A method for calculating liquid water content based on an infrared icing detector

Abstract

This application relates to the field of aircraft icing detection, specifically to a method for calculating liquid water content based on an infrared icing detector. It includes the following steps: Step 1: Calculate the air velocity ν at the tip of the icing rod of the infrared icing detector through simulation. 杆 Aircraft airspeed ν 空 Step 1: Calculate the water droplet collection coefficient η on the ice rod plane through simulation; Step 2: Establish the correspondence between ice density ρ and ambient temperature T; Step 3: Collect the output voltage signal U of the infrared icing detector and calculate the ice thickness H; Step 4: Calculate the ice mass m per unit time based on the ice thickness; Step 5: Calculate the spatial volume V swept by the ice rod per unit time; Step 6: Calculate the icing rate; Step 7: Calculate the liquid water content.

Description

Technical Field

[0001] This invention belongs to the field of aircraft icing detection, specifically relating to a method for calculating liquid water content based on an infrared icing detector. Background Technology

[0002] During flight, especially when passing through environments with high liquid water content (LWC) and low temperatures, aircraft often experience ice buildup on critical components such as wings and engine intakes, impacting flight safety and aircraft performance. To ensure aircraft safety, timely and accurate detection of icing, particularly detecting and calculating the liquid water content in the air, is crucial for preventing and mitigating its effects. Consequently, numerous icing detection devices and methods have been developed.

[0003] Currently, the icing detection technology widely used on aircraft mainly includes resonant icing detectors. These detectors rely on changes in the vibration frequency of their working surface to detect icing, and then combine this change in operating frequency with ice thickness to calculate the ice growth rate. Resonant icing detectors typically use empirical formulas to measure liquid water content; that is, they deduce the liquid water content in the environment from known environmental parameters and icing rates using empirical formulas. While this method simplifies the calculation process, the theoretical basis of these empirical formulas is limited, and the results are affected by many factors, such as temperature variations, detector installation location, and structure. This results in lower accuracy of liquid water content measurement by resonant icing detectors under different flight conditions, especially in complex environmental conditions, where they cannot provide stable and accurate measurement results.

[0004] Furthermore, traditional resonant icing detectors often exhibit nonlinear biases when handling high liquid water content, further reducing data accuracy. During aircraft flight, accurately determining the liquid water content in the air is crucial for preventing icing, directly impacting icing risk prediction and the timing of automatic de-icing system activation. Existing technologies have significant shortcomings in this regard and urgently need improvement. Summary of the Invention

[0005] Objective: To address the existing technical problems in this field, this invention proposes a method for calculating liquid water content based on an infrared icing detector. This method utilizes the structure and working principle of the infrared icing detector, combined with advanced calculation algorithms, to improve the measurement accuracy of liquid water content, providing a more reliable solution for aircraft icing detection.

[0006] The technical solution of this invention:

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

[0008] Step 1: Calculate the air velocity ν at the tip of the icing rod of the infrared icing detector through simulation. 杆 Aircraft airspeed ν 空 The correspondence;

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

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

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

[0012] Step 5: Calculate the mass of ice formed per unit time, m, based on the ice thickness;

[0013] Step 6: Calculate the volume V of 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 one, the specific process is as follows: modeling the infrared icing detector;

[0017] The air velocity at 5 mm from the tip of the icing rod was simulated at different airspeeds to obtain the correspondence between the air velocity at the tip of the icing rod and the aircraft airspeed.

[0018] ν 杆 =0.511ν 空 +42.69

[0019] For rotorcraft, airspeed affects the airflow field of infrared icing detectors. Including airspeed values ​​when calculating liquid water content can improve calculation accuracy.

[0020] Furthermore, in step three, the 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 is a distinction between clear ice and frost ice, and the two have a large difference in density, which has a significant impact on the calculation of icing quality. By establishing the relationship between icing density and temperature, the calculation accuracy can be further improved.

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

[0024] H = -0.35U + 1.06

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

[0026] The ice thickness has an approximately linear relationship with voltage, which makes it easy to calculate the ice formation rate over multiple unit times.

[0027] Furthermore, in step five, the formula for calculating the ice mass m is as follows:

[0028] m=L×W×H×ρ / η

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

[0030] The rectangular plane in front of the icing rod makes the ice formation more regular, approximating a cube, which facilitates the calculation of the ice volume.

[0031] Furthermore, in step six, the formula for calculating the spatial 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 This indicates the airflow velocity at the tip of the icing rod.

[0035] Furthermore, in step seven, the formula for calculating the freezing rate 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] Furthermore, in step eight, the formula for calculating the liquid water content (LWC) is 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 planar dimensions of the windward side of the icing rod of the infrared icing detector, and ν 杆 ρ is the wind speed in front of the icing rod, η is the water droplet collection coefficient of the icing rod, U is the collected voltage value, Δt is the unit time, and H is the ice thickness.

[0042] Beneficial effects

[0043] The liquid water content calculation method proposed in this invention has the characteristics of high reliability, simple measurement, and strong applicability. There are many mature and reliable solutions for the simulation, circuit and structural schemes required to implement this method, and they are easy to assemble.

[0044] Compared to traditional resonant icing detectors, the method of this invention improves measurement accuracy. Resonant icing detectors, using empirical formulas, typically achieve an accuracy of ±20% in measuring liquid water content, while the icing detector based on this method can reach an accuracy of ±10%.

[0045] This invention enables precise measurement of liquid water content under various environmental conditions, effectively improving the detector's sensitivity to minute changes in liquid water content and ensuring the accuracy of measurement results. The method supports real-time monitoring of liquid water content changes and can respond quickly to changes, making it suitable for scenarios requiring rapid detection and assessment of icing risks, such as aviation, meteorology, and transportation. Furthermore, this method exhibits good versatility and can be widely applied to liquid water content measurement under various icing conditions, including high humidity, low temperature environments, and complex meteorological conditions, thus having broad application scenarios.

[0046] Furthermore, the method of this invention can also be used in ground facilities such as ice wind tunnels where liquid water content needs to be measured. 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 ice wind tunnels, providing an effective measurement means for wind tunnel calibration and test state point calibration. Attached Figure Description

[0047] Figure 1 This is a simplified digital model of the infrared icing detector on which this invention is based;

[0048] Figure 2 This is the liquid water content calculation step of the present invention;

[0049] Figure 3 This is a schematic diagram illustrating the working principle of the fiber optic icing detector according to Embodiment 2 of the present invention. Detailed Implementation

[0050] The specific implementation of the present invention will be further described below with reference to the accompanying drawings.

[0051] A method for calculating liquid water content based on an infrared icing detector is described below:

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

[0053] ν 杆 =0.511ν 空+42.69

[0054] The typical airspeed of a helicopter is 77 m / s, and the calculated velocity before the icing rod is 82 m / s, i.e., ν 杆 =82m / s.

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

[0056] The water droplet collection coefficient at the center of the icing rod plane was 0.95 after simulation.

[0057] Step 3: Establish the relationship between ice density ρ and ambient temperature T. Since ice forms different shapes and densities 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] At an ambient temperature of -10℃, the density of ice is 0.8398 g / cm³. 3 .

[0060] Step 4: Collect the voltage signal V1 related to ice thickness. When the infrared icing detector is in normal use, collect the voltage signal related to ice thickness. The thicker the ice on the icing rod, the smaller the voltage value.

[0061] H = -0.35U1 + 1.06

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

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

[0064] m=L×W×H×ρ / η

[0065] L and W will be eliminated in the final formula, so they can be temporarily omitted from the calculation.

[0066] Step 6: Calculate the volume of space swept by the icing 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℃ and the aircraft airspeed is 77m / s, the voltage value collected by the infrared icing detector drops from 2.9V to 1.4V within 10 seconds. Based on the formula of this invention, the liquid water content of the environment in which the aircraft is located can be calculated to be 0.53g / L. 3 m.

[0072] In the formula,

[0073] Furthermore, the diameter of the icing rod is preferably 3mm. If the diameter of the icing rod is too large, small water droplets will be carried away by the airflow and bypass the icing rod. If the diameter of the icing rod is too small, large water droplets will splash when they hit the icing rod. Both situations will affect the accuracy of LWC calculation.

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

[0075] Furthermore, the bleed air pressure needs to be kept stable, or an bleed air pressure monitoring module can be 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 impurities may pass through the optical path of the icing rod during the actual process of the detector, or loose 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 LWC measurement more stable.

[0077] Furthermore, the airspeed is preferentially used based on the real-time airspeed sent from the aircraft to the icing detector to ensure the timeliness of the calculation results.

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

[0079] Furthermore, the temperature is preferably based on real-time static temperature data sent from the spacecraft to the icing detector, ensuring the timeliness of the calculation results.

[0080] Furthermore, the ice thickness on the icing rod should preferably not exceed 1 mm before heating and de-icing to ensure a relatively regular ice shape, which is beneficial for the accuracy of calculating the ice quality.

[0081] Furthermore, the time period selected by the method when calculating the voltage change rate is preferably located in the middle of the icing cycle, as the change rate fluctuates less in the middle period and the measurement accuracy is higher.

[0082] Example 1

[0083] Firstly, as attached Figure 1 Appendix Figure 2 As shown, this invention discloses a method for calculating liquid water content based on an infrared icing detector. The method for calculating liquid water content consists of the following steps:

[0084] 1) The relationship between the velocity of the probe before the icing rod and the air speed was calculated through simulation.

[0085] Infrared icing detectors are typically used in conjunction with rotorcraft. To detect icing in rotorcraft at low speeds or while hovering, infrared icing detectors use bleed air devices. This results in a certain difference between the velocity of the detector's icing rod and the airspeed of the aircraft. While the velocity of the detector's icing rod is difficult to measure, its relationship can be obtained by simulating it with the airspeed of the aircraft.

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

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

[0088] When an aircraft flies in icing weather conditions, supercooled water droplets suspended in the airflow have a greater mass and inertia than air particles. Therefore, the water droplets will form their own flow trajectory. Supercooled water droplets of different sizes in the airflow will have different trajectories due to different forces. Small water droplets have less inertia and will flow around the ice rods instead of freezing on them when they encounter them. Large water droplets have greater inertia and will collide with the ice rods when they encounter them, forming ice.

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

[0090] 3) Establish the correspondence 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 this invention involves collecting ice using an icing rod. The ice formed on the icing rod changes shape at different temperatures. At higher temperatures, the ice is clear ice, while at lower temperatures, it is frost ice. The densities of these two types differ significantly. By using a pre-defined density-temperature relationship, the mass of the liquid water droplets can be determined. Since the ice forms at different temperatures have different densities, it is necessary to establish a relationship between temperature and ice density.

[0092] ρ = 0.0001T² + 0.0123T + 0.9528

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

[0094] When the infrared icing detector is in normal use, three optical paths operate normally, collecting voltage signals related to ice thickness. The thicker the ice on the icing rod, the lower the voltage value. In actual operation, the median of the voltage values ​​from the three optical paths is usually selected as the sole valid value for subsequent calculations.

[0095] ν 杆 =0.511ν 空 +42.69

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

[0097] When the icing detector is working normally, ice gradually forms on the icing rod, and the voltage value gradually decreases until the ice thickness reaches a certain value. Then, the icing rod is heated to remove the ice, and the voltage value returns to its initial value. This is called a normal cycle. To collect more ice and ensure the regular shape of the ice, a rectangular plane is designed on the windward side of the icing rod. According to the following formula, L and W represent the length and width of the rectangular plane of the icing rod, respectively, H represents the ice thickness, and L×W×H×ρ represents the mass of ice formed on the icing rod per unit time. However, not all water droplets in the area swept by the icing rod will freeze on the icing rod, so it is necessary to divide by the current water droplet collection coefficient to obtain the mass of liquid water in the area swept by the icing rod:

[0098] m=L×W×H×ρ / η

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

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

[0101] This represents the distance traveled by the icing rod relative to the icing environment per unit time. Multiplying these three values ​​together yields the volume of space swept by the icing rod per unit time, providing volume data for subsequent calculations of liquid water content.

[0102] V = L × W × ν 杆 ×Δt

[0103] 7) Calculation of freezing rate or conversion of voltage change rate.

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

[0105] Regarding the relationship between ice thickness and time, it can be judged based on actual experiments. For example, using other probes that are easy to measure ice thickness, observe the actual ice thickness versus time curve. If the curve changes significantly, select the segment that is closest to linear as the measurement.

[0106] Based on the actual device measurement process, the relationship between voltage 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 LWC is calculated using the following formula:

[0109] LWC=(ΔH×ρ) / (ν 杆 ×Δt×η)

[0110] When performing calculations, pay attention to the unit conversions for each parameter.

[0111] Example 2

[0112] In this embodiment, the liquid water content can also be calculated using this method for other types of icing detectors. On fixed-wing aircraft, icing detectors are often required to have a level design. For level-designed icing detectors, there are fiber optic icing detectors and ultrasonic icing detectors. Both can measure the icing rate, and the measurement process is similar: both have a detection window on the wing and output a voltage value based on the icing thickness.

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

[0114] Step 1: Calculate the correlation between the velocity at the detection window and the airspeed through simulation. Since the fiber optic icing detector has no additional bleed air, the velocity at the detection window is the same as the aircraft velocity. The aircraft velocity is taken as 100 m / s as an example.

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

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

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

[0118] ρ = 0.0001T 2 +0.0123T+0.9528

[0119] When the ambient temperature is -20℃, the density of the ice is 0.7468 g / cm³. 3 .

[0120] Step 4: Acquire the voltage signal U related to ice thickness. When the fiber optic icing detector is in normal use, a single optical path works normally to acquire the voltage signal related to ice thickness. The thicker the ice on the icing rod, the smaller the voltage value.

[0121] H = -0.51U1 + 3.06

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

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

[0124] m=L×W×H×ρ / η

[0125] L and W will be eliminated in the final formula, so they can be temporarily omitted from the calculation.

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

[0127] Step 6: Calculate the volume of space swept by the probe 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℃ and the aircraft airspeed is 100m / s, the voltage value collected by the fiber optic icing detector drops from 3.2V to 2V within 15s. Based on the formula of this invention, the liquid water content of the environment in which the aircraft is located can be calculated to be 0.68g / L. 3 m.

[0133] In summary, this invention proposes a method for measuring liquid water content based on an infrared icing detector. This method involves simulating the relationship between the velocity of the probe's icing rod and airspeed, calculating the water droplet collection coefficient on the icing rod plane, establishing the relationship between ice density ρ and ambient temperature T, acquiring voltage signals related to ice thickness, calculating the icing mass per unit time and the volume of space swept by the icing rod, and finally calculating the liquid water content to obtain the detector's liquid water content calculation formula. This method can be applied to aircraft icing detection technology, improving the accuracy of liquid water content measurement on aircraft, and has significant practical application value.

[0134] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for calculating liquid water content based on an infrared icing detector, characterized in that, Includes the following steps: Step 1: Calculate the airflow velocity at the tip of the icing rod of the infrared icing detector through simulation. ν 杆 Aircraft airspeed ν 空 The correspondence is as follows: The specific process is as follows: Modeling the infrared icing detector; The air velocity at the tip of the icing rod (5 mm) was simulated at different air velocities and with an evacuation pressure of 0.17 MPa, yielding the air velocity ν at the tip of the icing rod. 杆 Aircraft airspeed ν 空 Correspondence: ν 杆 =0.511ν 空 +42.69 ; Step 2: Calculate the water droplet collection coefficient of the icing rod plane through simulation. η ; Step 3: Establish ice density ρ With ambient temperature T Correspondence: ρ=0.0001T 2 -0.0123T+0.9528 ； Step 4: Acquire the output voltage signal of the infrared icing detector U And calculate the ice thickness. H The formula is as follows: H = -0.35U + 1.06 in, H Indicates ice thickness, U This indicates the output voltage signal of the infrared icing detector; Step 5: Calculate the mass of ice formed per unit time, m, based on the ice thickness, using the following formula: m = L×W×H×ρ / η Where L and W represent the length and width of the rectangular plane of the icing rod, respectively; Step Six: Calculate the volume of space swept by the icing rod per unit time. V The formula is as follows: V = L × W × ν 杆 ×Δt ν 杆 ×Δt This indicates the distance traveled by the icing rod relative to the icing environment per unit time. ν 杆 This indicates the airflow velocity at the tip of the icing rod; 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 seven, the formula for calculating the freezing rate is as follows: H / Δt=(-0.35U+1.06) / Δt U For voltage, Δt Represents the unit of time.

3. The method according to claim 2, characterized in that: In step eight, the liquid water content... LWC The calculation formula is as follows: LWC = m / V=( L×W×H×ρ / η) / ( L×W×ν 杆 ×Δt) LWC = (H×ρ) / (ν) 杆 ×Δt×η) in, L and W Let be the rectangular planar dimension of the windward side of the icing rod of the infrared icing detector. ν 杆 It is the wind speed at the tip of the icing rod. ρ The density of ice, η The water droplet collection coefficient of the icing rod. U The voltage value collected. Δt It is a unit of time. H The ice is thick due to freezing.

Images