Aerodynamic interference model-based dual-rotor blade tip distance calculation method

Abstract

The invention provides a dual-rotor blade tip distance calculation method based on an aerodynamic interference model. The method comprises the steps that 1, a rotor / fuselage coupling dynamics theoretical model delta n is established; 2, according to the rotor / fuselage coupling dynamics theoretical model delta < n >, full-aircraft trimming under a corresponding flight strategy is completed, and a corresponding propeller hub load is obtained through calculation; 3, constructing an aerodynamic interference model, and calculating unsteady aerodynamic force after rotor wing balancing based on the aerodynamic interference model according to the propeller hub load; and 4, according to the unsteady aerodynamic force, rotor blade tip response is solved for the periodic kinetic equation of the rotor, and the blade tip spacing is obtained through calculation in combination with the azimuth angle.

Description

Technical Field

[0001] The patent of this invention belongs to aviation technology, and specifically relates to a method for calculating the spacing between twin rotor blade tips based on an aerodynamic interference model. Background Art

[0002] The twin-rotor adopts two rigid hingeless rotors with counter-rotation, so that there are forward blades on both sides of the helicopter rotor disc. The forward blades generate part of the lift to effectively unload the rearward blades, solving the speed limitation caused by the stall of the rearward blades. The tip spacing of the twin rotors is an important factor in ensuring flight safety in the design of coaxial helicopters. Once the tip spacing is too small, blade collision will cause serious safety accidents. However, while the twin-rotor aircraft uses lift bias to exert the potential of rotor lift, it also brings more stringent upper and lower rotor spacing working conditions. Therefore, establishing a reliable tip spacing estimation method is an important basis for the dynamic design of twin-rotor aircraft.

[0003] At present, in the prediction of blade tip spacing of twin-rotor aircraft, the isolated rotor is usually used as the calculation model, and the Pitt-Peters dynamic inflow model is used for calculation. This method cannot accurately reflect the influence of the whole machine attitude of the twin-rotor aircraft on the blade tip spacing during flight, and cannot reflect the influence of the aerodynamic interference of the upper and lower rotors on the blade tip spacing. Summary of the invention

[0004] The technical problem to be solved by this patent: A method for calculating the distance between the blade tips of a twin rotor based on an aerodynamic interference model

[0005] Technical solution: A method for calculating the distance between blade tips of a twin rotor based on an aerodynamic interference model, the method comprising:

[0006] Step 1: Establish the rotor / fuselage coupling dynamics theoretical model δ∏;

[0007] Step 2: According to the rotor / fuselage coupling dynamics theoretical model δ∏, complete the whole aircraft balance under the corresponding flight strategy and calculate the corresponding hub load;

[0008] Step 3: Construct an aerodynamic interference model and calculate the unsteady aerodynamic force after the rotor is trimmed based on the aerodynamic interference model according to the hub load;

[0009] Step 4: Based on the unsteady aerodynamic force, the rotor tip response is solved by the periodic dynamic equation of the rotor, and the blade tip spacing is calculated in combination with the azimuth angle.

[0010] Specifically, step 1 includes:

[0011] Step 11: Establish system strain Among them, U b1is the strain energy of the lower rotor blade, U b2 is the strain energy of the upper rotor blade, U F is the fuselage strain energy;

[0012] Step 12: Build system momentum Among them, T b1 The kinetic energy of a single blade of the lower rotor, T b2 is the kinetic energy of the upper rotor blade, T F is the kinetic energy of the fuselage;

[0013] Step 13: Establish system external force virtual work Among them, δW b1 Virtual work of external force on single blade of lower rotor, δW b2 is the virtual work of the external force of the single blade of the upper rotor, W F It is the virtual work of the external force on the fuselage;

[0014] Step 14: Construct the rotor / fuselage coupling dynamics theoretical model based on the system strain energy δU, system kinetic energy δT and system external force virtual work δW:

[0015] Specifically, step 2 includes:

[0016] Step 21: Based on the rotor / fuselage coupling dynamics theoretical model δ∏, perform full-aircraft trim calculation to obtain a full-aircraft trim result;

[0017] Step 22: According to the whole aircraft balancing result, calculate the hub load under the corresponding flight strategy;

[0018] Step 23: Based on the corresponding hub load, perform the next step of rotor trim calculation.

[0019] Specifically, the trim cycles of the whole aircraft trim and rotor trim use Newton-Raphson iteration, and the periodic responses of the rotor and fuselage are solved during the iteration process until the trim variables meet the trim conditions.

[0020] Specifically, step 3 includes:

[0021] Step 31: Make The aerodynamic interference model is constructed by using the free wake model to reflect the wake distortion caused by non-uniform induced velocity;

[0022] Step 32: Using the Biot-Saffar law, the induced velocity is solved to obtain the induced velocity of the vortex element at any point in space;

[0023] Step 33: Calculate the unsteady aerodynamic force based on the induced velocity using the ONERA model.

[0024] Specifically, the aerodynamic interference model is:

[0025]

[0026] Among them, r b represents the position vector of the vortex element at the radial station r on the blade, μ is the vector of the free velocity, ψ is the azimuth, and q * (ψ) is the induced velocity at azimuth angle ψ, is the vortex age, The tail distortion.

[0027] Specifically, step 32 includes:

[0028] Using the formula Calculate the induced velocity, is the induced velocity, Γ is the vortex element circulation, is the vortex element vector, l is the distance from the induced velocity point to the vortex element distance.

[0029] Specifically, step 33 includes:

[0030] Using the formula Calculation, where dF is the unsteady aerodynamic force of the blade unit, Cz1 ​​represents the lift coefficient of the airfoil without considering dynamic stall, Cz2 represents the correction term for the lift coefficient due to dynamic stall, and dL is the length of the blade unit.

[0031] Specifically, step 4 includes:

[0032] Step 41: Based on a numerical method, the rotor / fuselage coupling dynamics theoretical model δ∏ is solved to obtain the blade tip response;

[0033] Step 42: Convert the blade tip response to a reference rotor azimuth;

[0034] Step 43: Calculate the corresponding blade tip spacing based on the reference rotor azimuth angle.

[0035] In summary, the present application provides a method for calculating the blade tip spacing of a twin-rotor based on an aerodynamic interference model. The upper and lower hub loads under different flight strategies can be obtained by balancing the entire aircraft, and then the upper and lower rotors are balanced through a free wake model. The calculation speed is significantly improved, and the calculation results can reflect the influence of the aerodynamic interference of the upper and lower rotors on the blade tip spacing. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of the calculation results of the lower rotor tip response provided in this application;

[0037] Figure 2 A schematic diagram of the calculation results of the rotor tip response provided in this application;

[0038] Figure 3Schematic diagram of the calculation results of the upper and lower rotor tip spacing provided for this application. DETAILED DESCRIPTION

[0039] The present application provides a method for calculating the distance between the blade tips of a twin-rotor blades based on an aerodynamic interference model, the method comprising:

[0040] Step 1: Establish the rotor / fuselage coupling dynamics theoretical model δ∏;

[0041] Specifically, step 1 includes:

[0042] Step 11: Establish system strain Among them, U b1 is the strain energy of the lower rotor blade, U b2 is the strain energy of the upper rotor blade, U F is the fuselage strain energy;

[0043] Step 12: Build system momentum Among them, T b1 The kinetic energy of a single blade of the lower rotor, T b2 is the kinetic energy of the upper rotor blade, T F is the kinetic energy of the fuselage;

[0044] Step 13: Establish system external force virtual work Among them, δW b1 Virtual work of external force on single blade of lower rotor, δW b2 is the virtual work of the external force of the single blade of the upper rotor, W F It is the virtual work of the external force on the fuselage;

[0045] Step 14: Construct the rotor / fuselage coupling dynamics theoretical model based on the system strain energy δU, system kinetic energy δT and system external force virtual work δW:

[0046] It should be noted that this application describes the configuration of any point on the blade in the inertial coordinate system based on Lagrangian relative angular coordinates, and uses Hamilton's principle to derive the dynamic equations of the system. Since the rotor system or the rotor / fuselage coupling system is affected by non-conservative forces such as aerodynamic force and damping force, a rotor / fuselage coupling dynamics theoretical model is established based on the generalized Hamilton's principle.

[0047] The strain energy, kinetic energy and external virtual work of the rotor-fuselage coupling system are composed of three parts: the upper and lower rotors and the fuselage. The rotor kinetic energy, strain energy and external virtual work are the sum of Nb blades.

[0048] The overall matrix of the coupling system is assembled from the finite element matrix. The blade element matrix is ​​first assembled into the blade overall matrix, and then the multi-blade coordinate transformation and the fuselage coupling are used to assemble the overall matrix of the coupling system.

[0049] Step 2: According to the rotor / fuselage coupling dynamics theoretical model δ∏, complete the whole aircraft balance under the corresponding flight strategy and calculate the corresponding hub load;

[0050] Step 21: Based on the rotor / fuselage coupling dynamics theoretical model δ∏, perform full-aircraft trim calculation to obtain a full-aircraft trim result;

[0051] Step 22: According to the whole aircraft balancing result, calculate the hub load under the corresponding flight strategy;

[0052] Step 23: Based on the corresponding hub load, perform the next step of rotor trim calculation.

[0053] Specifically, the trim cycles of the whole aircraft trim and rotor trim use Newton-Raphson iteration, and the periodic responses of the rotor and fuselage are solved during the iteration process until the trim variables meet the trim conditions.

[0054] Since the rotor tip spacing is basically only related to the hub load under fixed rotor working conditions, it has little effect on the calculation results, but can greatly improve the calculation efficiency.

[0055] Step 3: Construct an aerodynamic interference model and calculate the unsteady aerodynamic force after rotor trim based on the aerodynamic interference model according to the hub load.

[0056] Specifically, step 3 includes:

[0057] Step 31: Use the free wake model to reflect the wake distortion caused by non-uniform induced velocity and construct an aerodynamic interference model

[0058] Preferably,

[0059] Among them, r b represents the position vector of the vortex element at the radial station r on the blade, μ is the vector of the free velocity, ψ is the azimuth, and q * (ψ) is the induced velocity at azimuth angle ψ, is the vortex age, is the wake distortion;

[0060] More specifically, the trail distortion in, Vortex age change

[0061] Step 32: Using the Biot-Saffar law, solve the induced velocity of the vortex element at any point in space;

[0062] Specifically, using the formula Calculate the induced velocity, is the induced velocity, Γ is the vortex element circulation, is the vortex element vector, l is the distance from the induced velocity point to the vortex element distance.

[0063] Step 33: Calculate the unsteady aerodynamic force based on the induced velocity using the ONERA model;

[0064] Specifically, using the formula Calculation, where dF is the unsteady aerodynamic force of the blade unit, Cz1 ​​represents the lift coefficient of the airfoil without considering dynamic stall, Cz2 represents the correction term for the lift coefficient due to dynamic stall, and dL is the length of the blade unit.

[0065] It should be noted that the rotor balancing process uses a free wake model to reflect the wake distortion caused by non-uniform induced speed, and establishes models of attached vortex, trailing vortex and tip vortex to further reflect the aerodynamic interference of the upper and lower rotors.

[0066] Step 4: Based on the unsteady aerodynamic force, the rotor blade tip response is solved for the periodic dynamic equation of the rotor, and the blade tip spacing is calculated in combination with the azimuth angle;

[0067] Specifically, step 4 includes:

[0068] Step 41: Based on a numerical method, the rotor / fuselage coupling dynamics theoretical model δ∏ is solved to obtain the blade tip response;

[0069] Step 42: Convert the blade tip response to a reference rotor azimuth;

[0070] It should be noted that the blade tip response changes with the rotor azimuth angle ψ. Since the twin rotors rotate in opposite directions, the blade tip response needs to be converted into a reference rotor azimuth angle.

[0071] Step 43: Calculate the corresponding blade tip spacing according to the reference rotor azimuth angle;

[0072] Specifically, the tip response of the lower rotor is converted according to the rotation azimuth angle of the upper rotor, and then the responses of the upper and lower rotors corresponding to the azimuth angles are subtracted, and then the installation spacing of the upper and lower rotors is added to obtain the tip spacing of the rotor.

[0073] The periodic dynamic equations of the rotor are solved by numerical methods to obtain the rotor tip response under the corresponding flight strategy, and the blade tip spacing that changes with the rotor azimuth angle ψ is further calculated. It is worth noting that the calculated blade tip responses all change with the rotor azimuth angle ψ, and the twin rotors rotate in opposite directions. Therefore, if the blade tip spacing is to be calculated, the time domain response of one rotation cycle of the upper and lower rotors needs to be extracted separately and converted to the same reference rotor azimuth angle, and then the corresponding blade tip spacing calculation result is calculated.

[0074] like Figure 1-2 As shown in the figure, it is the time domain response of the upper and lower rotor blade tips of the XH-59A twin-rotor helicopter. It is obvious that the blade tip response shows a 6Ω harmonic trend. Since the XH-59A has three blades, there is obvious aerodynamic interference between the upper and lower rotors. The calculation results are consistent with the actual situation. Figure 3 The figure shows the calculation results of the blade tip spacing of the XH-59A twin-rotor helicopter.

[0075] In summary, the invention proposes a method for calculating the tip spacing of a double rotor with aerodynamic interference between the upper and lower rotors. The hub load data under the corresponding control strategy is obtained by using the whole machine balancing, and then the double rotor balancing is further performed to improve the calculation efficiency. The aerodynamic interference model is used to reflect the geometric changes of the wake under non-uniform induced speed, and the Biot-Saffar law is used to solve the induced speed, further improving the calculation accuracy.

Claims

1. A method for calculating the distance between blade tips of a twin-rotor blades based on an aerodynamic interference model, characterized in that: The method comprises: Step 1: Establish the rotor / fuselage coupling dynamics theoretical model δ∏; Step 2: According to the rotor / fuselage coupling dynamics theoretical model δ∏, complete the whole aircraft balance under the corresponding flight strategy and calculate the corresponding hub load; Step 3: Construct an aerodynamic interference model and calculate the unsteady aerodynamic force after the rotor is trimmed based on the aerodynamic interference model according to the hub load; Step 4: Based on the unsteady aerodynamic force, the rotor tip response is solved by the periodic dynamic equation of the rotor, and the blade tip spacing is calculated in combination with the azimuth angle.

2. The method according to claim 1, characterized in that: Step 1 includes: Step 11: Establish system strain Among them, U b1 is the strain energy of the lower rotor blade, U b2 is the strain energy of the upper rotor blade, U F is the fuselage strain energy; Step 12: Build system momentum Among them, T b1 The kinetic energy of a single blade of the lower rotor, T b2 is the kinetic energy of the upper rotor blade, T F is the kinetic energy of the fuselage; Step 13: Establish system external force virtual work Among them, δW b1 Virtual work of external force on single blade of lower rotor, δW b2 is the virtual work of the external force of the upper rotor blade, W F It is the virtual work of the external force on the fuselage; Step 14: Construct the rotor / fuselage coupling dynamics theoretical model based on the system strain energy δU, system kinetic energy δT and system external force virtual work δW:

3. The method according to claim 1, characterized in that Step 2 includes: Step 21: Based on the rotor / fuselage coupling dynamics theoretical model δ∏, perform full-aircraft trim calculation to obtain a full-aircraft trim result; Step 22: According to the whole aircraft balancing result, calculate the hub load under the corresponding flight strategy; Step 23: Based on the corresponding hub load, perform the next step of rotor trim calculation.

4. The method according to claim 3, characterized in that The trim cycle of the whole aircraft trim and rotor trim adopts Newton-Raphson iteration. During the iteration process, the periodic response of the rotor and fuselage is solved until the trim variables meet the trim conditions.

5. The method according to claim 1, characterized in that Step 3 includes: Step 31: Use the free wake model to reflect the wake distortion caused by non-uniform induced velocity and construct an aerodynamic interference model Step 32: Using the Biot-Saffar law, the induced velocity is solved to obtain the induced velocity of the vortex element at any point in space; Step 33: Calculate the unsteady aerodynamic force based on the induced velocity using the ONERA model.

6. The method according to claim 5, characterized in that The aerodynamic interference model is: Among them, r b represents the position vector at the radial station r on the blade, μ is the vector of free velocity, ψ is the azimuth, and q * (ψ) is the induced velocity at azimuth angle ψ, is the vortex age change value, The tail distortion.

7. The method according to claim 5, characterized in that Step 32 includes: Using the formula Calculate the induced velocity, where is the induced velocity, Γ is the vortex element circulation, is the vortex element vector, l is the distance from the induced velocity point to the vortex element distance.

8. The method according to claim 5, characterized in that Step 33 includes: Using the formula Calculation, where dF is the unsteady aerodynamic force of the blade unit, Cz1 ​​represents the lift coefficient of the airfoil without considering dynamic stall, Cz2 represents the correction term for the lift coefficient due to dynamic stall, and dL is the length of the blade unit.

9. The method according to claim 1, characterized in that: Step 4 includes: Step 41: Based on a numerical method, the rotor / fuselage coupling dynamics theoretical model δ∏ is solved to obtain the blade tip response; Step 42: Convert the blade tip response to a reference rotor azimuth; Step 43: Calculate the corresponding blade tip spacing based on the reference rotor azimuth angle.

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