Abstract:
A fluid energy converter includes: a rotatable U-shaped rim rack having a raised along-edge wall forming a rail, a rotatable cylindrical frame and a plurality of vertical rectangular blades uniformly distributed and rotatably mounted in the frame. Each blade includes rollers alternately sliding in the recessed rail. The U-shape of the rim rack forms a hollow chamber in which a portion of the frame is received. The blades mounted in the frame are allowed to revolve about an arbor of the frame and at the same time, with the rollers being guided by the rail of the rim rack, the blades spin about their own axes. Instead of mechanical control, the rail formed in the rim rack is defined by a curve that has unique mathematic characteristics to set each blade to an optimum angle for receiving wind power so as to reduce resistance and better action of force thereon.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a fluid energy converter that utilizes fluid flow to generate rotational kinetic energy and uses the rotational kinetic energy to cause movement of fluid for flowing in a specific direction. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    An early vertical axis wind turbine (VAWT) was first patented by C. hand in 1846, of which the patent bearing a title of “Water wheel” was issued U.S. Pat. No. 4,517 on May 16, 1846. This invention provides blades that have one end coupled to an axle and an opposite end that is changeable in position for changing the angle of the blades in order to reduce resistance. 
         [0003]    In the design of the above discussed water wheel, the axle is coupled to multiple pairs of arms that extend radially. Each pair of arms carries a blade at ends thereof with the blade being pivotable. When the blade that takes a force is rotated about the axle by 180 degrees, the blade itself rotates by 90 degrees in order to reduce the resistance. During the rotation of the blade about the axle, the blade is also allowed to rotate about its own axis, whereby various angles may be dynamically formed between the blades and the fluid flow in order to reduce resistance and provide improved action of force. 
         [0004]    This type of arrangement that the blades are rotating about their own axes when rotated about a primary axle was known as early as the teaching given in a U.S. patent issued to C. R. Gutting on 1906, of which the title is “Wind Wheel” (U.S. Pat. No. 809,431 issued on Jan. 9, 1906). With the arrangement of a complicated mechanism, when blades are rotated about a central shaft, the blades also rotate about their own axes, whereby various angles are dynamically formed between the blades and wind to reduce the resistance and improve action of force. 
         [0005]    In 1907, C. F. Whisler was issued a U.S. patent, called “Wind Wheel” (U.S. Pat. No. 862,299 issued on Aug. 6, 1907). This is also an invention of the above discussed type, and this invention uses sprocket wheels and a chain to cause blades to rotate about their own axes when the blades are rotated about a central shaft, whereby the same result can be obtained. 
         [0006]    What is concerned in the present invention is how to make blades rotating about their own axes when the blades are rotated about a central shaft in order to reduce resistance and improve action of force. Many inventors proposed different solutions to address such an issue. Some of the recent prior art references are listed as follows: 
         [0007]    In 2010, Eldon L. Stroburg was issued a U.S. patent, called “Windmill with Pivoting Blades” (U.S. Pat. No. 7,766,602 issued on Aug. 3, 2010). This invention utilizes a gear train to cause blades to rotate about their own axes when the blades are rotated about a central axis in order to dynamically set the angles between the blades and wind. The same result can be obtained. 
         [0008]    In 2008, a Taiwan Patent Application disclosed a blade set of vertical wind power generator and a method for coupling variable winding for wind power generator (Taiwan Patent Publication No. 2008339453 published on Aug. 16, 2008). The legal status of the application is publication and teaches use of adjustable link bars to cause blades to rotate about their own axes when the blades are rotated about a central axis. Again, the same result can be obtained. 
         [0009]    In 2010, a US Patent Application, called “Wind and Water Turbine” and owned by Lester Hostetler, was published (US Publication No. 2010/0060008 A1 published on Mar. 11, 2010). The legal status of this application is publication. When blades are rotated about a central shaft, an elliptic channel is set up inside a circular channel along which the blades rotate about the central shaft. A mechanism switch is provided outside the channel, whereby the mechanical switch forces rollers of the blades to alternately enter the channel. The elliptic channel inside the circular channel along which the blades rotate about the central shaft causes the blades to rotate about their own axes so as to dynamically set various angles between the blades and wind and provide the same result. 
       SUMMARY OF THE INVENTION 
       [0010]    An objective of the present invention is to provide a fluid energy converter that reduces resistance and generates improved result of force action. 
         [0011]    To achieve the objective, the solution adopted in the present invention is as follows: 
         [0012]    A fluid energy converter comprises a rotatable rim-like rack, or simply rim rack hereinafter, having a U-shaped cross-section and having a raised along-edge wall having an end surface that is recessed to form a channel serving as a rail; and a rotatable frame that carries a plurality of blades each of which is mounted to the frame in a rotatable manner and each having an upper edge having opposite ends to which rollers are mounted for sliding in the rail channel of the rim rack. Flow energy of a fluid may be employed to cause motion of the blades and the motion of the blades drives the frame to rotate thereby generating kinetic energy. Oppositely, rotational kinetic energy of the frame can be used to cause motion of the blades and the motion of the blades causes a fluid to move. The rail channel of the wheel rim guides the movement of the blades, making the movement of the blades showing the greatest efficiency. 
         [0013]    The rotational motions of the frame and the wheel rim have a common rotation center, which, for easy description herein, will be referred to as “revolution axis”. Each blade has a center line that serves as a rotation center of the spinning of the blade about its own axis and will be referred to as “spin axis” herein. It is noted here that all the rotating interfaces found in the present invention are supported by bearings in order to reduce the frictional force. 
         [0014]    The rotatable frame comprises multiple pairs of support arms, and the two support arms of each are arranged, in a symmetrical manner, at upper and lower sides of the frame. The distal ends of the support arms of each pair support therebetween a rotatable blade, which has shoulders and feet to which rollers are respectively mounted in such a way that, when the blade spins, the blade rollers are slidable in a rail channel defined in a raised portion of the wheel rim. The frame has an arbor having outward projecting portions to serve as an interface for exchange between rotational energy of the frame and an external energy source. 
         [0015]    The U-shaped rim-like rack is arranged above the rotatable frame and both are individually rotatable about the revolution axis. The raised along-edge portion of the rim rack exceeds the thickness of the upper support arms and this is a hollow chamber formed in the rim rack for accommodating the upper support arms of the frame. The raised along-edge portion of the rim rack forms a recessed rail channel. The rail channel has a depth that is sufficient to the rollers mounted to the shoulders of the blade. When the rollers are moved in the recessed rail channel, the blades are caused to spin. Thus, when the blades revolute about the revolution axis, the rollers mounted to the shoulders thereof are sliding in the rail and are guided by the rail to cause spinning of the blades, thereby changing the directions of the blades. 
         [0016]    The recessed rail channel that is formed in the rim rack has an opening for receiving the entry of the rollers. The rail channel defines a curve of trace or locus that is of a special curve. Such a curve is similar to a tip of a cardioid of a polar coordinate system and no rail segment is arranged at and close to the tip to thereby serve as an entry opening for the rollers during the rotation of the blades. The curve of the rail channel adopted in the present invention is special mathematic characteristics, wherein at least one of the two rollers on the shoulders of each blade must be always kept on the recessed rail channel and the outer one of the rollers on the shoulders of the blade is always kept on the rail channel. When the blade rotates, the two rollers alternately enter the recessed rail, and at the moment when the two rollers interchangeably enter the rail, the two rollers are simultaneously on the recessed rail channel. 
         [0017]    The blades revolute about the revolution axis with the frame and the rollers of the blade are guided by the rail to cause spinning of the blades. When the blades revolute by one full turn about the revolution axis, the blades also make a half turn of spinning. Revolution of 180 degrees makes spinning of 90 degrees and revolution of 90 degrees makes spinning of 45 degrees. 
         [0018]    The curve of the rail channel is a symmetric smooth curve having an axis of symmetry When fluid enters in a direction perpendicular to the axis of symmetry, the fluid drives the blades to cause rotation of the frame. Being guided by the rail, the included angle of each blade and the fluid varies to provide the best result of force action for the frame. 
         [0019]    The rim rack has a surface on which a direction mark is made to perpendicular to the symmetry axis of the rail channel and will be referred to as “flow direction mark” for easy description. When the flow direction mark of the rim rack is consistent with the inflow direction of fluid, the action of force applied to the frame by the fluid is the best for the rotational motion of the frame. 
         [0020]    To receive the energy of the fluid, air rudders are mounted in the direction of the flow direction mark and the air rudders are driven by winds to have the flow direction mark of the rim rack consistent with the inflow direction of the fluid. Under this condition, the power of the fluid is the best for driving the rotational motion of the frame. Oppositely, to use the rotational kinetic energy to propel a fluid for flowing, the flow direction mark of the rim rack is set at a fixed direction so that the most efficient flow of the fluid in a flowing direction can be realized. 
         [0021]    As to the conversion of flow energy of fluid, the present invention provides a design that requires no mechanical gears, links, or switches and that may drive blades to spin about their own axes so as to dynamically set an angle between each blade and the direction of wind to be a proper value. Instead, a rail formed according to dynamic geometric principle is adopted and the rail is located outside the circle of revolution motion of the blades. Also, a proper operation mechanism is provided so that when the blades rotate about a center of the mechanism, the rail guides the blades to spin to dynamically set the blades to maintain various included angles with respect to the direction of wind or air flow, whereby the fluid energy converter according to the present invention may reduce resistance and better the action of force applied thereto. 
         [0022]    Such a design uses no chain, gear, or link to force the blades to spin and does not require mechanical switches that forcibly cause rollers of the blades to enter the rail. Instead, the geometry of a rail located outside the circular lotus of revolution of the blades to naturally guide the rollers of the blades to alternately enter the rail, allowing the blades to rotate and thus take the optimum direction and realizing the most efficient conversion of energy of fluid. In the present invention, the blades may have a maximum width that is close to the diameter of the frame. The number of the blades is generally not subjected to any limitation, but is associated with the width of the blades. The material that makes the blades is selected depending on the nature of the fluid used and can be for example a plate or a sail. 
         [0023]    Fluid used can be compressible or incompressible. The conversion of fluid energy can be either receiving fluid energy and generating rotational kinetic energy or using rotational kinetic energy to drive fluid to flow. Different accessory or ancillary mechanism may be used for different applications. 
         [0024]    Some local or partial modifications may be made on the essential mechanism of the present invention according to the nature of the fluid used and the direction of conversion and will be briefed as follows: 
         [0025]    (1) For reception of energy of compressible fluid in small scale, air rudders may be mounted according to the direction of the flow direction mark provided on the rim rack to tract the rail on the rim rack so as to dynamically set various included angle between each blade and the direction of wind for reducing resistance and bettering action of force. 
         [0026]    (2) For reception of energy of incompressible fluid or powerful fluid, to improve the strength of the device in order to take the powerful fluid, the structure of the device can be made symmetric between the upper and lower sides. Upper and lower ends of the arbor of the rotatable frame may be both provided with rim racks that are rotatable simultaneously and are both provided with rail channels. Rollers are respectively mounted to two shoulders and two feet of each of the blades. The rollers on the upper and lower sides of each blade are movable in the rails of the upper and lower sides. Similarly, fluid enters in the direction of the flow direction mark in order to reduce resistance and better action of force. 
         [0027]    (3) For using kinetic energy to drive fluid to flow, the mechanism that is described above for receiving energy of incompressible or powerful fluid is operated in a reversed way. No air rudder is provided and the rim racks that comprise rails are provided and fixed with the flow direction mark on the rim rack aligning with the direction in which the fluid is to be driven to flow. Under the guidance of the rails, the blades take a motion that is the best for driving the fluid to flow. 
         [0028]    (4) For receiving energy of compressible fluid in a large scale, the center axis of the fluid energy converter is defined by a vertically fixed hollow tower like shaft, wherein the hollow shaft provides a channel or space in which wires are received for mounting an alarm device thereon and to serve as a maintenance channel. The center axis of the frame is now formed as a sleeve that is fit over the center axis of the tower like shaft interfaced by bearings and an energy conversion unit is provided on an outward extension section of the sleeve of the frame. Such a large-scale compressible fluid energy receiving device comprises blades that are rectangular area-variable blades. The interior of each of the rectangular blades comprises a sail structure and an outer framework of the blade is a support structure that may contract and expand the sail. 
         [0029]    The inventor has identifies a curve for the rail, in respect of mathematic equation and proofs, which satisfies the above discussed requirements. The mathematic proofs will be published in the article “Mathematics on a Windmill with Non-mechanical Control Pivoting Blades” of Journal of Tungnan University. In addition, the inventor also makes numerical and graphic simulation on computers to verify that the operation of the curved lotus of the basic mechanism according to the present invention is feasible and correct. Also, a prototype is also completed for verification. The mathematic characteristics of the curve will be described in the following and graphic simulation is provided in the drawings. 
         [0030]    This curve contains a family of curves, Tw, and each individual curve Tw(r, s) contains two parameters, r and s. The parametric equation of Tw(r, s) is as follows: 
         [0000]        x =( r+s/ 2)cos( t/ 3)cos( t )−( r−s/ 2)sin( t/ 3)sin( t )
 
         [0000]        y =( r+s/ 2)cos( t/ 3)sin( t )+( r−s/ 2)sin( t/ 3)cos( t ) 
         [0000]    where −(3/2)cos −1 (−s/4r)≦t≦(3/2)cos(−s/4r) and r is the radius of the rotatable frame of the present invention, and more precisely, the distance from the center axis of the frame to the center axis of spinning of each blade; s is the width of the blade and more precisely, the distance between centers of left and right side rollers of the blade. The curve Tw(r, s) shows the following characteristics: having a radius r and being a circle O with the center located at the original point. For a line segment S having a length s&lt;2r, when the middle point M of the line segment S is located on the circumference of the circle O and an end of the line segment S is on the curve Tw(r, s), then a line of incidence that is parallel to y axis generates a line of reflection with respect to the line segment S and a parallel vector of the line of reflection is tangential to the circle at point M, see  FIGS. 1 and 2 . The curve Tw(r, s) has a shape similar to a cardioid of a polar coordinate system that is a curve that is symmetric and has a tip. The tip of the curve is located on the circumference and all the remaining points of the curve, other than the tip, are located outside the circle. In the present invention, the center of the circle O is the center axis of the mechanism and is also the revolution axis. The circle O is the track of revolution of the blades when the blades take the rotational motion and is also the lotus of revolution of the spinning axes of the blades when the blades revolve. The curve Tw is the recessed rail that guides the spinning of the blades. The middle point M is the spinning axis of the blade. The line segment S is the width of the blade and the two ends of the line segment S are respectively the centers of the left and right side rollers of the blade. 
         [0031]    The description of the present invention given herein is provided for the purposes of illustration of the operation mechanism according to the present invention, not to explain complicated mathematic formula, so that only the mathematic equation of the curve that defines the rail is shown herein. Some descriptions of the drawings will be given as follows. 
         [0032]      FIG. 1  shows the relationship among the curve Tw, the circumference of the rotatable frame, and the line segments of the blades. The shown Tw(1, 1.46) represents the curve of rail. The circle O that has a center o and a radius equal to 1 represents a circumference  2  of a rotatable frame having a radius equal to 1. Each line segment represents a blade line segment  3  having a width s=1.46. The middle point M of the line segment S is located on the circle and an end being located on the curve Tw.  FIG. 1  illustrates the different locations of a blade taking a constant-speed full-turn revolution about the revolution axis. 
         [0033]      FIG. 2  shows a characteristics diagram of the curve Tw. Characteristics of the curve Tw(1, 1.46) are illustrated. A line of incidence  4  that is parallel to y axis generates a line of reflection  5  with respect to the line segment S, providing a positive driving force to the circle. The line segment S represents a blade and the circle indicates the lotus of a spin axis of a blade revolving about the revolution axis. The force acting on the blade causes positive direction rotation of the frame. Theoretically, during the rotation of the blades, there is no resistance and the frame is driven by the maximum propelling force to rotate the frame. It can be seen from  FIG. 2 : the line segment S 1  is perpendicular to the line of incidence, namely the blade receives the complete force. The line segment S 4  is parallel to the line of incidence, namely the blade is parallel to the fluid and the fluid induces extremely small resistance to the blade. The line segments S 2 , S 6  forms an included angle of 45 degrees with respect to the line of incidence, whereby the blades still keep an excellent action of force. 
         [0034]    Then, it is illustrated the relationship and variation between the two rollers on the shoulders of the blade and the recessed rail in the process of rotation of the blades. The line segment S represents the blade. The line segment S has two ends respectively representing the two rollers on the shoulders of the blade. The curve Tw represents the recessed rail. It can be seen from  FIG. 2  that the two ends of each of the line segments S 4 , S 5  are on the curve Tw, namely the two rollers on the shoulders of the blade are both on the rail. The line segment S 3  has an end that is just about to enter the curve Tw, namely another roller on the shoulders of the blade is going into the rail. An end of the line segment S 6  is on the curve Tw and an end has already left the curve Tw, namely there is still one of the rollers kept on the rail. The line segment S 1  in operation is subjected to the variation through S 2 , S 3 , S 4 , S 5 , S 6  to eventually return to the position of S 1 . The line segment S 1  is exactly turned over by 180 degrees. It can be seen from  FIG. 2  that the two rollers on the shoulders of each blade are such that at least one of the rollers is always kept on the recessed rail. When the blade undergoes revolution, the two rollers alternately enter the recessed rail. At the moment when the two rollers interchangeably enter the rail, the two rollers are simultaneously on the recessed rail. Mathematic proof and empirical test indicate that for a rail having a configuration of the curve Tw, a normal operation can be realized with the two rollers being simultaneously on the rail. 
         [0035]      FIG. 3  illustrates successive phases of a full-turn rotation of a three-blade frame. The process that when the blade that contains two rollers, a and b, take a full turn of revolution about a center axis, the two rollers, a and b, alternately enter the rail is illustrated. In the drawing, the frame has a radius r=1, a blade width s=1.8. The frame revolves in a constant speed for a full turn and computer simulation is made to provide nine drawings of successive operation. Under the guidance of the rail, after a full turn of revolution, the blades return to the original position, but the rollers, a and b, switch with each other, and thus the blade makes a spin of 180 degrees about its own axis. 
         [0036]    The foregoing objectives and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. 
         [0037]    Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  illustrates relationship among a curve Tw, a circumference of a rotatable frame, and line segments representing blades. 
           [0039]      FIG. 2  shows a characteristic diagram of the curve Tw. 
           [0040]      FIG. 3  illustrates successive phases of a full-turn rotation of a three-blade frame. 
           [0041]      FIG. 4  illustrates an example of the present invention for an application to receiving and converting energy of compressible fluid into kinetic energy for generating of electrical power. 
           [0042]      FIG. 5  illustrates an example of converting rotational kinetic energy into flow energy of fluid. 
           [0043]      FIG. 5A  is a schematic view illustrating an application of the present invention to a propeller of a boat. 
           [0044]      FIG. 6  is a mechanism diagram of a fluid energy converter according to the present invention. 
           [0045]      FIG. 7  is a diagram illustrating a rotatable frame that carries blades. 
           [0046]      FIG. 8  is a diagram illustrating the rotatable frame. 
           [0047]      FIG. 9  is a diagram illustrating a rectangular blade that carries four rollers. 
           [0048]      FIG. 10  is a diagram illustrating a rim-like rack. 
           [0049]      FIG. 11  is a diagram showing a back side of the rim-like rack. 
           [0050]      FIG. 12  is a schematic view showing a hollowed rim-like rack. 
           [0051]      FIG. 13  is a schematic view illustrating a dual-rim rack structure. 
           [0052]      FIG. 14  is a diagram showing a symmetrically-arranged rotatable frame structure. 
           [0053]      FIG. 15  is a diagram showing a rim rack to which air rudders are mounted. 
           [0054]      FIG. 16  is a diagram showing a hollow shaft. 
           [0055]      FIG. 16A  is an enlarged view of  FIG. 16 . 
           [0056]      FIG. 17  illustrates a rotatable frame mounted to a hollow shaft. 
           [0057]      FIG. 18  is a diagram showing an area-adjustable rectangular blade. 
           [0058]      FIG. 19  is a diagram showing a local structure of the area-adjustable blade. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0059]    The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
         [0060]    To better explain the technical solution provided by the present invention, a detailed description will be given below with reference to embodiments of the present invention. The description given below, however, is provided only for illustration of a basic mechanism of the present invention and several modified embodiments thereof and the description should not be construed that the present invention is limited to such embodiments. 
         [0061]      FIG. 4  illustrates an example of the present invention for an application to receiving and converting energy of compressible fluid into kinetic energy for generating of electrical power. The present invention can also be used as an electrical power generation windmill or water mill. 
         [0062]      FIG. 5  illustrates an example of the present invention in which, opposite to generation of electrical power, rotational kinetic energy is converted into flow energy of fluid. The present invention can be used as a tool for propelling boats. 
         [0063]      FIG. 6  is a mechanism diagram of a fluid energy converter  39  according to the present invention. The fluid energy converter  39  comprises: a rack  6  that is configured similar to a wheel rim that is rotatable about a fixed axis and an along-edge raised wall having a surface that is recessed to form an open rail  7 ; and a rotatable frame  8  that carries rectangular blades  9 , each of which has an upper edge having opposite ends each carrying a roller  10  that is slidably received in the recessed rail  7  of the wheel rim. The rim-like rack  6  is arranged above the rotatable frame  8  and they can rotate individually about a common revolution axis.  FIG. 7  is a diagram of the rotatable frame  8  that carries the rectangular blades  9 . The rotatable frame  8  comprises multiple pairs of blade support arms  11  that are of equal length and are connected to a frame arbor  12  and are respectively arranged at upper and lower ends of the rotatable frame  8  in a uniformly distributed manner. Coupled between distal ends of the upper and lower blade support arms  11  of each pair is a vertically arranged blade spin axle  13  of each rectangular blade  9 . The upper and lower blade support arms  11  are spaced from each other by such a distance that allows the rectangular blade  9  that is provided with rollers  10  to undertake spinning motion, which means herein a rotation about its own axis. When the rectangular blades  9  spins, the rollers  10  do not interfere with or collide the blade support arms  11 .  FIG. 6  illustrates the raised along-edge wall of the rim-like rack  6  exceeds the thickness of the blade support arms  11  of the rotatable frame  8  and this defines a hollow chamber of the rim-like rack  6  in which the blade support arms  11  of the rotatable frame  8  are accommodated. The raised along-edge wall of the rim-like rack  6  has a lower end surface forming the recessed rail  7  and the rail  7  is recessed to such a depth that is sufficient to accommodate the rollers  10  of the rectangular blades  9 , whereby the rollers  10  of the rectangular blades  9  are movable along the recessed rail  7  to cause the rectangular blades  9  to spin about their own axes. 
         [0064]      FIG. 8  is a diagram illustrating the rotatable frame, which is the rotatable frame shown in  FIG. 7 . The upper and lower ones of each pair of blade support arms  11  of the rotatable frame  8  support between distal ends thereof a blade spin axle  13  of the respective blade. The rotatable frame  8  has a radius r that is the horizontal distance between a center of the frame arbor  12  and a center of the blade spin axle  13 . 
         [0065]      FIG. 9  is a diagram of the rectangular blade  9  that carries four rollers  10  and that is the rectangular blade  9  shown in  FIG. 7 . The rectangular blade  9  has upper and lower edges each having opposite ends each carrying a roller  10 . The roller  10  is slidable within the recessed rail  7  of the rim-like rack  6  for reducing resistance and noise. Depending upon applications, the rectangular blade  9  can be made of various materials, such as plate or a sail. The rectangular blade  9  has a center line that in the embodiment illustrated coincides with the blade spin axle  13 . The blade spin axle  13  has a height that is substantially equal to the thickness of the blade support arms  11  (see  FIG. 8 ) plus thickness of rollers, height of the rectangular blade  9 , and a suitable amount of tolerance. The parameter s of the curve Tw(r, s) is the distance between centers of left and right side rollers of the blade. 
         [0066]      FIG. 10  is a diagram of the rim-like rack  6 , which is the rim-like rack  6  shown in  FIG. 6 . The rim-like rack  6  has a raised along-edge wall having a surface that is recessed to form a recessed rail  7  for receiving the rollers  10  of the rectangular blades  9  to slide in the recessed channel of the recessed rail  7  and to guide spinning of the rectangular blades  9 . The recessed rail  7  is a curve that is the curve Tw(r, s) discussed above.  FIG. 10  shows a dashed circle that indicates the position of the rotatable frame  8 , namely the trace that the blade spin axles  13  (see  FIG. 8 ) revolute about a fixed common revolution axis. The rim-like rack  6  forms a hollow chamber that has a depth sufficient to accommodate the upper circular frame portion of the rotatable frame  8  (see  FIG. 6 ). The rack has an arbor bore  14  that is located at the center of the dashed circle, namely coincident with the arbor of the rotatable frame  8  (see  FIG. 6 ). 
         [0067]      FIG. 11  is a diagram showing the back side of the rim-like rack  6  that is the back of the rim-like rack  6  shown in  FIG. 10 . The curve of the rail of the rim-like rack  6  has an axis of symmetry and the rim-like rack  6  forms a flow direction mark  15  on the back thereof in a direction normal to the symmetry axis of the rail curve to indicate an optimum flow direction of fluid, thus being named the “flow direction mark”  15 . A tail vane or air rudder may be mounted at the location of the flow direction mark  15 . 
         [0068]      FIG. 12  is a schematic view showing a hollowed rim-like rack  6 , which is formed by hollowing the rim-like rack  6  of  FIG. 10 . The rim-like rack  6  used in the present invention can be suitably hollowed or not hollowed at all. Edges and corners of the rim-like rack  6  are preferably made rounded to reduce overall weight and the resistance of flowing fluid. To simplify the illustration of drawings, the rim-like rack  6  that forms the rail is still shown with reference to the not-hollowed and not-rounded structure. 
         [0069]      FIG. 13  is a schematic view of a dual-rim rack structure  38  that is the dual-rim rack shown in  FIG. 5 . A shell-like connection  16  is used to connect and fix two symmetrically arranged rim-like racks  6 . The recessed rails  7  are arranged to face inward in a symmetric manner and the shell-like connection  16  is mounted to sharp tips of the curves of the recessed rails  7  of the rim-like racks  6  to form the dual-rim rack structure  38 . The two rim-like racks  6  are spaced from each other by a distance that is sufficient to accommodate the rotatable frame  8  (see  FIG. 6 ) in such a way to allow the rollers  10  of the rectangular blades  9  to be received and slide in the recessed rails  7 . 
         [0070]      FIG. 14  is a diagram showing a symmetrically-arranged rotatable frame structure, which is the symmetric rotatable frame  8  shown in  FIG. 5  and is arranged in a dual-rim rack structure  38  shown in  FIG. 13 . The arbor  12  of the rotatable frame is received through arbor holes  14  defined in two ends of the dual-rim rack structure  38  (see  FIG. 13 ). Such a rotatable frame  8  shows the characteristics of balanced force action and improves stability of the fluid energy converter  39  (see  FIG. 6 ). 
         [0071]      FIG. 5  illustrates an example of the present invention in which rotational kinetic energy is converted into the flow energy of fluid.  FIG. 5  shows a shell-like connection  16  that is made in the form of an up-side down tray (see  FIG. 5A ) and is located above the fluid energy converter  39  (see  FIG. 6 ). The flow direction mark  15  is automatically set in horizon. Mounted atop the shell-like connection  16  is a rotating device  17 , which controls the flow direction mark  15  to point to the direction in which push is to be made. Under this condition, the present invention may serve as a propeller  19  of a boat  18 . 
         [0072]    The present invention is applicable to compressible fluids or incompressible fluids to convert rotational kinetic energy into the energy of flowing fluid. However, under an opposite operation, the present invention may be used to convert flow energy of fluid into rotational kinetic energy 
         [0073]      FIG. 15  is a diagram showing a rim rack to which air rudders are mounted and which may serve as a rim-like rack  6  of energy conversion device  40  for large-sized wind power generation shown in  FIG. 4 . The rim-like rack  6  may comprises a single or multiple air rudders  20  and can be a rim-like rack  6  for converting the flow energy of fluid into rotational kinetic energy. The air rudders  20  are dragged by an inflow of fluid so as to cause the rim-like rack  6  rotating, aligning the flow direction mark of the rim-like rack  6  in a direction substantially parallel to the flow of fluid and providing the fluid energy converter  39  (see  FIG. 6 ) with the optimum conversion efficiency. 
         [0074]      FIG. 16  is a diagram showing a hollow shaft  21 , which is a central shaft of the large-sized power generation energy conversion device  40  of  FIG. 4  and is a hollow shaft  21  mounted in an erected manner on a base  22 . Wires  23  are received in the hollow space of the shaft. Mounted to the hollow shaft  21  are an alarm device  24 , a rail brake device  25 , and a frame brake device  26 . 
         [0075]      FIG. 17  illustrates a rotatable frame  8  mounted to a hollow shaft  21  (see  FIGS. 17 and 4 ), which are a hollow shaft  28  and a rotatable frame  8  for the large-sized electrical power generation energy conversion device  40  of  FIG. 4 . The shaft of the rotatable frame  8  forms a sleeve  27  that is fit over the hollow shaft  28  in a rotatable manner. Mounted to the sleeve  27  are an energy transmission unit  29  and a brake drum  30  for maintenance of the large-sized electrical power generation energy conversion device  40 . 
         [0076]      FIG. 4  illustrates an embodiment of the present invention applicable to large-sized power generation. A rim-like rack  6  to which air rudders  20  are mounted and a rotatable frame  8  that carries rectangular blades  9  are mounted, in a rotatable manner, to the hollow shaft  28  in such a way that rollers  10  mounted to opposite ends of an upper edge of each of the rectangular blades  9  are slidably received in a recessed channel  7  defined in the rim-like rack  6  (see  FIG. 6 ) to thereby form the large-sized electrical power generation energy conversion device  40  shown in  FIG. 4 . The present invention provides area-adjustable rectangular blade  9 , which has an outer framework serving as a support structure for sail. Mounted inside the rectangular blade  9  is a sail, on which a plurality of uniformly spaced sail bars  36  are mounted, as shown in  FIG. 18 . 
         [0077]      FIG. 18  is a diagram showing an area-adjustable rectangular blade  9 , which is the rectangular blade  9  of the large-sized electrical power generation energy conversion device  40  shown in  FIG. 4 . The outer framework  31  of the blade have upper and lower edges made of C-shaped beams  32  having opening facing inwards and left and right edges made of H-shaped beams  33 . Both the C-shaped beams  32  and H-shaped beams  33  have openings facing inward. The upper C-shaped beam  32  of the blade outer framework  31  comprises a pulley assembly  34  mounted to each of opposite ends thereof. The pulley assemblies  34  and ropes are provided for contracting and expanding a sail  35 , see  FIG. 19 . The lower C-shaped beam  32  receives and fixes a lower edge of the sail. For the sail mounted inside the blade, each said bar  36  has two ends to which sail bar rollers  37  are respectively mounted and are respectively received inside the inner C-shaped openings of the left and right H-shaped beams of the blade outer framework  31 . The sail bar rollers  37  are slidably in the inner C-shaped openings of the H-shaped beams without being separated therefrom. The inner sides of the left and right H-shaped beams  33  of the outer framework receive therein the sail bar rollers  37  at opposite ends of each sail bar  36  and the outer sides receive the ropes of the pulley assemblies  34 . The outer sides of the H-shaped beams  33  may be provided with covers to protect the ropes and reduces the influence of winds. The ropes are tightened to the uppermost sail bar  36  to pull the uppermost sail bar  36  and to move the underside sail bars  36  through the sail. When the uppermost sail  36  is pulled to reach inside the upper C-shaped beam  32  of the rectangular blade  9 , the rectangular blade  9  shows the condition of having the greatest wind receiving area and when it is moved to the location that is closest to the lower sail bar  36 , the rectangular blade  9  shows the condition of having the smallest wind receiving area. 
         [0078]    It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. 
         [0079]    While certain novel features of this invention have been shown and described and are pointed out in the annexed claim, it is not intended to be limited to the details above, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention.