A method for controlling the speed of a propfan engine

Abstract

This invention provides a propfan engine speed control method, comprising the following steps: establishing a dual-row propfan aerodynamic mathematical model; aiming at optimal propeller efficiency, performing nonlinear optimization of the pairing relationship between the front row propeller pitch α1 and the rear row propeller pitch α2 at typical operating points within the flight envelope of the dual-row propfan aerodynamic mathematical model, obtaining the optimal control law as a virtual optimal pitch, which is respectively at a certain speed N. s At the flight envelope point, the optimal pitch of the front and rear propeller blades corresponding to the highest propeller efficiency η is determined; the pitch of the dual-row propeller is controlled to be at the optimal pitch based on the front and rear propeller blade pitches corresponding to the highest propeller efficiency. This invention provides an engineering-applicable propfan engine speed control law, which enables free and independent control of the propfan engine core speed and the dual-row propeller speed, meeting the aircraft's requirements for propfan engine use.

Description

Technical Field

[0001] This invention relates to the field of propfan engine technology, and more specifically to a method for controlling the speed of a propfan engine. Background Technology

[0002] The propfan engine combines the high propulsion efficiency of a conventional turboprop engine with the high cruise speed of a turbofan engine. Compared to conventional turboprop engines, propfan engines maintain the same high propulsion efficiency over a wider Mach number range. The maximum efficient flight Mach number range for propfan engines can reach 0.75 to 0.8 Mach, which is wider than the maximum efficient Mach number range of 0.5 to 0.6 Mach for propellers, allowing for higher flight speeds while maintaining high efficiency. Compared to turbofan engines, propfan engines have cruise speeds close to those of turbofan engines. During takeoff, climb, and landing, as well as in low-altitude, low-speed flight, propfan engines provide sufficient slipstream to remove the boundary layer from flaps, increasing lift and improving takeoff, landing, and low-altitude, low-speed performance. Their propulsion efficiency is 12% to 15% higher than that of turbofan engines, resulting in excellent fuel economy. Therefore, propfan engines have the potential to achieve a leap in fuel consumption and emissions for future civil and military transport aircraft, and are considered one of the most promising subsonic aviation propulsion systems.

[0003] The propfan engine, as an advanced engine configuration, is a development of the turboprop engine. It mainly consists of an engine core rotor and a double-row counter-rotating propeller driven by a power turbine via a reduction gearbox. The engine has many control variables, and its control laws are relatively complex. However, the core control laws are the engine core rotor speed control law and the double-row counter-rotating propeller speed control law. Currently, propfan engines in China are still under theoretical research, and there are no practically applicable propfan engine blade speed control laws for engineering use. Summary of the Invention

[0004] This invention, based on the optimization calculation results of a dual-row propfan aerodynamic mathematical model, proposes a pitch decoupling control method. This method achieves pitch control for the dual-row propfan engines and provides an engineering-applicable propfan engine speed control law. It enables free and independent control of the propfan engine core speed and the dual-row propeller speed, meeting the aircraft's requirements for propfan engines. The core engine speed and the dual-row propeller speed are implemented as two control loops within a single system. This decoupling control, achieved through this law, results in minimal mutual influence, which can be ignored, effectively making the two control loops independent.

[0005] The specific plan is as follows:

[0006] A method for controlling the rotational speed of a propfan engine, wherein the rotational speed of the dual-row propellers of the propfan engine is freely controlled, specifically including the following steps:

[0007] Step 1: Establish a mathematical model for the aerodynamics of a double-row propeller fan;

[0008] Step 2: With optimal propeller efficiency as the objective, the aerodynamic mathematical model of the dual-row propeller fan is subjected to nonlinear optimization of the pairing relationship between the front blade pitch α1 and the rear blade pitch α2 at typical operating points within the flight envelope to obtain the optimal control law. For virtual optimal propeller pitch, At a certain rotational speed N s And at the flight envelope point, the optimal pitch of the front and rear blades corresponding to the highest propeller efficiency η;

[0009] Step 3: Based on the pitch of the front and rear blades corresponding to the highest propeller efficiency obtained in Step 2, control the pitch of the double-row propeller to be at the optimal pitch.

[0010] Preferably, the propeller efficiency is the propeller blade propulsion efficiency.

[0011] Preferably, the specific steps for establishing the aerodynamic mathematical model of the double-row propeller fan in step 1 include:

[0012] 1) Using similarity theory, a propeller aerodynamic mathematical model is established with flight speed, flight altitude, blade angles α1 and α2, and blade rotation speed as model inputs and blade efficiency η as model output. This method has been reported in published literature and will not be described in detail in this paper.

[0013] 2) Given fixed values ​​for flight speed, flight altitude, and blade rotation speed, and using blade angles α1 and α2 as variables, with blade efficiency as the optimization objective, there must exist a blade angle that maximizes blade efficiency. This optimizes the blade efficiency. The optimization calculations using the model yielded the desired result. Introduction For the virtual optimal pitch, i.e. That is, the virtual optimal pitch corresponding to different flight envelope points. It consists of different groups. The components represent the optimal pitch under different flight envelopes and propeller speeds. The optimal control law controls the dual-row propeller pitch at the optimal pitch corresponding to different flight envelopes.

[0014] Preferably, step 3, which uses the pitch adjustment of the dual-row propeller to control the rotational speed, adopts a master-slave control structure. Specifically, it includes: controlling Ns using the pitch of the front row of propellers; when the pitch of the front row of propellers reaches... The range is then stopped, and the pitch of the rear blades is adjusted simultaneously. Within a certain range, the propeller maintains the required stable speed. That is, the rear blade α2 is in a follow-up state, changing with α1 according to the optimal control law until α1 reaches the desired speed. α2 reached

[0015] Preferably, in step 3, the pitch control of the dual-row propeller employs a restrictive control structure. That is, to address the issues of engine output power fluctuations, flight envelope fluctuations, and errors in the propeller aerodynamic mathematical model calculations that prevent the propeller speed from reaching the ideal speed at the optimal pitch, the actual α1 is allowed to deviate from the optimal range within a certain limit. To ensure the propeller speed, the deviation range is set at ±5° based on engineering development experience with single-row propellers. This deviation has a negligible impact on efficiency and meets practical application requirements. Specifically, based on the propeller speed deviation range, α1 is set within... The pitch of α1 is adjusted within a certain range, and α2 adjusts accordingly. That is, if α1 decreases the pitch, α2 also decreases the pitch; conversely, if α1 increases the pitch, α2 also increases the pitch. The angle adjustment remains consistent to simultaneously meet the requirements of speed control and high efficiency. A ±5° limit is imposed on the adjustment range of the Ns control loop for α1 to prevent its dynamic adjustment from exceeding this limit, which could lead to unstable speed oscillations and excessive efficiency deviations, adversely affecting propulsion.

[0016] The following is a further explanation of the solution of the present invention.

[0017] Profan engines have two rows of aerodynamically coupled blades. The blade pitch (blade angle) is changed by adjusting the pitch control hydraulic pressure, thus altering the blade load. This change in load affects the blade speed, allowing the engine to operate at its optimal speed under the current flight conditions. However, changes in the pitch of one row of blades can also affect the speed of the other row. For example, increasing the pitch of the front blades increases their load and decreases their speed. Even if the pitch of the rear blades remains unchanged, their speed will decrease accordingly. This creates an aerodynamic mismatch, requiring adjustment of the rear blades to a more efficient pitch for the next speed. However, adjusting the rear blade pitch again changes their speed, which in turn affects the speed of the front blades. Therefore, there is a strong mechanical and aerodynamic coupling between the two rows of blades, a complex and variable relationship that constitutes a core technology of propfan engines. The control principles and methods for the pitch of the dual-row blades have not yet been reported.

[0018] However, from the perspective of the practical applications of propfan engines, the purpose of pitch adjustment is still similar to that of traditional turboprop engines: to adjust the pitch so that the blades operate at a higher efficiency speed to generate greater thrust or pull. This efficiency can usually be measured by blade propulsion efficiency or propfan engine fuel consumption per unit area.

[0019] The control law of a single-row turboprop engine is usually as follows:

[0020] α→Ns =const,W f →N g =const

[0021] Where α is the pitch, N s W is the rotational speed of the propeller. f For fuel flow rate, N g This refers to the core machine speed.

[0022] In other words, by adjusting the blade pitch, the blade speed is maintained within a constant range of high efficiency. By adjusting the fuel flow, the engine core rotor operates within a high-efficiency speed range, and the output power drives the twin-row blades to deliver the thrust required by the aircraft.

[0023] From a control technology perspective, the control of propfan engines can employ either sensor-based control (SBC) or model-based control (MBC). Sensor-based control (SBC) controls the engine based on measurable system outputs such as rotor speed, temperature, and pressure, while model-based control (MBC) optimizes engine thrust / thrust online using an onboard adaptive model. Considering the current level of industrial technology maturity in China, SBC is chosen for engineering applications. Given that propfan engines are an evolution of turboprop engines, a similar control principle can be adopted:

[0024] α1,α2→N s =const,W f →N g =const

[0025] Where α1 and α2 are the pitches of the front and rear blades, respectively.

[0026] Based on the aerodynamic characteristics of the dual-row propeller of the propfan engine, at a certain speed N s At the point of the flight envelope, there exists a point where the propeller efficiency is maximized. A virtual optimal pitch can be introduced. The virtual optimal pitch This represents the point of highest efficiency at a given flight altitude, speed, and fixed propeller speed. To ensure flight comfort, one or two fixed propeller speeds are typically used for control during flight. For example, 1200 r / min is used for takeoff, and 900 r / min for cruise. At a fixed speed, the virtual propeller pitch combinations at different flight envelope points are combined into a matrix table, varying with flight altitude and speed. Virtual propeller pitches at non-calculated points are interpolated at the calculated points. Therefore, the optimal control law for a propfan engine can be expressed as:

[0027]

[0028] Based on the above control laws and combined with the structure of a traditional turboprop engine control system, a control system structure for a propfan engine can be obtained as follows: Figure 1 As shown. In Figure 1 In this design, the pitch controller is a two-variable control system with α1 and α2. Due to the aerodynamic coupling between the two rows of blades and the mechanical coupling caused by the two rows of blades being driven by the same power turbine through a reducer, there is a strong coupling problem between the two pitch control loops. Therefore, the decoupling problem of the two pitch control loops needs to be considered when designing this two-variable control system.

[0029] Figure 1 In the middle, the engine speed control loop W f →N g =const and the conventional engine speed control rules are no different.

[0030] in accordance with Figure 1 Based on the control system structure shown and the current status of domestic industrial applications, the following optimal control law and decoupling control algorithm design for the double-row blade pitch of a propfan engine are proposed.

[0031] a) Control Law Design Research. A full-flight envelope aerodynamic mathematical model of a dual-row propeller fan was established, incorporating elements such as blade pitch, rotational speed, flight Mach number, and altitude. With optimal efficiency as the objective, a nonlinear optimization study of the pitch pairing relationship (α1, α2) was conducted at typical operating points within the flight envelope, obtaining an optimal control pitch numerical table. Based on the similarity principle, a similarity representation and correction study of the control law was carried out, revealing the optimal pairing relationship between α1 and α2 that varies with flight conditions.

[0032] b) Research on control methods. Combined with... Figure 1 To address the coupling problem in dual-row blade pitch control, the following blade pitch control structure is proposed:

[0033] ① The pitch adjustment process adopts a master-slave control structure. Only the pitch α1 of the first row of blades is used to control Ns, and the following parameters are taken: The control command for the rear blade pitch α2 is given by α1 based on... It is given that the rear blade α2 is in a follower state, and the optimal control law set according to clause a) varies with α1. An over-control constraint control method is used to decouple the two pitch control loops. The control method is as follows:

[0034] 1) First adjust α1 to the desired optimal pitch. The rear blades are adjusted accordingly to achieve... Stop adjusting at that time;

[0035] 2) Determine if the propeller speed meets the target optimal speed. If it does not, first adjust α1 to adjust the speed by changing the pitch and load. For example, if the speed is too low, adjust α1 to reduce the pitch. If the speed meets the requirement, stop adjusting α1; otherwise, continue adjusting α1 until the target speed is reached. The pitch is limited, at which point adjustment of α1 is stopped.

[0036] 3) During α1 adjustment, α2 is adjusted synchronously. The adjustment pattern of α2 is consistent with that of α1. For example, if the speed is too low and the pitch needs to be reduced, α1 is reduced by 1°±0.5°, and α2 is also reduced by 1°±1°. The speed will increase. If this is still not enough, the pitch is further reduced. If adjusted to... If the speed still does not meet the requirements, stop adjusting the pitch and maintain it at the maximum limit value. Setting a pitch adjustment limit range is to avoid excessive speed oscillation caused by excessive pitch variation leading to excessive speed adjustment response time, as well as excessive efficiency deviation. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a propfan engine control system. Detailed Implementation

[0038] The ideas and design methods provided by this invention can serve as a valuable reference for the engineering development of propfan engines.

[0039] For example:

[0040] 1) Using the principle of similarity, conventional propeller aerodynamic modeling is carried out to establish a double-row propeller aerodynamic mathematical model. The angle of the front row of blades is fixed, and the appropriate blade angle of the rear row of blades can be calculated using the propulsion efficiency optimization method. With a control accuracy of 0.5° as the variable, the angle of the front row of blades is changed sequentially, and the corresponding rear row blade angle for each front row blade angle is calculated using the same propulsion efficiency optimization method.

[0041] 2) The dual-row blade aerodynamic mathematical model divides the entire flight envelope into a fine grid. Each grid's data uses flight altitude, Mach number, blade speed, and engine power as input conditions to derive the current optimal propulsion efficiency and blade angle. By changing only the flight altitude while keeping the Mach number, blade speed, and engine power constant, the optimal propulsion efficiency and blade angle at another flight altitude are obtained. By sequentially changing the flight altitude, Mach number, blade speed, and engine power, the optimal propulsion efficiency and blade angle across the entire flight envelope are obtained.

[0042] When the engine is running, the electronic controller uses the collected flight altitude, flight Mach number, and blade speed to find the corresponding blade angle under the current optimal propulsion efficiency in the grid data (see example table 1) by interpolation. Then, it controls the front row of blades to the target optimal angle through the pitch regulator. The rear row of blades adjusts and changes accordingly based on the angle obtained in step 1), thereby ensuring that the double row of blades obtains the best propulsion efficiency under the current flight envelope and engine power conditions.

[0043] Once the pitch adjustment is complete, if the propeller speed does not meet the requirement of 900 r / min, then the over-control limiting control described above will be applied, and the pitch of the front row propellers will be adjusted within a range of ±5° to meet the speed requirement.

[0044] 3) Example: Using the model, the propeller speed Ns = 900 r / min, at 0.2 Mach, and during cruise flight at 1 km, the highest efficiency is 88%, with the front and rear propeller pitches being 22° and 24° respectively. Multiple calculations using the model yield the following table (partial data example):

[0045] Example Table 1: Optimal fore-and-aft pitch within the flight envelope when Ns is cruising at 900 r / min

[0046] .

Claims

1. A method for controlling the speed of a propfan engine, characterized in that, The rotational speed of the dual-row propellers of the propfan engine can be freely controlled, specifically including the following steps: Step 1: Establish a mathematical model for the aerodynamics of a double-row propeller fan; Step 2: With optimal propeller efficiency as the objective, the pitch of the front blades is determined at typical operating points within the flight envelope of the dual-row propeller fan aerodynamic mathematical model. Rear blade pitch To obtain the optimal control law, nonlinear optimization of the pairing relationship is performed. =( , ), For virtual optimal propeller pitch, , At a certain speed And at the flight envelope point, the optimal pitch of the front and rear blades corresponding to the highest propeller efficiency η; Step 3: Based on the pitch of the front and rear blades corresponding to the highest propeller efficiency obtained in Step 2, control the pitch of the double-row propeller to be at the optimal pitch. The specific steps for establishing the aerodynamic mathematical model of the double-row propeller fan in step 1 include: 1) Using similarity theory, establish a system based on flight speed, flight altitude, and blade angle. and The propeller blade speed is used as the model input, and the propeller efficiency η is used as the model output in the propeller-fan aerodynamic mathematical model. 2) Given fixed values ​​for flight speed, flight altitude, and propeller speed, the propeller angle is used as the reference. and Using propeller efficiency as the optimization objective and employing a propeller-fan aerodynamic mathematical model for optimization calculations, the results are obtained. , ; Introduction For virtual optimal propeller pitch, =( , That is, the virtual optimal pitch corresponding to different flight envelope points. It consists of different groups. , The composition represents the optimal pitch under different flight envelopes and propeller speeds; the optimal control law is to control the double-row pitch at the optimal pitch corresponding to different flight envelopes. Step 3 utilizes a master-slave control structure to control the rotational speed by adjusting the pitch of the dual-row propellers. Specifically, this includes controlling Ns using the pitch of the front row of propellers, and when the pitch of the front row of propellers reaches a certain value... Stop adjusting within ±0.5°, and simultaneously adjust the pitch of the rear blades to within... To maintain the propeller at the required stable speed within a range of ±1°, the rear blades... In servo mode, following the optimal control law And change, until achieve ±0.5°, achieve ±1; In step 3, the pitch control of the dual-row propeller employs a restrictive control structure. This is to address the issue of fluctuations in engine output power, flight envelope variations, and errors in the propeller aerodynamic mathematical model, which prevent the propeller speed from reaching the ideal speed at the optimal pitch. Instead, a restrictive control structure is used to allow for actual... Deviation from optimality within a certain range To ensure the propeller speed, the deviation range is set at ±5° based on the engineering development experience of single-row propellers; specifically, based on the propeller speed deviation range, exist Adjustable within ±5° range Then follow Perform follow-up adjustment. Reduce the pitch Also reduce the pitch. Increasing the pitch Also increase the pitch, and decrease or increase the angle to maintain consistency, in order to simultaneously meet the requirements of speed control and high efficiency; through the... The Ns control loop adjustment range is limited to ±5° to avoid The dynamic adjustment exceeded the limit.

2. The propfan engine speed control method according to claim 1, characterized in that, The propeller efficiency refers to the propeller blade propulsion efficiency.

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