A method for controlling the water injection volume of a jet pre-cooled engine combined with trajectory optimization

Abstract

A method for controlling the water injection amount of a jet pre-cooled engine combined with trajectory optimization, which relates to a jet pre-cooled turbine engine. It includes: 1) Establishing an aircraft dynamics model: Considering the trajectory characteristics of the aircraft in the vertical plane climbing section, regarding the aircraft as a particle model moving in the vertical plane, and establishing a state differential equation about various state parameters; 2) Establishing an engine model: Assuming the relative corrected speed N of the compressor Cor , the dimensionless parameter β of the compressor characteristic C and the dimensionless parameter β of the turbine characteristic T Three unknowns, by constructing an inlet and outlet matching balance equation, solve the equilibrium state and performance parameters of the engine; 3) Establishing a trajectory optimization method: Using trajectory optimization software, setting the state variables and differential equations, control variables and evaluation indexes during the flight to comprehensively evaluate and optimize the flight route and flight control, and according to the optimal result, output the optimal control law of jet pre-cooling based on the optimal trajectory to improve the comprehensive performance of the engine.

Description

Technical Field

[0001] The present invention relates to a jet pre-cooled turbine engine, and more particularly to a method for controlling the water injection amount of a jet pre-cooled engine combined with flight path optimization. Background Art

[0002] With the continuous development of aerospace technology, there is an urgent need to significantly increase the maximum flight Mach number of aircraft while ensuring economic performance, both in civil and military aspects. At present, aviation turbine engines will still be the main aviation power for a long time to come. However, when the aircraft speed is greater than Mach 2.5, the turbine engine will face the problem of too high inlet temperature, resulting in a low corrected speed of the engine, a corresponding decrease in work capacity and thrust, and it is difficult to further accelerate the aircraft.

[0003] In order to further expand the working speed range of the turbine engine, adopting jet pre-cooling technology in front of the compressor becomes a feasible technical route. Abroad, a jet pre-cooling device was added to the R-15-300 engine of the MiG-25, enabling the MiG-25 interceptor to continuously operate at Mach 2.8 and instantaneously fly to Mach 3.2. Specifically, the jet pre-cooling technology is to install a water injection pre-cooling device in front of the compressor. At high speeds, the evaporation of water droplets will effectively absorb the heat of the oncoming flow and thus reduce the oncoming flow temperature, improving the working environment of the turbine engine and reducing the temperature of the air flow entering the engine by a certain amount. Theoretically, with jet pre-cooling technology, the maximum flight Mach number of the turbine engine can reach above 3 (Carter, P. and V. Balepin. Mass injection and precompressor cooling engines analyses. 2002. Indianapolis, IN, United States: AIAA International.).

[0004] The traditional jet pre-cooling water injection amount is determined by the temperature drop of the oncoming flow to ensure a constant temperature or a certain temperature drop at the inlet section of the engine compressor. The water injection amount control is simple and reliable (Rui Changsheng, Zhang Chao, and Yue Dongfeng, Research and Development of Jet Pre-cooled Turbine Engine Technology. Aeronautical Science and Technology, 2015. 26(10): pp. 53-59). However, the flight state and environment of the aircraft are complex and changeable, and using a fixed temperature or temperature drop cannot meet the multi-state optimization. For example, when accelerating above Mach 2, the inlet temperature of the engine has not exceeded the limit, but at this time, adopting jet pre-cooling technology can increase the effective thrust of the aircraft. Although the increase in water injection amount brought by jet pre-cooling will lead to an increase in the equivalent fuel consumption rate of the engine, the improvement of the aircraft acceleration characteristics may increase the total efficiency of the entire acceleration process, thereby realizing the comprehensive performance optimization of the aircraft / engine system.

[0005] In the transonic stage, the use of jet pre-cooling technology will increase the engine thrust, enabling the aircraft to quickly pass through the subsonic speed. At this time, the total inlet temperature of the oncoming flow is relatively low. If the traditional water injection control method is adopted, it will be difficult to achieve the water injection and thrust augmentation control in the transonic speed range.

[0006] Therefore, for the control of the jet pre-cooling water injection volume, on the one hand, the limitation of the engine inlet temperature needs to be considered, and on the other hand, the thrust-drag characteristics of the aircraft / engine also need to be taken into account. Summary of the Invention

[0007] The purpose of the present invention is to provide a water injection volume control method for a jet pre-cooled engine combined with trajectory optimization, which is applied to a jet pre-cooled turbine engine, cools the intake air by water injection in the high-speed situation, enhances the comprehensive performance of the turbine engine, and expands the engine operating range. The present invention comprehensively evaluates the performance indexes of the aircraft / engine through a trajectory optimization method, thereby designing the water injection volume control law for jet pre-cooling to achieve the optimal comprehensive performance of a wide-speed-range hypersonic aircraft.

[0008] The present invention includes the following steps:

[0009] 1) Establish a dynamic model of the aircraft

[0010] Considering the trajectory characteristics of the aircraft in the vertical plane climbing section, regarding the aircraft as a particle model moving in the vertical plane, establishing a state differential equation for each state parameter to describe the real-time flight state of the aircraft;

[0011] 2) Establish an engine model

[0012] Under a certain flight state (Mach number Ma / altitude H), assuming the relative converted speed N of the compressor Cor 、the dimensionless parameter β of the compressor characteristic C and the dimensionless parameter β of the turbine characteristic T Three unknowns, by constructing an inlet and outlet matching balance equation, solve the equilibrium state and performance parameters of the engine;

[0013] 3) Establish a trajectory optimization method

[0014] Adopt a trajectory optimization algorithm, set the state variables and differential equations, control variables and evaluation indexes during the flight process to comprehensively evaluate and optimize the flight route and flight control, and according to the optimal result, output the best control law for jet pre-cooling based on the optimal trajectory.

[0015] In step 2), the specific steps for solving the equilibrium state and performance parameters of the engine may be:

[0016] (1) Establish a working model of the turbine engine inlet. Configure the inlet model through the given design parameters. This model can output various parameters of the outlet airflow according to the given flight and inlet conditions.

[0017] (2) Establish a working model of jet precooling. This model can output various parameters of the outlet airflow by the given inlet conditions and water-vapor ratio.

[0018] (3) Establish a component-level performance model of the turbine engine, and combine it with the given jet precooling performance calculation module. By solving the balance equation, calculate the total temperature, total pressure, and flow parameters at the outlet of the turbine engine under different rotational speeds and back pressures (Li Long, Overall Performance Modeling and Working Characteristic Analysis of TBCC Propulsion System, 2008, Nanjing University of Aeronautics and Astronautics. Page 98).

[0019] (4) Establish a zero-dimensional model of the afterburner. Based on the given total temperature, total pressure, and flow at the outlet of the turbine engine, by introducing a combustion efficiency calculation model and imposing a temperature limit of 2200K at the outlet, calculate the total temperature, total pressure, and flow at the outlet under different fuel-air ratios.

[0020] (5) Establish an adjustable convergent nozzle model. Based on the total temperature, total pressure, flow, and outlet area at the outlet of the afterburner, determine the flow state and characteristics of the convergent nozzle through the critical pressure ratio. Under the given inlet state parameters and nozzle structure parameters, it can output the state parameters, flow, and thrust of the tail nozzle of the outlet airflow.

[0021] (6) Establish the inlet-outlet matching relationship of the turbine engine. Establish the inlet-outlet matching relationship formula according to the physical coupling relationship between the engine modules, so that the engine model is organically integrated into a whole, and can accurately reflect the performance parameters output according to the control action under different flight and atmospheric conditions.

[0022] In step (3), the trajectory optimization algorithm uses Gpops.

[0023] Compared with the prior art, the advantages of the present invention are as follows: The present invention is applied to a jet precooled turbine engine, sprays water to cool the inlet air at high speeds, enhances the comprehensive performance of the turbine engine, and expands the working range of the engine. Using the jet precooling water spraying law designed by the present invention can take into account both the engine efficiency and the flight efficiency of the aircraft, so that the flight control reaches the optimal, can improve the comprehensive performance of the engine, and achieve better safety and economy. Description of the Drawings

[0024] Figure 1 It is a model flow chart.

[0025] Figure 2 It is a simplified model of a jet precooled turbine engine. Detailed implementation manners

[0026] The following embodiments will further illustrate the present invention in conjunction with the accompanying drawings.

[0027] An embodiment of the present invention proposes a method for controlling the water injection amount of jet pre-cooling. The overall process is as Figure 1 shown. The jet pre-cooling device is located in the intake duct of the turbine engine to cool the oncoming flow temperature. The following assumptions are made for the structure and operation:

[0028] 1. The influence of the water injection structure device on the incoming air flow field is considered through the total pressure recovery coefficient; the influence of the unevaporated water on the subsequent components of the engine is not considered, the influence on the performance parameters due to the increase in humidity is not considered, and the influence of the vaporization of water on the oxygen concentration is not considered temporarily;

[0029] 2. The present invention does not involve the structural design and analysis of the jet pre-cooling device, and only verifies the principle and steps.

[0030] Taking the working Mach number of the turbine engine from 0 to 3 as an example for design, to achieve the above objectives, the specific implementation steps of the present invention are as follows:

[0031] I. Establish a dynamic model of the aircraft

[0032] The present invention only considers the trajectory characteristics of the aircraft during the vertical plane climbing section, and regards the aircraft as a particle model moving on a vertical plane (BRYSON J A E, DESAI M N, HOFFMAN W C. Energy-state approximation in performance optimization of supersonic aircraft[J]. Journal of Aircraft 1969, 6, 481-488). According to the flight physical laws, differential equations of each state variable are established to describe the real-time flight state of the aircraft (PARKER J T, BOLENDER M A, DOMAN D B. Control-oriented modeling of an air-breathing hypersonic vehicle[J]. J. Guid. Control Dyn, 2007. 30, 856–869):

[0033]

[0034]

[0035]

[0036]

[0037] Wherein:

[0038] V: flight speed; γ: climb angle; α: flight angle of attack; T: thrust; L: lift

[0039] Isp: specific impulse; m: vehicle mass; r: distance of the vehicle from the center of the earth

[0040] L = qSC L (α, Ma)

[0041] D = qSC D (α, Ma)

[0042] Wherein: q: dynamic pressure; S: reference wing area; C L : lift coefficient; C D : drag coefficient

[0043] II. Establishing an engine model

[0044] Under a certain flight condition (Mach number Ma / altitude H), assuming the relative corrected speed N of the compressor Cor , the dimensionless parameter β of the compressor characteristics C and the dimensionless parameter β of the turbine characteristics T are three unknowns. By constructing the advancement matching balance equation in Step 6, the equilibrium state and performance parameters of the engine are solved. The specific method for drawing the auxiliary line β table can be found in the reference literature (Li Long, Overall Performance Modeling and Working Characteristic Analysis of TBCC Propulsion System, 2008, Nanjing University of Aeronautics and Astronautics. Page 98).

[0045] The simulation process of the jet pre-cooled turbine engine model is as Figure 2 shown;

[0046] 1. Inlet model:

[0047] The inlet model is configured with the given design parameters. This model can output various parameters of the outlet air flow according to the given flight and inlet conditions. Specifically:

[0048] The focus of the present invention is on the realization of the jet pre-cooling water injection law. The inlet is taken as an example of a continuously adjustable structure for illustration; at this time, the inlet inputs the total inlet temperature Pt1 and the total pressure Tt1. The total pressure recovery coefficient is obtained by referring to the following empirical formula, the total temperature is processed according to the isentropic inlet, the flow rate is calculated to automatically meet the engine demand, and the part of the flow rate exceeding the required flow rate of the turbine engine is treated as overflow, considering the overflow resistance (calculated by the momentum theorem), and outputs the total temperature Pt2 and the total pressure Tt2 at the outlet of the inlet;

[0049] σ in,max = 0.97(1 - 0.075(Ma0 - 1) 1.35 )

[0050] 2. Spray Jet Precooling Model:

[0051] This model can output parameters such as the total temperature Pt3 and total pressure Tt3 of the outlet airflow under the given total inlet temperature Pt2, total pressure Tt2, and water-vapor ratio R. Assume the following conditions: w / a 1) The water mist evaporation process can be approximated as an isobaric endothermic process, and correction is made considering the total pressure recovery coefficient;

[0052] 2) The initial temperature of the precoolant is the ground normal temperature of 15°C. The heat absorption of the precoolant only considers the heat absorption of the evaporated part of the water droplets and the heat absorption during the vaporization process.

[0053] The total temperature of the output is calculated using the following formula:

[0054] T

[0055]

[0056] T ti : Total inlet temperature T to : Total outlet temperature R w / a : Water-vapor ratio

[0057] C wat : Specific heat capacity of water C air : Specific heat capacity of air LHOV: Latent heat of vaporization

[0058] T s : Saturation temperature ROE: Evaporation rate

[0059] 3. Turbine Engine Model

[0060] A working performance model of the turbine engine is established, and the compressor, combustion chamber, and turbine are coupled and modeled through a balance relationship. The following simplification is made in the present invention: The engine flow rate is mainly determined by the requirements of the turbine engine, and the inlet duct state can automatically meet the flow rate requirements of the turbine engine. Combining with the given jet precooling performance calculation module, by solving the balance equation, the total temperature, total pressure, and flow rate parameters of the turbine engine outlet under different rotational speeds and back pressures are calculated (Li Long, Overall Performance Modeling and Working Characteristic Analysis of TBCC Propulsion System, 2008, Nanjing University of Aeronautics and Astronautics. Page 98);

[0061] Specifically, the inlet conditions (total temperature Pt3, total pressure Tt3) of the turbine engine are uniquely determined. Assume the unknown relative conversion speed N of the compressor Cor , the parameter β of the compressor characteristic map C , and the parameter β of the turbine characteristic map T . Through interpolation of the characteristic map, the pressure ratios (π C , π T ) and efficiencies (η C, η T ) and the flow rate (M C , M T ). By constructing the advancement matching relationship in Step 6, three unknowns correspond to three balance equations, and there is a unique solution. Solving the equations can obtain the off-design point performance, where the output outlet gas parameters (total temperature Pt5, total pressure Tt5) and the flow rate is M5 (equal to M C *(1 + f) or M T ), and the fuel-air ratio is obtained from the empirical formula (Zhu Xingjian, Wang Xueyu, Principles and Performance of Gas Turbines. Beijing: National Defense Industry Press, 2001). The limiting conditions of the turbine engine can be set as the maximum temperature before the turbine is 1350K, and the maximum limit values of the relative physical speed and the corrected speed are 100%. If the turbine engine cannot operate normally under this inlet condition, it is considered that the inlet duct and the turbine engine cannot match and operate under this state.

[0062] 4. Afterburner model

[0063] The afterburner model uses the fuel-air ratio as the control variable. Based on the outlet gas parameters (total temperature Pt5, total pressure Tt5) and the flow rate M5 of the turbine engine, by introducing the combustion efficiency calculation model (Li Long, Overall Performance Modeling and Working Characteristic Analysis of TBCC Propulsion System, 2008, Nanjing University of Aeronautics and Astronautics. Page 98) and calculating according to the empirical formula (Zhu Xingjian, Wang Xueyu, Principles and Performance of Gas Turbines. Beijing: National Defense Industry Press, 2001), the outlet total temperature is obtained. The total pressure recovery coefficient is calculated as a fixed value. According to the temperature limit of 2200K at the outlet, the outlet gas parameters (total temperature Pt7, total pressure Tt7) and the flow rate M7 under different fuel-air ratio (f ab ) states are calculated.

[0064] 5. Nozzle model

[0065] The adjustable convergent nozzle considers three states: fully expanded, under-expanded, and over-expanded. Based on the outlet gas parameters (total temperature Pt7, total pressure Tt7), the flow rate M7 and the outlet area of the afterburner being certain, the total pressure recovery is treated as a fixed value. Combining with the high-altitude back pressure state determined by the flight altitude, the nozzle state is obtained, and then the outlet airflow velocity of the tail nozzle is solved. The engine thrust can be calculated by the momentum theorem. Subtracting the overflow resistance and the pressure difference resistance, the net thrust is obtained. The specific impulse is calculated from the thrust and the fuel consumption rate (the water consumption is converted into fuel consumption), and the state parameters (total temperature Pt8, total pressure Tt8) and the flow rate M8 of the outlet airflow are output.

[0066] 6. Construct the advancement matching relationship to realize the coupled modeling of the above-mentioned systems, so that the engine model is organically integrated into a whole, and can more accurately reflect the performance parameters output according to the control action under different flight and atmospheric conditions. It includes the following balance equations:

[0067] 1) The power balance between the compressor and the turbine. Since the variable specific heat calculation requires using the power balance to obtain the temperature before the turbine, the pressure ratio balance π C = π T is used to replace the power balance;

[0068] 2) The flow balance M between the compressor and the turbine C *(1 + f) = M T ;

[0069] 3) The flow balance M5*(1 + f ab ) = M8;

[0070] III. Establishing the trajectory optimization method

[0071] Based on the Gpops trajectory optimization method, the problem of solving the optimal problem is transformed into solving a nonlinear programming problem, and the problem of designing the water injection law of a wide-speed-range hypersonic turbine engine is transformed into the problem of solving the optimal trajectory of a multi-variable aircraft. By solving the optimal index, the optimal water injection control law under the input flight mission can be obtained.

[0072] Based on the state models of the aircraft and the engine, the following parameters are set, as shown in Table 1:

[0073] State variables: altitude, speed, climb angle, total mass, angle of attack, range;

[0074] Control variables: rate of change of angle of attack, water-vapor ratio, compressor corrected speed, afterburner fuel-air ratio, nozzle exit area;

[0075] Table 1 Boundary conditions and constraints

[0076]

[0077] Optimization objective: The total mass of fuel and water consumption for the entire trajectory is minimized; Based on the aircraft control equation, the optimization problem of the climbing trajectory can be expressed as the corresponding cost function and parameter constraints. The cost function is expressed as:

[0078] J min,fuel = -m(t f )

[0079] where t f and m(t f ) represent the end time and the end aircraft weight.

[0080] Through Figure 1 the flowchart shown, it can be seen that the models of each component of the engine can be comprehensively combined through the inlet and outlet matching relationship to obtain the entire jet pre-cooled engine model, which can output the corresponding performance parameters of the engine under given flight parameters and atmospheric conditions.

[0081] Through the trajectory optimization program, by inputting the corresponding atmospheric parameters, state variables, control variables, and optimization objectives, the program solves and outputs the optimal trajectory of the aircraft under the corresponding optimization objectives and the corresponding process state parameters, and simultaneously derives the water injection control law when operating under this condition.

Claims

1. A method for controlling the water injection amount of a jet pre-cooled engine combined with trajectory optimization, characterized in that It includes the following steps: 1) Establish an aircraft dynamics model Considering the track characteristics of the aircraft in the vertical plane climb section, the aircraft is regarded as a particle model moving on a vertical plane, and a state differential equation about various state parameters is established to describe the real-time flight state of the aircraft; 2) Establish an engine model Assume the compressor relative corrected speed N Cor , the dimensionless parameter β of the compressor characteristic C and the dimensionless parameter β of the turbine characteristic T For these three unknowns, by constructing the inlet matching balance equation, the equilibrium state and performance parameters of the engine are solved; The specific steps for solving the equilibrium state and performance parameters of the engine are as follows: (1) Establish a working model of the turbine engine inlet duct, configure the model of the inlet duct through the given design parameters, and this model can output various parameters of the outlet air flow according to the given flight and inlet conditions; (2) Establish a working model of jet precooling, and this model can output various parameters of the outlet air flow through the given inlet conditions and water-vapor ratio; (3) Establish a component-level performance model of the turbine engine, and combine it with the given jet precooling performance calculation module. By solving the equilibrium equation, calculate the total temperature, total pressure and flow parameters at the outlet of the turbine engine under different rotational speeds and back pressure conditions; (4) Establish a zero-dimensional model of the afterburner. Based on the total temperature, total pressure and flow at the outlet of the given turbine engine, by introducing a combustion efficiency calculation model and restricting the temperature according to the outlet total temperature of 2200K, calculate the total temperature, total pressure and flow at the outlet under different fuel-air ratio states; (5) Establish an adjustable convergent nozzle model. Based on the total temperature, total pressure, flow and outlet area at the outlet of the afterburner, determine the flow state and characteristics of the convergent nozzle through the critical pressure ratio. Under the condition of given inlet state parameters and nozzle structure parameters, it can output the state parameters, flow and tail nozzle thrust of the outlet air flow; (6) Establish the matching relationship between the inlet and the outlet of the turbine engine. According to the physical coupling relationship between the various modules of the engine, establish the inlet-outlet matching relationship formula, so that the engine model is organically integrated into a whole, and can accurately reflect the performance parameters output according to the control action under different flight and atmospheric conditions; 3) Establish a trajectory optimization method Adopt a trajectory optimization algorithm, set the state variables, differential equations, control variables and evaluation indexes during the flight process to comprehensively evaluate and optimize the flight route and flight control. According to the optimal result, output the optimal control law of jet precooling based on the optimal trajectory.

2. The jet pre-cooled engine water injection control method combined with flight path optimization according to claim 1, wherein In step 3), the trajectory optimization algorithm adopts Gpops.

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