JP2005003206A - Obtuse head object put in fluid stream - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an obtuse head object placed in a fluid stream and capable of reducing drag coefficient by stopping the fluid stream caused along the wake side front surface of the object according to the peeling of a boundary layer to prevent a large-scale Karman's vortex from generating and growing. <P>SOLUTION: A plate member as a flow stopping part is installed on the wake side of the obtuse head object 1 in which an upstream side surface is formed in an obtuse head curved surface relative to the flow F of the fluid to stop the flow of the fluid along the wake side front surface. In the plate member, parallel plates 7R and 7L as stopping plates are installed on the maximum thickness part 5 of a cylindrical body 2 on both right and left sides of the stream. A reverse flow reverse to a main stream direction occurs in the slightly downstream side of the maximum thickness part of the obtuse head object 1 to generate a pressure resistance. However, since the parallel plates are installed on the maximum thickness part of the cylindrical body, the reverse flow can be streamlined by the parallel plates and the resistance can be reduced less than that of the cylindrical body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a blunt body having a novel structure with reduced fluid resistance when placed in a fluid flow.

  Conventionally, in a gas such as the atmosphere, a liquid such as river water or seawater, or a fluid flowing in various pipes, a blunt body having a circular cross section or a shape close to it and a smooth curved surface is present. It is used. In particular, cylinders having a cylindrical shape are relatively easy to manufacture, so the manufacturing cost is low, and they are used in various fields. When such a blunt body is placed in a fluid flow, the boundary layer formed on the surface of the blunt body is separated by a strong pressure gradient, resulting in a large pressure loss downstream of the fluid flow, It is known to act on a body as a pressure resistance.

  For blunt bodies, fluid resistance due to pressure loss can be reduced if designed to be streamlined. I can't say that. However, depending on the application, the pressure resistance of the blunt body may not be negligible. In other words, when the pressure resistance increases, if the blunt body is on the fixed side and the fluid flows, the power cost required to flow the fluid cannot be ignored. The mechanical load associated with can be a problem. In addition, when the blunt body moves in the fluid, the energy required to overcome the pressure resistance and continue to move the blunt body increases.

As one of the blunt bodies, when a fluid flows at right angles to an axis with respect to an object having a cylindrical surface, the fluid resistance acting on the object has been experimentally determined. FIG. 3 shows a graph of the fluid resistance coefficient when a columnar object having a cylindrical surface is arranged alone as it is. The horizontal axis of FIG. 3 is a flow velocity U of the fluid, and the vertical axis represents the fluid resistance coefficient C _D. Here, the fluid resistance coefficient per unit length is defined by the following equation, as is well known.
C _D = D / [ρU2 · d / 2]
Here, D is fluid resistance per unit length [unit, N / m]
ρ is the density of the fluid [unit, kg / m ³ ]
d is the diameter of the columnar object [unit, mm], 50 mm in the experimental example
U is the fluid flow velocity [unit, m / s].
As can be seen from the graph shown in FIG. 3, there is a slight variation over the range from a flow velocity of 20 m / s to 60 m / s, but a value of about 1.3 is shown.

  FIG. 3 also shows a graph of the resistance coefficient of a D-shaped column having the same projected area in the flow direction and the same aspect ratio of the cross section parallel to the flow. The D-shaped column is a semi-cylinder with a half of the front edge side with respect to the fluid flow having a surface similar to that of a cylinder, and the rear edge side is a column with a quadrangular column. It shows a value of about 0.9 over the same flow range, and is known to be 30-35% smaller than that of a cylindrical body.

From the measurement results when the cylinder was placed in the flow, Karman vortex streets were alternately and periodically generated in the wake of the cylinder, indicating that the pressure loss was large and the pressure resistance was high. From the wall shear stress measurement results obtained by attaching a multi-heat film sensor to the surface of the cylinder, it has been observed that the entire boundary layer of the cylinder surface vibrates in synchronization with the frequency of the Karman vortex street. In addition, a backflow phenomenon indicating separation of the boundary layer is also observed before and after the maximum thickness position of the cylindrical body. From these measurement results or numerical calculations, for the cylinder placed in the flow, when the boundary layer peels, the fluid flow toward the boundary layer where the separation occurred along the downstream surface of the cylinder The formation of a Karman vortex, which forms a bridge-like vortex film and a secondary vortex, forms a large-scale vortex involving the wake, and releases it, occurs periodically. found. Conventionally, in order to reduce the resistance of such a cylindrical body, it has been proposed to provide protrusions and ribs on the outer peripheral surface of the cylindrical body (see Patent Documents 1 and 2), but this is not yet satisfactory.
Registered Utility Model No. 3063323 Microfilm of actual application No.54-114137

  Therefore, the problem to be solved by the present invention is that along the downstream surface of a blunt body such as a cylindrical body in a series of processes from separation of the boundary layer to generation / growth of a large-scale vortex structure. Focusing on the fluid flow, the fluid flow that is going to occur along the surface of the wake as the boundary layer separates is separated, thereby dividing the above series of processes into a large-scale Karman vortex. The idea is not to grow it.

  The object of the present invention is to devise the structure of the blunt body, to further reduce the fluid resistance coefficient due to pressure resistance, and to generate a fluid flow, the driving force required to drive such a flow, Also, when moving a blunt body in a fluid, the driving force to move it is reduced, and further, the mechanical force acting on the blunt body from the fluid can be reduced. It is to provide a blunt object.

  A blunt body placed in a fluid flow according to the present invention that solves the above problems includes a blunt body whose upstream surface is a blunt curved surface with respect to the fluid flow direction, and a downstream surface of the blunt body In order to inhibit the flow of the fluid along the flow head, the flow obstructing portion provided on the downstream side of the blunt body, the blunt body is in a state where the axis intersects the flow direction of the fluid A cylindrical object having a cylindrical surface arranged, and the flow blocking portion is attached to the wake side of the cylindrical object in a range within the projection width of the cylindrical object viewed in the main flow direction of the fluid. A plate member, and the plate member is a parallel plate attached in a state extending in parallel with the main flow direction from at least one position showing the maximum thickness with respect to the main flow of the fluid of the cylindrical object. It has the structure characterized by these.

  In the blunt body placed in the fluid flow, the upstream surface with respect to the fluid flow direction of the blunt body has a blunt curved surface similar to the conventional one, but the fluid flowing around the blunt body has the maximum thickness. When the boundary layer separation starts from near the depth, allowing a flow that flows toward the boundary layer separation region along the wake surface of the blunt body leads to the generation of a large-scale Karman vortex street. This leads to increased resistance. According to the blunt body according to the present invention, the flow inhibition portion inhibits the flow of the fluid that tends to flow toward the separation region along the posterior surface of the blunt body due to the separation of the boundary layer. ing. Therefore, even if a minute vortex is generated in response to the separation of the boundary layer from the vicinity of the maximum thickness of the blunt body, growth to the Karman vortex as a large-scale vortex street is hindered, and The width and the scale of the fluctuation component are reduced as compared with a simple blunt body that does not include a flow hindrance, and the pressure resistance of the blunt body is reduced.

  In the blunt body placed in the fluid flow, the blunt body is a cylindrical body having a cylindrical surface arranged in a state where the axis intersects with the fluid flow direction. Cylindrical objects are not only solid cylinders themselves, but are also used in various fields because they are easy to manufacture, such as circular pipes and cylinders, and can also be used in fluids. Many. For such a cylindrical object, the pressure resistance of the cylindrical object can be reduced only by providing a flow inhibiting part that inhibits the fluid flow that is to occur along the wake side surface in the Karman vortex generation process.

  In a blunt body having a cylindrical object as a blunt body, the flow blocking portion is attached to the downstream side of the cylindrical object in a range within the projection width of the cylindrical object viewed in the main flow direction of the fluid. A plate member is used. According to this blunt body, the flow of the fluid that tries to flow into the separation part of the boundary layer of the cylindrical object from the side surface of the cylindrical object along the downstream surface is obstructed by the plate member. Can reduce the growth of large-scale vortices such as Karman vortices and reduce pressure resistance. In addition, since the plate member as the flow blocking portion is attached within a range within the projection width of the cylindrical object, the normal flow around the cylindrical object is not unnecessarily disturbed by the plate.

  In the blunt body having a cylindrical body as the blunt body, the plate member extends in parallel with the main flow direction from at least one position indicating the maximum thickness with respect to the main flow of the fluid of the cylindrical body. Parallel plate attached to When such a parallel plate is used, even if the boundary layer of the fluid flow is separated, the range of the effect is shifted to the wake side along the parallel plate. The direct flow of the fluid from the side surface to the part where the boundary layer separation occurs is inhibited, and the boundary layer separation is prevented from growing into a large-scale vortex.

  In addition, the blunt body placed in the fluid flow of the present invention that achieves the above object includes a blunt body whose upstream surface is a blunt curved surface with respect to the fluid flow direction, and a wake side of the blunt body A flow blocking portion provided on the downstream side of the blunt body to block the flow of the fluid along the surface, the flow blocking portion being a maximum with respect to the main flow of the fluid of the blunt body It comprises a side edge provided in a state extending in parallel with the main flow direction from a position indicating a thickness, and a recess formed on the inner side of the side edge and on the back side of the blunt body. By adopting the configuration, it can be achieved more effectively.

  In the blunt body placed in the fluid flow, the flow blocking portion is provided at a side edge provided in a state extending in parallel with the main flow direction from a position indicating the maximum thickness with respect to the main flow of the fluid of the blunt body. And a recess formed on the inner side of the side edge and on the back side of the blunt body, the backflow region of the flow becomes wider than that of the cylinder, so that the amplitude of the backflow is reduced and the downstream region The velocity gradient is further reduced and the resistance is reduced.

  According to the blunt body placed in the fluid flow according to the present invention, when the fluid flowing around the blunt body tries to start separation of the boundary layer from around the maximum thickness, Allowing the flow to flow along the boundary layer separation region leads to the generation of large-scale Karman vortex streets and increases the pressure resistance, but toward the separation region along the downstream surface of this blunt body Since the flow of the fluid to be introduced is inhibited by the inhibition part, the growth to a large-scale vortex street such as Karman vortex is suppressed, and the pressure resistance of the blunt body is reduced. The smaller the pressure resistance coefficient, the smaller the resistance received from the fluid. When a fluid flow is generated, the driving force required to drive such a flow, or when moving a blunt body in the fluid The driving force for moving is reduced, and the load required for the driving source is reduced. Further, by reducing the pressure resistance, the strength required for the blunt body and its support structure can be reduced.

First, reference examples will be described before the embodiments of the present invention are described.
1 is a perspective view showing a reference example of a blunt body placed in a fluid flow, FIG. 2 is a cross-sectional view of the blunt body shown in FIG. 1, and FIG. 3 is a pressure resistance coefficient with respect to the flow velocity of the blunt body placed in a fluid flow. Is a graph in which is plotted.

  The blunt body 1 shown in FIG. 1 and FIG. 2 includes a cylindrical body 2 as a blunt body arranged with the axis L intersecting with the fluid flow direction F, and a wake side of the cylindrical body 2. It consists of a plate member 3 as an attached flow inhibiting part. The blunt body need not have a pointed tip, but is a cylindrical object 2 having the same upstream surface 2a as the cylindrical surface, which is the most common and most usable shape in this reference example. . Examples of the presence of such blunt bodies in a fluid flow include various sensors provided in wind tunnels and pipes through which gas or liquid flows, and their supports, or pantographs for trains, rods attached to flying objects, or Examples include wire-like objects whose aspect ratio cannot be easily changed to those close to streamline.

  The columnar body 2 may be a solid columnar body, a hollow circular tube body, or a cylindrical body. However, for the sake of simplicity, the columnar body 2 is abbreviated as a columnar body 2 hereinafter. The plate member 3 has the same plate width w as the diameter d of the cylindrical body 2, and the plate member 3 is an orthogonal plate attached tangentially to the last flow end portion 4 of the cylindrical body 2 at the center position of the plate width w. . By arranging the plate member 3 having such a structure so as to be located within the projection range in the direction of the fluid flow F, the blunt body 1 has a symmetrical structure with respect to the fluid flow F, and the blunt body The flow around 1 also becomes a relatively symmetric flow, so that the plate member 3 does not protrude from the shadow of the cylindrical body 2, and the occurrence of disturbance that increases the pressure resistance is reduced.

  When the blunt body 1 is placed in the fluid flow F, boundary layer separation occurs alternately and periodically on both sides of the surface of the cylindrical body 2 to generate and grow a Karman vortex as a large-scale vortex in the wake. Although it becomes easy, the plate member 3 is a portion where the boundary layer separation of the cylindrical body 2 occurs along the downstream surface 2b of the cylindrical body 2 every time boundary layer separation occurs when the plate member 3 is not present. The generation of a flow f (shown by an imaginary line) that attempts to flow as a fluid entrainment is hindered. As a result, in the wake of the blunt body 1, the generation of large-scale vortex streets such as Karman vortices is inhibited, and even if they occur, their growth can be inhibited. Pressure loss is reduced, and as a result, pressure resistance is reduced. In the blunted column 1, the plate member 3 is preferably arranged in a state of being within the projected width of the cylindrical body 2 viewed in the fluid flow direction. When the plate member 3 is accommodated within the range of the projection width of the cylindrical body 2, the fluid flow outside the boundary layer is not unnecessarily disturbed by the plate member 3, and the action of preventing the peeling shear layer from being involved. Can be effectively exhibited.

  The arrangement of the blunt column 1 with respect to the fluid flow F is preferably such that there is no component that the fluid flow F strikes the plate member 3 from the lateral direction, and in particular, the fluid flow F It is preferable to direct the direction of the flow F in a direction facing the plate member 3. By arranging the blunted columnar body 1 in this way, the fluid flow F does not directly hit the plate member 3 from each side of the columnar body 2, and the plate member 3 is likely to be generated in the columnar body 2. An inhibitory action against the entanglement of the peeling shear layer is evenly performed on each side of the cylindrical body 2 and can contribute to the reduction of the pressure resistance.

FIG. 3 shows a graph in which the resistance coefficient of the blunt body 1 placed in the fluid flow according to these reference examples is experimentally obtained and plotted against the flow velocity U. As understood from FIG. 3, the drag coefficient C _D of the bluff body 1, a reduction in 0.5 or more as compared to the cylindrical body 2 was observed, even in comparison with D Katachihashiratai substantially zero. One or more declines are recognized, and the effect of blocking the fluid flow along the posterior surface 2b of the blunt body appears by attaching the plate member.

  FIG. 4 is a graph showing the ratio of the fluid flow velocity U to the uniform flow velocity U∞ and the ratio of the fluctuation component u ′ to the uniform flow velocity U∞ in the wake of these blunt bodies. . As the wake of the blunt body, a position separated from the edge by a distance (X) three times the diameter D in the fluid flow direction is adopted. As the ratio Y / D to the diameter D, the ratio of the fluid flow velocity U to the uniform flow velocity U∞ (upper graph U / U∞) and the ratio of the fluctuation component u ′ to the uniform flow velocity U∞ ( The graph below u ′ / U∞) is obtained from measurement using a hot-wire anemometer. In the measurement of the wake, the blunt body 1 provided with the plate member is not only compared with the case of the cylindrical body 2 alone, but also the width of the wake is small and fluctuates as compared with the D-shaped column. It was confirmed that the components were also small.

  The blunt article according to the embodiment of the present invention will be described below based on the above reference example. The same parts as those in the reference example are denoted by the same reference numerals and the description thereof is omitted. FIG. 5 shows a blunt body 20 according to an embodiment of the present invention, and parallel plates 7L and 7R are attached to the cylindrical body 2 on the left and right sides with respect to the flow in the maximum thickness portion 5 as an inhibition plate. FIG. 6 shows a blunt body 30 according to another embodiment of the present invention. In this embodiment, a side edge extending parallel to the flow from the left and right positions of the blunt body 31 showing the maximum thickness with respect to the flow. 11L and 11R are provided, and it is comprised so that it may become the recessed part 12 inside the both-sides edge part 11L and 11R, and the back side of a blunt body may be smoothly curved.

  When the blunt bodies 20 and 30 of the present invention configured as described above are placed in a fluid flow flowing perpendicularly to the axis and parallel to the parallel plates 7L and 7R or parallel to the side edges 11L and 11R, The working fluid resistance was determined by experiment. The result is shown in FIG.

  FIG. 8 is a graph in which the vertical axis represents the Strouhal number St corresponding to the resistance coefficient of the blunt body when the horizontal axis is the flow velocity U (m / s). The Strouhal number St is a numerical value corresponding to the reciprocal of the resistance coefficient. In addition, the graph includes not only the above embodiment but also data obtained for several modified examples of the blunt object including the reference example shown in FIG. FIG. 7 shows cross-sections of various modifications of blunt bodies, where I) is a conventional cylinder, II) is a D-shaped cylinder, and III) is half-length in the radial direction as an obstruction plate on cylinder 2. An example in which the oblique plates 6L and 6R are attached, IV) is a blunt body according to an embodiment of the present invention in which the parallel plate 7L is attached only to the left side with respect to the flow in the maximum thickness portion 5 as the obstruction plate on the cylinder 2 ) Is an example in which an orthogonal plate 8R only on the right side with respect to the flow is attached to the cylinder body 2 as an obstruction plate, and VI) is a parallel plate 7L parallel to the left and right in the maximum thickness portion 5 as an obstruction plate to the cylinder body 2. VII) is a blunt body according to an embodiment of the present invention, to which 7R is attached, and VII) is an example in which oblique plates 9L and 9R extending in the projection range of the cylindrical body 2 in the radial direction are attached to the cylindrical body 2 as an inhibition plate, Is a half-length orthogonal to the last flow end 4 as an obstruction plate on the cylinder 2 Example in which the 10 at the center, IX), as shown in FIGS. 1 and 2, an example in which orthogonal plate (plate member 3) Finally stream end 4 as an inhibitor plate. X) has side edges 11 extending parallel to the flow from the left and right positions of the blunt body showing the maximum thickness with respect to the flow, and the back side of the blunt body is smoothly curved inside the side edges 11. It is the blunt body which concerns on embodiment of this invention comprised so that it might become the recessed part 12 which carried out.

As is clear from FIG. 8, the resistance coefficient in the case of only the cylindrical body 2 is the highest, and the blunt bodies shown in FIG. 7 other than the cylindrical body 2 have improved resistance coefficients. The blunt body provided with parallel plates on both sides of the cylindrical body shown in the embodiment VI) of the present invention also has an improved resistance coefficient in a wide range of flow velocity as in the reference example shown in FIG. It was found that the resistance coefficient C _D of the blunt body having the side edge portion 11 and the concave portion 12 shown in FIG. 2 is improved over the D-type body in a wide flow velocity range, and shows the smallest resistance coefficient C _D. .

In such a blunt body of this embodiment, the reason why the resistance coefficient is improved may be as follows, which is schematically shown in FIGS.
When the cylinder 2 is placed in the fluid flow F, as shown in FIG. 9 on both sides of the surface of the cylinder (only one side is shown), A in the region slightly downstream from the maximum thickness of the cylinder, for example, A In the region near the cylinder in the vicinity of the point, a flow in the direction opposite to the main flow direction is generated as indicated by an arrow 25. As a result, a stronger velocity gradient is generated in this region and a strong vortex is released. As a result, the velocity distribution at the point A becomes as shown in FIG. 9B, and a larger pressure resistance is generated. On the other hand, by providing a parallel plate in the maximum thickness portion of the cylindrical body as in the embodiment of the present invention, the forward flow that has advanced is rectified as shown by the arrow 26 by the parallel plates 7R and 7L, as shown in FIG. As a result, in the downstream region, the velocity gradient becomes gentler than that of the cylinder, and the velocity distribution at the downstream end B of the parallel plate is considered to have a clearly reduced resistance as shown in FIG.

  Further, as shown in FIG. 6, the blunt body has side edges 11L, 11R extending parallel to the flow from the left and right positions of the blunt body showing the maximum thickness with respect to the flow, and both side edges 11L, 11R. If the cross-sectional shape has the concave portion 12 that is smoothly curved on the back side of the blunt body, the backflow region of the flow is further widened compared to the cylindrical shape, so that the amplitude of the backflow is reduced and both side edges 11L , The flow rectified by 11R is also reduced. Therefore, in the downstream region of the side edge portions 11L and 11R, it is understood that the velocity gradient is further smaller than the shape in which the parallel plates 7L and 7R are attached to the left and right, and the resistance is further reduced.

It is a perspective view which shows the reference example of the blunt body placed on the fluid flow by this invention. It is sectional drawing of the blunt body shown in FIG. It is the graph which plotted the pressure resistance coefficient with respect to the flow velocity of the blunt body placed on the fluid flow. In the wake of the blunt body by a reference example, it is a graph which shows the ratio of the flow velocity U of the fluid with respect to the flow velocity U∞ of a uniform flow, and the fluctuation component u 'with respect to the flow velocity U∞ of a uniform flow. 1 is a perspective view of a blunt object according to an embodiment of the present invention. It is a perspective view of the blunt head object concerning other embodiments of this invention. It is sectional drawing which shows some modifications of a blunt body. It is the graph which calculated | required the Stroll number ST of various blunt bodies shown in FIG. 7 with respect to the Reynolds number. (A) is a schematic diagram which shows the pressure resistance generation | occurrence | production principle in the fluid flow field of a cylindrical body, (b) shows the velocity distribution in the A point. (A) is a schematic diagram showing the principle of generation of pressure resistance in a fluid flow field of a blunt body provided with a parallel plate in the maximum thickness portion of the cylindrical body of the present invention, and (b) is a velocity at the point B of the parallel plate tip. Show the distribution.

Explanation of symbols

1,20,30 Blunt object 2 Cylindrical object 3,10 Plate member (orthogonal plate)
4 Last flow end 5 Maximum thickness 6L, 6R, 9L, 9R Diagonal plate 7L, 7R Parallel plate 11L, 11R Side edge 12 Recess

Claims (3)

A blunt body whose upstream surface is a blunt curved surface with respect to the flow direction of the fluid, and a wake flow of the blunt body to inhibit the flow of the fluid along the posterior surface of the blunt body It consists of a flow blocking part provided on the side,
The blunt body is a cylindrical object having a cylindrical surface arranged in a state where the axis intersects the flow direction of the fluid,
The flow blocking portion is a plate member attached to the wake side of the cylindrical object in a range within the projection width of the cylindrical object viewed in the main flow direction of the fluid, and the plate member is the circle A blunt body placed in a fluid flow, wherein the columnar body is a parallel plate attached in a state extending in parallel with the main flow direction from at least one position showing a maximum thickness with respect to the main flow of the fluid.   2. The blunt body according to claim 1, wherein the parallel plate is a parallel plate extending in parallel with the main flow direction from the left and right in the maximum thickness portion of the cylindrical object.   A blunt body whose upstream surface is a blunt curved surface with respect to the flow direction of the fluid, and a downstream side of the blunt body to inhibit the flow of the fluid along the downstream side surface of the blunt body The flow inhibition portion is provided on the side edge provided in a state extending in parallel with the main flow direction from a position showing the maximum thickness with respect to the main flow of the fluid of the blunt body. A blunt body placed in a fluid flow, characterized in that the blunt body is composed of a recess and a recess formed on the back side of the blunt body and inside the side edge.

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