A closed air flow channel testing device for sample surface drag reduction performance with precisely adjustable flow angle

Abstract

The present invention belongs to the field of surface drag reduction performance testing, and specifically is a closed air flow channel testing device for sample surface drag reduction performance with precisely adjustable flow angle. The device is equipped with a high-precision rotary fine-tuning platform for precisely fine-tuning the angle and a rotary table for placing samples. While ensuring air tightness and the flatness of the inner plane of the flow channel, the flow angle is precisely adjustable, which solves the shortcomings of other traditional flow channel devices that are difficult to conveniently and accurately measure the surface drag reduction performance under multi-angle flow velocities, and provides a research method for the internal flow problem of the influence of different sample surfaces on the flow state under different flow angles in a closed flow channel. From the perspective of air tightness, it makes it possible to test the drag reduction performance of the surface under multi-angle flow velocities, and ensures the stability of the assembly error after adjustment, reducing the test error. Finally, the test of the drag reduction performance of the sample surface at different flow angles is achieved while ensuring air tightness; and the present invention adopts a flow channel testing method, the measuring device has a simple structure, low cost, and a short experimental cycle.

Description

Technical Field

[0001] The invention belongs to the field of surface drag reduction performance testing, in particular to a closed air flow channel testing device for sample surface drag reduction performance with a precisely adjustable flow direction angle. Background Art

[0002] During fluid flow, the viscosity of the fluid itself will transfer momentum with the surrounding interface, generating a reaction force that hinders the flow of the fluid, thereby generating friction resistance at the interface. Surface drag reduction technology can reduce friction resistance and greatly improve energy utilization, thus playing a great role in the fields of oil and gas, aerospace, navigation, fluid machinery, etc. When the drag reduction surface is actually applied to aerospace, navigation, wind turbines and other fluid machinery fields, the drag reduction surface is often in a working condition where the flow angle is constantly changing. Therefore, it is of great significance to test the drag reduction performance of the drag reduction surface at multiple flow angles.

[0003] The research on surface drag reduction performance is mainly carried out from the aspects of theoretical analysis, numerical simulation and test. At present, the test experiments of surface drag reduction performance in air are mainly wind tunnel experiments and flow channel experiments.

[0004] However, the existing multi-angle flow direction drag reduction test has the following limitations:

[0005] (1) Wind tunnel experimental research is an outflow problem. The current wind tunnel test laboratory has high construction costs, high testing costs, relatively complex operation and daily maintenance, and a long test surface drag reduction performance cycle.

[0006] (2) The current laboratory flow channel test experiment cannot conveniently and accurately test the drag reduction performance under multi-angle flow speed. When testing the drag reduction performance at different flow angles, it is usually necessary to disassemble the flow channel to replace the drag reduction samples at different flow angles for testing. The unstable assembly error leads to test errors. If a rotary fine-tuning platform is directly installed inside the flow channel, the flow channel width or the size and shape of the test sample will be adjusted. According to the two-dimensional flow channel model theory, the aspect ratio of the flow channel is greater than or equal to 15. In the closed flow channel drag reduction performance test reported in the literature, it was found that if the distance between the upper and lower surfaces in the flow channel is too close, the fluid vortex structure generated by the wall will be staggered, which will have a great impact on the drag reduction test results. Therefore, based on the data reference reported in the literature and the actual test requirements, the flow channel width in the conventional closed flow channel drag reduction performance test is designed to be about 30 mm. When the flow channel width is greater than the conventional flow channel width, the flow state in the flow channel is difficult to maintain stability, so there is instability in the test of placing the drag reduction sample directly inside the wide flow channel. When a rotating platform is used to adjust the flow angle at a conventional flow channel width, and a circular drag reduction sample is placed directly inside to facilitate angle adjustment, the sample size will be small (the maximum can only be the flow channel width). Due to the small size of the flow direction sample, it is impossible to achieve an obvious drag reduction performance test effect. Summary of the invention

[0007] The main purpose of the present invention is to provide a closed air flow channel testing device for testing the surface drag reduction performance of a sample with a precisely adjustable flow angle for studying internal flow problems. This solves the problem that the drag reduction performance at different flow velocities cannot be measured by the existing flow channel device in the surface drag reduction performance test, and achieves precise adjustment of the angle and ensures good air tightness.

[0008] The present invention is achieved through the following technical solutions:

[0009] A closed air flow channel test device for measuring the surface drag reduction performance of a sample with precisely adjustable flow direction angle comprises an upper cover plate, a lower base plate, a rubber sealing strip, a rotary fine-tuning platform and a rotary table. The upper cover plate and the lower base plate are fixed by bolts, and the sealing groove between the two plates is sealed on both sides with a rubber sealing strip to ensure air tightness. The upper cover plate is provided with a groove to form a closed flow channel with the lower base plate, and the air is only supplied by the air compressor from the front through the flow stabilizer and exhausted from the back. A through hole is provided in the middle of the lower base plate for installing the rotary table. The rotary table is connected to the lower base plate by bolts with a rotary fine-tuning platform to achieve proper compression. The circumferential freedom between the rotary table and the rotary fine-tuning platform is constrained by the cooperation of the circular hole on the bottom surface of the rotary table and the cylindrical head bolt installed on the rotary fine-tuning platform, so that the rotary platform and the rotary fine-tuning platform rotate synchronously. The air tightness between the lower base plate and the rotary table is ensured by the rubber sealing strip in the sealing groove on the step of the rotary table. There is a circular groove on the rotating truncated table for placing the test sample, and two holes are processed on the upper cover plate for installing pressure sensors, and the holes are located just at the two ends of the test sample along the flow direction. When measuring the drag reduction performance at different flow angles, use a wrench to loosen the bolts between the rotating fine-tuning platform and the lower bottom plate, adjust the rotating fine-tuning platform so that the sample rotates to a predetermined angle, and then tighten the bolts with a wrench to achieve proper compression, so that the surface of the rotating truncated table is flush with the bottom surface of the flow channel, and then the air compressor is used to intake air into the flow channel through the flow stabilizer, and the pressure difference is measured by two pressure sensors to measure the drag reduction performance of the sample surface.

[0010] The circular groove on the rotating truncated table is deeper than the thickness of the sample, and a thin rubber ring with a small elastic modulus and appropriate thickness is placed inside, so that after the test sample is placed in the circular groove of the rotating truncated table, the test sample protrudes a certain height from the top surface of the rotating truncated table. After the flow channel device is installed, because the bottom surface of the upper cover plate, the top surface of the rotating truncated table and the top surface of the lower bottom plate (i.e., the bottom surface of the flow channel) are flush, and the diameter of the circular groove of the rotating truncated table is larger than the width of the groove on the bottom surface of the upper cover plate, the bottom surface of the upper cover plate can be compressed by the thin rubber ring through the test sample, so the protruding height of the test sample will be pressed down by the bottom surface of the upper cover plate until the surface of the test sample is just flush with the top surface of the rotating truncated table, ensuring that there is no height difference between the test sample and the top surface of the rotating truncated table and the bottom surface of the flow channel, and at the same time, it also prevents the airtightness problem caused by the height difference between the test sample and the top surface of the rotating truncated table, ensuring the stability of the assembly and the accuracy of the test.

[0011] Preferably, after the connection between the rotating truncated table and the lower base plate is connected by bolts, a limit nut is screwed on the bolt, and when the rotating truncated table is installed, the limit nut is screwed to a position that supports the lower base plate. After adjusting the angle of the rotating truncated table, it is convenient to quickly install it. Using a wrench with a torque indicator for adjustment can prevent deformation of parts due to excessive assembly force, ensure that the top surface of the rotating truncated table is flush with the top surface of the lower base plate, achieve stable assembly, and reduce errors caused by assembly.

[0012] Preferably, the flushness between the rotating truncated table and the bottom surface of the flow channel (ie, the top surface of the lower cover plate) is ensured by installing the two together and milling the plane.

[0013] Beneficial effects of the present invention:

[0014] 1. A closed air flow channel test device for the drag reduction performance of sample surfaces with a precisely adjustable flow angle for studying internal flow problems is provided. A high-precision rotary fine-tuning platform is installed for precise fine-tuning of angles and a rotary table for placing samples. While ensuring air tightness and the flatness of the inner plane of the flow channel, the flow angle can be precisely adjusted, which solves the shortcoming of other traditional flow channel devices that it is difficult to conveniently and accurately measure the surface drag reduction performance under multi-angle flow velocities, and provides a research method for the internal flow problem of the influence of different sample surfaces on the flow state at different flow angles in a closed flow channel.

[0015] 2. This scheme ensures air tightness and the flushness of the sample with the top surface of the rotating table by placing an elastic rubber ring under the rotating table to raise the test sample, and then pressing it down from the bottom surface of the upper cover plate to the top surface of the rotating table. When the flow angle of the test sample needs to be adjusted, loosen the bolts between the rotating fine-tuning platform and the lower bottom plate, adjust the rotating table to the specified angle, and then tighten the bolts. Due to the nut limit on the bolt and the use of a wrench with a torque indicator for installation, a stable transfer between the top surface of the rotating table and the top surface of the lower bottom plate is achieved, and finally the flushness of the internal plane of the flow channel (the top surface of the rotating table, the surface of the test sample, the bottom surface of the upper cover plate, and the top surface of the lower bottom plate) is achieved, so that the height difference between different planes after rotation is extremely small and the air tightness is good. Therefore, from the perspective of air tightness, it is possible to test the drag reduction performance of the surface under multi-angle flow velocity, and the stability of the assembly error after adjustment is guaranteed, reducing the test error. Finally, the drag reduction performance of the sample surface at different flow angles is tested while ensuring air tightness.

[0016] 3. By replacing different rotating round tables, different sample surfaces can be quickly tested at multi-angle flow speeds. This facilitates comparative studies on the flow properties of different sample surfaces, making the study of surface aerodynamic drag reduction performance more convenient. In addition, the present invention adopts a flow channel test method, and the measuring device has a simple structure, low cost, and a short experimental cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an exploded view of the assembly of the device of the present invention;

[0018] Figure 2 It is a schematic diagram of the bottom surface structure of the upper cover plate of the device of the present invention;

[0019] Figure 3 This is an assembly diagram of the angle precision fine-tuning structure of the device of the present invention (half-section); Specific implementation plan

[0020] The present invention will be described in further detail below in conjunction with the accompanying drawings:

[0021] like Figure 1 As shown, a closed air flow channel test device for sample surface drag reduction performance with precisely adjustable flow angle includes an upper cover plate, a lower base plate, a rotating truncated table, adjustment bolts, limit nuts and a rotating fine-tuning platform, wherein two pressure sensor mounting holes are provided on the top surface of the upper cover plate for pressure measurement. The upper cover plate and the lower base plate are fixed and sealed by bolts and rubber sealing strips, and the rotating truncated table is fixed to the lower base plate by the rotating fine-tuning platform through adjusting bolts, so that the top surface of the rotating truncated table is kept flush with the top surface of the lower base plate.

[0022] like Figure 2 As shown, two sealing grooves are processed on both sides of the bottom surface of the upper cover plate, and rubber sealing strips are stuffed inside and connected to the lower bottom plate by bolts. There is a rectangular groove in the middle to form a closed flow channel with the lower bottom plate. A flow stabilizer installation position is processed at the airflow outlet for connecting the flow stabilizer to ensure that it provides stable airflow.

[0023] like Figure 3 As shown, the rotation and sealing structure between the rotating circular table, the lower base plate and the rotating fine-tuning platform are realized in the manner shown in the figure.

[0024] The following is a specific implementation plan of a closed air flow channel test device for sample surface drag reduction performance using a precisely adjustable flow angle:

[0025] First, before using the closed air flow channel test device for the drag reduction performance of the sample surface with precisely adjustable flow angle, the top surface of the rotating truncated table and the top surface of the lower bottom plate should be adjusted for flushness. After the top surface of the rotating truncated table and the top surface of the lower bottom plate are roughly flush, use a wrench with a torque indicator to properly tighten the adjustment bolts to ensure stable flushness without loosening, record the torque value, and then adjust the limit nut to the bottom surface of the lower bottom plate, so that the next test installation can quickly reach the specified position.

[0026] After completing the flush adjustment of the top surface of the rotating table and the top surface of the lower base plate, install the upper cover plate and the lower base plate, and then fill the test sample and the elastic rubber ring into the groove on the bottom surface of the rotating table. At this time, the test sample protrudes a little higher than the top surface of the rotating table, and then installs it into the lower base plate. Since the bottom surface of the upper cover plate is flush with the top surface of the lower base plate, tighten the bolts according to the previously recorded bolt torque and the position of the limit nut. When adjusting the bolts, the test sample will be pressed into a position flush with the top surface of the rotating table, so the top surface of the rotating table, the sample surface, the bottom surface of the upper cover plate and the top surface of the lower base plate remain flush.

[0027] Since there is a rubber sealing strip between the upper cover plate and the lower base plate, and there is also a rubber sealing strip between the shoulder of the rotating table and the bottom surface of the lower base plate, the sample and the bottom surface of the upper cover plate can also form a good seal because of the pre-pressure of the rubber sealing ring under the sample, thus ensuring the air tightness of the test device.

[0028] After the installation of the test sample is completed, the air compressor starts to supply air through the flow stabilizer and enters the air flow inlet of the test device. When passing through the surface of the test sample, a pressure drop will occur. There are two pressure measuring holes processed on the upper cover plate, corresponding to the two ends of the test sample surface. The pressure measuring holes are connected to the computer with a pressure sensor. After computer processing and comparison, the pressure difference ΔP at both ends of the surface is obtained. 1 .

[0029] After the test, loosen the adjustment bolt, adjust the rotary fine-tuning platform to the predetermined angle, tighten the adjustment bolt according to the previously recorded bolt torque and the position of the limit nut and continue the test. The pressure difference ΔP at both ends of the surface at different flow angles is obtained. i .

[0030] Finally, the drag reduction rate DR is obtained:

[0031]

[0032] Where ΔP 0 There is no groove on the rotating round table, and it is the pressure difference tested under a smooth plane, ΔP i It is the pressure difference under different flow angles. i The larger it is, the better the drag reduction effect is at angle i.

[0033] The closed air flow channel test device for the drag reduction performance of the sample surface with precisely adjustable flow angle solves the shortcoming that the traditional flow channel test device cannot conveniently and accurately measure the drag reduction performance of the sample surface. By adopting the installation of a rotary fine-tuning platform for precise fine-tuning of the angle and a rotary truncated table for placing samples, the inconvenience and error caused by the need to disassemble the flow channel to replace drag reduction samples with different flow angles are eliminated. The present invention uses a high-precision rotary fine-tuning platform to ensure high precision in adjusting the surface flow angle, and uses a replaceable rotary truncated table. It is convenient to fill in the test sample without disassembling the flow channel body, and it is relatively fast and convenient to test the drag reduction performance of different test samples.

Claims

1. A closed air flow channel test device for measuring the drag reduction performance of sample surface with precise and adjustable flow angle, It is characterized in that It includes an upper cover plate, a lower base plate, a rubber sealing strip, a rotary fine-tuning platform and a rotary table; the upper cover plate and the lower base plate are fixed by bolts, and the sealing groove between the two plates is sealed on both sides with a rubber sealing strip to ensure air tightness. The upper cover plate has a groove to form a closed flow channel with the lower base plate, and the air is only supplied by the air compressor from the front to the flow stabilizer and exhausted from the back; a through hole is opened in the middle of the lower base plate for installing the rotary table, and the rotary table is connected to the lower base plate with a rotary fine-tuning platform by bolts to achieve proper compression, and the rotary table and the rotary micro The circumferential freedom of the adjustment platforms is constrained by the cooperation of the circular hole on the bottom surface of the rotating truncated table and the cylindrical head bolts installed on the rotating fine-tuning platform, so that the rotating platform and the rotating fine-tuning platform rotate synchronously; the air tightness between the lower bottom plate and the rotating truncated table is ensured by the rubber sealing strip in the sealing groove on the step of the rotating truncated table; a circular groove is opened on the rotating truncated table for placing the test sample, which is deeper than the thickness of the sample and has a rubber ring placed inside; the top surface of the rotating truncated table inside the flow channel, the surface of the test sample, the bottom surface of the upper cover plate and the top surface of the lower bottom plate are flush; The upper cover plate is processed with two holes for installing pressure sensors, and the holes are located just at the two ends of the test sample along the flow direction; when measuring the drag reduction performance at different flow angles, use a wrench to loosen the bolts between the rotating fine-tuning platform and the lower base plate, adjust the rotating fine-tuning platform to make the sample rotate to a predetermined angle, and then tighten the bolts with a wrench to achieve proper compression so that the surface of the rotating table is flush with the bottom surface of the flow channel, and then the air compressor is used to draw air into the flow channel through the flow stabilizer, and the pressure difference is measured by two pressure sensors to measure the drag reduction performance of the sample surface.

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