PIV test method based on 0.3m transonic cryogenic wind tunnel

Abstract

The present invention belongs to the field of cryogenic test technology, and discloses a PIV test method based on a 0.3-meter transonic cryogenic wind tunnel, including determining the power of a particle generator; installing a heating device and a temperature sensor in the particle generator to conduct a ground test; installing a normal temperature nitrogen pipeline on the particle generator; building and connecting a liquid nitrogen flash tank; installing a matching regulating valve assembly on each pipeline; manufacturing and adjusting the ice particle size; and conducting a PIV test. The test method uses pure water as a tracer particle material, avoiding the pollution problem of traditional oily tracer particles and solid tracer particles on cryogenic wind tunnel protective materials. The ice particles produced have uniform particle size, good light scattering, low cost, and controllable concentration, which can meet the PIV test requirements of a 0.3-meter transonic cryogenic wind tunnel, and can also be used for other low-temperature environment PIV test requirements that have high requirements for tracer particle pollution problems, and has engineering practical value.

Description

Technical Field

[0001] The invention belongs to the technical field of low-temperature testing, and in particular relates to a PIV testing method based on a 0.3-meter transonic low-temperature wind tunnel. Background Art

[0002] PIV technology uses a double-pulse laser to irradiate the object to be measured (such as the airflow in a wind tunnel), spread tracer particles in the object to be measured, obtain two consecutive particle images, and use a cross-correlation algorithm to obtain the particle displacement, thereby obtaining the tracer particle velocity. Since the tracer particles move with the object to be measured, the measured tracer particle velocity can be considered to be the velocity of the object to be measured (provided that the particles can truly follow the object to be measured). In the PIV test, the tracking ability, light scattering characteristics and concentration of the tracer particles play a decisive role in the quality of the test data.

[0003] The tracking and light scattering properties of tracer particles mainly depend on the density and particle size of the tracer particle material. For the same tracer particle material, the smaller the particle size of the tracer particle, the better the tracking and the higher the data credibility. However, too small a particle size will cause the particle brightness to deteriorate, affecting the signal-to-noise ratio of the original image. Conversely, the larger the particle size, the higher the particle brightness, the better the image signal-to-noise ratio, but the tracking will deteriorate. In the PIV test, it is necessary to select appropriate tracer particles according to the actual application requirements to ensure that the tracer particles achieve a good balance in terms of tracking and light scattering.

[0004] PIV test technology has been widely used in conventional wind tunnels. At present, the traditional tracer particles used in conventional wind tunnels are mainly divided into two categories: one is based on oily liquids such as DEHS and vegetable oil, which can produce oily particles with a particle size of about 1μm using the Laskin nozzle atomization principle; the other is based on SiO 2 Solid powders such as solid powders can be produced by using the fluidized bed principle to produce stable nano-scale solid powder particles.

[0005] With the rise of cryogenic wind tunnels, the above-mentioned traditional tracer particle generation technology has become no longer applicable. The main reason is the problem of tracer particle contamination of wind tunnels: on the one hand, the interior of the cryogenic wind tunnel is wrapped with a large amount of insulation material, and oily particles or solid powder particles will contaminate the insulation material; on the other hand, the cryogenic wind tunnel is a continuous wind tunnel, and the physical properties of oily liquids and solid particles are very stable. After the test, they will remain in the cryogenic wind tunnel for a long time and cannot evaporate or degrade.

[0006] Therefore, to carry out PIV experimental research in a low-temperature wind tunnel, it is necessary to adopt a new clean particle generation and transmission system, and it must meet the following technical requirements at the same time: 1) Use clean tracer particle materials; 2) The physical properties of the tracer particles are stable and easy to clean after the test; 3) The particle size and density of the tracer particles meet the flow field followability requirements; 4) The scattering properties of the tracer particles meet the optical measurement requirements; 5) The tracer particle concentration is high and controllable.

[0007] In summary, using water as tracer particle material can effectively solve the problem of cave pollution. However, how to convert water into a tracer particle flow with controllable particle size and concentration is a problem that needs to be solved. Literature research and ground research have found that there are three main ways to generate micro water droplets: one is to use the principle of ultrasonic atomization. This device is easy to buy on the market, and its water mist concentration is very large and easy to control, but the average measured value of the particle size is basically 5μm~10μm. For PIV tests, the followability does not meet the standards; the second is to use the principle of micro atomization nozzles. This device is also easy to buy on the market and is inexpensive. Its technical indicators often claim that the particle size reaches 1μm or even lower. However, the measured results show that its particle size is often greater than 20μm or even 100μm, and the particle size uniformity is poor, which cannot meet the requirements of PIV tests; the third method is to condense water vapor instantly. In this way, the author successfully generated water particles or ice particles with a particle size of about 1μm during ground debugging. From the principle of generation, it can meet the requirements of tracer particle fluidity and followability, but to be successfully used in low-temperature wind tunnel PIV tests, it is also necessary to make the entire tracer particle generation process in a controllable state.

[0008] Currently, there is an urgent need to develop a PIV test method based on a 0.3-meter transonic cryogenic wind tunnel. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a PIV clean particle generation and transmission system for low temperature environment, so as to verify the feasibility of using water as a tracer particle material for PIV testing.

[0010] The PIV test method based on a 0.3 m transonic low temperature wind tunnel of the present invention comprises the following steps:

[0011] S10. Determine the power of the particle generator;

[0012] Calculate the ice particle flow rate required for the PIV test in a 0.3 m transonic cryogenic wind tunnel and determine the power of a single particle generator;

[0013] S20. Install a heating device and a temperature sensor in the particle generator and conduct ground tests;

[0014] A heating device and a temperature sensor are arranged inside the particle generator;

[0015] The medium-pressure nitrogen storage tank of the 0.3-meter transonic cryogenic wind tunnel is connected to the particle generator through a medium-pressure nitrogen pipeline, and the medium-pressure nitrogen in the medium-pressure nitrogen storage tank drives the Laskin nozzle in the particle generator to generate water vapor;

[0016] Conduct ground tests on particle generators to establish the corresponding relationship between water temperature and water vapor saturation, and determine that heating the pure water in the particle generator to 50°C will achieve the best water vapor saturation;

[0017] S30. Install a normal temperature nitrogen pipeline on the particle generator;

[0018] A new normal temperature nitrogen pipeline is added to the particle generator. The new normal temperature nitrogen pipeline is also connected to the medium pressure nitrogen storage tank of the 0.3m transonic cryogenic wind tunnel to accelerate the outflow of water vapor generated by the particle generator and then introduce it into the cooling mixing device.

[0019] S40. Build and connect liquid nitrogen flash tanks;

[0020] Build a liquid nitrogen flash tank with two inlets. One inlet is connected to the liquid nitrogen interface of the 0.3m transonic cryogenic wind tunnel through a cryogenic nitrogen pipeline, and the other inlet is connected to the medium-pressure nitrogen pipeline of the 0.3m transonic cryogenic wind tunnel's normal temperature nitrogen gas source through a normal temperature nitrogen pipeline;

[0021] In the liquid nitrogen flash tank, liquid nitrogen is mixed and flashed with room temperature nitrogen to obtain cryogenic nitrogen, which is then output to a cooling and mixing device through a cryogenic nitrogen pipeline; the cooling and mixing device is connected to a 0.3-meter transonic cryogenic wind tunnel through an ice particle transmission pipeline;

[0022] S50. Install matching regulating valve assemblies on each pipeline;

[0023] A pressure flow regulating valve assembly is provided on the normal temperature nitrogen pipeline, and a flow regulating valve assembly is provided on the low temperature nitrogen pipeline; and a particle regulating valve assembly is provided on the ice particle transmission pipeline;

[0024] The pressure flow regulating valve assembly includes a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the on and off of the particle generator, and the pressure reducing valve is used to adjust the working pressure;

[0025] The flow control valve assembly includes a manual low-temperature stop valve, a filter, a pressure gauge, an electric control valve and a check valve arranged in sequence from front to back along the air flow direction to control the on-off and flow of the liquid nitrogen pipeline;

[0026] The particle regulating valve assembly includes an exhaust valve, an electric switch valve and a manual stop valve arranged in sequence from front to back along the airflow direction to perform on-off, exhaust and flow control on the ice particle transmission pipeline;

[0027] S60. Manufacturing and adjusting the size of ice particles;

[0028] In the cooling and mixing device, the water vapor meets the low-temperature nitrogen and freezes into ice particles;

[0029] Perform ice particle size detection. If the ice particle size is less than or equal to 1 μm, the test requirement is met. Otherwise, adjust the ice particle size by adjusting the regulating valve assembly of each pipeline.

[0030] S70. Conduct PIV testing experiments;

[0031] A laser was installed on the top window of the test section of the 0.3-meter transonic cryogenic wind tunnel to generate a sheet light source to illuminate the test section area, and a camera was installed on the side window of the test section to take pictures; a particle spreading rack was installed in front of the test section and connected to the ice particle transmission pipeline;

[0032] Start the 0.3-meter transonic cryogenic wind tunnel. After the temperature, pressure and Mach number of the 0.3-meter transonic cryogenic wind tunnel are stable, open the regulating valve assemblies of each pipeline, inject ice particles into the 0.3-meter transonic cryogenic wind tunnel through the particle spreading rack, take pictures of the test section with a camera, obtain the original image, close the 0.3-meter transonic cryogenic wind tunnel, and then close the regulating valve assemblies of each pipeline;

[0033] If the original image shows that the brightness of the ice particles is clearly visible, the bright spots are uniform, and fill the entire test section area, it means that the ice particles are uniform in size and the concentration meets the PIV test requirements.

[0034] The PIV test method based on a 0.3-meter transonic cryogenic wind tunnel of the present invention utilizes pure water as the tracer particle material, avoiding the pollution problem of traditional oily tracer particles and solid tracer particles on the cryogenic wind tunnel protective materials. The generated ice particles have uniform particle size, good light scattering properties, low cost, and controllable concentration. It can meet the PIV test requirements of a 0.3-meter transonic cryogenic wind tunnel, and can also be used for other PIV test requirements in low-temperature environments that have high requirements for tracer particle pollution problems, and has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the PIV test method based on a 0.3-meter transonic cryogenic wind tunnel of the present invention;

[0036] Figure 2 This is the original image of the tracer particles obtained by the PIV test method based on a 0.3-meter transonic low-temperature wind tunnel of the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0038] like Figure 1 As shown, the PIV test method based on a 0.3 m transonic low temperature wind tunnel of the present invention comprises the following steps:

[0039] S10. Determine the power of the particle generator;

[0040] Calculate the ice particle flow rate required for the PIV test in a 0.3 m transonic cryogenic wind tunnel and determine the power of a single particle generator;

[0041] S20. Install a heating device and a temperature sensor in the particle generator and conduct ground tests;

[0042] A heating device and a temperature sensor are arranged inside the particle generator;

[0043] The medium-pressure nitrogen storage tank of the 0.3-meter transonic cryogenic wind tunnel is connected to the particle generator through a medium-pressure nitrogen pipeline, and the medium-pressure nitrogen in the medium-pressure nitrogen storage tank drives the Laskin nozzle in the particle generator to generate water vapor;

[0044] Conduct ground tests on particle generators to establish the corresponding relationship between water temperature and water vapor saturation, and determine that heating the pure water in the particle generator to 50°C will achieve the best water vapor saturation;

[0045] S30. Install a normal temperature nitrogen pipeline on the particle generator;

[0046] A new normal temperature nitrogen pipeline is added to the particle generator. The new normal temperature nitrogen pipeline is also connected to the medium pressure nitrogen storage tank of the 0.3m transonic cryogenic wind tunnel to accelerate the outflow of water vapor generated by the particle generator and then introduce it into the cooling mixing device.

[0047] S40. Build and connect liquid nitrogen flash tanks;

[0048] Build a liquid nitrogen flash tank with two inlets. One inlet is connected to the liquid nitrogen interface of the 0.3m transonic cryogenic wind tunnel through a cryogenic nitrogen pipeline, and the other inlet is connected to the medium-pressure nitrogen pipeline of the 0.3m transonic cryogenic wind tunnel's normal temperature nitrogen gas source through a normal temperature nitrogen pipeline;

[0049] In the liquid nitrogen flash tank, liquid nitrogen is mixed and flashed with room temperature nitrogen to obtain cryogenic nitrogen, which is then output to a cooling and mixing device through a cryogenic nitrogen pipeline; the cooling and mixing device is connected to a 0.3-meter transonic cryogenic wind tunnel through an ice particle transmission pipeline;

[0050] S50. Install matching regulating valve assemblies on each pipeline;

[0051] A pressure flow regulating valve assembly is provided on the normal temperature nitrogen pipeline, and a flow regulating valve assembly is provided on the low temperature nitrogen pipeline; and a particle regulating valve assembly is provided on the ice particle transmission pipeline;

[0052] The pressure flow regulating valve assembly includes a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the on and off of the particle generator, and the pressure reducing valve is used to adjust the working pressure;

[0053] The flow control valve assembly includes a manual low-temperature stop valve, a filter, a pressure gauge, an electric control valve and a check valve arranged in sequence from front to back along the air flow direction to control the on-off and flow of the liquid nitrogen pipeline;

[0054] The particle regulating valve assembly includes an exhaust valve, an electric switch valve and a manual stop valve arranged in sequence from front to back along the airflow direction to perform on-off, exhaust and flow control on the ice particle transmission pipeline;

[0055] S60. Manufacturing and adjusting the size of ice particles;

[0056] In the cooling and mixing device, the water vapor meets the low-temperature nitrogen and freezes into ice particles;

[0057] Perform ice particle size detection. If the ice particle size is less than or equal to 1 μm, the test requirement is met. Otherwise, adjust the ice particle size by adjusting the regulating valve assembly of each pipeline.

[0058] S70. Conduct PIV testing experiments;

[0059] A laser was installed on the top window of the test section of the 0.3-meter transonic cryogenic wind tunnel to generate a sheet light source to illuminate the test section area, and a camera was installed on the side window of the test section to take pictures; a particle spreading rack was installed in front of the test section and connected to the ice particle transmission pipeline;

[0060] Start the 0.3-meter transonic cryogenic wind tunnel. After the temperature, pressure and Mach number of the 0.3-meter transonic cryogenic wind tunnel are stable, open the regulating valve assemblies of each pipeline, inject ice particles into the 0.3-meter transonic cryogenic wind tunnel through the particle spreading rack, take pictures of the test section with a camera, obtain the original image, close the 0.3-meter transonic cryogenic wind tunnel, and then close the regulating valve assemblies of each pipeline;

[0061] If the original image shows that the brightness of the ice particles is clearly visible, the bright spots are uniform, and fill the entire test section area, it means that the ice particles are uniform in size and the concentration meets the PIV test requirements.

[0062] Embodiment: The interface size of the room temperature nitrogen pipeline in this embodiment is DN20; 4 particle generators are used, and the room temperature nitrogen pipeline is divided into 8 routes before entering the particle generator, and each 2 routes supply a particle generator, one of which is used for Laskin nozzle drive and the other is used for particle flow acceleration discharge. The overall dimensions of each particle generator are Φ410mm (tank diameter) × 405mm (tank height), with 2 DN40 tracer particle outlets and 7 Laskin nozzle pipelines; each Laskin nozzle pipeline has 12 Laskin nozzles with a diameter of f1.5mm, and each particle generator has 84 Laskin nozzles. The particle generator is equipped with an electric heater with a maximum power of 3kW, and the heater power can be adjusted through a remote control system; the temperature sensor set in the particle generator can feedback the water temperature of the pure water in real time and perform closed-loop control. The water vapor flow generated by the particle generator is transmitted to the cooling mixing device by a DN40 pipeline and mixed with the low-temperature nitrogen provided by the low-temperature nitrogen pipeline.

[0063] The liquid nitrogen interface size of the liquid nitrogen storage tank is DN15; the volume of the liquid nitrogen flash tank is about 1.24m 3 , diameter 800mm, height 2150mm, maximum pressure bearing 1.2MPa.

[0064] The cooling and mixing device is a tank with an outer diameter of DN350, a length of 2000mm, and an internal volume of about 0.21m 3 Pressure sensors and temperature sensors are arranged on the tank body to detect and control the operating status of the cooling and mixing device. A safety valve is also provided. When the internal pressure of the cooling and mixing device exceeds 0.8MPa, the safety valve automatically opens to release the pressure. The air inlet of the cooling and mixing device includes 8 DN40 water vapor pipelines and 3 DN65 low-temperature nitrogen pipelines, and the air outlet is a DN150 ice particle transmission pipeline, which is connected to the flow channel in the wind tunnel.

[0065] Within 1 minute after the start of the PIV test in the 0.3-meter transonic cryogenic wind tunnel, bright spots of ice particles in the wind tunnel loop can be observed with the naked eye. After 5 minutes, the following Figure 2 The original image is shown. It can be seen that the brightness and concentration of the ice particles are relatively uniform, and the probability of large spots appearing is very low, indicating that the PIV test method based on the 0.3-meter transonic cryogenic wind tunnel of the present invention can effectively control the ice particle size and ensure the flow followability of the tracer particles; the tracer particle distribution density increases rapidly, indicating that the test system can effectively provide the particle concentration required for the PIV test.

[0066] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. For those familiar with the art, without departing from the principles of the present invention, all features disclosed in the present invention, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way. The present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. The PIV test method based on a 0.3m transonic cryogenic wind tunnel is characterized by: The following steps are involved: S10. Determine the power of the particle generator; S20. Install a heating device and a temperature sensor in the particle generator and conduct ground tests; S30. Install a normal temperature nitrogen pipeline on the particle generator; S40. Build and connect liquid nitrogen flash tanks; Build a liquid nitrogen flash tank with two inlets. One inlet is connected to the liquid nitrogen interface of the 0.3m transonic cryogenic wind tunnel through a cryogenic nitrogen pipeline, and the other inlet is connected to the medium-pressure nitrogen pipeline of the 0.3m transonic cryogenic wind tunnel's normal temperature nitrogen gas source through a normal temperature nitrogen pipeline; In the liquid nitrogen flash tank, liquid nitrogen is mixed and flashed with room temperature nitrogen to obtain cryogenic nitrogen, which is then output to a cooling and mixing device through a cryogenic nitrogen pipeline; the cooling and mixing device is connected to a 0.3-meter transonic cryogenic wind tunnel through an ice particle transmission pipeline; S50. Install matching regulating valve assemblies on each pipeline; A pressure flow regulating valve assembly is provided on the normal temperature nitrogen pipeline, and a flow regulating valve assembly is provided on the low temperature nitrogen pipeline; and a particle regulating valve assembly is provided on the ice particle transmission pipeline; The pressure flow regulating valve assembly includes a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the on and off of the particle generator, and the pressure reducing valve is used to adjust the working pressure; The flow control valve assembly includes a manual low-temperature stop valve, a filter, a pressure gauge, an electric control valve and a check valve arranged in sequence from front to back along the air flow direction to control the on-off and flow of the liquid nitrogen pipeline; The particle regulating valve assembly includes an exhaust valve, an electric switch valve and a manual stop valve arranged in sequence from front to back along the airflow direction to perform on-off, exhaust and flow control on the ice particle transmission pipeline; S60. Manufacturing and adjusting the size of ice particles; In the cooling and mixing device, the water vapor meets the low-temperature nitrogen and freezes into ice particles; Perform ice particle size detection. If the ice particle size is less than or equal to 1 μm, the test requirement is met. Otherwise, adjust the ice particle size by adjusting the regulating valve assembly of each pipeline. S70. Conduct PIV testing experiments.

2. The PIV test method based on a 0.3 m transonic cryogenic wind tunnel according to claim 1 is characterized in that: The S10 determines the power of the particle generator, including the following: Calculate the ice particle flow rate required for the PIV test in a 0.3 m transonic cryogenic wind tunnel and determine the power of a single particle generator.

3. The PIV test method based on a 0.3 m transonic cryogenic wind tunnel according to claim 2 is characterized in that: A heating device and a temperature sensor are installed in the particle generator of the S20 to conduct a ground test, including the following contents: A heating device and a temperature sensor are arranged inside the particle generator; The medium-pressure nitrogen storage tank of the 0.3-meter transonic cryogenic wind tunnel is connected to the particle generator through a medium-pressure nitrogen pipeline, and the medium-pressure nitrogen in the medium-pressure nitrogen storage tank drives the Laskin nozzle in the particle generator to generate water vapor; A ground test of the particle generator was conducted to establish the corresponding relationship between water temperature and water vapor saturation. It was determined that the best water vapor saturation was obtained by heating the pure water in the particle generator to 50°C.

4. The PIV test method based on a 0.3 m transonic cryogenic wind tunnel according to claim 3 is characterized in that: The particle generator of the S30 is equipped with a normal temperature nitrogen pipeline, including the following contents: A new room-temperature nitrogen pipeline is added to the particle generator. The new room-temperature nitrogen pipeline is also connected to the medium-pressure nitrogen storage tank of the 0.3-meter transonic cryogenic wind tunnel. It is used to accelerate the outflow of water vapor generated by the particle generator and then introduce it into the cooling mixing device.

5. The PIV test method based on a 0.3 m transonic cryogenic wind tunnel according to claim 4 is characterized in that: The S70 PIV test experiment includes the following contents: A laser was installed on the top window of the test section of the 0.3-meter transonic cryogenic wind tunnel to generate a sheet light source to illuminate the test section area, and a camera was installed on the side window of the test section to take pictures; a particle spreading rack was installed in front of the test section and connected to the ice particle transmission pipeline; Start the 0.3-meter transonic cryogenic wind tunnel. After the temperature, pressure and Mach number of the 0.3-meter transonic cryogenic wind tunnel are stable, open the regulating valve assemblies of each pipeline, inject ice particles into the 0.3-meter transonic cryogenic wind tunnel through the particle spreading rack, take pictures of the test section with a camera, obtain the original image, close the 0.3-meter transonic cryogenic wind tunnel, and then close the regulating valve assemblies of each pipeline; If the original image shows that the brightness of the ice particles is clearly visible, the bright spots are uniform, and fill the entire test section area, it means that the ice particles are uniform in size and the concentration meets the PIV test requirements.

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