Abstract:
An object of the invention is to reduce a fluid resistance generated on a cylindrical body. A fluid resistivity reducing structure for reducing the fluid resistance generated on the cylindrical body B which relatively moves in a fluid comprises: a groove M provided on a surface S of the cylindrical body B, wherein: the groove M is constituted so as to extend roughly in a longitudinal direction of the cylindrical body; and so as to introduce the fluid moving along the surface of the body into the groove.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a fluid resistivity reducing structure for reducing a resistive force generated on a cylindrical body which has a cylindrical surface and moves relatively in a fluid.  
           [0003]    2. Brief Description of the Prior Art  
           [0004]    A conventional cylindrical body, for instance, a club shaft has in general a cylindrical smooth surface. On the other hand, a conventional suspending rope for suspending a bridge has another cylindrical smooth surface on which minute projections for accelerating a transition from a laminar flow status to a turbulent flow status are embedded.  
           [0005]    However, if the shaft and the rope respectively having those shapes are located in an air ambient (a sort of fluid) to move in a certain relative velocity range, a slipless flow inherent to a fluid velocity distribution on the cylindrical smooth surface cannot be avoided enough, which causes to enlarge the fluid resistive forces of the shaft and the suspending rope.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is carried out to solve the so far conventional problems as mentioned above. An object of the invention is to provide a fluid resistivity reducing structure for reducing a resistive force generated on a cylindrical body moving in a fluid wherein a surface shape of the cylindrical body is modified so that a pressure at a stagnation point is reducible, a burble point is movable toward a downstream of the fluid and a fluid velocity distribution along the surface of the cylindrical body does not satisfy a slipless flow condition.  
           [0007]    As shown in FIG. 1, a frictional resistive force generated on the surface S of the cylindrical body (referred simply to as “body” hereinafter) B is proportional to a frictional reaction force τ which is defined by Equation (1) as follows: 
           τ=μ du/dy|   y=0   (1). 
           [0008]    Herein μ is a viscosity coefficient of the fluid while du/dy is a linear gradient of the velocity distribution u toward a perpendicular direction y of a fluid flow direction x which can take any values: positive, zero and negative. Further, a suffix: y=0 means a value of the gradient du/dy just on the surface S of the body B. Accordingly, either a reduction in an absolute value of the linear gradient du/dy or transforming a sign of the gradient from a normally positive region as shown in FIG. 1 into a negative region can reduce the fluid friction resistivity.  
           [0009]    In order to realize the phenomena as mentioned above, it would be enough either to bring a difference in a velocity component in a vicinity of the surface S of the body B close to zero or to produce a reverse flow of the fluid on the surface S of the body B thereby to turn the sign of the linear gradient du/dy negative.  
           [0010]    Consequently, a groove M for introducing the fluid, which moves tangentially along the surface S of the body B, and for rotating the fluid toward the moving direction are provided on the surface S of the body B according to the present invention as can be seen from FIG. 2.  
           [0011]    By constituting the structure like this, the rotation of the fluid toward the flowing direction generates the reverse flow on a bottom of the groove M, which changes the sign in linear gradient of the velocity component in the fluid flow direction into a negative value.  
           [0012]    Simultaneously, the absolute value in linear gradient of the fluid velocity component can be reduced in a region of the groove M. As a result, a “slip flow” takes place on the surface S of the body B.  
           [0013]    If the “slip flow” is generated by the groove M on the surface S of the body B as mentioned above, the burble point Q which is located on an upstream side of the fluid with respect to body B as shown in FIG. 3 moves toward the downstream side as shown in FIG. 4.  
           [0014]    As a result, the downstream width W 1  of the body B shown in FIG. 4 turns narrower than that W 2  of the body B unequipped with the groove M as shown in FIG. 3, which raises a pressure of a base region K located on a downstream-sided end of the body B higher. Simultaneously, the turbulent flow in the fluid flow is terminated on the downstream sided end of the body B. Accordingly, the pressure resistance of the body B lowers.  
           [0015]    Whereas a pressure of a stagnation point Y of which body B is unequipped with the groove M as shown in FIG. 3 is in general high, the groove M located on a stagnation line L as shown in FIG. 4 reduces the stagnation pressure of the stagnation point Y, which lowers the pressure resistance generated on the body B.  
           [0016]    The grooves M according to the present invention might be provided either on a whole surface of the body B or partially on the surface. The long grooves might be provided continuously as well as the short grooves might be provided intermittently according to the present invention. It need scarcely be said that a combination of the long grooves with the short grooves is herein employable.  
           [0017]    Any cross-sectional shapes of the grooves M can herein be employed so long as they have the shapes which can reduce the fluid friction resistivity as mentioned above, namely so long as the velocity of the fluid which flows along the surface of the body does not satisfy the slipless flow condition. Representative cross-sectional shapes of the grooves M are exemplifiably shown in FIGS.  5 - 9 . In the drawings, arrow marks indicate the flowing directions of the fluids. In some cases, the fluids flow in parallel with the surfaces of the bodies while, in other cases, the fluids flow slantingly with respect to the surfaces of the bodies (in intersecting directions). In still other cases, the fluids flow, of course, perpendicularly to the surfaces.  
           [0018]    A groove M 1  shown in FIG. 5 has a rectangular cross-section while another groove M 2  shown in FIG. 6 has another rectangular cross-section which is equipped with two visors H 1  and H 2  on an upstream edge and on a downstream edge of the groove M 2 , respectively. Still another groove M 3  shown in FIG. 7 has a “U”-shaped cross-section which is equipped with curvatures on two corners formed between a bottom surface and side wall surfaces. Further still another groove M 4  which is shown in FIG. 8 has an approximately ellipsoidal cross-section while moreover further still another groove M 5  shown in FIG. 9 has a substantially circular cross-section.  
           [0019]    As the bodies cited according to the present invention have roughly the cylindrical shapes, the cross-sectional shapes of the bodies are not limited to the circular cross-sections but include conic sections. The circular cross-sections substantially resembling the ellipsoidal shape, polygonal cross-sections, corolla-shaped cross-sections constituted of petals etc. are all included in the cross-sections of the cylindrical bodies according to the present invention.  
           [0020]    As examples of the polygonal cross-sections, you can easily realize them if you planarize the cylindrical surfaces located between grooves M 1 -MS which are respectively shown in FIGS.  5 - 9 .  
           [0021]    The surface S of the body B whereon the groove M is provided might herein be smooth, coarse or uneven.  
           [0022]    The body B itself might be a rigid body, a soft body or an elastic body herein. Sorts of materials used for the body B are unrestricted so long as they are capable of being provided with the groove M. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a view showing a fluid velocity distribution generated on a vicinity of a smooth surface of a cylindrical body;  
         [0024]    [0024]FIG. 2 is another view showing fluid velocity distributions generated in a groove and on a vicinity of the surface of the cylindrical body;  
         [0025]    [0025]FIG. 3 is a view showing a behavior of a fluid which flows on the smooth surface of the cylindrical body;  
         [0026]    [0026]FIG. 4 is another view showing another behavior of the fluid flowing on the surface of the cylindrical body which is either engraved or provided with convex stripes on the surface;  
         [0027]    [0027]FIG. 5 is a cross-sectional view showing a groove which is employable according to the present invention;  
         [0028]    [0028]FIG. 6 is another cross-sectional view showing another groove which is employable according to the present invention;  
         [0029]    [0029]FIG. 7 is still another cross-sectional view showing still another groove which is employable in the present invention;  
         [0030]    [0030]FIG. 8 is further still another cross-sectional view showing further still another groove which is employable according to the present invention;  
         [0031]    [0031]FIG. 9 is moreover further still another cross-sectional view showing moreover further still another groove employable in the present invention;  
         [0032]    [0032]FIG. 10 is a side view showing a shaft according to Embodiment  1 ;  
         [0033]    [0033]FIG. 11 is a cross-sectional view taken along a line H-H of FIG. 10;  
         [0034]    [0034]FIG. 12 is another cross-sectional view of another shaft according to Embodiment 2;  
         [0035]    [0035]FIG. 13 (PRIOR ART) is a cross-sectional view of a conventional shaft which is referred to as a comparative example;  
         [0036]    [0036]FIG. 14 is a graph for comparing tip end velocity depedences of rotational torques of the shafts among Embodiment 1, Embodiment 2 and Comparative Example; and  
         [0037]    [0037]FIGS. 15A and 15B are views showing a schematic constitution of a rotational torque testing machine used for measuring the rotational torques to obtain relationships illustrated in FIG. 14. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Hereinafter are detailed the preferred embodiments according to the present invention with reference to the drawings from FIG. 10 to FIG. 15B. The best modes contemplated by the inventors during carrying out the invention into practice will also be described corresponding to the preferred embodiments.  
       EMBODIMENT 1  
       [0039]    [0039]FIG. 10 is a side view showing a shaft S 1  of Embodiment 1 wherein an illustration of the groove M 2  to be described later is omitted.  
         [0040]    Herein the shaft S 1  is 1170 millimeters (referred to as “mm” hereinafter)-long, an outer diameter r 1  of a tip end point E is 9.3 mm φ, another outer diameter r 2  of a grip end point G is 15.8 mm φ and still another outer diameter r 3  of an intermediate point F which is located at 900 mm-remote from the tip end point E is 15.15 mm φ. A shaft portion extended from the intermediate point F to the tip end point E corresponds to a measurement range of the rotational torque testing machine to be described later.  
         [0041]    [0041]FIG. 11 is an enlarged cross-sectional view taken along a line H-H of FIG. 10 wherein the line H-H is located at a position (referred to as “Position H” hereinafter) which is located 320 mm-remote from a tip end point E of the shaft S 1 .  
         [0042]    As can be seen from FIG. 11, the shaft S 1  is manufactured by means that eleven pieces of longitudinally extending straight convex stripes  3  are monolithically provided in an equiangular interval with respect to a center axis on a surface of a main body  1  of a conventional shaft S 0  cited as a comparative example shown in FIG. 13 having a circular cross-section and a 0.8 mm-thick tube wall, which consequently results in eleven pieces of grooves  2  relatively formed between each convex stripe  3 .  
         [0043]    The groove  2  is 1.2 mm-wide and 0.4 mm-deep at Position H while a cross-sectional shape of the groove  2  is approximately quadrangular. A cross-sectional shape of the convex stripe  3  is also quadrangular and angles of outer edge corners are approximately rectangular. Accordingly, the outer diameter of the shaft S 1  is larger by a height of the convex stripe  3  than that of the shaft S 0  by comparison.  
         [0044]    The shaft S 1  is a so called carbon shaft having 65 grams (referred to as “g”) which is fabricated from a compact made of carbon filaments and epoxy resin.  
       EMBODIMENT 2  
       [0045]    [0045]FIG. 12 is a cross-sectional view showing a shaft S 2  according to Embodiment 2 to be compared with FIG. 11. The 1170 mm-long shaft S 2  is cross-sectioned at a position which is equivalent to the previously mentioned Position H and shown being enlarged in FIG. 12.  
         [0046]    The shaft S 2  is manufactured by means that four pieces of longitudinally extending straight convex stripes  4  are monolithically provided with the shaft S 2  in another equiangular interval with respect to the center axis partially on the surface of the main body  1  of the shaft, which consequently results in three pieces of grooves  5  in total relatively formed between each convex stripe  4 .  
         [0047]    As shown in FIG. 12, the shaft S 2  has the cross-sectional shape sectioned at Position H wherein four pieces of the convex stripes  4  are provided with a 1.2 mm interval within a range of 90 degrees with respect to the center axis onto the surface of the main body  1  of the shaft of which outer diameter is 10.0 mm. A cross-sectional shape of the convex stripe  4  is quadrangular and outer edge corners are approximately rectangular. The convex stripe  4  is 1.0 mm-wide and 0.4 mm-high at Position H while the groove  5  is 1.2 mm-wide and 0.4 mm-deep, respectively.  
         [0048]    The shaft S 2  is also a so called carbon shaft the same as the shaft S 1  but has a weight of 62 g.  
       COMPARATIVE EXAMPLE  
       [0049]    [0049]FIG. 13 is a view showing a conventional shaft S 0  having a circular cross-section which is cited as Comparative Example of the shafts S 1  and S 2  of Embodiments 1 and 2, respectively. Namely, the shaft S 0  is referred to demonstrate by comparison how much air resistances of the shafts S 1  and S 2  are improved.  
         [0050]    The shaft S 0  is 1170 mm-long, the same as the shafts S 1  and S 2 .  
         [0051]    Referring to FIG. 10, an outer diameter r 1  of a tip end point E is 8.5 mm φ, an outer diameter r 2  of a grip end point G is 15.0 mm φ, an outer diameter r 3  of an intermediate point F which is located 900 mm-remote from the tip end point E is 14.35 mm φ and a tube wall is 0.8 mm in thickness.  
         [0052]    [0052]FIG. 14 is a graph showing tip end velocity dependences of rotational torques (namely air resistances). In the graph, the tip end velocity dependence of the air resistances are compared among the shafts S 1 , S 2  and S 0  of Embodiments 1, 2 and Comparative Example.  
         [0053]    The rotational torques (namely air resistances) of the shafts S 0 , S 1  and S 2  are respectively measured by a rotational torque testing machine which is shown in FIGS. 15A and 15B. Namely, the shafts S 0 , S 1  and S 2  are loaded individually on a rotation arm  13  which is perpendicularly installed with respect to a rotating axle  12  to be rotated being driven by a motor  11 . Rotational torques (kg·m) are measured by a torque meter  4  at adequate rotating speeds of the shaft. A measurement range of the air resistance is restricted to a region located between two points which are 691 and 1591 mm-remote from a rotational center, respectivly, namely within 900 mm in length from the tip end point E to the intermediate point F, because an air resistance value measured without loading the shaft is subtracted from the value measured during loading the shaft as illustrated in FIGS. 15A and 15B. Rotating directions of the shafts S 0 , S 1  and S 2  are indicated by arrows which are shown in FIGS.  11 - 13 . Herein Reynolds&#39; numbers during measurement are about an order of  1 E 4 .  
         [0054]    As can be clarified from FIG. 14, the rotational torque (air resistance) of the shaft S 1  according to Embodiment 1 is reduced by about 20% than that of the conventional shaft S 0  at 40 meters per second (referred to as “m/sec”) in tip end velocity. Simultaneously, that of the shaft S 2  according to Embodiment 2 is reduced also by about 20% under the same conditions.  
         [0055]    As the shafts S 1  and S 2  according to Embodiments 1 and 2 are reduced in air resistance as mentioned above, golf clubs equipped with those shafts can be swung faster than the conventional golf clubs if the conditions except for the shafts are unified to be the same. Being capable of swinging faster accelerates head speeds of the golf club, which lengthens flying distances of golf balls compared with the golf club equipped with the conventional type golf shaft.  
         [0056]    Though they are unshown in drawings, working effects are the same as those of Embodiments 1 and 2 when 1.2 mm-wide and 0.5 mm-deep convex stripes which extend either spirally or snakily in the longitudinal direction of the shaft on a whole surface of the shaft are, for instance, provided instead of the grooves M 2  and MS according to Embodiments 1 and 2.  
         [0057]    As the grooves for generating the slip flow of the fluid are provided on the surface of the cylindrical body according to the present invention as mentioned above, the grooves can effectively reduce the fluid resistivity which is induced on the cylindrical body, namely the fluid friction resistance and the pressure resistance. Accordingly, the fluid friction resistance and the pressure resistance which are induced on the cylindrical bodies such as on the shaft of the golf club, on the suspension rope of the bridge, on a guy for lifting a sail of a yacht, on an electric cable, on an electric wire, on a supporting pole for a pantograph collector etc. can be reduced according to the present invention.