An icing test bench and method with adjustable reverse pressure gradient

Abstract

This invention relates to an icing test rig and method with an adjustable reverse pressure gradient, belonging to the technical field of icing mechanism research. It aims to solve the problem of difficulty in studying the coupling effect between the microscopic boundary layer and droplets in icing experiments. The rig includes a nozzle, a droplet injector, a fan, a heat exchanger, a liquid nitrogen tank, a waste gas tank, and a sensing device. The fan, heat exchanger, and nozzle are sequentially connected to form an air cooling system; the liquid nitrogen tank, nozzle, and waste gas tank are sequentially connected to form a refrigeration system; the droplet injector is connected to the nozzle to form a dripping system; and the sensing device is connected to the nozzle. The nozzle model used in this invention can create an environment with a reverse pressure gradient. The detachable wall panel further allows for adjustment of the reverse pressure gradient. This test rig, combined with the icing direction, facilitates the study of droplet icing within the boundary layer. Simultaneously, the use of a refrigeration system with negative feedback regulation allows for convenient and accurate control of the wall surface temperature.

Description

Technical Field

[0001] This invention relates to an icing test bench and method, belonging to the technical field of icing mechanism research. Background Technology

[0002] Gas turbines are widely used in aviation, shipbuilding, power generation, and pipeline transportation, but they also present numerous challenges during operation. With my country's expanding ocean-going capabilities and the imminent opening of polar shipping routes, the research on the polar environment adaptability of marine gas turbines is of paramount importance. Icing in marine gas turbines primarily occurs in the intake system, inlet guide vanes, and the first few stages of the compressor blades. When the intake air temperature is below the critical temperature or contains supercooled water droplets, water impacting the engine inlet components freezes rapidly, causing ice buildup. This alters the internal flow channel profile, affecting the overall engine power output and, in severe cases, leading to engine stall and surge. Icing on the inlet guide vanes and first-stage blades directly alters the blade profile, reducing the intake channel area and decreasing the compressor intake flow rate. It also exacerbates airflow separation, distorting the internal flow field and potentially causing compressor instability or even surge, impacting the compressor's pressure ratio and efficiency.

[0003] To ensure the safe and stable operation of engines, research on icing and its hazards in engine intake components is necessary through experiments and numerical simulations. Over decades of research, the fundamental theories of icing, icing test equipment and measurement methods, and numerical calculation methods for icing have all developed rapidly. Research on icing in my country started relatively late. Although progress has been rapid, most studies focus on icing on aircraft surfaces, with relatively little research on icing in marine gas turbine intake components, especially on icing from saline droplets in marine environments. Therefore, establishing methods for predicting icing in marine environments and exploring the potential applications of anti-icing technologies are of significant scientific and practical value. Among the many icing factors, supercooled droplets play a crucial role. Research on their kinematic characteristics, solidification characteristics, and heat transfer mechanisms when impacting the solid walls of blades helps to deduce the icing patterns on compressor components. The near-wall boundary layer viscosity of blades is an important factor affecting icing, and conducting related research is of great significance. Current icing experiments have the following problems:

[0004] 1. Most traditional icing test rigs are used for static experiments in a static flow field environment. A few test rigs can conduct droplet icing experiments at low wind speeds, but this still cannot capture all the elements of the flow field; it is difficult to use this to study the coupling effect between the micro boundary layer and the droplets.

[0005] 2. Traditional icing cooling surfaces mostly use semiconductor cooling chips. These chips are small, highly efficient, and their temperature can be precisely controlled by the amount of current. However, as the area of ​​the cooling chip increases, the temperature difference on the surface also becomes very large.

[0006] Therefore, there is an urgent need to propose an icing test bench and method with an adjustable reverse pressure gradient to solve the above-mentioned technical problems. Summary of the Invention

[0007] This invention aims to address the difficulty in studying the coupling effect between the microscopic boundary layer and droplets in icing experiments. To overcome these technical deficiencies, the present invention provides an icing test bench and method with an adjustable reverse pressure gradient. A brief overview of the invention is given below to provide a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention.

[0008] The technical solution of the present invention:

[0009] An icing test bench with an adjustable reverse pressure gradient includes a nozzle, a droplet injector, a fan, a heat exchanger, a liquid nitrogen tank, an exhaust gas box, and a sensing device. The fan, heat exchanger, and nozzle are connected in sequence to form an air cooling system, the liquid nitrogen tank, nozzle, and exhaust gas box are connected in sequence to form a refrigeration system, the droplet injector is connected to the nozzle to form a dripping system, and the sensing device is connected to the nozzle.

[0010] Preferably, the nozzle includes a top plate, a bottom plate, side plates, a test plate, a track, and a thermocouple. The top plate and bottom plate are respectively provided at the upper and lower ends of the two symmetrically arranged side plates. The track is provided on the side plates. The test plate is connected to the side plates on both sides through the track. The test plate is located in the nozzle cavity between the top plate and the bottom plate. The thermocouple is provided on the test plate. The test plate divides the nozzle cavity into an upper inner cavity and a lower cooling chamber. A temperature and humidity measuring instrument is installed in the upper part of the nozzle cavity.

[0011] Preferably, the top plate is arc-shaped or V-shaped, the bottom plate is horizontal, the closest point between the top plate and the bottom plate is the throat of the nozzle, the inlet cross-section of the nozzle is smaller than the outlet cross-section, the upper inner chamber between the throat and the outlet cross-section is the nozzle test section, and the droplet injector is set in the nozzle test section.

[0012] Preferably, the number of thermocouples is nine, arranged in an array, the number of tracks is three sets, the three sets of tracks are arranged at equal intervals, the tracks are slide rails, the slide rails include slides and sliders, the test plate is bolted to the sliders, the sliders are slidably connected to the slides, the test plate is a droplet impact plate, and the test plate is a convex plate, a concave plate, or a flat plate.

[0013] Preferably, an icing test bench with an adjustable reverse pressure gradient further includes a frequency modulator, a constant temperature circulating refrigeration pump, and a Pitot tube speedometer. The frequency modulator is electrically connected to a fan, and the constant temperature circulating refrigeration pump is connected to the tube side of a heat exchanger. The fan, the shell side of the heat exchanger, the inlet Pitot tube equipped with the Pitot tube speedometer, the inlet of the nozzle, the intermediate Pitot tube located at the throat of the nozzle, the outlet of the nozzle, and the outlet Pitot tube are sequentially connected to form an air cooling system.

[0014] Preferably, an icing test bench with an adjustable reverse pressure gradient further includes a control valve and a flow meter. The control valve is an adjustable throttle valve. The liquid nitrogen tank, control valve, flow meter, cooling chamber of the nozzle, and exhaust gas box are connected in sequence to form a refrigeration system.

[0015] Preferably, the sensing device includes a high-speed camera and an infrared thermometer, the side panel is made of plexiglass, the high-speed camera and the infrared thermometer are connected to the horizontal platform frame through the connection, the sensing device is located outside the nozzle, and the detection end of the sensing device is located above the test plate.

[0016] Preferably, an icing test bench with an adjustable reverse pressure gradient further includes a computer, a high-speed camera, and an infrared thermometer, wherein the computer is electrically connected to a frequency modulator, a constant temperature circulating refrigeration pump, a Pitot tube speedometer, a control valve, a flow meter, a high-speed camera, an infrared thermometer, and a thermocouple.

[0017] An icing test method with an adjustable reverse pressure gradient, using the aforementioned icing test bench with an adjustable reverse pressure gradient, includes the following steps:

[0018] Step a: Calibrate the high-speed camera and establish a standard scale;

[0019] Step b: Cold plate temperature control

[0020] Turn on the refrigeration system, adjust the speed control valve to the minimum flow rate, and then turn on the fan until the thermocouple temperature stabilizes.

[0021] Step c: Ambient temperature control

[0022] Turn on the heat exchanger and the thermostatic refrigeration circulation pump until the temperature inside the nozzle stabilizes.

[0023] Step d: Droplets impact the wall surface

[0024] Adjust the position of the burette and measure the initial position;

[0025] Pushing the droplet injector, the water is ejected and forms a stable droplet at the outlet of the burette. The temperature of the droplet is measured by an infrared thermometer. When the temperature of the droplet reaches a stable level, the droplet can be allowed to fall.

[0026] The process of droplet falling is recorded by a high-speed camera or high-speed camera. The velocity of droplet hitting the wall is calculated by solving the vertical height difference of droplet in two consecutive frames before impact with the wall and the time difference between the two frames.

[0027] Step e: Cleaning the test plate.

[0028] Preferred method: In step b, the criterion for judging the stability of the thermocouple temperature is: after setting a specified temperature and opening the speed control valve, the temperature of the thermocouple is recorded every 5 minutes.

[0029] To proceed to the next stage of the experiment, the following condition must be met: The average temperature T of the nine thermocouples must be calculated. a If the average temperature change between two time intervals is less than ±0.5℃, then it indicates that the temperature of the cold plate (test plate) has reached stability.

[0030] In step c, when the experiment needs to be conducted in a low-temperature environment, turn on the heat exchanger to control the air temperature (ambient temperature); turn on the thermostatic refrigeration circulation pump, set the temperature, and use a temperature sensor to measure the air temperature; once the air temperature stabilizes, the next step of the experiment can be carried out.

[0031] In step d, the moment the droplet contacts the wall is taken as the initial moment, and timing begins. A high-speed camera or high-speed video camera is used to record the kinematic characteristics of the droplet during the impact process and the solidification phase transition process.

[0032] In step e, the convex plate and the concave plate are replaced by a track.

[0033] The present invention has the following beneficial effects:

[0034] 1. This invention is designed for the boundary layer of a wall surface. There is an adverse pressure gradient within the boundary layer. When the boundary layer develops to a certain extent, flow separation will occur, forming various vortices. It is difficult to capture these two factors in laminar flow at low wind speeds. This invention macroscopically realizes the two microscopic features within the boundary layer. The nozzle structure slows down and diffuses the air during the flow process, thus forming an adverse pressure environment, simulating the features within the boundary layer, and capturing the dynamic behavior of droplets within the boundary layer.

[0035] 2. This invention uses liquid nitrogen to fill the cooling chamber to cool the plate. This method can make the plate temperature uniform. The refrigeration system is connected to a computer and the temperature of the cold plate is controlled through negative feedback.

[0036] 3. The droplet impact plate of the present invention is detachable. By changing the fit between the droplet impact plate and the track, the area ratio of the nozzle throat and the outlet can be changed, thereby changing the reverse pressure gradient. At the same time, it is easy to replace the plate or the curved plate, thus improving adaptability. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of the experimental system;

[0038] Figure 2 This is a structural diagram of the nozzle model, one of the main components of this experimental system;

[0039] Figure 3 This is a magnified view of point A on the nozzle model;

[0040] Figure 4 This is a diagram of a convex flat plate structure;

[0041] Figure 5 This is a diagram of a concave flat plate structure;

[0042] Figure 6 This is a distribution diagram of thermocouples impacting a plate by a droplet;

[0043] Figure 7 This is a flowchart of the feedback regulation of a liquid nitrogen refrigeration system.

[0044] In the diagram: 1-Nozzle, 2-Droplet Injector, 3-Frequency Controller, 4-Fan, 5-Heat Exchanger, 6-Constant Temperature Circulating Refrigeration Pump, 7-Pitto Tachometer, 8-Liquid Nitrogen Tank, 9-Exhaust Gas Box, 10-Control Valve, 101-Top Plate, 102-Bottom Plate, 103-Side Plate, 104-Test Plate, 105-Railway, 106-Convex Plate, 107-Concave Plate, 108-Thermocouple, 11-Flow Meter, 12-Computer, 13-High-Speed ​​Camera, 14-Infrared Thermometer. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0046] Specific implementation method one: Combining Figure 1-6This embodiment describes an icing test bench with an adjustable reverse pressure gradient, comprising a nozzle 1, a droplet injector 2, a fan 4, a heat exchanger 5, a liquid nitrogen tank 8, an exhaust gas tank 9, and a sensing device. The fan 4, heat exchanger 5, and nozzle 1 are sequentially connected to form an air cooling system; the liquid nitrogen tank 8, nozzle 1, and exhaust gas tank 9 are sequentially connected to form a refrigeration system; the droplet injector 2 is connected to nozzle 1 to form a dripping system; and the sensing device is connected to nozzle 1. The nozzle model used in this invention can create an environment with a reverse pressure gradient, and the detachable wall panel further makes the reverse pressure gradient adjustable. This test bench, combined with the icing direction, facilitates the study of droplet icing within the boundary layer (with a reverse pressure gradient). Simultaneously, the use of a refrigeration system with negative feedback regulation allows for convenient and accurate control of the wall surface temperature.

[0047] The nozzle 1 includes a top plate 101, a bottom plate 102, a side plate 103, a test plate 104, a track 105, and a thermocouple 108. The top plate 101 and the bottom plate 102 are respectively provided at the upper and lower ends of the two symmetrically arranged side plates 103. The track 105 is provided on the side plates 103. The test plate 104 is connected to the side plates 103 on both sides through the track 105. The test plate 104 is located in the nozzle cavity between the top plate 101 and the bottom plate 102. The thermocouple 108 is provided on the test plate 104. The test plate 104 divides the nozzle cavity into an upper inner cavity and a lower cooling chamber. A temperature and humidity measuring instrument is installed in the upper inner cavity of the nozzle 1.

[0048] The top plate 101 is arc-shaped or V-shaped, and the bottom plate 102 is a horizontal plate. The closest point between the top plate 101 and the bottom plate 102 is the throat of the nozzle 1. The inlet cross-section of the nozzle 1 is smaller than the outlet cross-section. The upper inner chamber between the throat and the outlet cross-section is the nozzle experimental section. The top plate 101 is provided with mounting holes, and the droplet injector 2 is installed on the upper side of the nozzle experimental section through the mounting holes on the top plate 101. The droplet injector 2 is a miniature droplet injector. The bottom plate 102 of the nozzle 1 is placed on a horizontal platform frame. The droplet injector 2 is connected to the horizontal platform frame through an adjustable height lifting frame. The outlet of the droplet injector 2 is connected to one end of a burette for titration. The other end of the tube is set at the mounting hole, and the burette is located on the upper inner side of the test section of the nozzle 1. This invention is designed for the boundary layer of the wall. There is an adverse pressure gradient in the boundary layer. When the boundary layer develops to a certain extent, flow separation will occur, forming various vortices. It is difficult to capture these two factors in laminar flow at low wind speeds. This invention realizes the macroscopic nature of the two microscopic features in the boundary layer, which can capture all the elements of the flow field and facilitate the study of the coupling effect between the microscopic boundary layer and the droplets. The nozzle structure slows down and diffuses the air during the flow process, so the overall environment forms an adverse pressure environment, simulating the features in the boundary layer.

[0049] There are nine thermocouples arranged in a three-row, three-column array. There are three sets of tracks 105, with two tracks 105 corresponding to the two side plates 103 forming one set. The three sets of tracks 105 are vertically equidistant. Each track 105 is a slide rail, consisting of a slide path and a slider. The test plate 104 is bolted to the slider, the slider is slidably connected to the slide path, and the slide path is bolted to the side plate 103; alternatively, the slide rail is grooved, and the test plate is inserted into it. The test plate 104 is a droplet impact plate, with a wall surface on its top. 104 adopts a convex plate 106, a concave plate 107, or a flat plate, that is, the impact surface (wall) of the upper test plate 104 is an upwardly convex arc, a downwardly concave arc, or a straight line; the droplet impact plate of the present invention is detachable, with three equally spaced slide rails installed between the plexiglass, and the plate is installed on the test platform through the slide rails. This can change the area ratio of the nozzle throat and the outlet, thereby achieving the purpose of changing the reverse pressure gradient. On the other hand, the plate can be changed to a plate with a slight curvature, which can adapt to different working conditions;

[0050] The air cooling system also includes a frequency converter 3, a constant temperature circulating refrigeration pump 6, and a Pitot tube speedometer 7. The frequency converter 3 is electrically connected to the fan 4, and the constant temperature circulating refrigeration pump 6 is connected to the tube side of the heat exchanger 5. The fan 4, the shell side of the heat exchanger 5, the inlet Pitot tube equipped with the Pitot tube speedometer 7, the inlet of the nozzle 1, the intermediate Pitot tube located at the throat of the upper inner chamber of the nozzle 1, the outlet of the upper inner chamber of the nozzle 1, and the outlet Pitot tube are connected in sequence to form an air cooling system, and the air is directly discharged into the atmosphere.

[0051] The refrigeration system also includes a control valve 10 and a flow meter 11. The control valve 10 is an adjustable throttle valve. The liquid nitrogen tank 8, control valve 10, flow meter 11, cooling chamber of nozzle 1, and exhaust gas box 9 are connected in sequence to form the refrigeration system. The flow meter 11 is connected to the inlet side of the nozzle cooling chamber. The exhaust gas box 9 is connected to the outlet side of the nozzle cooling chamber through a pipeline. The nitrogen exhaust gas is collected in the exhaust gas collection box through the pipeline. The control valve is controlled by a computer. The control valve, thermocouple, and computer together form a negative feedback regulation. The size of the control valve is adjusted by the temperature of the cold plate measured by the thermocouple. The exhaust gas generated in the cooling chamber is discharged into the exhaust gas treatment box for centralized treatment. This invention uses traditional refrigeration technology to refrigerate the plate by filling the cooling chamber with liquid nitrogen. This method can make the plate temperature uniform. The refrigeration system is connected to a computer and the temperature of the liquid droplet impacting the plate 104 is controlled through negative feedback regulation.

[0052] The sensing device includes a high-speed camera 13 and an infrared thermometer 14. The side plate 103 is made of plexiglass. The inlet of the nozzle 1 is provided with an plexiglass channel, which is connected to the fan 4 to achieve sealing while facilitating information collection. The high-speed camera 13 and the infrared thermometer 14 are connected to the horizontal platform frame through the channel. The sensing device is located outside the test section of the nozzle 1, and the detection end of the sensing device is located above the test plate 104. The sensing device detects through the plexiglass and is used to collect the entire process of the droplets in the dripping system falling from the droplet injector 2 and colliding with the test plate 104. The test section for the freezing test is a diffuser section. A hole is opened on the upper side of the nozzle to allow the droplet tube to penetrate into the test chamber. The droplets are generated by a micro-droplet injector, which is installed on a lifting frame with lifting function to adjust the droplet falling height. The temperature of the droplets is measured by an infrared thermometer outside the chamber. The high-speed camera is used to capture the droplet falling process and measure the droplet diameter. All data are saved to the computer.

[0053] An icing test bench with adjustable reverse pressure gradient also includes a computer 12, a high-speed camera 13, and an infrared thermometer 14. The computer 12 is electrically connected to a frequency modulator 3, a constant temperature circulating refrigeration pump 6, a Pitot tube speedometer 7, a control valve 10, a flow meter 11, the high-speed camera 13, the infrared thermometer 14, and a thermocouple. Parameters are set through the computer, and the collected data is controlled by the technical unit and saved to the computer.

[0054] Specific Implementation Method Two: Combining Figure 1-7This embodiment describes an icing test method with an adjustable reverse pressure gradient. An icing test bench with an adjustable reverse pressure gradient is used. The top plate 101 and bottom plate 102 of the nozzle 1 are connected to the side plates 103 on both sides by screws. The side plates 103 are bolted to the slide rails 105, facilitating the installation and removal of the droplet impact plate. The droplet impact plate is positioned above the viewpoint on the slide rails, facilitating photography. After the nozzle 1 is installed, it is placed on a horizontal platform. Then, the air cooling system at the nozzle inlet is installed. At the far left is a fan 4 with a frequency converter 3. The blown air passes through a heat exchanger 5 controlled by a constant-temperature circulating refrigeration pump 6, and then enters the nozzle 1 through a short glass channel. The cooling chamber of the nozzle 1 is connected to a liquid nitrogen refrigeration system. Liquid nitrogen is introduced into the cooling chamber from the liquid nitrogen tank 8 via a pipeline. A control valve 10 and a flow meter are connected to the pipeline. Meter 11 and control valve 10 are flow valves (adjustable throttle valves). The cooled exhaust gas is collected in the exhaust gas treatment box 9 for centralized treatment. After the main body is installed, the measuring instruments are installed. First, a Pitot tube speedometer 7 (for measuring velocity and static pressure) needs to be installed at the nozzle inlet to measure the inlet wind speed. A Pitot tube is installed at the nozzle throat and outlet to measure the static pressure at both points and calculate the pressure difference. A temperature and humidity measuring instrument should also be installed in the nozzle test section to record the temperature and humidity during the experiment. The high-speed camera and infrared thermometer 14 used in the experiment are installed on the bracket and taken at appropriate positions. The micro-syringe 2 is installed on the adjustable height lifting frame, which can adjust the droplet height at any time. The burette is inserted into the nozzle through a small hole above the nozzle. After installation, the measurement work begins. An icing test method with adjustable reverse pressure gradient includes the following steps:

[0055] Step a: Calibrate the high-speed camera 13 and establish the standard scale;

[0056] Step b: Cold plate temperature control

[0057] Turn on the refrigeration system, adjust the speed control valve 10 to the minimum flow rate, and then turn on the fan 4 until the temperature of the thermocouple 108 stabilizes.

[0058] In step b, the criterion for judging the temperature stability of thermocouple 108 is: after setting the specified temperature on computer 12 and opening speed control valve 10, the temperature of thermocouple 108 is recorded every 5 minutes.

[0059] To proceed to the next stage of the experiment, the following condition must be met: The average temperature T of the nine thermocouples must be calculated. a If the average temperature change between two time intervals is less than ±0.5℃, then it indicates that the temperature of the cold plate (test plate) has reached stability.

[0060] Step c: Ambient temperature control

[0061] Turn on heat exchanger 5 and thermostatic refrigeration circulation pump 6 until the temperature inside nozzle 1 stabilizes.

[0062] In step c, when certain experimental conditions require a low-temperature environment, the heat exchanger 5 before the inlet needs to be turned on to control the air temperature (ambient temperature). The air temperature is easier to control than the cold plate temperature. Turn on the thermostatic refrigeration circulation pump 6, set the temperature, and wait for a period of time. The temperature of the air inside the nozzle 1 can be measured by the temperature sensor (temperature and humidity measuring instrument). When the air temperature stabilizes (reaches the set temperature), the next experiment can be carried out.

[0063] Step d: Droplets impact the wall surface

[0064] Fix the droplet injector 2 on the lifting frame. Before starting, adjust the position of the droplet injector tube and measure the initial position. If you want to change the droplet falling height later, you can change it through the lifting frame.

[0065] Push the droplet injector 2 to push out a certain volume of water, forming a stable water droplet at the outlet of the burette. The temperature of the droplet is measured by the infrared thermometer 14. When the temperature of the droplet reaches a stable state, the droplet can be allowed to fall.

[0066] The process of droplet falling is recorded by high-speed camera 14 or high-speed camera. The velocity of droplet hitting the wall can be calculated by solving the vertical height difference of droplet in two consecutive frames before impact with the wall and the time difference between the two frames.

[0067] In step d, the moment the droplet contacts the wall is taken as the initial moment, and timing begins. The kinematic characteristics and solidification phase transition process of the droplet during the impact are recorded by a high-speed camera or high-speed video camera. The end of a working condition is considered when the next droplet reaches a completely stable state.

[0068] Step e: Cleaning the test plate

[0069] In step e, the plate needs to be cleaned before the next set of experiments. Cleaning is easier after the droplets hit the room temperature wall, but it is more complicated after they hit the cold wall. The refrigeration system needs to be turned off before processing, which is time-consuming. If you want to study the effect of the wall curvature on the icing of droplet impact, you can replace the convex plate 106 and the concave plate 107 with the track 105.

[0070] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be permuted and combined. Those skilled in the art can exhaust all possibilities based on the mathematical knowledge of permutation and combination. Therefore, the present invention will not describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An icing test bench with an adjustable reverse pressure gradient, characterized in that: The system includes a nozzle (1), a droplet injector (2), a fan (4), a heat exchanger (5), a liquid nitrogen tank (8), an exhaust gas tank (9), and a sensing device. The fan (4), the heat exchanger (5), and the nozzle (1) are connected in sequence to form an air cooling system. The liquid nitrogen tank (8), the nozzle (1), and the exhaust gas tank (9) are connected in sequence to form a refrigeration system. The droplet injector (2) is connected to the nozzle (1) to form a dripping system. The sensing device is connected to the nozzle (1). The nozzle (1) includes a top plate (101), a bottom plate (102), a side plate (103), a test plate (104), a track (105), and a thermocouple (108). The top plate (101) and the bottom plate (102) are respectively provided at the upper and lower ends of the two symmetrically arranged side plates (103). The track (105) is provided on the side plates (103). The test plate (104) is connected to the side plates (103) on both sides through the track (105). The test plate (104) is located in the nozzle cavity between the top plate (101) and the bottom plate (102). The thermocouple (108) is provided on the test plate (104). The test plate (104) divides the nozzle cavity into an upper inner cavity and a lower cooling chamber. A temperature and humidity measuring instrument is installed in the upper inner cavity of the nozzle (1). The top plate (101) is arc-shaped or V-shaped, and the bottom plate (102) is a horizontal plate. The closest point between the top plate (101) and the bottom plate (102) is the throat of the nozzle (1). The inlet end cross section of the nozzle (1) is smaller than the outlet end cross section. The upper inner chamber between the throat and the outlet end cross section is the nozzle test section. The droplet injector (2) is set in the nozzle test section.

2. The icing test bench with an adjustable reverse pressure gradient according to claim 1, characterized in that: There are nine thermocouples arranged in an array. There are three sets of tracks (105). The two tracks (105) corresponding to the two side plates (103) are one set. The three sets of tracks (105) are arranged at equal intervals. The test plate (104) is a droplet impact plate. The top of the test plate (104) is a wall. The test plate (104) is a convex plate (106), a concave plate (107), or a flat plate.

3. An icing test bench with an adjustable reverse pressure gradient according to claim 2, characterized in that: The air cooling system also includes a frequency converter (3), a constant temperature refrigeration circulation pump (6), and a Pitot tube speedometer (7). The frequency converter (3) is electrically connected to the fan (4), and the constant temperature refrigeration circulation pump (6) is connected to the tube side of the heat exchanger (5). The fan (4), the shell side of the heat exchanger (5), the inlet Pitot tube equipped with the Pitot tube speedometer (7), the inlet of the nozzle (1), the intermediate Pitot tube set at the throat of the nozzle (1), the outlet of the nozzle (1), and the outlet Pitot tube are connected in sequence to form the air cooling system.

4. An icing test bench with an adjustable reverse pressure gradient according to claim 3, characterized in that: The refrigeration system also includes a control valve (10) and a flow meter (11). The control valve (10) is an adjustable throttle valve. The liquid nitrogen tank (8), control valve (10), flow meter (11), cooling chamber of nozzle (1), and exhaust gas box (9) are connected in sequence to form the refrigeration system.

5. An icing test bench with an adjustable reverse pressure gradient according to claim 4, characterized in that: The sensing device includes a high-speed camera (13) and an infrared thermometer (14). The side plate (103) is made of plexiglass. The high-speed camera (13) and the infrared thermometer (14) are connected by a horizontal platform frame between them. The sensing device is located outside the nozzle (1), and the detection end of the sensing device is located above the test plate (104).

6. An icing test bench with an adjustable reverse pressure gradient according to claim 5, characterized in that: It also includes a computer (12), which is electrically connected to a frequency modulator (3), a constant temperature refrigeration circulation pump (6), a Pitot tube speedometer (7), a control valve (10), a flow meter (11), a high-speed camera (13), an infrared thermometer (14), and a thermocouple.

7. An icing test method with an adjustable reverse pressure gradient, characterized in that: The icing test bench with an adjustable reverse pressure gradient as described in claim 6 includes the following steps: Step a: Calibrate the high-speed camera (13) and establish a standard scale; Step b: Temperature control of the test plate Turn on the refrigeration system, adjust the control valve (10) to the minimum flow rate, and then turn on the fan (4) until the temperature of the thermocouple (108) stabilizes; Step c: Ambient temperature control Turn on the heat exchanger (5) and the thermostatic refrigeration circulation pump (6) until the temperature inside the nozzle (1) stabilizes; Step d: Droplets impact the wall surface Adjust the position of the burette and measure the initial position; Push the droplet injector (2) to push out water to form a stable droplet at the outlet of the burette. The temperature of the droplet is measured by an infrared thermometer (14). When the temperature of the droplet reaches a stable state, the droplet can fall. The droplet falling process was recorded by a high-speed camera (13). The velocity of the droplet hitting the wall was calculated by solving the vertical height difference of the droplet in two consecutive frames before it hits the wall and the time difference between the two frames. Step e: Cleaning the test plate.

8. The icing test method with an adjustable reverse pressure gradient according to claim 7, characterized in that: In step b, the criterion for judging the temperature stability of thermocouple (108) is: after setting the specified temperature and opening the control valve (10), the temperature of thermocouple (108) is recorded every 5 minutes. To proceed to the next stage of the experiment, the following condition must be met: The average temperature T of the nine thermocouples must be calculated. a If the average temperature change between two time intervals is less than ±0.5℃, then the temperature of the test plate has reached stability. In step c, when the experiment needs to be carried out in a low-temperature environment, turn on the heat exchanger (5) to control the air temperature; turn on the thermostatic refrigeration circulation pump (6), set the temperature, and use the temperature sensor to measure the air temperature; when the air temperature is stable, proceed to the next step of the experiment. In step d, the moment the droplet contacts the wall is taken as the initial moment, and timing begins. A high-speed camera is used to record the kinematic characteristics and solidification phase transition process of the droplet during the impact. In step e, the convex plate (106) or concave plate (107) is replaced by the track (105).

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