Tilting type aircraft aerodynamic characteristic analysis and control strategy making method

Abstract

The invention provides a method for analyzing aerodynamic characteristics of a tilting aircraft in a tilting transition state, and the method comprises the steps: carrying out the grid division of a computational domain according to the characteristics of a research object; setting a grid region motion type and a boundary type, and establishing a calculation model; a tilting transition state control strategy is given, the movement speed and boundary conditions of a calculation area are given according to the control strategy, calculation time steps are set, and the aerodynamic force and the flow field of the aircraft are obtained through calculation; meanwhile, the invention further provides a tilting type aircraft control strategy making method, and the method comprises the steps that a force balance equation and a motion equation are established according to the characteristics of a research object, the whole tilting transition state is divided into a plurality of small intervals, and a control strategy is made through iterative calculation.

Description

Technical Field

[0001] The present application belongs to the technical field of aerodynamic characteristic calculation and analysis, and in particular, relates to a method for aerodynamic characteristic analysis and control strategy formulation of a tilt-rotating aircraft. Background Art

[0002] Tilt-rotor aircraft is a new type of rotorcraft, mainly including tilt-rotor aircraft and tilt-wing aircraft. It combines the advantages of helicopters and fixed-wing aircraft, and its working modes include helicopter mode, fixed-wing mode and tilt-transition mode. In the tilt-transition mode, the aerodynamic interference between the rotor and the wing is complex, and the unsteady characteristics of the flow are strong. The tilt-transition process is complex to control. The formulation of the tilt-transition control strategy requires accurate aerodynamic force of the aircraft, so the aerodynamic calculation of the tilt-transition state is of great significance.

[0003] In the aerodynamic calculation of the tilt transition state, calculations are often performed for a fixed tilt angle without considering the unsteady effects in the tilt transition; or a low-precision calculation model is used instead of the rotor to carry out continuous tilt transition strategy research and aerodynamic calculations, without considering the aerodynamic interference between the rotor and the wing.

[0004] The existing calculation methods for tilt transition state have the following shortcomings:

[0005] First, quasi-steady calculations are carried out for fixed tilt angles, ignoring the unsteady effects. Only the tilt transition strategy calculated by a low-precision calculation model or measured can be used as input. This method cannot consider the unsteady effects of the tilt process, and at the same time, the tilt transition strategy cannot be calculated;

[0006] Second, low-precision calculation methods such as momentum theory or free wake are used to carry out research on continuous tilt transition strategies and calculate the aerodynamic force of tilt transition states. The calculation cannot accurately simulate the aerodynamic interference between the wing and the rotor, and the calculation accuracy of this method is low. Summary of the invention

[0007] Purpose of the invention: In view of the above-mentioned technical problems, a calculation model is established which can calculate the aerodynamic characteristics of the continuous tilt transition state. By combining the force balance equation and the motion equation, the formulation of the tilt control strategy of the tilt transition state can be realized. This method can take into account the unsteady characteristics of the tilt transition state when calculating the aerodynamic characteristics of the transition state. At the same time, in formulating the tilt control strategy, the influence of aerodynamic interference on the aerodynamic force of each component can be more accurately considered.

[0008] In a first aspect, the present application provides a method for analyzing aerodynamic characteristics of a tilting aircraft in a tilting transition state, the method comprising:

[0009] Divide the computational domain into grids according to the characteristics of the research object;

[0010] Set the grid area motion type and boundary type, and establish a calculation model;

[0011] Given a tilt transition state control strategy, the motion speed and boundary conditions of the calculation area are given according to the control strategy, the calculation time step is set, and the aerodynamic force and flow field of the aircraft are calculated.

[0012] Preferably, before dividing the computational domain into grids according to the characteristics of the research object, the method further includes:

[0013] Determine the research object and analyze it.

[0014] Preferably, dividing the computational domain into grids according to the characteristics of the research object includes:

[0015] When the research object is a tilt-rotor aircraft, it is divided into the following parts: the tilt-rotor area of ​​the front wing is the first sub-grid area, the tilt-rotor area of ​​the rear wing is the second sub-grid area, the fuselage, wings and other parts are the third sub-grid area, and the fluid domain is the first background grid area;

[0016] The first sub-grid area and the second sub-grid area are nested in the third sub-grid area, and the third sub-grid area is nested in the first background grid area.

[0017] Preferably, dividing the computational domain into grids according to the characteristics of the research object includes:

[0018] When the research object is a tilt-wing aircraft, it is divided into the following parts: the front wing and rotor area is the fourth sub-grid area, the rear wing and rotor area is the fifth sub-grid area, the fuselage and other parts are the sixth sub-grid area, and the fluid domain is the second background grid area;

[0019] The fourth sub-grid area and the fifth sub-grid area are nested in the sixth sub-grid area, and the sixth sub-grid area is nested in the second background grid area.

[0020] Preferably, the setting of the grid area movement type includes:

[0021] The motion types of the first sub-grid area and the second sub-grid area are set to forward flight motion superimposed on tilt motion, the motion type of the first background grid area is set to stationary, and the motion type of the third sub-grid area is set to forward flight motion.

[0022] Preferably, the setting of the grid area movement type includes:

[0023] The movement type of the fourth sub-grid area and the fifth sub-grid area is set to forward flight movement superimposed on tilt movement, the movement type of the sixth sub-grid area is set to forward flight movement, and the movement type of the second background grid area is set to stillness.

[0024] Preferably, setting the boundary type of the grid area includes:

[0025] The boundary type of the longitudinal symmetric surface of the background grid area is set to a symmetric boundary, and the boundary types of other surfaces of the background grid area are set to a pressure far field; wherein the background grid area includes a first background grid area and a second background grid area.

[0026] In a second aspect, the present application also provides a method for formulating a tilt-type aircraft control strategy, the method comprising:

[0027] According to the characteristics of the research object, the force balance equation and motion equation are established, the entire tilt transition state is divided into multiple small intervals, and the manipulation strategy is formulated through iterative calculation;

[0028] Beneficial technical effects of this application:

[0029] The present invention proposes a method for calculating the aerodynamic characteristics and control strategies of a tilting aircraft in a tilting state. The method can carry out aerodynamic calculation analysis and control strategy formulation for the tilting transition state of the tilting aircraft, and has certain application value for the aerodynamic layout and control strategy analysis of the tilting transition state of the tilting aircraft.

[0030] The present invention adopts a momentum source method to replace the rotor, which can achieve a compromise between calculation speed and calculation accuracy. It adopts a nested grid method to simulate the movement of the wing, fuselage and rotor, and can calculate and simulate the continuous state of the tilt transition. Compared with the conventional fixed-angle quasi-steady calculation method, the present invention can consider the unsteady characteristics of the tilt transition state when calculating the aerodynamic characteristics of the transition state; compared with the conventional tilt transition strategy formulation method, the aerodynamic calculation method of the present invention has higher accuracy and can more accurately calculate the aerodynamic forces of each component under aerodynamic interference.

[0031] Using the method of the present invention, under the condition of a given control strategy, the calculation results of the method are compared with the wing aerodynamic calculation of the quasi-steady calculation as follows: Figure 4 As shown, this method can calculate the wing aerodynamic force during the continuous tilting process. Compared with the conventional quasi-steady calculation method, it can calculate the influence of unsteady effects on the wing aerodynamic force. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of a method for analyzing aerodynamic characteristics and formulating a control strategy for a tilt-type aircraft provided in an embodiment of the present application;

[0033] Figure 2 is a schematic diagram of grid division of a tilt-wing aircraft provided in an embodiment of the present application;

[0034] Figure 3 is a schematic diagram of grid division of a tilt-rotor aircraft provided in an embodiment of the present application;

[0035] Figure 4 is a comparison chart of the calculation results of the method provided in the embodiment of the present application and the wing aerodynamic calculation by quasi-steady calculation;

[0036] Among them, 1-front rotor; 2-front wing; 3-fuselage; 4-rear rotor; 5-rear wing. DETAILED DESCRIPTION

[0037] The present invention proposes a method for calculating the aerodynamic characteristics and control strategy of a tilting aircraft in a tilting state. The method adopts a momentum source method to replace the rotor, which can achieve a compromise between calculation speed and calculation accuracy. At the same time, a nested grid method is used to simulate the movement of the wing and the rotor, which can achieve the simulation of any movement. For the tilt transition strategy, the calculation method can perform aerodynamic calculation of the tilt transition state according to a given tilt strategy, and can also formulate a tilt transition strategy under aerodynamic interference, and then carry out aerodynamic calculation of the tilt transition state according to the formulated tilt transition strategy.

[0038] See also Figure 1-Figure 4 First, determine the research object and analyze it; then, divide the calculation domain into grids according to the characteristics of the research object; set the grid area motion type and boundary conditions, and establish a calculation model; if the tilt transition control strategy is determined, then implement aerodynamic calculations based on the boundary conditions and motion parameters of the calculation area given by the control strategy. If a control strategy needs to be formulated, establish the force balance equation and motion equation according to the characteristics of the research object, divide the entire tilt transition state into multiple small intervals, and implement the control strategy formulation through iterative calculations, while completing the aerodynamic characteristics calculation. Finally, analyze the aerodynamic calculation results. The method flow chart is shown below. Figure 1 shown.

[0039] In the embodiment of the present application, the present invention adopts the following technical solution: a method for calculating the aerodynamic characteristics and control strategy of a rotorcraft in a tilting state, comprising the following design steps:

[0040] The first step is to determine the research object and analyze it;

[0041] Tilt-rotor aircraft refers to tilt-rotor aircraft and tilt-wing aircraft. This type of aircraft has wings and rotors. In the tilt transition state, the tilt-rotor aircraft achieves the conversion of different working modes by tilting the rotors, and the tilt-wing aircraft achieves the conversion of different working modes by tilting the rotors and wings at the same time. This type of aircraft has 2n rotors (n is greater than or equal to 1) and k wings (k is greater than or equal to 1).

[0042] The second step is to divide the computational domain into grids according to the characteristics of the research object;

[0043] When the research object is a tilt-rotor aircraft, the nested grid method is used to realize the tilting motion of the rotor and the forward flight motion of the wing, rotor and fuselage. Figure 3 This is a schematic diagram of the mesh division of a tiltrotor aircraft (4 rotors and 2 wings). The mesh is a multi-nested mesh. Since the tiltrotor aircraft is bilaterally symmetrical, the half-span model is used for calculation. The tiltrotor area of ​​the front wing is the first sub-grid area, the tiltrotor area of ​​the rear wing is the second sub-grid area, the fuselage, wings and other components are the third sub-grid area, and other components include the nacelle, horizontal tail, vertical tail, etc. The fluid domain is the first background grid area. Set the grid nesting relationship, the first sub-grid area and the second sub-grid area are nested in the third sub-grid area, and the third sub-grid area is nested in the first background grid area.

[0044] When the research object is a tilt-wing aircraft, the nested grid method is used to realize the tilting motion of the wing and rotor and the forward flight motion of the wing, rotor and fuselage. Figure 2 This is a schematic diagram of the mesh division of a tilt-wing aircraft (4 rotors and 2 wings). The mesh is a multi-nested mesh. Since the tilt-wing aircraft is bilaterally symmetrical, the half-span model is used for calculation. The front wing and rotor area is the fourth sub-grid area, the rear wing and rotor area is the fifth sub-grid area, the fuselage and other parts are the sixth sub-grid area, and other parts include the nacelle, horizontal tail, vertical tail, etc. The fluid domain is the second background grid area. Set the mesh nesting relationship, the fourth sub-grid area and the fifth sub-grid area are nested in the sixth sub-grid area, and the sixth sub-grid area is nested in the second background grid area.

[0045] The third step is to set the grid area motion type and boundary type and establish a calculation model;

[0046] The motion types of the first sub-grid area, the second sub-grid area, the fourth sub-grid area and the fifth sub-grid area are forward flight motion superimposed on tilting motion;

[0047] The motion type of the third sub-grid area and the sixth sub-grid area is forward flight, the motion type of the first background grid area and the second background grid area is stationary, the boundary type of the longitudinal symmetry plane of the first background grid area and the second background grid area is set to symmetric boundary, and the boundary type of other surfaces of the first background grid area and the second background grid area is set to pressure far field; complete the setting of grid area motion type and boundary conditions, and establish a calculation model for the aircraft under study.

[0048] The fourth step is, if a tilt transition state control strategy is given, then the motion speed and boundary conditions of the calculation area are given according to the control strategy, the calculation time step is set, and the aerodynamic force and flow field of the aircraft are calculated; if the tilt transition control strategy is not given, it is necessary to formulate a control strategy, establish the force balance equation and motion equation according to the characteristics of the research object, divide the entire tilt transition state into multiple small intervals, and realize the control strategy formulation through iterative calculation, and complete the aerodynamic characteristics calculation at the same time.

[0049] If the control strategy is given, that is, the relationship between the forward flight speed, tilt speed, rotor control and time of the tilt-rotating aircraft is given, the pressure far-field boundary speed of the first background grid area and the second background grid area is set to the forward flight speed at the beginning of the tilting movement, the forward flight speed of the first sub-grid area, the second sub-grid area, the third sub-grid area, the fourth sub-grid area, the fifth sub-grid area and the sixth sub-grid area is set to the forward flight speed given by the tilting strategy, the tilt speed of the first sub-grid area, the second sub-grid area, the fourth sub-grid area and the fifth sub-grid area is set to the tilt speed given by the tilting strategy, the rotors in the first sub-grid area, the second sub-grid area, the fourth sub-grid area and the fifth sub-grid area are simulated using a momentum source model, the momentum source model is widely used in rotor simulation of rotor and wing interference problems, and the control amount of the momentum source model is given according to the tilting control strategy.

[0050] If the control strategy is not given, a tilt transition control strategy is formulated based on the equilibrium equation and the motion equation, and the entire tilt transition state is iteratively calculated.

[0051] (1) According to the reference tilt transition strategy, the motion speed and boundary conditions of the calculation model established in step 3 of the given tilt strategy are given, and the aerodynamic coefficients (including lift coefficient and drag coefficient) of the wing and fuselage and the pitching moment coefficient about the center of gravity at different tilt angles are calculated.

[0052] (2) Establish the equilibrium equation in the longitudinal plane:

[0053] Tcosθ+FY=G (1)

[0054] Tsinθ-FX=ma (2)

[0055] MY r+MY f =0 (3)

[0056] Among them, T is the total thrust of all rotors, FX and FY are the drag and lift of the wings and fuselage, G is the total gravity of the aircraft, m is the total mass of the aircraft, a is the acceleration, θ is the tilt angle (the angle between the rotor axis and the horizontal plane), MY r is the pitch moment of all rotors about the center of gravity, MY f is the pitch moment of the fuselage and wing about the center of gravity.

[0057] Rotor control variables include rotor collective pitch, longitudinal cyclic pitch, etc.

[0058] (3) The tilt transition state is divided into multiple small intervals. Since the angle interval Δθ of the division is very small, it is considered that the tilt velocity, forward flight velocity and acceleration are unchanged in each interval.

[0059] (4) Given the initial tilt velocity ω0 and the forward flight acceleration threshold a n When the tilt transition state begins, the speed of the entire machine is v0, the acceleration is a0, and within a very small tilt angle interval Δθ, the tilt time is Δt=Δθ / ω0.

[0060] (5) Calculate the forward flight speed at the next tilt angle, forward flight speed v1 = v0 + a0 * Δt. Calculate the lift, drag and pitching moment of the wing and fuselage based on the forward flight speed at this angle and the aerodynamic coefficients and pitching moment coefficients of the fuselage and wing calculated in step (1).

[0061] (6) According to formula (1), the total thrust T1 of the rotor is solved; according to formula (2), the acceleration a1 of the angle is solved; according to formula (3), the pitch moment MY of all rotors about the center of gravity is solved R1

[0062] (7) In the established tilt-rotor transition calculation model, according to the total thrust T1 of all rotors and the total pitch moment MYR1 of all rotors about the center of gravity solved in step (6), the Newton iterative balancing method is used to solve the corresponding control variables of all rotors (corresponding to single-wing tilt-rotor aircraft, the control variables are the rotor collective pitch and longitudinal cyclic pitch; for multi-wing tilt-rotor aircraft, the control variables are the front rotor collective pitch and the rear rotor collective pitch).

[0063] (8) The rotor control obtained in step (7) and the forward flight speed obtained in step (5) are input into the tilt transition calculation model established in step 3. The trim equations are (1) and (3), and the trim variables are the rotor control variables. The Newton iteration method is used to obtain a more accurate rotor control value, and the aerodynamic forces of the wing, fuselage and rotor are calculated at the same time.

[0064] (9) Based on (8), the aerodynamic forces of the wing, fuselage and rotor are obtained, and the forward flight acceleration is solved according to formula (2);

[0065] (10) Determine whether the forward flight acceleration value exceeds a given threshold value a n If the threshold is exceeded, the tilting speed needs to be reduced to 95% of the given initial tilting speed, and steps (4) to (9) are repeated until the forward flight acceleration is less than the threshold; if the threshold is not exceeded, proceed to the next step;

[0066] (11) Repeat steps (4)-(10) to calculate the aerodynamic forces and rotor control at the next angle. The calculation is iterated in this way to complete the calculation of the entire tilt transition state and obtain the tilt transition strategy and the aerodynamic forces and flow field of the transition state.

[0067] The fifth step is to analyze the calculation results to see whether the aerodynamic changes of the wing, fuselage and rotor are in line with the actual situation and whether the rotor control amount exceeds the reasonable range. If the calculation result is correct, the calculation ends. If the calculation result is incorrect, adjust the calculation settings and return to step one to recalculate.

[0068] The present invention proposes a method for calculating the aerodynamic characteristics and control strategy of a tilting aircraft in a tilting state. The method adopts a momentum source method to replace the rotor, which can achieve a compromise between calculation speed and calculation accuracy. At the same time, a nested grid method is used to simulate the movement of the wing and the rotor, which can achieve the simulation of any movement. For the tilt transition strategy, the calculation method can perform aerodynamic calculation of the tilt transition state according to a given tilt strategy, and can also formulate a tilt transition strategy under aerodynamic interference, and then carry out aerodynamic calculation of the tilt transition state according to the formulated tilt transition strategy.

Claims

1. A method for analyzing aerodynamic characteristics of a tilt-type aircraft in a tilt transition state, characterized in that: The method comprises: Divide the computational domain into grids according to the characteristics of the research object; Set the grid area motion type and boundary type, and establish a calculation model; If the control strategy for the transition state of the tilting has not been determined, make a control strategy; If a tilt transition state control strategy is given, the motion speed and boundary conditions of the calculation area are given according to the control strategy, the calculation time step is set, and the aerodynamic force and flow field of the aircraft are calculated.

2. The method according to claim 1, characterized in that Before dividing the computational domain into grids according to the characteristics of the research object, the following steps are also included: Determine the research object and analyze it.

3. The method according to claim 2, characterized in that The grid division of the computational domain according to the characteristics of the research object includes: When the research object is a tilt-rotor aircraft, it is divided into the following parts: the tilt-rotor area of ​​the front wing is the first sub-grid area, the tilt-rotor area of ​​the rear wing is the second sub-grid area, the fuselage, wings and other parts are the third sub-grid area, and the fluid domain is the first background grid area; The first sub-grid area and the second sub-grid area are nested in the third sub-grid area, and the third sub-grid area is nested in the first background grid area.

4. The method according to claim 2, characterized in that: The grid division of the computational domain according to the characteristics of the research object includes: When the research object is a tilt-wing aircraft, it is divided into the following parts: the front wing and rotor area is the fourth sub-grid area, the rear wing and rotor area is the fifth sub-grid area, the fuselage and other parts are the sixth sub-grid area, and the fluid domain is the second background grid area; The fourth sub-grid area and the fifth sub-grid area are nested in the sixth sub-grid area, and the sixth sub-grid area is nested in the second background grid area.

5. The method according to claim 3, characterized in that: The setting of the grid area movement type includes: The motion types of the first sub-grid area and the second sub-grid area are set to forward flight motion superimposed on tilt motion, the motion type of the first background grid area is set to stationary, and the motion type of the third sub-grid area is set to forward flight motion.

6. The method according to claim 4, characterized in that The setting of the grid area movement type includes: The movement type of the fourth sub-grid area and the fifth sub-grid area is set to forward flight movement superimposed on tilt movement, the movement type of the sixth sub-grid area is set to forward flight movement, and the movement type of the second background grid area is set to stillness.

7. The method according to claim 3 or 4, characterized in that: Set the border type of the grid area, including: The boundary type of the longitudinal symmetric surface of the background grid area is set to a symmetric boundary, and the boundary types of other surfaces of the background grid area are set to a pressure far field; wherein the background grid area includes a first background grid area and a second background grid area.

8. A method for formulating a tilt-rotating aircraft control strategy, characterized in that: The method comprises: According to the characteristics of the research object, the force balance equation and motion equation are established, the entire tilt transition state is divided into multiple small intervals, and the manipulation strategy is formulated through iterative calculation.

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