WO2021201811A2

WO2021201811A2 - Partially flexible airfoil formed with silicone based flexible material

Info

Publication number: WO2021201811A2
Application number: PCT/TR2021/050739
Authority: WO
Inventors: Mustafa Serdar Genç; Gamze GENÇ
Original assignee: Msg Teknoloji Ltd Sirketi
Current assignee: Msg Teknoloji Ltd Sirketi
Priority date: 2020-12-22
Filing date: 2021-07-19
Publication date: 2021-10-07
Anticipated expiration: 2023-06-22
Also published as: TR202021171A2; WO2021201811A3

Abstract

The invention is on the airfoil (1) in the case of low speed operations of aircraft, micro and unmanned aerial vehicles and turbine blade structures used in the aviation and energy sectors; it contains its leading edge (10), which is the part where the fluid first meets the front, and its trailing edge (20) left by the fluid entering from its leading edge (10). It is the airfoil (1) that increases the aerodynamic performance and efficiency with the controlling the flow on the suction or the upper (30) and the pressure or the lower (40) surfaces, thus increasing. The airfoil (1) contains suction (30) the upper silicone-based flexible plate (70) and the lower silicone-based flexible plate (71) inserted into the upper gap (60) and the lower gap (61), located between the leading edge (10) and the trailing edge (20), which prevents the formation of separation bubbles on the suction (30) and the pressure (40) surfaces of the airfoil (1).

Description

PARTIALLY FLEXIBLE AIRFOIL FORMED WITH SILICONE BASED FLEXIBLE

MATERIAL

Technical Area This invention related to airfoils used in aircraft, propeller and turbine structures.

The invention, in particular, relates to an airfoil that provides increasing the aerodynamic performance of wing structures with adding flexibility using silicone-based flexible material to the wing/blade structures of aircraft, micro and unmanned aerial vehicles and wind/gas/steam turbine systems used in the sectors serving in the field of energy and aviation.

State of the Art

Airfoils are curved or straight, usually drop-shaped sections, designed to give the optimum lift/drag (L/D) ratio to a vehicle moving in any fluid, such as air or water. Different performances are obtained according to the amount of flow passing over these airfoils. Some flows are quite turbulent, while others are smooth and regular. The very regular flow indicated by smooth streamlines is called "laminar flow". Highly disordered fluid motion usually occurs at high velocities and is described by so-called "turbulent flow ".

The Reynolds (Re) number is used to describe and compare the flow velocity that affects the performance of a wing. The “Re number” is known as the ratio of inertial forces to viscous forces. The force that occurs perpendicular to the movement of a fluid and in the upward direction is called the "lift force (F_L)", and the force that occurs in the opposite direction to the flow is called the "drag force (F_D)". The ratio of the lift force on an airfoil to the drag force is expressed as L/D. The dimensionless equation that expresses the magnitude of the lift force is called the “lift coefficient (C_L) equation” given by the expression C_L = F_L /0.5*intensity*squared velocity). The dimensionless equation that expresses the magnitude of the drag force is called the drag coefficient (C_D). It is expressed as C_D = F_D / (0.5 * density * velocity squared).

Accelerated and less pressurized flow on the airfoil, as it moves towards the trailing edge, it slows down and its pressure increases after maximum camber. In this case, the pressure gradient becomes positive because the pressure in the previous region increases rather than decreases, and this is called the "adverse pressure gradient". At low Re number flows, as flow moves from the leading edge to the trailing edge, the laminar flow is affected very quickly by the viscous forces and the transition to turbulent region becomes longer. In the transition region, even at low angles of attack, the flow cannot overcome viscous effects and adverse pressure gradients, and it may separate from the airfoil surface.

As the flow over the airfoil moves from the leading edge to the trailing edge, the separated flow becomes turbulent due to the increase in the local Re number which is calculated according to the distance from the leading edge. Hereby, due to the turbulence fluctuations and the high turbulence energy, adverse pressure gradient and viscous effects are overcome which causes the flow to reattach to the airfoil surface. This separated and reattached counterflow region is called the “separation bubble”, and the separation phenomenon is called “laminar boundary layer separation” or “leading edge separation”. As the angle of attack increases in cambered airfoils, the pressure increase starts earlier, and early flow separations (the flow separation from the leading edge of the airfoil at low angles of attack) may occur. These separation bubbles cause vibration and instability on the airfoil/wing/blade, thus reducing the efficiency of the wing, in other term, the aerodynamic performance.

In the current application, additional aerodynamic device/devices (vortex generators) are used to control the separated flow on the wing/blade. By increasing the turbulence kinetic energy and irregularities of the low Re number flow on the wing by using vortex generators, both early transition to turbulence without separation and a decrease in lift force are prevented. In this case, with vortex generators, flow kinetic energy and airfoil drag coefficient increase. In this current application, the flow control mechanism on the airfoil is different from the silicon-based partially flexible airfoil.

In the current application, there are deformable (morphing) wings in which articulated production from different parts, and these types of structures allow the entire wing to be bent and twisted and the area under the wing to be increased without the need to use mechanisms such as slats or flaps. In this current application, the control mechanism of the flow on the wing is different from the silicon-based partially flexible airfoil. In the current application, a segmented vertical axis wind turbine blade is considered in the patent numbered US 2011/0194938 A1 and there are gaps between each piece in this blade. The blade is hollow and mounted in adjacent relationship spaced to create openings between them. In a vertical axis wind turbine containing a large number of rigid plate parts, the wind flow passes through the gaps according to the position of the turbine blades, increasing the turbine efficiency. In this current application, there is a different structure from the silicon-based partially flexible airfoil.

In current application, Hefeng et al. (Numerical Research on Segmented Flexible Airfoils Considering Fluid-structure Interaction, Procedia Engineering vol. 99, pp.57-66, 2015) studied numerically to control the separated flow over NACA0012 airfoil and to delay the stall using the flexibility considering different four segmented airfoil configurations at Re=135 000 with the angle of attack between 8 and 16 degrees (at the pre-stall and the post stall angles). As a result, it was concluded that the lift coefficient increased up to 39% by partially controlling the completely separated flow on the airfoil at 13 degrees (the post-stall angle) for the situation made with the assumption of different flexible structure in 3 different regions at the same time. In this study, the separation bubble on the rigid airfoil did not form, flexibility was applied on three different regions with the completely separated flow and the separated flow was partially improved.

In addition, there is a national patent entitled "Aerodynamic Performance Enhanced Airfoil with Flexibility" with the registration number TR 2016/20123. Also, two international publications (1. Gen9 MS, Atjikel HH, Koca K., Effect of partial flexibility over both upper and lower surfaces to flow over wind turbine airfoil, Energy Conversion and Management, 219, 113042, 2020; 2. Atjikel HH, Gen9 MS, Control of Laminar Separation Bubble over Wind Turbine Airfoil Using Partial Flexibility on Suction Surface, Energy, vol.165, pp.176- 190, 2018) were published by the inventors of this patent, numbered 2016/20123.

This invention and its publications; it is on a partially flexible airfoil made of membrane material that increases the aerodynamic performance and efficiency of wing/blade structures of aircraft, micro or unmanned aerial vehicles and wind turbines used in the aviation and energy sectors in case of low velocities. Here, the flexibility can be positioned partially on the upper or lower surface of the wing, or on both the upper and lower surfaces, and the membrane material is used as the flexible material. However, this flexible membrane material is not long-lasting and loses its properties over time. In addition, aircraft, micro and

B unmanned aerial vehicles and wind turbines used in the aviation and energy sectors are exposed to all kinds of weather conditions and will not be durable in hot weather in summer and rainy cold weather in winter and will deteriorate immediately. As a result, the flexible membrane material creates a big problem, cannot be used in practice, and the existence of this problem has made it necessary to make an improvement in the relevant technical field.

Purpose of the Invention

This invention relates to a partially flexible airfoil made of silicone-based material, which has been developed to eliminate the above-mentioned disadvantages and provide new advantages to the related technical field.

The main purpose of the airfoil that is the subject of the invention is to create a partially flexible airfoil by using a silicone-based flexible material and to make the flexible part more durable. With the use of silicone-based flexible material, the partially flexible airfoil will be more durable than the partially flexible airfoil produced by a membrane material registered in the national patent and numbered 2016/20123. It is seen that the membrane material deteriorates quickly in different weather conditions (rainy, snowy, sunny weathers) in which the micro and unmanned aerial vehicle or wind turbine blades operate, a silicon-based material has been adopted to be the best solutions in this invention.

Another aim of this invention is to increase the aerodynamic performance by preventing or reducing the formation of laminar separation bubbles on the airfoil, especially at low Re number flows and at low angles of attack (such as a=0°-12°) with silicon-based partial flexibility.

Another aim of this invention is to prevent the stall, instability and vibrations due to the separation bubble which occurs from low angles of attack as 0° in micro-aerial vehicles or wind turbines at low Re-number flows, moving towards the front of the wing and growing as the angle of attack increases.

Another purpose of this invention is to eliminate or minimize the separation bubble and the vortices formed by the bubble which occur generally in the region between (x/c)=0.1- 0.9 which is the distance from the leading edge to airfoil chord length (between 10% and 90% of the chord length from the airfoil leading edge of the upper or lower area of the airfoil) by using different lengths of silicone-based flexible material at different start and end regions. Another objective of this invention is to dampen the separation bubbles and vortices formed on the airfoil, to provide stability on the airfoil using silicone-based flexible material at the certain regions. In other term, to increase the lift coefficient and to decrease the drag coefficient by using silicon-based flexible material in certain regions of the airfoil (on only the upper surface, only lower surface or both upper and lower surfaces).

In the realization of the invention, the weight of the airfoil is also reduced by using silicone-based flexible material. Thus, the efficiency of wind turbines or micro and unmanned aerial vehicles with the wing/blade with lighter and stable flow can be increased.

In the registered invention numbered 2016/20123 and the related international publications, the flow was controlled experimentally by observing the physical flow changes and its differences from the sudy of Hefeng et al. in the current technique (2016/20123) were revealed as follows:

• The partially flexible airfoil in the invention numbered by 2016/20123 and the related international publications is NACA4412 and this is a cambered airfoil. The flow structure on this wing is different from the flow structure on the symmetrical NACA0012 airfoil in the study of Hefeng et al. In the cambered airfoils, at low Re numbers (low velocity flows), the separation bubble forms and this bubble changes the flow structure and the aerodynamic performance of the airfoil.

• The working range of Re number in the invention numbered by 2016/20123 and the related international publications is between 25 000-75 000 and it is lower Re number flow than the working ranges in the study of Hefeng et al. Due to the low Re number, the separation bubble forms over the airfoil between 0°-12° attack angles. In the invention numbered by 2016/20123 and the related international publications, the investigation is concentrated between 0°-12°, considering that the laminar separation bubble will be controlled by the flexible region, which will increase efficiency of the airfoil. In the current technique, 8°-16° attack angles have been studied in the study of Hefeng et al.

• In the membrane flexibility application of the airfoil of the invention numbered by 2016/20123 and its international publications; it was focused on the suppression of the separation bubble at low Re numbers flows and lower angles of attack which is not studied by Hefeng et al., and certain benefits were obtained. In the numerical study of Hefeng et al., it was seen that the flexible part between x/c=0.25- 0.85 on upper surface of the airfoil given in Case 1 did not give good results, while in the solution provided by the partial flexibility in the invention numbered by 2016/20123 and its related international publications, by using membrane flexible material on upper surface of the airfoil between x/c=0.2-0.7 (See (a) of Figure 1 given below), the lift coefficient was increased and the drag coefficient was reduced. Unlike the study of Hefeng et al., when observing result of the experiments of the partial flexibility used in 2016/20123 invention and its related international publications, that was between x/c=0.2-0.7 by using membrane flexible material both on the upper and lower surfaces of the airfoil at Re number of 25 000 (see Figure 1 (c) below), it gave excellent results such as 100% lift coefficient increase and 25% drag coefficient decrease at the angle of attack of 0°.

Graphic 1: Re = 25 000 (a) upper partial flexible airfoil (b) lower partial flexible airfoil (c) lower-upper partial flexible airfoil

With the airfoil that is the subject of this invention, a partially flexible airfoil will be produced using silicone-based flexible material and it is planned to use silicone material to make the flexible part more durable which will be the best choice to prevent the problem in the invention numbered by 2016/20123 and its related international publications. With the use of the silicone-based flexible material, a more durable partially flexible airfoil will be realized comparing with the partial flexibile airfoil with membrane material in the patent numbered by 2016/20123 and in the international publications.

In order to achieve the above-mentioned objectives, the invention includes the leading edge, which is the part where the fluid first encounters and the trailing edge where the fluid entering from the leading edge leaves; It is an airfoil that increases aerodynamic performance and efficiency by using the silicon-based partially flexible material on the upper surface, lower surface and both upper and lower surfaces of the wing structures of aircraft, micro and unmanned aerial vehicles and turbines used in the aviation and energy sectors. The partially flexible airfoil with a silicone-based flexible material contains;

• the upper gap positioned between the leading edge and the trailing edge on the upper surface of the airfoil,

• the lower gap positioned between the leading edge and the trailing edge on the lower surface of the airfoil,

• a silicon-based flexible plate (it can be pure silicon with different flexibility or reinforced composite materials such as glass, carbon, graphene) that prevents the formation of the separation bubbles on the surface of the airfoil by placing at the upper and the lower gap by casting or sticking.

The structural and characteristic properties of the invention and all its advantages will be understood more clearly by inspecting the figures given below, along with the detailed description written with reference to these figures. For this reason, the evaluation should be made by considering these figures and detailed explanation. Description of Figures

Figure- 1. Presents the top perspective view of the airfoil based on the invention.

Figure-2. Presents the side view of the airfoil based on the invention. Figure-3. Presents the side section view of the airfoil based on the invention.

Description of Reference Numbers 1. The Airfoil

10. Leading edge 20. Trailing edge 30. Suction surface

40. Pressure surface 50. Chord line

60. Upper gap

61. Lower gap 70. Upper silicone-based flexible plate

71. Bottom silicone-based flexible plate

To understand the present invention, drawings are not drawn to scale and unnecessary details are ignored. Moreover, elements that are substantially identical or have substantially identical functions been indicated by the same number. Detailed Description of the Invention

In this detailed explanation, the preferred alternatives of the airfoil (1) that is the subject of the invention are explained only for a better understanding of the subject and in a way that does not create any limiting effect. The invention is on the airfoil in the case of low speed operations of aircraft, micro and unmanned aerial vehicles and turbine blade structures used in the aviation and energy sectors; as seen in Figure 1, it contains its leading edge (10), which is the part where the fluid first meets the front, and its trailing edge (20) left by the fluid entering from its leading edge (10). It is the airfoil (1) that increases the aerodynamic performance and efficiency with the controlling the flow on the suction or the upper (30) and the pressure or the lower (40) surfaces, thus increasing, additionally it may contain;

• the upper gap (60) positioned between the leading edge (10) and the trailing edge (20) on the suction surface (30) of the airfoil (1),

• the upper silicone-based flexible plate (70) which is placed in the upper cavitiy (gap) (60) prevents the formation of separation bubbles on the suction surface (30) of the airfoil (1).

• the lower gap (61), located on the pressure surface (40) of the airfoil (1), between the leading edge (10) and the trailing edge (20),

• the lower silicone-based flexible plate (71) is placed in the lower cavity (gap) (61), which prevents the formation of separation bubbles on the pressure surface (40) of the airfoil (1).

In Figure 1, there is a perspective view of the airfoil (1) based on the subject of the invention. The leading edge (10), which is the largest edge of the airfoil (1), is the first place where the fluid meets the airfoil (1). The suction (30) and pressure (40) surfaces of the airfoil (1) are carved to form the upper gap/cavity (60) and lower gap/cavity (61) regions seen in Figure 1.

In Figure-2 and Figure 3, which present the side view and the cross-sectional view respectively, the upper gap (60) and the lower gap (61) parts of the airfoil (1), are attached to the carved airfoil (1), where the upper silicone-based flexible plate (70) and the lower silicone-based flexible plate (71) are placed. Instead of placing the upper silicone-based (70) and the lower silicone-based (71) flexible plates on the airfoil (1), it can also be in the form of directly pouring silicone-based flexible material into the upper gap (60) and the lower gap (61) regions. The preferred structure of the mentioned the upper silicone-based flexible plate (70) and the lower silicone-based flexible plate (71) is the silicone-based flexible material. The silicon-based material can also be pure silicon with different flexibility or reinforced composite materials such as glass, carbon, graphene. Due to the upper silicon-based flexible plate (70) and the lower silicon-based flexible plate (71) placed on the suction (30) and the pressure (40) surfaces of the airfoil (1), micro and unmanned aircraft or turbine blades are lightened and aerodynamic performance increased at low speeds. In addition, with the use of the silicone-based flexible material, a more durable airfoil (1) is adopted comparing with the partially flexible airfoil made of membrane material in the patent numbered by 2016/20123. Since the membrane material used in micro and unmanned aerial vehicle or turbine blade deteriorate quickly in different weather conditions (rainy, snowy, sunny weather), a silicon- based material solution has been employed in this invention.

The vortices formed due to separation bubbles or leading edge (10) separations cause vibrations, aerodynamic performance reduction and instabilities in the airfoil (1). The region where the separation bubble is formed can occur within the regions where the upper silicone- based flexible plate (70) and the lower silicone-based flexible plate (71) are positioned on the suction (30) and the pressure (40) surfaces of the airfoil (1), depending on the value of the angle of attack. In these regions, by using the upper silicone-based flexible plate (70) and the lower silicone-based flexible plate (71); it is ensured that the eddy vortices are weaken or reduced in this particular flexible region. Thus, it is ensured that the flow attachments to the airfoil (1), resulting the increase of lift coefficient, and reduction in the drag coefficient.

Claims

1. An airfoil (1) including a leading edge (10), which is the part where the fluid first meets the front edge, and a trailing edge (20) where the fluid entering from the leading edge (10) leaves when wing structures of aircraft, micro and unmanned aerial vehicles and wind turbines used in the aviation and energy sector are exposed to low speeds or when it is exposed to low speeds characterized in that

In the upper gap part (60) located on the suction surface (30)a flexible plate (70) made of pure silicon or silicon-based material reinforced with reinforcing composite materials such as glass, carbon, graphene is positioned in the upper gap part (60) located on the suction surface (30).

2. An airfoil (1) according to Claim 1, characterized in that a flexible plate (71) made of pure silicon or a silicon-based material reinforced with reinforcing composite materials such as glass, carbon, graphene, is positioned in the lower gap (61) part located on the pressure surface (40).

3. An airfoil (1) according to Claim 1, characterized in that it is an airfoil (1) obtained by pouring composite reinforced silicone-based flexible material into at least one of the upper gap part (60) located on the suction surface (30) and the lower gap part (61) located on the pressure surface (40).