阅读说明：本技术 一种低雷诺数旋翼桨叶 (Low reynolds number rotor blade ) 是由 李尚斌 樊枫 袁明川 黄水林 吴令华 刘平安 江露生 罗骏 于 2019-10-10 设计创作，主要内容包括：本发明属于直升机旋翼桨叶设计,具体涉及一种适用于低雷诺数的旋翼桨叶气动布局方案。本发明低雷诺数旋翼桨叶由桨根、桨叶内侧、桨尖三部分组成,其中,桨叶弦长最大处位于桨叶内侧,且桨叶上方前缘距变距轴线的距离小于桨叶后缘距变距轴线的距离,且桨叶内侧弦长最大处临近桨根,而远离桨尖。本发明低雷诺数旋翼桨叶通过对桨叶结构、形状,特别是其几何外形及参数进行优化设计,从而提高提高其气动性能,以某全机20kg电动四旋翼无人机为例,采用本发明桨叶其悬停时间超过常规四旋翼时间的1倍,有效载荷重量超过常规旋翼载荷重量,因此极大的提高了旋翼飞行器的飞行性能,具有较大的实际应用价值。(The invention belongs to the design of a helicopter rotor blade, and particularly relates to a rotor blade aerodynamic layout scheme suitable for low Reynolds number. The low Reynolds number rotor blade consists of three parts, namely a blade root, an inner side of the blade and a blade tip, wherein the maximum chord length position of the blade is positioned at the inner side of the blade, the distance from the upper front edge of the blade to a variable pitch axis is smaller than the distance from the lower front edge of the blade to the variable pitch axis, and the maximum chord length position of the inner side of the blade is close to the blade root and far away from the blade tip. The low Reynolds number rotor blade improves the aerodynamic performance by optimally designing the structure and the shape of the blade, particularly the geometric appearance and the parameters of the blade, and takes a 20kg electric four-rotor unmanned aerial vehicle as an example, the hovering time of the blade exceeds 1 time of the conventional four-rotor unmanned aerial vehicle, and the effective load weight exceeds the conventional rotor load weight, so the flight performance of a rotor craft is greatly improved, and the low Reynolds number rotor blade has higher practical application value.)

1. The low Reynolds number rotor blade consists of three parts, including blade root, blade inside and blade tip, and features that the maximum chord length of the blade is located inside the blade, the distance between the blade upper front edge and the distance varying axis is smaller than that between the blade back edge and the distance varying axis, and the maximum chord length inside the blade is near the blade root and far away from the blade tip.

2. The low reynolds number rotor blade according to claim 1 wherein the pitch axis distribution is divided into three sections, the pitch axis being located at a mid-point of a section chord line for a relative chord length R/R ≤ 0.18, the pitch axis being free to transition for a relative chord length of 0.18 ≤ R/R < 0.25, and the pitch axis being located at a quarter-point of a section airfoil chord line for a relative chord length R/R ≥ 0.25, where R is a blade radius and R is a blade local radius.

3. The low reynolds number rotor blade according to claim 1 wherein the function of the chord length distribution is: C/C_max＝a1×(r/R)²+ a2 × (R/R) + a3, where C is the local chord of the blade and C is_maxThe blade has the maximum chord length which is positioned at 0.3R/R, the minimum chord length is positioned at 1.0R/R, a1, a2 and a3 are respectively a quadratic term coefficient, a first order term coefficient and a constant term of a chord length distribution function of the blade, and R/R is more than or equal to 0.3 and less than or equal to 1.0.

4. The low Reynolds number rotor blade according to claim 1 wherein the blade local chord length to blade radius C/R is in the range 0.0285 to 0.1912.

5. The low reynolds number rotor blade according to claim 1 wherein a local chord length of the blade above the pitch axis at the tip is less than a local chord length of the blade above the pitch axis at the root.

6. The low reynolds number rotor blade according to claim 1, wherein the local chord length at the root is symmetrically distributed about the local pitch axis.

7. The low reynolds number rotor blade according to claim 1 wherein the entirety has a positive twist and wherein the root twist angle is greater than the twist angle at the tip.

8. According to claim 7The low Reynolds number rotor blade is characterized in that the function of the torsion distribution is α/α_max＝b1×(r/R)²+ b2 × (R/R) + b3 where α is the local twist, α_maxThe maximum torsion is at 0.25R/R, the minimum torsion is at 1.0R/R, and b1, b2 and b3 are respectively a quadratic term coefficient, a first order term coefficient and a constant term of a blade torsion distribution function, wherein R/R is more than or equal to 0.25 and less than or equal to 1.0.

9. A low Reynolds number rotor blade according to claim 7 wherein the maximum twist of the blade is in the range 10.32 ° to 23.32 °.

Technical Field

The invention belongs to the design of a helicopter rotor blade, and particularly relates to a rotor blade aerodynamic layout scheme suitable for low Reynolds number.

Background

The multi-rotor aircraft can realize vertical take-off and landing and hovering at fixed points in the air, and is more easily miniaturized in space, so that the multi-rotor aircraft is widely applied to military fields (such as enemy monitoring, relay communication, humanitarian mine elimination and the like) and civil fields (such as damage assessment of natural disasters, power line patrol, traffic supervision and the like). In recent years, with rapid development of new materials, sensors, flight control and other technologies, many studies have been conducted on multi-rotor aircraft technologies in various universities and many research institutes. Colleges and scientific research institutions making certain achievements abroad are many, mainly including American Stanford university, Japan Qianye university, American Massachusetts university, and the like; in addition to the universities and research institutes mentioned above, some foreign commercial companies such as the atomic energy agency in france have also joined multi-rotor aircraft research lines, such as Draganfly, inc.

The research on the four-rotor aircraft is relatively late in China, the research work is mainly focused on some universities and part of model airplane companies or airlines, the research of the universities is mainly focused on theoretical research in the early stage, for example, the aspects of design and application of modeling and control methods and the like, in recent years, various universities begin to combine the early theoretical research with engineering practice, design the mechanical structure of the four-rotor aircraft by themselves, and research and develop a control system for actual flight. Commercial unmanned aerial vehicle has also developed very rapidly in recent years, and commercial flight control has greatly reduced the technical cost who carries out the aerial photograph by the aircraft like the phantom series, the muscle cloud series of big jiang company to and the many rotor crafts of M series that north journey aviation technology development limited company produced, has taken hold of most domestic market, has extensive application prospect.

However, the aerodynamic efficiency of the blades of the existing electric multi-rotor aircraft is low, so that the following problems exist in the common electric multi-rotor aircraft:

(1) small payload

The more common results are generally limited to a payload of 5 kg.

(2) Short voyage time

The endurance time of the common research results is generally 20-30 min.

Disclosure of Invention

The purpose of the invention is as follows: the rotor blade is high in effective load, high in pneumatic efficiency, and suitable for long-endurance and low Reynolds number.

The technical scheme of the invention is as follows: the low Reynolds number rotor blade consists of three parts, including blade root, blade inside and blade tip, and the maximum chord length of the blade is inside the blade, and the distance between the blade top front edge and the variable pitch axis is smaller than that between the blade back edge and the variable pitch axis.

The variable pitch axis is divided into three sections, when the relative chord length R/R is less than or equal to 0.18, the variable pitch axis is located at the midpoint of a section chord line, when the relative chord length R/R is more than 0.18 and less than 0.25, the variable pitch axis is in free transition, and when the relative chord length R/R is more than or equal to 0.25, the variable pitch axis is located at the quarter point of the section airfoil chord line, wherein R is the radius of the blade, and R is the local radius of the blade.

The function of the chord length distribution is: C/C_max＝a1×(r/R)²+ a2 × (R/R) + a3, C is the local chord of the blade, C is the blade chord length_maxThe blade has the maximum chord length which is positioned at 0.3R/R, the minimum chord length is positioned at 1.0R/R, a1, a2 and a3 are respectively a quadratic term coefficient, a first order term coefficient and a constant term of a chord length distribution function of the blade, and R/R is more than or equal to 0.3 and less than or equal to 1.0.

The relative blade radius C/R range of the local chord length of the blade is 0.0285-0.1912.

The local chord length of the blade above the pitch axis at the tip is smaller than the local chord length of the blade above the pitch axis at the root.

The local chord length at the root of the paddle is symmetrically distributed relative to the local pitch axis.

The blade has positive torsion as a whole, wherein the root torsion angle is larger than the torsion angle at the blade tip.

The function of the torsion distribution is α/α_max＝b1×(r/R)²+ b2 × (R/R) + b3 where α is the local twist, α_maxThe maximum torsion is at 0.25R/R, the minimum torsion is at 1.0R/R, and b1, b2 and b3 are respectively a quadratic term coefficient, a first order term coefficient and a constant term of a blade torsion distribution function, wherein R/R is more than or equal to 0.25 and less than or equal to 1.0.

The maximum torsion range of the blade is 10.32-23.32 degrees.

The invention has the beneficial effects that: the low Reynolds number rotor blade improves the aerodynamic performance by optimally designing the structure and the shape of the blade, particularly the geometric appearance and the parameters of the blade, takes a 20kg electric four-rotor unmanned aerial vehicle as an example of a certain whole aircraft, and adopts the blade to suspend for 1 time longer than the conventional four-rotor time and the effective load weight longer than the conventional rotor load weight, thereby greatly improving the flight performance of the rotor craft and having higher practical application value.

Drawings

FIG. 1 is a graph of lift coefficient versus drag coefficient for an airfoil according to an embodiment of the present invention, with the lift coefficient on the abscissa and the drag coefficient on the ordinate;

FIG. 2 is a plan view of a blade according to an embodiment of the invention, the pitch axis being the axis with a value of y-0, the abscissa being the relative radius and the ordinate being the relative chord length y/C_max，C_maxIs the maximum chord length;

FIG. 3 is a blade chord length distribution plot with the abscissa being the relative radius and the ordinate being the relative chord length C/C according to an embodiment of the invention_maxWherein C is the local chord length_maxIs the maximum chord length;

FIG. 4 is a blade twist profile according to an embodiment of the present invention with relative radii on the abscissa and relative twists α/α on the ordinate_maxWherein α is the local twist, α_maxIs the maximum twist;

FIG. 5 is a graph of pull rate versus torque coefficient with pull rate on the abscissa and torque coefficient on the ordinate according to an embodiment of the present invention;

fig. 6 is a plot of hover efficiency for a rotor according to an embodiment of the present invention, with pull coefficient on the abscissa and hover efficiency on the ordinate.

Figure 7 is an illustration of the effect of a rotor blade according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the embodiment, based on a certain four-rotor electric unmanned aerial vehicle, the design weight is 20kg, and R is 0.9m, wherein the aerodynamic layout design of the low Reynolds number rotor blades comprises airfoil profile selection, pitch-variable axis distribution, chord length distribution and torsion distribution.

The low Reynolds number rotor blade comprises a blade root, the inner side of the blade and a blade tip, wherein the maximum chord length position of the blade is positioned at the inner side of the blade, the distance from the upper front edge of the blade to a variable pitch axis is smaller than the distance from the lower front edge of the blade to the variable pitch axis, and the maximum chord length position of the inner side of the blade is close to the blade root and far away from the blade tip.

As shown in FIG. 1, the relationship between the lift coefficient and the drag coefficient of the aerodynamic characteristics of the airfoil is shown, the lift-drag ratio at the design lift coefficient point is high, and the lift-drag ratio in a wide range near the design lift coefficient point can be kept high.

The variable pitch axis in the low Reynolds number rotor blade is divided into three sections, the variable pitch axis is located at the middle point of a section chord line along the blade direction when the relative chord length R/R is less than or equal to 0.18, the variable pitch axis is in free transition when the relative chord length R/R is more than 0.18 and less than 0.25, the variable pitch axis is located at the quarter point of the section airfoil chord line when the relative chord length R/R is more than or equal to 0.25, the abscissa of which the y is 0 in the figure 2 is the variable pitch axis of the blade, and R is the local blade position along the blade direction. By adopting the three-section variable pitch axis distribution, the pitching moment of the blade can be reduced, the operation load is reduced, and the stability of the rotor wing is better.

The function of the chord length distribution is: C/C_max＝-1.0×(r/R)²+0.6 (R/R) +0.1, where 0.3. ltoreq. R/R. ltoreq.1.0, C_maxFor maximum chord, see FIG. 3 in particular, the maximum chord is at 0.3R/R and the minimum chord is at 1.0R/R. Theoretically, analysis shows that the chord length is larger as being closer to the blade root for providing efficiency, the maximum chord length is positioned at 0.3R/R by considering the existing blade processing technology, and therefore the blade processing technology can be met while the pneumatic efficiency is high.

The function of the torsion distribution is α/α_max＝-1.0×(r/R)²+0.5 × (R/R) +0.9375 where 0.25. ltoreq. R/R.ltoreq.1.0, α is the local twist, α_maxFor the maximum torsion, particularly shown in FIG. 4, the maximum torsion is at 0.25R/R, and the minimum torsion is at 1.0R/R, and the torsion distribution can enable the whole blade ring volume to be basically consistent, so that the hovering aerodynamic efficiency of the blade is improved.

Please refer to fig. 7, which is a diagram illustrating the design effect of the low reynolds number rotor blade according to the present embodiment, and trial flight on a prototype shows that the technical solution of the present embodiment has significant effect, and has a hovering duration of about 50 minutes and a force effect of about 20kg/kw under the conditions of a total aircraft weight of 20kg and an effective load of 5kg, which far exceeds the aerodynamic efficiency and performance of a conventional rotor blade with the same mass.

The foregoing is merely a detailed description of the embodiments of the present invention, and some of the conventional techniques are not detailed. The scope of the present invention is not limited thereto, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention will be covered by the scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.