Mode conversion control method for tandem TBCC engine

Abstract

The present invention discloses a modal conversion control method for a tandem TBCC engine, wherein the tandem TBCC engine is used as a low-speed channel accelerator for a parallel TBCC engine. The modal conversion of the tandem TBCC engine is controlled in the following partitions according to the incoming flow Mach number: when the incoming flow Mach number is in the range of 0 to the first Mach number, the tandem TBCC engine is controlled to operate in the maximum state of the turbofan mode; when the incoming flow Mach number is in the range of the first Mach number to the second Mach number, the low-speed channel ramjet duct is opened, and the opening of the low-speed channel ramjet duct is made greater than 0 and less than or equal to the critical opening; when the incoming flow Mach number is in the range of the second Mach number to 4.0, the tandem TBCC engine is controlled to operate in the full ramjet mode. Compared with the prior art, the present invention can effectively avoid thrust traps and achieve high acceleration at the same time.

Description

Technical Field

[0001] The invention relates to a mode conversion control method for a tandem turbine-based combined cycle (TBCC) engine, belonging to the technical field of aerospace propulsion system control. Background Art

[0002] As the core component of hypersonic vehicles, the turbine-based combined cycle (TBCC) engine has always been a hot topic of attention and research in the field of combined power. For the parallel turbine-based combined cycle (TBCC) engine, the low-speed channel engine as an accelerator needs to further expand the flight envelope to Mach 4 or above on the basis of the traditional Mach 2 first-stage turbine engine to adapt to the starting range of the high-speed channel dual-mode ramjet engine. The low-speed channel engine should have sufficient thrust to maintain the thrust continuity of the entire propulsion system during the entire working process and the conversion process of the working mode. With the increase of the flight Mach number, the relative conversion speed of the high / low pressure rotor of the traditional Mach 2 first-stage turbine engine decreases due to the increase of the inlet total temperature. It is close to the windmill state near the low-speed-high-speed channel mode conversion point, and the common working point is far away from the design point, and the engine thrust is extremely low [Haney J W. Highly reusable space transportation system study [C] / / AIP Conference Proceedings. American Institute of Physics, 1997, 387 (1): 1277-1284.]. In this process, it is very likely that the installed engine thrust is less than the aircraft drag (thrust-drag imbalance), causing the aircraft to continue to decelerate and unable to provide suitable inflow conditions for the normal start of the high-speed channel engine, or even if the high-speed channel engine can be started, it still cannot achieve thrust-drag balance, resulting in modal conversion failure. This type of problem in which the aircraft cannot complete the modal conversion from the low-speed channel to the high-speed channel due to thrust-drag imbalance is called the thrust trap problem of the parallel TBCC engine [Zheng Riheng, Chen Caobin. Solution to the thrust trap problem of turbine-based combined cycle engines [J]. Rocket Propulsion, 2021, 47(06): 21-32.], such as Figure 1 shown.

[0003] At present, the research on the mode conversion control method of the tandem TBCC engine is mainly based on the fixed-point mode conversion control, that is, the mode conversion is completed under a certain constant flight Mach number and flight altitude condition (called the mode conversion design point), and the total thrust of the engine is kept constant during the mode conversion process [Chen M, Tang H, Zhang K, et al. Turbine-based combined cycle propulsion system integration concept design [J]. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2013, 227 (7): 1068-1089.]. However, under the fixed-point mode conversion control, due to the limitation of the minimum working Mach number of the sub-combustion mode of the tandem TBCC engine, the mode conversion design point is still at the upper limit of the working Mach number of the turbine engine. Although the mode conversion Mach number of the low-speed-high-speed channel is lower than that of the parallel TBCC engine, the turbine engine is still in a relatively low thrust working range at this time and is still prone to fall into a thrust trap. Another desirable mode conversion control method is interval mode conversion control, that is, starting the mode conversion at a relatively low flight Mach number, and completing the mode conversion when the minimum working Mach number of the sub-combustion mode is reached as the Mach number increases. The Japanese HYPR90-C engine performs mode conversion between 2.5 and 3 Mach, and the ramjet engine works alone when the Mach number is above 3 [Soga Y, Kurosaki M, Tsuzuki Y, et al. Control of HYPR demonstrator engine [C] / / 34th AIAA / ASME / SAE / ASEE Joint Propulsion Conference and Exhibit. 1998: 3283.]. Huang Hongchao [Huang Hongchao, Wang Zhanxue, Cai Yuanhu. Analysis of the modal conversion process of a small turboramjet engine based on the thrust continuity criterion [J]. Journal of Aerospace Power, 2009, 24 (12): 2756-2762. DOI: 10.13224 / j.cnki.jasp.2009.12.020.] analyzed the influence of different flow control valve openings on the parameter changes in the modal conversion process. According to the thrust continuity criterion, the variation law of the flow control valve opening with the Mach number in the modal conversion process was determined. Compared with the fixed-point modal conversion, the interval modal conversion control method can obtain a larger engine thrust during the conversion process because the ramjet channel is opened in a lower Mach number range, which provides a possibility for solving the thrust trap problem.However, there are few studies on interval mode conversion, and the focus of research in public literature is mostly on the smooth connection and smooth transition of engine thrust and air flow before and after mode conversion. There has been no in-depth study on the mode conversion control scheme with the goal of solving thrust traps and increasing thrust. At the same time, there is a lack of analysis of the principle of increasing thrust by interval mode conversion. For the tandem TBCC engine used as a low-speed channel accelerator of the parallel TBCC engine, in order to avoid thrust traps and achieve high acceleration at the same time, it is urgent to formulate a mode conversion control scheme for the tandem TBCC engine with the goal of achieving high thrust performance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a modal conversion control method for a tandem TBCC engine. For a tandem TBCC engine used as a low-speed channel accelerator of a parallel TBCC engine, the thrust trap can be effectively avoided while achieving high acceleration.

[0005] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0006] A mode conversion control method for a tandem TBCC engine, wherein the tandem TBCC engine is used as a low-speed channel accelerator for a parallel TBCC engine; the mode conversion of the tandem TBCC engine is controlled in the following manner:

[0007] In the range of the incoming flow Mach number from 0 to the first Mach number, the tandem TBCC engine is controlled to operate in the maximum state of the turbofan mode, wherein the first Mach number is the return flow margin of the ramjet duct when the engine operates in the maximum state. The Mach number when it is 2%, P 131 is the total pressure at the inlet duct outlet, P s61 is the static pressure at the outlet of the first-stage mixing chamber;

[0008] When the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the low-speed channel ramjet duct is opened, and the low-speed channel ramjet duct opening is set to be greater than 0 and less than or equal to a critical opening; the critical opening refers to the ramjet duct opening that makes the sum of the ramjet duct airflow and the turbine channel airflow equal to the maximum intake amount that the intake duct can provide under the current incoming flow Mach number, and the second Mach number is the minimum Mach number that satisfies the low-speed channel ramjet engine to work alone;

[0009] When the incoming flow Mach number is within the range of the second Mach number to 4.0, the tandem TBCC engine is controlled to operate in a full ramjet mode.

[0010] Preferably, when the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the opening of the low-speed channel ramjet duct is always equal to the critical opening.

[0011] Preferably, the turbofan duct is H ∞ Closed-loop control.

[0012] Preferably, the opening of the low-speed channel ram duct is open-loop controlled.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0014] The present invention analyzes and designs a mode conversion control scheme for a series TBCC engine as a low-speed channel of a parallel TBCC engine with the goal of achieving high thrust from a principle perspective. The ramjet duct can be opened while keeping the turbofan components operating at their maximum state, thereby increasing the engine's air intake flow capacity and reducing the engine's overflow resistance, thereby improving the engine's maximum installed thrust performance and achieving better inlet-engine matching, thereby effectively solving the thrust trap problem of the parallel TBCC engine. The present invention further proposes an optimal ramjet duct opening adjustment scheme, which can maximize the engine's thrust during the mode conversion process and achieve the best and most effective utilization of the inlet air volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the thrust trap problem of the parallel TBCC engine;

[0016] Figure 2 The flight trajectory with a dynamic pressure of 34.29 kPa;

[0017] Figure 3 It is a schematic diagram of the relationship between the engine thrust F and Ma under the conventional fixed-point mode conversion control plan;

[0018] Figure 4 It is a schematic diagram of the variation of key engine parameters with Mach number in turbofan mode;

[0019] Figure 5 It is a schematic diagram of the change of the reflow margin RM with Ma;

[0020] Figure 6 This is a schematic diagram of the thrust-increasing control structure proposed by the present invention;

[0021] Figure 7 Schematic diagram of the structural principle of H∞ robust control;

[0022] Figure 8 The effect of RVABI opening on engine characteristics when Ma=2.5;

[0023] Fig. 9 The effect of RVABI opening on engine characteristics under different incoming flow Mach numbers;

[0024] Fig.10 The optimal regulation law of RVABI opening;

[0025] Fig.11 This is a schematic diagram of the structural principle of the component-level model of the external parallel thrust-increasing TBCC engine;

[0026] Fig.12 It is a schematic diagram of flight trajectory and mode division;

[0027] Fig.13 Simulation comparison results of different mode conversion control schemes for parallel TBCC engines. DETAILED DESCRIPTION

[0028] The task of the tandem TBCC engine used as a low-speed channel accelerator of the parallel TBCC engine is to accelerate the parallel TBCC engine to the minimum starting Mach number Ma=4 of the high-speed channel dual-mode scramjet engine, and provide sufficient thrust in the process to avoid the generation of thrust traps; in view of this problem, the solution of the present invention is to adopt a mode conversion control scheme between partitions, which is as follows:

[0029] The following partition control is performed on the mode conversion of the tandem TBCC engine:

[0030] In the range of the incoming flow Mach number from 0 to the first Mach number, the tandem TBCC engine is controlled to operate in the maximum state of the turbofan mode, wherein the first Mach number is the return flow margin of the ramjet duct when the engine operates in the maximum state. The Mach number when it is 2%, P 131 is the total pressure at the inlet duct outlet, P s61 is the static pressure at the outlet of the first-stage mixing chamber;

[0031] When the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the low-speed channel ramjet duct is opened, and the low-speed channel ramjet duct opening is set to be greater than 0 and less than or equal to a critical opening; the critical opening refers to the ramjet duct opening that makes the sum of the ramjet duct airflow and the turbine channel airflow equal to the maximum intake amount that the intake duct can provide under the current incoming flow Mach number, and the second Mach number is the minimum Mach number that satisfies the low-speed channel ramjet engine to work alone;

[0032] When the incoming flow Mach number is within the range of the second Mach number to 4.0, the tandem TBCC engine is controlled to operate in a full ramjet mode.

[0033] Preferably, when the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the opening of the low-speed channel ramjet duct is always equal to the critical opening.

[0034] Preferably, the turbofan duct is H ∞Closed-loop control.

[0035] Preferably, the opening of the low-speed channel ram duct is open-loop controlled.

[0036] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0037] Hypersonic vehicles powered by TBCC propulsion systems generally climb along the isodynamic pressure line. The dynamic pressure of the STARRUNNER concept aircraft's flight trajectory is about 95 kPa, and the dynamic pressure of the HYPR program's flight trajectory is about 20 kPa. Increasing the dynamic pressure of the aircraft can fully develop its performance, but the increase in dynamic pressure will also increase the mechanical load and temperature load on the aircraft, so the aircraft must climb at a suitable maximum dynamic pressure. The definition of dynamic pressure q0 is shown in formula (1).

[0038]

[0039] Wherein, ρ0 and V0 represent the density and velocity of the free flow respectively, k0 is the adiabatic index of the free flow, p0 is the static pressure of the free flow, which is determined by the flight altitude H, and Ma is the flight Mach number. When the dynamic pressure of the flight trajectory is known, the flight Mach number Ma and the altitude H are one-to-one corresponding.

[0040] Taking the flight trajectory of a hypersonic vehicle with a dynamic pressure value of q0 = 34.29 kPa (H = 24 km, Ma = 4) as an example, Ma ≤ 4 is the working range of the tandem TBCC engine, and its task is to accelerate the parallel TBCC engine to the minimum starting Mach number Ma = 4 of the high-speed channel dual-mode scramjet engine, and Ma ≥ 4 is the working range of the dual-mode scramjet engine, such as Figure 2 shown.

[0041] While pursuing high engine thrust, the engine state parameter limits must be considered. The main limits of the tandem TBCC engine during operation include the maximum mechanical / aerodynamic load limit, the maximum thermal load limit, and the aerodynamic stability limit. Based on the existing engine level, the limit parameter values ​​that must be met are shown in Table 2.

[0042] Table 2 Engine status parameter limits

[0043]

[0044]

[0045] Along the above q0 = 34.29 kPa isodynamic pressure working line, the variation of the working parameters of the tandem TBCC engine with the incoming flow Mach number Ma under the conventional fixed-point mode conversion control plan is simulated. It is known that the minimum Mach number of the ramjet mode of the tandem TBCC engine is Ma = 3. According to the conventional mode conversion control method, the Mach number Ma = 3 and the flight altitude H = 20 km working point on the flight trajectory are selected as the mode conversion point for mode conversion. In the Ma≤3 range, it works in the maximum state of the turbofan mode, and in the 3≤Ma≤4 range, it works in the ramjet mode alone.

[0046] Along the flight trajectory, the engine thrust changes as follows Figure 3 As shown:

[0047] like Figure 3 As shown in the figure, with the increase of Mach number, the engine thrust in the turbofan mode decreases significantly. At the mode transition point (Ma=3, H=20km), the maximum thrust of the turbofan engine is only 41% of the ground state. After Ma>3, it enters the ramjet mode and the engine thrust rises again. During the whole process, the thrust drops seriously near the mode transition point, and thrust-drag imbalance is very likely to occur.

[0048] The reasons for the insufficient modal thrust of turbofans under high Mach number conditions are mainly two-fold: On the one hand, as the flight Mach number Ma increases, the total temperature T2 of the incoming air increases significantly. From formula (2), it can be seen that as T2 increases, the relative conversion speed n of the fan increases. fcor and the relative conversion speed of the compressor n ccor Rapidly decrease (see Figure 4 (a) in Figure 1). It can be seen from the common working line on the fan and compressor characteristic diagram (see Figure 4 In (b) and (c), under the condition of low reduced speed and large flow rate, the fan pressure ratio π f and compressor pressure ratio π C are relatively small, the engine can use the boost ratio (π=π f ×π C ) decreases, resulting in a decrease in the engine's ability to do work, which in turn leads to a decrease in total thrust. On the other hand, as the flight Mach number Ma increases, the engine's required flow rate W a2 The available airflow W at the inlet of the air intake drops sharply. a1max Greater than the engine required flow W a2 , generating overflow resistance (see Figure 4 (e)), it is usually necessary to adjust the inlet geometry, otherwise the engine installed thrust will be greatly reduced.

[0049]

[0050] Where n f ,n care the physical speeds of the fan and compressor respectively. The subscript “des” represents the parameter values ​​under standard conditions.

[0051] From the above analysis, it can be seen that during the operation of the tandem TBCC engine, the total thrust of the engine decreases significantly near the mode transition point, and the inlet works in a subcritical state, with large overflow resistance, resulting in a serious decrease in the engine installed thrust, and a thrust-drag imbalance is very likely to occur. Therefore, it is extremely necessary to carry out research on the thrust increase control scheme under high Mach number conditions.

[0052] For a certain flight altitude and Mach number, the thrust formula of the tandem TBCC engine can be expressed as:

[0053] F=W g9 v9-(W a2 +W a131 )·v0+(p s9 -p s0 )·A9 (3)

[0054] Where W g9 is the gas flow rate at the engine nozzle outlet; W a2 is the engine fan inlet air flow; W a131 is the ram duct inlet air flow; v0 is the flight speed; exhaust speed v9=Ma9·c9; p s9 is the static pressure at the nozzle outlet; p s0 is the atmospheric back pressure; A9 is the nozzle outlet cross-sectional area.

[0055] According to the relationship between the static parameters of temperature and pressure and the hysteresis parameters (Formula (4), the calculation formula of the nozzle exit Mach number Ma9 can be obtained as shown in Formula (5).

[0056]

[0057]

[0058] Local sound velocity at nozzle exit section Where k is the specific heat ratio; R is the gas constant, T s9 , T9 are the static temperature and total temperature of the nozzle outlet, and p9 is the total pressure of the nozzle outlet.

[0059]

[0060] Ignoring the difference between gas flow and air flow, we have:

[0061]

[0062] When the nozzle expansion section is a full-tube supersonic flow, there are only three possible states at the nozzle outlet: outlet oblique shock wave, design state, and outlet expansion wave. The corresponding nozzle outlet static pressure p s9 The characteristic pressure p b1 The thrust formula can be further rewritten as:

[0063]

[0064] Further assume that there is no heat exchange between the nozzle and the outside world. Then T 75 =T8=T9. The thrust formula can be further simplified as:

[0065]

[0066] Where σ7 is the total pressure recovery coefficient of the afterburner, σ8 is the total pressure recovery coefficient from the nozzle inlet to the throat, and σ9 is the total pressure recovery coefficient of the nozzle expansion section.

[0067] From formula (9), it can be seen that if the ramjet duct is opened in the working range of high Mach number thrust of the turbofan mode, and the fan inlet flow rate W is guaranteed, a2 , the total pressure p6 at the outlet of the ramjet mixing chamber remains unchanged, and the total temperature T at the outlet of the afterburner chamber 75 =T 75max , then as the ram duct flow area A RVABI The increase of intake air flow W a131 The total flow rate required by the engine is increasing. a2 ′=W a2 +W a131 Increase, the engine thrust F will also increase. At the same time, the increase in the total flow required by the engine can reduce the overflow flow of the inlet when working in the high Mach number range, thereby reducing the engine overflow resistance and further improving the installed thrust.

[0068] Based on the above principle analysis, in order to obtain the maximum output thrust, the fan inlet flow rate W must be guaranteed. a2 , the total pressure p6 at the outlet of the ram mixing chamber remains unchanged, while the total temperature T at the outlet of the afterburner chamber remains unchanged. 75 However, the air flow rate W a2 and the total temperature at the afterburner outlet T 75 It is impossible to accurately measure based on sensors, so in actual control it is usually characterized by indirect parameters. Under the same fan inlet conditions, ensure that the low-pressure rotor speed command n fref The relative conversion speed n of the low-pressure rotor remains unchanged fcor unchanged, it can be seen from the component characteristic formula (10) that the fan inlet conversion flow W can be basically guaranteed a22c unchanged, as shown in formula (11), to a certain extent, the fan inlet flow W a2control.

[0069] W a22C =f(n fcor ,π f ) (10)

[0070]

[0071] In addition, under certain flight conditions, the fan inlet total pressure p2 remains unchanged, so ensuring that the engine total pressure ratio EPR = p6 / p2 remains unchanged can ensure that the ramjet mixing chamber outlet total pressure p6 remains unchanged; the afterburner outlet total temperature T 75 The composite parameter W fa / p3 characterization. Therefore, the engine thrust increase control scheme is designed as shown in formula (12):

[0072]

[0073] As shown in formula (12), through closed-loop control W fb ,A8,W fa , keep the turbine components working at the maximum load allowed, and at the same time open-loop adjust the variable area duct ejector outlet area A RVABI To change the ram duct flow W a131 , thereby achieving the purpose of increasing engine thrust.

[0074] In order to ensure that the thrust increase control process is smooth and safe, the applicable conditions of thrust increase control need to meet the engine maximum mechanical / aerodynamic load limit, maximum thermal load limit and aerodynamic stability limit (see Table 2), and the following three conditions must also be met:

[0075] 1) The ramjet duct airflow does not flow back (if the high-temperature gas after the turbine flows back to the fan inlet through the ramjet duct, it will form a gas backflow phenomenon, which will cause the engine fan to overheat and be damaged). 2) The afterburner / ramjet combustion chamber combustion is stable during the conversion process. 3) The total flow rate W flowing into the engine a2 ′=W a2 +W a131 Should not be greater than the maximum intake flow W that the intake duct can provide a1max If the total flow rate flowing into the engine is greater than the maximum intake flow rate that the intake duct can provide, the intake duct will operate in a supercritical state, and the total pressure recovery coefficient of the intake duct will decrease, which will lead to a decrease in engine thrust and a significant increase in fuel consumption.

[0076] No backflow is the basic requirement for opening the ram duct during the thrust increase control process. The ram duct backflow margin RM is defined as shown in formula (13). In order to ensure no backflow, it is necessary to ensure that the total pressure at the inlet duct outlet P 131 Greater than the static pressure P at the outlet of the first mixing chamber s61Therefore, RM>0 must be satisfied during the thrust increase control process. Considering the measurement error during engine operation, the reflux margin RM≥2% must be ensured during the thrust increase control process.

[0077]

[0078] The reflux margin RM is mainly affected by the engine operating state and the flight Mach number Ma. When the engine is operating at the maximum state, the size of RM is mainly determined by the flight Mach number. Figure 5 shown.

[0079] Depend on Figure 5 It can be seen that when the flight Mach number is less than 2.2, the reflux margin RM < 2%, and if the ram duct is opened, gas backflow will occur; when the flight Mach number is greater than 2.2, RM ≥ 2%, and the conditions for opening the ram duct are met. As the flight Mach number increases, RM continues to increase, indicating that the higher the flight Mach number, the less likely the ram duct will produce reflux.

[0080] In order to realize the above-mentioned thrust-increasing control scheme, the following is designed in the working range that meets the applicable conditions of the thrust-increasing control scheme: Figure 6 The thrust increase control structure is divided into two parts, including the H ∞ Closed-loop control and open-loop control of the variable area duct ejector after the ram duct.

[0081] H ∞ Robust control has strong robustness and anti-interference, which can ensure the stability of the engine closed-loop system. Figure 7 shown.

[0082] Among them, ω is the disturbance signal, and a suitable controller K(s) needs to be designed to suppress its influence on the output y and ensure the stability of the controlled object P(s). In order to achieve zero-error tracking, W1(s) needs to include an integral link, and when ω→0, ‖W1‖ ∞ >>‖W2‖ ∞ At the same time, when ω→∞, ‖W2‖ must be satisfied ∞ >>‖W1‖ ∞ , to enhance the ability to resist noise.

[0083] In order to ensure the safe and stable operation of the engine throughout the whole process, an engine limit protection circuit is added to the control structure, including n cor Maximum limit controller, T4 maximum limit controller and T 75 Maximum limit controller (n cor ≤100%,T4≤1800K,T 75≤2400K). A high and low selector is used to select the control variable that meets all constraints. On this basis, a ram duct thrust control system is added. If the ram duct reflux margin RM ≥ 2%, the ram duct ejector outlet area A is changed. RVABI Adjust the ram duct inlet flow W a131 , thereby increasing the total thrust of the engine. If RM<2%, keep the ram duct closed: MR=0, A RVABI =0.

[0084] use Figure 6 The thrust increase control structure shown in the figure shows the influence of different openings of the variable area ducted ejector (RVABI) on the engine performance at different incoming flow Mach numbers on the isodynamic pressure line. The definition of the RVABI opening α is shown in formula (14).

[0085]

[0086] Among them, A RVABI,max It is the maximum value of the RVABI area, α=0 represents that the ram duct is completely closed, and α=100% represents that the ram duct is fully open.

[0087] First, we select the flight condition of Ma=2.5 to simulate the effect of different openings of RVABI on engine performance parameters, such as Figure 8 As shown in Figure 2, as α increases, the ram duct air flow W a131 The engine thrust F is increasing, and the fuel consumption rate S is increasing. fc When α increases to α = α0 = 66%, the combined flow of the ram duct airflow and the turbine channel airflow W a2 ′=W a2 +W a131 Equal to the maximum air volume W that the intake duct can provide a1max , the opening of RVABI at this time is defined as the critical opening α0, as shown in formula (15):

[0088] α=α0(when:W a1max =W a2 ′=W a2 +W a131 ) (15)

[0089] At this time, if α is further increased, the air flow of the turbofan engine will decrease, the inlet will work in a supercritical state, the total pressure recovery coefficient σ will decrease, and then the thrust F will decrease, and the fuel consumption rate S fc A sharp increase, such as Figure 8 shown.

[0090] Fig. 9The effect of RVABI opening on engine performance under different incoming flow Mach numbers was simulated. Fig. 9 As shown in FIG. 1 , under different incoming Mach numbers, the thrust increase control scheme proposed in the present invention can increase the engine thrust F and reduce the fuel consumption rate S at the same time. fc The maximum increase in thrust is about 35.7%, the fuel consumption rate is reduced by about 0.13%, and the reflux margin RM gradually increases with the increase of the incoming flow Mach number Ma, which means that the larger the Mach number, the less likely it is for gas reflux to occur.

[0091] Depend on Fig. 9 It can be seen from (b) and (c) in that there is a critical opening α0 of RVABI at different flight Mach numbers. At this opening, the inlet works in a critical state, the inlet airflow is all used to do work, there is no overflow flow and overflow resistance, and the engine installed thrust F also reaches the maximum value. This opening is the optimal opening of RVABI at the current Mach number. The optimal opening at different Mach numbers is as follows Fig.10 Therefore, Fig.10 The curve of α0 changing with the incoming flow Mach number Ma is the ram duct outlet area A. RBABI The optimal regulation law.

[0092]

[0093] Using the above-mentioned tandem TBCC engine as a low-speed channel accelerator, a component-level model of the parallel TBCC engine was further developed, such as Fig.11 shown.

[0094] The low-speed channel adopts the tandem TBCC engine model established above, and the high-speed channel is a dual-mode scramjet engine. In the subcombustion mode of the high-speed channel, the tail nozzle flow balance equation of formula (17) must be satisfied; in the dynamic process, the combustion chamber volume dynamic equation must be satisfied, as shown in formula (18). In the scramjet mode, since the airflow in the high-speed channel is supersonic throughout the entire process, the upstream airflow will not be affected by the downstream airflow conditions, so no iterative calculation is required.

[0095]

[0096]

[0097] Wherein, the subscript “s” refers to the cross-sectional parameters of the dual-mode scramjet engine, W g8cs ,V nets They are the gas flow rate allowed to pass through the tail nozzle and the volume of the combustion chamber control body.

[0098] Along the isodynamic line flight trajectory, the working mode of the external parallel thrust-increasing TBCC engine is divided as follows: Fig.12As shown. The Mach number for the conversion of the low-speed channel tandem TBCC engine to the high-speed channel dual-mode scramjet engine is Ma=4. The working mode can be divided into the following stages as the incoming flow Mach number increases: (1) In the range of Ma=0 to 2.2, it is in the turbofan mode and works at the maximum state of the turbofan mode; (2) In the range of Ma=2.2 to 3.0, the low-speed channel ramjet duct is opened, and this mode is defined as the thrust-increasing mode. The opening of the low-speed channel ramjet duct is adjusted according to Fig.10 The optimal regulation law changes; (3) In the range of Ma3.0 to 4.0, the flow conditions for the low-speed channel ramjet engine to work alone are met, and the tandem TBCC engine enters the full ramjet mode; (4) Above Ma4.0, the tandem TBCC engine stops working and enters the high-speed channel dual-mode scramjet working mode.

[0099] Along the above flight trajectory, for the parallel TBCC engine, the conventional control scheme of the low-speed channel and the control scheme of the present invention are respectively adopted, and the thrust, air flow rate and fuel consumption rate are compared. Fig.13 As shown:

[0100] Depend on Fig.13 As can be seen from (a) in the figure, when the flight Mach number Ma>2.7, the thrust-drag imbalance phenomenon occurs because the engine installed thrust is less than the aircraft drag, causing the aircraft to continue to decelerate, unable to provide suitable incoming flow conditions for the normal start of the ramjet engine, and falling into a thrust trap. When the thrust increase control plan is adopted, the maximum increase in engine thrust ΔF max The thrust is about 7.036 kN (an increase of 29.8%), and the thrust is greater than the aircraft resistance throughout the flight trajectory, effectively avoiding the occurrence of thrust trap phenomenon. Fig.13 As can be seen from (b) in the figure, the thrust increase control can effectively utilize the maximum intake volume of the engine intake duct. By adopting the optimal ram duct area adjustment law designed, almost all of the original overflow air can enter the ram duct of the series TBCC engine to do work. The total flow rate required by the engine is W a2 ′=W a2 +W a131 The maximum air intake volume W a1max equal, thereby maximizing the installed thrust of the engine. Fig.13 As can be seen from (c) in the figure, after adopting the thrust increase control, the fuel consumption rate of the engine has also decreased to a certain extent, and the economy of the engine has been slightly improved.

Claims

1. A mode conversion control method for a tandem TBCC engine, wherein the tandem TBCC engine is used as a low-speed channel accelerator for a parallel TBCC engine; characterized in that: The following partition control is performed on the mode conversion of the tandem TBCC engine: In the range of the incoming flow Mach number from 0 to the first Mach number, the tandem TBCC engine is controlled to operate in the maximum state of the turbofan mode, wherein the first Mach number is the return flow margin of the ramjet duct when the engine operates in the maximum state. The Mach number when it is 2%, P 131 is the total pressure at the inlet duct outlet, P s61 is the static pressure at the outlet of the first-stage mixing chamber; When the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the low-speed channel ramjet duct is opened, and the low-speed channel ramjet duct opening is set to be greater than 0 and less than or equal to a critical opening; the critical opening refers to the ramjet duct opening that makes the sum of the ramjet duct airflow and the turbine channel airflow equal to the maximum intake amount that the intake duct can provide under the current incoming flow Mach number, and the second Mach number is the minimum Mach number that satisfies the low-speed channel ramjet engine to work alone; When the incoming flow Mach number is within the range of the second Mach number to 4.0, the tandem TBCC engine is controlled to operate in a full ramjet mode.

2. The mode conversion control method of a tandem TBCC engine according to claim 1, characterized in that: When the incoming flow Mach number is within the range of the first Mach number to the second Mach number, the opening of the low-speed channel ramjet duct is always set equal to the critical opening.

3. The mode conversion control method of a tandem TBCC engine as claimed in claim 1, characterized in that: H of turbofan duct ∞ Closed-loop control.

4. The mode conversion control method of a tandem TBCC engine as claimed in claim 1, characterized in that: The opening of the low-speed channel ram duct is open-loop controlled.

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