Friction resistance measuring device and measuring method

Abstract

A resistance measuring device, wherein a flat plate body is placed on the upper end surface of the shell, and a research plate is embedded in the geometric center of the flat plate body. The front end of the guide rail corresponds to the lifting bolt on the bottom plate of the shell. Two telescopic mechanisms are hinged to the sliders on the guide rail through connecting pieces. The upper end surface of each support rod in the telescopic mechanism is fixedly connected to the lower surface of the flat plate body. The dynamometer is horizontally fixedly connected to the front end shell in the shell. The shell is movably connected to the guide rail, and the angle θ between the guide rail and the horizontal plane in the vertical plane can be adjusted; the shell is fixedly connected to the flat plate body and has a sealing function, so that the friction resistance module and the force measurement module are not disturbed by the flow from the lower surface of the flat plate model during measurement. The present invention eliminates the interference of static friction force changes on the friction resistance measurement during the measurement process, and improves the measurement accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of aerodynamic friction resistance measurement, in particular to a device for measuring the friction resistance of a flat plate boundary layer and a corresponding measuring method. Background Art

[0002] In today's world, people pay more attention to environmental protection and resource conservation, and put forward higher requirements for the development of modern engineering and technology in terms of energy consumption and pollutant emissions. Considering the increase in fossil fuel prices and the intensification of the greenhouse effect, even a small reduction in viscous drag will bring huge economic benefits. Billions of liters of fossil fuels are consumed every year to overcome viscous drag. From the perspective of energy conservation, any small amount of drag reduction can save a lot of energy. Therefore, reducing viscous drag is an important topic in the field of flow control.

[0003] The existing friction resistance measurement methods mainly include the following: 1. Measuring the boundary layer velocity type and fitting to obtain the shear pressure. The measuring devices include hot wire anemometer, LDV laser speed measurement equipment and PIV system. The disadvantages are that the measurement time is long, the device and operation are complicated, and it is only suitable for low-speed flow measurement; 2. The force balance directly measures the friction resistance on the surface of the floating unit. Although the accuracy is high, the device and operation are complicated, and other friction resistance measurement methods need to be used to calibrate the force balance, such as method 1; 3. The oil film interference method, according to the relationship between oil film thickness and shear stress, the shear stress is obtained by measuring the oil film thickness. This method is complicated to operate, and the oil film will change the surface shape of the measurement model and interfere with the flow field. Therefore, in summary, there is a lack of a friction resistance measurement method that is simple to operate, fast and accurate. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art of complex operation and low measurement accuracy, the present invention proposes a friction resistance measuring device.

[0005] The present invention comprises a plate body, a research plate, four support rods, two telescopic mechanisms, a slide block, a guide rail, a housing and a dynamometer, wherein:

[0006] The plate body is placed on the upper end surface of the shell, and an opening for embedding the research plate is opened at the geometric center of the plate body. A lifting bolt is installed on the bottom plate of the shell, and the position of the lifting bolt corresponds to the front end of the guide rail; a connecting rod support is fixed on the upper surface of the bottom plate inside the shell, and the connecting rod is hinged on the connecting rod support, and the position of the connecting rod corresponds to the rear end of the guide rail. The front end of the guide rail is placed on the top of the lifting bolt; the rear end of the guide rail is fixed to the top of the connecting rod; two sliders are installed on the guide rail. The two telescopic mechanisms are hinged to each slider through a connecting piece. The upper end surface of each support rod in each telescopic mechanism is fixedly connected to the lower surface of the research plate located at the geometric center of the plate body. The dynamometer is horizontally fixedly connected to the front end shell inside the shell, and the dynamometer is a high-precision digital dynamometer.

[0007] There are gaps of less than 0.15 mm between the four sides of the research plate and the four sides of the opening.

[0008] A copper wire is connected between the dynamometer and the crossbar in the telescopic mechanism; the copper wire is in a horizontal state.

[0009] The telescopic mechanism includes two support rods and two sleeves, wherein the lower ends of the two support rods are respectively embedded in the sleeves and fastened by set screws. The lower surface of each sleeve is fixedly connected to the connecting member. The two support rods are supported by a cross bar. The relative position of the research plate and the plate body can be changed by adjusting the embedding depth of each support rod in the sleeve.

[0010] The sleeve plate is provided with a blind hole for embedding the support rod. The aperture of the blind hole is slightly larger than the outer diameter of the support rod, so that the two are clearance-matched. The housing of the sleeve plate is provided with a radial set screw hole.

[0011] The specific process of using the friction resistance measuring device to perform measurement proposed by the present invention is:

[0012] Step 1, installing the friction resistance measuring device: horizontally install the flat plate body in the friction resistance measuring device in the wind tunnel test section.

[0013] Step 2, adjust the angle θ between the guide rail and the horizontal plane:

[0014] The angle θ between the guide rail and the horizontal plane is obtained by the formula:

[0015] tanθ=μ

[0016] Where μ is the maximum static friction coefficient between the guide rail and the slider.

[0017] The tanθ=μ is obtained through the force balance mathematical model:

[0018] F=Ncosθ(tanθ-μ), when F=0, tanθ=μ;

[0019] The force balance mathematical model is to analyze the force on the guide rail by taking the research plate, two telescopic mechanisms and two sliders as a whole M. In this model, the horizontal component of the resultant force on the whole M is F; the support force of the guide rail on the slider is N, and the direction of the support force N is perpendicular to the surface of the guide rail; μ is the maximum static friction coefficient between the guide rail and the slider.

[0020] When adjusting the angle θ between the guide rail and the horizontal plane, rotate the jacking bolt to jack up the front end of the guide rail, thereby increasing the angle θ between the guide rail and the horizontal plane. When tanθ=μ, the jacking bolt is tightened.

[0021] Step 3, adjust the position of the research plate and the direction of the dynamometer pull:

[0022] The relative position between the research plate and the plate body is changed by adjusting the telescopic mechanism, and the two telescopic mechanisms are tightened when the height difference between the upper surface of the research plate and the upper surface of the plate body is less than 0.1 mm. The copper wire is in a horizontal state, so that the pulling direction of the dynamometer is in a horizontal direction.

[0023] The length of the copper wire was adjusted so that the gaps between the four sides of the research plate and the four sides of the plate body opening were less than 0.15 mm.

[0024] Step 4, measuring the tension L1 when there is no friction resistance: turn on the dynamometer, close the wind tunnel test section, and the wind tunnel is in a non-winding state, with no incoming flow and no friction resistance. The tension L1 measured by the dynamometer is equal to 0.

[0025] Step 5, measuring the tension L2 when there is friction resistance: Turn on the wind tunnel and set the incoming flow velocity to 20 m / s. When the incoming flow velocity stabilizes, the upper surface of the research plate is subjected to friction resistance. The dynamometer starts to measure and record the tension value as L2. Turn off the wind tunnel, open the side wall of the housing, and turn off the dynamometer.

[0026] Step 6, determine the friction resistance τ on the upper surface of the study plate.

[0027] The friction resistance is horizontally opposite to the direction of the dynamometer pulling force and is equal in magnitude, and the friction resistance τ=L2.

[0028] τ is the friction resistance of the research plate under the flow velocity of 20m / s.

[0029] In the present invention, one end of the copper wire is connected to the measuring end of the dynamometer, and the other end is connected to the crossbar connected to the research plate. The dynamometer is a high-precision digital dynamometer, and the measuring end of the dynamometer does not expand or contract with the size of the pulling force, so that the research plate is in a static state during the measurement process.

[0030] The shell in the present invention is movably connected to the guide rail, and the angle θ between the guide rail and the horizontal plane in the vertical plane can be adjusted; the shell is fixedly connected to the plate body and has a sealing function, so that the pressure in the shell and the pressure at the junction of the research plate and the plate body are equal during measurement, and the flow field is not disturbed.

[0031] Compared with the prior art, the beneficial technical effects achieved by the present invention are:

[0032] 1. In this application, the research plate is kept stationary during the measurement and does not disturb the flow field.

[0033] 2. In the present application, the guide rail is set at an angle θ with the horizontal plane, so that the static friction between the guide rail and the slider is the maximum static friction, eliminating the interference of the static friction change on the friction resistance measurement during the measurement process.

[0034] 2. In the present application, a guide rail is used to form an angle θ with the horizontal plane, so that the resultant force of the vertical downward force on the research plate, telescopic mechanism and slider as a whole M and the support force of the guide rail on the whole M is equal to the maximum static friction force in magnitude and opposite in direction, thereby eliminating the maximum static friction force change caused by the unequal pressure on the upper and lower surfaces of the research plate during the measurement process, which is effective for accurate measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a top view of the friction resistance measuring device;

[0036] Figure 2 is a front view of the friction resistance measuring device;

[0037] Figure 3 yes Figure 2 AA section view in the figure;

[0038] Figure 4 yes Figure 2 A partial enlarged view of the B area;

[0039] Figure 5 yes Figure 2 CC section view in the figure;

[0040] Figure 6 It is the left side view of the friction resistance measuring device;

[0041] Figure 7 is a flow chart of the friction resistance measurement scheme;

[0042] Figure 8 This is the force balance principle diagram in the friction resistance measurement scheme.

[0043] In the figure: 1. Plate body; 2. Study plate; 3. Support rod; 4. Telescopic mechanism; 5. Pin; 6. Slider; 7. Guide rail; 8. Housing; 9. Connecting rod; 10. Lifting bolt; 11. Copper wire; 12. Dynamometer; 13. Cross bar; 14. Bushing; 15. Set screw; 16. Front wall panel; 17. Side wall panel. DETAILED DESCRIPTION

[0044] Example 1

[0045] This embodiment is a friction resistance measuring device, comprising a plate body 1, a research plate 2, four support rods 3, two telescopic mechanisms 4, a slider 6, a guide rail 7, a housing 8 and a dynamometer 12, wherein:

[0046] The flat plate body 1 is a rectangular plate, which is placed on the upper end surface of the shell 8, and the end of the flat plate body corresponding to the wind tunnel flow direction is the leading edge; a rectangular opening is opened at the geometric center of the flat plate body, which is used to embed the research plate 2, and the four sides of the research plate have a gap of less than 0.15mm with the four sides of the opening. A lifting bolt 10 is installed on the bottom plate of the shell 8, and the position of the lifting bolt corresponds to the front end of the guide rail 7; a connecting rod support is fixed on the upper surface of the bottom plate inside the shell, and the connecting rod 9 is hinged on the connecting rod support, and the position of the connecting rod corresponds to the rear end of the guide rail. The front end of the guide rail 7 is placed on the top of the lifting bolt; the rear end of the guide rail is fixed on the top of the connecting rod; two sliders are installed on the guide rail. The two telescopic mechanisms 4 are hinged to each slider through a connecting piece. The upper end surface of each support rod 3 in each telescopic mechanism is fixed to the lower surface of the research plate 2 located at the geometric center of the flat plate body.

[0047] The dynamometer 12 is horizontally fixedly connected to the front end shell inside the shell 8, and the dynamometer is a high-precision digital dynamometer; one end of the copper wire 11 is connected to the measuring end of the dynamometer 12, and the other end of the copper wire is connected to the cross bar in the telescopic mechanism, and the two ends of the copper wire are in the same horizontal plane, so that the direction of tension is horizontal.

[0048] The telescopic mechanism 4 includes two support rods 3, two set screws 15 and two sleeves 14, wherein the lower ends of the two support rods are respectively embedded in the sleeves and fastened by the set screws. The lower surface of each sleeve is fixedly connected to the connecting member. The two support rods 3 are supported by a cross bar 13. When working, the embedding depth of each support rod in the sleeve is adjusted to change the relative position of the research plate 2 and the plate body 1, and is fastened by the set screws.

[0049] The sleeve plate is provided with a blind hole for embedding the support rod. The aperture of the blind hole is slightly larger than the outer diameter of the support rod, so that the two are clearance-matched. The housing of the sleeve plate is provided with a radial set screw hole.

[0050] The front end wall plate 16 and the rear end wall plate of the shell are both fixed wall plates, and the two side wall plates 17 of the shell are both movable wall plates, which are connected to the front end wall plate and the rear end wall plate by bolts to facilitate the operation of the device located in the shell during the experiment.

[0051] In this embodiment, the size of the tablet body 1 is 1500×400×10 mm, and the size of the opening on the tablet body 1 is 200×150 mm. The size of the research tablet 2 is 199.8×149.8×10 mm. Both the tablet body and the research tablet are made of acrylic plates.

[0052] Example 2

[0053] This embodiment is a method for measuring using the friction resistance measuring device, see attached Figure 6 , the specific process is:

[0054] Step 1, installing the friction resistance measuring device: horizontally install the flat plate body in the friction resistance measuring device in the wind tunnel test section according to the conventional method.

[0055] Step 2, adjust the angle θ between the guide rail and the horizontal plane:

[0056] The angle θ between the guide rail and the horizontal plane is obtained by the formula:

[0057] tanθ=μ

[0058] Where μ is the maximum static friction coefficient between the guide rail and the slider.

[0059] The tanθ=μ is obtained through the force balance mathematical model F.

[0060] The research plate, two telescopic mechanisms and two sliders are regarded as a whole M, and the force of the whole M on the guide rail 7 is analyzed, as shown in Figure 8 shown.

[0061] F=Ncosθ(tanθ-μ), when F=0, tanθ=μ;

[0062] In this model, the horizontal component of the resultant force acting on the whole M is F; the support force of the guide rail on the slider is N, and the direction of the support force N is perpendicular to the surface of the guide rail; the maximum static friction between the slider and the guide rail in the whole M is f; the vertical downward force exerted by the whole M on the guide rail is P; μ is the maximum static friction coefficient between the guide rail and the slider.

[0063] When adjusting the angle θ between the guide rail and the horizontal plane, the jacking bolt 10 is rotated to jack up the front end of the guide rail 7, thereby increasing the angle θ between the guide rail 7 and the horizontal plane. When tanθ=μ, the jacking bolt 10 is tightened.

[0064] Step 3, adjust the position of the research plate and the direction of the dynamometer pull:

[0065] By adjusting the telescopic mechanism 4 to change the relative position between the research plate and the plate body, when the height difference between the upper surface of the research plate 2 and the upper surface of the plate body 1 is less than 0.1 mm, the two telescopic mechanisms 4 are fastened by the set screws 15. At this time, the copper wire 11 is in a horizontal state, so that the pulling direction of the dynamometer is in the horizontal direction.

[0066] The length of the copper wire 11 is adjusted so that the gaps between the four sides of the research plate and the four sides of the opening of the plate body are less than 0.15 mm.

[0067] Step 4, measure the tension L1 when there is no friction resistance: open the dynamometer 12, close the side wall of the shell 8, and close the wind tunnel test section. At this time, the wind tunnel is in a non-winding state, there is no incoming flow, and there is no friction resistance. The dynamometer 12 starts measuring. According to step 2, F=0 at this time, so the tension L1=0.

[0068] Step 5, measuring the tension L2 when there is friction resistance: Open the wind tunnel and set the incoming flow velocity to 20 m / s. When the incoming flow velocity is stable, the upper surface of the research plate 2 is subjected to friction resistance. The dynamometer 12 starts to measure and record the tension value as L2. Close the wind tunnel, open the side wall of the housing 8, and close the dynamometer 12.

[0069] Step 6, determine the friction resistance τ on the upper surface of the study plate.

[0070] The friction resistance is horizontally opposite to the direction of the dynamometer pulling force and is equal in magnitude, and the friction resistance τ=L2.

[0071] τ is the friction resistance of the research plate under the flow velocity of 20m / s.

Claims

1. A resistance measuring device, characterized in that: It includes a plate body, a research plate, four support rods, two telescopic mechanisms, a slider, a guide rail, a housing and a dynamometer, wherein: The plate body is placed on the upper end surface of the shell, and an opening for embedding the research plate is opened at the geometric center of the plate body; a lifting bolt is installed on the bottom plate of the shell, and the position of the lifting bolt corresponds to the front end of the guide rail; a connecting rod support is fixed on the upper surface of the bottom plate inside the shell, and the connecting rod is hinged on the connecting rod support, and the position of the connecting rod corresponds to the rear end of the guide rail; the front end of the guide rail is placed on the top end of the lifting bolt; the rear end of the guide rail is fixed to the top end of the connecting rod; two sliders are installed on the guide rail; the two telescopic mechanisms are respectively hinged to the sliders through connecting pieces; the upper end surface of each support rod in each telescopic mechanism is fixedly connected to the lower surface of the research plate located at the geometric center of the plate body; the dynamometer is horizontally fixedly connected to the front end shell inside the shell; A copper wire is connected between the dynamometer and the crossbar in the telescopic mechanism; the copper wire is in a horizontal state; The telescopic mechanism includes two support rods and two sleeves, wherein the lower ends of the two support rods are respectively embedded in the sleeves and fastened by set screws; the lower surface of each sleeve is fixedly connected to the connecting piece; the two support rods are supported by a cross bar; and the relative position of the research plate and the plate body can be changed by adjusting the embedding depth of each support rod in the sleeve.

2. A resistance measuring device as claimed in claim 1, characterized in that: There are gaps of less than 0.1 mm between the four sides of the research plate and the four sides of the opening.

3. A resistance measuring device as claimed in claim 1, characterized in that: The sleeve plate is provided with a blind hole for embedding the support rod; the aperture of the blind hole is slightly larger than the outer diameter of the support rod; the gap between the two is matched; and the shell of the sleeve plate is provided with a radial fixing screw hole.

4. A method for measuring using the resistance measuring device according to claim 1, characterized in that: The specific process is: Step 1, install the resistance measurement device: The flat plate body in the drag measuring device is installed horizontally in the wind tunnel test section; Step 2, adjust the angle θ between the guide rail and the horizontal plane: The angle θ between the guide rail and the horizontal plane is obtained by the formula tanθ=μ: Where μ is the maximum static friction coefficient between the guide rail and the slider; When adjusting the angle θ between the guide rail and the horizontal plane, rotate the jacking bolt to jack up the front end of the guide rail, thereby increasing the angle θ between the guide rail and the horizontal plane. When tanθ=μ, tighten the jacking bolt. Step 3, adjust the position of the research plate and the direction of the dynamometer pull: The relative position between the research plate and the plate body is changed by adjusting the telescopic mechanism, and the two telescopic mechanisms are tightened when the height difference between the upper surface of the research plate and the upper surface of the plate body is less than 0.1 mm; the pulling direction of the dynamometer is horizontal; Adjust the length of the copper wire so that the gap between the four sides of the research plate and the four sides of the plate body opening is less than 0.15 mm; Step 4, measure the pulling force L1 when there is no friction resistance: Turn on the dynamometer and close the wind tunnel test section. The wind tunnel is in a closed state, with no incoming flow and no friction resistance. The tension L1 measured by the dynamometer is 0. Step 5, measure the pulling force L2 when there is friction resistance: The wind tunnel is turned on and the incoming flow velocity is set to 20 m / s; when the incoming flow velocity is stable, the upper surface of the research plate is subjected to friction resistance; the dynamometer starts to measure and record the tension value as L2; ​​the wind tunnel is turned off, the side wall of the housing is opened, and the dynamometer is turned off; Step 6, determine the friction resistance τ on the upper surface of the study plate: Friction resistance τ = L2; τ is the friction resistance of the research plate under the incoming flow velocity of 20m / s.

5. The method according to claim 4, characterized in that The tanθ=μ is obtained through the force balance mathematical model: F=Ncosθ(tanθ-μ), when F=0, tanθ=μ; The force balance mathematical model is to analyze the force of the whole M on the guide rail by taking the research plate, two telescopic mechanisms and two sliders as a whole M; in the model, the horizontal component of the resultant force on the whole M is F; the support force of the guide rail on the slider is N, and the direction of the support force N is perpendicular to the surface of the guide rail; μ is the maximum static friction coefficient between the guide rail and the slider.

6. The method according to claim 5, characterized in that The force balance mathematical model is to study the plate, two telescopic mechanisms and two sliders as a whole M, and analyze the force of the whole M on the guide rail; in this model, the horizontal component of the resultant force on the whole M is F; the support force of the guide rail on the slider is N, and the direction of the support force N is perpendicular to the surface of the guide rail; the maximum static friction force between the slider and the guide rail in the whole M is f; the vertical downward force generated by the whole M on the guide rail is P; μ is the maximum static friction coefficient between the guide rail and the slider.

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