Adaptive mode conversion control plan design method for TBCC engine suitable for wide envelope

Abstract

The invention provides a TBCC engine adaptive mode conversion control plan design method suitable for a wide envelope, and the method comprises the steps: designing single-point mode conversion control plans at a plurality of typical fan inlet temperatures in a mode conversion window, and carrying out the adaptive obtaining of a mode conversion plan suitable for the current fan inlet total temperature through linear interpolation; on the basis of the isotherm similar conversion theory, for envelope points with the same fan inlet temperature, it is guaranteed that similar conversion parameters of control parameters are consistent, and the envelope points can share the same set of control plans through similar inverse transformation. The control plan designed by the method effectively breaks through the limitation that a conventional control method is only suitable for a single envelope point, the stable and safe mode conversion process can be achieved at each envelope point in the whole mode conversion window, and in the process, the engine does not have the phenomena of over-temperature, over-rotation and surge.

Description

Technical Field

[0001] The present invention belongs to the technical field of supersonic engine mode conversion and control plan, and in particular relates to a TBCC engine adaptive mode conversion control plan design method. Background Art

[0002] Turbine-based combined cycle (TBCC) engines, as a power source for hypersonic vehicles, have long been a hot topic of research in the field of combined propulsion. TBCC engines, structurally combining a turbine engine and a ramjet (or scramjet), offer flight Mach numbers ranging from subsonic and supersonic to hypersonic, and possess advantages such as horizontal takeoff and landing, wide range, and high economic efficiency. The mode transition process refers to the transition between a turbine engine (referred to as the turbine mode) and a ramjet engine (referred to as the ramjet mode). During this transition, actuators adjust the turbofan duct, gradually closing the turbofan and opening the ramjet duct, allowing air flow at the inlet outlet to gradually shift from the turbofan duct to the ramjet duct. This ability to transition between these two modes enables TBCC engines to operate efficiently across a wide flight envelope. Mode transition control design involves designing the curves for each engine actuator during the transition process to ensure a smooth and safe turbofan-ramjet transition within parameter constraints. Since the turbine engine components and ramjet engine components work together during the modal conversion process, the number of adjustable mechanisms becomes more than twice the number of conventional engine adjustment mechanisms. The increase in the number of working parts and the increase in the number of adjustable mechanisms greatly increases the difficulty of designing the process control plan.

[0003] Qiu Xiaojie from the Control Systems Research Institute of China Aero Engine Corporation used the sequential quadratic optimization (SQP) method to optimize the engine fuel flow, tail nozzle throat area, and various flow control valves during the mode conversion process for a small parallel TBCC engine, and obtained the mode conversion control plan [Qiu X., Su W., Tang Y. The mode switch control research of small-type parallel TBCC engine based on SQP method [C]. AIAA Modeling and Simulation Technologies Conference, AIAA 2015-2656, Dallas: 2015]. Zhang Mingyang from Northwestern Polytechnical University studied the performance variation law of a small series TBCC engine and obtained the control plan of various engine adjustment parameters during the mode conversion process based on the thrust and flow continuity criteria [Zhang Mingyang, Wang Zhanxue, Zhang Xiaobo, et al. Simulation of windmill ramjet modal performance of series TBCC engine [J]. Journal of Aerospace Power, 2018, 33(12): 2939-2949.]. Chen Min from the Beijing University of Aeronautics and Astronautics studied the multi-objective control problem of a tandem turbo-ramjet engine [Chen M., Tang H., Zhu Z. Goal Programming for Stable Mode Transition in Tandem Turbo-ramjet Engines [J]. Chinese Journal of Aeronautics, 2009, 22(05): 486-492.], using the Newton-Raphson method to study the modal transition control plan for a component-level model of a TBCC engine at the rated modal transition point of Mach 3. The modal transition control plan obtained based on the above method can basically achieve a smooth transition of state parameters such as thrust during the modal transition process. However, most current modal transition control plans are designed under a specific flight condition (rated modal transition point), and the designed control plan is also only applicable to that specific flight condition. When the modal transition flight condition deviates from the given flight condition, satisfactory transition performance cannot be achieved, and even flight safety is affected. However, according to actual flight mission requirements, it is usually impossible to ensure that mode transitions only occur under given flight conditions. Properly expanding the scope of application of the mode transition control plan has practical engineering application value. Currently, there is a lack of effective means to expand the scope of application of the mode transition control plan.

[0004] The similarity conversion method converts the characteristics of complex systems under different conditions by finding the proportional relationship between physical phenomena. At present, some studies have applied the similarity conversion method [Fan Siqi. Aeroengine Control [M]. Northwestern Polytechnical University Press, 2008.] to the formulation of aeroengine acceleration and deceleration control plans, and expanded the acceleration and deceleration control plan obtained by single working point design to the full envelope through the similarity conversion method. However, there are few reports on the application of the similarity conversion method to the formulation of control plans for modal conversion processes. Due to the strong nonlinear characteristics of modal conversion, the direct application of conventional similarity conversion methods will affect the modal conversion effect due to conversion accuracy issues, resulting in large thrust fluctuations during the modal conversion process, and even safety issues such as overheating and surge. The literature [Liu Zihe, Zheng Qiangang, Liu Minglei, et al. Research on Improved Methods for Turbofan Engine Full Envelope Acceleration Control Plans [J]. Propulsion Technology, 2022, 43(1): 2004-16.] proved through theoretical derivation that the key parameters have a high similarity conversion accuracy when the fan inlet temperature is constant. Summary of the Invention

[0005] Technical solution: In order to break through the limitation that the traditional modal conversion control plan can only be applied to a single operating point, and to improve the technical problem that the conventional similarity conversion method is not accurate enough and cannot be directly applied to the strongly nonlinear process of modal conversion, the present invention takes the series TBCC engine as the research object and proposes an adaptive modal conversion control plan design method based on isothermal similarity conversion. This method can achieve a smooth and safe modal conversion process at each envelope point within the modal conversion window near the rated modal conversion point.

[0006] The present invention provides a TBCC engine mode conversion control plan design method, specifically a TBCC engine adaptive mode conversion control plan design method with wide envelope applicability, the specific steps are:

[0007] (1) Divide the modal conversion window

[0008] On the TBCC engine envelope, around the rated modal transition point, N different typical envelope points are selected at equal intervals according to the fan inlet temperature, called isothermal reference points, to construct a modal transition window, where N is a positive integer greater than 1.

[0009] (2) Calculate the isothermal reference point and extend the isothermal line

[0010] The fan inlet static temperature T is calculated independently based on the flight altitude H and Mach number Ma for the above N+1 typical envelope points. s2 and total temperature T2; then, within the modal conversion window, the envelope points having the same fan inlet total temperature as the above N+1 typical envelope points are connected to form N+1 isothermal reference lines;

[0011] (3) Obtain the modal conversion control plan corresponding to each isothermal reference point and perform similarity conversion processing

[0012] At each isothermal reference point in the modal conversion window, by establishing an optimization mathematical model and using the PSO optimization method to optimize the modal conversion control plan, we can obtain the modal conversion control plan of each adjustable variable of the engine under N+1 groups of different fan inlet temperatures, where α MSV =f1(t),W fbcor =f2(t),A8=f3(t),W facor =f4(t),A FVABI =f5(t),A RVABI =f6(t);

[0013] The control plan parameters of each adjustable variable are converted according to the similar conversion criteria to obtain N+1 groups of modal conversion control plans represented by conversion parameters, including α MSV =F1(n Hcor ), W fbcor =F2(n Hcor ), A8=F3(n Hcor ), W facor =F4(n Hcor ), A FVABI =F5(n Hcor ), A RVABI =F6(n Hcor ); where t is time, n Hcor is the high-pressure turbine conversion speed, α MSV Select valve opening, W for mode fbcor is the fuel conversion flow rate of the main combustion chamber, A8 is the tail nozzle throat area, W facor is the fuel conversion flow rate of the afterburner, A FVABI For the front variable area duct ejector, A RVABI It is the rear variable area duct ejector;

[0014] (4) Method for obtaining and applying the modal transition control plan for each envelope point within the modal transition window

[0015] For each envelope point on the isothermal reference line, the modal conversion control plan of the corresponding isothermal reference point is shared. When using it, the conversion parameters of the corresponding adjustable variables must be equal. The conversion parameters must be converted into physical parameters through similar inverse transformation and then input into the engine for execution.

[0016] For envelope points on the non-isothermal baseline, the total fan inlet temperature at that point is measured. The adjacent isothermal baselines on both sides are first located, and then the control plans of the two baselines are linearly interpolated to adaptively obtain the modal conversion control plan applicable to the envelope point. Subsequently, the conversion parameters are converted into physical parameters by similar inverse transformation and then input into the engine for execution.

[0017] As an improvement, the envelope range of the turbofan mode is: Ma=0-3, H=0-22km; the operating range of the ramjet mode is: Ma=2.6-4, H=14.1-26.6km.

[0018] As an improvement, the rated modal transition point in step (1) is Ma=2.8, H=19.16 km; the modal transition window is Ma=2.6-3, H=18.2-20 km, and N is 4.

[0019] As an improvement, the specific method for obtaining the modal conversion control plan for different isothermal reference points in step (3) is:

[0020] (3.1) Keeping the total thrust of the propulsion system and the position of the normal shock wave constant during the modal conversion process, the objective function J of the TBCC modal conversion process is expressed as follows:

[0021]

[0022] Where, F is the engine thrust, F before is the engine thrust at the start of mode conversion, x A,opt is the inlet normal shock wave position at the start of mode conversion, x A is the real-time normal shock wave position in the inlet, n L is the real-time fan speed, n L,idle is the fan slow speed, ω1, ω2, ω3 are the objective function weight coefficients; the optimization variable u=[W fb ,W fa ,A8,α MSV ,A FVABI ,A RVABI ],W fb is the fuel flow rate, W fa is the afterburner fuel flow, A8 is the tail nozzle throat area, α MSV is the mode selection valve opening, A FVABI ,A RVABI are the front and rear variable area duct ejector outlet areas respectively;

[0023] (3.2) The engine state limit parameter is set as the constraint boundary function. The constraint boundary function is set as follows:

[0024]

[0025] Where, T7 is the total temperature at the ramjet combustion chamber outlet, T 7,max is the maximum threshold of the total temperature at the ramjet combustion chamber outlet, far4 is the fuel-air ratio of the main combustion chamber, far 4,min is the fuel-air ratio at the flameout boundary, S mL is the fan surge margin, S mH is the compressor surge margin, RM is the return flow margin, du is the adjustment amount of the actuator in a single step, du max It is the maximum threshold value of the allowed adjustment amount;

[0026] (3.3) The particle swarm optimization (PSO) method is used to solve the optimization problem composed of (1) and (2), and the regulation rules of each control variable in the modal conversion process are obtained.

[0027] As an improvement, when performing similarity conversion processing in step (3), the similarity conversion criteria used include:

[0028]

[0029] Among them, C1, C2, C3, C4, C5, and C6 are constants, T2 and p2 are the total temperature and pressure at the fan inlet, and T s is the static temperature, p s is the static pressure, n is the speed, W f is the fuel flow rate, W a is the air flow, F is the engine thrust, and the subscript "cor" represents the dimensionless parameter after similar conversion of the corresponding parameters: W fcor is the fuel flow similarity conversion parameter, T scor is the static temperature similarity conversion parameter, p scor is the static pressure similarity conversion parameter, n cor is the speed similarity conversion parameter, W acor is the air flow similarity conversion parameter, F cor is the thrust similarity conversion parameter.

[0030] As an improvement, within the modal transition window, the modal transition control plan obtained from any two isothermal reference points is used to adaptively calculate the modal transition control plan corresponding to the envelope point m where the fan inlet total temperature is between the two isothermal reference points according to the current fan inlet total temperature. The specific steps are as follows:

[0031] Assume that the total temperature of the fan inlet at envelope point m is T 2,3 Between two known isothermal reference points (the total temperature of the fan inlet is T 2,1 and T 2,2 ), first, obtain the control plan curve of the control variables corresponding to the two reference points, and convert the parameter W to the fuel flow of the main combustion chamber. fbcor Taking the control plan curve as an example, an equal number of discrete points are selected on each curve;

[0032] Then, the temperature ratio coefficient T is calculated by formula (3): ratio ,

[0033]

[0034] According to T 2,1 and T 2,2 Select several discrete points on the control curve under the envelope point m, and calculate the coordinates of the points on the control curve under the envelope point m by using equations (4) to (7).

[0035] n Hcor,5 =T ratio (n Hcor,3 -n Hcor,1 )+n Hcor,1 (4)

[0036] (W fbcor )5=T ratio ((W fbcor )3-(W fbcor )1)+(W fbcor )1 (5)

[0037] n Hcor,6 =T ratio (n Hcor,4 -n Hcor,2 )+n Hcor,2 (6)

[0038] (W fbcor )6=T ratio ((W fbcor )4-(W fbcor )2)+(W fbcor )2 (7)

[0039] Where, point 1 and point 2 are T 2,1 The corresponding parameters of the adjacent discrete points selected on the lower control curve are represented by the subscripts "1" and "2"; points 3 and 4 are T 2,2 The corresponding adjacent discrete points selected on the lower control curve are represented by the subscripts "3" and "4"; points 5 and 6 are the calculated T 2,3 The corresponding parameters of the corresponding adjacent discrete points on the lower control curve are represented by subscripts “5” and “6”;

[0040] Finally, through the above interpolation calculation, we can get the envelope point m, W fbcor Multiple points on the modal conversion control plan curve are connected to obtain the envelope point m, W fbcor Modal switching control scheme for control variables.

[0041] As an improvement, the obtained adaptive modal conversion control plan is subjected to an inverse similarity transformation, converted into physical parameters and then input into the engine for execution, wherein the inverse similarity transformation criterion is the inverse operation of the similarity conversion criterion.

[0042] As an improvement, it also includes simulation and verification, integrating the optimized modal conversion control plan of each isothermal point into the component-level model of the TBCC propulsion system, selecting at least three envelope points in the modal conversion window, including the rated modal conversion point, the conversion Mach number greater than the rated modal conversion point, and the conversion Mach number less than the rated modal conversion point, to adaptively obtain the parameters corresponding to the modal conversion control plan, perform simulation, calculate the key state parameters of the engine during the modal conversion, and verify whether the control plan meets the smooth and safe requirements of the modal conversion process. The key state parameters include the position of the positive shock wave, the overall thrust fluctuation amplitude, the fan and compressor speed of the engine, the surge margin, the backflow margin, and the total temperature of the afterburner outlet.

[0043] Compared with conventional methods, the adaptive mode conversion control plan design method of the present invention has the following advantages:

[0044] (1) In the present invention, N groups, for example, 5 groups, of typical flight conditions with different fan inlet temperatures are uniformly selected within a transition window near the rated mode transition point. Under each flight condition, the engine mode transition control plan curve is obtained by the particle swarm optimization (PSO) method.

[0045] (2) In the present invention, for operating points with the same fan inlet temperature as the above-mentioned N groups, for example, 5 groups of typical flight conditions, the modal transition control plan curve on the same isothermal line can be applied; for other envelope points within the transition window, the unknown modal transition control plan is obtained by linear interpolation based on the known modal transition control plan under the adjacent typical isothermal line.

[0046] Beneficial effects: The present invention proposes an adaptive modal transition control plan design method based on isothermal similarity conversion. The modal transition control plan designed by the present invention can achieve smooth state transition at each envelope point within the modal transition window (Ma=2.6~3.0, H=18~20km), and the maximum fluctuation of the engine net thrust, installed thrust and normal shock wave position is less than 3%. Compared with the conventional modal conversion method, the relative fluctuation of the net thrust, installed thrust and normal shock wave position can be reduced by more than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the rated modal transition point and modal transition window of the present invention.

[0048] Figure 2 Schematic diagram of the isothermal line division results of the five envelope points selected in the present invention in the modal conversion window.

[0049] Figure 3 This is the control plan for the conversion process of the rated mode conversion point (Ma=2.8) of the present invention, including (a) mode selection valve; (b) main combustion chamber fuel flow, (c) tail nozzle throat area, (d) afterburner combustion chamber fuel flow; (e) front variable area ducted ejector; (f) rear variable area ducted ejector.

[0050] Figure 4 The control plan for the conversion process of the five envelope points within the modal conversion window of the present invention includes: (a) mode selection valve; (b) main combustion chamber fuel flow; (c) tail nozzle throat area; (d) afterburner fuel flow; (e) front variable area ducted ejector; and (f) rear variable area ducted ejector.

[0051] Figure 5 Schematic diagram of embodiment 1 of the linear interpolation principle of the mode conversion control scheme of the present invention.

[0052] Figure 6 This is a block diagram of the modal conversion control based on isothermal similarity conversion of the present invention.

[0053] Figure 7 Figure 3. Changes of key state parameters during the transition process at the rated modal transition point (Ma=2.8): (a) thrust; (b) normal shock wave position; (c) speed; (d) air flow; (e) total temperature at the main combustion chamber outlet; (f) total temperature at the afterburner combustion chamber outlet; (g) surge margin; and (h) backflow margin.

[0054] Figure 8 For Ma <Ma rated Comparison of the modal conversion control effect at the non-rated point Mach number, (a) thrust; (b) normal shock wave position; (c) speed; (d) air flow; (e) total temperature at the main combustion chamber outlet; (f) total temperature at the afterburner combustion chamber outlet; (g) surge margin; (h) backflow margin.

[0055] Figure 9 For Ma>Ma rated Comparison of the modal conversion control effect at the non-rated point Mach number, (a) thrust; (b) normal shock wave position; (c) speed; (d) air flow; (e) total temperature at the main combustion chamber outlet; (f) total temperature at the afterburner combustion chamber outlet; (g) surge margin; (h) backflow margin. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present invention will be described clearly and completely below so that those skilled in the art can better understand the advantages and features of the present invention and thus more clearly define the scope of protection of the present invention. The embodiments described in the present invention are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without making any creative work shall fall within the scope of protection of the present invention.

[0057] The present invention provides an improved design method for an adaptive modal transition control plan based on isothermal similarity conversion. Traditional modal transition control plan research mainly focuses on the design of rated modal transition points. During actual flight, due to mission requirements, it is inevitable to perform modal transition at non-rated modal transition points. Based on the isothermal similarity conversion principle, the present invention proposes a modal transition control plan design method that is applicable to all points in the modal transition window near the rated modal transition point. Typical flight conditions with different fan inlet temperatures are equidistantly selected within the modal transition window, and multiple groups of modal transition control plan curves are obtained through optimization methods. Then, modal transition control plan curves under different isothermal lines within the transition window are obtained through linear interpolation, thereby adaptively obtaining a modal transition control plan applicable to the entire transition window based on different fan inlet total temperatures.

[0058] The following is an introduction and explanation of the specific implementation methods. First, a modal conversion window division scheme based on isotherms is given, and then an isotherm similarity conversion adaptive modal conversion control plan is designed.

[0059] 1.1 Mode transition window division scheme based on isotherms

[0060] a) Isotherm similarity conversion principle:

[0061] In the performance research of engines and their components, the principle of similarity conversion plays an extremely important role. When the working conditions of engines are similar, they have the following important properties:

[0062] 1) The ratio of the physical quantities of the same name on each corresponding cross section remains unchanged, that is, p s,i / p2=Const,T s,i / T2=Const (i is the subscript of any cross section on the engine flow path).

[0063] 2) The flight Mach number Ma and component efficiency η on each cross section remain unchanged, that is, Ma i =Const,η j =Const (i is the subscript of any cross section on the engine flow path; j is any component).

[0064] From the above two properties, we can derive some similarity criteria for engine state quantities. Commonly used engine similarity conversion criteria are shown in Table 1.

[0065] Table 1 Similar conversion criteria used in the present invention

[0066]

[0067] As shown in Table 1, C1, C2, C3, C4, C5, and C6 are constants, T2 and p2 are the total temperature and total pressure at the fan inlet, and T s is the static temperature, p s is the static pressure, n is the speed, W f is the fuel flow rate, W a is the air flow, F is the engine thrust, and the subscript "cor" represents the dimensionless parameter after similar conversion of the corresponding parameters: W fcor is the fuel flow similarity conversion parameter, T scor is the static temperature similarity conversion parameter, p scor is the static pressure similarity conversion parameter, n cor is the speed similarity conversion parameter, W acor is the air flow similarity conversion parameter, F cor is the thrust similarity conversion parameter.

[0068] It can be inferred from the temperature conversion rule that

[0069]

[0070] Where T is the total temperature of a certain section of the engine.

[0071] The specific heat of an ideal gas at constant pressure is usually expressed as a polynomial with respect to temperature as follows,

[0072] c p =a0+a1T s +a2T s 2 +a3T s 3 +a4T s 4 (2)

[0073] The coefficients a0-a4 in the formula can be obtained from relevant thermodynamics literature.

[0074] From engineering thermodynamics, we know that

[0075]

[0076] Where c p is the specific heat capacity at constant pressure, c v is the specific heat at constant volume, R is the universal gas constant, and γ is the ratio of specific heats.

[0077] From the above deduction, we can know that different engine inlet temperatures will cause the c of the air in the flow channel to p Different, and the specific heat ratio γ is about c p Therefore, performing similarity conversion along the same fan inlet temperature can effectively reduce the temperature similarity conversion error between different operating points.

[0078] Similarly, according to the pressure similarity conversion criterion,

[0079]

[0080] Where p is the total pressure at a certain section of the engine.

[0081] From equations (4) and (5), we can see that in the process of pressure similarity conversion, the invariance of γ is still the key to ensuring the constant pressure ratio of different sections. Therefore, similarity conversion along the isotherm can effectively improve the accuracy of pressure conversion. The same principle also applies to the similarity conversion derivation of fuel flow, air flow and thrust. Therefore, c p It is an important factor affecting the accuracy of similar conversion. p Invariance can reduce similarity conversion errors more effectively than traditional similarity conversion methods.

[0082] b) Modal conversion window division scheme

[0083] According to the simulation results of the TBCC engine model established in the early stage, the envelope range of the turbofan mode is: Ma = 0-3, H = 0-22 km; the operating range of the ramjet mode is: Ma = 2.6-4, H = 14.1-26.6 km. Figure 1 Without loss of generality, we select the flight trajectory (Ma rated =2.8,H rated =19.16km) as the rated modal transition point, and the overlapping area of ​​the turbofan and ram envelope near the rated modal transition point (Ma = 2.6-3, H = 18.2-20km) is selected as the modal transition window. A total of 5 flight condition points with different fan inlet temperatures are evenly selected around a rated modal transition point to construct a modal transition window, such as Figure 1 and as shown in Table 2.

[0084] Table 2 Isothermal reference points

[0085]

[0086] Based on the aforementioned isothermal similarity conversion theory, similarity conversion along isotherms is more effective in reducing similarity conversion errors than traditional similarity conversion methods. Within the modal conversion window, the fan inlet total temperature at each point is calculated using Equation (6). The envelope points with the same fan inlet total temperature as the five typical envelope points are connected to form five isothermal baselines.

[0087]

[0088] The obtained isotherms divide the mode transition window, such as Figure 2 Similar conversion along the isothermal line can effectively reduce the effect of temperature on the constant pressure specific heat capacity c. p The influence of the specific heat ratio γ is analyzed to improve the similarity conversion accuracy. Next, the design method of the modal transition control plan suitable for the modal transition window is studied.

[0089] 1.2 Isotherm similarity conversion adaptive mode conversion control plan design

[0090] The traditional single-operating-point mode conversion control plan mainly optimizes the mode conversion rated point. The primary goal of the optimization is to keep the total thrust of the propulsion system and the position of the positive shock wave constant (that is, the engine required air flow is constant). Therefore, the objective function expression of the TBCC mode conversion process is shown in Equation (7). In order to ensure that the fan speed is adjusted to the slow speed n as soon as possible, Lidle , the objective function of the optimization process also includes the fan speed n L .

[0091]

[0092] Where F is the engine thrust, F before is the engine thrust at the start of the mode conversion, x A,opt is the inlet normal shock wave position at the start of mode conversion, x A is the real-time normal shock wave position in the inlet, n L is the real-time fan speed, n L,idle is the fan slow speed, ω1, ω2, ω3 are the objective function weight coefficients; the optimization variable u=[W fb ,W fa ,A8,α MSV ,A FVABI ,A RVABI ],W fb is the fuel flow rate, W fa is the afterburner fuel flow, A8 is the tail nozzle throat area, α MSV is the mode selection valve opening, A FVABI ,A RVABI are the front and rear variable area duct ejector outlet areas respectively;

[0093] During the mode conversion process, the engine limit parameters must be kept within a reasonable range. Therefore, the present invention sets the engine state limit parameters as constraint boundary functions. This includes limiting the total temperature at the ramjet combustion chamber outlet (T7≤T 7,max ); constrain the fuel-gas ratio of the main combustion chamber (far4≥far 4,min ), far 4,min is the fuel-air ratio at the flameout boundary; at the end of the mode conversion, the turbofan engine is in the idling state, and the fan speed is equal to the idling speed n L,idle , so it is necessary to limit the minimum speed (n L ≥n L,idle ); At the same time, during the mode conversion process, it is also necessary to ensure that the engine does not gasp (S mL ≥S ML,min ,S mH ≥S mH,min ), the backflow margin is greater than 0 (RM>0), and the inlet positive shock wave position is located downstream of the throat (x A >1); the adjustment amount of the actuator within a single step is not greater than the maximum allowable adjustment amount (|du| <du max ). In summary, the constraint boundary function is set as shown in formula (8).

[0094]

[0095] Where, T7 is the total temperature at the ramjet combustion chamber outlet, T 7,max is the maximum threshold of the total temperature at the ramjet combustion chamber outlet, far4 is the fuel-air ratio of the main combustion chamber, far 4,min is the fuel-air ratio at the flameout boundary, S mL is the fan surge margin, S mH is the compressor surge margin, RM is the return flow margin, du is the adjustment amount of the actuator in a single step, du max It is the maximum threshold of the allowed adjustment amount.

[0096] At this point, the mathematical model for optimizing the engine mode conversion control plan at the rated point is established (as shown in Equations (7) and (8)). This mathematical model is a multi-objective optimization problem with multiple constraints. The particle swarm optimization (PSO) method is used to solve it, and the regulation law of each control variable in the mode conversion process is obtained: MSV =f1(t),W fbcor =f2(t),A8=f3(t),W facor =f4(t),A FVABI =f5(t),A RVABI =f6(t) form, see Figure 3 .

[0097] Next, at each isothermal point selected in the modal transition window, an optimization mathematical model is established using the same approach as for the rated point, and the PSO optimization method is used to optimize the modal transition control plan for each point, thereby obtaining the optimized modal transition control plan at different typical fan inlet temperatures T2. In order to facilitate the acquisition of the adaptive modal transition control plan for any point within the modal transition window, the similarity conversion criterion in Table 1 is used. The present invention expresses the control plan parameters obtained by optimizing the typical isothermal point as conversion parameters, expressed as α MSV =F1(n Hcor ), W fbcor =F2(n Hcor ), A8=F3(n Hcor ), W facor =F4(n Hcor ), A FVABI =F5(n Hcor ), A RVABI =F6(n Hcor ), the obtained mode conversion control plan is shown in Figure 4 .

[0098] 1.3 Obtaining and applying the modal transition control plan for any envelope point within the modal transition window

[0099] Theoretical derivation of isothermal similarity conversion errors indicates that all operating points on the same isothermal line can be applied to the same set of modal transition control plans, ensuring safe and stable engine operation during the modal transition process. For modal transition control plans at points outside the isothermal envelope within the modal transition window, the present invention employs linear interpolation to interpolate the unknown modal transition control plan based on the known modal transition control plan at the nearest typical T2. The interpolated modal transition control plan is then applied to all operating points on the same isothermal line. The following describes and illustrates the linear interpolation method in detail through examples.

[0100] Example 1

[0101] like Figure 5 As shown, select two obtained T t2,1 and T t2,2 The modal conversion control plan under T t2,3 The modal conversion control scheme under W fbcor As an example, we first select several points on two known control plans. Here we take points 1 to 4 as an example.

[0102]

[0103] Using the temperature ratio remainder, we can get the speed and oil-gas ratio at points 5 and 6 as follows:

[0104] n Hcor,5 =Tratio (n Hcor,3 -n Hcor,1 )+n Hc or,1 (10)

[0105] (W fbcor )5=T ratio ((W fbcor )3-(W fbcor )1)+(W fbcor )1 (11)

[0106] n Hcor,6 =T ratio (n Hcor,4 -n Hcor,2 )+n Hcor,2 (12)

[0107] (W fbcor )6=T ratio ((W fbcor )4-(W fbcor )2)+(W fbcor )2 (13)

[0108] In formulas (10)-(13), W fbcor Similar conversion parameter for fuel flow in main combustion chamber, n Hcor is the similarity conversion parameter of high-pressure turbine speed; point 1 and point 2 are T 2,1 The corresponding parameters of the adjacent discrete points selected on the lower control curve are represented by the subscripts "1" and "2"; points 3 and 4 are T 2,2 The corresponding adjacent discrete points selected on the lower control curve are represented by the subscripts "3" and "4"; points 5 and 6 are the calculated T 2,3 The corresponding parameters of the corresponding adjacent discrete points on the lower control curve are represented by subscripts “5” and “6”;

[0109] Then, multiple values ​​are taken and calculated according to equations (10)-(13). Therefore, under the premise that two acceleration control plans are known, the acceleration control plan of any isotherm between the isotherms can be obtained by adaptive interpolation according to the current fan inlet total temperature, which is the adaptive mode conversion control plan.

[0110] In the present invention, when used, the modal conversion control plan obtained by interpolation needs to be subjected to an inverse similarity transformation, and the inverse similarity transformation is performed according to the inverse operation of Table 1, that is, the modal conversion control plan represented by the similarity conversion parameter is: α MSV =F1(n Hcor ), W fbcor =F2(n Hcor ), A8=F3(n Hcor ), W facor =F4(n Hcor), A FVABI =F5(n Hcor ), A RVABI =F6(n Hcor ), expressed as a physical quantity that changes with time: α MSV =f1(t),W fbcor =f2(t),A8=f3(t),W facor =f4(t),A FVABI =f5(t),A RVABI =f6(t) in the form of input to the TBCC propulsion system for execution. Specifically, the control block diagram of the mode conversion control plan based on the isothermal similarity conversion is as follows: Figure 6 shown.

[0111] 2 Simulation Verification

[0112] At least three envelope points in the modal conversion window, including the rated modal conversion point, the conversion Mach number greater than the rated modal conversion point, and the conversion Mach number less than the rated modal conversion point, are selected to adaptively obtain the parameters corresponding to the modal conversion control plan. Simulation is performed to calculate the key state parameters of the engine during the modal conversion, and to verify whether the control plan meets the smooth and safe requirements of the modal conversion process. The key state parameters include the position of the positive shock wave, the overall thrust fluctuation amplitude, the fan and compressor speeds of the engine, the surge margin, the backflow margin, and the total temperature of the afterburner outlet.

[0113] 2.1 Simulation verification of the rated modal transition point position

[0114] See Figure 7 Shown is the rated modal transition point (Ma rated =2.8, H rated =19.16km) changes in key state parameters during the conversion process. From the simulation results in the figure, it can be seen that the modal conversion control law optimized by the present invention can ensure the constant thrust during the modal conversion, and the overall thrust fluctuation amplitude is less than 0.09% (ΔF<0.09%). The positive shock wave position can reflect the change in the engine demand flow. The fluctuation amplitude of the positive shock wave position is less than 0.83% (Δx A <0.83%). The engine limit parameters are also within a reasonable range, and no significant parameter jitter occurs. The above simulations show that the modal conversion control plan design method proposed in this invention can achieve satisfactory modal conversion effects at the traditional rated modal conversion point.

[0115] 2.2 Simulation verification of non-rated modal transition point position

[0116] like Figure 8 As shown, when the mode conversion Mach number (Ma=2.73,H=18.8km) is less than the rated point Mach number (Ma rated=2.8, H rated =19.16km) when converting to a non-rated point Mach number, the conventional modal conversion method results in a large thrust fluctuation of ΔF = 110N (0.56%). After the modal conversion is completed, the thrust decreases slightly compared to before the conversion, and the thrust before and after the conversion cannot be guaranteed to be consistent. However, the maximum thrust fluctuation using the isothermal conversion method is approximately ΔF = 30N (0.2%), which significantly reduces the thrust fluctuation and ensures that the thrust before and after the modal conversion is basically the same. Figure 8 (b) shows that another advantage of the isotherm conversion method is that the fluctuation of the positive shock wave position during the conversion process is significantly reduced compared with the conventional method, with a reduction of 1.1%. The positive shock wave position before and after the conversion is basically maintained at x A,opt =1.1 is the optimal working position, while the conventional method deviates from the optimal position and approaches the throat position, which easily causes the inlet to fail to start. In addition, from the conversion results, the engine's fan and compressor speeds, surge margin, and backflow margin are all within a reasonable range, and no overspeed, surge, or ram duct airflow backflow occurs. However, from Figure 8 (d) It can be seen that under normal mode conversion, the total temperature T7 at the afterburner outlet has exceeded the temperature at the highest point, which is not allowed during engine use.

[0117] Further, when the mode conversion Mach number (Ma=2.85,H=19.4km) is greater than the rated point Mach number (Ma rated =2.8, H rated =19.16km), a comparative simulation of the modal conversion effect was conducted, such as Figure 9 As shown. Figure 9 As shown in (a) and (b), the maximum fluctuation amplitude of the thrust during the conversion process is ΔF = 50N (0.26%), and the maximum fluctuation amplitude of the positive shock wave position is Δx A =0.42%, which is within the acceptable range. The thrust and normal shock wave position can be kept consistent before and after the conversion. Figure 9 (c~f) It can be seen that all state parameters of the engine can be kept within a reasonable range. Using the conventional state conversion method, the fluctuation amplitude of the thrust is ΔF=95N(0.47%), and the fluctuation amplitude of the positive shock wave position is Δx A =0.018(1.5%), which is higher than the isotherm conversion method. <Ma rated The thrust drops significantly when the propulsion system is running, but the overall thrust value is still lower than the thrust obtained by the isothermal conversion method. The positive shock wave position also moves downstream from the optimal position, which reduces the overall efficiency of the propulsion system. Figure 9 (d) It can be seen that when Ma>Ma ratedUnder these conditions, there was no over-temperature phenomenon in the total temperature at the afterburner outlet.

[0118] The above simulations show that the modal conversion control plan design method proposed in the present invention performs modal conversion at non-rated points, regardless of the Ma>Ma rated Still Ma <Ma rated The modal conversion can be completed smoothly under all conditions, and the modal conversion time can be basically controlled to be completed in about 30s. Although the overall conversion effect is slightly worse than the rated point state, it can still ensure that the thrust is basically constant and the position of the positive shock wave remains basically unchanged. The conversion effect is significantly better than the traditional modal conversion control method.

[0119] Furthermore, the conversion effects of the conventional method and the isothermal conversion method proposed in this invention were compared within the modal conversion window of Ma = 2.6-3.0 and H = 18-20 km, at intervals of ΔMa = 0.02 and ΔH = 0.1 km. Simulation results show that the improved modal conversion control plan design method can achieve smooth state transitions at all points within the modal conversion window. The maximum fluctuations in the engine net thrust, installed thrust, and normal shock wave position are 122N (1.15%), 0.026 (2.36%), and 122.5N (1.75%), respectively. Compared with the conventional modal conversion method, the fluctuations in net thrust, installed thrust, and normal shock wave position can be reduced by 97%, 84%, and 97.5%, respectively. Throughout the modal conversion process, the engine does not experience overheating, overspeed, or surge, and the inlet remains in a good operating state of mild supercriticality.

[0120] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for designing an adaptive mode conversion control plan for a TBCC engine with wide envelope, characterized by: The specific steps include (1) Divide the modal conversion window On the TBCC engine envelope, around the rated modal transition point, N different typical envelope points are selected at equal intervals according to the fan inlet temperature, called isothermal reference points, to construct a modal transition window, where N is a positive integer greater than 1. (2) Calculate the isothermal reference point and extend the isothermal line The fan inlet static temperature T is calculated independently based on the flight altitude H and Mach number Ma for the above N+1 typical envelope points. s2 and total temperature T2; then, within the modal conversion window, the envelope points having the same fan inlet total temperature as the above N+1 typical envelope points are connected to form N+1 isothermal reference lines; (3) Obtain the modal conversion control plan corresponding to each isothermal reference point and perform similarity conversion processing At each isothermal reference point in the modal conversion window, by establishing an optimization mathematical model and using the PSO optimization method to optimize the modal conversion control plan, we can obtain the modal conversion control plans of each adjustable variable of the engine at N+1 groups of different fan inlet temperatures, where α MSV =f1(t),W fbcor =f2(t),A8=f3(t),W facor =f4(t),A FVABI =f5(t),A RVABI =f6(t); The control plan parameters of each adjustable variable are converted according to the similarity conversion principle to obtain N+1 groups of modal conversion control plans represented by conversion parameters, including α MSV =F1(n Hcor ), W fbcor =F2(n Hcor ), A8=F3(n Hcor ), W facor =F4(n Hcor ), A FVABI =F5(n Hcor ), A RVABI =F6(n Hcor );in t is time, n Hcor is the high-pressure turbine conversion speed, α MSV Select valve opening, W for mode fbcor is the fuel conversion flow rate of the main combustion chamber, A8 is the tail nozzle throat area, W facor is the fuel conversion flow rate of the afterburner, A FVABI For the front variable area duct ejector, A RVABI It is the rear variable area duct ejector; (4) Method for obtaining and applying the modal transition control plan for any envelope point within the modal transition window For each envelope point on the isothermal reference line, the modal conversion control plan of the corresponding isothermal reference point is shared. When using it, the conversion parameters of the corresponding adjustable variables must be equal. The conversion parameters must be converted into physical parameters through similar inverse transformation and then input into the engine for execution. For envelope points on the non-isothermal baseline, the total fan inlet temperature at that point is measured. The adjacent isothermal baselines on both sides are first located, and then the control plans of the two baselines are linearly interpolated to adaptively obtain the modal conversion control plan applicable to the envelope point. Subsequently, the conversion parameters are converted into physical parameters by similar inverse transformation and then input into the engine for execution.

2. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1, characterized in that: The envelope range of the turbofan mode is: Ma=0-3, H=0-22km; the operating range of the ramjet mode is: Ma=2.6-4, H=14.1-26.6km.

3. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1 or 2, characterized in that: The rated modal transition point in step (1) is Ma=2.8, H=19.16 km; the modal transition window is Ma=2.6-3, H=18.2-20 km, and N is 4.

4. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1, characterized in that: The specific method for obtaining the modal conversion control plan for different isothermal reference points in step (3) is: (3.1) Keeping the total thrust of the propulsion system and the position of the normal shock wave constant during the modal conversion process, the objective function J of the TBCC modal conversion process is expressed as follows: Where, F is the engine thrust, F before is the engine thrust at the start of the mode conversion, x A,opt is the inlet normal shock wave position at the start of mode conversion, x A is the real-time normal shock wave position in the inlet, n L is the real-time fan speed, n L,idle is the fan slow speed, ω1, ω2, ω3 are the objective function weight coefficients; the optimization variable u=[W fb ,W fa ,A8,α MSV ,A FVABI ,A RVABI ],W fb is the fuel flow rate, W fa is the afterburner fuel flow, A8 is the tail nozzle throat area, α MSV is the mode selection valve opening, A FVABI 、A RVABI are the front and rear variable area duct ejector outlet areas respectively; (3.2) The engine state limit parameter is set as the constraint boundary function. The constraint boundary function is set as formula (2). Where, T7 is the total temperature at the ramjet combustion chamber outlet, T 7,max is the maximum threshold of the total temperature at the ramjet combustion chamber outlet, far4 is the fuel-air ratio of the main combustion chamber, far 4,min is the fuel-air ratio at the flameout boundary, S mL is the fan surge margin, S mH is the compressor surge margin, RM is the return flow margin, du is the adjustment amount of the actuator in a single step, du max It is the maximum threshold value of the allowed adjustment amount; (3.3) The particle swarm optimization (PSO) method is used to solve the optimization problem composed of (1) and (2), and the regulation rules of each control variable in the modal conversion process are obtained.

5. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1, characterized in that: When performing similarity conversion processing in step (3), the similarity conversion criteria used include: Among them, C1, C2, C3, C4, C5, and C6 are constants, T2 and p2 are the total temperature and pressure at the fan inlet, and T s is the static temperature, p s is the static pressure, n is the speed, W f is the fuel flow rate, W a is the air flow, F is the engine thrust, and the subscript "cor" represents the dimensionless parameter after similar conversion of the corresponding parameters: W fcor is the fuel flow similarity conversion parameter, T scor is the static temperature similarity conversion parameter, p scor is the static pressure similarity conversion parameter, n cor is the speed similarity conversion parameter, W acor is the air flow similarity conversion parameter, F cor is the thrust similarity conversion parameter.

6. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1, characterized in that: Within the modal transition window, the modal transition control plan obtained from any two isothermal reference points is used to adaptively calculate the modal transition control plan corresponding to the envelope point m where the fan inlet total temperature is between the two isothermal reference points according to the current fan inlet total temperature. The specific steps are as follows: Assume that the total temperature of the fan inlet at envelope point m is T 2,3 Between two known isothermal reference points, the total temperature of the fan inlet is T 2,1 and T 2,2 First, obtain the control plan curves of the control variables corresponding to the two reference points, and convert the parameter W to the fuel flow rate of the main combustion chamber. fbcor Taking the control plan curve as an example, an equal number of discrete points are selected on each curve; Then, the temperature ratio coefficient T is calculated by formula (3): ratio , According to T 2,1 and T 2,2 Select several discrete points on the control curve under the envelope point m, and calculate the coordinates of the points on the control curve under the envelope point m by using equations (4) to (7). n Hcor,5 =T ratio (n Hcor,3 -n Hcor,1 )+n Hcor,1 (4) (W fbcor )5=T ratio ((W fbcor )3-(W fbcor )1)+(W fbcor )1 (5) n Hcor,6 =T ratio (n Hcor,4 -n Hcor,2 )+n Hcor,2 (6) (W fbcor )6=T ratio ((W fbcor )4-(W fbcor )2)+(W fbcor )2 (7) Where W fbcor Similar conversion parameter for fuel flow in main combustion chamber, n Hcor is the similarity conversion parameter of high-pressure turbine speed; point 1 and point 2 are T 2,1 The corresponding parameters of adjacent discrete points selected on the lower control curve are represented by subscripts "1" and "2"; points 3 and 4 are T 2,2 The corresponding adjacent discrete points selected on the lower control curve are represented by subscripts "3" and "4" for their corresponding parameters; points 5 and 6 are the calculated T 2,3 The corresponding parameters of the corresponding adjacent discrete points on the lower control curve are represented by subscripts "5" and "6"; Finally, the above interpolation calculation is repeated to obtain the envelope point m, W fbcor Multiple points on the modal conversion control plan curve are connected to obtain the envelope point m, W fbcor Mode-switching control scheme for control variables.

7. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1, characterized in that: The method also includes performing an inverse similarity transformation on the obtained adaptive modal conversion control plan, converting it into physical parameters and then inputting it into the engine for execution, wherein the inverse similarity transformation criterion is the inverse operation of the similarity conversion criterion.

8. The method for designing an adaptive mode conversion control plan for a wide-envelope TBCC engine according to claim 1 is characterized by: The modal conversion control plan after optimization of each isothermal point is integrated into the component-level model of the TBCC propulsion system, and the modal conversion process is simulated and verified. At least three envelope points including the rated modal conversion point, the conversion Mach number greater than the rated modal conversion point, and the conversion Mach number less than the rated modal conversion point are selected in the modal conversion window. The parameters corresponding to the modal conversion control plan are adaptively obtained, and simulation is performed to calculate the key state parameters of the engine during the modal conversion. It is verified whether the control plan meets the smooth and safe requirements of the modal conversion process. The key state parameters include the position of the positive shock wave, the overall thrust fluctuation amplitude, the fan and compressor speeds of the engine, the surge margin, the backflow margin, and the total temperature at the afterburner outlet.

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