Method for controlling rotating speed of paddle fan engine

Abstract

The invention provides a paddle fan engine rotating speed control method. The paddle fan engine rotating speed control method comprises the following steps that a double-row paddle fan pneumatic mathematical model is established; with the optimal propeller efficiency as the target, pairing relation nonlinear optimization is conducted on the front-row propeller blade pitch alpha 1 and the rear-row propeller blade pitch alpha 2 of the double-row propeller fan pneumatic mathematical model at the typical working condition point in the flight envelope, the optimal control rule # imgabs0 # imgabs1 # is obtained and serves as the virtual optimal propeller pitch, and the optimal control rule # imgabs2 # is obtained and serves as the virtual optimal propeller pitch at a certain rotating speed Ns and the flight envelope point; the highest propeller efficiency eta corresponds to the optimal propeller pitch of the front-row blades and the rear-row blades; and controlling the propeller pitch of the double-row propeller to be the optimal propeller pitch according to the front-row blade pitch and the rear-row blade pitch corresponding to the highest propeller efficiency. The invention provides a paddle fan engine rotating speed control rule available for engineering, free and independent control of the rotating speed of the core engine and the rotating speed of the double-row propellers of the paddle fan engine can be realized, and the use requirement of an airplane on the paddle fan engine is met.

Description

Technical Field

[0001] The present invention relates to the technical field of propfan engines, and in particular to a method for controlling the rotation speed of a propfan engine. Background Art

[0002] The propfan engine has the technical advantages of both the high propulsion efficiency of conventional turboprop engines and the high cruising speed of turbofan engines. Compared with conventional turboprop engines, propfan engines have the same high propulsion efficiency as turboprop engines in a wider Mach number range. The high-efficiency flight Mach number range of propfan engines can reach up to 0.75 to 0.8 Ma, which is wider than the maximum range of high-efficiency Mach numbers of propellers of 0.5 to 0.6 Ma. It can maintain high efficiency while flying at a faster speed. Compared with turbofan engines, the cruising speed of propfan engines is close to that of turbofan engines. During takeoff, climb and landing, as well as low-altitude and low-speed flight, propfan engines can provide sufficient slipstream to blow away the flap boundary layer, increase lift, and improve takeoff, landing and low-altitude and low-speed performance. Its propulsion efficiency is 12% to 15% higher than that of turbofan engines, and it has excellent fuel economy. Therefore, propfan engines have the potential to achieve a step-by-step improvement in fuel consumption and emissions for future civil aircraft and military transport aircraft, and are regarded as one of the most promising subsonic aviation propulsion systems.

[0003] As an engine with advanced configuration, the propfan engine is a development form of the turboprop engine. It is mainly composed of the engine core rotor and the double-row counter-rotating propellers driven by the power turbine through the reducer. The engine has many control variables and its control law is relatively complex. However, the core control law is the engine core rotor speed control law and the double-row counter-rotating propeller speed control law. At present, the propfan engine is under theoretical research in China, and there is no propfan engine blade speed control law that can be applied in actual engineering. Summary of the invention

[0004] Based on the results of the optimization calculation of the double-row propeller aerodynamic mathematical model, the present invention proposes a pitch decoupling control method, realizes the pitch control of the double-row propeller blades, provides a propeller fan engine speed control law that can be used in engineering, realizes the free and independent control of the core engine speed and the double-row propeller speed of the propeller fan engine, and meets the aircraft's use requirements for the propeller fan engine. The core engine speed and the double-row propeller speed realize two control loops in a system. Decoupling control is realized through the design of this law, and the mutual influence is very small and can be ignored, which is equivalent to the two control loops being independent.

[0005] The specific plan is:

[0006] A propfan engine speed control method, wherein the speed of a double-row propeller of the propfan engine is freely controlled, specifically comprising the following steps:

[0007] Step 1: Establish a double-row propeller fan aerodynamic mathematical model;

[0008] Step 2: Taking the optimal propeller efficiency as the goal, the aerodynamic mathematical model of the double-row propeller fan is nonlinearly optimized for the pairing relationship of the front row blade pitch α1 and the rear row blade pitch α2 at the typical operating point in the flight envelope to obtain the optimal control law is the virtual optimal pitch, At a certain speed N s and the optimal pitch of the front and rear blades corresponding to the maximum propeller efficiency η at the flight envelope point;

[0009] Step 3: Control the pitch of the double-row propeller to the optimal pitch according to the front row propeller pitch and the rear row propeller pitch corresponding to the highest propeller efficiency obtained in step 2.

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

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

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

[0013] 2) Given the flight speed, flight altitude and blade speed as fixed values, with blade angles α1 and α2 as variables and blade efficiency as the optimization target, there must be a blade angle that maximizes blade efficiency. The blade efficiency is optimized. The model is used to calculate the optimal Introduction is the virtual optimal pitch, that is That is, the virtual optimal pitch corresponding to different flight envelope points It is composed 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.

[0014] Preferably, in step 3, the speed is controlled by adjusting the pitch of the double-row propellers using a master-slave control structure, specifically including: using the front row of propeller pitch to control Ns, when the front row of propeller pitch reaches The adjustment stops within the range and the rear row propeller pitch is adjusted to The propeller is maintained within the required stable speed range. That is, the rear blade α2 is in a follow-up state and changes with α1 according to the optimal control law until α1 reaches α2 reaches

[0015] Preferably, in step 3, the double-row propeller pitch speed control adopts a restrictive control structure. That is, in order to solve the problem that the propeller speed cannot reach the ideal speed under the optimal pitch due to the fluctuation of engine output power, the fluctuation of flight envelope and the error of propeller aerodynamic mathematical model calculation model, the actual α1 is allowed to deviate from the optimal speed within a certain range. To ensure the propeller speed, the deviation range is set to ±5° based on the single-row propeller engineering development experience. The impact of this deviation on efficiency can be basically ignored and can meet the actual use requirements. α1 is adjusted within the range, and α2 is adjusted with α1, that is, if α1 reduces the pitch, α2 also reduces the pitch, that is, if α1 increases the pitch, α2 also increases the pitch, and the angle is reduced or increased to keep consistent, so as to meet the requirements of speed control and high efficiency at the same time. By giving a ±5° limit to the adjustment range of the Ns control loop of α1, it is prevented that the dynamic adjustment of α1 exceeds the limit range, resulting in unstable speed oscillation and too much deviation in efficiency, which has an adverse effect on propulsion.

[0016] The scheme of the present invention is further explained below.

[0017] The propfan engine has two rows of front and rear blades that are pneumatically coupled to each other. The pitch (blade angle) is changed by adjusting the pitch oil pressure through the pitch regulator, so that the blade load changes. The blade load changes and the blade speed changes to adjust its speed, so that it works at the best working speed under the current flight line conditions. However, the speed change caused by the change in the pitch of each row of blades can also affect the speed of the other row of blades. For example, the pitch of the front row of blades increases, causing its load to increase and the speed to decrease. Even if the pitch of the rear row of blades remains unchanged at this time, its speed will also decrease. At this time, the double row of blades will be in an aerodynamic mismatch state, and the rear row of blades must be adjusted to an efficient pitch corresponding to another speed. However, adjusting the pitch of the rear row of blades will cause its speed to change, thereby causing the speed of the front row of blades to change. Therefore, there is a strong mechanical and aerodynamic coupling between the double rows of blades, and the relationship is complex and changeable, which belongs to the core technology of the propfan engine. The control law and control method of the pitch of the double row of blades have not been reported.

[0018] However, from the actual use of propfan engines, the purpose of pitch adjustment is still similar to that of traditional turboprop engines, which is to adjust the pitch so that the blades work at a higher efficiency speed to generate greater thrust or pull. This efficiency can usually be measured by the propeller propulsion efficiency or the specific fuel consumption of the propfan engine.

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

[0020] α→Ns =const,W f →N g =const

[0021] Where α is the propeller pitch, N s is the propeller speed, W f is the fuel flow rate, N g is the core engine speed.

[0022] That is, by adjusting the pitch, the blade speed is maintained within a constant range with higher efficiency. By adjusting the fuel flow, the engine core rotor operates within a higher efficiency speed range, and the output power drives the double-row blades to output the thrust required by the aircraft.

[0023] For the control of propfan engines, from the perspective of control technology, sensor-based control mode (SBC) or model-based control mode (MBC) can be used. The former controls the engine based on the system's measurable outputs such as rotor speed, temperature, pressure, etc., while the latter controls the engine thrust / thrust based on online optimization of the onboard adaptive model. Considering the current maturity of domestic industrial technology, the SBC control mode is selected for engineering applications. In view of the fact that propfan engines are the development of turboprop engines, the control law of propfan engines can be similarly selected as:

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

[0025] Among them, α1 and α2 are the front and rear row blade pitches respectively.

[0026] According to the aerodynamic characteristics of the double-row propeller of the propfan engine, at a certain speed N s At the flight envelope point, there is a point where the propeller efficiency is the highest. A virtual optimal pitch can be introduced The virtual optimal pitch Represents the highest efficiency point at a certain flight altitude, flight speed, and fixed propeller speed. In order to ensure flight comfort, one or two fixed constant propeller speeds are generally used for control during flight. For example, 1200r / min is used for takeoff and 900r / min is used for cruising. At a fixed speed, the virtual pitch combination at different flight envelope points is combined into a matrix table as the flight altitude and flight speed change. The virtual pitch of non-calculated points is interpolated at the calculated points. That is, the optimal control law of the propfan engine can be expressed as:

[0027]

[0028] According to the above control law, combined with the traditional turboprop engine control system structure, a control system structure of the propfan engine can be obtained as follows: Figure 1 As shown. Figure 1 In the figure, the pitch controller is a dual variable control system of α1 and α2. Since the two rows of blades have aerodynamic coupling between the front and rear, and the two rows of blades are driven by the same power turbine through a reducer and have mechanical coupling, that is, the two pitch control loops have a strong coupling problem, so the decoupling problem of the two pitch control loops needs to be considered when designing this dual variable control system.

[0029] Figure 1 In the engine speed control loop W f →N g =const has nothing special to do with the conventional engine speed control rules.

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

[0031] a) Research on control law design. An aerodynamic mathematical model of a double-row propeller fan with full flight envelope including blade pitch, rotation speed, flight Mach number, altitude and other factors is established. With the goal of optimizing efficiency, a nonlinear optimization study of the pitch pairing relationship (α1, α2) is conducted at typical operating points in the flight envelope to obtain the optimal control pitch numerical table. Based on the similarity principle, a similarity representation and correction study of the control law is conducted to reveal the optimal pairing relationship between α1 and α2 that changes with flight conditions.

[0032] b) Research on control methods. Figure 1 In order to solve the coupling problem in the double-row pitch control process, the following blade pitch control structure is proposed:

[0033] ① The pitch adjustment process adopts a master-slave control structure. Only one front row blade pitch α1 is used to control Ns, and The control command of the rear blade pitch α2 is determined by α1 according to Given, that is, the rear blade α2 is in a follow-up state, and the optimal control law set in item a) changes with α1. The overriding control method is used to achieve the decoupling of the two pitch control loops. The control method is as follows:

[0034] 1) First adjust α1 to the required optimal pitch The rear blades are adjusted to achieve Stop adjusting when

[0035] 2) Determine whether the propeller speed meets the target optimal speed. If it does not meet the speed requirement, adjust α1 first 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. If not, continue adjusting α1 until it reaches the target optimal speed. The pitch is limited and the adjustment of α1 is stopped at this time.

[0036] 3) During the α1 adjustment process, α2 is adjusted synchronously. The adjustment rule 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 it is still not satisfied, the pitch will continue to be reduced. If it is adjusted to If the speed still does not meet the requirement, the pitch adjustment is stopped and maintained at the maximum limit value. The pitch adjustment limit range is set to avoid speed oscillation caused by too large a pitch change range, which leads to too long a speed adjustment response time, and the problem of too much efficiency deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a schematic diagram of the control system structure of a propfan engine. DETAILED DESCRIPTION

[0038] Referring to the ideas and design methods provided by the present invention, a good reference can be provided for the engineering development of propfan engines.

[0039] Here are some examples:

[0040] 1) Use the similarity principle to carry out conventional propeller aerodynamic modeling, establish a double-row blade aerodynamic mathematical model, fix the front blade angle, and calculate the blade angle that the rear blade should be at by the propulsion efficiency optimization method. According to the control accuracy of 0.5° that the controller can achieve, change the front blade angle in turn, and also calculate the rear blade angle corresponding to each front blade angle by the propulsion efficiency optimization method.

[0041] 2) The aerodynamic mathematical model of the double-row blades divides the entire flight envelope into fine grids. Each grid data is input by the flight altitude, flight Mach number, blade speed, and engine power to obtain the current optimal propulsion efficiency and blade angle. Only the flight altitude is changed, and the flight Mach number, blade speed, and engine power remain unchanged, and the optimal propulsion efficiency and blade angle at another flight altitude are obtained. By changing the flight altitude, flight Mach number, blade speed, and engine power in turn, the optimal propulsion efficiency and blade angle within the entire envelope are obtained.

[0042] When the engine is working, 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 method, and controls the front row of blades to the target optimal angle through the pitch regulator. The rear row of blades is adjusted accordingly according to the angle obtained in step 1), thereby ensuring that the double row of blades obtain the best propulsion efficiency under the current flight envelope and engine power state.

[0043] When the pitch adjustment is completed, if the propeller speed does not meet the requirement of 900r / min, the above-mentioned override limiting control is performed and the front row pitch is adjusted within the range of ±5° to meet the speed requirement.

[0044] 3) Example: Using the model to calculate the propeller speed Ns = 900r / min, 0.2Ma, 1km cruising flight, the highest efficiency is 88%, and the front and rear row pitches are 22° and 24° respectively. Using the model for multiple calculations, the following table (partial data example) can be obtained:

[0045] Example Table 1 Ns is the optimal front and rear propeller pitch within the flight envelope when cruising at 900 r / min

[0046] .

Claims

1. A propfan engine speed control method, characterized in that: The double-row propeller speed free control of the propfan engine specifically includes the following steps: Step 1: Establish a double-row propeller fan aerodynamic mathematical model; Step 2: Taking the optimal propeller efficiency as the goal, the aerodynamic mathematical model of the double-row propeller fan is nonlinearly optimized for the pairing relationship of the front row blade pitch α1 and the rear row blade pitch α2 at the typical operating point in the flight envelope to obtain the optimal control law is the virtual optimal pitch, At a certain speed N s and the optimal pitch of the front and rear blades corresponding to the maximum propeller efficiency η at the flight envelope point; Step 3: Control the pitch of the double-row propeller to the optimal pitch according to the front row propeller pitch and the rear row propeller pitch corresponding to the highest propeller efficiency obtained in step 2.

2. A propfan engine speed control method according to claim 1, characterized in that: The propeller efficiency is the propulsion efficiency of the propeller blades.

3. A propfan engine speed control method according to claim 1, characterized in that: The specific steps of establishing the aerodynamic mathematical model of the double-row propeller fan in step 1 include: 1) Using similarity theory, a propeller fan aerodynamic mathematical model is established with flight speed, flight altitude, blade angles α1 and α2, and blade speed as model inputs and propeller efficiency η as model output; 2) Given the flight speed, flight altitude and blade speed as fixed values, with blade angles α1 and α2 as variables and propeller efficiency as the optimization target, the propeller fan aerodynamic mathematical model is used to perform optimization calculations. Introduction is the virtual optimal pitch, that is That is, the virtual optimal pitch corresponding to different flight envelope points It is composed of different groups It 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.

4. A propfan engine speed control method according to claim 1, characterized in that: In step 3, the speed is controlled by adjusting the pitch of the double-row propellers using a master-slave control structure, which specifically includes: using the front row of propeller pitch to control Ns, when the front row of propeller pitch reaches The adjustment stops within the range and the rear propeller pitch is adjusted to The propeller is maintained within the required stable speed range. That is, the rear blade α2 is in a follow-up state and changes with α1 according to the optimal control law until α1 reaches α2 reaches 5. A propfan engine speed control method according to claim 1, characterized in that: In step 3, the double-row propeller pitch speed control adopts a restricted control structure, that is, in order to solve the fluctuation of engine output power, the fluctuation of flight envelope and the error of propeller aerodynamic mathematical model calculation model, the propeller speed cannot reach the ideal speed under the optimal pitch, and the actual α1 is allowed to deviate from the optimal speed within a certain range. To ensure the propeller speed, the deviation range is set to ±5° based on the single-row propeller engineering development experience; according to the propeller speed deviation range, α1 is set to ±5°. The Ns control loop adjustment range of α1 is limited to ±5° to avoid the dynamic adjustment of α1 exceeding the limit range.

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