CN102722612B - Helicopter rotor airframe coupling system model and application thereof - Google Patents

Abstract

The invention discloses a helicopter rotor body coupling system model and an application thereof, which are used for analyzing the dynamic stability judgment of articulated, hingeless and bearingless rotor helicopter systems, and belong to the technical field of helicopter design. In the present invention, the rotor blade adopts an equivalent blade rigid body model with an equivalent hinge overhanging beam or a beam unit model with 15 degrees of freedom, and the body structure adopts a rigid body model with pitch and roll degrees of freedom or a beam unit with 15 degrees of freedom The model uses lift line theory to calculate the aerodynamic force of the blade section. The blade motion equation, the airframe motion equation and the aerodynamic model equation are combined to form a motion equation group, that is, the motion equation of the helicopter rotor and the body coupling system is obtained, and the dynamic stability of the helicopter system is obtained by solving the motion equation. The helicopter rotor body coupling system model proposed by the invention has high reliability, and the dynamic stability performance of the helicopter system can be accurately analyzed by using the time domain analysis method.

Description

A Coupling System Model of Helicopter Rotor Body and Its Application

technical field

The invention belongs to the field of helicopter design, in particular to a helicopter rotor body coupling system model, which can be used to judge the dynamic stability of the rotor body coupling system of articulated, hingeless and bearingless rotor helicopters.

Background technique

Helicopter system is a complex dynamical system, and dynamic stability is one of the basic issues in its dynamic design, among which ground and air resonance have always been the main considerations of designers. The main vibration sources of helicopters are various, mainly including main rotor system, tail rotor and engine. The helicopter system is extremely complex, mainly including the rotor and the body. Not only there are coupling effects such as flapping, shimmy and torsion inside the rotor blades, but also there are coupling effects between the rotor and the body. Exciting vibration. In order to improve the performance of the helicopter and avoid the dynamic instability of the helicopter, the airworthiness regulations of the helicopter have carried out detailed regulations on this.

Due to the complexity of the helicopter system and its dynamic stability, how to judge the dynamic stability of the helicopter considering the coupling of the rotor and the body system has become an urgent problem to be solved. The main methods for in-depth understanding of helicopter performance include experimental research and theoretical analysis. Although the experimental method can accurately evaluate the dynamic stability of the helicopter system, the cost of experimental research is high and it is not economical and practical in the initial stage of design. Therefore, it is necessary to establish accurate structure, aerodynamic and its coupling model to accurately describe the helicopter. Helicopter analysis technology has made great progress, but the problem of reliable and accurate vibration prediction is still a great challenge. The traditional helicopter vibration analysis is mainly divided into two stages. In the first stage, the rotor hub is assumed to be fixed, and the loads of the rotor blades and the rotor hub are obtained by solving complex structural and aerodynamic models; in the second stage, the The calculated hub loads are applied to the helicopter finite element model to predict the vibration of the helicopter fuselage. But in the actual helicopter system, the vibration of the body will also affect the movement of the rotor blades, but this method does not consider the influence of the body on the rotor, so it is difficult to accurately predict the dynamic stability of the helicopter.

Contents of the invention

The present invention aims at the deficiencies of the existing helicopter rotor body coupling system analysis model, and proposes a new model for judging the dynamic stability of articulated, hingeless and bearingless rotor helicopter systems. Accuracy, the rotor blade in this model can use the equivalent rigid body model of the blade with the equivalent hinge outrigger beam or the elastic beam element model with 15 degrees of freedom of flapping bending, shimmy bending, axial deformation and elastic torsion, while the body’s The structural model adopts a rigid body model with pitch and roll degrees of freedom or an elastic beam element model with 15 degrees of freedom. The aerodynamic force of the blade section is calculated by using the lift line theory. The dynamic inflow model, the extended Pitt/Peters dynamic inflow model and the steady inflow model are used to judge the dynamic stability of the helicopter in the low frequency state, the disturbed motion state and the steady state state respectively. According to d'Alembert's principle, the body motion equation is established, so that the dynamic stability model of the helicopter rotor and body coupling system can be obtained. The invention can solve the coupling system equation of the helicopter rotor and the body by adopting the eigenvalue analysis method and the time domain analysis method to obtain the modal damping, thereby achieving the purpose of accurately judging the dynamic stability of the helicopter rotor and the body coupling system.

The present invention also provides a method for establishing the above-mentioned model. The rotor blade motion equation, the body motion equation and the aerodynamic model equation are combined to form the motion equation group of the helicopter rotor and body coupling system, that is, the motion of the helicopter rotor and body coupling system is obtained. equation. For the above-mentioned helicopter rotor and body coupling system model, the present invention also provides a kind of application of above-mentioned model, promptly apply described model, adopt eigenvalue analysis method or time-domain analysis method to solve, obtain the dynamics of helicopter rotor and body coupling system Stability, the helicopter rotor and body coupling system model proposed by the present invention and its application can obtain the dynamic stability of the helicopter rotor and body coupling system, and has higher calculation accuracy.

Description of drawings

Fig. 1 is the schematic diagram of helicopter rotor and body coupling system among the present invention;

Fig. 2 is the blade equivalent rigid body model that the present invention adopts;

Fig. 3 is the rotor blade structure model that the present invention adopts 15 degrees of freedom beam elements to form;

Fig. 4 is the elastic body and rotor blade model that the present invention adopts;

Fig. 5 is a flowchart of the eigenvalue analysis method of the present invention;

Fig. 6 is a flow chart of the time domain analysis method of the present invention;

In the picture:

1. Propeller blade; 2. Propeller hub; 3. Body;

4. Spring constraint; 5. Rotor center; 6. Rigid body blade;

7. Beam unit; 8. Elastic body model.

Detailed ways

A helicopter rotor body coupling system model proposed by the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The invention provides a rotor-body coupling system model and its establishment method, which can be used to judge the dynamic stability of the helicopter rotor-body coupling system.

Figure 1 is a schematic diagram of the coupling system between the helicopter rotor and the body. The engine drives the rotor blade 1 to rotate, and the blade 1 produces a vibration response during the rotation process, which is transmitted to the hub 2, and then the hub 2 transmits the vibration load to the body. 3. The body 3 generates vibration and deformation, which will generate a feedback response to the propeller hub 2, and finally affect the movements such as waving and shimmy of the propeller. The invention constructs a rotor-body coupling system model and uses an eigenvalue analysis method or a time-domain analysis method to solve the model, thereby accurately judging the dynamic stability of the helicopter rotor-body coupling system.

A complete helicopter rotor and body coupling system model includes the rotor structure model, body structure model and aerodynamic model. The motion equations of the helicopter rotor and body coupling system can be established through the motion equations of each model.

details as follows:

(1) Structural model of the rotor.

When the coupled system model of the helicopter rotor and body is mainly used for the research and analysis of the parameters of the helicopter rotor and body (such as rotor speed and forward ratio, etc.), only the basic blade flapping and swinging are considered in the construction of the rotor structure model. vibration mode. As shown in Figure 2, the equivalent rigid body model of the blade, the blade 1 is connected at the center of the rotor 5, and the flapping hinge and the shimmy hinge are assumed to be spring constraints 4, so the hingeless or bearingless rotor blade 1 is equivalent to Rigid-body paddle 6 biased by hinged spring-constrained 4 . The blade equivalent rigid body model can be used to simulate articulated, hingeless and bearingless rotors. In the structural model of the rotor, the flapping and shimmy structural coupling is considered, and the structural model of the rotor can accurately analyze the influence of the parameters of the rotor and the body (such as the rotor speed and forward ratio, etc.) on the coupling system of the rotor and the body.

When it is necessary to determine the aeroelastic stability and air resonance stability of the helicopter rotor and body coupling system in forward flight, a more accurate structural model of the rotor is required. The present invention considers the rotor blade as an elastic beam including flapping bending, shimmy bending, axis deformation and elastic torsion, and the model can reflect the motion state of the real blade. As shown in Figure 3, the blade 1 connected to the hub 2 is discretized into several beam units 7, the linear displacement and angular displacement between two adjacent beam units 7 are continuous, each beam unit 7 There are two outer nodes and three inner nodes, the two outer nodes have six degrees of freedom respectively, and the three inner nodes have only one degree of freedom, so each beam element 7 has fifteen degrees of freedom. Using this rotor model can accurately analyze aeroelastic stability and air resonance stability.

(2) The structural model of the body.

For the helicopter rotor and body coupling system, considering that the elastic influence of the helicopter structure is relatively small in the analysis of this coupling system, the helicopter fuselage structure is regarded as a rigid body model, and its pitching and rolling motions are considered. In the case of forward flight, the rotor and the body model rotate around their respective centers of gravity; the ground resonance analysis uses the instantaneous center of rotation of the body mode as the center of rotation of the body.

In order to obtain the vibration characteristics of the body in the helicopter rotor body coupling system model, the present invention also provides a more accurate structural model of the body, as shown in Figure 4, the body is simplified into an elastic body model 8, the elastic body model 8 top It is connected to the rotor blade 1, and the elastic body model 8 also adopts the above-mentioned beam unit 7 structure with 15 degrees of freedom, so that the mass of the body 3 is evenly distributed on the beam unit 7, and the body 3 is composed of several beam units 7 , at this time, the body 3 considers translational motion in three directions and rotational degrees of freedom in three directions, which can simulate the deformation of the body structure more accurately.

(3) Aerodynamic model:

The invention adopts the lift line theory to calculate the aerodynamic force of the blade section. Different aerodynamic models are used for different states. If the helicopter resonance problem is evaluated in the low-frequency state, the dynamic inflow model is used; for the disturbance motion, the extended Pitt/Peters dynamic inflow model involving unsteady aerodynamic effects is used. ; Finally, for the steady state, the steady inflow model is adopted. These three models are prior art, and here only explain the induced velocity v of any point on the rotor blade, which can be expressed in the following form:

v＝v ₀ +v _s (r+e)sin(ψ _k -ξ _k )+v _c (r+e)cos(ψ _k -ξ _k ) (1)

where e is the overhanging beam of the dimensionless equivalent hinge, r is the distance from any section of the blade to the shimmy hinge, v ₀ is the average induced velocity on the plane of the paddle disk, v _s and v _c are the aerodynamic roll and pitch of the rotor The resulting induced velocity, ξ _k is the shimmy displacement of the k-th blade, and ψ _k is the azimuth of the k-th blade.

(4) Coupling model of rotor blade and airframe:

Firstly, the motion equations such as flapping and shimmy of the rotor blades are established, and then the multi-blade coordinate transformation (MCT) is implemented to convert the degree of freedom of blade motion in the rotating coordinate system into the degree of freedom of the overall motion of the rotor. The present invention can adopt implicit or explicit Formula MCT method.

Then the equation of motion of the body is established by using d'Alembert's principle.

Finally, the blade motion equation, body motion equation and aerodynamic model equation are combined to form the motion equation group of the helicopter rotor and body coupling system, that is, the motion equation of the helicopter rotor and body coupling system is obtained. At this time, the rotor and the body are in the same fixed coordinate system.

Based on this, the dynamic model of the helicopter rotor/body coupling system is established.

The dynamic model of the helicopter rotor/body coupling system is established, and the next step is to solve the dynamic stability of the helicopter rotor and body coupling system. The model proposed by the invention can determine the dynamic stability by means of eigenvalue analysis or time domain analysis.

Figure 5 shows the flow chart of the eigenvalue analysis method, which needs to adopt the small disturbance assumption of the equilibrium position. The specific steps are as follows:

(1) Firstly, it is required to obtain the balance value of rotor flapping, shimmy and airframe in the steady state, that is, the steady response of the helicopter rotor and airframe coupling system. In the specific solution process, first remove the time-related quantities, and then solve the balance equation. .

(2) After obtaining the balance value from the previous step, assuming that the helicopter rotor and body coupling system has a small disturbance at the equilibrium position, then solve the dynamic stability according to the disturbance motion equation, but the dynamic stability equation in the case of hovering and forward flight is solved The process is different.

When judging the dynamic stability of the hovering state, since the disturbance equation is a constant coefficient differential equation, the modal eigenvalue of the system can be obtained by solving the matrix eigenvalue, the imaginary part of the eigenvalue is the modal frequency, and the real part is the modal Damping, if the real part is negative, it means that the modal damping is negative and the system is stable, otherwise it is unstable.

When judging the dynamic stability of the helicopter rotor and body coupling system in forward flight, since the disturbance equation is a differential equation with periodic coefficients, it can be solved by Floquet theory. In the specific calculation process, the transfer matrix method can be used to obtain the system The modal damping and modal frequencies of . So as to achieve the purpose of judging the dynamic stability of the helicopter rotor and body coupling system.

In addition to the eigenvalue analysis method, the helicopter rotor and body coupling system model proposed by the present invention can also be solved by the time domain analysis method as shown in Figure 6, and the main steps are as follows:

In the first step, according to the established differential equation of motion of the helicopter rotor and body coupling system, the differential equation is integrated in the time domain, so that the response curve of each degree of freedom over time can be obtained;

The second step is to perform Fourier transform (FFT) on the time domain response curve obtained in the previous step to obtain the frequency response curve, and the frequency of each mode can be easily obtained from the frequency response curve;

In the third step, the damping of the mode can be obtained by using methods such as moving a rectangular window, the logarithmic decay rate of the envelope, or Prony curve fitting. Thus, the process of time domain analysis is completed, and the modal damping of the helicopter rotor and body coupling system and the dynamic stability of the modal frequency judgment system are obtained.

Example

In order to verify the validity of the helicopter rotor and airframe coupling system model proposed by the present invention and its application, this embodiment is adopted for verification. The model parameters of the helicopter rotor and airframe coupling system used are: 3 blades, the rotor radius is 0.81m, the section chord length is 0.0419m, the section airfoil is NACA 2301, the equivalent hinge overhang is 0.0851m, the blades are hinged The moment of inertia is 0.0173kg.m ² , the natural frequencies of blade flapping and shimmy are 3.14Hz and 6.70Hz respectively, the damping ratio of shimmy structure is 0.52%, and the pitching moment of inertia, restraint stiffness and damping ratio of the body are 0.607kg.m ² , 11.20kg.m.rad ^-1 and 3.2%, the body rolling moment of inertia, damping ratio and constraint stiffness are 0.177kg.m ² , 6.19kg.m.rad ^-1 and 0.929% respectively.

Adopt the helicopter rotor and airframe coupling system dynamics model that the present invention proposes, the rotor adopts blade equivalent rigid body model, and airframe then adopts the rigid body model that has considered pitch and roll, and aerodynamic model adopts Pitt/Peters power inflow model, adopts respectively Eigenvalue analysis method and time domain analysis method to solve. In this calculation example, the collective pitch angle is 9° and the rotor speed is 700r/min. The shimmy receding mode damping value can be obtained as 0.502s ^-1 , and the experimental value is 0.512s ^-1 , with an error of only 2%. The real part of the eigenvalue obtained by using the eigenvalue analysis method is 0.410s ^-1 , and the error is 18.3%. It can be concluded that the model and analysis method proposed by the present invention are accurate and reliable, and the time domain analysis method has higher calculation precision than the eigenvalue analysis method.

Claims (4)

1. a helicopter rotor body coupling system model, is characterized in that: described model comprises the structure model of rotor, the structure model of body and aerodynamic model, establishes the equation of motion of helicopter rotor and body coupling system by the equation of motion of each model, Solving described motion equation obtains the dynamic stability of helicopter rotor and body coupling system; The structural model of the rotor: When the coupled system model of the helicopter rotor and body is used for parameter research and analysis of the helicopter rotor and body, only the basic blade flapping and shimmy modes are considered in the establishment of the rotor structure model, and the blade equivalent rigid body model; and when it is necessary to determine the aeroelastic stability and air resonance stability of the helicopter rotor and airframe coupling system in forward flight, the structural model of the rotor used is to discretize the blades connected to the hub into several beams unit, the linear displacement and angular displacement between two adjacent beam units are continuous, each beam unit has two external nodes and three internal nodes, the two external nodes have six degrees of freedom, and the three internal nodes Each node has only one degree of freedom, so each beam unit has fifteen degrees of freedom; the equivalent rigid body model of the blade is: the blade is connected at the center of the rotor, and the flapping hinge and the shimmy hinge are assumed to be spring constraints, Hingeless or bearingless rotor blades are equivalent to offset-hinged, spring-constrained rigid-body blades; The structural model of the body: The helicopter fuselage structure is considered as a rigid body model considering the pitch and roll motions. In the case of hovering and forward flight, the rotor and the body model rotate around their respective centers of gravity; the ground resonance analysis uses the instantaneous center of rotation of the body mode as the body's Rotation center; when it is necessary to determine the vibration characteristics of the body in the helicopter rotor and the body coupling system, the body adopts an elastic body model, and the elastic body model also adopts a beam unit structure with 15 degrees of freedom, and the body mass is evenly distributed on the beam unit , the body is composed of several beam units, at this time, the body considers the translational motion in three directions and the rotational degrees of freedom in three directions; The aerodynamic model described: Use the lift line theory to calculate the aerodynamic force of the blade section, and use different aerodynamic models for different states. If evaluating the helicopter's aerial resonance problem in the low-frequency state, use the dynamic inflow model; The expanded Pitt/Peters power inflow model of aerodynamic effect; Finally, for the steady state, the steady inflow model is adopted; the establishment method of the helicopter rotor body coupling system model is as follows: Firstly, the flapping and shimmy motion equations of the rotor blades are established, and then multi-blade coordinate transformation is implemented to transform the blade motion degrees of freedom in the rotating coordinate system into the overall rotor motion degrees of freedom; Then use d'Alembert's principle to establish the motion equation of the body; Finally, the rotor blade motion equation, the body motion equation and the aerodynamic model equation are combined to form the motion equation group of the helicopter rotor and body coupling system, that is, the motion equations of the helicopter rotor and body coupling system are obtained. At this time, the rotor and body are in the same fixed In the coordinate system, the dynamic model of the helicopter rotor-body coupling system is established. 2. a method for establishing the helicopter rotor body coupling system model according to claim 1, characterized in that: Firstly, the flapping and shimmy motion equations of the rotor blades are established, and then multi-blade coordinate transformation is implemented to transform the blade motion degrees of freedom in the rotating coordinate system into the overall rotor motion degrees of freedom; Then use d'Alembert's principle to establish the motion equation of the body; Finally, the rotor blade motion equation, the body motion equation and the aerodynamic model equation are combined to form the motion equation group of the helicopter rotor and body coupling system, that is, the motion equations of the helicopter rotor and body coupling system are obtained. At this time, the rotor and body are in the same fixed In the coordinate system, the dynamic model of the helicopter rotor-body coupling system is established. 3. the application of a helicopter rotor body coupling system model according to claim 1, is characterized in that: adopt eigenvalue analysis method to solve the dynamic model of helicopter rotor body coupling system, obtain the dynamic stability of helicopter rotor and body coupling system ,Specific steps are as follows: (1) Firstly, the balance value of rotor flapping, shimmy and body in steady state is required, that is, the steady response of the helicopter rotor and body coupling system. In the specific solution process, the time-related quantities are removed first, and then the balance equation is solved; (2) Adopt the small disturbance assumption of the equilibrium position, assuming that the helicopter rotor and the body coupling system have a small disturbance at the equilibrium position, and then solve the dynamic stability according to the disturbance motion equation, but the dynamic stability equation in the case of hovering and forward flight is solved The process is different: When judging the dynamic stability of the hovering state, since the disturbance equation is a constant coefficient differential equation, the modal eigenvalue of the system is obtained by solving the matrix eigenvalue, the imaginary part of the eigenvalue is the modal frequency, and the real part is the modal damping , if the real part is negative, it means that the modal damping is negative and the system is stable, otherwise it is unstable; When judging the dynamic stability of the helicopter rotor and airframe coupling system during forward flight, since the disturbance equation is a differential equation with periodic coefficients, the Floquet theory is used to solve it to obtain the modal damping and modal frequency of the system. 4. the application of a helicopter rotor body coupling system model according to claim 1, is characterized in that: adopt time domain analysis method to solve the dynamic model of helicopter rotor body coupling system, obtain the dynamic stability of helicopter rotor and body coupling system ,Specific steps are as follows: In the first step, according to the established differential equation of motion of the helicopter rotor and body coupling system, the differential equation is integrated in the time domain to obtain the response curve of each degree of freedom with time; In the second step, Fourier transform is performed on the time domain response curve obtained in the previous step to obtain a frequency response curve, and the frequency of each mode is obtained from the frequency response curve; In the third step, the modal damping is finally obtained by using the moving rectangular window, the logarithmic decay rate of the envelope curve or the Prony curve fitting method, thus completing the time-domain analysis process, and obtaining the modal damping sum of the helicopter rotor and the body coupling system The modal frequencies determine the dynamic stability of the system.

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