A device and method for measuring pressure of small rotational-static gap

Abstract

The present invention discloses a pressure measurement device and method for a tiny rotary-static gap, belonging to the technical field of measurement and testing. In view of the problem that the shear flow pressure of the tiny eccentric rotary-static gap of the existing air dynamic pressure bearing is difficult to measure accurately, a pressure device and method comprising an adjustable movable platform and several static pressure measurement channels are proposed. Each static pressure measurement channel comprises: a static pressure stepped through hole opened on the wall of a stationary cylinder, a capillary needle, a silicone hose, an obliquely installed U-shaped tube and a clamp-type ultrasonic flow sensor. By arranging several static pressure stepped through holes with gradually decreasing apertures along the circumference to reduce the interference of the wall openings on the shear flow of the rotary-static gap, the static pressure stepped through holes are used to transmit the fluid pressure in the tiny eccentric gap to the U-shaped tube filled with a low-density solution, and the measured gap pressure value is converted according to the measurement value of the clamp-type flow meter. The present invention can realize the rapid and accurate measurement of the conventional pressure value in the tiny gap and the pressure value in the low-pressure zone.

Description

Technical Field

[0001] The invention discloses a pressure measuring device and method for a tiny rotary-static gap, relates to a technology for directly measuring the pressure in the tiny gap by using an experiment, and belongs to the technical field of measurement and testing. Background Art

[0002] With the rapid development of technologies in aerospace, precision machining, and other fields, the bearing structure in rotating machinery has gradually become one of the key technologies restricting its development. To overcome the shortcomings of traditional bearings, gas-lubricated bearings have emerged. These bearings use gas as the working medium, leveraging the gas's diffusivity, viscosity, compressibility, and adsorption properties. As the bearing rotates, static and dynamic pressure effects are generated, forming an air film within the gap that can support loads and reduce frictional resistance. Therefore, compared with traditional contact bearings, gas-lubricated bearings offer high speeds, low power consumption, zero pollution, and a long life. As an important branch of gas-lubricated bearings, hydrodynamic gas bearings utilize the widely available air as a medium, simplifying the lubrication systems required for other bearings. At the same time, their wedge-shaped gap generates dynamic pressure to provide load-bearing capacity. Therefore, hydrodynamic gas bearings offer many advantages, including simple structure, flexible use, and a wide range of applications.

[0003] Aerodynamic bearings use air as a lubricant. Their operating principle is that a wedge-shaped gap forms between the relatively moving surfaces of the bearing during high-speed operation. Due to the viscosity of the gas, the dynamic pressure effect when the gas enters the wedge-shaped gap generates air film pressure within the gap, further generating load-bearing capacity to support the rotating shaft. The flow in the gap of an aerodynamic bearing can be viewed as a flow within a tiny rotor-static gap under eccentricity, with gap dimensions ranging from mm to μm. Compared with macroscale rotational flow, the flow mechanisms within the gap at the microscale differ significantly, and many macroscale laws no longer apply to microgaps. Therefore, a systematic and in-depth study of microgap rotational shear flow is necessary. The pressure distribution formed by the tiny rotor-static gap under eccentricity exhibits both regions of high and low pressure differentials. These high-pressure regions and low-pressure regions together constitute a continuous pressure distribution within the tiny rotor-static gap.

[0004] Typically, the pressure of a macroscopic rotor-static gap is detected through static pressure holes. Pressure-testing holes are machined into the wall, and the hole gaps are directly connected to devices such as electronic pressure sensors or pressure scanning valves to output pressure values. For example, a dynamic and static pressure gas bearing dynamic film pressure test device and test method utilizes a rotatable bearing seat. The rotatable bearing seat is provided with test holes at the air inlet holes corresponding to the two test bearings. Each test hole is equipped with an air inlet pipe connected to a pressure sensor. During measurement, the pressure sensor reads the air film pressure at the corresponding position, and measurements at different circumferential positions can be achieved by manually adjusting the angle of the rotating bearing seat. Another air film pressure measurement device utilizes multiple air channels on the rotor, one end of which connects to the air film gap. The other end of the air channels is connected to a pressure sensor. The pressure sensor data is transmitted to a receiver via a wireless telemetry device to prevent the dynamic characteristics of the test device from being affected. All of the above methods for detecting macroscopic rotor-static gap pressure utilize electronic pressure sensors. Pressure sampling requires adjusting the sampling frequency of the electronic pressure sensor to match the rotor speed, and also requires considering issues such as delayed response. When measuring the circumferential pressure distribution, the measurement point position must be manually adjusted, making it relatively complex to use.

[0005] The numerous difficulties in measuring pressure in small rotor-stator gaps at high speeds pose challenges to the design and use of gas bearings. The boundary walls of rotating gaps are all curved. Using electronic pressure sensors or pressure scanning valves within the high-speed, small rotor-stator gap not only disrupts the smoothness of the walls but also disrupts the flow boundary to a certain extent, causing disturbances in the flow field and resulting in measurement errors. Therefore, due to the small size and curved walls, pressure sensors, piezoelectric plates, and other measuring devices are difficult to install within small gaps, making it difficult for traditional pressure sensors to effectively measure pressure in small rotor-stator gaps. Furthermore, the pressure distribution created by the small rotor-stator gap under eccentricity makes it difficult to accurately measure the pressure in the low-pressure zone using traditional measuring devices. This is partly due to the large measurement range, low resolution, and poor measurement accuracy of traditional devices. Furthermore, the compressibility of the gas fluid within the small gap, combined with factors such as ambient noise and system vibration, leads to large fluctuations in the measured values ​​in the low-pressure zone, reducing measurement accuracy.

[0006] In summary, the present invention aims to provide a device and method for measuring the pressure of a small rotor-static gap, so as to solve the problem of measuring the pressure of a small rotor-static gap. Summary of the Invention

[0007] The purpose of the present invention is to address the shortcomings of the above-mentioned background technology and the problem of shear flow pressure measurement of small eccentric rotor-static gaps of air dynamic bearings on the mm to μm scale, and to provide a pressure measurement device and method for small rotor-static gaps, so as to solve the technical problem that the macro-scale rotor-static gap pressure measurement technology is not suitable for small rotor-static gap pressure measurement, and to achieve the purpose of accurately measuring the conventional pressure value in the small rotor-static gap while reducing the disturbance to the flow field, and accurately measuring the smaller pressure value below 100Pa in the small rotor-static gap without being affected by system vibration and environmental noise.

[0008] The present invention adopts the following technical solutions to achieve the above-mentioned purpose:

[0009] A pressure measuring device for a small rotary-static gap comprises a small rotary-static gap formed by the outer wall of a rotating cylinder and the inner wall of a stationary cylinder, and at least two static pressure measurement channels. The stationary cylinder is fixed on an adjustable movable platform, and a fixed eccentricity is set by laterally adjusting the adjustable movable platform. Each static pressure measurement channel comprises: a static pressure stepped through hole, a capillary needle, a silicone hose, a U-shaped tube, and a clamp-type ultrasonic flow sensor. The static pressure stepped through hole is machined on the stationary cylinder, and the capillary needle is inserted into the static pressure stepped through hole from the outside of the stationary cylinder. The static pressure stepped through hole and the U-shaped tube are connected by a silicone hose. The U-shaped tube is fixed to a vertical plate, and one side of the U-shaped tube is perpendicular to the ground. The other side of the U-shaped tube is equipped with a clamp-type ultrasonic flow sensor, and the other side of the U-shaped tube is connected to the atmosphere.

[0010] Furthermore, the rotating cylinder that forms a small rotation-static gap is driven by a high-speed motor. The stationary cylinder and the rotating cylinder form an annular gap and ensure that no collision or friction occurs under the small gap. The stationary cylinder is installed as a whole on an adjustable movable platform. Through lateral displacement adjustment, the stationary cylinder and the rotating cylinder form a fixed eccentricity.

[0011] Furthermore, in order to facilitate the connection of the external air circuit and to reduce the impact of the opening on the inner wall of the stationary cylinder on the fluid flow, a three-level stepped hole structure is processed on the wall of the stationary cylinder to form a static pressure stepped through hole. The aperture of the three-level stepped hole structure gradually decreases from the outer wall to the inner wall of the stationary cylinder. The apertures from the outer wall to the inner wall are 1.5-2mm, 1-1.2mm, and 0.4-0.8mm respectively.

[0012] Furthermore, the static pressure stepped holes in each static pressure measurement channel are distributed along the axial center section of the stationary cylinder and circumferentially around the cylinder wall, bleed air from the tiny rotor-to-static gap. The circumferential angle between adjacent static pressure stepped holes on the side with the minimum gap height is 10-20°, while the circumferential angle between adjacent static pressure stepped holes on the side with the maximum gap height is 20-40°.

[0013] Furthermore, the static pressure stepped through-holes in each static pressure measurement channel are staggered circumferentially around the stationary cylinder wall, meaning adjacent static pressure stepped through-holes are offset axially. This is to reduce the disruption to the circumferential flow caused by the fluid passing through multiple openings, and to account for significant pressure variations in the axial direction. To meet this requirement, the axial offset distance between the openings is no less than the minimum diameter of the static pressure stepped through-holes, but should not be excessively large, i.e., 0.5-1mm.

[0014] Furthermore, a capillary needle is inserted into the largest hole in the three-stepped hole, and the gap at the joint is coated with sealant to secure the capillary needle and prevent gas leakage within the airway. One end of a silicone hose is inserted into the capillary needle, and the other end of the silicone hose is connected to the side of the U-shaped tube perpendicular to the ground, thus forming a pressure measuring airway. The angle between the two sides of the U-shaped tube is 30°-60°, and the inner diameter of the tube is 5-8mm. The U-shaped tube is mounted on a vertical plate.

[0015] Furthermore, the solution within the U-shaped tube should have a low density. This allows the liquid column to rise higher under the same pressure, reducing the number of graduations per scale and improving reading accuracy. To ensure safety, non-toxic solutions should be selected whenever possible. In the present invention, a 75%-99% alcohol solution is used as the solution within the U-shaped tube. When there is no pressure, the liquid levels are flat at rest. When pressure is applied, a difference in liquid level is formed within the U-shaped tube.

[0016] Furthermore, a clamp-on ultrasonic flow sensor is installed below the center height of the tube wall on the side of the U-shaped tube that is connected to the atmosphere. The clamp-on ultrasonic flow sensor is connected to a controller. The sensor transmits ultrasonic waves in opposite and same directions in the direction of liquid flow. By measuring the time difference between the controller receiving the ultrasonic waves in opposite and same directions, the solution flow rate is calculated. The solution flow rate is then integrated over time to obtain the total volume of the solution flowing through the sensor. The flow rate measured by the clamp-on ultrasonic flow sensor is integrated over time to obtain the volume V of the solution, and the formula is used:

[0017]

[0018] Calculate the vertical height Δh of the liquid level rise, where V is the total volume of solution flowing through the sensor, a is the cross-sectional area of ​​the U-shaped tube, and θ is the inclination angle of the U-shaped tube. The clamp-type ultrasonic flow sensor has a measurement accuracy of 0.003 mL.

[0019] The present invention adopts the above technical solution and has the following beneficial effects:

[0020] (1) The static pressure stepped holes of the present invention adopt three-level stepped through holes with gradually decreasing apertures, so that the through holes on the outer wall of the stationary cylinder facing the inner wall transition from a larger diameter to a smaller diameter, ensuring that the flow field boundary is not damaged due to excessive openings, thereby improving the accuracy of measurement; the static pressure stepped through holes are staggered in the circumferential direction of the wall of the stationary cylinder, which can reduce the interference of the fluid on the flow when it passes through multiple static pressure openings continuously when flowing along the circumferential direction, further improving the accuracy of flow measurement.

[0021] (2) The present invention adopts a tilted fixed U-shaped tube and a clamp-type ultrasonic flow sensor fixed on the U-shaped tube as the flow detection device of each static pressure measurement channel. The pressure in the tiny eccentric static gap is introduced into the U-shaped tube filled with low-density solution through the static pressure stepped through hole, capillary needle tube and silicone hose. The tilted fixed U-shaped tube can appropriately amplify the moving distance of the liquid in the tube under the same pressure, thereby improving the response accuracy of the sensor. The tilt angle of the U-shaped tube is set to 30°-60°, which can theoretically amplify the liquid surface displacement distance by 1.4-2 times, while ensuring that the liquid in the tube is not subjected to large viscous resistance due to excessive tilt.

[0022] (3) The clamp-type ultrasonic flow sensor used in the present invention can accurately measure the flow product of the solution flowing through it and convert it into a pressure detection value with high accuracy, short response time, high resolution and strong anti-interference ability. The measurement can be completed without direct contact with the liquid, thereby improving the overall pressure distribution measurement accuracy.

[0023] (4) The micro-rotor-static gap pressure measuring device proposed in the present invention has a simple structure, is easy to operate, and has a low cost. It does not require additional complex pressure measuring equipment, and at the same time overcomes the shortcomings of pressure sensors, pressure scanning valves and other equipment that cannot accurately measure pressure values ​​in a lower range. In particular, it can quickly and accurately measure low pressure values ​​in the range of 10-100Pa without being affected by system vibration and environmental noise, saving time and cost, and having the advantages of high efficiency and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a pressure measuring device for a small rotary-static gap according to the present invention.

[0025] Figure 2 Axial cross-section of small rotor-static clearance.

[0026] FIG3( a ) is a schematic diagram of the distribution of the static pressure stepped through holes, and FIG3( b ) is a structural diagram of the static pressure stepped through holes.

[0027] Figure 4 It is a structural diagram of an inclined U-shaped tube.

[0028] Figure 5 This is a test result diagram of pressure distribution.

[0029] Explanation of the numbers in the figure: 1. Small rotary-static gap, 2. Adjustable movable table, 3. Static pressure stepped through hole, 4. Capillary needle, 5. Silicone hose, 6. U-shaped tube, 7. Vertical plate, 8. Clamp-type ultrasonic flow sensor. DETAILED DESCRIPTION

[0030] The following describes in detail how the technical solution of the invention realizes the pressure measurement of a small rotor-static gap in conjunction with the accompanying drawings.

[0031] like Figure 1 As shown, a pressure measurement device for a small rotary-static gap comprises: a rotating cylinder, a stationary cylinder, a capillary needle 4, a silicone hose 5, a U-shaped tube 6, and a clamp-type ultrasonic flow sensor 8. The stationary cylinder is fixed on an adjustable movable platform 2. The rotating cylinder is placed in the interior space of the stationary cylinder. The stationary cylinder is sleeved outside the rotating cylinder. The outer wall of the rotating cylinder and the inner wall of the stationary cylinder form a small rotary-static gap 1 for rotary shear flow. The small rotary-static gap 1 prevents friction between the rotating cylinder and the stationary cylinder. The adjustable movable platform 2 is used to adjust the displacement of the stationary cylinder laterally to achieve a fixed eccentricity between the stationary cylinder and the rotating cylinder. The rotating cylinder has a smooth surface. One end of the rotating cylinder is connected to the high-speed motor main shaft via a coupling, while the other end of the rotating cylinder is suspended in the air. The rotating cylinder has an operating speed of 10,000-30,000 rpm. A static pressure stepped through hole 3 is processed on the stationary cylinder, and the front end of the capillary needle tube 4 is inserted into the static pressure stepped through hole 3 from the outside of the stationary cylinder. One end of the silicone hose 5 is connected to the capillary needle tube 4, and the other end of the silicone hose 5 is connected to the side wall of the U-shaped tube 6 perpendicular to the ground. The U-shaped tube 6 is fixed on the vertical plate 7, and the clamp-type ultrasonic flow sensor 8 is fixed on the other side wall of the U-shaped tube 6. The other side wall of the U-shaped tube is connected to the atmosphere.

[0032] like Figure 1 As shown, several stepped static pressure holes 3 are machined into the wall of the stationary cylinder. These holes are distributed along the axial mid-section of the stationary cylinder and circumferentially form a circle. These holes are used to measure the pressure distribution caused by the dynamic pressure effect generated by eccentricity within the small rotor-static gap. The diameter of the three-stage stepped holes gradually decreases from the outer wall of the stationary cylinder to the inner wall.

[0033] In order to reduce the number of openings that the fluid in the small gap passes through when flowing circumferentially and reduce the interference to the flow, the adjacent static pressure stepped through holes 3 are offset in the axial direction to form a staggered arrangement. Figure 2As shown in the figure, h represents the gap height. The value of the gap height h varies with the circumferential angle of the small gap, with the maximum gap occurring at the circumferential angle θ = 0 and the minimum gap occurring at the circumferential angle θ = π. On the side with the minimum gap height (i.e., the gap circumferential angle range is [π / 2, 3π / 2]), the circumferential angle θ of adjacent static pressure stepped through holes is 8-10°. On the side with the maximum gap height (i.e., the gap circumferential angle range is [3π / 2, 5π / 2]), the circumferential angle θ of adjacent static pressure stepped through holes is 18-20°. There is an axial offset of 0.5-1mm between adjacent static pressure stepped through holes. The distribution of the static pressure stepped through holes is shown in Figure 3(a). The vertical axis represents the circumferential angle, with the circumferential angles of adjacent static pressure stepped through holes being 10°, 20°, 30°, and 40°, respectively. The horizontal axis represents the axial position, with the axial spacing between adjacent static pressure stepped through holes being 1.5mm.

[0034] In order to reduce the impact of the openings on the static cylinder wall on fluid flow, the inner wall of the static cylinder requires an extremely small aperture. Therefore, a three-level stepped through hole as shown in Figure 3(b) is used as the static pressure stepped through hole of the present invention. The apertures of the three-level stepped through hole gradually decrease from the outer wall to the inner wall, with apertures of 1.5-2mm, 1-1.2mm, and 0.4-0.8mm, respectively. A capillary needle tube 4 with an outer diameter of 1.4mm-2mm is inserted into the maximum diameter end of the static pressure stepped through hole 3. The outer diameter of the capillary needle tube 4 is slightly smaller than the maximum diameter of the static pressure stepped through hole to facilitate insertion. At the same time, the plug-in interface of the capillary needle tube is fixed with glue to prevent air leakage. The inner diameter of the silicone hose 5 is approximately 1.4-1.8mm. One end is inserted into the capillary needle tube, and the other end is connected to the side wall of the U-shaped tube 6 perpendicular to the ground, and anti-leakage measures are taken.

[0035] Insert the silicone hose 5 on the capillary needle 4, and connect the other end of the silicone hose 5 to the wall of the U-shaped tube 6 perpendicular to the ground, thereby forming a pressure measuring airway. Figure 4 As shown, the U-shaped tube 6 is made of a transparent resin. One side of the U-shaped tube 6 is perpendicular to the ground, while the other side is inclined and open to the atmosphere. The angle between the inclined side and the vertical side is 45°-60°. The tube has an inner diameter of 5-8 mm and a length of 300 mm. An ethanol solution with a concentration of 75%-99% is injected into the U-shaped tube 6. In the test experiments of the present invention, to measure pressure at multiple points, multiple static pressure stepped through-holes 3 are machined on the stationary cylinder at different azimuths of the small rotating-static gap 1. These stepped through-holes are connected to their corresponding U-shaped tubes in the same manner as described above. These U-shaped tubes are installed together with the vertical plate 7 to simultaneously display the instantaneous pressure values ​​at different gap positions. A clamp-type ultrasonic flow sensor 8 is installed below the mid-height of the inclined side of the U-shaped tube 6 and connected to a controller. The clamp-type ultrasonic flow sensor 8 calculates the rise in the liquid level on the inclined side of the U-shaped tube by measuring the discharge volume, i.e., the volume of solution flowing through. The clamp-type ultrasonic flow sensor 8 has a diameter of 6-10 mm.

[0036] Each static pressure stepped through hole 3, capillary needle 4, silicone hose 5, inclined U-shaped tube 6, and clamp-type ultrasonic flow sensor 8 form a set of pressure measurement gas circuits. In order to measure the pressure value at multiple points along the circumference of the rotor-static gap, multiple static pressure measurement channels need to be built simultaneously.

[0037] Static pressure hole pressure measurement uses the Bernoulli principle. The Bernoulli equation follows the law of conservation of energy and mainly describes the relationship between flow velocity, height and pressure:

[0038]

[0039] In formula (2), p represents pressure, ρ represents density, gz represents gravitational potential energy, In Bernoulli's principle, different flow velocities correspond to different flow field pressures. By arranging a static pressure measurement channel perpendicular to the flow velocity, the flow field pressure value can be obtained.

[0040] When the rotating cylinder is stationary, the liquid levels on both sides of the U-shaped tube are level. Once the cylinder begins to rotate, the viscosity of the fluid creates shear flow within the tiny gap between the rotating and static parts. This dynamic pressure effect generates pressure within the gap. A static pressure measurement channel, perpendicular to the flow velocity, creates a height difference Δh in the liquid within the U-shaped tube. This height difference is recorded and the pressure is calculated using the formula p = ρgΔh.

[0041] After the experimental device is built, the specific implementation process is as follows:

[0042] Adjust the relative position of the stationary cylinder and the rotating cylinder using an adjustable stage 2. Adjustable stage 2 uses a micrometer to achieve lateral displacement with an accuracy of 0.01mm. Based on the desired eccentricity, the corresponding displacement is calculated and the stationary cylinder is moved to the corresponding position using the adjustable stage.

[0043] Liquid was injected into the inclined side of the U-shaped tube 6 until the liquid level was at a reference line. The reference line is the centerline of the inclined side or at the vertical mid-height of the U-shaped tube. In the test experiment of the present invention, the injected solution was a 99% ethanol solution. Since there was no flow and no pressure generated in the pipe at this time, the liquid level on the inclined side of the U-shaped tube 6 did not change. The clamp-on ultrasonic flow sensor 8 was powered on and initialized and calibrated.

[0044] Starting the motor generates shear flow within the tiny rotor-static gap. Simultaneously, the dynamic pressure effect caused by the eccentricity generates pressure within the tiny rotor-static gap. Based on the principle of static pressure, the inclined side of the U-shaped tube 6, under pressure, creates a liquid level difference. During this process, the clamp-on ultrasonic flow sensor 8 records the volume of liquid flowing through, calculates the liquid level height based on the liquid volume, and then calculates the pressure value. In the test experiments of the present invention, the angle between the inclined side of the U-shaped tube 6 and the side perpendicular to the ground was 60°. Therefore, for the same vertical height of liquid level rise, the liquid displacement distance was magnified by 2 times, which improves sensing accuracy and also prolongs the liquid level change time, further enhancing the sensor's sensing accuracy. In the experiments, the clamp-on ultrasonic flow sensor achieved a measurement accuracy of 0.003 mL. The pressure tube inner diameter was 5 mm, and the solution used was a 99% ethanol solution. After conversion, the solution accuracy was calculated to be 1.74 Pa. Therefore, at a pressure value of 100 Pa, the measurement accuracy error was less than 2%, and at a pressure value of 50 Pa, the measurement accuracy error was less than 4%.

[0045] In the present invention, the pressure at all static pressure hole positions is measured to obtain the pressure values ​​at multiple points, thereby fitting the circumferential distribution curve of the pressure in the small rotor-static gap. The circumferential pressure measurement results when the average gap height is 0.5mm and the eccentricity is 0.5 are as follows: Figure 5 As shown, the horizontal axis represents the circumferential angle and the vertical axis represents the static pressure value. The circumferential pressure measurement result includes both the high-pressure area with a higher pressure value and the low-pressure area with a pressure value lower than 100 Pa. About 70% of the data in this measurement can control the measurement error within 4%.

[0046] In summary, the present invention can quickly and accurately measure the pressure in a tiny rotor-static gap of less than 0.5 mm. It can not only accurately measure the conventional pressure value of the high-pressure area, but also accurately measure the pressure value of the low-pressure area below 100 Pa without being affected by system vibration and environmental noise, thereby obtaining the overall pressure distribution law of the tiny rotor-static gap at high speed under eccentric state.

Claims

1. A pressure measuring device for a small rotary-static gap, characterized in that: include: A stationary cylinder, a rotating cylinder, an adjustable movable platform, and at least two static pressure measurement channels. The stationary cylinder is fixed on the adjustable movable platform, and the stationary cylinder is sleeved on the outside of the rotating cylinder. The inner wall of the stationary cylinder and the outer wall of the rotating cylinder form a small static-rotation gap. Each static pressure measurement channel includes: a static pressure stepped through hole opened on the wall of the stationary cylinder, a capillary needle, a silicone hose, a U-shaped tube, and a clamp-type ultrasonic flow sensor. The capillary needle is inserted into the static pressure stepped through hole from the outer wall of the stationary cylinder. The U-shaped tube is fixed on the vertical plate in a manner that one side of the tube wall is perpendicular to the ground. The angle between the other side of the tube wall of the U-shaped tube and the side of the tube wall perpendicular to the ground is an acute angle. The side of the tube wall of the U-shaped tube perpendicular to the ground is connected to the capillary needle through the silicone hose. The clamp-type ultrasonic flow sensor is installed on the other side of the tube wall of the U-shaped tube, and the other side of the tube wall of the U-shaped tube is connected to the atmosphere.

2. A pressure measuring device for a small rotary-static gap according to claim 1, characterized in that: The static pressure stepped through holes in each static pressure measurement channel surround the cross-sectional position of the stationary cylinder. The circumferential angle between the two adjacent static pressure stepped through holes on the side of the minimum gap height is 8°-10°, the axial circumferential angle between the two adjacent static pressure stepped through holes on the side of the maximum gap height is 18°-20°, and the axial offset interval between the two adjacent static pressure stepped through holes is 0.5mm-1mm.

3. The pressure measuring device for a small rotary-static gap according to claim 2, characterized in that: The minimum gap height side is a small rotating-static gap with a circumferential angle of [π / 2, 3π / 2], and the maximum gap height side is a small rotating-static gap with a circumferential angle of [3π / 2, 5π / 2].

4. A pressure measuring device for a small rotary-static gap according to claim 1, 2 or 3, characterized in that: The static pressure stepped through hole is a three-step through hole with decreasing apertures, the through hole with the largest aperture is communicated with the outer wall surface of the stationary cylinder, and the through hole with the smallest aperture is communicated with the inner wall surface of the stationary cylinder.

5. The pressure measuring device for a small rotational-static gap according to claim 4, characterized in that: The outer diameter of the capillary tube is smaller than the maximum aperture of the static pressure stepped through hole. The capillary tube is inserted into the through hole with the maximum aperture from the outer wall of the static cylinder. Sealant is applied at the joint between the capillary tube and the maximum aperture.

6. The pressure measuring device for a small rotary-static gap according to claim 1, characterized in that: The angle between the other side wall of the U-shaped tube and the side wall perpendicular to the ground is 45°-60°, the inner diameter of the tube walls on both sides of the U-shaped tube is 5-8mm, and the length of the other side wall is 300mm.

7. The pressure measuring device for a small rotary-static gap according to claim 1, characterized in that: The clamp-type ultrasonic flow sensor is installed at a position below the center line of the pipe wall height on the other side of the U-shaped pipe.

8. A method for measuring pressure of a small rotary-static gap, characterized in that: This is achieved by the device according to claim 1, specifically: Calculating the lateral displacement of the adjustable movable stage according to the eccentricity condition to be measured, and operating the adjustable movable stage to adjust the relative position of the stationary cylinder and the rotating cylinder until the eccentricity condition to be measured is met; Inject a 75%-99% ethanol solution into the wall of the U-shaped tube in each static pressure measurement channel on the side connected to the atmosphere until the liquid level of the ethanol solution is at the height centerline position. Power on each clamp-type ultrasonic flow sensor and perform initialization calibration. The rotating cylinder is driven to read the liquid flow recorded by each clamp-type ultrasonic flow sensor, and the liquid level difference of the tube wall on the side of each U-shaped tube connected to the atmosphere is calculated based on the liquid flow recorded by each clamp-type ultrasonic flow sensor. The pressure detection value of each static pressure measurement channel is calculated based on the liquid level difference of the tube wall on the side of each U-shaped tube connected to the atmosphere.

9. A method for measuring pressure of a small rotary-static gap according to claim 8, characterized in that: A high-speed motor is used to drive the rotating cylinder.

10. The method for measuring pressure of a small rotary-static gap according to claim 8, characterized in that: The expression for calculating the liquid level difference on the side of each U-shaped tube connected to the atmosphere based on the liquid flow recorded by each clamp-type ultrasonic flow sensor is: Δh is the liquid level difference on the side of the U-shaped tube connected to the atmosphere, V is the volume of the liquid flowing through it calculated based on the time integral of the liquid flow recorded by the clamp-type ultrasonic flow sensor, a is the cross-sectional area of ​​the U-shaped tube, and θ is the angle between the other side of the U-shaped tube and the side perpendicular to the ground.

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