A variable-parameter drag reduction device and method for a column with a perforated protective cover

Abstract

This invention provides a variable-parameter drag-reducing device for a cylindrical body with a perforated cover, comprising a cylinder and a perforated cover. The perforated cover is fitted over the outer layer of the cylinder, and the perforated cover and the cylinder are aligned along the same centerline. The perforated cover completely encloses the cylinder. The perforated cover includes an outer cover and an inner cover. The outer cover can rotate relative to the inner cover around the centerline. Both the outer and inner covers have multiple through holes. When the outer cover rotates relative to the inner cover around the centerline, the overall porosity of the perforated cover can be adjusted. The length of the separation zone at the rear of the device is significantly increased, and the vortex shedding suppression effect is significant, resulting in increased pressure on the leeward side of the cylinder and reduced drag. Simultaneously, a significant vibration reduction effect is achieved. This invention further explores the influence of parameters such as the size of the perforated cover and changes in porosity on the overall drag-reduction effect, providing guidance for the design of perforated covers.

Description

Technical Field

[0001] This invention relates to the field of drag reduction technology for cylindrical flow, and particularly to a drag reduction device and method for a cylindrical body with a perforated protective cover and variable parameters. Background Technology

[0002] The generation and evolution of eddies during flow around a cylinder are significant causes of flow resistance, structural vibration, and noise. In existing flow control methods, using flow dividers to modify the wake structure to suppress eddy shedding or reduce drag is widely applied. Regarding drag reduction, many researchers, inspired by bionics, have studied the influence of surface roughness on cylinder drag. Studies have shown that arranging ribs, pits, and protrusions on the cylinder surface can significantly reduce drag. However, bionic structures not only have strict requirements on shape parameters but also have significant limitations in engineering applications. Perforated shields have proven to be an effective way to suppress eddy shedding while also significantly reducing cylinder vibration. Porous media coatings, as a relatively new passive control method, have gradually become a research hotspot in recent years. However, the selection of porous media materials and the potential blockage of their internal pores threaten the effective lifespan of this passive control method.

[0003] For the classic fluid mechanics problem of flow around a cylinder, it is of practical significance to explore a more convenient and faster way to suppress vortex shedding and reduce flow resistance, given the shortcomings of its application in engineering practice. This can effectively broaden its engineering application scope, such as the cylindrical shapes of the foundations of transportation pipelines and bridge piers in marine engineering, and the pantograph system of high-speed trains. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a drag reduction solution for a perforated shield column based on flow state and with variable parameters.

[0005] To achieve the above objectives, the present invention provides a variable parameter drag reduction device for a cylindrical body with a perforated cover, comprising a cylinder and a perforated cover. The perforated cover is sleeved on the outer layer of the cylinder and is arranged along the same center line as the cylinder. The perforated cover completely covers the cylinder. The perforated cover includes an outer cover and an inner cover. The outer cover is rotatable relative to the inner cover around a center line. Both the outer cover and the inner cover have multiple through holes. When the outer cover rotates relative to the inner cover around a center line, the overall porosity of the perforated cover can be adjusted.

[0006] Furthermore, a pore control component is provided between the outer protective cover and the inner protective cover. The pore control component includes a ball bearing and a retainer. The ball bearing is installed at a corresponding position on the retainer and can rotate freely. The ball bearing makes rolling contact with both the outer protective cover and the inner protective cover. After the outer protective cover or the inner protective cover rotates to a preset angle, it is locked and fixed so that the perforated protective cover has different porosities.

[0007] Furthermore, the ball bearings have different diameter specifications to adjust the thickness of the perforated cover, and the outer cover and the inner cover also have a variety of different diameter specifications to adjust the outer diameter and inner diameter of the perforated cover.

[0008] Furthermore, the inner protective cover is connected to the cylinder via a connector, and / or the ends of the inner protective cover and the cylinder are both connected to the support base.

[0009] Furthermore, the through holes on the outer protective cover and the inner protective cover are uniformly or non-uniformly distributed.

[0010] Furthermore, the diameter of the cylinder is D, the outer diameter of the perforated cover is Ds, and the variation range of Ds / D is 1.2-2.

[0011] Furthermore, the larger the gap W between the cylinder and the perforated shield, the smaller the thickness of the perforated shield, the smaller the total resistance and the greater the drag reduction rate.

[0012] This invention also provides a variable parameter drag reduction method for a column with a perforated protective cover, applied to a variable parameter drag reduction device for a column with a perforated protective cover as described above. Ds / D is kept at 1.25. The relationship between the dimensionless clearance W / D and the drag coefficient under different operating conditions is fitted to obtain the following formula. ,in For total resistance, This refers to the gap between the perforated shield and the cylinder.

[0013] This invention also provides a drag reduction method for a column with a perforated protective cover and variable parameters, applicable to a drag reduction device for a column with a perforated protective cover and variable parameters as described above. The drag coefficient and Reynolds number fitting curve satisfies... ,in The Reynolds number is... The drag coefficient is the coefficient of friction at the Reynolds number. Within this range, the perforated shield can significantly reduce drag. Reducing the outer diameter and thickness of the perforated shield within this range is beneficial to its drag reduction effect.

[0014] When the Reynolds number is at When the Reynolds number is within a certain range, reduce the thickness of the perforated shield. When doing so, reduce the outer diameter of the perforated shield.

[0015] The above-described solution of the present invention has the following beneficial effects:

[0016] The present invention provides a variable-parameter drag reduction device and method for a cylindrical body with a perforated shield. By setting a perforated shield on the outer layer of the cylinder, a "1+1>2" effect is achieved. The inner cylinder and the outer perforated shield are considered as an organic whole. Compared with a smooth cylinder, the total drag and vibration are reduced. Compared with changing the shape of the cylinder itself, the perforated shield is easy to manufacture, obtain, and install, and has high engineering feasibility. After the cylinder is surrounded by the perforated shield, the length of its rear separation zone is significantly increased, the vortex shedding suppression effect is significant, resulting in increased pressure on the leeward side of the cylinder and reduced drag. At the same time, the application of the perforated shield can stabilize the flow separation on the rear side of the cylinder, greatly reducing lift fluctuations and achieving a significant vibration reduction effect. The present invention further explores the influence of parameters such as the size of the perforated shield and changes in porosity on the overall drag reduction effect. The results are verified by numerical simulation, and the corresponding laws are obtained, which have a guiding role in the design of the perforated shield.

[0017] Other beneficial effects of the present invention will be described in detail in the following detailed description section. Attached Figure Description

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

[0019] Figure 2 This is a schematic diagram of the pore control component of the present invention;

[0020] Figure 3 This is a side view of the overall structure of the present invention (simulation model);

[0021] Figure 4 The diagram shows a pressure comparison of the perforated shield with different gaps according to the present invention, where (a) is W / D=0.1 and (b) is W / D=0.12.

[0022] Figure 5 This is a schematic diagram of the vortex structure in the XY plane of the present invention (W / D=0.12).

[0023] Figure 6 This is a graph showing the variation of the drag coefficient of the present invention with the gap.

[0024] [Explanation of Labels in the Attached Image]

[0025] 1-Cylinder; 2-Perforated cover; 3-Outer cover; 4-Inner cover; 5-Through hole; 6-Ball; 7-Retainer. Detailed Implementation

[0026] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Furthermore, the technical features involved in the different embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] like Figure 1 As shown, an embodiment of the present invention provides a variable-parameter drag-reducing device for a cylindrical body with a perforated shield, comprising a cylinder 1 and a perforated shield 2. The perforated shield 2 is fitted around the cylinder 1 and is concentrically positioned with the cylinder 1, i.e., their centerlines coincide, and the perforated shield 2 covers the cylinder 1 360 degrees. The perforated shield 2 has a double-layer structure, comprising an outer shield 3 and an inner shield 4. The outer shield 3 (inner shield 4) can rotate relative to the inner shield 4 (outer shield 3) around its centerline. Both the outer shield 3 and the inner shield 4 have multiple through holes 5, thus both have a certain porosity. The through holes of the outer shield 3 and the inner shield 4 are one-to-one (or partially corresponding, etc.). Therefore, when the outer shield 3 rotates relative to the inner shield 4 around its centerline, the overall porosity of the perforated shield 2 can be adjusted and controlled.

[0030] It should be noted that, in this embodiment, the porosity of the perforated cover 2 is defined as the ratio of the opening area of ​​the perforated cover 2 to the total surface area.

[0031] In this embodiment, D is the diameter of cylinder 1, and Ds is the outer diameter of perforated cover 2. Figure 2 The porosity control assembly is shown, installed at one end of the perforated cover 2. Specifically, the porosity control assembly includes a ball bearing 6 and a retainer 7. The ball bearing 6 is installed at a corresponding position on the retainer 7 and can rotate freely. The entire porosity control assembly is located between the outer cover 3 and the inner cover 4, forming a shape similar to a ball bearing. Therefore, the outer cover 3 can rotate relative to the inner cover 4, and after rotating to a certain angle, it can be fixed by a locking mechanism, thereby allowing the perforated cover 2 to have different porosities.

[0032] The thickness T of the perforated shield 2, as well as Ds / D, can be adjusted by changing the size of the ball bearing 6. Of course, the dimensions of the outer shield 3, inner shield 4, etc., also need to be adjusted accordingly.

[0033] It should be noted that in practical applications, the position between the perforated cover 2 and the cylinder 1 needs to be stable. Therefore, a connector can be used to connect and fix the inner cover of the perforated cover 2 to the cylinder 1. The connector can be a connecting rod, with multiple rods arranged around the center to ensure a stable connection and consistent strength in all directions. Alternatively, the perforated cover 2 can be fitted onto the cylinder 1 as a whole, with the inner ring of the perforated cover 2, the end of the cylinder 1, and the support fixed. This maintains positional stability of the inner ring of the perforated cover 2 relative to the cylinder 1, while the outer ring of the perforated cover 2 is movably connected to the support and locked in place using a latch after adjustment.

[0034] Figure 3 The diagram shows a side view of this design, with a span of πD / 2. The inner cylinder 1 and the outer perforated cover 2 are considered as a single unit in both numerical simulation and practical applications. It should be noted that the through holes 5 on the perforated cover 2 can be evenly or unevenly distributed. Considering strength and manufacturing factors, a uniform distribution is preferable.

[0035] This solution differs from existing passive flow control methods for cylinder 1 (primarily involving changes to the surface shape of cylinder 1). By installing a perforated shield 2 on the outer layer of cylinder 1, a "1+1>2" effect is achieved. The inner cylinder 1 and the outer perforated shield 2 are considered as a single organic entity. Compared to a smooth cylinder 1, the total drag and vibration are reduced. Compared to changing the shape of cylinder 1 itself, the perforated shield 2 is easier to manufacture, obtain, and install, exhibiting high engineering feasibility. After being surrounded by the perforated shield 2, the length of the rear separation zone of cylinder 1 is significantly increased, resulting in a significant suppression of vortex shedding and increased pressure on the leeward side of cylinder 1, while reducing drag. Simultaneously, the application of the perforated shield 2 stabilizes the flow separation on the rear side of cylinder 1, substantially reducing lift fluctuations and achieving a significant vibration reduction effect.

[0036] The following case further illustrates the effectiveness of this solution. By constructing a cylindrical model 1 with a perforated shield 2, numerical simulation of it is performed using large eddy simulation (LES) based on the Smagorinsky subgrid model. It is preliminarily estimated that it will bring a maximum drag reduction effect of 33% and a vibration reduction of more than 95%. In addition, the wake region around the cylinder 1 is extended, and the effect of suppressing vortex shedding is significant. By changing the thickness of the perforated cover 2, while keeping Ds / D constant at 1.25, the thickness T of the perforated cover 2 is the variable, ranging from 0.001D to 0.05D. This corresponds to a range of 0.075D to 0.124D for the gap W between the inner cylinder 1 and the perforated cover 2 (in specific examples, W is 0.1D, 0.105D, 0.11D, 0.115D, and 0.12D, respectively, corresponding to thicknesses of the perforated cover 2 of 0.625mm, 0.5mm, 0.375mm, 0.25mm, and 0.125mm, respectively).

[0037] From the pressure comparison chart ( Figure 4 As shown in Table 1, the perforation shield has a better suppression effect when the gap W / D = 0.12. Specifically, when W / D = 0.12, the model exhibits better suppression in the XY plane vortex structure. Figure 5 As shown.

[0038] Table 1. Resistance coefficients of perforated protective cover columns with different gaps.

[0039]

[0040] Further testing explored the relationship between the gap W between cylinder 1 and the perforated cover 2 and the drag coefficient. With Ds / D maintained at 1.25, the drag coefficients for different gaps W are shown in Table 1. The drag coefficient of the smooth cylinder 1 without the perforated cover 2 was approximately 1.24. When the gap was 0.1D, the drag reduction rate was 18%; when the gap was 0.105D, the drag reduction rate was 23%; when the gap was 0.11D, the drag reduction rate was 27%; when the gap was 0.115D, the drag reduction rate was 31%; and when the gap was 0.12D, the drag reduction rate was 33%. The dimensionless gap (W / D) and drag coefficient relationship under different operating conditions were fitted to obtain the following formula: ,in For total resistance, The gap between the perforated shield 2 and the cylinder 1, such as Figure 6As shown in the diagram. Therefore, the drag reduction law can be derived: the larger the gap (W / D) and the thinner the perforated cover 2, the smaller the total resistance of the drag reduction device, i.e., the greater the drag reduction rate. When the gap (W / D) is 0.12 and the thickness is 0.005D, the drag reduction rate reaches 33%. In practical applications, while maintaining structural strength, the thickness of the perforated cover 2 can be kept at 0.005D or less to achieve good drag reduction.

[0041] Testing revealed that the optimal range for Ds / D is 1.2-2; values ​​that are too large or too small are detrimental to the drag reduction effect of the perforated cover 2. Furthermore, when the porosity is between 20% and 50%, the pore size is best maintained at 0.125D, as reducing the pore size is not conducive to drag reduction. When the porosity is greater than 50%, the total resistance of the drag reduction device decreases slightly. Of course, in practical applications, the selection of porosity should be based on a comprehensive consideration of factors such as strength and processing.

[0042] It should also be noted that the uniform or non-uniform distribution of the through holes 5 does not affect the drag reduction effect of the perforated cover 2.

[0043] Meanwhile, in this embodiment, the Reynolds number in the subcritical region is defined as follows: , For fluid density, The gas flow velocity, The characteristic length of the column. Let the fluid dynamic viscosity be denoted by the Reynolds number, representing the flow state of the incoming flow. The drag coefficient and Reynolds number fitting curve satisfy... ,in The Reynolds number is... The drag coefficient is the coefficient of friction at the Reynolds number. Within this range, the perforated shield 2 can significantly reduce drag. Within this range, reducing the outer diameter and thickness of the perforated shield 2 both contribute to its drag reduction effect; based on this, actual tests have shown that when the Reynolds number is within a certain range... When the Reynolds number is within a certain range, it is recommended to reduce the thickness of the perforated shield by 2 (increase W). When this is the case, it is recommended to reduce the outer diameter of the perforated shield 2 (W remains unchanged or is reduced).

[0044] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A drag-reducing device for a column with a perforated protective cover and variable parameters, characterized in that, The device includes a cylinder and a perforated cover. The perforated cover is fitted over the cylinder and is arranged along the same center line as the cylinder. The perforated cover completely covers the cylinder. The perforated cover includes an outer cover and an inner cover. The outer cover can rotate relative to the inner cover around the center line. Both the outer cover and the inner cover have multiple through holes. When the outer cover rotates relative to the inner cover around the center line, the porosity of the perforated cover can be adjusted.

2. The variable parameter drag reduction device for a column with a perforated protective cover according to claim 1, characterized in that, A pore control component is provided between the outer protective cover and the inner protective cover. The pore control component includes a ball bearing and a retainer. The ball bearing is installed at the corresponding position of the retainer and can rotate freely. The ball bearing makes rolling contact with both the outer protective cover and the inner protective cover. After the outer protective cover or the inner protective cover rotates to a preset angle, it is locked and fixed so that the perforated protective cover has different porosities.

3. The variable parameter drag reduction device for a column with a perforated protective cover according to claim 2, characterized in that, The ball bearings have different diameter specifications to adjust the thickness of the perforated cover. The outer cover and the inner cover also have various different diameter specifications to adjust the outer and inner diameters of the perforated cover.

4. The drag reduction device for a variable parameter column with a perforated protective cover according to claim 1, characterized in that, The inner protective cover is connected to the cylinder via a connector, and / or the ends of the inner protective cover and the cylinder are both connected to the support base.

5. The variable parameter drag reduction device for a column with a perforated protective cover according to claim 1, characterized in that, The through holes on the outer protective cover and the inner protective cover are uniformly or non-uniformly distributed.

6. The variable parameter drag reduction device for a column with a perforated protective cover according to claim 1, characterized in that, The diameter of the cylinder is D, the outer diameter of the perforated cover is Ds, and the ratio of Ds to D varies from 1.2 to 2.

7. A variable parameter drag reduction device for a column with a perforated protective cover according to claim 6, characterized in that, The gap W between the cylinder and the perforated shield is the largest when W / D is larger and the thickness of the perforated shield is smaller, resulting in a smaller total resistance and a greater drag reduction rate.

8. A method for reducing drag of a column with a perforated protective cover using variable parameters, applied to the drag reduction device for a column with a perforated protective cover using variable parameters as described in claim 7, characterized in that... With Ds / D kept at 1.25, the relationship between the dimensionless clearance W / D and the drag coefficient under different working conditions was fitted to obtain the following formula. ,in For total resistance, This refers to the gap between the perforated shield and the cylinder.

9. A method for reducing drag of a column with a perforated protective cover and variable parameters, applied to a drag reduction device for a column with a perforated protective cover and variable parameters as described in any one of claims 1-7, characterized in that, The drag coefficient and Reynolds number fitting curves satisfy ,in The Reynolds number is... The drag coefficient is the coefficient of friction at the Reynolds number. Within this range, the perforated shield can significantly reduce drag. Within this range, reducing the outer diameter and thickness of the perforated shield is beneficial to its drag reduction effect. When the Reynolds number is at When the Reynolds number is within a certain range, reduce the thickness of the perforated shield. When doing so, reduce the outer diameter of the perforated shield.

Images