A method for designing a horizontal tail of a helicopter for reducing the influence of aerodynamic interference

Abstract

The application provides a helicopter tail design method for reducing the influence of aerodynamic interference, and the method comprises the following steps: step 1, a helicopter is provided with an upper tail and a lower tail, and reference is made to the original reference machine parameters; step 2, the initial area of the upper tail and the lower tail is S / 2, the initial span of the upper tail and the lower tail is L, the initial chord length of the upper tail and the lower tail is B / 2, and the initial height difference of the upper tail and the lower tail is B; step 3, a rotor / tail interference calculation model of a design helicopter is established, the rotor / tail interference flow field of the design helicopter is calculated and analyzed, and the rotor wake downwash angle γ of the original reference machine tail position under a strong interference state is obtained; the angle between the line connecting the 1 / 4 chord points of the upper tail and the lower tail and the horizontal plane is equal to the rotor wake downwash angle γ; and step 5, a CFD method combined with a momentum source model and an optimization method based on a Kr i gi ng model are used to perform parameter optimization to obtain the final installation angle, the final span and the final height difference of the upper tail and the lower tail.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of helicopter aerodynamic design, and particularly relates to a helicopter tail design method. BACKGROUND

[0002] The helicopter tail is one of the main aerodynamic components of the helicopter, which plays a role in improving the longitudinal operability and stability of the helicopter. When the helicopter is flying forward, the rotor wake hits the tail, causing the load of the tail to suddenly change, which will cause a sudden change in the pitch moment of the helicopter, adversely affecting the operation of the helicopter. Due to the increase in the rotor disc load of the modern helicopter and the increasingly compact fuselage structure, the rotor / tail interference problem is more prominent, so the rotor / tail interference problem needs to be considered in the design of the tail.

[0003] In the conventional helicopter tail design method, the rotor downwash coefficient at the tail is calculated by engineering method, and the aerodynamic interference is considered by optimizing the arrangement position and other parameters of the tail. There are three conventional tail layouts, one is the front tail, such as "dolphin", the second is the rear down tail, such as AH-64, and the third is the high tail, such as RAH-66. The tail arrangement position of the high tail is far away from the rotor, which can avoid the rotor wake hitting the tail at low speed forward flight, but the rotor wake will still hit the tail at a larger forward ratio, causing strong aerodynamic interference. The tail of a small number of helicopters is movable, such as UH-60A, the tail installation angle of which is adjusted through a feedback system, which can improve the performance of the tail.

[0004] The conventional tail design method has the following disadvantages: 1. The optimization of the tail arrangement parameters cannot fundamentally avoid the occurrence of the tail load mutation; 2. The movable tail has a complex structure, is heavy and has high cost.

[0005] The article "Suppression Mechanism of Double-layer Tail on Rotor / Tail Interference" in Helicopter Technology, No. 4, 2021, Article No. 1673-1220(2021)04-001-06, preliminarily studies the suppression mechanism of the double-layer tail on the rotor / tail interference. According to the flow field analysis, the suppression mechanism is preliminarily given: the upper and lower double-layer design of the double-layer tail reduces the chord length of the single-layer tail, thereby reducing the interference load caused by the rotor wake hitting; in the small forward ratio state, the shielding effect of the upper tail weakens the impact interference of the rotor wake on the lower tail, and the rotor / tail interference is suppressed. SUMMARY

[0006] The application provides a helicopter tail design method for reducing the influence of aerodynamic interference, which can be used for the design of the rear down tail of the helicopter, can avoid the occurrence of the tail load mutation caused by the rotor interference, and can prevent the pitch moment mutation of the helicopter at low speed flight.

[0007] Technical solution: 1. A helicopter tail design method for reducing the influence of aerodynamic interference, the method comprising:

[0008] Step 1: The helicopter is provided with an upper tail and a lower tail, and the original tail area S, tail span L, tail chord B, horizontal distance W from the tail to the rotor hub, and vertical distance H from the tail to the rotor hub are obtained.

[0009] Step 2: The initial area of the upper tail and the lower tail is S / 2, the initial span of the upper tail and the lower tail is L, the initial chord of the upper tail and the lower tail is B / 2, the initial height difference of the upper tail and the lower tail is B, the horizontal distance from the midpoint of the 1 / 4 chord line connecting the upper tail and the lower tail to the rotor hub is W, and the vertical distance from the midpoint of the 1 / 4 chord line connecting the upper tail and the lower tail to the rotor hub is H.

[0010] Step 3: A rotor / tail interference calculation model of the helicopter is established, and the rotor / tail interference flow field of the designed helicopter is calculated and analyzed to obtain the rotor wake downwash angle γ at the original tail position of the helicopter in a strong interference state; the angle between the 1 / 4 chord line connecting the upper tail and the lower tail and the horizontal plane is equal to the rotor wake downwash angle γ.

[0011] Step 4: Determine the initial installation angle of the upper tail and the lower tail of the helicopter.

[0012] Step 5: Based on the initial area, initial span, initial chord, initial installation angle, and initial height difference of the upper tail and the lower tail, the chord and the midpoint of the 1 / 4 chord line of the upper tail and the lower tail are kept unchanged, and the CFD (Computational Fluid Dynamics) method combined with the momentum source model and the optimization method based on the Kriging model are used to obtain the final installation angle, the final span of the upper tail and the lower tail, and the final height difference of the upper tail and the lower tail.

[0013] Further, step 3 comprises:

[0014] Step 31: Establish a rotor / tail interference calculation model of the helicopter and divide the grid.

[0015] Step 32: Establish a momentum source model of the rotor.

[0016] Step 33: Solve the N-S equation to obtain the variation of the tail load under the interference of the original rotor and tail with the forward ratio;

[0017] Step 34: Solve the N-S equation to obtain the variation of the tail load under the interference of the original rotor and tail with the forward ratio;

[0018] Step 35: Calculate the change rule of the interference load of the original tail with the advance ratio, and determine the strong interference state;

[0019] Step 36: Obtain the downwash angle γ of the rotor wake at the position of the original tail of the original tail in the strong interference state.

[0020] Further, step 4 comprises:

[0021] Step 41: Set the initial installation angle of the upper tail to 0 degrees;

[0022] Step 42: The initial installation angle of the lower tail is 2 times the installation angle α of the original tail.

[0023] Further, step 5 comprises:

[0024] Step 51: Keep the chord length of the upper tail and the lower tail unchanged, determine the optimization parameters as the span length of the upper tail, the span length of the lower tail, the installation angle of the lower tail, the installation angle of the upper tail, and the height difference between the upper tail and the lower tail, and determine the optimization target as the interference load in the strong interference state;

[0025] Step 52: Sample the optimization variables using the Latin hypercube sampling method to obtain a sample space, and obtain the double-layer tail interference load in the strong interference state corresponding to the sample by using the CFD method combined with the momentum source model;

[0026] Step 53: Establish an approximate response model of the optimization variables and the optimization target by using the Kriging model through the sampling point data;

[0027] Step 54: Take the minimum upper tail and lower tail interference load in the strong interference state as the optimization target, and use the genetic algorithm to find multiple optimization schemes for the approximate model established by the Kriging model;

[0028] Step 55: Among the found optimization schemes, comprehensively consider that the control efficiency of the double-layer tail is similar to that of the original tail and the interference load in the strong interference state is smaller, and determine the final optimization scheme.

[0029] Further, the tail installation angle ranges from -10° to 2°;

[0030] The ratio of the tail area to the rotor disc area ranges from 0.002 to 0.025.

[0031] Further, the ratio of the distance from the tail to the rotor hub to the rotor radius is 0.6-1.4.

[0032] Further, the span length of the upper tail and the lower tail ranges from 0.5L to 1.5L.

[0033] Further, the height difference between the upper tail and the lower tail ranges from 0 to 4B.

[0034] In summary, the application provides a helicopter tail design method for reducing the influence of aerodynamic interference, which analyzes the rotor / tail interference mechanism by numerical simulation of helicopter flight, and establishes a helicopter tail design method for reducing the influence of aerodynamic interference. This method can design a helicopter double-layer tail that reduces the influence of rotor interference. The double-layer tail is arranged as shown in Figure 1 The tail design can avoid the occurrence of tail load mutation caused by rotor interference and prevent the pitch moment mutation of the helicopter during low-speed flight. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 A structure diagram of a helicopter tail for reducing the influence of aerodynamic interference is provided in the application.

[0036] Figure 2 A diagram of a double-layer tail 1 / 4 line angle equal to the rotor wake downwash angle is provided in the application.

[0037] Figure 3 A diagram of the variation of tail load with forward ratio is provided in the application.

[0038] Wherein: 1-upper tail, 2-lower tail. DETAILED DESCRIPTION

[0039] The core idea of the application is as follows: first, refer to the original machine with good longitudinal control and stability to select the tail area and other parameters, and preliminarily design the upper and lower tail area and other parameters according to the double-layer tail interference suppression mechanism; then, use the CFD method combined with the momentum source model to calculate and analyze the rotor / tail interference flow field, and determine the 1 / 4 chord point line angle of the upper and lower layer tails according to the wake downwash angle; then, use the engineering experience method to adjust the initial installation angle of the upper and lower layer tails under the premise of ensuring the control efficiency; then, use the CFD method combined with the momentum source model and the optimization method based on the Kriging model to optimize the parameters to obtain the final installation angle, final span length and final height difference of the upper and lower tails.

[0040] As shown in Figure 1 The application provides a helicopter tail design method for reducing the influence of aerodynamic interference, which includes the following design steps:

[0041] Step 1: Set the upper and lower tails of the helicopter to obtain the tail area S, tail span length L, tail chord length B, horizontal distance W from the tail to the hub, and vertical distance H from the tail to the hub of the original machine.

[0042] Step 2: the initial area of the upper and lower horizontal tail is S / 2, the initial span of the upper and lower horizontal tail is L, the initial chord length of the upper and lower horizontal tail is B / 2, the initial height difference of the upper and lower horizontal tail is B, the horizontal distance from the midpoint of the 1 / 4 chord line of the upper and lower horizontal tail to the center of the paddle is W, and the vertical distance from the midpoint of the 1 / 4 chord line of the upper and lower horizontal tail to the center of the paddle is H;

[0043] It should be noted that the total area of the horizontal tail (including the span, chord length), the initial installation angle and the installation position are selected according to the original machine with good longitudinal maneuverability and stability. Since the upper horizontal tail needs to shield the rotor wake, the areas of the upper and lower horizontal tails are equal, each being half of the total area of the horizontal tail, the span of the upper and lower horizontal tails is the same as that of the original machine, and the chord length of the upper and lower horizontal tails is half of that of the original machine.

[0044] Step 3: a rotor / horizontal tail interference calculation model of the designed helicopter is established, the rotor / horizontal tail interference flow field of the designed helicopter is calculated and analyzed, and the rotor wake downwash angle γ at the position of the horizontal tail of the original machine under the strong interference state is obtained; the angle between the line connecting the 1 / 4 chord points of the upper and lower horizontal tails and the horizontal plane is equal to the rotor wake downwash angle γ;

[0045] Specifically, step 3 includes:

[0046] Step 31: an original machine rotor / horizontal tail interference calculation model is established, and a grid is divided;

[0047] The present application establishes a calculation model including a rotor and an original machine horizontal tail and a calculation model including only an original machine horizontal tail, and the grid near the position of the real rotor is encrypted when the momentum source model is used instead of the real rotor.

[0048] Step 32: a momentum source model of the rotor is established;

[0049] According to the real rotor blade profile parameters (such as the number of blades, diameter, chord length and airfoil arrangement, etc.) and the airfoil performance parameter table, the momentum source model of the rotor is established, that is, the rotating blades are equivalent to the action disc through the momentum source model, and the influence of the rotor blades on the flow field is simulated.

[0050] Step 33: according to the original machine rotor / horizontal tail interference calculation model and the momentum source model, the N-S equation is solved, and the variation law of the horizontal tail load under the interference of the original machine rotor and the horizontal tail with the forward ratio is obtained;

[0051] Wherein, the space is discretized by using the finite volume method when calculating the N-S equation, the five-step Runge-Kutta format is adopted for time discretization, the gradient method selects the Green Gauss method, the turbulence model selects the SA model, the wall boundary condition is the non-slip wall, and the far field boundary condition is the pressure far field. The Mach number of the pressure far field is changed to simulate different forward ratios.

[0052] The rotor / fin interference flow field of the original prototype helicopter at different advance ratios is calculated under the same rotor tension coefficient, and the balancing method is Newton iteration to obtain the change rule of fin load with advance ratio.

[0053] Step 34: solving N-S equation to obtain the change rule of fin load without rotor interference of the original prototype helicopter with advance ratio;

[0054] The space is discretized by finite volume method in N-S equation calculation, five-step Runge-Kutta format is adopted for time discretization, Green Gauss method is selected for gradient method, SA model is selected for turbulence model, and no-slip wall is selected for wall boundary condition, and pressure far field is selected for far field boundary condition. The Mach number of the pressure far field is changed to simulate different advance ratios, and the change rule of fin load without rotor interference with advance ratio is obtained.

[0055] Step 35: calculating the change rule of interference load of the fin of the original prototype helicopter with advance ratio to determine the strong interference state.

[0056] Under the same advance ratio, the change rule of interference load of the fin of the original prototype helicopter with advance ratio is obtained by subtracting the fin load without rotor interference obtained in step 34 from the fin load under rotor interference obtained in step 33, wherein the advance ratio state with the maximum fin load is the strong interference state of the rotor / fin of the original prototype helicopter.

[0057] Step 36: obtaining the rotor wake downwash angle γ at the position of the fin of the original prototype helicopter under the strong interference state.

[0058] The streamlines of the symmetric section of the fuselage under the strong interference state are obtained by processing the flow field, and the angle between the streamlines at the position of the fin of the original prototype helicopter and the horizontal plane is the rotor wake downwash angle at the position of the fin of the original prototype helicopter under the strong interference state.

[0059] The CFD method combined with the momentum source model is adopted to equivalent the rotating blades to action discs, the force of the action discs on the flow field is used to simulate the influence of the rotor blades on the flow field, so as to establish the rotor / fin interference calculation model of the designed helicopter, then the rotor / fin interference flow field of the designed helicopter is calculated and analyzed to obtain the rotor wake downwash angle at the position of the fin of the original prototype helicopter under the strong interference state, so that the angle between the connecting line of the 1 / 4 chord points of the upper and lower fins and the horizontal plane is equal to the rotor wake downwash angle at the position of the fin of the original prototype helicopter under the strong interference state, as shown in Figure 2 so that the upper fin can well shield the rotor wake and prevent the rotor wake from hitting the lower fin;

[0060] Step 4: determining the initial installation angle of the upper fin and the lower fin of the helicopter;

[0061] Specifically, step 4 includes:

[0062] Step 41: Set the initial installation angle of the upper horizontal tail to 0 degree;

[0063] Step 42: The initial installation angle of the lower horizontal tail is 2 times the original horizontal tail installation angle a of the original prototype machine.

[0064] The installation angles of the upper and lower horizontal tails are determined by using engineering experience method under the premise of ensuring the control effectiveness. The upper horizontal tail mainly plays a role in shielding the rotor wake. The initial installation angle of the upper horizontal tail is set to 0 degree. Assuming that the distances from the upper and lower horizontal tails to the hub center are equal to the distance from the horizontal tail of the original prototype machine to the hub center, the installation angle of the lower horizontal tail is determined by using the following formula:

[0065] Step 5: According to the initial areas, initial spans, initial chord lengths, initial installation angles of the upper and lower horizontal tails, and the initial height difference between the upper and lower horizontal tails, the chord lengths and the midpoint positions of the 1 / 4 chord lines of the upper and lower horizontal tails are kept unchanged. The CFD method combined with the momentum source model and the optimization method based on the Kriging model are used to perform parameter optimization to obtain the final installation angles, final spans of the upper and lower horizontal tails, and the final height difference between the upper and lower horizontal tails.

[0066] Specifically, step 5 includes:

[0067] Step 51: Keep the chord lengths of the upper and lower horizontal tails unchanged. The optimization parameters are determined to be the span of the upper horizontal tail, the span of the lower horizontal tail, the installation angle of the lower horizontal tail, the installation angle of the upper horizontal tail, and the height difference between the upper and lower horizontal tails. The optimization target is the interference load in the strong interference state.

[0068] Step 52: The Latin hypercube sampling method is used to sample the optimization variables to obtain a sample space. The CFD method combined with the momentum source model is used to obtain the double-layer horizontal tail interference load in the strong interference state corresponding to the samples.

[0069] Step 53: The Kriging model is used to establish an approximate response model of the optimization variables and the optimization target through the sample point data.

[0070] Step 54: The genetic algorithm is used to find multiple optimization schemes for the approximate model established by the Kriging model, with the minimum upper and lower horizontal tail interference loads in the strong interference state as the optimization target.

[0071] Step 55: Among the optimization schemes found, the last optimization scheme is determined by comprehensively considering that the control effectiveness of the double-layer horizontal tail is similar to that of the original prototype machine and the interference load in the strong interference state is relatively small.

[0072] Specifically, the horizontal tail installation angle range is -10° to 2°

[0073] The ratio range of the horizontal tail area to the rotor disc area is 0.002-0.025.

[0074] The range of the span length of the upper and lower flat tail: 0.5L-1.5L;

[0075] The range of the height difference of the upper and lower flat tail: 0-4B;

[0076] The ratio of the distance from the flat tail to the paddle core to the radius of the rotor: 0.6-1.4.

[0077] It should be noted that the CFD method combined with the momentum source model is used to obtain the final flat tail design scheme by optimizing the parameters based on the initial design of the double-layer flat tail.

[0078] In summary, the application provides a helicopter flat tail design method for reducing the influence of aerodynamic interference, which can design a helicopter double-layer flat tail for reducing the influence of rotor interference, and has certain application value for the aerodynamic design and development of the helicopter flat tail. Figure 3 For the load comparison of the double-layer flat tail designed by the method and the original flat tail of the helicopter, under the condition of small forward speed ratio, the load of the original flat tail of the helicopter suddenly increases due to the interference of the rotor wake, which will bring adverse effects on the control of the helicopter, and the load of the double-layer flat tail designed by the method does not change suddenly, which shows that the flat tail designed by the method can reduce the interference of the rotor on the flat tail.

Claims

1. A method for designing a horizontal tail of a helicopter for reducing the effect of aerodynamic interference, characterized in that, The method comprises: Step 1: the helicopter is provided with an upper horizontal tail and a lower horizontal tail, and the original horizontal tail area S, the horizontal tail span L, the horizontal tail chord B, the horizontal tail to the rotor center horizontal distance W, and the horizontal tail to the rotor center vertical distance H are obtained; Step 2: the initial area of the upper horizontal tail and the lower horizontal tail is S / 2, the initial span of the upper horizontal tail and the lower horizontal tail is L, the initial chord of the upper horizontal tail and the lower horizontal tail is B / 2, the initial height difference of the upper horizontal tail and the lower horizontal tail is B, the midpoint of the 1 / 4 chord line of the upper horizontal tail and the lower horizontal tail to the rotor center horizontal distance is W, and the midpoint of the 1 / 4 chord line of the upper horizontal tail and the lower horizontal tail to the rotor center vertical distance is H; Step 3: a rotor / horizontal tail interference calculation model of the helicopter is established, the rotor / horizontal tail interference flow field of the designed helicopter is calculated and analyzed, and the rotor wake downwash angle γ at the original horizontal tail position under the strong interference state is obtained; the angle between the 1 / 4 chord line of the upper horizontal tail and the lower horizontal tail and the horizontal plane is equal to the rotor wake downwash angle γ; Step 4: the initial installation angle of the upper horizontal tail and the lower horizontal tail of the helicopter is determined; Step 5: according to the initial area, the initial span, the initial chord, the initial installation angle of the upper horizontal tail and the lower horizontal tail, and the initial height difference of the upper horizontal tail and the lower horizontal tail, the chord and the midpoint of the 1 / 4 chord line of the upper horizontal tail and the lower horizontal tail are kept unchanged, the CFD (Computational Fluid Dynamics) method combined with a momentum source model and an optimization method based on a Kriging model are used to perform parameter optimization to obtain the final installation angle, the final span of the upper horizontal tail and the lower horizontal tail, and the final height difference of the upper horizontal tail and the lower horizontal tail; The horizontal tail installation angle ranges from -10° to 2°.

2. The method of designing a tail for a helicopter according to claim 1, wherein, Step 3 comprises: Step 31: a rotor / horizontal tail interference calculation model of the helicopter is established, and a grid is divided; Step 32: a momentum source model of the rotor is established; Step 33: N-S equations are solved to obtain the change rule of the horizontal tail load under the rotor / horizontal tail interference of the original prototype with respect to the forward ratio; Step 34: N-S equations are solved to obtain the change rule of the horizontal tail load under the horizontal tail without rotor interference of the original prototype with respect to the forward ratio; Step 35: the change rule of the interference load of the original prototype horizontal tail with respect to the forward ratio is calculated, and the strong interference state is determined; Step 36: the rotor wake downwash angle γ at the original horizontal tail position under the strong interference state is obtained.

3. The method of claim 1, wherein, Step 4 comprises: Step 41: the initial installation angle of the upper horizontal tail is set to 0°; Step 42: the initial installation angle of the lower horizontal tail is 2 times the original horizontal tail installation angle α.

4. The method of claim 1, wherein, Step 5 comprises: Step 51: the chord of the upper horizontal tail and the lower horizontal tail is kept unchanged, the optimization parameters are determined to be the upper horizontal tail span, the lower horizontal tail span, the lower horizontal tail installation angle, the upper horizontal tail installation angle, and the height difference of the upper horizontal tail and the lower horizontal tail, and the optimization target is determined to be the interference load under the strong interference state; Step 52: a Latin hypercube sampling method is used to sample the optimization variables to obtain a sample space, and a CFD method combined with a momentum source model is used to obtain the double-layer horizontal tail interference load under the strong interference state corresponding to the sample; Step 53: an approximate response model of the optimization variables and the optimization target is established by using a Kriging model through the sampling point data. Step 54: Genetic algorithm is used to search for multiple optimization schemes for the approximate model established by Kriging model, with the minimum interference load of the upper and lower horizontal tails in the strong interference state as the optimization goal; Step 55: The final optimization scheme is determined by comprehensively considering that the control efficiency of the double-layer horizontal tail is similar to that of the original aircraft and the interference load in the strong interference state is small.

5. The helicopter tail design method according to claim 1, wherein the ratio of the tail area to the rotor disc area is in the range of 0.002-0.

025.

6. The helicopter tail design method according to claim 1, wherein the ratio of the tail-to-rotor hub distance to the rotor radius is in the range of 0.6-1.

4.

7. The helicopter tail design method according to claim 1, wherein the span of the upper and lower horizontal tails is in the range of 0.5L-1.5L.

8. The helicopter tail design method according to claim 1, wherein the height difference between the upper and lower horizontal tails is in the range of 0-4B. ​ ​ ​ ​ ​

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