Technical Field of the Present Invention

The present invention relates to an airfoil-shaped medium so as to generate an aerodynamic force. The present invention more particuiariy relates to an airfoil of a wing, a propulsion system blade attachment or sailboat keel. For instance, the present invention proposes a propulsion system in the form of a propeller, rotor or turbine.

Background of the Present Invention

An airfoil-shaped medium typically has a leading edge, i.e. the foremost edge of the airfoil-shaped medium and a trailing edge where the airflow separated by the leading edge rejoins.

State of the art on the technical field of the present invention has a general emphasis on airfoils that operate based on unsteady lift generation. It is known that for unsteady lift, low drag and delayed stall condition are the main challenges to overcome.

It is also to be noted that when high and rapid maneuverability is desired, the stability of the airfoil (wind turbine blade element or race sailboat keel and rudder) performance is crudal.

Most of the flow control mechanisms rely on active systems. Examples may include covering the airfoil surface by small injection ports or using small force activators that are made-up of piezoelectric systems or utilizing drag reducing polymers. The particular disadvantages in association with these existing flow control systems can be viewed as the costly manufacturing processes and the specific difficulties therein as for instance the entire flow surface needs to be covered by activators if small force activators are to be used.

It is also worthy of note that the performance benefits of the existing active systems are not very dear. Most importantly they are designed for steady operating conditions and adjusting control parameters for off design flight conditions are not feasible.

One of the prior publications in the technical field of the present invention can be referred to as EP2159559, which discloses a fluid dynamic polymer-based contact sensor measuring ambient pressure based on the resistivity changes across the sensor under different ambient pressures. The sensor may be applied to airfoil structures such as wind turbine blades without impacting the blade structure and fluid dynamic characteristics. The sensor may also be applied to fluid measurements. A pressure-sensing element may be disposed between a base plate at a first end of the pressure-sensing element and a pressure-sensitive diaphragm at a second end. The pressure-sensitive element may be formed from conductive composite material formed of a polymer and a conductive filler. The pressure-sensitive element may be formed of a piezoelectric material or an element with a piezoelectric coating layer on top, in the middle or at the bottom of it.

The present invention, on the other hand, provides a system specifically suitable for unsteady flapping foil systems naturally assuring low-power rapid dynamic maneuverability. By controlling the span of uncontrolled region, the structural design according to the invention fits to a large range of airfoils covering both micro and macro applications.

The present invention's structural approach is advantageous in that it ensures stability and maneuverability at high vehicle speeds with delayed stall while at the same time avoiding use of bulky flow control hardware. Objects of the Present Invention

Primary object of the present invention is to improve the existing propulsion systems used in turbo machinery and wind turbines, by passive flow control, as well as in aircrafts and underwater vehicles that operate by unsteady flapping wings. Likewise, an improved keel design for use in sailing boats is proposed.

The airfoil-shaped medium accordin to the present invention is therefore devised under the recognition that stability of the airfoil performance with rapid maneuverability remains a great need to achieve.

Brief Description of the Figures of the Present Invention

Accompanying drawings are given solely for the purpose of exemplifying an airfoil- shaped medium, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said daims without recourse to the technical disclosure in the description of the present invention. Fig. 1 demonstrates a general schematic view of an airfoil's initial structure according to a first embodiment present invention. Fig. 2a and 2b demonstrate general schematic views of the airfoil's structural reaction in response to different conditions according to the first embodiment of the present invention. Fig. 3 demonstrates a general schematic view of a propulsion system according to a second embodiment of the present invention. Fig. 4 demonstrates a general schematic view of a strengthening structure of a flexible part according to the present invention. Fig. 5 demonstrates a general schematic view of the flexible part according to the present invention. Fig. 6 demonstrates a general schematic view of a keel together with a free part according to the present invention. Fig. 7 demonstrates a general schematic view of a keel together with a free part according to the present invention. Fig. 8 demonstrates a schematic view of the airflow structure exhibiting delayed flow separation according to the first embodiment of the present invention.

Detailed Description of the Present Invention

The following numerals are assigned to different parts demonstrated in the drawings:

21) Central hub

22) Connection point

23) Strengthening system

24) Branched structure

25) Distal end

26) Proximal end

27) Branch segment

28) Keel

29) Keel flexible portion

The present invention proposes a propulsion system in the form of a propeller, rotor or turbine. The invention further relates to a sailboat keel.

An airfoil-shaped medium such as a wing typically has a leading edge, i.e. the foremost edge of the airfoil-shaped medium and a trailing edge where the airflow separated by the leading edge rejoins. The airfoil, i.e. the shape of a wing or blade as seen in cross-section allows that the air is split and passes above and below the wing. The airfoil structure (11) ensures that the air below the wing pushes upward so as to lift the wing.

According to exemplary embodiments in Fig. 1, Fig. 2a and 2b, the airfoil structure (11) is provided with a fixed body portion (13), for instance in the form of an aircraft wing conventionally having a body portion structurally attached to the fuselage of the aircraft. The airfoil structure (11) further comprises a flexible body portion (14) that is joined with the fixed body portion (13) through a connection line (12). The connection establishes a durable connection between the two parts such that the flexible body portion (14) remains securely attached to the fixed body portion (13) during dynamic flow conditions. Further details on the structural integrity and material characteristics of the two parts (namely, the fixed body portion (13) and the flexible body portion (14)) will be explained in the following parts of the detailed description. In accordance with the exemplary embodiments in Fig. 1, Fig. 2a and 2b, an aircraft wing having an airfoil structure (11) is demonstrated, consisting of the fixed body portion (13) and the flexible body portion (14) wherein the flexible body portion (14) is not connected to the fuselage of the aircraft so that it is able to produce an effect of increased stability and maneuverability in case of reduced drag. Fig. 2a and Fig. 2b respectively demonstrate the airfoil structure's (11) reaction to different flow conditions. To this end, the airfoil structure (11) performs in an improved manner so as to provide lift generation with low drag force. Therefore a far improved performance in terms of stability and maneuverability at vehicle high speeds is obtainable in flow conditions which would otherwise typically lead to loss of lift and stall. The enhanced performance stems from the fact that the flexible body portion (14) of the airfoil structure (11) being non-attached to the aircraft fuselage and due to the self- adapting and flexible nature, acts to dynamically synchronize with the flow. In sum, the flexible body portion (14) performs to maintain increased stability in low drag.

According to a second embodiment of the present invention, a propulsion system (15) is proposed, typically comprising a plurality of propulsion system blades (16). The propulsion system (15) can for instance be embodied as a propeller, rotor or turbine.

The propulsion system (15) as exemplified in Fig. 3 has propulsion system blades (16), each blade having a blade fixed part (17) fixedly attached to a central hub of the propulsion system (15) and a blade flexible part (18) attached to the blade fixed part (17) of the blade. The fixed and flexible parts (namely the blade fixed part (17) and the blade flexible part (18)) are joined through a propulsion system connection line (19). Said connection line, while featuring a sturdy connection between the two parts, allows free movement of the blade flexible part (18) with respect to the blade fixed part (17). The blade flexible part (18) having no part attached to the hub of the propulsion system (15), it features a linear or preferably arc-shaped (not shown) edge portion (20) spaced from the neighboring hub and intersecting therewith only at a connection point (22) with the blade fixed part (17). It is established that this structure of the arc-shaped edge portion (20) following the circumference of the hub with an increasing in-between distance starting from the connection point advantageously provides that the propulsion system (15) delivers an improved performance. On the other hand, the advantageous effect of the invention is also achievable by a linear edge portion (20).

According to the present invention, the propulsion system (15) preferably comprises an additional propulsion system blade (16) entirely consisting of a blade fixed part (17). This blade fixed part (17) is configurable to be ahead in the direction of rotation so that it advantageously provides stability during the initial phase of the rotational movement.

Further, according to the present invention, a stator of the propulsion system (15) preferably comprises a plurality of equally spaced emptied regions preferably in a number equal to the number of the propulsion system blades (16). The emptied regions extend peripherally towards the inside of the stator from the peripheral surface thereof so as to face the linear edge portions (20) of the rotor, i.e. the propulsion system blades (16). In other words, the emptied regions of the stator extends symmetrical to the linear edge portions (20) so as to form a V-shape space between a linear edge portion (20) and an opposite corresponding emptied region of the stator. This arrangement is found to be particularly advantageous in that it ensures a much more concentrated airflow to the rotor.

According to a third embodiment of the present invention, exemplified in Fig. 6, a keel (28) is provided with a keel flexible portion (29). The flexible part of the airfoil structure (11) as well as the blade flexible part (18) and the keel flexible portion (29) are made from an elastic material, preferably from polymer and more preferably silicone rubber. Determined mechanical properties of the silicone rubber as found to be effective in the performance of the flexible parts of the invention are shown in the table below. It is to be noted that these mechanical properties should be met in order for ensuring an acceptable performance on the part of the flexible parts.

Further, a strengthening system (23) embedded within the flexible body portion (14), the blade flexible part (18) or the keel flexible portion (29) involves a branched structure (24) having a plurality of branch segments (27), each branch segment (27) having a first distal end (25) and an attachment portion attached at a second proximal end (26).

The strengthening system (23) is made from composite material in which titanium filaments are used to create the branched structure (24). Determined mechanical properties of the branched structure (24) as found to be effective in preserving mechanical durability of the flexible part of the airfoil structure (11) as well as the blade flexible part (18) and the keel flexible portion (29) of the keel (28) according to the present invention are shown in the table below. It is also to be noted that these mechanical properties must be met in order for ensuring an acceptable performance on the part of the branched structure (24).

According to the present invention, the strengthening system (23) embedded within the flexible body portion (14) preferably comprises a first network of branched structure consisting of composite material in which titanium filaments are used and a second network of branched structure consisting of elastomeric material such as a synthetic rubber less flexible than silicon rubber. The two networks can be formed as separately branched structures extending side-by-side or preferably the second structure can be configured so as to fully cover the first network around the same, thereby providing a more homogenized effect This embodiment provides that a strengthening system (23) that comprises titanium filaments and additionally optionally a second network of branched structure with a synthetic rubber can be designed according to the needs of the specific application. When the branched structure (24) is welded, it is putted inside a mold which is manufactured by polymer injection molding. Subsequently, silicon injection process is effectuated. The process is carried out at room temperature.

Performed finite element analysis of the airfoil structure (11) as well as the propulsion system (15) and the keel (28) proves superior performance and ensures delayed separation delay as demonstrated by simulation results of Fig. 7. The proposed systems according to the present invention can be used in unsteady micro air vehicles, wind turbine systems as well as high performance sail boats. According to a further embodiment of the present invention as shown in Fig. 7, a propulsion system (15) with propulsion system blades (16) in tandem and a first set of propulsion system blades (16) movable relative to a second set of propulsion system blades (16) is proposed. Fig. 7 demonstrates the offset of the two sets of propulsion system blades (16) attached to the central hub (21) by offset angle between lines AB and CD.

The airfoil structures (11) of the propulsion system (15) is configured in the manner that the offset angle between the two sets of propulsion system blades (16) is adjustable depending on the speed of rotation. Two sets of propulsion system blades (16) with the distance between two respective propulsion system blades (16) in relative alignment is adjustable to be increased for greater speeds and decreased in the case of lower rotational speeds, which is found to be effective in providing a certain degree of performance increase and greater stability at differing speeds.

In particular, the tandem vanes 12 may be configured to optimize, promote or enhance an aerodynamic efficiency In a nutshell, the present invention proposes an airfoil-shaped medium having a leading edge, in the form of a first edge of the airfoil-shaped medium and a trailing edge where the airflow separated by the leading edge rejoins, said airfoil-shaped medium having an airfoil structure (11) provided with a fixed portion, said fixed portion being structurally attachable to a body portion of a carrier body.

In one embodiment of the present invention, said airfoil structure (11) further comprises a flexible portion that is joined with said fixed portion through a connection line. In a further embodiment of the present invention, said airfoil structure's (11) fixed portion is a blade fixed part (17) structurally attachable to the carrier body and said flexible portion is a blade flexible part (18) joined with said blade fixed part (17).

In a still further embodiment of the present invention, said carrier body is propulsion system (15) having a central hub (21) and said airfoil-shaped medium is a propulsion system blade (16).

In a yet still further embodiment of the present invention, said blade fixed part (17) of the propulsion system blade (16) is joined with said blade flexible part (18) through a propulsion system connection line (19) while said blade flexible part (18) remains unattached to the central hub (21) of the propulsion system (15).

In a yet still further embodiment of the present invention, said blade flexible part (18) has an edge portion (20) spaced from the central hub (21) and intersecting therewith at a connection point (22) with the blade fixed part (17).

In a yet still further embodiment of the present invention, said edge portion (20) in the form of an arc-shaped edge follows the circumference of the central hub (21) with an increasing in-between distance starting from said connection point (22). In a yet still further embodiment of the present invention, said edge portion (20) is a linearly extending portion.

In a yet still further embodiment of the present invention, wherein said flexible portion of the airfoil structure (11) is made from an elastic material.

In a yet still further embodiment of the present invention, wherein said flexible portion comprises an embedded strengthening system (23) in the form of a branched structure (24) having a plurality of branch segments (27), each segment having a first distal end (25) and an attachment portion attached to another branch segment (27) at a second proximal end (26). In a yet still further embodiment of the present invention, said flexible portion of the airfoil structure (11) is made from silicone rubber.

In a yet still further embodiment of the present invention, said flexible portion of the airfoil structure (11) has a Young's modulus of between about 1 and 5 MPa.

In a yet still further embodiment of the present invention, said flexible portion of the airfoil structure (11) has a tensile strength of between 5 and 8 MPa. In a yet still further embodiment of the present invention, said flexible portion of the airfoil structure (11) has an elongation of between about 200 percent and 800 percent.

In a yet still further embodiment of the present invention, said strengthening system (23) is made from titanium.

In a yet still further embodiment of the present invention, said strengthening system (23) has a Young's modulus of approximately 115000. In a yet still further embodiment of the present invention, said strengthening system (23) has a tensile strength of approximately 1150.

In a yet still further embodiment of the present invention, said strengthening system (23) has an elongation of approximately 8 percent

In a yet still further embodiment of the present invention, said propulsion system (15) comprises an additional propulsion system blade (16) entirely consisting of a Wade fixed part (17). In a yet still further embodiment of the present invention, said additional propulsion system blade (16) is configurable to be ahead in the direction of rotation of said propulsion system (15).

In a yet still further embodiment of the present invention, a stator of the propulsion system (15) comprises a plurality of equally spaced emptied regions.

In a yet still further embodiment of the present invention, the number of equally spaced emptied regions equals to the number of the propulsion system blades (16).

In a yet still further embodiment of the present invention, the emptied regions extend peripherally towards the inside of the stator from the peripheral surface thereof facing the linear edge portions (20) of the propulsion system blades (16).

In a yet still further embodiment of the present invention, said strengthening system (23) comprises a first network of branched structure consisting of composite material in which titanium filaments are used and a second network of branched structure consisting of e!astomeric material.

In a yet still further embodiment of the present invention, second network of branched structure consists of a synthetic rubber compound.

In a yet still further embodiment of the present invention, synthetic rubber compound is less flexible than silicon rubber.

In a yet still further embodiment of the present invention, said propulsion system (15) comprises a first set of propulsion system blades (16) in tandem with a second set of propulsion system blades (16).

In a yet still further embodiment of the present invention, said first set of propulsion system blades (16) is movable relative to the second set of propulsion system blades (16). In a yet still further embodiment of the present Invention, an offset angle is provided between the two sets of propulsion system blades (16) attached to the central hub (21). In a yet still further embodiment of the present invention, the airfoil structures (11) of the propulsion system (15) is configured in the manner that the offset angle between the two sets of propulsion system blades (16) is adjustable depending on the speed of rotation. In a yet still further embodiment of the present invention, the first and second set of propulsion system blades (16) with the distance between two respective propulsion system blades (16) in relative alignment with each other is adjustable to be increased for greater speeds and decreased in the case of lower rotational speeds. In a yet still further embodiment of the present invention, the emptied regions of the stator extends symmetrical to the linear edge portions (20) so as to form a V-shape space between a linear edge portion (20) and an opposite corresponding emptied region of the stator. In a yet still further embodiment of the present invention, the two networks are formed as separately branched structures extending side-by-side or the second network is configured so as to fully cover the first network around the same.

The invention's system is specifically suitable for unsteady flapping foil systems naturally assuring low-power rapid dynamic maneuverability. By controlling the span of uncontrolled region, the structural design according to the invention fits to a large range of airfoils covering both micro and macro applications.