A measuring system and method for the internal flow field structure of unsteady cavitation flow

Abstract

The application discloses a kind of non-steady cavitation flow internal flow field structure measurement system.The measurement system is composed of closed cavitation hydraulic circuit and synchronous radiation X-ray fast imaging system, and the cavitation hydraulic circuit includes experimental section, water storage tank, variable frequency circulating pump, cooling water tank, pipe type electric heater, turbine flowmeter and K-type thermocouple;X-ray fast imaging system includes synchronous radiation light source, shutter device, optical magnifier, X-ray detector, 90° reflector and high-speed CCD camera.The measurement method of the measurement system is also disclosed.The application generates non-steady cavitation flow in the experimental section of cavitation hydraulic circuit, and builds an imaging system based on high-energy high-frequency pulsed synchronous radiation X-ray, which breaks through the optical shielding problem of cavitation vapor-liquid mixture, realizes high spatiotemporal resolution cavitation internal vapor-liquid two-phase form visualization and velocity field measurement, and solves the problem that conventional optical measurement technology cannot accurately obtain cavitation internal information.

Description

Technical Field

[0001] This invention belongs to the field of experimental measurement technology for complex multiphase flow, and specifically relates to a measurement system and method for the internal flow field structure of unsteady cavitation flow. Background Technology

[0002] Cavitation is an unsteady multiphase flow phenomenon involving mass and heat transfer between the liquid and vapor phases. Cavitation occurs when the local pressure of the liquid drops below the saturated vapor pressure due to acceleration, flow separation, vortices, or other factors. Depending on the flow field conditions, cavitation can manifest in various forms, such as wandering bubble cavitation, sheet cavitation, cloud cavitation, and vortex cavitation. Cloud cavitation is a large-scale cloud-like vapor-liquid mixture structure formed after the overall instability and collapse of sheet cavitation. The intense unsteady shedding and collapse processes of cavitation can lead to negative effects such as decreased unit performance, noise, vibration, and structural damage. Therefore, cavitation is a fundamental scientific problem with significant engineering applications in the field of hydrodynamics. To effectively suppress or reduce the adverse effects of cavitation, it is necessary to conduct in-depth research on its instability dynamic mechanisms.

[0003] Numerical simulation of cavitation currently faces many difficulties and challenges, and experimental observation remains the primary means of in-depth research on cavitation flow. Visualization of the vapor-liquid two-phase morphology within cavitation and measurement of the two-phase flow field are of great significance for revealing the mechanism of cavitation instability flow. However, due to the high reflection and multiple scattering of visible light at the vapor / liquid interface, cavitation flow becomes optically opaque. Therefore, existing optical measurement techniques (high-speed photography, particle image velocimetry, and laser Doppler velocimetry, etc.) cannot accurately obtain information on the internal structure and flow field of cavitation. Summary of the Invention

[0004] To address the shortcomings of existing cavitation measurement technologies or methods, the purpose of this invention is to provide a measurement system and method for the vapor-liquid two-phase morphology and flow field inside cavitation based on synchrotron X-ray rapid imaging.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A measurement system for the internal flow field structure of unsteady cavitation flow, comprising a closed cavitation hydraulic loop and a synchrotron radiation X-ray rapid imaging system;

[0007] The synchrotron radiation X-ray rapid imaging system comprises, in sequence, a synchrotron radiation source, a shutter device, an optical magnifying glass, an X-ray detector, a 90° reflecting mirror, and a high-speed CCD camera. The synchrotron radiation source is used to emit high-energy, high-frequency pulsed X-rays. The shutter device is a mechanical device that opens and closes vertically to limit the X-ray dose received in a short period of time. The optical magnifying glass is used to increase the area of ​​the X-ray irradiation region. The X-ray detector is made of a scintillation crystal, which converts X-rays into visible light, which is then deflected by the 90° reflecting mirror and recorded by the high-speed CCD camera.

[0008] The closed-loop cavitation hydraulic circuit includes an experimental section, a pressure sensor, a water storage tank, a vacuum pump, a variable frequency circulating pump, a cooling water tank, a pipe-type electric heater, a turbine flow meter, a K-type thermocouple, a flow feedback regulator, and a pressure feedback regulator. The experimental section, water storage tank, variable frequency circulating pump, cooling water tank, pipe-type electric heater, turbine flow meter, and K-type thermocouple are sequentially connected via flexible metal hoses to form a closed-loop circulating water tunnel. The vacuum pump is connected to the water storage tank above the free surface via a plastic hose. The flow feedback regulator is connected to the turbine flow meter and variable frequency circulating pump via a data transmission line to form a flow feedback regulation circuit, enabling remote automatic flow control. The pressure feedback regulator is connected to the pressure sensor and vacuum pump via a data transmission line to form a pressure feedback regulation circuit, enabling remote automatic pressure control. The entire cavitation hydraulic circuit is fixed to an aluminum frame structure.

[0009] Furthermore, the experimental section is located between the optical magnifying glass and the X-ray detector.

[0010] Furthermore, the experimental section is a square Venturi structure, including an upper wall component, a lower wall component, a front wall component, a rear wall component, and front and rear clamping plates; the lower wall component has a throat on one side relative to the upper wall component; the upper wall component, lower wall component, front wall component, and rear wall component are connected by bolts and fixed with nuts through the front and rear clamping plates, forming a square Venturi flow channel for fluid to flow through. Unsteady cavitation flow is formed in the throat region of the Venturi flow channel, which is also the X-ray imaging region.

[0011] Furthermore, X-ray passing windows are symmetrically opened at the positions corresponding to the Venturi throats of the front and rear wall components, which can reduce the wall thickness of the X-ray imaging area of ​​the experimental section.

[0012] Furthermore, the upper wall component, lower wall component, front wall component, and rear wall component are made of transparent plexiglass; the front and rear clamps are made of stainless steel.

[0013] Furthermore, the Venturi-type experimental section has threaded holes at both ends for fixed connection with the cavitation hydraulic loop pipeline.

[0014] A method for measuring the internal flow field structure of an unsteady cavitation flow, which uses the measurement system described above, and includes the following steps:

[0015] Step 1: Add an appropriate amount of silver-plated hollow glass spheres with an average diameter of 17 μm and a specific gravity of 1.4 to the water storage tank as tracer particles, and stir evenly.

[0016] Step 2: Adjust the flow parameters such as flow rate, pressure and temperature to generate the required unsteady cavitation flow in the throat region of the Wenqiuli-type experimental section of the closed circulating water tunnel.

[0017] Step 3: Fix the experimental section on the sample stage of the synchrotron radiation X-ray rapid imaging system, and finely adjust the position of the sample stage according to the direction of the X-rays to ensure that the X-rays irradiate the throat region formed by the window opened in the experimental section.

[0018] Step 4: Synchronize the high-speed CCD camera with the X-ray pulse, turn on the synchrotron radiation source, and let the X-ray pulse pass through the shutter device, optical magnifier, throat region of the experimental section, X-ray detector and 90° reflector in sequence. Finally, the high-speed CCD camera records the transient image of the cavitation flow, which includes the vapor-liquid two-phase morphology and structure inside the cavitation and the information of the scattered tracer particles. Perform cross-correlation analysis on the tracer particles in two consecutive images to obtain the transient velocity field distribution of the cavitation flow.

[0019] Step 5: Perform multi-condition measurements on the acquired image information and data.

[0020] The beneficial effects of this invention are:

[0021] 1. Feedback regulators for flow rate and pressure were added to the closed cavitation hydraulic loop, which can remotely and automatically adjust various flow parameters according to the set values, avoiding the radiation hazard to experimental personnel from being close to high-energy X-rays;

[0022] 2. The experimental section in this invention is not manufactured as a single piece, but is assembled from multiple simple components. Each component is easy to process and has low cost. For the throat area that is prone to damage, individual damaged components can be replaced without replacing the entire experimental section, which greatly saves replacement costs. The entire experimental section is fixed by two stainless steel clamps, which can ensure the airtightness of the flow channel without any adhesive.

[0023] 3. Compared with conventional optical measurement techniques, this invention utilizes high-energy, high-frequency pulsed synchrotron radiation X-rays to overcome the optical shielding problem of cavitation vapor-liquid mixtures, achieving high spatiotemporal resolution visualization of the vapor-liquid two-phase morphology within cavitation and measurement of the velocity field. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the measurement system for the internal flow field structure of an unsteady cavitation flow according to the present invention;

[0025] Figure 2 This is a three-dimensional assembly view of the Chinese-style hill-shaped experimental section of the present invention;

[0026] Figure 3 for Figure 2 View in the Z direction;

[0027] Figure 4 for Figure 2 Sectional view on the YZ plane;

[0028] Figure 5 for Figure 2 A three-dimensional view of the upper and lower wall components of the middle experimental section;

[0029] Figure 6 for Figure 2 A three-dimensional view of the front wall components of the experimental section;

[0030] Figure 7 for Figure 2 A three-dimensional view of the rear wall components of the experimental section;

[0031] Figure 8 This is a schematic diagram of the synchronization scheme between the X-ray pulse and the camera.

[0032] The components include: 1. Experimental section; 101. Upper wall component of experimental section; 102. Lower wall component of experimental section; 103. Front wall component of experimental section; 104. Rear wall component of experimental section; 105. Front clamping plate of experimental section; 106. Rear clamping plate of experimental section; 107. Window; 2. Pressure sensor; 3. Water storage tank; 4. Vacuum pump; 5. Variable frequency circulating pump; 6. Cooling water tank; 7. Pipeline electric heater; 8. Turbine flow meter; 9. K-type thermocouple; 10. Flow feedback regulator; 11. Pressure feedback regulator; 12. Synchrotron radiation source; 13. Shutter device; 14. Optical magnifier; 15. X-ray detector; 16. 90° reflector; 17. High-speed CCD camera. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Example: Combining Figure 1-8 As shown, a measurement system for the internal flow field structure of an unsteady cavitation flow consists of a closed cavitation hydraulic loop and a synchrotron radiation X-ray rapid imaging system.

[0035] like Figure 1As shown, the closed cavitation hydraulic loop includes an experimental section 1, a pressure sensor 2, a water storage tank 3, a vacuum pump 4, a variable frequency circulating pump 5, a cooling water tank 6, a pipeline electric heater 7, a turbine flow meter 8, a K-type thermocouple 9, a flow feedback regulator 10, and a pressure feedback regulator 11.

[0036] The experimental section 1, water storage tank 3, variable frequency circulating pump 5, cooling water tank 6, pipeline electric heater 7, turbine flow meter 8, and K-type thermocouple 9 are connected end-to-end via flexible metal hoses to form a closed hydraulic loop. Pressure sensor 2 is installed upstream and downstream of the throat of the Venturi-type experimental section 1. Vacuum pump 4 is connected above the free liquid surface of water storage tank 3 and can reduce the pressure in the loop by evacuating. Variable frequency circulating pump 5 can precisely adjust the flow rate by changing its speed through frequency conversion. The cooling water tank 6 has a spiral water pipe embedded inside for connecting to an external cooling water source. The cooling water tank 6 and pipeline electric heater 7 work together to stabilize the water temperature in the loop. K-type thermocouple 9 is used to measure the fluid temperature at the inlet of experimental section 1. Flow feedback regulator 10 is connected to turbine flow meter 8 and variable frequency circulating pump 5 via data transmission lines to form a flow feedback regulation loop, which can remotely and automatically adjust the flow rate according to the set value. Pressure feedback regulator 11 is connected to pressure sensor 2 and vacuum pump 4 via data transmission lines to form a pressure feedback regulation loop, which can remotely and automatically adjust the pressure value.

[0037] like Figure 2 , 3 As shown, experimental section 1 is assembled from an upper wall component 101, a lower wall component 102, a front wall component 103, and a rear wall component 104. These components are connected by bolts and secured with nuts via a front clamping plate 105 and a rear clamping plate 106. A square Venturi-type flow channel is formed in the middle for fluid to flow through. The flow channel has a height of 21 mm and a throat height of 10 mm. Unsteady cavitation flow is formed in the throat region of the Venturi-type flow channel, which is also the imaging region for X-rays. Threaded holes are opened at both ends of the entire experimental section 1 for fixed connection with the cavitation hydraulic loop pipe.

[0038] like Figure 4 , 5 As shown, the upper wall component 101 and the lower wall component 102 of the experimental section are made of transparent plexiglass with a thickness of 5 mm. The lower wall component 102 has a Venturi-shaped contraction and expansion profile on its surface relative to the upper wall component 101, with contraction angle and expansion angle of 18° and 8°, respectively.

[0039] like Figure 4 , 6As shown in Figure 7, the front wall component 103 and the rear wall component 104 of the experimental section are two symmetrical structures made of 15mm transparent plexiglass. X-ray passing windows 107 are symmetrically opened on the front wall component 103 and the rear wall component 104 at positions corresponding to the Venturi throat, reducing the wall thickness of the X-ray imaging area to 0.5mm, which is beneficial to improving the X-ray imaging quality. When the front wall component 103 and the rear wall component 104 are damaged at the window 107 position, the damaged component can be replaced individually without replacing the entire experimental section.

[0040] The front clamp 105 and the rear clamp 106 of the experimental section are two identical components made of 3mm thick stainless steel plate; the components of the experimental section are fixed together by the front and rear clamps, and the airtightness of the flow channel can be guaranteed without any adhesive.

[0041] The synchrotron radiation X-ray rapid imaging system includes a synchrotron radiation source 12, a shutter device 13, an optical magnifier 14, an X-ray detector 15, a 90° reflector 16, and a high-speed CCD camera 17.

[0042] The experimental section is located between the optical magnifying glass and the X-ray detector.

[0043] The main body of the synchrotron radiation source 12 is an electron energy storage ring. When the electron beam moving at near the speed of light in the energy storage ring is bent by the magnetic field generated by the undulator, it will radiate approximately parallel high-energy pulsed X-rays with a frequency as high as 270,000 Hz in the tangential direction of the trajectory.

[0044] The shutter device 13 is a mechanical device that opens and closes rapidly up and down. It operates at a frequency of 1Hz and each opening lasts for 20ms. It can limit the X-ray dose received by experimental section 1 and X-ray detector 15 and other devices in a short period of time, preventing them from being damaged due to overheating.

[0045] The optical magnifying glass 14 magnifies the cross-sectional area of ​​the X-rays, making it easier to irradiate the entire cavitation region at once. After the X-rays penetrate the throat region of the experimental section, they reach the X-ray detector 15 made of a scintillation crystal, which converts the X-rays into visible light. The X-rays are then deflected by the 90° reflector 16 and the cavitation flow image is recorded by the high-speed CCD camera 17.

[0046] The method for measuring the internal flow field structure of unsteady cavitation flow using the measurement system described above includes the following steps:

[0047] Step 1: Fill the water tank 3 with 2 / 3 water, add an appropriate amount of silver-plated hollow glass spheres with an average diameter of 17μm and a specific gravity of 1.4 as tracer particles, and stir evenly.

[0048] Step 2: Adjust appropriate flow parameters such as flow rate, pressure and temperature to generate the required unsteady cavitation flow in the throat region of the Zhongwenqiuli-type experimental section 1 of the closed circulating water tunnel.

[0049] Step 3: Fix experimental section 1 on the sample stage of the synchrotron radiation X-ray rapid imaging system, and finely adjust the position of the sample stage according to the direction of X-rays to ensure that X-rays irradiate the throat region formed by the window 107 opened in the experimental section.

[0050] Step 4, connect the high-speed CCD camera and the X-ray pulse... Figure 8 The synchronization is set up in the manner shown, and the X-ray subpulse is skipped by the cross-frame interval to ensure that only one X-ray main pulse is contained in a frame.

[0051] Step 5: The synchrotron radiation source 12 is turned on. The X-ray pulse passes sequentially through the shutter device 13, the optical magnifying glass 14, the throat region of experimental section 1, the X-ray detector 15, and the 90° reflector 16. Finally, the high-speed CCD camera 17 records the transient image of the cavitation flow, which includes the vapor-liquid two-phase morphology and structure inside the cavitation and the information of the scattered tracer particles. Cross-correlation analysis is performed on the tracer particles in two consecutive images to obtain the transient velocity field distribution of the cavitation flow.

[0052] Step 6: Perform repeated measurements on the collected image information and data under multiple operating conditions.

[0053] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A measurement system for the internal flow field structure of an unsteady cavitation flow, characterized in that, Including a closed cavitation hydraulic loop and a synchrotron radiation X-ray rapid imaging system; The synchrotron radiation X-ray rapid imaging system includes: a synchrotron radiation source (12) for emitting high-energy pulsed X-rays, a shutter device (13), an optical magnifying glass (14), an X-ray detector (15), and a 90° reflector (16) arranged sequentially along the straight optical path of the high-energy pulsed X-rays emitted by the synchrotron radiation source (12), and the high-energy pulsed X-rays are deflected by the 90° reflector (16) and recorded by a high-speed CCD camera (17); The closed cavitation hydraulic circuit includes: an experimental section (1) connected end to end by a metal hose, a water storage tank (3), a variable frequency circulating pump (5), a cooling water tank (6), a pipeline electric heater (7), a turbine flow meter (8), and a K-type thermocouple (9), forming a closed circulating water tunnel; and a vacuum pump (4) connected to the water storage tank (3) above the free liquid surface by a plastic hose. The experimental section (1) is hollow to form a fluid flow channel. A throat is provided in the fluid flow channel. Pressure sensors (2) are connected to the front and rear of the throat. The throat causes the flow channel to first contract and then expand. When the liquid flows through the throat, it generates unsteady cavitation flow. The experimental section (1) is located between the optical magnifying glass (14) and the X-ray detector (15).

2. The measurement system for the internal flow field structure of unsteady cavitation flow according to claim 1, characterized in that, The closed cavitation hydraulic circuit further includes: a flow feedback regulator (10) that is connected to the turbine flow meter (8) and the variable frequency circulating pump (5) via a data transmission line to form a flow feedback regulation circuit; and a pressure feedback regulator (11) that is connected to the pressure sensor (2) and the vacuum pump (4) via a data transmission line to form a pressure feedback regulation circuit.

3. The measurement system for the internal flow field structure of unsteady cavitation flow according to claim 1 or 2, characterized in that, The experimental section (1) is assembled into a Venturi structure by an upper wall component (101), a lower wall component (102), a front wall component (103), and a rear wall component (104) made of transparent material. The upper wall component (101) and the lower wall component (102) are arranged opposite each other with a spacing of 20cm to 25cm. A throat is provided on the side of the lower wall component (102) opposite to the upper wall component (101). The throat is a bridge with a height of 8cm to 10cm formed by two straight edges. The front wall component (103) and the rear wall component (104) are arranged in a Venturi-shaped structure. The wall component (104) is clamped on both sides of the upper wall component (101) and the lower wall component (102) along the length direction; a front clamping plate (105) and a rear clamping plate (106) made of stainless steel are respectively clamped on both sides of the front wall component (103) and the rear wall component (104) away from the upper wall component (101) and the lower wall component (102), and the fluid flow channel is formed between the upper wall component (101), the lower wall component (102), the front wall component (103) and the rear wall component (104).

4. The measurement system for the internal flow field structure of unsteady cavitation flow according to claim 3, characterized in that, The front wall component (103) and the rear wall component (104) are symmetrically provided with windows (107) for X-rays to pass through, corresponding to the position of the throat, thereby reducing the wall thickness of the imaging area.

5. The measurement system for the internal flow field structure of unsteady cavitation flow according to claim 3, characterized in that, The experimental section (1) is provided with threaded holes at both ends of the fluid flow channel for connecting the water storage tank (3) and the K-type thermocouple (9).

6. The measurement system for the internal flow field structure of unsteady cavitation flow according to claim 3, characterized in that, The upper wall component (101), lower wall component (102), front wall component (103), rear wall component (104), front clamping plate (105), and rear clamping plate (106) are respectively provided with through holes, which are passed through by bolts and fixed with nuts.

7. A measurement method using a measurement system for the internal flow field structure of an unsteady cavitation flow according to any one of claims 1-6, comprising the following steps: Add an appropriate amount of silver-plated hollow glass spheres as tracer particles to the water storage tank (3) and stir evenly; Adjust the flow rate, pressure and temperature parameters to generate the required unsteady cavitation flow in the throat region of the experimental section (1) in the closed circulating water tunnel; The experimental section (1) is fixed on the sample stage of the synchrotron radiation X-ray rapid imaging system. The position of the sample stage is precisely adjusted according to the direction of the X-rays to ensure that the X-rays irradiate the throat region formed by the window (107) opened in the experimental section (1). The high-speed CCD camera (17) and the X-ray pulse are synchronized. The synchrotron radiation source (12) is turned on. The X-ray pulse passes through the shutter device (13), the optical magnifying glass (14), the throat region of the experimental section (1), the X-ray detector (15), and the 90° reflector (16) in sequence. Finally, the high-speed CCD camera (17) records the transient image of the cavitation flow, which includes the vapor-liquid two-phase morphology and structure inside the cavitation and the information of the scattered tracer particles. The cross-correlation analysis of the tracer particles in two consecutive images is performed to obtain the transient velocity field distribution of the cavitation flow. Multi-condition measurements are performed on the collected image information and data.

Images