Supercooled water droplet spray system and control method for aircraft engine icing test

Abstract

The application provides a supercooled water droplet spraying system and a control method for an aero-engine icing test. The water supply inlet and the gas supply inlet of each centrifugal nozzle of the supercooled water droplet spraying system are respectively connected with independent water supply solenoid valves and gas supply solenoid valves. The water supply system further comprises a backwater pump, a backwater pipeline and a back pressure regulating valve. The water supply pipeline and the backwater pipeline constitute a water supply and backwater circulation loop with a water storage tank as a common node. The back pressure regulating valve is arranged in series on the backwater pipeline. The test control system comprises a PLC programmable controller, an upper computer, pressure sensors and flow meters. The pressure sensors are arranged on the water supply pipeline and the gas supply pipeline respectively, convert the pipeline pressure into current signals and input the PLC programmable controller. The PLC programmable controller implements PID closed-loop control on the water supply regulating valve and the gas supply regulating valve respectively according to the feedback signals of the pressure sensors. The application has the advantages of simple structure and strong applicability.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, specifically to a supercooled water droplet spray system and control method for aero-engine icing tests. Background Technology

[0002] The study of icing characteristics on the surface of aero-engine rotating blades is of great significance for the design of aero-engine anti-icing and de-icing systems. Icing cloud and fog simulation facilities, as important equipment for simulating aircraft flight icing conditions, are often used for functional verification of aircraft anti-icing and de-icing systems. The spraying effect of supercooled water droplets in the icing wind tunnel directly determines the icing characteristics on the engine blade surface and affects the effectiveness of the aero-engine anti-icing and de-icing system design.

[0003] To address the requirements of supercooled water droplet cloud testing conditions in wind tunnels, a supercooled water droplet spray system and control method for aero-engine icing tests are invented. The system mixes water and compressed air in an internally mixed centrifugal nozzle to generate atomized water droplets. After leaving the nozzle, the water droplets undergo heat and mass transfer under the entrainment effect of the wind tunnel airflow, and their temperature drops rapidly to reach a supercooled state, thereby forming an icing cloud containing supercooled water droplets in the wind tunnel. Summary of the Invention

[0004] In view of this, the present invention provides a supercooled water droplet spray system and control method for icing tests of aero-engines, so as to achieve the ability to simulate the process of supercooled water droplets impacting the rotating blades of aero-engines at high altitudes under ground conditions, and to provide experimental support for obtaining the icing characteristics of the engine blade surface.

[0005] This invention provides the following technical solution: a supercooled water droplet spray system for icing tests of aero-engines, comprising a spray assembly, a water supply system, an air supply system, and a test control system; the spray assembly includes several centrifugal nozzles, a water supply pipeline, an air supply pipeline, and a control valve; the water supply system includes a water tank, a water pump, a water supply pipeline, and a water supply regulating valve; the air supply system includes an air compressor, an air supply pipeline, and an air supply regulating valve; the test control system includes a controller, sensors, and a host computer.

[0006] Each centrifugal nozzle has an independent water supply solenoid valve and an air supply solenoid valve connected to its water supply inlet and air supply inlet, respectively. The number of working nozzles can be configured by selectively controlling the on / off state of the water supply solenoid valve and air supply solenoid valve corresponding to each centrifugal nozzle. The water supply system also includes a return water pump, a return water pipeline, and a back pressure regulating valve; the water supply pipeline and the return water pipeline form a water supply and return circulation loop with the water storage tank as a common node; the back pressure regulating valve is connected in series on the return water pipeline and works in conjunction with the water supply regulating valve to stabilize the water supply pressure at the centrifugal nozzle; The test and control system includes a PLC programmable controller, a host computer, pressure sensors, and a flow meter. The pressure sensors are respectively installed on the water supply pipeline and the gas supply pipeline, converting the pipeline pressure into a current signal and inputting it into the PLC programmable controller. The PLC programmable controller implements PID closed-loop control on the water supply regulating valve and the gas supply regulating valve respectively based on the feedback signal from the pressure sensors.

[0007] A control method for a supercooled water droplet spray system used in aircraft engine icing tests, wherein the supercooled water droplet spray system comprises several centrifugal nozzles, each centrifugal nozzle having an independent water supply solenoid valve and an air supply solenoid valve respectively installed at its water supply inlet and air supply inlet; a water supply regulating valve is connected in series on the system's water supply pipeline, a back pressure regulating valve is connected in series on the return water pipeline, and an air supply regulating valve is connected in series on the air supply pipeline; the water supply pipeline and the return water pipeline form a water supply and return circulation loop with a water storage tank as a common node; the control method includes the following steps: S1. By switching the water supply solenoid valve and air supply solenoid valve of each centrifugal nozzle, check the spray cone angle and spray range of each centrifugal nozzle one by one, select the number of working nozzles that meet the requirements of the freezing test, and close the water supply solenoid valve and air supply solenoid valve corresponding to the nozzles that are not in use; switch between spray mode and return water mode by configuring the on / off state of the solenoid valve of the nozzle water supply branch. S2. First, it operates in open-loop mode. The host computer sets the opening degree of the water supply regulating valve and the air supply regulating valve. The system feeds back the error between the actual valve opening degree and the set opening degree, and records the measurement data of the pressure sensor and flow meter under this condition. Then, it switches to PID closed-loop mode, using the water supply pressure and air supply pressure recorded in the open-loop stage as the set value. The PLC programmable controller calculates the deviation between the set pressure and the pressure sensor feedback value, executes PID calculation, and outputs the adjustment amount to control the opening degree of the water supply regulating valve and the air supply regulating valve respectively. The back pressure regulating valve always adopts an open-loop mode to cooperate with the water supply regulating valve to stabilize the water supply pressure at the centrifugal nozzle. S3. Under the conditions that the wind tunnel inflow velocity and temperature meet the test settings, the droplet size and droplet distribution uniformity after atomization are calibrated using a holographic three-dimensional imaging measuring instrument, and the liquid water content is measured using the standard ice knife method to confirm that the cloud and fog parameters sprayed by the supercooled water droplet spray system meet the requirements of the aero-engine icing test. S4. Set the target values ​​for water supply pressure and air supply pressure on the host computer. The regulating valve adopts PID closed-loop control. Start the water supply pump and return water pump in sequence, and open the water supply solenoid valve, return water solenoid valve and air supply solenoid valve. The host computer selects the spray mode and starts the test. After the supercooled water droplet spray system sprays the cloud mist, start the wind tunnel blowing and the aircraft engine in sequence to start the icing test. The test monitoring software of the host computer monitors the process parameters of the entire system in real time. After the test is completed, switch to the return water mode, open the vent valve to remove the residual gas in the system, and complete the system shutdown procedure.

[0008] Compared with existing technologies, the beneficial effects achieved by at least one of the above-mentioned technical solutions of this invention include: a supercooled water droplet spray system and control method for aero-engine icing tests, characterized by simple system structure, reliable operation, and a designed water supply and return system capable of stabilizing water pressure fluctuations generated during the test spraying process. The use of open-loop and closed-loop PID control methods enables continuous and stable adjustment of liquid water content, droplet size, and uniformity parameters, creating a cloud and fog environment required for aero-engine icing tests. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 For the supercooled water droplet spray system inside the wind tunnel; Figure 2 This is a schematic diagram of a supercooled water droplet spray system; Figure 3 This is a schematic diagram of the spray assembly; Figure 4 Diagram of the control system composition; Figure 5 This is a block diagram for water supply pressure control. Figure 6 This is a block diagram for gas supply pressure control. Figure 7 For control program flowchart; Figure 8 This is the system control program flowchart. Detailed Implementation

[0011] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0012] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0013] like Figures 1 to 6As shown, this embodiment of the invention provides a supercooled water droplet spray system for aircraft engine icing tests, comprising four subsystems: a spray assembly, a water supply system, an air supply system, and a test control system. These four subsystems are interconnected via pipelines, electrical wiring, and Ethernet, working together to create a supercooled water droplet cloud environment within an icing wind tunnel that meets airworthiness standards. Specifically, pressurized liquid water and compressed air are mixed in a vortex chamber inside a centrifugal nozzle and then sprayed out in cloud form. The liquid water particles are rapidly cooled by the entrainment effect of the low-temperature airflow from the wind tunnel, reaching a supercooled state and forming a supercooled water droplet cloud. This cloud impacts the surface of the aircraft engine (or test piece), simulating the icing process of rotating blades during high-altitude flight.

[0014] The spray assembly is used to atomize liquid water and compressed air into a supercooled water droplet cloud that meets the experimental requirements. The spray assembly has a square frame structure, which is made of profiled steel and has sufficient rigidity to maintain shape stability under wind tunnel airflow loads. Several centrifugal nozzles are arranged inside the frame. The centrifugal nozzles have an internal mixing structure. Liquid water and compressed air are fully mixed in the swirling grooves inside the nozzles before being accelerated and sprayed out to form a fine atomized water droplet cloud.

[0015] The piping arrangement of the spray assembly is as follows: water supply pipes and air supply pipes are arranged side by side, both perpendicular to the windward side of the spray assembly. There are 2 to 5 horizontal air supply pipes and 2 to 5 horizontal water supply pipes; in this embodiment, the horizontal air supply pipes are 3 DN15 stainless steel pipes, and the horizontal water supply pipes are 3 DN15 stainless steel pipes, with both ends of the pipes connected to the main pipe on the frame via flanges. Nozzles are installed at equal intervals at the intersections of the water supply pipes and air supply pipes, covering the effective cross-section of the wind tunnel test section.

[0016] Each centrifugal nozzle has an independent water supply solenoid valve and an independent air supply solenoid valve connected to its water and air supply inlets, respectively. A PLC programmable controller issues commands to selectively control the on / off state of the corresponding water and air supply solenoid valves for each centrifugal nozzle, thus enabling flexible configuration of the number of working nozzles. The solenoid valves of unselected nozzles remain closed, without affecting the normal spraying of other working nozzles.

[0017] The spray assembly is installed inside the icing wind tunnel, located at a distance of no less than 2 m from the wind tunnel outlet section. In this embodiment, the spray assembly is placed 3 m from the wind tunnel outlet section to ensure that the atomized droplets have sufficient heat and mass transfer time before reaching the test section, forming a stable supercooled water droplet state. Under the conditions of fixed wind speed and fixed nozzle diameter, the particle size of the sprayed cloud water droplets can be continuously adjusted within the range of 10–200 μm by coordinating the adjustment of water supply pressure and air supply pressure, and the liquid water content can be adjusted within the range of 0.3–2.0 g / m³. 3 The uniformity of liquid water content is no greater than ±0.15 g / m³.3 A vent valve is installed at the end of the gas supply line to remove residual compressed gas from the gas supply line after the test, preventing the system from being stored under pressure for a long time.

[0018] The water supply system is used to pressurize and regulate the purified liquid water, and then stably deliver the water at a set flow rate to each working centrifugal nozzle, where it is sprayed out after merging with compressed air. The water supply system consists of an insulated water storage tank, a water filter, a water supply solenoid valve, a water supply pump, a return water pump, a DN15 water supply pipeline, a water supply regulating valve, a back pressure regulating valve, and a DN15 return water pipeline.

[0019] The insulated water tank has a heat preservation function, which can maintain a relatively stable water temperature in low-temperature test environments, preventing the water temperature from being too low and causing the pipes to freeze and clog the nozzles. After the water flows out of the insulated water tank, it first passes through a water filter to remove particulate impurities and prevent nozzle clogging. Then, it is pressurized by the water supply solenoid valve and the water supply pump and enters the water supply regulating valve to deliver the water to the spray assembly at the set pressure.

[0020] The water supply system adopts a dual-circulation design with parallel supply and return water paths: the water supply pump outlet is divided into two paths. One path enters the working centrifugal nozzles of the spray assembly through the water supply pipeline and water supply regulating valve, participating in atomization spraying; the other path returns to the insulated water storage tank through the return water pipeline, return water solenoid valve, back pressure regulating valve, and return water pump, forming a supply and return water circulation loop. The back pressure regulating valve is connected in series on the return water pipeline, working in conjunction with the water supply regulating valve to stabilize the water supply pressure at the nozzles. Specifically, during spraying, by adjusting the opening of the back pressure regulating valve (set to 30% in this embodiment), a certain back pressure is maintained in the return water pipeline, thereby effectively suppressing fluctuations in water supply pressure caused by changes in nozzle flow rate; the water supply regulating valve is responsible for precisely controlling the amount of water entering the nozzles. The system is equipped with a return water pump, which, on the one hand, assists in maintaining the circulation pressure in spray mode, and on the other hand, in return water mode after the test, pumps the remaining liquid water in the water supply pipeline back to the insulated water storage tank to prevent water accumulation in the pipeline from freezing in a low-temperature environment.

[0021] The air supply system provides clean compressed air to the spray assembly. This compressed air mixes with liquid water in each working centrifugal nozzle, accelerating the breakdown of the liquid water into fine particles before spraying it out. The air supply system consists of an air filter, air compressor, air tank, air supply pipeline, air supply solenoid valve, air supply regulating valve (pressure regulating valve), and venting valve.

[0022] Air is filtered through an air filter before entering the air compressor for compression, removing moisture and impurities to ensure air purity and prevent contaminants from entering the nozzles and affecting atomization. Compressed gas is stored in an air tank to stabilize the supply pressure. After opening the supply solenoid valve, compressed air flows through the supply pipeline and the supply regulating valve to enter the spray assembly at the set pressure, distributing it to the air inlet of each working centrifugal nozzle. The air tank reduces supply pressure fluctuations, ensuring stable atomization. A vent valve is installed at the end of the supply pipeline. After system testing, the vent valve is opened to release residual compressed air in the pipeline, ensuring safe system shutdown.

[0023] The test and control system is used to collect system operating parameters, select control modes, and precisely control the water and gas supply pressures to ensure that the liquid water content and droplet size meet the requirements of the freezing test. It also monitors the overall system operation status in real time. The test and control system consists of a PLC programmable controller, a switch, a host computer, temperature sensors, pressure sensors, flow meters, and test monitoring software.

[0024] The PLC (Programmable Logic Controller) is the core control unit of the system. Through the DO (Distribution Module) expansion module, it controls the switching of various solenoid valves and actuators, including the water supply solenoid valve, air supply solenoid valve, and return water solenoid valve. Through the AI ​​(Analysis Module) expansion module, it acquires analog signals from pressure sensors (4–20 mA current signals), temperature sensors, and flow meters. Through the AO (Analog Module) expansion module, it outputs analog control signals to adjust the opening of the water supply regulating valve, back pressure regulating valve, and air supply regulating valve. Pressure sensors are installed on both the water supply and air supply pipelines, converting the pipeline pressure into a standard 4–20 mA current signal, which is then input to the PLC for feedback in the pressure closed-loop PID control.

[0025] The host computer serves as the human-machine interface, running the test monitoring software and communicating bidirectionally with the PLC programmable controller via Ethernet through a switch. Operators set target values ​​for water and air supply pressure, control mode (manual open-loop / automatic PID closed-loop), nozzle configuration, and system operation mode (spray mode / return water mode) on the host computer. The PLC programmable controller reports process parameters such as pressure, temperature, and flow rate to the host computer in real time. The test monitoring software uses configuration software to achieve online monitoring and process browsing of various process parameters, and supports historical data recording and query functions, providing support for the analysis and reproduction of test data.

[0026] like Figure 7 and Figure 8 As shown, the control method for the supercooled water droplet spray system provided by this invention includes four steps, S1 to S4: S1 Centrifugal nozzle system configuration; S2 Open-loop and closed-loop PID switching control of the regulating valve; S3 Supercooled water droplet cloud parameter calibration; S4 System operation and spraying. The detailed execution process of each step is as follows.

[0027] Step S1: Based on the windward cross-section dimensions of the aero-engine (or test piece) and the cloud coverage required for the icing test, the operator issues instructions on the host computer. The PLC programmable controller controls the water supply solenoid valves and air supply solenoid valves of each centrifugal nozzle to open and close one by one, and individually verifies the spray cone angle and effective spray range of each centrifugal nozzle. During verification, the system is in open-loop control mode of the regulating valve. Under given water and air supply pressures, each centrifugal nozzle is activated one by one and its spray pattern is observed. For nozzles with a spray cone angle that is too small, a spray range that does not meet the requirements, or that are blocked, the corresponding water supply solenoid valves and air supply solenoid valves are closed to disable them, and the reason for disabling is recorded for future maintenance.

[0028] After selecting the number of nozzles, the switching between spray mode and return water mode is achieved by configuring the on / off state of the solenoid valves in the nozzle water supply branch: In spray mode, the water supply solenoid valves of each working nozzle on the water supply pipeline are open, and liquid water enters the working nozzles through the water supply regulating valve to participate in atomization; in return water mode, the water supply solenoid valves on the water supply pipeline are closed, and the return water solenoid valves on the return water pipeline are open, and the return water pump starts to pump the remaining liquid water in the pipeline back to the insulated water storage tank. In addition, in step S1, the initial parameter settings for the system water supply pressure target value, air supply pressure target value, and manual / automatic PID control mode are also completed.

[0029] Step S2: Open-loop and closed-loop PID switching control of the regulating valve. This step is divided into two sub-stages: an open-loop stage and a closed-loop PID stage. The aim is to quickly establish reference operating condition data for water and gas supply using the open-loop mode, and then switch to the closed-loop PID mode to achieve precise and stable control of water and gas supply pressure.

[0030] (1) Open-loop stage. First, start the wind tunnel and adjust the liquid nitrogen injection rate according to the test settings. The liquid nitrogen (temperature approximately...) The gas (196℃) is atomized in the wind tunnel nozzle and evaporates rapidly, absorbing a large amount of heat from the circulating air in the wind tunnel, causing the wind tunnel intake temperature to drop rapidly. Based on the measurement data of the intake temperature sensor, when the intake temperature meets the test set value, the wind tunnel power section fan is started, and the low-temperature gas enters the wind tunnel flow channel, with the incoming flow velocity and temperature meeting the test requirements.

[0031] Once the air intake conditions are met, the host computer controls the regulating valves in open-loop mode: Given the opening degree of the water supply regulating valve (25% in this embodiment), the water supply pump is started, and the water supply solenoid valve is opened; given the opening degree of the air supply regulating valve (25% in this embodiment), the air supply solenoid valve is opened; the back pressure regulating valve is opened (15% opening degree), the return water pump is started, and the return water solenoid valve is opened. The PLC programmable controller collects the valve position feedback signals of the water supply regulating valve and the air supply regulating valve in real time. The error between the actual valve opening degree fed back by the system and the given opening degree is no greater than ±1%. After the open-loop operation stabilizes, the measured values ​​of the water supply pipeline pressure sensor and the air supply pipeline pressure sensor, as well as the flow rate data of the flow meter, are recorded as the initial setpoints for the closed-loop PID stage.

[0032] (2) Closed-loop PID stage. The host computer inputs the water supply pressure and gas supply pressure data recorded in the open-loop stage into the PLC programmable controller as the set value, and the system switches to the PID closed-loop control mode of the regulating valve.

[0033] The closed-loop PID control process for water supply pressure: The pressure sensor on the water supply pipeline converts the pipeline pressure into a 4-20mA current signal and inputs it into the PLC programmable controller. The PLC programmable controller calculates the deviation e(t) between the set pressure A(t) and the pressure sensor feedback value B(t), that is: e(t) = A(t). B(t).

[0034] The proportional (P), integral (I), and derivative (D) errors are linearly combined to form the control quantity, which controls the regulating valve. The control algorithm expression is as follows:

[0035] The controlled output of the PID controller. This is the proportionality coefficient. The integral time constant is... Given the differential time constant, the Laplace transform of the above equation yields the corresponding transfer function form:

[0036] Values ​​were obtained through simulation and multiple debugging sessions. It is 0.015. The value is 2. The value is 0.3; The PID controller transfer function of the valve closed-loop PID control algorithm is:

[0037] Precise control of the water supply pressure employs a composite control strategy of open-loop rapid response and closed-loop precise adjustment: First, an open-loop control algorithm quickly drives the water supply regulating valve to rapidly bring the water supply pressure close to the set value. Then, a closed-loop PID control algorithm is switched to precisely control the regulating valve, ultimately achieving stable maintenance of the water supply pressure at the nozzles. The back pressure regulating valve always operates in an open-loop manner, working in conjunction with the water supply regulating valve. By maintaining a fixed opening (15% in this embodiment), it maintains the back pressure in the return water pipeline, eliminating water supply pressure fluctuations caused by changes in the number of working nozzles and ensuring spray uniformity.

[0038] The closed-loop PID control principle for air supply pressure is the same as that for water supply pressure control: the pressure sensor on the air supply pipeline converts the pipeline pressure signal into a 4-20 mA current signal, which is input to the PLC programmable controller. The controller calculates the deviation between the set air pressure and the actual air pressure, executes PID calculations, and outputs an adjustment amount to control the opening of the air supply regulating valve, thereby achieving precise regulation of the air supply pipeline pressure. The PID parameters are the same as those for water supply pressure control. After the closed-loop debugging is completed, the wind tunnel is shut down, and step S3, the calibration of the subcooled water droplet cloud parameters, begins.

[0039] Step S3: Supercooled Water Droplet Cloud Parameter Calibration. The purpose of cloud parameter calibration is to confirm, before the formal icing test, whether the droplet size, liquid water content, and droplet distribution uniformity of the supercooled water droplet spray system under the current operating conditions meet the airworthiness requirements of the icing test. Calibration involves two types of measurements: droplet size and uniformity are calibrated using a holographic three-dimensional imaging measuring instrument; liquid water content is calibrated using the standard ice blade method.

[0040] (1) Calibration of water droplet size and uniformity. A holographic three-dimensional imaging measuring instrument was used to calibrate the particle diameter and cloud distribution uniformity of the atomized water droplets. During measurement, the holographic three-dimensional imaging measuring instrument was fixed at the center height of the icing wind tunnel test section using a dedicated support base, ensuring that the measuring instrument was aligned with the incoming flow direction. The wind tunnel was started, and the incoming flow velocity and temperature were adjusted to the test settings (in this embodiment, the incoming flow velocity was 24 m / s, and the incoming flow temperature was...). (9 ℃); The supercooled water droplet spray system is started, and the system is kept stable under the closed-loop PID control mode of the regulating valve, so that the cloud and fog are evenly distributed to the wind tunnel test section. The holographic three-dimensional imaging measuring instrument records the cloud and fog images under different working conditions. Based on the test parameters such as water flow rate, air supply pressure, and wind tunnel inflow velocity, the water droplet size (characterized by equivalent diameter) and water droplet distribution uniformity are obtained through image data analysis.

[0041] In this embodiment, the incoming flow velocity is 24 m / s and the incoming flow temperature is... Under operating conditions of 9 ℃, water supply pressure of 0.25 MPa, and air supply pressure of 0.30 MPa, the calibrated cloud and fog water droplet size was 20 μm, and the droplet distribution uniformity was 0.15 g / m². 3It meets the requirements of Appendix C of the airworthiness standard for supercooled water droplet cloud parameters.

[0042] (2) Liquid water content calibration. The liquid water content (LWC) was measured using the standard ice blade method. The standard ice blade was fixed to the measurement section inside the wind tunnel, ensuring that the ice blade section was perpendicular to the direction of the incoming flow velocity to ensure that the ice blade's collection efficiency met the assumptions of the theoretical calculation. The wind tunnel and spray system were started, and ice began to form at the leading edge of the ice blade under the low-temperature airflow. After continuous operation for a period of time (icing time t), the spray was stopped, the ice blade was removed, and the ice thickness ΔS at the leading edge of the ice blade was measured using vernier calipers. The final ice thickness was obtained by taking the average value of multiple repeated tests to eliminate random errors. The liquid water content was calculated according to the following formula:

[0043] In the formula: C is the unit conversion factor; ρ ice The density of the ice accumulation is taken as 900 kg / m³ (assuming the ice is pure ice); ΔS is the thickness of the ice accumulation at the leading edge of the skate blade (m); E b V is the collection coefficient for the ice skates, obtained through theoretical calculation or calibration based on the ice skate geometry and the incoming flow velocity; m t represents the inflow velocity (m / s); t represents the freezing time (s). In this embodiment, under the above operating conditions, the liquid water content LWC was measured to be 0.45 g / m³. 3 This meets the design requirements for liquid water content in the icing test and confirms that the cloud parameters sprayed by the supercooled water droplet spray system meet the airworthiness requirements for the icing test of the aero-engine.

[0044] Step S4: System operation and spraying. After the supercooled water droplet cloud parameters have been calibrated and passed in step S3, the system can be started according to the following procedure to conduct the formal icing test.

[0045] (1) Control parameter settings. Input the water supply pressure setting value and the gas supply pressure setting value on the host computer (determined according to the calibration result of step S3); select PID closed-loop mode for the regulating valve control mode; set the back pressure regulating valve opening (30% given in this embodiment) and the water supply regulating valve opening (100% given in this embodiment).

[0046] (2) System Startup Sequence. Each subsystem shall be started strictly according to the following sequence: First, start the wind tunnel's fan unit, open the liquid nitrogen control valve, start the liquid nitrogen pump, and adjust the liquid nitrogen injection rate to lower the wind tunnel's inlet temperature to and maintain it at the test set value (in this embodiment, ). After the temperature stabilizes (9 ℃), start the wind tunnel power section fan and adjust the incoming flow velocity to the test set value (24 m / s in this embodiment). After the air intake conditions are met, start the water supply pump and return water pump in sequence, and open the water supply solenoid valve, return water solenoid valve and air supply solenoid valve; the host computer selects the spray mode, and the supercooled water droplet spray system starts spraying mist. The regulating valve automatically maintains the water supply pressure and air supply pressure in PID closed-loop mode; after the spray system is running stably, start the aircraft engine (or test piece) to start the icing test.

[0047] (3) Operation monitoring. During the test, the host computer's test monitoring software monitored and recorded all process parameters of the entire system in real time (including water supply pressure, gas supply pressure, incoming flow temperature, incoming flow velocity, readings of each flow meter, opening degree of each valve, etc.). The system's PID control step response time was 0.5 s, the water supply pressure and gas supply pressure remained stable, and the cloud and fog parameters met the test requirements.

[0048] (4) System shutdown procedure. After the icing test is completed, the host computer shall execute the shutdown procedure in the following sequence: first, stop the operation of the aircraft engine (or test piece); then turn off the water supply pump and stop the water supply to the nozzle; stop the air supply and close the air supply solenoid valve; the host computer shall switch to the return water mode and start the return water pump to pump the remaining liquid water in the water supply pipeline back to the insulated water storage tank to prevent the water in the pipeline from freezing in the low temperature environment; open the vent valve to release the residual compressed gas in the air supply pipeline; turn off the wind tunnel power section fan and turn off the liquid nitrogen supply; finally, close all valves to complete the system shutdown.

[0049] Table 1 summarizes the key parameters of the supercooled water droplet spray system under the main test conditions in this embodiment.

[0050] Table 1

[0051] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. A supercooled water droplet spray system for icing tests of aircraft engines, comprising a spray assembly, a water supply system, an air supply system, and a test control system; the spray assembly comprising a plurality of centrifugal nozzles, a water supply pipeline, an air supply pipeline, and a control valve; the water supply system comprising a water tank, a water pump, a water supply pipeline, and a water supply regulating valve; the air supply system comprising an air compressor, an air supply pipeline, and an air supply regulating valve; the test control system comprising a controller, sensors, and a host computer; characterized in that, Each centrifugal nozzle has an independent water supply solenoid valve and an air supply solenoid valve connected to its water supply inlet and air supply inlet, respectively. The number of working nozzles can be configured by selectively controlling the on / off state of the water supply solenoid valve and air supply solenoid valve corresponding to each centrifugal nozzle. The water supply system also includes a return water pump, a return water pipeline, and a back pressure regulating valve; the water supply pipeline and the return water pipeline form a water supply and return circulation loop with the water storage tank as a common node; the back pressure regulating valve is connected in series on the return water pipeline and works in conjunction with the water supply regulating valve to stabilize the water supply pressure at the centrifugal nozzle; The test and control system includes a PLC programmable controller, a host computer, pressure sensors, and a flow meter. The pressure sensors are respectively installed on the water supply pipeline and the gas supply pipeline, converting the pipeline pressure into a current signal and inputting it into the PLC programmable controller. The PLC programmable controller implements PID closed-loop control on the water supply regulating valve and the gas supply regulating valve respectively based on the feedback signal from the pressure sensors.

2. The supercooled water droplet spray system according to claim 1, characterized in that, The spray assembly has a square frame structure, and the water supply pipeline and air supply pipeline are arranged side by side and both are perpendicular to the windward side; the spray assembly is installed inside the wind tunnel and located at a distance of not less than 2 m from the wind tunnel outlet section.

3. The supercooled water droplet spray system according to claim 1, characterized in that, The centrifugal nozzle has an internal mixing structure, in which liquid water and compressed air are mixed in the swirling groove inside the centrifugal nozzle before being sprayed out. By adjusting the water supply pressure and air supply pressure, the particle size of the sprayed cloud-like water droplets can be adjusted from 10 to 200 μm, the liquid water content can be adjusted from 0.3 to 2.0 g / m³, and the uniformity of liquid water content is less than or equal to ±0.15 g / m³.

4. The supercooled water droplet spray system according to claim 1, characterized in that, The water storage tank in the water supply system is an insulated water storage tank, and a water filter is connected in series between the water storage tank and the water supply pump; the air supply system also includes an air filter connected to the air intake side of the air compressor and an air storage tank connected to the air outlet side of the air compressor; the air supply pipeline of the spray assembly is provided with a vent valve at the end to remove residual gas in the air supply pipeline.

5. The supercooled water droplet spray system according to claim 1, characterized in that, The test control system also includes a switch and test monitoring software; the host computer establishes a communication connection with the PLC programmable controller via the switch through Ethernet; the PLC programmable controller realizes the switching control of the actuator, the acquisition of analog signals from the sensor, and the analog output control of the valve opening through the DO expansion module, AI expansion module, and AO expansion module, respectively; the test monitoring software uses configuration software to realize online monitoring and process browsing of the system's operating process parameters.

6. A control method for a supercooled water droplet spray system used in aircraft engine icing tests, wherein the supercooled water droplet spray system comprises a plurality of centrifugal nozzles, each centrifugal nozzle having an independent water supply solenoid valve and an air supply solenoid valve respectively installed at its water supply inlet and air supply inlet; a water supply regulating valve is connected in series on the system's water supply pipeline, a back pressure regulating valve is connected in series on the return water pipeline, and an air supply regulating valve is connected in series on the air supply pipeline; the water supply pipeline and the return water pipeline form a water supply and return circulation loop with a water storage tank as a common node; characterized in that... The control method includes the following steps: S1. By switching the water supply solenoid valve and air supply solenoid valve of each centrifugal nozzle, check the spray cone angle and spray range of each centrifugal nozzle one by one, select the number of working nozzles that meet the requirements of the freezing test, and close the water supply solenoid valve and air supply solenoid valve corresponding to the nozzles that are not in use; switch between spray mode and return water mode by configuring the on / off state of the solenoid valve of the nozzle water supply branch. S2. First, it operates in open-loop mode. The host computer sets the opening degree of the water supply regulating valve and the air supply regulating valve. The system feeds back the error between the actual valve opening degree and the set opening degree, and records the measurement data of the pressure sensor and flow meter under this condition. Then, it switches to PID closed-loop mode, using the water supply pressure and air supply pressure recorded in the open-loop stage as the set value. The PLC programmable controller calculates the deviation between the set pressure and the pressure sensor feedback value, executes PID calculation, and outputs the adjustment amount to control the opening degree of the water supply regulating valve and the air supply regulating valve respectively. The back pressure regulating valve always adopts an open-loop mode to cooperate with the water supply regulating valve to stabilize the water supply pressure at the centrifugal nozzle. S3. Under the conditions that the wind tunnel inflow velocity and temperature meet the test settings, the droplet size and droplet distribution uniformity after atomization are calibrated using a holographic three-dimensional imaging measuring instrument, and the liquid water content is measured using the standard ice knife method to confirm that the cloud and fog parameters sprayed by the supercooled water droplet spray system meet the requirements of the aero-engine icing test. S4. Set the target values ​​for water supply pressure and air supply pressure on the host computer. The regulating valve adopts PID closed-loop control. Start the water supply pump and return water pump in sequence, and open the water supply solenoid valve, return water solenoid valve and air supply solenoid valve. The host computer selects the spray mode and starts the test. After the supercooled water droplet spray system sprays the cloud mist, start the wind tunnel blowing and the aircraft engine in sequence to start the icing test. The test monitoring software of the host computer monitors the process parameters of the entire system in real time. After the test is completed, switch to the return water mode, open the vent valve to remove the residual gas in the system, and complete the system shutdown procedure.

7. The control method according to claim 6, characterized in that, In step S2, the water supply pressure control process is as follows: first, the open-loop control quickly responds to the water supply pressure setpoint, and then switches to PID closed-loop control for precise adjustment. The system step response time is 0.5 s. The gas supply pressure control adopts the same open-loop and PID closed-loop switching method as the water supply pressure control.

8. The control method according to claim 6, characterized in that, In step S3, the holographic three-dimensional imaging measuring instrument is fixed at the center height of the wind tunnel test section using a special support base, and records cloud and fog images under different working conditions. Data analysis yields the water droplet size and distribution uniformity. In the standard ice blade method, the ice blade cross-section is perpendicular to the direction of the incoming flow velocity. The ice thickness is obtained by taking the average value of multiple repeated tests, and then calculated according to the formula... Calculate the liquid water content using the formula, where C is the unit conversion factor, and ρ ice E represents the density of the ice, ΔS represents the thickness of the ice, and E represents the density of the ice. b V represents the collection coefficient of the ice skates. m t represents the incoming flow velocity, and t represents the freezing time.

9. The control method according to claim 6, characterized in that: In step S1, under open-loop control mode, the host computer sends instructions to each centrifugal nozzle one by one. Under given water supply pressure and air supply pressure, the spray cone angle and effective spray range of each centrifugal nozzle are individually checked. Based on the check results, the spatial distribution combination of the working nozzles is determined, and the final configuration of the number of working nozzles is completed by the on / off state of the corresponding solenoid valve.

10. The control method according to claim 6, characterized in that, In step S4, the system startup sequence is as follows: First, start the wind tunnel and adjust the incoming flow temperature and wind speed to the test set value; then start the water supply pump and return pump in sequence, and open the water supply solenoid valve, return solenoid valve and air supply solenoid valve; start the spray system to spray.

Images