A flexible oscillating adaptive wind turbine blade

Abstract

The present application relates to a kind of flexible vibration self-adaptive wind turbine blades, including blade body, trailing edge of the blade body is flexibly connected flap by inflatable expansion body, inflatable chamber is arranged on both sides of chord line in the expansion body, the compression degree is changed with flap swing to adaptively adjust the reaction force of expansion body to flap in both sides chamber of chord line, and the flap angle between the blade body and the flap is tended to stable.The present application, simple and compact structure, light in weight, high strength, foldable, quick installation;When blade is working, when wind is larger, flexible structure is influenced by wind force, will be bent upwards, ensure the stability of the whole blade.When wind is reduced, flexible structure is influenced by the pressure difference of two air chambers, will be bent downwards, will improve the operating efficiency of blade at low wind speed, has the effect of increasing efficiency and expanding stability.

Description

Technical Field

[0001] This invention relates to a wind turbine blade, specifically a flexible vibration-adaptive wind turbine blade. Background Technology

[0002] Wind energy, as an inexhaustible and clean energy source, helps reduce human dependence on fossil fuels. To improve the utilization efficiency of wind energy on limited land resources and reduce the cost per kilowatt-hour, the trend towards larger single-unit wind turbines is inevitable. In recent years, global wind power generation has grown at an average rate of over 30%. The rapid development of the global wind power industry has driven the rapid development of wind turbine units. Blades are one of the key components of wind turbine units, and their performance directly affects the wind energy utilization efficiency and the load on the unit. Wind turbine flaps, by changing the shape and area of ​​the blade surface, can influence the airflow state on the blades, thereby adjusting the lift and drag of the blades. Effective control of the flap angle can optimize these aerodynamic characteristics, thereby improving the power generation efficiency of the wind turbine. Reasonable control of the flap angle can also reduce the ultimate load and fatigue load on the blades, thus extending the service life of the wind turbine. This is because adjusting the flap angle can change the aerodynamic characteristics of the blades, reducing the stress on the blades under extreme wind conditions and reducing blade wear and fatigue damage. Controlling the angle of the wind turbine flaps can also improve the stability and adaptability of the wind turbine.

[0003] Currently, flap angle control is mainly achieved through electrical control, mechanical transmission, and advanced avionics technology. This requires complex actuators and control mechanisms, which leads to a sharp increase in weight and manufacturing costs, as well as cumbersome blade transportation, hindering the development of wind turbines and reducing the overall performance of the units and the economic viability of wind power development and utilization. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a flexible, vibration-adaptive wind turbine blade. This blade features a simple and compact structure, light weight, high strength, foldability, and quick installation. During operation, under strong winds, the flexible structure bends upwards to ensure the stability of the entire blade. When the wind speed decreases, the flexible structure bends downwards due to the pressure difference between the two air chambers, improving the blade's operating efficiency at low wind speeds and thus enhancing its stability.

[0005] The objective of this invention is achieved as follows: a flexible vibration-adaptive wind turbine blade.

[0006] The blade body includes a blade body whose trailing edge is flexibly connected to a flap via an inflatable expander. The expander has inflatable chambers on both sides of the chord line. The chambers on both sides of the chord line change their compression degree as the flap swings to adaptively adjust the reaction force of the expander on the flap and to stabilize the flap angle between the blade body and the flap.

[0007] The blade body includes a first main spars and a second main spars arranged along the wingspan direction. The proximal ends of the first main spars and the second main spars are connected to the blade root. It also includes a first beam arranged perpendicular to the wingspan direction. The main beams and / or the second beams are flexible inflatable membrane structures. The two ends of the first beams are connected to the first main spars and the second main spars respectively. The main beams and the second beams are connected to form the skeleton structure of the blade body. The surface of the skeleton structure is covered with a plurality of inflatable chambers. The outer walls of the plurality of inflatable chambers form the airfoil of the blade body.

[0008] The flap includes a third main beam arranged along the wingspan direction and a second beam arranged perpendicular to the wingspan direction. The front end of the second beam is connected to the third main beam. The main beam and / or the second beam is a flexible inflatable membrane structure. The connection between the front end of the second beam and the third main beam forms a flap frame structure. The surface of the flap frame structure is covered with several inflatable chambers, and the outer wall of the several inflatable chambers forms the flap surface.

[0009] The main beam includes a first inflatable column, a second inflatable column disposed at the center of the first inflatable column, and at least three inflatable columns arranged in the annular space between the first inflatable column and the second inflatable column. The inflatable columns are made of membrane.

[0010] Several chambers are set on both sides of the string from front to back.

[0011] The inflation pressure in the chamber gradually decreases from front to back along the chord side, so that the chambers adjacent to the flaps respond first to the change in flap angle and thus change the degree of gas compression in the chambers.

[0012] Adjacent chambers on the same side of the string are connected by a check valve and a pressure relief valve.

[0013] Several air chambers laid on the skeleton structure are connected to the adjacent secondary beams through connection ports equipped with one-way valves.

[0014] The one-way valve includes two leaflets, the edges of which extend along the air intake direction and close together to shut off; the expansion body is made of an elastic material.

[0015] The flaps include multiple independently movable flap segments arranged along the wingspan, with inflatable chambers on both sides of the chord of each flap segment.

[0016] This invention features a simple and compact structure, lightweight, high strength, foldability, and quick installation. When the blades are operating, under strong winds, the flexible structure bends upwards to ensure the stability of the entire blade. When the wind decreases, the flexible structure bends downwards due to the pressure difference between the two air chambers, increasing the blade's operating efficiency at low wind speeds and providing enhanced stability. The flexible connection of the expansion body reduces the vibration impact of flap attitude changes on the blade body. It also reduces the blade's ultimate load and fatigue load, thereby extending the wind turbine's service life. By adjusting the flap angle, the wind turbine can maintain stable operation under complex and changing wind conditions, reducing fluctuations and instability caused by wind changes. This helps improve the reliability and safety of the wind turbine and reduce maintenance costs.

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention;

[0019] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0020] Figure 3 This is a schematic diagram of a one-way valve.

[0021] Figure 4 This is a streamline diagram of the blade of the present invention under low wind speed;

[0022] Figure 5 This is a streamline diagram of a conventional blade at low wind speeds.

[0023] Figure 6 The streamline diagram of the blades under high wind speeds;

[0024] Figure 7 This is a comparison chart of the lift coefficients of the improved airfoil and the original airfoil at a 10° angle of attack.

[0025] In the attached diagram, 100 is the blade body, 110 is the first main beam, 120 is the second main beam, 150 is the first beam, 200 is the expansion body, 201 is the one-way valve, 202 is the pressure relief valve, 210 is the chamber (210), 220 is the third main beam, 240 is the second beam, 300 is the flap, a is the inflation column, b is the inflation chamber, and c is the leaflet. Detailed Implementation

[0026] Referring to the accompanying drawings, specific embodiments of the present invention will be described in detail.

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] In the description of this application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" can be used to explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more. It should be noted that in practical applications, due to limitations in equipment accuracy or installation errors, absolute parallelism or perpendicularity is difficult to achieve. The descriptions of vertical, parallel, or unidirectional in this application are not absolute limitations, but rather indicate that vertical or parallel structural settings can be achieved within a preset error range, and the corresponding preset effects can be achieved. In this way, the technical effects of the defined features can be maximized, and the corresponding technical solutions can be easily implemented, thus having high feasibility.

[0029] See Figure 1-7 An embodiment of a flexible vibration adaptive wind turbine blade is provided. The blade includes a trailing edge and a leading edge. The leading edge typically has a curved and rounded shape, while the trailing edge typically has a sharp or blunt edge. The straight line between the trailing and leading edges is called a chord, which divides the airfoil into a pressure side and an intake side. In this embodiment, the flexible vibration adaptive wind turbine blade includes a blade body 100. The trailing edge of the blade body 100 is flexibly connected to a flap 300 via an inflatable expander 200. The expander 200 has inflatable chambers 210 on both sides of the chord. The chambers 210 on both sides of the chord change their compression degree as the flap 300 swings to adaptively adjust the reaction force of the expander 200 on the flap 300, and to stabilize the flap angle between the blade body 100 and the flap 300.

[0030] See Figure 1The expander 200 has inflatable chambers 210 on both sides of the chord, with the upper chamber 210 located above the chord and the lower chamber 210 located below the chord. Gas is filled into the inflatable chambers 210 on both sides of the chord. The chambers 210 are compressible. When the inflatable chambers 210 on both sides of the chord have different inflation pressures, the expander 200 forms a bending shape with different curvatures. The expander 200 flexibly connects the blade body 100 and the flap 300. The flexible body structure formed by body 200 can form connection structures with different rotation angles, so that the flap angle maintains the desired angle. The combined pressure of the inflatable chambers 210 on both sides of the two chords and the wind pressure on the blade's frontal surface on the flap 300 maintains a stable balance. When the wind pressure on the frontal surface changes, this balance is disrupted. The lower chamber 210, which is closer to the windward surface, can balance the combined wind pressure with the inflation pressure of the upper chamber 210, which is under compression, and the flap 300 swings to a new equilibrium position. In this embodiment, the blade can passively adjust the flap angle in response to the flow state on the blade surface. The adjustment of the flap angle can be performed without any mechanical or electric actuators or controllers.

[0031] The expansion body 200 is made of a flexible material, and the membrane structure of the chamber 210 can be deformed according to the stress conditions; preferably, the expansion body 200 is made of an elastic material, specifically rubber or elastic plastic, so that when the gas is compressed, the surface of the chamber 210 can contract with the compression, so that the outer wall of the chamber 210 always remains in an expanded state.

[0032] refer to Figure 1-7 The air pressure in the upper inflation chamber 210 located above the chord line is greater than that in the lower inflation chamber 210 located below the chord line, causing the entire expansion body 200 to bend downwards, which in turn causes the entire flexible connection structure to bend downwards. When the blade is operating, under strong winds, the flexible connection structure will bend upwards due to the wind force, reducing the flap angle and ensuring the stability of the entire blade. When the wind force decreases, the flexible connection structure will bend downwards due to the pressure difference between the two chambers 210, increasing the flap angle and increasing the operating efficiency of the blade at low wind speeds, thus enhancing efficiency and stability.

[0033] In some embodiments, the inflatable chambers 210 on both sides of the two chords can be connected to an inflation device. The pressure of the two chambers 210 in different initial states can be adjusted by actively "inflating" or "deflating" the volume, so that the flexible connection structure has different initial bending stiffness, thereby adjusting the response torque and response speed of the flap angle change.

[0034] The behavior of the flap 300 will depend on the rotational speed of the blade and also on the angle of attack in that segment of the blade. Since the tangential velocity at a point along the blade depends on the rotational speed of the rotor and the distance of that point from the blade root, the behavior of the flap 300 will also depend on its position along the blade. In some embodiments, the flap 300 includes a plurality of independently movable flap segments arranged along the wingspan direction. Each flap segment has inflatable chambers 210 on both sides of its chord. Corresponding to each flap segment's different distance from the blade root, it has different wind pressures, enabling different flap angles at different distances along the wingspan.

[0035] In some examples, several chambers (210) are arranged from front to back on both sides of the chord. The inflation pressure in the chambers 210 along the chord gradually decreases from front to back, so that the chambers 210 adjacent to the flaps 300 respond first to the change in flap angle and the degree of gas compression in the chambers 210 changes. It can be understood that in the change of the angle of the expander 200, the arrangement of multiple chambers 210, which are independent of each other, can make the corresponding local area of ​​the chamber have a strong air pressure, and the local area can bear pressure independently. It can make the number of chambers 210 respond to the change of different loads, so that the angle change is more continuous and stable, and it is easy to fine-tune. When the wind speed is high, the chambers 210 are arranged from the front side of the flaps 300, and the chambers 210 gradually deform one by one, so that the entire expander 200 forms a bent structure. When the wind speed is low, the part of the chambers 210 near the flaps 300 deforms.

[0036] See Figure 1-2Furthermore, adjacent chambers 210 on the same side of the chord are connected by a one-way valve 201 and a pressure relief valve 202. In a static state, the pressure in the high-pressure side chamber 210 is higher than that in the low-pressure side chamber 210. During operation, when wind blows onto the flaps 300, the load acts on the flaps 300. The low-pressure side chamber 210 has lower pressure and begins to deform, causing the flaps to move upwards. When the wind speed increases, the wind load increases, the low-pressure side chamber 210 is compressed, and its pressure increases. Gas enters the high-pressure side through the one-way valve 201, bending towards the high-pressure side. The high-pressure side bends, and its pressure increases, adapting to the magnitude of the wind load. When the wind speed decreases, the load on the flaps decreases, and the force generated by the chamber 210 on the blades is greater than the wind load. The flaps begin to bend downwards, and the high-pressure side chamber 210 first returns to its normal state. Air is then introduced into the low-pressure side chamber 210 through the pressure relief valve 202. The low-pressure side chamber 210 also begins to adaptively recover and restore the pressure difference. During operation, the low-pressure side chamber deforms, and the pressure in the low-pressure side chamber 210 begins to increase to adapt to the wind load. When the pressure in the low-pressure side chamber 210 is greater than that in the high-pressure side chamber 210, gas from the low-pressure side chamber 210 flows into the high-pressure side through a one-way valve, and the high-pressure side chamber 210 begins to deform to adapt to the wind load. When the wind load decreases, the high-pressure side chamber 210 first returns to its original shape, and then the pressure relief valve 202 gradually restores the pressure difference between the low-pressure and high-pressure side chambers 210. When the pressure in the low-pressure side chamber 210 is slightly lower than that in the high-pressure side chamber 210, the high-pressure side chamber 210 will fill the low-pressure side chamber 210 with gas to maintain a certain pressure difference. With this structure, the pressure difference can be adjusted through the one-way valve 201 and the pressure relief valve 202, resulting in a more continuous response and better adaptation to wind speed changes under natural conditions. In some examples, to give the blade body 100 features such as light weight, high strength, foldability, and quick installation, the blade body 100 includes a first main beam 110 and a second main beam arranged along the wingspan direction. The proximal ends of the first main beam 110 and the second main beam 120 are connected to the blade root 130. It also includes a first beam 150 arranged perpendicular to the wingspan direction. The main beam and / or the second beam is a flexible inflatable membrane structure. The two ends of the first beam 150 are respectively connected to the first main beam 110 and the second main beam. The main beam and the second beam are connected to form the skeleton structure of the blade body 100. The surface of the skeleton structure is covered with a plurality of air chambers b. The air chambers b can be made of flexible material. The outer walls of the plurality of air chambers b form the airfoil of the blade body 100. By inflating, the first main beam 110 and the second main beam 120 can form a stable load-bearing structure to withstand all or most of the bending moment and shear force. During transportation, by keeping them in an uninflated state, they have the advantages of small size and foldability. During installation, inflation can achieve rapid installation.

[0037] In some embodiments, the main beam includes a first inflatable column a, a second inflatable column a centrally disposed within the first inflatable column a, and at least three inflatable columns a arranged in the annular space between the first inflatable column a and the second inflatable column a. The inflatable columns a are made of a membrane. Specifically, refer to Figure 1-2 The first main beam 110 and the second main beam 120 provide support for the entire blade. Both the first main beam 110 and the second main beam 120 are composed of eight air columns a. Each air column a can consist of two layers, with flexible filling material used to fill the gaps between the membranes. Each air column is inflated to 100 MPa, supporting the entire flexible blade.

[0038] refer to Figure 1-2 Secondary beam 5 provides support for the entire blade, and the inflation pressure reaches 60MPa. Inflation chamber b can be built on secondary beam 5 to maintain the overall strength of the blade. The inflation ports of the first main beam 110 and the second main beam 120 are located on the blade root 130, and the inflation port of the third main beam 220 is located on the blade root 130. Inflation at the blade root 130 allows the main beams to quickly form a skeletal structure.

[0039] Similarly, in some embodiments, the flap 300 includes a third main beam 220 arranged along the wingspan direction and a second beam 240 arranged perpendicular to the wingspan direction. The front end of the second beam 240 is connected to the third main beam 220. The main beam and / or the second beam is a flexible inflatable membrane structure. The connection between the front end of the second beam 240 and the third main beam 220 forms the flap 300 skeleton structure. A plurality of inflatable chambers b are provided on the surface of the flap 300 skeleton structure, and the outer wall of the plurality of inflatable chambers b forms the wing surface of the flap 300. (Reference) Figure 1-2 The third main beam 220 consists of five inflatable columns a, inflated to 100 MPa. These columns are filled with a thin film, and a flexible filling material fills the gaps between the films. Through inflation, the third main beam 220 and the second beam 240 form a stable load-bearing structure to withstand all or most of the bending moment and shear force. During transportation, by remaining in an uninflated state, it offers advantages such as small size and foldability. During installation, inflation allows for rapid installation.

[0040] In some embodiments, several air chambers b laid on the skeleton structure are connected to adjacent secondary beams through connection ports equipped with one-way valves 201. The secondary beams may also consist of multiple columnar chambers, and any chamber or all of the chambers in the secondary beam can be used as air inlets. The one-way valves 201 allow the gas in the several air chambers b to be independent of each other, enabling each air chamber b to bear pressure independently, and preventing localized damage from causing structural failure. Figure 3As shown, further, one structure of the one-way valve is provided. The one-way valve 201 includes two leaflets c. The edges of the two leaflets c extend along the air intake direction and close together in the center. During inflation, the airflow at the upstream end of the leaflets c is under high pressure, causing the two leaflets c to open and inflate the inflation chamber b. After inflation is complete, when the air pressure at the upstream end of the two leaflets c is low, the edges of the two leaflets c extend along the air intake direction and close together in the center, thereby sealing the inflation chamber b. With this structure, the one-way valve 201 has a simple structure and low cost. It can also be made of flexible materials, making it easy to store.

[0041] This invention, compared to conventional non-adjustable blades, see [link to related document]. Figure 7 For example, due to natural wind variations or the operating state of the wind turbine, the angle of attack decreases. The flap angle between the blade body 100 and the flap 300 is automatically adjusted based on the pressure difference between the two air chambers and the wind pressure at the windward surface. This passive adjustment of the air chambers allows for a higher lift coefficient, resulting in a corresponding increase in lift, enabling the wind turbine to extract more energy from the wind. See also Figure 4-7 In a flow field simulation at an 18° angle of attack, the wind speed adaptively adjusts the trailing edge curvature of the blades, further stabilizing the operation of the wind turbine.

[0042] Using this invention, the improved trailing edge flexible structure exhibits a bent state at low wind speeds, such as... Figure 4 As shown in Figure 5, the streamline of the original airfoil blade is as follows at low wind speeds. With the improved blade, the trailing edge is curved at low wind speeds, allowing for better energy absorption from the wind. At high wind speeds, the flexible structure of the trailing edge curves upwards, as shown in Figure 5. Figure 6 As shown, at high wind speeds, the overall streamline of the blade remains stable. Furthermore, due to the adaptive characteristics of the flexible structure, compared to fixed equipment such as vortex generators, it can change with the flow conditions, thus suppressing stall over a wider range, significantly reducing the blade stall zone, and greatly increasing the blade's aerodynamic stability.

[0043] Comparison of lift coefficients between the improved airfoil and the original airfoil at a 10° angle of attack. Figure 7As shown below, the downward deflection of the flexible structure causes the trailing edge to bend, increasing the airfoil's backload and effectively reducing the angle of attack for the same design lift coefficient. This reduced angle of attack shortens the airflow acceleration zone near the nose of the upper wing, lowers the negative pressure peak, and brings the shock wave closer to the leading edge. The downward deflection of the trailing edge increases the expansion velocity of the airflow flowing over the trailing edge of the upper wing, thus increasing the gradient of the trailing edge pressure coefficient recovery. For these reasons, the downward deflection of the flexible structure increases backload and lift on one hand, and weakens the shock wave intensity on the upper wing, thereby reducing wave drag on the other. The blades of this invention can respond to changes in the flap angle, and the response to changes in the flap angle is completely passive. During operation at a given rotational speed, the lift coefficient of the airfoil section is directly related to the angle of attack, increasing the blade's operating efficiency at low wind speeds and providing enhanced efficiency and stability. This invention has significantly lower manufacturing and maintenance costs and features lightweight, high strength, foldability, and quick installation.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A flexible vibration-adaptive wind turbine blade, characterized in that, The blade body (100) is included. The trailing edge of the blade body (100) is flexibly connected to the flap (300) through an inflatable expander (200). The expander (200) has inflatable chambers (210) on both sides of the chord. The chambers (210) on both sides of the chord change their compression degree as the flap (300) swings to adaptively adjust the reaction force of the expander (200) on the flap (300) and make the flap angle between the blade body (100) and the flap (300) tend to be stable. Several chambers (210) are set on both sides of the string from front to back. The inflation pressure in the chamber (210) along the chord line from front to back gradually decreases, so that the chamber (210) adjacent to the flap (300) responds first to the change in flap angle and changes the degree of gas compression in the chamber (210); Adjacent chambers (210) on the same side of the chord are connected by a one-way valve (201) and a pressure relief valve (202).

2. The flexible vibration adaptive wind turbine blade according to claim 1, characterized in that, The blade body (100) includes a first main spar (110) and a second main spar arranged along the wingspan direction. The proximal ends of the first main spar (110) and the second main spar are connected to the blade root (130). It also includes a first beam arranged perpendicular to the wingspan direction and along the wingspan direction. The main beam and / or the second beam is a flexible inflatable membrane structure. The two ends of the first beam are connected to the first main spar (110) and the second main spar, respectively. The main beam and the second beam are connected to form the skeleton structure of the blade body (100). The surface of the skeleton structure is covered with a plurality of inflatable chambers (b). The outer walls of the plurality of inflatable chambers (b) form the airfoil of the blade body (100).

3. The flexible vibration adaptive wind turbine blade according to claim 1, characterized in that, The flap (300) includes a third main beam (220) arranged along the wingspan direction and a second beam (240) arranged perpendicular to the wingspan direction. The front end of the second beam (240) is connected to the third main beam (220). The main beam and / or the second beam is a flexible inflatable membrane structure. The front end of the second beam (240) is connected to the third main beam (220) to form the flap (300) skeleton structure. The surface of the flap (300) skeleton structure is covered with a plurality of inflatable chambers (b). The outer wall of the plurality of inflatable chambers (b) forms the wing surface of the flap (300).

4. The flexible vibration adaptive wind turbine blade according to claim 2 or 3, characterized in that, The main beam includes a first inflatable column, a second inflatable column (a) disposed at the center of the first inflatable column, and at least three inflatable columns (a) arranged in the annular space between the first inflatable column and the second inflatable column (a). The inflatable columns (a) are made of membrane.

5. The flexible vibration adaptive wind turbine blade according to claim 2 or 3, characterized in that, Several air chambers (b) laid on the skeleton structure are connected to the adjacent secondary beams through the connection ports of one-way valves (201).

6. The flexible vibration adaptive wind turbine blade according to claim 5, characterized in that, The one-way valve (201) includes two leaflets (c), the edges of which extend along the air intake direction and close together to shut off; the expansion body (200) is made of an elastic material.

7. The flexible vibration adaptive wind turbine blade according to claim 1, characterized in that, The flaps include multiple independently movable flap segments arranged along the wingspan direction, and each flap segment has an inflatable chamber (210) on both sides of the chord.

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