CN103407574B - Novel efficient notch airfoil shape of parafoil unmanned plane and optimum design method thereof - Google Patents

Abstract

The invention provides a notched airfoil for a stamping parafoil and an optimization design method thereof, comprising selecting a basic airfoil with high aerodynamic efficiency, designing a leading edge notch, and optimizing the parameters of the leading edge notch. Compared with the conventional traditional CLARK-Y notched airfoil, the notched airfoil of the present invention has a larger maximum thickness, and the thickness distribution is uniform, and the air chamber space of the parafoil is larger, which is more conducive to improving the inflation efficiency and inflation stiffness of the parafoil; the surface pressure is along the chord The distribution of the line direction is more uniform, which is beneficial to the arrangement of the parafoil line and improves the pitch control efficiency; the stall angle of attack is large, the available aerodynamic efficiency is high, and it has a large range of stable control angle of attack.

Description

A new type of high-efficiency notched airfoil for parafoil UAV and its optimal design method

technical field

The invention relates to a stamped parafoil profile for a parafoil drone, in particular to a notched airfoil for a parafoil drone. In addition to being applicable to parafoil drones, the present invention is also applicable to the design and manufacture of other stamping parafoils.

Background technique

The parafoil UAV technology is a new type of UAV formed by using a stamped parafoil to replace the traditional wing to provide lift for the parafoil UAV. The stamped parafoil is limited by the plane shape and the characteristics of the parafoil, and cannot be optimized for aerodynamic parameters like the traditional fixed wing. Therefore, the optimized design of the notched airfoil becomes the key to improving the aerodynamic performance of the parafoil UAV. The efficiency and efficiency are decisive factors for the performance of the ram parafoil, and directly affect the parachute opening of the ram parafoil and the flight performance of the parafoil UAV.

The study of high-performance airfoil is a basic research for the development of stamped parafoil. High lift, low drag, large stall angle of attack, high maximum lift-to-drag ratio, good inflation effect, and high inflation stiffness are the goals pursued by the stamped parafoil cut airfoil. The traditional notched airfoil is basically based on CLARK-Y and Liesman 7808, and the leading edge is opened. The lift of these notched airfoils is not large enough, the stall angle of attack is not large enough, and the maximum thickness is not large enough. Therefore, it is necessary to design a notched airfoil with high aerodynamic efficiency and large thickness.

Due to the low flying speed of parafoil drones, low-speed airfoils are usually selected, such as CLARK-Y or NACA four-digit airfoil modification. The airfoil of the early parafoil was CLARK-Y. In the 1980s, an airfoil called Liesmann appeared. It has better performance than CLARK-Y, and the glide ratio increases by about 0.2 to 0.4, but the aerodynamic efficiency is still not good enough. The improved closed leading edge parafoil no longer uses the common CLARK-Y airfoil, but adopts the LS (1) wing section that can reduce induced drag. At present, most of the notched airfoils of stamped parafoils in my country are airfoils designed with leading edge notches based on the CLARK-Y airfoil. As a stamped wing parafoil section, the CLARK-Y notched airfoil has the following disadvantages:

(1) The position of the maximum camber is near the front, which is likely to cause uneven distribution of aerodynamic load along the chord direction, mainly concentrated near the front edge, causing uneven force on the parachute;

(2) The lower airfoil is straight, and the starting point of the leading edge cut is above the most leading point of the chord line, which may easily cause the upper surface of the parafoil to separate prematurely, as shown in Figure 1;

(3) The CLARK-Y notched airfoil stalls at a small angle of attack, and the stall angle of attack is about 5°, as shown in Figure 2, which is not conducive to the use of the maximum lift-to-drag ratio, reduces aerodynamic efficiency, and also makes the ram parafoil Pitch state control is limited.

Contents of the invention

The problem to be solved by the present invention is to overcome the shortcomings of the CLARK-Y notched airfoil and design a new type of high-efficiency notched airfoil, which is a low-speed high-lift airfoil with a large stall angle of attack, good stall characteristics, and aerodynamic load along the chord Uniform distribution characteristics.

The technical solution of the present invention is to select the basic airfoil with high aerodynamic efficiency, design the leading edge cutout according to a certain angle and height, and carry out the optimized design of the leading edge cutout parameters.

Basic airfoil selection: It is very critical to choose a suitable airfoil as the basic airfoil, and it is necessary to take into account both the aerodynamic performance and the structural characteristics of the stamped parafoil. From the perspective of aerodynamic performance, the airfoil is required to have a high lift-to-drag ratio, gentle stall characteristics, and a wide range of stable angles of attack when the trailing edge is deflected; at the same time, the structure and process requirements of the stamped parafoil are taken into account. Table 1 shows the upgrade characteristics of some airfoils during low-speed flight (Re=300000, α=6°). The data show that GA(W)-1, E387(A), E387(C), E387(E), Goe 417a , LRN1007(B) has high aerodynamic efficiency.

Table 1 Upgrade characteristics of some airfoils (Re=300000)

The base airfoil in the present invention selects GA (W)-1 airfoil, mainly has the following aspects reasons:

First, the GA(W)-1 airfoil is an advanced high-lift airfoil designed by computational aerodynamics. In terms of aerodynamic performance and geometric characteristics, it has the following characteristics:

①The radius of the leading edge on the upper surface is large to reduce the peak value of negative pressure at high angles of attack, and thus delay the stall of the airfoil;

②The upper surface of the airfoil is relatively flat, and the load distribution is uniform;

③The lower surface of the airfoil near the trailing edge has a large curvature, and has a blunt trailing edge with approximately equal slopes on the upper and lower surfaces.

Secondly, from the perspective of the geometric structure of the basic airfoil of a stamped parafoil, the GA(W)-1 airfoil has the following advantages:

① The upper and lower surfaces of the GA(W)-1 airfoil are relatively flat, the airflow can pass through more smoothly, the load is evenly distributed, and the force on the parachute is even;

② The thickness of the airfoil is relatively large, with a relative thickness of 17%. In comparison, the relative thickness of the traditional CLARK-Y parafoil airfoil is 11.7%. The relative thickness is large, the inflation space is relatively large, and the inflation efficiency and inflation stiffness of the parafoil can be improved at the same time;

③The leading edge radius of the airfoil is large, the airflow is less likely to be separated, and the canopy is easier to sew accurately.

The optimal design of the notch parameters of the notched airfoil considers two aspects of the leading edge notch angle and the notch height. The two are related to each other. When the starting position of the incision is determined, the incision angle and the incision height correspond one-to-one.

The angle and height of the leading edge incision are determined: the design of the position and size of the leading edge incision is generally a compromise solution, and the incision should be kept as far as possible to form a positive stamping condition with the incoming flow, which can ensure the inflation of the stamped parafoil and maintain the shape of the parafoil without Too much loss of aerodynamic performance. By weighing the aerodynamic performance and inflatable performance, the leading edge incision angle (the angle between the horizontal line of the airfoil and the extension line of the incision) θ of the notched airfoil of the present invention is determined to be 39°, the starting point of the incision is the most leading edge point of the airfoil, and the corresponding incision height (The ratio of the straight-line distance of the incision to the chord length) h is 5.2%, see Figure 4.

Determination of installation angle: In order to utilize the optimal aerodynamic characteristics of the slit airfoil, the range of installation angle of the slit airfoil is 6°～8°.

When the stamped parafoil of the parafoil drone is deployed, the parafoil first realizes the inflation of the stamped parafoil through the leading edge cutout, and the airflow enters the inner air chamber of the parafoil through the leading edge cutout. After the inflation is completed, the parafoil maintains the "wing shape" ” to enter the cruising working state.

3. Beneficial effects—it is proved by numerical simulation method that, compared with the CLARK-Y notched airfoil, the rigid model aerodynamic characteristics of the notched airfoil of the present invention under low-speed, low-altitude, steady-level flight state has the following advantages:

(1) Compared with the conventional CLARK-Y notched airfoil, the notched airfoil of the present invention has a larger maximum thickness, and the thickness distribution is uniform, and the air chamber space of the parafoil is larger, which is more conducive to improving the inflation efficiency and inflation stiffness of the parafoil. See Attached Figure 5;

(2) Compared with the conventional CLARK-Y notched airfoil, the surface pressure of the notched airfoil of the present invention is more evenly distributed along the chord line direction, which is beneficial to the arrangement of parafoil paracords and improves the pitch control efficiency;

(3) Compared with the conventional CLARK-Y notched airfoil, the notched airfoil of the present invention has a larger stall angle of attack, high available aerodynamic efficiency, and a larger stable control angle of attack range.

Description of drawings

Fig. 1 is a schematic diagram of boundary layer separation caused by leading edge incision in the prior art;

Fig. 2 is the lift characteristic of CLARK-Y wing section in the prior art;

Fig. 3 is the GA(W)-1 geometric shape among the present invention;

Fig. 4 is the leading edge notch of notch airfoil of the present invention;

Fig. 5 is a comparison between the present invention and the conventional wing profile geometry;

Fig. 6 is a schematic diagram of the installation and use of the slit airfoil in the present invention;

Fig. 7 is the aerodynamic characteristics of the slit airfoil in the present invention;

Fig. 8 is the installation angle in the present invention is the flow of 6 ° inflation end state;

Fig. 9 is a comparison between the pressure distribution of the wing section of the present invention and the traditional cruising state.

Explanation of reference signs:

11: laminar boundary layer; 12: turbulent boundary layer; 21: CLARK-Y notched airfoil; 22: notched airfoil of the present invention; 1: parafoil leading edge notch; 2: parachute rope; 3: trailing edge control rope; 4: canopy; 5: air chamber.

Detailed ways

【Example 1】

As shown in accompanying drawing 6, the notched airfoil of the present invention is connected with the fuselage of the drone through the parachute 2, and is connected with the steering gear on the fuselage through the trailing edge control rope 3. When inflated, the air flow enters and exits the parafoil air chamber 5 through the leading edge cutout 1, so that the canopy 4 takes the shape of an airfoil and maintains the inflation stiffness. After the inflation is completed, the parafoil and the horizontal plane form an angle of α, which is used to pull the trailing edge through the steering gear Manipulate the rope to realize the control of α.

[Example 2]

The CFD method is used to analyze the aerodynamic characteristics of the slit airfoil of the present invention after inflation. When the Reynolds number Re=0.66e+06, the lift characteristics and the lift-to-drag ratio characteristics are shown in Figure 7. When the installation angle α=6°-8° , has the largest lift-to-drag ratio, and the present invention has a stable pitch control range within the installation angle α=0°-12°. The flow characteristics when the installation angle α=6° are shown in Figure 8, and the pressure distribution of the notched airfoil is shown in Figure 9.

Among them, the Reynolds number Re is the ratio of the fluid inertial force to the viscous force, ρVl/μ, where V is the flow velocity, l is the length of the flowing object, ρ is the density, and μ is the fluid viscosity coefficient. The characteristics of the airfoil are greatly affected by the Reynolds number during its motion, which affects whether the flow is laminar or turbulent, and whether flow separation occurs.

Compared with the conventional traditional CLARK-Y notched airfoil, the notched airfoil of the present invention has a larger maximum thickness, and the thickness distribution is uniform, and the air chamber space of the parafoil is larger, which is more conducive to improving the inflation efficiency and inflation stiffness of the parafoil; the surface pressure is along the chord The distribution of the line direction is more uniform, which is beneficial to the arrangement of the parafoil line and improves the pitch control efficiency; the stall angle of attack is large, the available aerodynamic efficiency is high, and it has a large range of stable control angle of attack.

Those skilled in the art can make improvements or transformations according to the above description, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention.

Claims (5)

1. A notch airfoil for stamping parafoil, this airfoil is a low-speed high-lift airfoil, it is characterized in that, the basic airfoil of described notch airfoil is to select GA (W)-1 airfoil; The leading edge notch angle θ of the notched airfoil is 39°, and the corresponding notch height h is 5.2%; The starting point of the cut is the most leading edge point of the airfoil; The installation angle α of the notched airfoil ranges from 6° to 8°. 2. The notched airfoil according to claim 1, wherein the notched height represents the ratio of the straight line distance of the notch to the chord length. 3. The cutout airfoil according to claim 1, characterized in that said airfoil is used for parafoil drones. 4. A slit airfoil installation method, for installing the slit airfoil as claimed in claim 3, characterized in that, the slit airfoil is connected with the UAV fuselage by the parachute rope, and connected with the UAV fuselage by the trailing edge control rope. The steering gear on the fuselage is connected. When inflating, the airflow enters and exits the air chamber of the parafoil through the cutout on the leading edge, so that the canopy takes the shape of an airfoil and maintains the rigidity of inflation. Pull the trailing edge control rope to realize the control of the installation angle α. 5. a kind of optimal design method of slit airfoil for stamping parafoil, it is characterized in that, described method comprises the following steps: 1) Select the basic airfoil with high aerodynamic efficiency: the basic airfoil is to choose the GA(W)-1 airfoil; 2) Design the leading edge incision: the leading edge incision should be kept in a positive stamping condition with the incoming flow as much as possible, which can ensure the inflation of the stamped parafoil and maintain the shape of the parafoil without losing too much aerodynamic performance. 3) Optimum design of leading edge notch parameters: By weighing the aerodynamic performance and inflation performance, the leading edge notch angle θ of the notched airfoil of the present invention is determined to be 39°, the starting point of the notch is the most leading edge point of the airfoil, and the corresponding notch height h is 5.2 %.