolution of 1024×1024pixel, a maximum frequency of 3.6kHz, a minimum frame interval of <1μs, a dynamic range of 12bit, a laser wavelength of 527nm, and a laser energy of 2×100mJ@50Hz;

[0056] S3. Take the average of all the calculated results. Since the circumference of the rotating disk being measured is an arc surface, the velocity distribution in the entire area is not equal. Although the camera is facing the measurement area, its horizontality and inclination errors in all directions cannot be completely eliminated. Therefore, the maximum velocity distribution on any straight line in the longitudinal direction is taken as the final measurement result. The measurement result is compared with the theoretical value calculated using the formula v=ωr=2πnr / 60=πnd / 60 to verify the accuracy of the velocity measurement of the PIV test system.

[0057] S4. The particle image velocimetry (PIV) system uses the FLUENT computing software to construct the physical and computational model of the coaxial staged combustion chamber of a natural gas gas turbine, couples the simplified chemical reaction mechanism of natural gas, and performs numerical calculations on the flow field in the coaxial staged combustion chamber of a natural gas gas turbine under multiple operating conditions; analyzes the combustion chamber head structure, and determines the optimal combustion chamber head structure and aerodynamic matching scheme.

[0058] Test conditions:

[0059] The material and material of this test piece are resin glass, which has certain limitations on the temperature and pressure it can withstand. The temperature cannot be too high and the pressure cannot be too large. Therefore, based on the performance parameters of resin glass, the test conditions of the single-head combustion chamber flow field characteristic test are shown in Table 1.

[0060] Table 1 Flow field characteristics test conditions

[0061]

[0062] Test conclusion:

[0063] Velocity vector distribution:

[0064] In working condition 3, the axial velocity (u) vector and radial velocity (v) vector at a position 50 mm away from the cyclone outlet section are intercepted, as shown in Figure 2 The vertical scale Y / D is the ratio of the combustion chamber height to the swirler outlet height, and the value of 0 indicates the position of the central axis of the swirler outlet.

[0065] from Figure 2 (a) shows that when the distance from the swirler is 50mm, as the Y / D increases, the axial velocity gradually increases from the maximum negative velocity of -3m / s to the maximum, which is about 18m / s at 0.5 of Y / D, i.e. the lower edge of the swirler; as it approaches the wall of the flame tube, the axial velocity gradually decreases. Figure 2 (b) shows that as Y / D increases, the absolute value of the radial velocity gradually increases and decreases. When Y / D is 0.37, the radial velocity reaches a maximum of about 3.2 m / s. When approaching the wall of the flame tube, the radial velocity is close to 0. In general, the maximum flow velocity area in the combustion chamber is located above and below the outermost ring outlet of the swirler.

[0066] Flow field cloud map and traces:

[0067] Figure 3 The flow field cloud map and trajectory map of the vertical section at the center of the combustion chamber under working condition 3 are given. It can be seen from the figure that the negative axial velocity area in the center section of the combustion chamber is very obvious, with the highest radial Y / D position being about 0.2; the axial position is about 0.13m, about 1.7D. Downstream of the external swirler outlet, the axial velocity reaches the maximum. The streamline in the lower left corner of the figure is caused by the existence of the corner recirculation zone.

[0068] Reynolds stress and turbulence intensity:

[0069] Figure 4 The Reynolds stress cloud diagram and turbulence intensity cloud diagram of the vertical section in the center of the combustion chamber under working condition 3 are given. It can be seen from the figure that the maximum Reynolds stress in the center section of the combustion chamber is located near the periphery of the recirculation zone. Figure 4 , the minimum Reynolds stress is located in the maximum axial velocity region because of the negative radial velocity. Figure 4 (b) It can be seen that in a section of the cyclone outlet, the turbulence intensity is relatively large, and the turbulence intensity at the edge of the central recirculation zone is also relatively large.

[0070] Recirculation zone location:

[0071] Figure 5 The size of the recirculation zone in the vertical section of the center of the combustion chamber under working condition 3 is given, and the line is the line of axial velocity 0. It can be seen from the figure that the central recirculation zone basically presents a symmetrical shape along the center line, which is approximately a rectangular structure, which is very similar to the test results of the conventional recirculation zone. The height of the recirculation zone is about 0.5 times Y / D, and the width is about 0.12m, 1.5 times Y / D. Along the airflow direction, the recirculation zone has a small degree of expansion. The tail of the recirculation zone is not very regular, indicating that the airflow velocity here is not very regular.

[0072] Effect of air temperature on flow field characteristics:

[0073] Figure 6 The velocity vector, velocity cloud diagram and recirculation zone of the vertical section at the center of the combustion chamber are given. The air flow rate is 0.2 kg / s, and the air flow temperature is at room temperature (286 K) and heated (313 K). Figure 6 (a) The upper part shows the velocity contour when the airflow temperature is 313K, and the lower part shows the velocity contour when the airflow temperature is 286K. Figure 6 (a) It can be seen that the maximum velocity area is similar, and the central negative velocity area is also relatively similar. The farther away from the cyclone end face, the radial velocity of the airflow expands to a certain extent. Compared with 286K, the radial velocity expansion of the airflow is slightly larger when the airflow temperature is 313K. At the same air volume, as the airflow temperature increases, the velocity increases from a maximum of 13m / s to 18m / s. From Figure 6 (b) It can be seen that the 0-speed line area of ​​the higher temperature airflow is slightly larger, but the farthest position of the 0-speed line remains almost unchanged.

[0074] Effect of air flow rate on flow field characteristics:

[0075] Figure 7The velocity vector, velocity cloud diagram and recirculation zone of the vertical section at the center of the combustion chamber are given. The air flow rates are 0.2kg / s and 0.3kg / s respectively, and the air flow temperature is room temperature (286K). Figure 7 (a) The upper part shows the velocity cloud diagram when the air flow rate is 0.2 kg / s, and the lower part shows the velocity cloud diagram when the air flow rate is 0.3 kg / s. Figure 7 (a) It can be seen that with the increase of gas volume, the negative velocity area is greatly expanded, including along the radial direction of the cyclone and along the downstream direction of the airflow, which can also be seen from Figure 7 (b) It can be seen that the main airflow velocity increases from 13m / s to 16m / s, and the overall airflow velocity increases. Figure 7 (b) It can be seen that when the air flow rate is 0.2kg / s, the 0-speed line is close to a rectangle. When the air flow rate is 0.3kg / s, the 0-speed line shrinks when it is close to the end face of the cyclone, and then rapidly increases, becomes wider and longer. At the same time, the air volume increases by 50%, and the 0-speed line area increases by nearly 1 times.

[0076] Numerical calculation:

[0077] The numerical calculation part uses FLUENT calculation software to build the physical and computational model of the coaxial staged combustion chamber of the natural gas gas turbine, and couples the natural gas

[0078] The chemical reaction mechanism of natural gas is simplified, and the flow field in the coaxial staged combustion chamber of the natural gas gas turbine under multiple working conditions is numerically calculated; the combustion chamber head structure is analyzed to determine the optimal combustion chamber head structure and aerodynamic matching scheme.

[0079] Calculation method:

[0080] The basic governing equation is as follows:

[0081] (1) Law of Conservation of Mass

[0082] The law of conservation of mass can be expressed as follows: the increase in mass in a fluid microelement per unit time is equal to the net mass flowing into the microelement during the same time interval, as shown in formula (1):

[0083]

[0084] Where: u j represents the velocity component in the j direction, j = 1, 2, 3…; ρ represents density; t represents time.

[0085] The simulation calculation of the aircraft engine combustion chamber carried out in this paper belongs to the steady-state combustion type, at this time j = x, y, z; t = 0, that is, Then we have:

[0086]

[0087] (2) Law of Conservation of Momentum

[0088] The law of conservation of momentum can be expressed as follows: the rate of change of the momentum of the fluid in the microelement with respect to time is equal to the sum of various forces acting on the microelement from the outside, as shown in formula (3):

[0089]

[0090] In the formula

[0091] Where: τ ij represents the stress tensor; μ represents the fluid viscosity coefficient; P represents the static pressure; gi represents the gravitational body force; Fi represents other model-related source terms.

[0092] According to the actual situation of this paper, Fi=0.

[0093] (3) Law of Conservation of Energy

[0094] The law of conservation of energy can be expressed as follows: the rate of increase of energy in a microelement is equal to the net heat flow entering the microelement plus the work done by the volume force and surface force on the microelement, as shown in formula (4):

[0095]

[0096] Where: E is the total energy of the fluid microgroup, usually the sum of kinetic energy K = 1 / 2 (u2 + v2 + w2), potential energy P and internal energy i; J i represents the diffusion flux of component i; h i represents the enthalpy value of i; k eff Represents the thermal conductivity; S h Source terms representing the heat of reaction and volume heat.

[0097] (4) Law of Conservation of Components

[0098] The law of conservation of components can be expressed as follows: the rate of change of the mass of a chemical component in the system over time is equal to the sum of the net diffusion through the system interface and the production rate of the component produced by chemical reaction, as shown in formula (5):

[0099]

[0100] Where: Y i Represents the quality score; R i It represents the net generation rate of the reactant; S i Represents the additional production rate of this reactant caused by other sources.

[0101] (5) Ideal gas state equation

[0102] P=ρRT (6)

[0103] Where: R represents the universal gas constant.

[0104] The numerical simulations all adopt the steady-state model, the Simple algorithm based on pressure, the Realizable k-ε turbulence model, the partially premixed FGM combustion model, and the P1 radiation model. The wall adopts an adiabatic wall with no velocity slip, and the turbulence parameter at the wall is zero. The mass flow inlet is selected for the calculation of air and fuel inlet, and the natural flow outlet is selected for the outlet. The control equation is discretized using the first-order upwind scheme, and the sub-relaxation factor is used to accelerate convergence. The reaction mechanism of natural gas adopts the single-step reaction mechanism and the simplified reaction mechanism.

[0105] The calculation conditions are shown in Table 2.

[0106] Table 2 Flow field characteristics calculation conditions

[0107]

[0108] Comparative analysis of flow field characteristics between experiments and numerical calculations:

[0109] Axial / radial average velocity:

[0110] Figure 8 The figure shows the comparison between the experimental and calculated values ​​of the axial velocity under working condition 3. It can be seen from the figure that the axial velocity distribution obtained by numerical calculation and experiment is relatively close. At a distance of 50mm from the swirler, as Y / D increases, the axial velocity gradually increases from the maximum negative velocity to the maximum. The maximum negative velocity obtained by the experiment is about -5m / s, and the maximum axial velocity is about 18m / s at Y / D of 0.5; the maximum negative velocity obtained by numerical calculation is about -8m / s, and the maximum axial velocity is about 19m / s at Y / D of 0.55; both are located at the lower edge of the swirler, and as they gradually approach the wall of the flame tube, the axial velocity gradually decreases.

[0111] Flow field cloud map and traces:

[0112] Fig. 9 The comparison between the experimental and calculated values ​​of the center section flow field cloud map and trajectory map under working condition 3 is shown. It can be seen from the figure that the negative axial velocity area of ​​the center section obtained by numerical calculation and experiment is very obvious. The radial position of the negative axial velocity area obtained by numerical calculation is slightly higher than the experimental value, about 0.3, and the axial position is similar, about 0.12m, about 1.6D. The degree of radial velocity expansion of the airflow obtained by numerical calculation away from the end face of the cyclone is more obvious than the experimental value.

[0113] Analysis of flow field characteristics in the combustion chamber under different working conditions:

[0114] Axial / radial velocity distribution:

[0115] Fig.10 The velocity distribution of the combustion chamber center section at 50 mm from the swirler outlet under different working conditions is given. It can be seen from the figure that with the increase of air pressure and temperature under different working conditions, the directions of the axial velocity and radial velocity remain unchanged, and the magnitudes of the axial velocity and radial velocity gradually increase.

[0116] Flow field cloud map and trace map:

[0117] Fig.11 , Fig.12 The velocity contour, trajectory and vector diagram of the central section of the combustion chamber under different working conditions are given. It can be seen from the figure that the shape of the recirculation zone under different working conditions is very regular, and the upper and lower vortex cores are basically symmetrically distributed.

[0118] Recirculation zone location:

[0119] Fig.13 The position of the recirculation zone in the center section of the combustion chamber under different working conditions is given. It can be seen from the figure that the shape of the recirculation zone under the four working conditions is a "water drop shape", and there is no obvious change in the position and size of the recirculation zone in working conditions 6, 7, and 8. The recirculation zone in working condition 5 is the smallest.

[0120] Turbulence intensity cloud map:

[0121] Fig.14 The turbulence intensity cloud diagram of the flow field in the central section of the combustion chamber under different working conditions is given. It can be seen from the figure that in a section of the swirler outlet, the turbulence intensity is relatively large, and the turbulence intensity at the edge of the central recirculation zone is also relatively large. With the change of working conditions, the area with relatively large turbulence intensity gradually increases, and the overall turbulence intensity gradually increases.

[0122] In summary, the present invention ultimately determined the flow field characteristic information such as the axial / radial average flow velocity, flow field cloud diagram and trajectory, Reynolds stress and turbulence intensity, recirculation zone position, and the influence of key factors such as air temperature and flow rate on the flow field characteristics of the single-head graded swirl model combustion chamber under different operating conditions, providing theoretical support for the research related to the combustion and emission characteristics of natural gas gas turbine combustion chambers.

[0123] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A low-emission gas turbine combustion chamber flow field simulation test method, which is used to perform experimental tests in the vertical direction of the swirler center axis to obtain the flow field characteristics of the swirler outlet and the combustion chamber head; the single-head graded swirl model combustion chamber includes a combustion chamber and a swirler, the combustion chamber and the swirler are both made of resin glass, the combustion chamber and the swirler are designed in 1:1 size according to the actual structure of the reflow combustion chamber and the swirler, the upper wall of the combustion chamber is a flat resin glass structure without air film holes, and the lower wall of the combustion chamber is provided with a complete air film cooling structure, and the flow field analysis mainly analyzes the position below the center line of the swirler; the swirler outlet diameter is 78mm; it is characterized in that, The following steps are involved: S1. Select a lens and measuring distance suitable for the field of view of the particle image velocimetry (PIV) system, so that the camera of the particle image velocimetry (PIV) system faces the measurement area of ​​the turntable, and the lens plane is parallel to the measurement plane; use a body laser to project onto the measurement surface to evenly illuminate the measurement area, and use the particle image velocimetry (PIV) system to control the camera and laser to trigger the acquisition synchronously; S2. Use a typical two-dimensional calibration method to convert the pixel size corresponding to the known circumference width to obtain the image magnification ratio; use the particle image velocimetry PIV system to synchronously trigger the camera and laser to continuously collect 50 pairs of images of the measurement area and save them. According to the acquisition interval △t value, substitute the field of view size and camera resolution for calculation; select the calculation area, take the cross-correlation calculation window of 32×32 pixels, iterate once, and calculate the velocity field of each pair of images respectively. The experiment uses a high-frequency PIV system produced by a certain company, with a resolution of 1024×1024pixel, a maximum frequency of 3.6kHz, a minimum frame interval of <1μs, a dynamic range of 12bit, a laser wavelength of 527nm, and a laser energy of 2×100mJ@50Hz; S3. Take the average of all the calculated results. Since the circumference of the rotating disk being measured is an arc surface, the velocity distribution in the entire area is not equal. Although the camera is facing the measurement area, its horizontality and inclination errors in all directions cannot be completely eliminated. Therefore, the maximum velocity distribution on any straight line in the longitudinal direction is taken as the final measurement result. The measurement result is compared with the theoretical value calculated using the formula v=ωr=2πnr / 60=πnd / 60 to verify the accuracy of the velocity measurement of the PIV test system. S4, Particle Image Velocimetry (PIV) system uses FLUENT computing software to build a physical and computational model of the coaxial staged combustion chamber of a natural gas gas turbine, coupled with the simplified chemical reaction mechanism of natural gas, and numerically calculates the flow field in the coaxial staged combustion chamber of a natural gas gas turbine under multiple operating conditions; Analyze the combustion chamber head structure and determine the optimal combustion chamber head structure and aerodynamic matching solution.

2. The low-emission gas turbine combustion chamber flow field simulation experimental test method according to claim 1 is characterized in that: In step S4, the numerical calculation specifically includes: (1) Law of Conservation of Mass The law of conservation of mass is expressed as follows: the increase in mass in a fluid microelement per unit time is equal to the net mass flowing into the microelement during the same time interval, as shown in formula (1): Where: u j represents the velocity component in the j direction, j = 1, 2, 3…; ρ represents density; t represents time; j = x, y, z; t = 0, that is Then we have: (2) Law of Conservation of Momentum The law of conservation of momentum is expressed as follows: the rate of change of the momentum of the fluid in the microelement with respect to time is equal to the sum of various forces acting on the microelement from the outside, as shown in formula (3): Where: Where: τ ij represents the stress tensor; μ represents the fluid viscosity coefficient; P represents the static pressure; g i Represents gravitational body force; F i represents other model-related source terms; F i =0; (3) Law of Conservation of Energy The law of conservation of energy is expressed as follows: the rate of increase of energy in a microelement is equal to the net heat flow entering the microelement plus the work done on the microelement by the volume force and the surface force, as shown in formula (4): Where: E is the total energy of the fluid microgroup, usually kinetic energy K = 1 / 2 (u 2 +v 2 +w 2 ), the sum of potential energy P and internal energy i; J i represents the diffusion flux of component i; h i represents the enthalpy value of i; k eff Represents the thermal conductivity; S h Source terms representing the heat of reaction and volume heat; (4) Law of Conservation of Components The law of conservation of components is expressed as follows: the rate of change of the mass of a chemical component in the system with respect to time is equal to the sum of the net diffusion through the system interface and the production rate of the component produced by chemical reaction, as shown in formula (5): Where: Y i Represents the quality score; R i It represents the net generation rate of the reactant; S i represents the additional generation rate of this reactant caused by other sources; (5) Ideal gas state equation P=ρRT (6) Where: R represents the universal gas constant.

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