Liquid water content resolving method based on infrared icing detector

Abstract

The invention relates to the field of aircraft icing detection, in particular to a liquid water content resolving method based on an infrared icing detector. Comprising the following steps: 1, calculating a corresponding relation between an air velocity v rod at the front end of an icing rod of the infrared icing detector and an aircraft airspeed v empty through simulation; 2, calculating a water drop collection coefficient eta of an icing rod plane through simulation; 3, establishing a corresponding relation between the ice density rho and the environment temperature T; step 4, acquiring an output voltage signal U of the infrared icing detector and calculating an icing thickness H; 5, the icing mass m in unit time is calculated according to the icing thickness; 6, calculating the volume V of the space swept by the icing rod in unit time; 7, the freezing rate is calculated; and 8, calculating the liquid water content.

Description

Technical Field

[0001] The invention belongs to the field of aircraft icing detection, and in particular relates to a method for calculating liquid water content based on an infrared icing detector. Background Art

[0002] During the flight of an aircraft, especially when passing through an environment with high liquid water content (LWC) and low temperature, ice often accumulates on key parts such as wings and engine air intakes, affecting flight safety and aircraft performance. To ensure the safety of the aircraft, timely and accurate detection of icing, especially detection and calculation of liquid water content in the air, is of great significance for preventing and mitigating the impact of icing. Therefore, many icing detection devices and methods have emerged.

[0003] At present, the ice detection technology widely used in aircraft mainly includes resonant ice detectors. This type of detector relies on the change of the vibration frequency of its working surface to detect the ice situation, and combines the change of its working frequency and the thickness of ice accumulation to infer the growth rate of the ice layer. Resonant ice detectors usually use a solution method based on empirical formulas to measure the liquid water content, that is, through known environmental parameters and ice formation rate, combined with empirical formulas, the liquid water content in the environment is inferred. The calculation process of this method is relatively simple, but because the theoretical basis of the empirical formula is relatively limited, its solution results are affected by many factors, such as temperature changes, detector installation position and structure, etc. This results in the low measurement accuracy of the liquid water content of the resonant ice detector under different flight conditions, especially when the environmental conditions are more complex, it cannot provide stable and accurate measurement results.

[0004] In addition, the traditional resonant ice detector solution method often has nonlinear deviations when dealing with high liquid water content, which further reduces the accuracy of the data. During the flight of an aircraft, accurately understanding the liquid water content in the air is the key to preventing icing, which is directly related to the prediction of icing risks and the timing of starting the aircraft's automatic de-icing system. Existing technical means have obvious shortcomings in this regard and urgently need to be improved. Summary of the invention

[0005] Purpose of the invention: In order to solve the technical problems existing in this field, the present invention proposes a method for calculating liquid water content based on an infrared ice detector. The method utilizes the structure and working principle of the infrared ice detector and combines it with an advanced calculation algorithm to improve the measurement accuracy of liquid water content and provide a more reliable solution for aircraft ice detection.

[0006] The technical solution of the present invention:

[0007] A method for calculating liquid water content based on an infrared ice detector comprises the following steps:

[0008] Step 1: Calculate the air velocity ν at the front end of the infrared ice detector ice rod through simulation 杆 and the aircraft airspeed ν 空 The corresponding relationship;

[0009] Step 2: Calculate the water droplet collection coefficient η on the ice rod plane through simulation;

[0010] Step 3: Establish the corresponding relationship between ice density ρ and ambient temperature T;

[0011] Step 4: Collect the output voltage signal U of the infrared ice detector and calculate the ice thickness H;

[0012] Step 5: Calculate the ice mass m per unit time according to the ice thickness;

[0013] Step 6: Calculate the volume V of the space swept by the icing rod per unit time;

[0014] Step 7: Calculate the freezing rate;

[0015] Step 8: Calculate the liquid water content.

[0016] Furthermore, in step 1, the specific process is as follows: modeling the infrared ice detector;

[0017] The air velocity at 5 mm from the front end of the icing rod was simulated at different airspeeds, and the corresponding relationship between the air velocity at the front end of the icing rod and the aircraft airspeed was obtained.

[0018] ν 杆 =0.511v 空 +42.69

[0019] For rotorcraft, the airspeed will affect the induction flow field of the infrared ice detector. Adding the airspeed value when calculating the liquid water content can improve the calculation accuracy.

[0020] Furthermore, in step 3, the corresponding relationship between ice density ρ and ambient temperature T is as follows

[0021] ρ=0.0001T 2 +0.0123T+0.9528

[0022] For aircraft icing, there are two types of ice: clear ice and frost ice. The density difference between the two is large, which has a great impact on the calculation of icing quality. By establishing the relationship between ice density and temperature, the calculation accuracy can be further improved.

[0023] Further, in step 4, the formula for ice thickness H is as follows:

[0024] H=-0.35U+1.06

[0025] Wherein, H represents the ice thickness and U represents the output voltage signal of the infrared ice detector.

[0026] The relationship between ice thickness and voltage is approximately linear, which makes it easy to calculate the ice rate over multiple unit times.

[0027] Further, in step 5, the calculation formula of the ice mass m is as follows:

[0028] m=L×W×H×ρ / η

[0029] Wherein, L and W represent the length and width of the rectangular plane of the ice rod, respectively.

[0030] The rectangular plane in front of the ice rod makes the ice more regular, approximating a cube, which makes it easier to calculate the ice volume.

[0031] Further, in step 6, the calculation formula of the space volume V is as follows:

[0032] V=L×W×ν 杆 ×Δt

[0033] ν 杆 ×Δt represents the distance traveled by the icing rod relative to the icing environment per unit time;

[0034] ν 杆 Indicates the air velocity at the front end of the ice rod.

[0035] Further, in step seven, the freezing rate calculation formula is as follows:

[0036] ΔH / Δt=(-0.35U+1.06) / Δt

[0037] ΔH represents the ice thickness per unit time, U is the voltage, and Δt represents the unit time.

[0038] Further, in step eight, the liquid water content LWC is calculated as follows:

[0039] LWC=m / V=(L×W×ΔH×ρ / η) / (L×W×ν 杆 ×Δt)

[0040] LWC=(ΔH×ρ) / (ν 杆 ×Δt×η)

[0041] Where L and W are the rectangular plane dimensions of the windward side of the infrared ice detector ice rod, ν 杆 is the wind speed in front of the icing rod, ρ is the density of ice, η is the water drop collection coefficient of the icing rod, U is the collected voltage value, Δt is the unit time, and H is the thickness of the ice.

[0042] Beneficial Effects

[0043] The liquid water content calculation method proposed in the present invention has the characteristics of high reliability, simple measurement, strong applicability, etc. The simulation, circuit, and structural solutions required to implement the method all have mature and reliable solutions and are easy to assemble.

[0044] Compared with the traditional resonant ice detector, the method of the present invention has improved measurement accuracy. The resonant ice detector uses an empirical formula to measure the liquid water content with an accuracy of generally ±20%, while the ice detector based on this method can achieve a measurement accuracy of ±10%.

[0045] The method of the present invention can accurately measure the liquid water content under a variety of environmental conditions, effectively improving the sensitivity of the detector to tiny changes in liquid water content and ensuring the accuracy of the measurement results. The method supports real-time monitoring of changes in liquid water content and can respond quickly to changes. It is suitable for scenarios that require rapid detection and judgment of icing risks, such as aviation, meteorology, and transportation. At the same time, the method also has good versatility and can be widely used in the measurement of liquid water content under various icing conditions, including high humidity, low temperature environments, and complex meteorological conditions, and has a wide range of application scenarios.

[0046] In addition, the method of the present invention can also be used in ground facilities such as ice wind tunnels that need to measure liquid water content. Compared with other methods, the liquid water content detector made according to this method can quickly and in real time measure the liquid water content in the ice wind tunnel, providing an effective measurement method for wind tunnel calibration and test state point calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A simplified digital-analog diagram of the infrared ice detector on which the present invention is based;

[0048] Figure 2 The step of calculating the liquid water content of the present invention;

[0049] Figure 3 This is a working principle diagram of the optical fiber ice detector according to Example 2 of the present invention. DETAILED DESCRIPTION

[0050] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings.

[0051] A method for calculating liquid water content based on infrared ice detectors, the process is as follows:

[0052] Step 1: Calculate the corresponding relationship between the velocity in front of the probe ice rod and the airspeed through simulation. Perform flow field simulation on the ice detector and establish the relationship between the velocity in front of the ice rod and the airspeed, preferably a linear relationship.

[0053] ν 杆 =0.511v 空+42.69

[0054] Normally the helicopter airspeed is 77m / s, and the speed before the ice rod is calculated to be 82m / s, that is, ν 杆 =82m / s.

[0055] Step 2: Calculate the water droplet collection coefficient on the ice rod plane through simulation. Based on the simulation of the detector flow field, calculate the water droplet collection coefficient η on the ice rod plane.

[0056] The water droplet collection coefficient at the center of the ice rod plane was simulated to be 0.95.

[0057] Step 3: Establish the corresponding relationship between ice density ρ and ambient temperature T. Since different ice types and densities are formed at different temperatures, it is necessary to establish the relationship between temperature and ice density.

[0058] ρ=0.0001T 2 +0.0123T+0.9528

[0059] When the ambient temperature is -10°C, the density of ice is 0.8398 g / cm 3 .

[0060] Step 4: Collect the voltage signal V related to ice thickness 1 When the infrared ice detector is in normal use, a voltage signal related to ice thickness is collected. The thicker the ice on the ice rod, the smaller the voltage value.

[0061] H=-0.35U 1 +1.06

[0062] Within 10 seconds, the collected voltage value dropped from 2.9 V to 1.4 V. The change in ice thickness was calculated to be ΔH = 0.5 mm.

[0063] Step 5: Calculate the ice mass per unit time. When the ice detector works normally, ice gradually forms on the ice rod, and the voltage value gradually decreases until the ice thickness reaches a certain value. The ice rod is heated to remove ice, and the voltage value returns to the initial value. This is called a normal cycle. The ice mass per unit time in the ice cycle is

[0064] m=L×W×H×ρ / η

[0065] L and W will be eliminated in the final formula and can be temporarily ignored.

[0066] Step 6: Calculate the volume of space swept by the freezing rod per unit time.

[0067] V=L×W×ν 杆 ×Δt

[0068] Step 8: After unit conversion, calculate the freezing rate and liquid water content.

[0069] LWC=(ΔH×ρ) / (ν 杆 ×Δt×η)

[0070] LWC=(0.5×10 -3 ×0.8398×10 6 ) / (82×10×0.95)=0.53g / m 3

[0071] That is, when the ambient temperature is -10°C and the aircraft airspeed is 77m / s, the voltage value collected by the infrared ice detector drops from 2.9V to 1.4V within 10s. At this time, the liquid water content of the aircraft environment can be calculated according to the formula of the present invention to be 0.53g / 3 m.

[0072] In the formula,

[0073] Furthermore, the diameter of the ice rod is preferably 3 mm. If the diameter of the ice rod is too large, water droplets with small particle sizes will bypass the ice rod with the airflow. If the diameter of the ice rod is too small, water droplets with large particle sizes will splash when they hit the ice rod. Both situations affect the accuracy of calculating LWC.

[0074] Furthermore, the plane depth of the freezing rod does not exceed 1 / 3 of the diameter of the freezing rod, which can ensure that the shape of the ice in front of the freezing rod is relatively regular and the calculated ice mass is more accurate.

[0075] Furthermore, the bleed air pressure needs to be kept stable, or a bleed air pressure monitoring module is added to improve the accuracy of the wind speed in front of the icing rod.

[0076] Furthermore, the voltage signal needs to be filtered during calculation, because in the actual process of the detector, impurities may pass through the optical path of the icing rod, or the loosely frozen ice particles on the icing rod may be blown away by the wind, causing interference to the voltage signal. Filtering the voltage signal can make the measurement of LWC more stable.

[0077] Furthermore, the airspeed preferably uses the real-time airspeed sent from the aircraft to the ice detector to ensure the timeliness of the calculation result.

[0078] Furthermore, the freezing rate in the last formula can be converted according to the voltage change rate. The formula is based on the fact that both are linear functions of time. The relationship between the freezing rate and time can be fitted with multiple polynomials to obtain a more accurate LWC value.

[0079] Furthermore, the temperature is preferably the real-time static temperature sent from the aircraft to the ice detector, so as to ensure the timeliness of the calculation results.

[0080] Furthermore, when the ice thickness of the ice rod is preferably no more than 1 mm, the ice rod is started to heat and de-ice, so as to ensure that the ice shape is relatively regular, which is beneficial to the accuracy of calculating the ice mass.

[0081] Furthermore, the time period selected by the method when calculating the voltage change rate is preferably in the middle period of the freezing cycle, and the change rate in the middle period has small fluctuations and higher measurement accuracy.

[0082] Example 1

[0083] First, as attached Figure 1 , Attachment Figure 2 As shown, the present invention discloses a method for calculating liquid water content based on an infrared ice detector, and the method for calculating liquid water content comprises the following steps:

[0084] 1) The corresponding relationship between the speed in front of the probe icing rod and the airspeed is calculated through simulation.

[0085] Infrared ice detectors are usually used in conjunction with rotorcraft. In order to realize ice detection when the rotorcraft is at low speed or hovering, the infrared ice detector will use an air bleed device, which causes a certain difference between the speed in front of the detector's ice rod and the aircraft's airspeed. The speed in front of the detector's ice rod is difficult to measure, but its corresponding relationship can be obtained by simulating it with the aircraft's airspeed.

[0086] During simulation, the probe digital model is simplified, the air bleed conditions for actual use are set, and the speed 5 mm in front of the icing rod at different airspeeds is simulated respectively. The airspeed can be selected within the airspeed range of the actual supporting aircraft.

[0087] 2) Calculate the water droplet collection coefficient η on the ice rod plane through simulation.

[0088] When an aircraft flies under icing weather conditions, the supercooled water droplets suspended in the airflow have a greater mass and inertia than air particles, so the water droplets will form their own circumferential motion trajectories. Supercooled water droplets of different sizes in the air have different trajectories in the airflow due to different forces. Small water droplets have small inertia, and when they encounter an ice rod, they will flow around from both sides instead of freezing on the ice rod. Large water droplets have large inertia, and when they encounter an ice rod, they will collide with the ice rod to form ice.

[0089] The water droplet collection coefficient η on the rectangular plane of the ice rod can be calculated through simulation, which helps to accurately calculate the mass of liquid water in the area swept by the ice rod.

[0090] 3) Establish the corresponding relationship between ice density ρ and ambient temperature T.

[0091] To calculate the liquid water content, the mass of the liquid water droplets must be known. The method of the present invention is to collect ice with an ice rod. The ice rod forms different ice types at different temperatures. When the temperature is high, the ice type formed by the ice rod is clear ice, and when the temperature is low, the ice type is frost ice. The density of the two is very different. The mass of the liquid water droplets is determined by the corresponding relationship between the density and temperature calibrated in advance. Since the ice types formed at different temperatures are different, the density is also different, so it is necessary to establish the relationship between temperature and ice density.

[0092] ρ=0.0001T2+0.0123T+0.9528

[0093] 4) Collect the voltage signal U related to ice thickness.

[0094] When the infrared ice detector is in normal use, three optical paths work normally to collect voltage signals related to ice thickness. The thicker the ice on the ice rod, the smaller the voltage value. In actual work, the median of the voltage values ​​of the three optical paths is usually selected as the only valid value and the voltage value involved in subsequent calculations.

[0095] ν 杆 =0.511v 空 +42.69

[0096] 5) Calculate the mass of ice per unit time.

[0097] When the ice detector works normally, ice gradually forms on the ice rod, and the voltage value gradually decreases until the ice thickness reaches a certain value. The ice rod is heated to remove ice, and the voltage value returns to the initial value. This is called a normal cycle. In order to collect more ice and ensure the regular shape of ice, a rectangular plane is designed on the windward side of the ice rod. According to the following formula, L and W represent the length and width of the rectangular plane of the ice rod, H represents the thickness of ice, and L×W×H×ρ represents the mass of ice on the ice rod per unit time. However, not all water droplets in the area swept by the ice rod can freeze on the ice rod, so it must be divided by the water drop collection coefficient of the current state, so that the mass of liquid water in the area swept by the ice rod is:

[0098] m=L×W×H×ρ / η

[0099] 6) Calculate the volume of space swept by the freezing rod per unit time.

[0100] In order to collect more ice and ensure the regular shape of ice, a rectangular plane is designed on the windward side of the ice rod. According to the following formula, L and W represent the length and width of the rectangular plane of the ice rod, respectively, and ν 杆 ×Δt

[0101] It represents the distance traveled by the freezing rod relative to the freezing environment per unit time. The three are multiplied together to obtain the volume of space swept by the freezing rod per unit time, which provides volume data for the subsequent calculation of liquid water content.

[0102] V=L×W×ν 杆 ×Δt

[0103] 7) Freezing rate calculation or voltage change rate conversion.

[0104] In the present invention, the freezing rate can be directly calculated. In some ice detectors, the freezing rod is located inside the probe, and in each freezing cycle of the detector, the thickness of the ice on the freezing rod does not exceed 1 mm, so it is difficult to directly measure the ice thickness of the freezing rod; at the same time, the freezing rod is located inside the probe, so that the commonly used three-dimensional ice shape scanning equipment cannot scan it, and it can be solved by converting it into a voltage change rate.

[0105] The relationship between ice thickness and time can be judged based on actual tests. For example, use other probes that are easy to measure ice thickness and observe the curve of the relationship between actual ice thickness and time. If the curve changes greatly, the section closest to linearity can be selected as the measurement.

[0106] According to the actual device measurement process, the relationship between the voltage value and time is also close to linear, and the error of fitting using a linear function is small.

[0107] 8) Calculate the liquid water content.

[0108] The calculation of LWC is shown in the following formula:

[0109] LWC=(ΔH×ρ) / (ν 杆 ×Δt×η)

[0110] When calculating, please pay attention to the unit conversion of each parameter.

[0111] Example 2

[0112] In this embodiment, for other types of ice detectors, the liquid water content can also be calculated according to this method. In fixed-wing aircraft, ice detectors are often required to be designed to be flat. For ice detectors with flat designs, there are fiber optic ice detectors and ultrasonic ice detectors, both of which can measure the ice rate and have similar measurement processes. Both have a detection window on the wing and output a voltage value according to the ice thickness.

[0113] Taking the fiber optic ice detector as an example, the thicker the ice on the detection window, the smaller the output voltage value. The following are the calculation steps:

[0114] Step 1: Calculate the corresponding relationship between the speed in front of the detection window and the airspeed through simulation. Since the fiber optic ice detector has no additional air bleed, the speed at the detection window is the aircraft speed. Take the aircraft speed as 100m / s as an example.

[0115] Step 2: Calculate the water droplet collection coefficient η of the detection window through simulation.

[0116] The fiber optic ice detector was installed on the leading edge of the fixed-wing wing, and the droplet collection coefficient was calculated to be 0.98.

[0117] Step 3: Establish the corresponding relationship between ice density ρ and ambient temperature T.

[0118] ρ=0.0001T 2 +0.0123T+0.9528

[0119] When the ambient temperature is -20°C, the ice density is 0.7468 g / cm 3 .

[0120] Step 4: Collect the voltage signal U related to ice thickness. When the optical fiber ice detector is used normally, a single optical path works normally to collect the voltage signal related to ice thickness. The thicker the ice on the ice rod, the smaller the voltage value.

[0121] H=-0.51U 1 +3.06

[0122] Within 15 seconds, the collected voltage value dropped from 3.2 V to 2 V. The change in ice thickness was calculated to be ΔH = 1.38 mm.

[0123] Step 5: Calculate the ice mass per unit time. When the ice detector is working normally, ice gradually forms on the detection window, and the voltage value gradually decreases. When the ice thickness reaches a certain value, the detection window is heated to de-ice, and the voltage value returns to the initial value. This is called a normal cycle. The window ice mass per unit time is

[0124] m=L×W×H×ρ / η

[0125] L and W will be eliminated in the final formula and can be temporarily ignored.

[0126] L and W are the length and width of the detection window, and H is the ice thickness.

[0127] Step 6: Calculate the volume of space swept by the detection window per unit time.

[0128] V=L×W×ν 杆 ×Δt

[0129] Step 7: Calculate the freezing rate and liquid water content after converting units

[0130] LWC=(ΔH×ρ) / (ν 窗 ×Δt×η)

[0131] LWC=(1.38×10 -3 ×0.7468×10 6 ) / (100×15×0.98)=0.68g / m 3

[0132] That is, when the ambient temperature is -20°C and the aircraft airspeed is 100m / s, the voltage value collected by the optical fiber ice detector drops from 3.2V to 2V within 15s. At this time, according to the formula of the present invention, it can be calculated that the liquid water content of the aircraft environment is 0.68g / 3 m.

[0133] In summary, the present invention proposes a method for measuring liquid water content based on an infrared ice detector. The method simulates and calculates the corresponding relationship between the velocity in front of the probe ice rod and the airspeed, calculates the water droplet collection coefficient on the ice rod plane, establishes the corresponding relationship between ice density ρ and ambient temperature T, then collects the voltage signal related to ice thickness, calculates the ice mass per unit time and the space volume swept by the ice rod, and finally calculates the liquid water content to obtain the liquid water content solution formula of the detector. It can be used for aircraft ice detection technology, improves the accuracy of aircraft measurement of liquid water content, and has great practical application value.

[0134] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the scope disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for calculating liquid water content based on an infrared ice detector, characterized in that: The following steps are involved: Step 1: Calculate the air velocity ν at the front end of the infrared ice detector ice rod through simulation 杆 and the aircraft airspeed ν 空 The corresponding relationship; Step 2: Calculate the water droplet collection coefficient η on the ice rod plane through simulation; Step 3: Establish the corresponding relationship between ice density ρ and ambient temperature T; Step 4: Collect the output voltage signal U of the infrared ice detector and calculate the ice thickness H; Step 5: Calculate the ice mass m per unit time according to the ice thickness; Step 6: Calculate the volume V of space swept by the icing rod per unit time; Step 7: Calculate the freezing rate; Step 8: Calculate the liquid water content.

2. The method according to claim 1, characterized in that: In step 1, the specific process is as follows: model the infrared ice detector; The air velocity at the front end of the ice rod 5mm is simulated at different airspeeds when the bleed air pressure of the infrared ice detector is 0.17MPa, and the air velocity ν at the front end of the ice rod is obtained. 杆 and the aircraft airspeed ν 空 The corresponding relationship: n 杆 =0.511ν 空 +42.

69.

3. The method according to claim 2, characterized in that: In step 3, the corresponding relationship between ice density ρ and ambient temperature T is as follows: p=0.0001T 2 -0.0123T+0.9528.

4. The method according to claim 3, characterized in that: In step 4, the formula for ice thickness H is as follows: H=-0.35U1+1.06 Wherein, H represents the ice thickness and U represents the output voltage signal of the infrared ice detector.

5. The method according to claim 4, characterized in that: In step 5, the calculation formula of ice mass m is as follows: m=L×W×H×ρ / η Wherein, L and W represent the length and width of the rectangular plane of the ice rod, respectively.

6. The method according to claim 5, characterized in that: In step 6, the calculation formula of the space volume V is as follows: V=L×W×ν 杆 ×Δt ν 杆 ×Δt represents the distance traveled by the icing rod relative to the icing environment per unit time; ν 杆 Indicates the air velocity at the front end of the ice rod.

7. The method according to claim 6, characterized in that: In step 7, the freezing rate calculation formula is as follows: H / Δt=(-0.35U+1.06) / Δt U is voltage and Δt represents unit time.

8. The method according to claim 7, characterized in that: In step eight, the liquid water content LWC is calculated using the following formula: LWC=m / V=(L×W×H×ρ / η) / (L×W×ν 杆 ×Δt) LWC=(H×ρ) / (ν 杆 ×Δt×η) Where L and W are the rectangular plane dimensions of the windward side of the infrared ice detector ice rod, ν 杆 is the wind speed in front of the icing rod, ρ is the density of ice, η is the water drop collection coefficient of the icing rod, U is the collected voltage value, Δt is the unit time, and H is the thickness of the ice.

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