Helicopter blade surface distributed jet active flow control analysis method

Abstract

The invention provides a helicopter blade surface distributed jet flow active flow control analysis method, which comprises the following steps of: determining a hole opening position and a jet flow deflection angle of a jet flow hole on the upper surface of a helicopter blade based on the position of an airflow separation point; performing grid division on the blade hexahedron containing the jet holes to obtain a blade grid; carrying out background grid division; the blade grids are loaded to the background grids, a combined calculation model is formed, and the total pitch of the blade grids is adjusted; defining a jet boundary of the blade grid and a boundary condition of a background grid; according to the jet boundary and the boundary condition, calculating the combined calculation model to obtain aerodynamic characteristics; the jet holes are formed in the surfaces of the reference blades to load the jet boundaries, so that airflow analysis during high-attack-angle flight can be reduced, airflow separation can be reduced, airflow adhesiveness can be enhanced, stall can be delayed, and aerodynamic performance during high-pitch flight can be improved.

Description

Technical Field

[0001] The present application belongs to the technical field of rotor active flow control, and in particular relates to an analysis method for distributed jet active flow control on the surface of a helicopter blade. Background Art

[0002] During the operation of a helicopter rotor, as the pitch gradually increases, the thrust and torque also increase, and the rotor's aerodynamic performance also improves. At a certain stage, the thrust reaches its peak and the performance reaches its optimal level. Further increasing the pitch causes the airflow on the blade surface to separate, and unsteady separation vortices appear on the blade surface, causing the rotor to stall, resulting in a sharp drop in lift and hovering efficiency. At this point, helicopter control becomes extremely important. Once the rotor enters a high angle of attack stall, power increases, lift decreases, and the helicopter instantly enters a descent state, which is extremely dangerous. Conventional rotors have a narrow control range, and rotors without any flow control cannot maximize their performance.

[0003] To slow airflow separation on the blade surface, a jet controller is installed inside the blade to generate a jet. This inducing the airflow in the separation zone to adhere to the blade surface, accelerating the flow on the upper surface and reducing the pressure on the upper surface. This increases the pressure difference between the upper and lower surfaces, increasing lift, minimizing airflow separation, and reducing drag, thereby improving rotor performance. The jet can, to a certain extent, reduce the extent of the separation zone, improve the flow on the airfoil surface, and enhance stall performance.

[0004] At present, the main measures to improve rotor performance include airfoil optimization, rotor aerodynamic layout optimization, and jet change of blade wing profile airflow separation. The former has limited room for performance improvement, and the latter belongs to new technology exploration. In order to study the influence characteristics of jet active flow control on rotor, an analysis method of distributed jet active flow control on helicopter blade surface is proposed. Summary of the Invention

[0005] Purpose of the invention: To analyze the rotor jet scheme through numerical methods, guide the design of rotor distributed jet, and provide design direction for improving rotor stall performance.

[0006] The present application provides a method for analyzing active flow control of a distributed jet on a helicopter blade surface, the method comprising:

[0007] Based on the position of the airflow separation point, the opening position of the jet hole and the jet deflection angle are determined on the upper surface of the helicopter blade;

[0008] Mesh the blade hexahedron containing the jet hole to obtain the blade mesh;

[0009] Perform background grid division;

[0010] Loading the blade grid into the background grid to form a combined calculation model, and adjusting the collective pitch of the blade grid;

[0011] defining the boundary conditions of the jet boundary of the blade grid and the background grid;

[0012] The combined calculation model is calculated according to the jet boundary and the boundary condition to obtain aerodynamic characteristics.

[0013] Preferably, before determining the opening position and jet deflection angle of the jet hole on the upper surface of the helicopter blade based on the position of the airflow separation point, the method further includes:

[0014] Based on the airfoil and the stall angle of attack, the location of the airflow separation point on the airfoil surface is determined.

[0015] Preferably, the meshing of the blade hexahedron containing the jet holes comprises:

[0016] Divide the blade into 6 equal sections along the span direction, and then perform o-grid division;

[0017] Cut each blade section and divide the jet hole position on the upper surface of the blade into blocks in the chord direction and span direction.

[0018] The structure block of each jet hole is divided into grid blocks. The division process is controlled by nodes to make the transition uniform, and the blade grid configuration block is completed.

[0019] The boundary layer mesh of the blade surface is divided, the jet hole mesh is refined, and the surrounding meshes are evenly transitioned to complete the blade mesh division.

[0020] Preferably, the background grid division includes:

[0021] A background grid area is established with a characteristic size 10 times that of the blade, and the background grid is initialized for meshing;

[0022] The mesh in the area nested with the blades is adaptively encrypted so that the mesh scale of the encrypted area is close to the mesh scale of the blade outer boundary.

[0023] Preferably, the densified area is a cylindrical area 0.5R above and below the blade and with a radius of 1.2R.

[0024] Preferably, the step of loading the blade grid into the background grid to form a combined calculation model and adjusting the collective pitch of the blade grid comprises:

[0025] Read the background mesh, then use the Fluent software to rotate the blade mesh BLADE1 with the jet hole 180° around the Z axis and save it as BLADE2. Then, use the Fluent software to attach the original blade mesh BLADE1 and the copied blade mesh BLADE2 to the background mesh, forming a calculation model of the background mesh and the two blade meshes.

[0026] The outer boundary of the blade mesh is set to the overlapped mesh boundary condition, the blade surface is set to the wall boundary condition, the turbulence model adopts the K-ωSST common engineering model, and the jet boundary condition adopts the velocity inlet to facilitate the decomposition in different directions;

[0027] Define blade pitch torsion. The rotor blade undergoes a compound motion during operation, with rotation accompanied by pitch torsion, flapping, and shimmying. In hovering, the main motions are rotation and pitch variation. The blade's initial mesh is based on a 0° collective pitch. Through secondary development, the target collective pitch can be achieved during rotation, or multiple collective pitches can be achieved in a stepped manner using if statements. The ZONE_MOTION function is used to implement real-time pitch variation.

[0028] axis[0]=cos(ψ1+ψ0)

[0029] axis[1]=sin(ψ1+ψ0)

[0030] ψ1=ω·t

[0031]

[0032] t>n·Δt,θ(t)=0

[0033] Where: the blade rotates around the z-axis, axis[0] and axis[1] are the projections of the pitch axis of each blade on the x-axis and y-axis of the coordinate system respectively, ψ0 is the initialization azimuth angle of each blade, ω is the rotor speed, and the rotor rotation motion is realized by CG_MOTION, ψ1 is the real-time rotation azimuth angle of the blade, the variable θ(t) is the pitch angular velocity, which is a piecewise function, Δt is the time step defined as the time for the blade to rotate 1° azimuth, n is the number of calculation steps, n·Δt represents the total pitch θ change within a certain period of time, and t is the current time;

[0034] After the collective pitch reaches the target value, the θ(t) rotor does not change pitch.

[0035] Preferably, the boundary conditions defining the jet boundary of the blade grid and the background grid include:

[0036] Define the distributed jet on the blade surface. Since the direction of the jet changes in real time with the blade during its rotational and pitch-varying motion, secondary development of the jet boundary ensures that the direction of the jet generated by each jet hole keeps following the blade's motion. The PROFILE function is used to define the jet boundary.

[0037] V jet_x =V jet ·cos(α)·cos(ωt)

[0038] V jet_y =V jet ·cos(α)·sin(ωt)

[0039] V jet_y =V jet sin(α)

[0040] α=β-θ

[0041] Where: V jet is the jet velocity, V jet_x 、V jet_y 、V jet_z are the components of the jet on the x-axis, y-axis, and z-axis, respectively; β is defined as the angle between the jet deflection angle and the local chord direction of the blade; θ is the local total distance of the blade jet position; and α is the angle between the jet and the rotation plane.

[0042] Set the background grid side and above the rotor as pressure inlet boundary conditions, and set the bottom of the rotor as pressure outlet boundary conditions. Read the user-defined function developed in the secondary development and compile it. Then, mount the PROFILE program on the jet boundary.

[0043] Preferably, the calculating of the combined calculation model according to the jet boundary and the boundary condition to obtain aerodynamic characteristics includes:

[0044] Calculate the set combined calculation model containing the jet boundary, initialize the far field calculation, set the time step and the inner iteration time step, and directly calculate until the rotor aerodynamic force converges at the target collective distance;

[0045] In order to analyze the influence of the jet on the aerodynamic characteristics of the blade, the benchmark rotor model must also be calculated and analyzed. The motion settings of the blade in the benchmark rotor model calculation are the same as above, and the jet boundary on the blade surface is changed to the wall boundary. The other boundary conditions are set to the same. The above operations can be repeated until the aerodynamic force converges at the target collective distance.

[0046] Beneficial technical effects of this application:

[0047] The present application provides an active flow control analysis method based on a distributed jet on the surface of a helicopter blade. By opening jet holes on the surface of a reference blade to load the jet boundary, the airflow analysis during high angle of attack flight can be reduced, airflow separation can be reduced, airflow adhesion can be enhanced, stall can be delayed, and aerodynamic performance during high pitch flight can be improved. The application of this calculation method can improve the visualization and accuracy of the flow field, predict the effect of the jet on the rotor stall, and provide guidance for the active jet flow control of the blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of rotor distributed jet calculation provided by an embodiment of the present invention;

[0049] Figure 2 It is a NACA23012 two-dimensional airfoil jet grid provided by an embodiment of the present invention;

[0050] Figure 3 This is a lift comparison diagram of a NACA23012 two-dimensional airfoil at different jet positions at a 20° angle of attack provided by an embodiment of the present invention;

[0051] Figure 4 This is a comparison chart of the drag coefficients of a NACA23012 two-dimensional airfoil with a 20° angle of attack and a non-jet, provided by an embodiment of the present invention;

[0052] Figure 5 This is a comparison chart of the lift coefficients of a NACA23012 two-dimensional airfoil with a 20° angle of attack and without a jet, provided by an embodiment of the present invention;

[0053] Figure 6 This is a comparison chart of the lift-to-drag ratio of a NACA23012 two-dimensional airfoil with a 20° angle of attack and without a jet, provided by an embodiment of the present invention;

[0054] Figure 7 1 is an aerodynamic diagram of a distributed jet rotor model provided by an embodiment of the present invention;

[0055] Figure 8 This is a grid block structure diagram of a rotor structure provided by an embodiment of the present invention;

[0056] Figure 9 is a jet grid diagram on the blade surface provided by an embodiment of the present invention;

[0057] Figure 10 is a boundary layer grid diagram of a blade surface provided by an embodiment of the present invention;

[0058] Figure 11 This is a diagram showing the relationship between the jet deflection angle and the total pitch based on the three-dimensional blade surface provided by an embodiment of the present invention;

[0059] Figure 12This is a flow field comparison diagram based on the presence or absence of jets for different airfoil sections at a 20° total pitch angle in a three-dimensional blade hovering state, provided by an embodiment of the present invention;

[0060] Figure 13 This is a comparison chart of surface pressure coefficients with and without jets based on the same wing section 0.67R at a 20° total pitch angle in a three-dimensional blade hovering state provided by an embodiment of the present invention.

[0061] Figure 14 This is a comparison diagram of lift force distribution between a jet rotor blade and a reference rotor blade in a three-dimensional blade hovering state at a collective pitch angle of 20°-25°, provided by an embodiment of the present invention;

[0062] Figure 15 This is a comparison diagram of torque distribution on a jet rotor blade and a reference rotor blade based on a 20°-25° collective pitch angle in a three-dimensional blade hovering state provided by an embodiment of the present invention;

[0063] Figure 16 This is a comparison chart of the hovering efficiency of a jet rotor and a reference rotor based on a 20°-25° total pitch angle in a three-dimensional blade hovering state provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0064] This application provides a rotor distributed jet calculation method, including two-dimensional airfoil jet parametric analysis, structural grid processing of three-dimensional jet blades according to jet hole position and jet deflection scheme, and then using a nested grid method to calculate the rotor jet and master the method of improving the aerodynamic performance of the rotor in the stall state.

[0065] In the examples of this application, please refer to Figures 1-16 , the solution provided by the present invention is described in further detail below.

[0066] Based on the NACA23012 airfoil, conventional rectangular layout, and straight, non-twisted blade model, in order to reduce the amount of grid calculation, a blade section was taken for analysis. The blade chord length C was 124mm and the radius R was 450mm for jet influence analysis. The influence mechanism of the jet on the aerodynamic characteristics was verified through numerical simulation.

[0067] First, the influence of the jet hole position and the jet deflection angle is analyzed. Different airfoils, different stall angles of attack, and the positions of the airflow separation points on the airfoil surface are different. Therefore, different opening positions have different effects on the flow field. Taking the NACA23012 airfoil at a stall angle of attack of 20° as an example, 2mm jet holes are opened at 10%C, 15%C, and 20%C on the upper surface of the airfoil. By analyzing the NACA23012 two-dimensional airfoil, the jet contribution of 10%C to 15%C is optimal. At the same time, the lift is maximum when the jet deflection angle is 2.5° with the incoming flow direction. Figure 7 , after the jet is loaded at 15% C, the lift is increased by about one-fold. Figure 6 , the resistance is reduced by about half. Figure 5 The lift-to-drag ratio is increased by 3 times. The three-dimensional blades are different from the two-dimensional ones, and the jet will have certain consumption in the span direction.

[0068] Secondly, according to the calculation results of the above two-dimensional airfoil, a jet hole is opened at 15%C on the upper surface of the blade, and the diameter of the jet hole is 2mm. In order to reduce the amount of calculation, the jet holes are distributed at 0.5R~0.7R along the span direction. In order to make the jet effect more obvious, a hole is distributed at an interval of 3mm along the span direction to form a numerical model. Figure 1 .

[0069] Then the blade model with jet holes is meshed, and the blade hexahedron mesh is divided using ICEMCFD. First, the blade is divided into 6 equal sections along the span direction, and then the o-mesh is divided. Next, each blade section is cut, and the jet hole position on the upper surface of the blade is divided into blocks in the chord direction and span direction. Again, the structure block of each jet hole is meshed. The division process is controlled by nodes to make the transition uniform and to make it as orthogonal as possible, and the blade mesh configuration is completed. Figure 2 Finally, the boundary layer mesh is divided on the blade surface (the first layer mesh thickness is 10 -5 C) Figure 4 , the jet hole grid is refined, and the surrounding grids are evenly transitioned to it, so that the overall grid quality is higher than 0.25, and the blade grid division is completed as follows Figure 3 .

[0070] Background grid division: establish a background grid area with a characteristic size 10 times that of the blade, and perform initial grid division on the background grid. Then, perform adaptive grid encryption on the area nested with the blade. The encrypted area is a cylindrical area 0.5R above and below the blade and with a radius of 1.2R. Finally, the grid scale of the encrypted area is close to the grid scale of the outer boundary of the blade.

[0071] The general fluid mechanics software fluent is used to load the external flow field background grid and the blade grid. The outer boundary of the blade is set to the overlapped grid boundary condition. The turbulence model adopts the K-ωSST engineering model, the second-order upwind scheme, and the object surface is the adiabatic wall condition. The jet boundary uses velocity inlet or pressure far field.

[0072] Jet loading, first calculate the original model, after the residual curve converges, load the distributed jet based on its stable flow field, and use the custom function jet boundary

[0073] V jet_x =V jet ·cos(θ+2.5°)·cos(ωt)

[0074] Vjet_y =V jet ·cos(θ+2.5°)·sin(ωt)

[0075] V jet_y =V jet sin(θ+2.5°)

[0076] Forward flight state: pitch angle θ=A·cos(ωt)+B·sin(ωt)+C

[0077] Where: θ is the local angle of attack A, B at the blade jet position, and C is the total pitch. For straight and no-twist conditions, the local angle of attack is consistent with the pitch angle.

[0078] Since the pitch angle of the rotor rotates one circle in the forward flight state, the pitch angles of different azimuths are inconsistent, the wing separation points are also different, and the jet deflection angle has different effects. Therefore, only the jet effect analysis in the hovering state is currently performed. The total pitch angle θ = 20° and the rotor blade tip speed V tip =104.1m / s After the jet is loaded, the jet velocity V jet =208.2m / s Figure 8 The airflow adhesion of the wing section in the jet loading area is better, and the airflow separation on the upper surface is serious when the jet is not loaded. Figure 9 , the negative pressure on the upper wing section increases significantly. Figure 10 , thereby increasing the rotor lift. Calculation results show that lift increased by 17.16%, torque decreased by 7.31%, and hovering efficiency increased by 36.82%.

[0079] The present application provides a calculation method for active flow control based on a distributed jet on the surface of a helicopter blade. By opening jet holes on the surface of a reference blade to load the jet boundary, the airflow analysis during high angle of attack flight can be reduced, airflow separation can be reduced, airflow adhesion can be enhanced, stall can be delayed, and aerodynamic performance during high pitch flight can be improved. The application of this calculation method can improve the visualization and accuracy of the flow field, predict the effect of the jet on the rotor stall, and provide guidance for the active jet flow control of the blade.

[0080] In other embodiments of the present application, the present application provides a method for analyzing distributed jet active flow control on the surface of a helicopter blade, the flow chart of which is as follows: Figure 1 The method comprises the following steps:

[0081] Step 1: Based on the airfoil and stall angle of attack, determine the location of the airflow separation point on the airfoil surface.

[0082] Among them, the influence of the jet hole position and the jet deflection angle is analyzed through the two-dimensional airfoil. Different types of airfoils, different stall angles of attack, and different airflow separation positions on the airfoil surface have different effects on the flow field. Based on the conventional airfoil NACA23012, pointwise software is used to divide the structured grid as follows Figure 2 , when the incoming flow Mach number Ma=0.3, the jet velocity V jet =208m / s, taking the 20° high angle of attack state as an example, 2mm wide jet holes were opened at 10%C, 15%C, and 20%C on the upper surface of the airfoil, and the jet impact was evaluated in turn. The results show that the jet impact at the small angle of attack state is not obvious, and the airfoil drag is even greater with the jet. At the large angle of attack state, the jet at 15%C has the best lift effect on the airfoil. Figure 3 , and delayed the stall characteristics of the airfoil. When the angle between the jet deflection and the incoming flow direction is 2.5°, the lift is the largest. After the jet is set at 15% C, the lift is increased by about one-fold, the drag is reduced by about one-fold, and the maximum lift-to-drag ratio is increased by 3 times. Figure 4-Figure 6 .

[0083] Step 2: Based on the position of the airflow separation point, determine the opening position of the jet hole and the jet deflection angle on the upper surface of the helicopter blade.

[0084] Among them, the rotor surface distributed jet modeling is carried out. Based on the NACA23012 airfoil, conventional rectangular layout, straight non-twisted blade model, in order to reduce the amount of grid calculation, the blade chord length C is taken as 124mm, and the radius R is taken as 450mm to analyze the influence of the distributed jet on the blade surface. Based on the calculation results of the two-dimensional airfoil in step 1, a jet hole is opened at 15%C on the upper surface of the blade, and the jet hole diameter is 2mm. Because only the mechanism research is done, in order to improve the calculation efficiency, the jet holes are distributed at 0.5R~0.7R along the span direction. In order to make the jet effect more obvious, a jet hole is distributed at intervals of 3mm along the span direction to form a numerical model such as Figure 7 .

[0085] Step 3: Mesh the blade hexahedron containing the jet hole to obtain a blade mesh.

[0086] Among them, the blade model with jet holes is meshed, and the blade hexahedron mesh is divided by ICEMCFD. First, the blade is divided into 6 equal sections along the span direction, and then the o-mesh is divided. Secondly, each blade section is cut, and the jet hole position on the upper surface of the blade is divided into chord and span directions. The structure block of each jet hole is again divided into o-mesh blocks. The division process is controlled by nodes to make the transition uniform and make it as orthogonal as possible to complete the blade mesh configuration block. Figure 8 Finally, the boundary layer mesh of the blade surface is divided (the first layer mesh thickness is 10-5C) as follows Figure 10, the jet hole grid is refined, and the surrounding grids are evenly transitioned to it, so that the overall grid quality is higher than 0.25, and the blade grid division is completed as follows Figure 9 .

[0087] Step 4: Divide the background grid.

[0088] Among them, a background grid area is established with a characteristic size of 10 times the blade radius, and the background grid is initialized. Then, the grid in the area nested with the blade is adaptively encrypted. The encrypted area is a cylindrical area 0.5R above and below the blade and with a radius of 1.2R. Finally, the grid scale of the encrypted area is close to the grid scale of the blade outer boundary.

[0089] Step 5: Load the blade grid into the background grid to form a combined calculation model, and adjust the collective pitch of the blade grid.

[0090] Fluent software was used to analyze the impact of jet flow on three-dimensional propeller blade performance. First, the background mesh was read in. Then, using Fluent, the blade mesh BLADE1 with the jet hole was rotated 180° around the Z axis and saved as BLADE2. The original blade mesh BLADE1 and the duplicated blade mesh BLADE2 were then attached to the background mesh using Fluent, forming a computational model combining the background mesh and the two blade meshes. The outer boundary of the blade mesh was set to an overlapped mesh boundary condition, and the blade surface was set to a wall boundary condition. The turbulence model used was the commonly used K-ωSST engineering model, and the jet boundary condition used a velocity inlet to facilitate decomposition in different directions.

[0091] Calculations based on the distributed jet rotor model must first define blade pitch torsion. The blades perform a compound motion during rotor operation, with rotation accompanied by pitch torsion, flapping, and shimmying. The main motions of the blades in the hovering state are rotation and pitch variation. In this case, the blades are initially meshed based on a 0° collective pitch. Through secondary development, they achieve the target collective pitch during rotation, or achieve stepped pitch variation with multiple collective pitches through if statements. This improves computational efficiency, and the ZONE_MOTION function is used to implement real-time pitch variation.

[0092] axis[0]=cos(ψ1+ψ0)

[0093] axis[1]=sin(ψ1+ψ0)

[0094] ψ1=ω·t

[0095]

[0096] t>n·Δt,θ(t)=0

[0097] Where: the blade rotates around the z-axis, axis[0] and axis[1] are the projections of each blade pitch axis on the x-axis and y-axis of the coordinate system respectively, ψ0 is the initial azimuth angle of each blade, ω is the rotor speed, and the rotor rotation motion is realized through CG_MOTION, ψ1 is the real-time rotation azimuth angle of the blade, the variable θ(t) is the pitch angular velocity, which is a piecewise function, Δt is the time step defined as the time for the blade to rotate 1° azimuth, n is the number of calculation steps, n·Δt represents the change in the total pitch θ within a certain period of time, t is the current time, and after the total pitch reaches the target value, θ(t) the rotor does not change pitch. The compiled CG_MOTION and ZONE_MOTION programs are mounted on the blade mesh through the Dynamic Mesh module and the Mesh Motion module to realize the rotation and pitch motion of the blade.

[0098] Step 6: Define the boundary conditions of the jet boundary of the blade grid and the background grid.

[0099] Among them, the definition of the distributed jet on the blade surface is carried out. Because the jet direction changes in real time with the blade during the rotational motion and pitch change process, the jet boundary is secondary developed to make the jet direction generated by each jet hole keep running with the blade, and the PROFILE function is used to realize the jet boundary definition.

[0100] V jet_x =V jet ·cos(α)·cos(ωt)

[0101] V jet_y =V jet ·cos(α)·sin(ωt)

[0102] V jet_y =V jet sin(α)

[0103] α=β-θ

[0104] Where: V jet is the jet velocity, V jet_x 、V jet_y 、V jet_z are the components of the jet on the x-axis, y-axis, and z-axis respectively. β is defined as the angle between the jet deflection angle and the local chord direction of the blade (the angle with the radial direction is not considered in this case), θ is the local total distance of the blade jet position, and α is the angle between the jet and the rotating plane. Figure 11

[0105] Finally, the side of the background grid and the top of the rotor are set as pressure inlet boundary conditions, and the bottom of the rotor is set as pressure outlet boundary conditions. The user-defined function of secondary development is read and compiled, and then the PROFILE program is mounted on the jet boundary.

[0106] Step 7: Calculate the combined calculation model according to the jet boundary and the boundary conditions to obtain aerodynamic characteristics.

[0107] The calculation is performed on the combined calculation model containing the jet boundary, the far field is initialized, and the time step and inner iteration time step are set to directly calculate until the rotor aerodynamic force converges and the calculation is completed at the target collective distance. Secondly, in order to analyze the impact of the jet on the aerodynamic characteristics of the blade, the baseline rotor model is also calculated and analyzed. The blade motion settings in the baseline rotor model calculation are the same as above, only the jet boundary on the blade surface is changed to the wall boundary. The other boundary conditions are set the same. The above steps can be repeated until the aerodynamic force converges at the target collective distance.

[0108] The calculated state total pitch angle θ is from 20° to 25°, the rotor speed ω is 110.5rad / s, and the jet speed V jet =208.2m / s, the angle between the jet on the blade surface and the rotating plane is 2.5°. Figure 11 The airflow adhesion of the wing section with the jet loaded is better, and the airflow separation on the upper surface of the wing section is serious without the jet loaded. Figure 12 , the negative pressure on the upper wing section increases significantly. Figure 13 , the pressure difference increases, thereby increasing the lift of the rotor. Figure 14 The lift of the jet loading part is significantly increased, and the jet also has a good effect on the flow field and lift characteristics nearby. The torque of the rotor jet loading part is significantly increased. Figure 15 , but the hovering efficiency increases significantly after the rotor is loaded with jet. Figure 16 Table 1 shows the gains in hovering performance after the rotor is loaded with a jet. The lift is increased by a maximum of 11.6%, the torque is increased by a maximum of 13.16%, and the hovering efficiency is increased by a maximum of 4.63%. Analysis based on the distributed jet numerical method shows that active control of the distributed jet is beneficial to improving the rotor performance in high-angle-of-attack flight conditions.

[0109] Table 1

[0110]

Claims

1. A method for analyzing distributed jet active flow control on helicopter blade surface, characterized in that: The method comprises: Based on the position of the airflow separation point, the opening position of the jet hole and the jet deflection angle are determined on the upper surface of the helicopter blade; Mesh the blade hexahedron containing the jet hole to obtain the blade mesh; Perform background grid division; Loading the blade grid into the background grid to form a combined calculation model, and adjusting the collective pitch of the blade grid; defining the boundary conditions of the jet boundary of the blade grid and the background grid; The combined calculation model is calculated according to the jet boundary and the boundary condition to obtain aerodynamic characteristics.

2. The method according to claim 1, characterized in that Before determining the opening position and jet deflection angle of the jet hole on the upper surface of the helicopter blade based on the position of the airflow separation point, the method further includes: Based on the airfoil and the stall angle of attack, the location of the airflow separation point on the airfoil surface is determined.

3. The method according to claim 1, characterized in that The meshing of the blade hexahedron containing the jet holes comprises: Divide the blade into 6 equal sections along the span direction, and then perform o-grid division; Cut each blade section and divide the jet hole position on the upper surface of the blade into blocks in the chord direction and span direction. The structure block of each jet hole is divided into grid blocks. The division process is controlled by nodes to make the transition uniform, and the blade grid configuration block is completed. The boundary layer mesh of the blade surface is divided, the jet hole mesh is refined, and the surrounding meshes are evenly transitioned to complete the blade mesh division.

4. The method according to claim 1, wherein The background grid division includes: A background grid area is established with a characteristic size 10 times that of the blade, and the background grid is initialized for meshing; The mesh in the area nested with the blades is adaptively encrypted so that the mesh scale of the encrypted area is close to the mesh scale of the blade outer boundary.

5. The method according to claim 4, characterized in that The densified area is a cylindrical area 0.5R above and below the blade and with a radius of 1.2R.

6. The method according to claim 1, characterized in that The step of loading the blade grid into the background grid to form a combined calculation model and adjusting the collective pitch of the blade grid includes: Read the background mesh, then use the Fluent software to rotate the blade mesh BLADE1 with the jet hole 180° around the Z axis and save it as BLADE2. Then, use the Fluent software to attach the original blade mesh BLADE1 and the copied blade mesh BLADE2 to the background mesh, forming a calculation model of the background mesh and the two blade meshes. The outer boundary of the blade mesh is set to the overlapped mesh boundary condition, the blade surface is set to the wall boundary condition, the turbulence model adopts the K-ωSST common engineering model, and the jet boundary condition adopts the velocity inlet to facilitate the decomposition in different directions; Define blade pitch torsion. The rotor blade undergoes a compound motion during operation, with rotation accompanied by pitch torsion, flapping, and shimmying. In hovering, the main motions are rotation and pitch variation. The blade's initial mesh is based on a 0° collective pitch. Through secondary development, the target collective pitch can be achieved during rotation, or multiple collective pitches can be achieved in a stepped manner using if statements. The ZONE_MOTION function is used to implement real-time pitch variation. axis[0]=cos(ψ1+ψ0) axis[1]=sin(ψ1+ψ0) ψ1=ω·t t>n·Δt,θ(t)=0 Where: the blade rotates around the z-axis, axis[0] and axis[1] are the projections of the pitch axis of each blade on the x-axis and y-axis of the coordinate system respectively, ψ0 is the initialization azimuth angle of each blade, ω is the rotor speed, and the rotor rotation motion is realized by CG_MOTION, ψ1 is the real-time rotation azimuth angle of the blade, the variable θ(t) is the pitch angular velocity, which is a piecewise function, Δt is the time step defined as the time for the blade to rotate 1° azimuth, n is the number of calculation steps, n·Δt represents the total pitch θ change within a certain period of time, and t is the current time; After the collective pitch reaches the target value, the θ(t) rotor does not change pitch.

7. The method according to claim 1, characterized in that The boundary conditions defining the jet boundary of the blade grid and the background grid include: Define the distributed jet on the blade surface. Since the direction of the jet changes in real time with the blade during its rotational and pitch-varying motion, secondary development of the jet boundary ensures that the direction of the jet generated by each jet hole keeps following the blade's motion. The PROFILE function is used to define the jet boundary. V jet_x =V jet ·cos(α)·cos(ωt) V jet_y =V jet ·cos(α)·sin(ωt) V jet_y =V jet ·sin(α) α=β-θ Where: V jet is the jet velocity, V jet_x 、V jet_y 、V jet_z are the components of the jet on the x-axis, y-axis, and z-axis, respectively; β is defined as the angle between the jet deflection angle and the local chord direction of the blade; θ is the local total distance of the blade jet position; and α is the angle between the jet and the rotation plane. Set the background grid side and above the rotor as pressure inlet boundary conditions, and set the bottom of the rotor as pressure outlet boundary conditions. Read the user-defined function developed in the secondary development and compile it. Then, mount the PROFILE program on the jet boundary.

8. The method according to claim 7, characterized in that The step of calculating the combined calculation model according to the jet boundary and the boundary condition to obtain aerodynamic characteristics includes: Calculate the set combined calculation model containing the jet boundary, initialize the far field calculation, set the time step and the inner iteration time step, and directly calculate until the rotor aerodynamic force converges at the target collective distance; In order to analyze the influence of the jet on the aerodynamic characteristics of the blade, the benchmark rotor model must also be calculated and analyzed. The motion settings of the blade in the benchmark rotor model calculation are the same as above, and the jet boundary on the blade surface is changed to the wall boundary. The other boundary conditions are set to the same. The above operations can be repeated until the aerodynamic force converges at the target collective distance.

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