Wall shear stress sensor

Abstract

The invention provides a wall shear stress sensor, which is used for measuring the shear stress of a flow field, and comprises a base; the sample plate is arranged in the base; the sensitive element is arranged in the base, the lower surface of the sensitive element is connected with the upper surface of the sample plate, and the sensitive element is used for converting friction force borne by the sample plate into displacement of the sensitive element; the two-dimensional grid disc is arranged on the upper surface of the sensitive element; the reading assembly is connected with the upper surface of the base; the reading assembly comprises a reading head adapter plate connected with the upper surface of the base; the reading head is arranged on the reading head adapter plate and is used for emitting visible light to the two-dimensional grid disc; and the lens is arranged between the reading head and the two-dimensional grating disc and is used for adjusting the visible light into parallel visible light. The sensor can adapt to working conditions of gas-liquid two-phase flow and dissolved matters in fluid, and is suitable for working conditions of researching influence of surface treatment on wall surface friction force. The test result of the sensor is slightly influenced by environment temperature and has no temperature drift.

Description

Technical Field

[0001] The invention belongs to the field of fluid wall shear stress measurement, and in particular relates to a wall shear stress sensor. Background Art

[0002] The shear stress generated by the viscous fluid acting on the wall of an object has always been an important topic in the research of drag reduction, noise reduction, boundary layer transition, etc. There are two measurement methods for wall shear stress: indirect measurement method and direct measurement method. The indirect measurement method refers to the use of parameters such as fluid pressure drop, velocity gradient and heat transfer rate to obtain the shear stress of the fluid wall by theoretical calculation, such as Preston tube method, Stanton method, and velocity type method; the direct measurement method uses surface friction balance, oil film technology and liquid crystal coating technology to directly obtain the wall shear stress. Most of the current shear stress sensors have complex manufacturing and installation methods, and can only measure the magnitude of the wall shear stress but not its direction.

[0003] Therefore, there is an urgent need for a method that can directly measure the wall shear stress vector without having to determine the direction of the wall shear stress in advance and can effectively reduce the error of the measured shear stress direction. Summary of the invention

[0004] An embodiment of the present invention provides a wall shear stress sensor.

[0005] In view of this, the first aspect of the present invention proposes a wall shear stress sensor for measuring the shear stress of a flow field, the wall shear stress sensor comprising: a base; a sample plate arranged in the base; a sensitive element arranged in the base, the lower surface of the sensitive element being connected to the upper surface of the sample plate, the sensitive element being used to convert the friction force exerted on the sample plate into the displacement of the sensitive element; a two-dimensional grating arranged on the upper surface of the sensitive element; a reading assembly connected to the upper surface of the base; the reading assembly comprising: a reading head adapter plate connected to the upper surface of the base; a reading head arranged on the reading head adapter plate, for emitting visible light to the two-dimensional grating; a lens arranged between the reading head and the two-dimensional grating, for adjusting the visible light into parallel visible light.

[0006] Furthermore, the sensitive element includes: a floating unit and a beam spring.

[0007] Furthermore, the beam spring is composed of two symmetrical sub-beam springs connected in parallel.

[0008] Further, the sub-beam spring is formed by at least one elastic beam connected in series.

[0009] Furthermore, the width of the gap between the sample plate and the base is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

[0010] Furthermore, the wall shear stress sensor also includes a plug gauge, which is arranged between the sample plate and the base and is used to adjust the gap between the sample plate and the base.

[0011] Furthermore, the thickness of the plug gauge is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

[0012] Furthermore, the wall shear stress sensor also includes: a positioning bolt, which is used to fix the sensitive element on the base.

[0013] Furthermore, the wall shear stress sensor also includes: an adjusting bolt for connecting the sample plate and the sensitive element, and by adjusting the adjusting bolt, the lower surface of the sample plate and the lower surface of the base can be adjusted to be coplanar.

[0014] Furthermore, the wall shear stress sensor also includes: a foam rubber ring, which is sleeved on the adjusting bolt.

[0015] The beneficial effects brought by the present invention are as follows: The sensor involved in the present invention can measure the magnitude and direction of the wall shear stress vector. The sensitive elements used for measurement can be batch processed using wire cutting processing technology, without the need for complex etching processes, and the processing cost is low; the sensitive element material is metal, which is easy to obtain and has high strength. The process of calculating the wall shear stress of the sensor is simple and does not require repeated calibration; the wall shear stresses measured in two directions are decoupled from each other. The sensor can adapt to working conditions of gas-liquid two-phase flow and the presence of dissolved substances in the fluid; the sample plate can be sprayed with a coating or constructed with a microstructure, which is suitable for studying the influence of surface treatment on wall friction. The test results of the sensor are less affected by the ambient temperature and have no temperature drift. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a wall shear stress vector sensor provided by an embodiment of the present invention;

[0017] Figure 2 A cross-sectional view of a wall shear stress vector sensor provided by an embodiment of the present invention;

[0018] Figure 3 A schematic diagram of shear stress vector measurement provided by an embodiment of the present invention;

[0019] Figure 4 One of the schematic diagrams of the effect of the isolation plate on the internal flow of the wall shear stress vector sensor provided by the embodiment of the present invention;

[0020] Figure 5 A second schematic diagram of the effect of the isolation plate on the internal flow of the wall shear stress vector sensor provided by an embodiment of the present invention;

[0021] Figure 6 A schematic diagram of the installation of a sample plate provided in an embodiment of the present invention;

[0022] Figure 7 A schematic diagram of an installed wall shear stress vector sensor provided by an embodiment of the present invention;

[0023] Figure 8 A schematic diagram of an interface of a host computer of a wall shear stress vector sensor provided in an embodiment of the present invention.

[0024] in, Figures 1 to 7 The corresponding relationship between the reference numerals and component names is as follows:

[0025] 1 reading head, 2 two-dimensional grating disk, 3 reading head adapter plate, 4 lens, 5 sensitive element, 6 sample plate, 7 base, 8 foam rubber ring, 9 plug gauge, 10 positioning surface, 11 positioning bolt, 12 isolation plate, 13 wall surface, 14 flow field to be measured, 15 mounting groove, 16 pneumatic valve, 17 floating unit, 18 encoder counter card, 19 host computer, 20 beam spring, 21 adjusting bolt. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The first aspect of the present invention provides a wall shear stress sensor for measuring the shear stress of a flow field, such as Figure 1 and Figure 2 As shown, the wall shear stress sensor includes: a base 7; a sample plate 6, which is arranged in the base 7; a sensitive element 5, which is arranged in the base 7, and the lower surface of the sensitive element 5 is connected to the upper surface of the sample plate 6, and the sensitive element 5 is used to convert the friction force exerted on the sample plate 6 into the displacement of the sensitive element 5; a two-dimensional grating disk 2, which is arranged on the upper surface of the sensitive element 5; a reading component, which is connected to the upper surface of the base 7; the reading component includes: a reading head adapter plate 3, which is connected to the upper surface of the base 7; a reading head 1, which is arranged on the reading head adapter plate 3, and is used to emit visible light to the two-dimensional grating disk 2; a lens 4, which is arranged between the reading head 1 and the two-dimensional grating disk 2, and is used to adjust the visible light into parallel visible light.

[0028] Furthermore, the sensitive element 5 includes a floating unit 17 and a beam spring 20 .

[0029] Furthermore, the beam spring 20 is composed of two symmetrical sub-beam springs connected in parallel.

[0030] Further, the sub-beam spring is formed by at least one elastic beam connected in series.

[0031] Furthermore, the gap width between the sample plate 6 and the base 7 is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

[0032] Furthermore, the wall shear stress sensor further includes a plug gauge 9 , which is disposed between the sample plate 6 and the base 7 and is used to adjust the gap between the sample plate 6 and the base 7 .

[0033] Furthermore, the thickness of the plug gauge 9 is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

[0034] Furthermore, the wall shear stress sensor further includes: a positioning bolt 11 for fixing the sensitive element 5 on the base 7 .

[0035] Furthermore, the wall shear stress sensor further includes: an adjusting bolt 21 for connecting the sample plate 6 and the sensitive element 5 . By adjusting the adjusting bolt 21 , the lower surface of the sample plate 6 and the lower surface of the base 7 can be adjusted to be coplanar.

[0036] Furthermore, the wall shear stress sensor further includes: a foam rubber ring 8 sleeved on the adjusting bolt 21 .

[0037] The beneficial effects brought by the present invention are as follows: the sensor involved in the present invention can measure the magnitude and direction of the wall shear stress vector. The sensitive element 5 used for measurement can be batch processed using a wire cutting process, without the need for a complex etching process, and the processing cost is low; the material of the sensitive element 5 is metal, which is easy to obtain and has high strength. The process of calculating the wall shear stress of the sensor is simple and does not require repeated calibration; the wall shear stresses measured in two directions are decoupled from each other. The sensor can adapt to working conditions of gas-liquid two-phase flow and the presence of dissolved substances in the fluid; the sample plate 6 can be sprayed with a coating or constructed with a microstructure, which is suitable for studying the influence of surface treatment on wall friction. The test results of the sensor are less affected by the ambient temperature and have no temperature drift.

[0038] The proposed wall shear stress sensor includes a reading head 1, a two-dimensional grating disk 2, a reading head adapter plate 3, a lens 4, a sensitive element 5, a base 7, and a sample plate 6.

[0039] The sensitive element 5 (floating unit 17) of the wall shear stress sensor can convert the component forces F1 and F2 of the wall friction force F in two directions perpendicular to each other into displacements Δx and Δy in corresponding directions through a beam spring 20 whose elastic coefficients are k1 and k2 in corresponding directions, and there is no coupling relationship between the displacements in the two directions generated when the sensitive element 5 is subjected to shear stress.

[0040] The sensor converts the shear stress vector to be measured into displacements Δx and Δy in the flow direction and span direction, and the reading head 1 outputs the displacement signal. The data is input into the computer through the encoder counter card 18, and the wall shear stresses in two perpendicular directions are obtained by F1=k1Δx and F2=k2Δy. The output (shear stress) is linearly related to the input (displacement), and the conversion coefficient (elastic coefficient) is a constant, so the test result is not affected by the ambient temperature.

[0041] The base 7 fixes the sensor at the test position of the device to be tested (navigation body or model), and its lower surface is flush with the wall of the device to be tested; the lower surface of the sample plate 6 is coplanar with the lower surface of the base 7, and is used to sense the wall shear stress applied to it by the flow field; the sensitive element 5 is fixedly connected to the base 7, and the lower surface of the floating unit 17 of the sensitive element 5 is fixedly connected to the sample plate 6 to convert the wall shear stress on the sample plate 6 into displacements Δx and Δy in two directions perpendicular to each other, and a small two-dimensional grating disk 2 is installed on the upper surface; the reading head 1 is installed on the reading head adapter plate 3, and emits parallel light to the two-dimensional grating disk 2 through the lens 4 and receives the light and dark stripes reflected by the grating disk, and outputs displacement signals in two directions perpendicular to each other; the reading head adapter plate 3 is fixed on the base 7 to provide support and positioning for the reading head 1 and the lens 4.

[0042] The gap width between the sample plate 6 and the wall is gh = 0.05mm ~ 0.2mm, and the internal fluid is connected to the external flow field. Under the influence of the external flow, internal flow will occur between the sensitive element 5 and the sample plate 6, such as Figure 4 To prevent the internal flow from affecting the sensitive element 5 and the sample plate 6, an isolation plate 12 is provided between the sample plate 6 and the sensitive element 5 to suppress the internal flow and prevent the internal flow from acting on the inner surface of the sample plate 6 and the floating unit 17 at the same time. Figure 5 shown.

[0043] Since the two-dimensional grating disk 2 is at zero position when stationary, the positive and negative signs of the two stress components can be determined by the positive and negative signs of the displacement signal output by the reading head 1 after being subjected to force, so there is no need to determine the direction of the wall shear stress in advance, and the wall shear stress vector can be directly measured; the beam spring 20 of the shear stress sensor sensitive element 5 is processed by slow-feed wire cutting, with high processing accuracy, which can effectively reduce the error of the measured shear stress direction.

[0044] The proposed wall shear stress sensor includes a reading head 1, a two-dimensional grating disk 2, a reading head adapter plate 3, a lens 4, a sensitive element 5, a base 7, and a sample plate 6. Figure 2 shown.

[0045] The sensitive element 5 of the sensor and the force measurement principle are further described as follows in conjunction with the accompanying drawings:

[0046] The sensitive element 5 (floating unit 17) of the wall shear stress sensor includes the floating unit 17 and the beam spring 20, which can convert the component force F1 of the wall friction force in the x direction and the component force F2 in the y direction into displacements in corresponding directions, such as Figure 3 As shown. Among them, the elastic coefficients of beam spring 20a and beam spring 20c are both k1 / 2, and the elastic coefficients of beam spring 20b and beam spring 20d are both k2 / 2. The four beam springs 20 are each composed of two symmetrical sub-beam springs in parallel, and each sub-beam spring is formed by a number of elastic beams in series; the connection between the elastic beams can be basically regarded as rigid, and the rotation angles at both ends of a single beam are zero, so the elastic coefficient of a single beam is:

[0047]

[0048] In the formula, k i is the elastic coefficient, E is the Young's modulus of the material used for the folding beam, t is the thickness of the single beam, w is the width of the single beam, and L is the length of the single beam. According to simulation calculations, there is no coupling relationship between the displacements in the two directions generated by the sensitive element 5 when subjected to shear stress.

[0049] The sensor converts the shear stress vector to be measured into displacements Δx and Δy in the flow direction and span direction, and the reading head 1 outputs the displacement signal. The data is input into the host computer 19 through the encoder counter card 18, and the wall shear stress in two perpendicular directions is obtained by F1=k1Δx and F2=k2Δy. The output (shear stress) is linearly related to the input (displacement), and the conversion coefficient (elastic coefficient) is a constant, so the test result is not affected by the ambient temperature.

[0050] The composition of the sensor and the force measurement process are further described as follows in conjunction with the attached drawings:

[0051] The base 7 fixes the sensor at the test position of the device to be tested (navigation body or model), and its lower surface is flush with the wall 13 of the device to be tested; the lower surface of the sample plate 6 is coplanar with the lower surface of the base 7, and is used to sense the wall shear stress applied to it by the flow field; the sensitive element 5 is fixedly connected to the base 7, and the lower surface of the floating unit 17 of the sensitive element 5 is fixedly connected to the sample plate 6 to convert the wall shear stress on the sample plate 6 into displacements Δx and Δy in two directions perpendicular to each other, and a small two-dimensional grating disk 2 is installed on the upper surface; the reading head 1 is installed on the reading head adapter plate 3, and emits parallel light to the two-dimensional grating disk 2 through the lens 4 and receives the light and dark stripes reflected by the grating disk, and outputs displacement signals in two directions perpendicular to each other; the reading head adapter plate 3 is fixed on the base 7 to provide support and positioning for the reading head 1 and the lens 4.

[0052] The sensor replacement sample plate 6 and installation process are further described as follows in conjunction with the accompanying drawings:

[0053] The process of installing the sensor or replacing the sample plate 6 is as follows Figure 6 Tighten the four positioning bolts 11 to fix the floating unit 17 to prevent the tightening torque applied to the screws in the subsequent process of fixing the sample plate 6 from acting on the beam spring 20 and causing the beam spring 20 to deform; fix the sensitive element 5 on the base 7, as shown. Figure 6 After that, the sample plate 6 is placed on the sensitive element 5, and a plug gauge 9 is inserted along the four sides of the sample plate 6 into the gap between the sample plate 6 and the mounting groove 15 for mounting the sample plate 6, as shown in FIG. Figure 6 As shown; use a torque wrench to fix the sample plate 6 on the floating unit 17 of the sensitive element 5 with four screws, and adjust the tightening torque to ensure that the outer surface of the sample plate 6 of the floating unit 17 is coplanar with the wall surface 13. Among them, the thickness of the plug gauge 9 is 0.05mm-0.2mm, and the specific value depends on the sensor range and elastic coefficient. The length is the same as the length of the sample plate 6, and the width is slightly larger than the depth of the installation groove 15 to ensure the gap width between the sample plate 6 and the side wall of the installation groove 15, so that the range of the wall friction force measurement device meets the design requirements.

[0054] The process of installing the reading head adapter plate 3 and calibrating the grating encoder is as follows Figure 6 As shown. First, use the positioning surface 10 to position the read head adapter plate 3 and fix it with screws; then, cover the read head 1 (fixed on the adapter plate) once to enter the calibration mode, and the red light of the read head 1 flashes; put the read head 1 into the slot of the read head adapter plate 3 and fix it with screws, so that the green light of the read head 1 flashes, then power off and power on again, so that the blue light of the read head 1 flashes, and after 5 seconds, make the read head 1 completely pass through the optical zero position from the positive direction and the reverse direction along the moving axis of the read head 1. At this time, the indicator light of the read head 1 will turn blue and light up steadily, and the calibration of the read head 1 is completed. The built-in EEPROM of the read head 1 will automatically save the calibration parameters.

[0055] Schematic diagram of wall shear stress vector sensor measuring shear stress Figure 7 As shown. The sensor installation and measurement process is as follows: First, fix the shear stress vector sensor with four screws so that the outer surface of the sample plate 6 is flush with the wall surface 13 to be measured, so that the sample plate 6 can feel the wall friction force applied by the flow field 14 to be measured; after fixing, if bubbles are observed inside the sensor through the reading head adapter plate 3, open the pneumatic valve 16 to discharge the bubbles inside the shear stress vector sensor; then, connect the reading head 1 to the power supply and encoder counter card 18 in turn, and connect the encoder counter card 18 to the host computer 19 through the USB serial port; turn on the power supply and the host computer 19, and the size and direction of the shear stress vector applied by the flow field to the wall surface 13 can be measured. The measurement interface is as shown in the figure. Figure 8 shown.

[0056] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A wall shear stress sensor, characterized in that: Used to measure the shear stress of the flow field, the wall shear stress sensor comprises: Base; A sample plate, disposed in the base; A sensitive element is arranged in the base, the lower surface of the sensitive element is connected to the upper surface of the sample plate, and the sensitive element is used to convert the friction force exerted on the sample plate into the displacement of the sensitive element; A two-dimensional grating disk is arranged on the upper surface of the sensitive element; A reading assembly connected to the upper surface of the base; The reading assembly includes: a reading head adapter plate connected to the upper surface of the base; A reading head, arranged on the reading head adapter plate, for emitting visible light to the two-dimensional grating disk; A lens is arranged between the reading head and the two-dimensional grating disk, and is used for adjusting the visible light into parallel visible light.

2. The wall shear stress sensor according to claim 1, characterized in that: The sensitive element includes: a floating unit and a beam spring.

3. The wall shear stress sensor according to claim 2, characterized in that: The beam spring is composed of two symmetrical sub-beam springs connected in parallel.

4. The wall shear stress sensor according to claim 3, characterized in that: The sub-beam spring is formed by at least one elastic beam connected in series.

5. The wall shear stress sensor according to any one of claims 1 to 4, characterized in that: The width of the gap between the sample plate and the base is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

6. The wall shear stress sensor according to claim 5, characterized in that: A plug gauge is also included, which is arranged between the sample plate and the base and is used to adjust the gap between the sample plate and the base.

7. The wall shear stress sensor according to claim 6, characterized in that: The thickness of the plug gauge is greater than or equal to 0.05 mm and less than or equal to 0.2 mm.

8. The wall shear stress sensor according to any one of claims 1 to 4, characterized in that: Also includes: The positioning bolt is used to fix the sensitive element on the base.

9. The wall shear stress sensor according to any one of claims 1 to 4, characterized in that: Also includes: The adjusting bolt is used to connect the sample plate and the sensitive element. By adjusting the adjusting bolt, the lower surface of the sample plate and the lower surface of the base can be adjusted to be coplanar.

10. The wall shear stress sensor according to claim 9, characterized in that: It also includes a foam rubber ring which is sleeved on the adjusting bolt.

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