CN116127815B - Modeling method of turbofan engine with injection nozzle - Google Patents
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Abstract
The invention discloses a modeling method of a turbofan engine with an injection nozzle. The invention is improved by considering the pumping characteristic of the jet nozzle on the basis of a mathematical model of a conventional turbofan engine, wherein the pumping characteristic is a jet coefficient change curve of the jet nozzle under the conditions of different nozzle drop pressure ratios and secondary main flow total pressure ratios. Compared with the prior art, the invention can accurately simulate the change of the internal parameters and the performance parameters of the turbofan engine with the injection nozzle in the flight envelope range, provides theoretical basis and data support for the research of the engine, saves test runs in the development process of the engine, shortens the development period and has important engineering application value.
Description
Technical Field
The invention relates to a modeling method of an aeroengine, in particular to a modeling method of a turbofan engine with an injection nozzle.
Background
Aeroengines are highly complex and sophisticated modern industrial products, and in order to achieve effective control, performance prediction and fault diagnosis of the engine, it is necessary to build mathematical models capable of accurately simulating the engine operating conditions. From the study of the characteristics of the engine, mathematical models can be classified into linear small deviation models and nonlinear aerodynamic thermodynamic models. The nonlinear model modeling method is widely applied to a component method, firstly, a model of each component is built according to a aerodynamic and thermodynamic principle followed in the working process of an engine, then, a common working relation of each component is built to form an engine complete machine model, and the model can be used for simulating the change of internal parameters and performance parameters of the engine within a large envelope range.
The team of Nanjing aviation aerospace university Sun Jianguo, li Qiugong, zhou Wenxiang and the like carries out intensive research on engine modeling technology, an engine component level real-time mathematical model is built by adopting C++ language based on an object-oriented method, and rich research results are obtained. At present, the modeling technology of the turbofan engine component method with conventional configuration is mature and widely applied in China, and the students such as Wang Yuan and Chen Haoying succeed in establishing a component-level real-time mathematical model for a novel variable-circulation turbofan engine, but the modeling technology of the engine with a special structure adopting infrared inhibition measures is rarely researched, and particularly the modeling technology aiming at the turbofan engine with an injection nozzle is lacking. The component method modeling is highly dependent on the characteristic data of the component, the characteristic data of the jet nozzle must be obtained first to build a real-time mathematical model of the turbofan engine component level with the jet nozzle, and the method can be used for carrying out calculation numerical simulation by means of finite element analysis software.
The finite element analysis software is a main flow tool for carrying out flow field numerical simulation on the jet pipe at present, and a numerical simulation method such as Liu Fucheng is adopted to research and obtain the influence rule of the space ratio change and the area ratio change of the two-dimensional jet pipe on the thrust characteristic and the infrared characteristic; deng Wenjian, and the like, design various jet nozzle schemes by changing the diameter and the length of an outlet of the outer sleeve, and explore the flow and thrust performance of the jet nozzle under various states by adopting CFX; zhang Kexin and the like develop regular researches on main profile design parameters of the jet nozzle at design points, and explore the influence of different profile parameters on internal flow shear layer characteristics and thrust performance. The research shows that the numerical simulation can be carried out to accurately simulate the flow field state in the jet nozzle, but the contradiction point is that the single jet nozzle simulation cannot reflect the influence of the single jet nozzle simulation on the whole engine performance, and the whole engine simulation has large calculated amount and long time consumption, and is difficult to be applied to engineering practice. If the influence of the jet nozzle on the overall performance of the engine is to be studied, the engine modeling technology and the finite element numerical simulation technology can be combined, the respective advantages are brought into play, and the turbofan engine parameters with the jet nozzle are rapidly and accurately calculated, so that the test cost is reduced, and the research and development period is shortened. However, no relevant modeling method is reported at present.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects of the prior art and provides a modeling method of a turbofan engine with an injection nozzle.
The technical scheme adopted by the invention specifically solves the technical problems as follows:
a modeling method of turbofan engine with an injection nozzle,
firstly, obtaining the pumping characteristic of an injection nozzle by using a finite element numerical simulation method, wherein the pumping characteristic is an injection coefficient change curve of the injection nozzle under the conditions of different nozzle drop pressure ratios and secondary and main flow total pressure ratios;
and then, establishing a calculation model of each part of the engine according to the aerodynamic thermodynamic principle, wherein the method for establishing the calculation model of the part of the injection duct comprises the following steps: taking the injection bypass ratio under the design point as an iteration initial value alpha ej,i Then calculating the inlet parameters of the main flow and the secondary flow of the jet nozzle, and further calculating the nozzle drop pressure ratio NPR under the state i And the sum of the secondary and primary flow total pressure ratios (P ts /P tp ) i Then by NPR i And (P) ts /P tp ) i Interpolation injection coefficient omega is interpolated from the injection coefficient change curve i At the same time, according to the iteration initial value alpha ej,i Calculating the actual injection coefficient omega i 'A'; will be alpha ej Adding the initial guess value arrayAdding a common working equation set, calculating all components, and using Newton-Lawson method to initially guess value alpha according to residual values ej Correcting, wherein epsilon is a preset minimum value;
and finally, establishing a joint working relationship of all the components.
Preferably, the co-operation relation of all the components is established, specifically, the following 7 co-operation equations are combined and the newton-lavson method is adopted to iteratively solve: the method comprises the following steps of a low-pressure rotor power balance equation, a high-pressure rotor power balance equation, a balance equation of high-pressure turbine inlet flow and compressor outlet flow, combustion chamber oil supply quantity and first air cooling quantity, a balance equation of low-pressure turbine inlet flow and high-pressure turbine outlet flow and second air cooling quantity, a static pressure balance equation of air flow in and out of a mixing chamber inlet, a balance equation of main spray pipe outlet flow and low-pressure turbine outlet flow, air flow entering the mixing chamber and afterburner oil supply quantity, and a practical injection coefficient and interpolation injection coefficient match equation.
Further, the modeling method further includes: the method comprises the following steps of establishing a forward and backward infrared radiation calculation model of the injection exhaust system by considering the relation of secondary and main stream blowing ratios and wall surface shielding, wherein the forward and backward infrared radiation calculation model is specifically as follows:
in the method, in the process of the invention,for the corrected forward and backward infrared radiation intensity of the exhaust system,/->The projection area (corresponding to 28-31) which can be detected in the forward and backward directions of the high-temperature wall surface after correction according to the shielding relation is +.>For wall temperature (corresponding to 25) corrected according to blowing ratio, sigma λ The infrared radiation detection method is characterized in that the infrared radiation detection method comprises the steps of adding up all detectable high-temperature wall infrared radiation for the transmittance of air to wavelength lambda infrared radiation, epsilon is the emissivity of a surface material, pi is the circumference rate; wherein (1)>f(M br ) The blowing ratio M br Interpolation calculation of the cooling coefficient eta c Blowing ratio M br Defined as the ratio of the secondary and primary flow through the dense flow, the cooling coefficient η c Is defined as the ratio of the difference between the main stream temperature and the solid wall temperature to the main stream temperature and the secondary stream temperature, T p Temperature of main flow, T s Is the temperature of the secondary stream.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) According to the component-level real-time mathematical model established by the method, the change of the internal parameters and the performance parameters of the turbofan engine with the injection nozzle in the flight envelope range can be accurately simulated, and theoretical basis and data support are provided for the research of the engine of the type.
(2) The component-level real-time mathematical model established by the method further considers the secondary and main stream blowing ratios and the wall shielding relation to realize forward and backward infrared radiation calculation of the injection exhaust system, and has an infrared prediction function which is not possessed by the conventional component-level model.
Drawings
FIG. 1 is a schematic view of a turbofan engine with an injection nozzle;
FIG. 2 is a schematic diagram of a finite element numerical simulation calculation domain;
FIG. 3 is a graph of pumping characteristics of a jet nozzle;
FIG. 4 is an injection bypass ratio iterative flow chart;
FIG. 5 is a schematic illustration of injection coefficient two-dimensional interpolation;
FIG. 6 is a schematic diagram of forward and backward infrared radiation prediction of an injection exhaust system;
fig. 7 is a graph of the model calculated altitude and speed characteristics of a certain engine.
Detailed Description
Aiming at the defects of the prior art, the invention solves the problems that the pumping characteristic of the jet nozzle is obtained by a finite element numerical simulation method, the characteristic data of the jet nozzle is utilized to establish a real-time mathematical model of the part level of the turbofan engine with the jet nozzle on the basis of the model of the part level of the conventional turbofan engine, and the model can accurately simulate the parameter change of the turbofan engine with the jet nozzle during operation.
The modeling method of the turbofan engine with the injection nozzle provided by the invention comprises the following specific steps:
firstly, obtaining the pumping characteristic of an injection nozzle by using a finite element numerical simulation method, wherein the pumping characteristic is an injection coefficient change curve of the injection nozzle under the conditions of different nozzle drop pressure ratios and secondary and main flow total pressure ratios;
and then, establishing a calculation model of each part of the engine according to the aerodynamic thermodynamic principle, wherein the method for establishing the calculation model of the part of the injection duct comprises the following steps: taking the injection bypass ratio under the design point as an iteration initial value alpha ej,i Then calculating the inlet parameters of the main flow and the secondary flow of the jet nozzle, and further calculating the nozzle drop pressure ratio NPR under the state i And the sum of the secondary and primary flow total pressure ratios (P ts /P tp ) i Then by NPR i And (P) ts /P tp ) i Interpolation injection coefficient omega is interpolated from the injection coefficient change curve i At the same time, according to the iteration initial value alpha ej,i Calculating the actual injection coefficient omega i 'A'; will be alpha ej Adding the initial guess value arrayAdding a common working equation set, calculating all components, and using Newton-Lawson method to initially guess value alpha according to residual values ej Correcting, wherein epsilon is a preset minimum value;
and finally, establishing a joint working relationship of all the components.
For the convenience of public understanding, the following detailed description of the technical solution of the present invention will be given with reference to a specific embodiment in conjunction with the accompanying drawings:
in this embodiment, an aviation turbofan engine with an injection nozzle is described as an example, and the injection nozzle is shown in fig. 1 and comprises a convergent-divergent main nozzle and a convergent-divergent outer sleeve. In the figure, the long dashed line represents the high-temperature main flow from the core machine, and the short dashed line represents the injected low-temperature secondary flow; for ease of description, table 1 gives the cross-sectional numbers and meanings for an engine of the type shown in fig. 1.
TABLE 1 turbofan engine section numbering and meaning with jet nozzle
The modeling process of the component-level model is specifically as follows:
step one, obtaining the pumping characteristic of the jet nozzle adopted by the engine of fig. 1 by adopting a finite element numerical simulation method.
The two-dimensional geometric model is established according to the structural size of the spray pipe design, and the injection spray pipe adopted in the embodiment is rotationally symmetrical with the central line, so that the established two-dimensional geometric model can be used for simulating the flow and heat transfer of the three-dimensional flow field. As shown in figure 2, the simulation calculation domain and boundary conditions are that the main and secondary flow inlets of the jet nozzle adopt pressure inlets, and the inlet and outlet of the external flow field are also set as pressure inlets and outlets due to the high-altitude supersonic flight of the design point. P in the figure t And T t Respectively representing total temperature and total pressure, P and T respectively representing static temperature and static pressure, and subscripts P, s and f respectively representing primary flow, secondary flow and external flow field.
After meshing the established two-dimensional geometric model, finite element analysis software (such as FLUENT) can be imported for simulation. In order to obtain pumping characteristics, a plurality of groups of spray pipe drop pressure ratios NPR and secondary and primary flow total pressure ratios pi are arranged before simulation sp And (3) obtaining the injection coefficient omega according to the flow value displayed by the secondary and main flow inlets after the finite element calculation is converged. The pumping characteristics of the jet nozzle obtained by numerical simulation are shown in figure 3. Each curve can be divided into 3 sections according to the state of the injection secondary flow: at the intersection of the curve and the transverse axis (occlusionPoint) is arranged on the left side of the flow control valve, the total pressure of the injection secondary flow is low, the secondary flow is always zero, and the section is a secondary flow blocking area; between the blocking point and the choke line (dashed line), the injection secondary flow starts to appear and flows in a subsonic state, the injection coefficient rises rapidly along with the increase of NPR, and the area is a secondary flow non-choke area; on the right side of the choke line, the entrainment effect and the expansion of the main flow reduce the flow area of the secondary flow, so that the secondary flow reaches a critical state, the injection coefficient is stabilized near a certain value and is not changed along with NPR, and the area is a secondary flow choke area. The pumping characteristic is an injection coefficient change curve of the injection jet pipe under the conditions of different jet pipe drop pressure ratios and secondary and main flow total pressure ratios, so that the pumping characteristic of the injection jet pipe can be described as follows:
ω＝f(NPR,π sp ) (1)
wherein ω is injection coefficient, defined as the ratio of secondary to primary flow, NPR is nozzle pressure drop ratio, pi sp F is the function mapping relation of the parameters, which is the ratio of the total pressures of the secondary flow and the main flow.
Step two, building a calculation model of each part of the engine according to the aerodynamic thermodynamic principle:
for turbofan engines with jet nozzles, the components to be modeled include an intake duct, a fan, a high pressure compressor, a combustor, a high pressure turbine, a low pressure turbine, an outer culvert, a mixing chamber, an afterburner, a jet culvert, a main nozzle, and an outer sleeve, wherein the components upstream of the jet nozzle (intake duct to afterburner) are the same as conventional turbofan engine modeling methods, and therefore the modeling methods of the jet culvert, the main nozzle, and the outer sleeve are focused below.
Injection duct and main spray pipe:
the part of the air flow which does not enter the mixing chamber and is mixed with the core machine air flow at the outer culvert outlet enters the injection culvert, and the calculation of the injection culvert is characterized in that the injection air flow or the injection culvert ratio is determined. If the injection duct ratio is taken as a first guess value, a static pressure balance equation similar to the inlet of the mixing chamber is added at the outlet of the main spray pipe, and then a Newton-Lawson method is adopted to iteratively solve the injection duct ratio. However, the jet duct is not a receiving-expanding structure, forcing two streamsThe body maintains static pressure balance at the junction, and the Mach number at the outlet of the jet culvert calculated at the non-design point is likely to be greater than 1, which is contrary to the fundamental principles of fluid mechanics. Therefore, the pumping characteristics of the jet nozzle obtained by numerical simulation are utilized in the modeling of the jet duct, and the total pressure ratio pi of multiple times and main flow is calculated sp The injection pipe pressure drop ratio NPR and the injection coefficient omega corresponding to the lines are made into an interpolation table and are read for use in model calculation, wherein the iterative calculation flow of the injection duct ratio is shown in figure 4.
First, the injection bypass ratio alpha at the design point is given in the design parameters of the engine ej,i Taking the value as an iteration initial value, then calculating a mixing chamber, an afterburner and a main spray pipe part to obtain inlet parameters of main and secondary flows of the jet spray pipe, and further calculating the spray pipe drop pressure ratio NPR under the state i And the sum of the secondary and primary flow total pressure ratios (P ts /P tp ) i ：
Wherein P is b For ambient back pressure, P t27 And P t8 The total pressure of the secondary and main flow inlets of the jet pipe are respectively adopted.
Then, by NPR i And (P) ts /P tp ) i Can interpolate on the characteristic diagram to obtain an injection coefficient omega i The two-dimensional interpolation principle is shown in fig. 5.
At the same time, according to the initial alpha ej,i An actual injection coefficient can also be calculated:
in the formula, the symbol m represents the mass flow rate of the cross section.
Because the two injection coefficients obtained by calculation are equal in the same state of the same injection nozzle, in actual modeling, the residual error of the two injection coefficients can be considered to be smaller than a certain minimum epsilon:
to establish (5), it is necessary to repeatedly apply the initial value α to ej And (5) performing correction. Due to alpha ej The numerical change also affects the calculation of the mixing chamber, and the multi-layer calculation iteration among the components easily causes the coupling relation, so that unstable oscillation is generated in the model calculation result. Thus here will be alpha ej And adding the initial guess value array, matching the corresponding interpolation flow with the actual flow, adding the interpolation flow and the actual flow into a common working equation set, and calculating all components still follows a 'one-pass' principle, namely, in one iteration, the components which are calculated upstream do not return to recalculation. After all the components are calculated, the Newton-Lawson method is used for initially guessing the value alpha according to the residual value ej Correction is carried out, and alpha is obtained after multiple iterations ej Can converge to a stable value.
An outer sleeve:
the outer sleeve of the jet nozzle adopts a collecting-expanding structure, and is similar to the conventional collecting-expanding tail nozzle in calculation method, except that a jet secondary flow exists in the jet nozzle, and the secondary flow wraps the outer side of the main flow and converts part of pressure potential energy into kinetic energy along with the main flow to be discharged from the nozzle outlet at high speed to generate thrust. It is therefore necessary to calculate the expansion process of the main and secondary streams separately.
When the air flow at the outlet of the main spray pipe reaches the critical sound velocity and the whole flow is adiabatic isentropic, the flow continuous formula is adopted for the outlet of the main spray pipe and the outlet of the jet spray pipe, so that the method is that:
wherein A is 8 And A 9 The throat and the outlet area of the main flow channel of the jet nozzle are respectively gamma 9 For the specific heat ratio of the main flow at the outlet section of the nozzle,λ 9 is the velocity coefficient (ratio of flow velocity to critical sound velocity) of the main flow at the nozzle outlet cross section.
Equation (6) has two solutions, one solution λ 9,sub Another solution lambda corresponds to the velocity coefficient at the outlet subsonic flow 9,sup Corresponding to the velocity coefficient at the outlet supersonic flow.
The outlet air flow of the receiving-expanding outer sleeve has multiple flow states, and for a jet nozzle with a certain main nozzle area, the key parameter for determining the flow states is an NPR value, and 3 characteristic NPR values are calculated in nozzle modeling to distinguish the flow states.
(1) Design Point NPR (1)
NPR when spray tube is in the design state, the export air current is supersonic speed, and the inside and outside shock wave that does not have of spray tube:
(2) Forward shock sealing NPR (2)
The normal shock wave is just positioned at the outlet section of the spray pipe, the wave front airflow is supersonic, and the wave back airflow is subsonic:
(3) Critical NPR (3)
Only the air flow at the outlet section of the main spray pipe reaches sound velocity, and the rest is subsonic flow:
velocity V of primary and secondary flow at outlet of final jet nozzle 9 、V 29 The method comprises the following steps of:
wherein C is pp And C ps Constant pressure specific heat capacity, T, of the primary and secondary flows respectively t9 And T 9 Indicating the total temperature and static temperature of the main flow at the outlet section of the spray pipe, T t29 And T 29 Indicating the total gentle and static temperature of the secondary flow at the nozzle outlet cross section.
Thrust F:
F＝m 9 V 9 +m 29 V 29 -m 0 V 0 +(P 9 -P b )A 9 +(P 29 -P b )A 29 (11)
wherein m is 9 、m 29 Mass flow rate m of main flow and secondary flow respectively at outlet section of spray pipe 0 And V 0 The inlet air flow rate and the flow rate of the engine, P 9 And P 29 The static pressure of the primary flow and the secondary flow is respectively positioned on the section of the outlet of the spray pipe.
Fuel consumption S:
wherein m is f For supplying oil to main combustion chamber, m fAB The oil supply to the afterburner.
Step three, establishing a joint working relationship of all the components:
referring to a common working equation set of a conventional turbofan engine, and simultaneously combining flow field calculation requirements of an injection exhaust system, the embodiment selects a low-pressure rotating speed n l High-pressure rotational speed n h Fan pressure ratio coefficient z f Pressure ratio coefficient z of compressor cH High pressure turbine pressure ratio coefficient z tH Low pressure turbine pressure ratio coefficient z tL Injection bypass ratio alpha ej As an unknown parameter, it is therefore necessary to solve 7 simultaneous co-operating equations iteratively using the newton-lavson method. According to the flow continuity and power balance principle in the engine operation, the common operation equation selected in this embodiment is:
(1) Low pressure rotor power balance equation
H f -H tL η mL -H TOL η mPL ＝0 (13)
Wherein H is f 、H tL And H TOL Respectively the power consumption of the fan, the power generated by the low-pressure turbine and the low-pressure shaft power, eta mL And eta mPL The low-pressure shaft power transmission efficiency and the work extraction efficiency are respectively.
(2) High-voltage rotor power balance equation
H cH -H tH η mH -H TOH η mPH ＝0 (14)
Wherein H is cH 、H tH And H TOH Respectively the consumed power of the compressor, the generated power of the high-pressure turbine and the extracted power of the high-pressure shaft, eta mH And eta mPH The high-pressure shaft power transmission efficiency and the work extraction efficiency are respectively.
(3) A balancing equation for the high pressure turbine inlet flow and compressor outlet flow, combustor oil supply and first cool air flow:
m 41 -m 31 -m f -m c1 ＝0 (15)
(4) A balancing equation for the low pressure turbine inlet flow and the high pressure turbine outlet flow and the second amount of cool air:
m 45 -m 44 -m c2 ＝0 (16)
(5) Static pressure balance equation of the inner and outer culvert air flow of the inlet of the mixing chamber:
P 6 -P 16 ＝0 (17)
(6) And a balancing equation of the main spray pipe outlet flow and the low-pressure turbine outlet flow, the external culvert inlet mixing chamber flow and the afterburner oil supply amount:
m 8 -m 6 -m 16 -m fAB ＝0 (18)
wherein m is fAB The afterburner is supplied with oil.
(7) The actual injection coefficient and interpolation injection coefficient are matched with the equation:
ω-ω'＝0 (19)
step four, establishing a forward and backward infrared radiation calculation model of the injection exhaust system by considering the relation between the secondary flow blowing ratio, the main flow blowing ratio and the wall surface shielding relation:
the infrared radiation of the engine exhaust system is composed of two parts, one part is the infrared radiation emitted by the high temperature wall surface outwards, and the other part is the infrared radiation generated by the high Wen Weiliu. The research object is a small-bypass-ratio turbofan engine with an ejector jet pipe, the jet pipe adopts an axisymmetric collecting-expanding structure, and the detector can capture infrared radiation emitted by a high-temperature wall surface from front and back directions.
FIG. 6 shows a schematic view of forward and backward infrared radiation prediction of an injection exhaust system, possibly marked by thick lines for the detected high temperature walls, including a center cone, turbine outlet, culvert, convergent main nozzle, and outer sleeve divergent section. A length of height Wen Weiliu is present behind the exhaust system, which is indicated by a dashed box.
Based on Planck's blackbody radiation law, calculating the forward and backward infrared radiation of the exhaust system wall in a certain wavelength range can be expressed as the accumulated sum of a series of high temperature wall infrared radiation:
wherein I is the forward and backward infrared radiation intensity of the exhaust system, A is the forward and backward detectable projection area of the height Wen Bimian, epsilon is the emissivity of the surface material, pi is the circumference rate, lambda is the wavelength of infrared radiation, T is the surface temperature, and subscripts c, bp, be, p and D respectively represent a central cone, a turbine outlet, an outer culvert inlet section of the mixing chamber, an injection culvert inlet section, a converging main spray pipe and an outer sleeve expansion section. The integrated term M (λ, T) is an expression of the energy density spectrum with respect to wavelength in planck's blackbody radiation law:
wherein h is a Planck constant, c is the speed of light, k is a Boltzmann constant, and the constant terms are combined to obtain a first radiation constant and a second radiation constant:
the outer sleeve of the jet nozzle comprises two fluids, namely a high-temperature main fluid and a low-temperature secondary fluid, and the calculation of the solid wall surface temperature cannot be directly given according to the temperature of a single fluid. Because the injection coefficient of the small bypass is generally smaller than that of the engine jet pipe, the temperature of the solid wall surface of the expansion section of the outer sleeve is calculated according to the bleed air cooling efficiency of the expansion section of the jet pipe provided by the related literature.
Defining bleed air cooling efficiency:
wherein T is p Temperature of main flow, T s T is the temperature of the secondary stream w Is the solid wall temperature.
Defined as the ratio of secondary to primary flow through:
wherein ρ is s And ρ p Density of secondary and primary flow, V s And V p The flow rates of the secondary and primary flows, respectively.
Table 2 shows the air-entraining cooling efficiency measured by the test under different blowing ratios, so that the cooling efficiency of the wall surface can be obtained by interpolation under the condition of knowing the primary and secondary flow gas parameters, and the actual wall temperature of the expansion section of the outer sleeve is calculated by the formula 23.
TABLE 2 Cooling efficiency corresponding to blowing ratio of nozzle expansion section
Therefore, the calculation formula of the wall surface temperature of the expansion section of the spray pipe considering the secondary and main flow blowing ratios is as follows:
T w ＝T p -f(M br )(T p -T s ) (25)
wherein f (M) br ) The blowing ratio M br Interpolation calculation of the cooling coefficient eta c 。
The formula (20) calculates the total amount of infrared radiation emitted by the high-temperature wall, and if the absorption effect of wake on the infrared radiation is considered, each cumulative term should be modified accordingly:
in sigma λ Is the gas transmission of the wake for the wavelength lambda infrared radiation.
Studies have shown that in the 3-5 μm band, water and carbon dioxide are the two main infrared radiation absorbing species in the wake composition, thus σ λ And can also write:
in the method, in the process of the invention,and->The gas absorption of water and carbon dioxide, respectively, for light of wavelength lambda.
The movement of the adjustable parts of the spray pipe will change the shielding relation between the parts, and thus the contribution rate of the high temperature walls to the infrared radiation. The adjustable component area referred to herein includes the primary nozzle outlet area A 8 Throat area A of outer sleeve s Nozzle outlet area A e Compared with the conventional jet pipe, the jet pipe is added with an outer sleeve, which makes the shielding relation more complex and requires roots in calculationThe projected area in equation (20) is corrected according to different shielding relationships, and for the turbofan engine with the injection nozzle in this embodiment, the projected area corrected according to the shielding relationships is specifically as follows:
according to the analysis, the forward and backward infrared radiation calculation model of the injection exhaust system, which is established by the invention and is corrected by considering the secondary and main stream blowing ratios and the wall surface shielding relation, is obtained, and is specifically as follows:
in the method, in the process of the invention,for the intensity of the positive backward infrared radiation of the exhaust system, +.>The projection area (corresponding to 28-31) which can be detected in the forward and backward directions of the high-temperature wall surface after correction according to the shielding relation is +.>For wall temperature (corresponding to 25) corrected according to blowing ratio, sigma λ Is the transmission of air to the infrared radiation with the wavelength lambdaThe rate ε is the emissivity of the surface material, pi is the circumference rate, Σ represents the summation of all detectable high temperature wall infrared radiation.
In order to verify the effect of the technical scheme of the invention, the steady-state performance simulation of the design points is carried out on the established component level model, the comparison of the engine design parameters and the calculation results of the component level model is given in the table 3, and the data in the table shows that the established component level model of the turbofan engine with the small bypass ratio of the injection nozzle is basically consistent with the parameter circulation analysis model, so that the accuracy requirement is met.
TABLE 3 simulation results for engine design points
To evaluate engine full envelope performance, simulations of internal altitude and speed characteristics were performed based on the established engine component level model. Fig. 7 shows the established turbofan engine height and speed characteristics with an injection nozzle, all of which are obtained with the low pressure rotor maintained at 95% relative to the physical speed. As can be seen from the graph, the inlet flow and the thrust of the engine are always reduced along with the increase of the flying height, and the fuel consumption, the relative physical rotating speed of the high-pressure rotor, the injection coefficient and the infrared radiation intensity are firstly reduced and then stabilized. When the flying height exceeds 11km, the temperature of the external atmosphere environment is not changed any more, the total inlet temperature of the fan is the same under the same Mach number condition, so that the working points of all the rotating parts including the fan on the characteristic diagram are the same, and further, the fact that the air flow in the engine is almost not changed about enthalpy and entropy thermodynamic cycles is known, and the reason that thermodynamic related parameters such as fuel consumption rate, relative physical rotating speed of the high-pressure rotor and infrared radiation remain stable after 11km is known. For injection, the injection ratio is a function of the nozzle drop pressure ratio and the total pressure ratio of the main flow and the secondary flow, the drop of the inlet pressure of the air inlet channel inevitably leads to the drop of the total pressure of the main flow and the secondary flow, and the drop of the total pressure of the main flow and the secondary flow and the environmental pressure can be almost considered as equal proportion because the working point of the rotating part is kept unchanged, so that the injection coefficient of the nozzle is kept stable.
Claims (3)
1. A modeling method of turbofan engine with an injection nozzle is characterized in that,
firstly, obtaining the pumping characteristic of an injection nozzle by using a finite element numerical simulation method, wherein the pumping characteristic is an injection coefficient change curve of the injection nozzle under the conditions of different nozzle drop pressure ratios and secondary and main flow total pressure ratios;
and then, establishing a calculation model of each part of the engine according to the aerodynamic thermodynamic principle, wherein the method for establishing the calculation model of the part of the injection duct comprises the following steps: injection bypass ratio alpha under design point ej,i As the injection bypass ratio alpha ej Then calculating the initial iteration guess of the mixing chamber, afterburner and main nozzle components to obtain the inlet parameters of the main and secondary flows of the jet nozzle, and further calculating the nozzle pressure drop ratio NPR under the state i And the sum of the secondary and primary flow total pressure ratios (P ts /P tp ) i Then by NPR i And (P) ts /P tp ) i Interpolation injection coefficient omega is interpolated from the injection coefficient change curve i At the same time, according to the iteration initial guess value alpha ej,i Calculating the actual injection coefficient omega i 'A'; will be alpha ej,i Adding the initial guess value arrayAdding a common working equation set, calculating all components, and then utilizing Newton-Lawson method to inject the bypass ratio alpha according to residual values ej Correcting, wherein epsilon is a preset minimum value;
and finally, establishing a joint working relationship of all the components.
2. The modeling method of the turbofan engine with the injection nozzle according to claim 1, wherein the joint working relation of all the components is established, specifically, the following 7 joint working equations are combined and the newton-lavson method is adopted to iteratively solve: the method comprises the following steps of a low-pressure rotor power balance equation, a high-pressure rotor power balance equation, a balance equation of high-pressure turbine inlet flow and compressor outlet flow, combustion chamber oil supply quantity and first air cooling quantity, a balance equation of low-pressure turbine inlet flow and high-pressure turbine outlet flow and second air cooling quantity, a static pressure balance equation of air flow in and out of a mixing chamber inlet, a balance equation of main spray pipe outlet flow and low-pressure turbine outlet flow, air flow entering the mixing chamber and afterburner oil supply quantity, and a practical injection coefficient and interpolation injection coefficient match equation.
3. The modeling method of a turbofan engine with an injection nozzle of claim 1, further comprising: the method comprises the following steps of establishing a forward and backward infrared radiation calculation model of the injection exhaust system by considering the relation of secondary and main stream blowing ratios and wall surface shielding, wherein the forward and backward infrared radiation calculation model is specifically as follows:
in the method, in the process of the invention,for the intensity of the positive backward infrared radiation of the exhaust system, +.>For the projection area which can be detected in the forward and backward directions of the high temperature wall surface after correction according to the shielding relation, < > is provided>For correcting wall temperature according to blowing ratio sigma λ The infrared radiation detection method is characterized in that the infrared radiation detection method comprises the steps of adding up all detectable high-temperature wall infrared radiation for the transmittance of air to wavelength lambda infrared radiation, epsilon is the emissivity of a surface material, pi is the circumference rate; wherein (1)>f(M br ) The blowing ratio M br Interpolation calculation of the cooling coefficient eta c Blowing ratio M br Defined as the ratio of the secondary and primary flow through the dense flow, the cooling coefficient η c Is defined as the ratio of the difference between the main stream temperature and the solid wall temperature to the main stream temperature and the secondary stream temperature, T p Temperature of main flow, T s For the temperature of the secondary stream>Is an expression of the energy density spectrum with respect to wavelength in planck's law of blackbody radiation.
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