Method for resolving liquid water content by using resonant icing detector

Abstract

The invention belongs to the technical field of icing detection, and relates to a method for resolving liquid water content by using a resonant icing detector. Acquiring the output frequency of the resonant icing detector and the flight speed of the aircraft; calculating a frequency change value and icing time in each change period of the output frequency; taking the wave crest as a timing starting point t1 after the typical frequency value declines, and taking the wave crest as a timing ending point t2 after decline; the freezing time t is equal to t2-t1; calculating the liquid water content according to the following formula, in the formula, t represents timing time, and the unit is s; the coefficient is an ice freezing coefficient and is a non-volume outline constant; the coefficient is a total collection coefficient; the frequency change is the frequency change corresponding to the ice thickness per unit thickness; the water content is liquid water content, and the unit is g / m < 3 >; the frequency variation is the frequency variation in the timing time; the density is the density of ice and the unit is g / cm < 3 >.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of icing detection, and relates to a method for calculating liquid water content by using a resonant icing detector. BACKGROUND

[0002] Icing problem has been a major technical problem bothering the aviation industry, and an icing detector can give an icing alarm signal in time after the aircraft encounters icing, so that the crew can take measures in time. At present, the mainstream icing detector can only give an icing alarm signal and an icing rate signal, and due to the difference in structure form, the collection coefficients of different parts of the aircraft are different, and the icing rate is also different, so it is necessary to combine the icing rate signal of the icing detector with the icing condition of the specific part of the aircraft, which is meaningful, which brings great complexity to the design and use of the aircraft. The liquid water content is the most direct feedback index of the icing severity of the environment, and at present, most of the equipped icing detectors cannot give the liquid water content information in the environment.

[0003] The purpose of the present application is to provide a method for calculating liquid water content by using a resonant icing detector.

[0004] The technical solution of the present application is: A method for calculating liquid water content by using a resonant icing detector, the process is as follows: Collecting the output frequency of the resonant icing detector and the flight speed of the aircraft ; Calculating the frequency change value in each change cycle of the output frequency and the icing time; taking the typical frequency value after the peak drop as the timing starting point t1, and taking the frequency value after the drop as the timing end point t2; The icing time t=t2-t1; According to the following formula to calculate the liquid water content:

[0005] In the formula, t represents the timing time, and the unit is s; is the icing freezing coefficient, which is a dimensionless constant; is the total collection coefficient; is the frequency change corresponding to the unit thickness of ice thickness; is the liquid water content, and the unit is g / m 3 ; is the frequency change amount in the timing time; is the density of ice, and the unit is g / cm 3 .

[0006] Further, the freezing coefficient is related to the temperature, The value range is 0-1, which can be determined by simulation calculation, and is 1 when lower than -18 DEG C.

[0007] Further, due to the influence of temperature and water droplet impact characteristics, the ice density formed under different conditions is different, so the density of the ice needs to be selected according to the type of the ice, and the range is 0.82 g / cm 3 ~0.917 g / cm 3 0.917 g / cm when the temperature is higher than -5 DEG C 3 0.82 g / cm when the temperature is lower than -18 DEG C 3 , and the intermediate temperature range can be obtained by the following formula.

[0008]

[0009] Further, the probe position incoming flow velocity is related to the accuracy of the liquid water content calculation accuracy, and the velocity information in claim 1 can be obtained by total static pressure / total temperature measurement or received from the aircraft input.

[0010] Further, due to the manufacturing and assembly errors of the probe structure, the frequency change corresponding to the unit thickness ice layer will have certain differences, and generally 350 Hz-400 Hz.

[0011] Further, in order to reduce the system acquisition error, the frequency change and the period for liquid water content calculation should be as long as possible, therefore, The value range is 200 Hz-550 Hz.

[0012] Further, affected by temperature, the resonant frequency of the resonant icing detector will fluctuate, and the initial frequency acquisition will affect the calculation accuracy, and the initial frequency acquisition should avoid the influence of temperature fluctuation. Therefore, the value range of A2 is 40000 Hz-39800 Hz, and the typical A2 is 39830 Hz.

[0013] Further, the corresponding relationship between the ice thickness and the frequency of the resonant icing detector is linear only within a certain range, and the end point of the frequency acquisition should be within the linear range. Therefore, the value range of A3 is 39800 Hz-39400 Hz, and the typical A3 is 39660 Hz.

[0014] The present application has the advantages and beneficial effects that: the present application utilizes the frequency change characteristics of the vibrating head after icing of the icing sensor, combines the incoming flow velocity, the density of the ice, the vibration head collection coefficient and other parameters, and finally realizes the measurement of liquid water in the atmosphere. The method has the characteristics of simple algorithm, high precision, and no need for additional hardware circuit design. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Fig. 2 is a schematic diagram of the relationship between the frequency change of the icing detector and time when icing occurs. DETAILED DESCRIPTION

[0016] The liquid water content calculation formula contains the frequency change ΔHz, the icing time t, the incoming flow speed , the liquid water content LWC, the freezing coefficient n, the collection coefficient , and the density of ice . In the icing environment, the frequency change of the icing detector is related to the thickness of the ice.

[0017] The liquid water content calculation formula is as follows:

[0018] In the formula, t represents the timing time, and the unit is s; is the ice freezing coefficient, and is a dimensionless constant; is the total collection coefficient; is the frequency change corresponding to the unit thickness of ice; is the liquid water content, and the unit is g / m 3 ; is the frequency change in the timing time; is the density of ice, and the unit is g / cm 3 .

[0019] The freezing coefficient is related to the temperature, and the value range is 0-1, which can be determined through simulation calculation, and is 1 when it is lower than -18℃. Due to the influence of temperature and water droplet impact characteristics, the density of ice formed under different conditions is different, so the density of ice needs to be selected according to the type of ice, and the range is 0.82g / cm 3 -0.917g / cm 3 . When the temperature is higher than -5℃, it is 0.917g / cm 3 , when the temperature is lower than -18℃, it is 0.82g / cm 3 , and the intermediate temperature range can be obtained through the following formula.

[0020]

[0021] The probe position incoming flow speed is related to the accuracy of the liquid water content calculation precision, and the speed information can be obtained through the total static pressure / total temperature measurement method or received from the aircraft input.

[0022] Due to the manufacturing and assembly errors of the probe structure, the frequency change corresponding to the unit thickness of ice layer will have certain differences, and generally is 350Hz-400Hz.

[0023] To reduce system acquisition errors, the frequency and period for calculating liquid water content should be as long as possible. The value range is 200 Hz to 550 Hz.

[0024] Due to temperature variations, the resonant frequency of the resonant icing detector will fluctuate. Inaccurate initial frequency acquisition will affect the calculation accuracy. Therefore, the acquisition of the initial frequency should avoid the influence of temperature fluctuations. The value range of A2 is 40000Hz to 39800Hz, with a typical A2 value of 39830Hz.

[0025] The relationship between ice thickness and frequency in resonant icing detectors is linear only within a certain range, and the endpoint of frequency acquisition should be within this linear range. Therefore, the value range of A3 is 39800Hz to 39400Hz, with a typical A3 value of 39660Hz.

[0026] Example A certain type of helicopter uses a resonant icing detector. The method for calculating the liquid water content using the aforementioned resonant icing detector is as follows: The first step is to calculate the total collection coefficient.

[0027] The helicopter has a flight speed of 56.5 m / s and uses a certain type of resonant icing detector. Under the condition of the detector probe structure, the comprehensive collection coefficient is 0.88 obtained through simulation calculation.

[0028] The second step is to determine the freezing factor. The freezing factor can be obtained through simulation analysis using software. When the temperature is below -18℃, it can be taken as 1. This example is calculated based on a temperature below -18℃, so the freezing factor is taken as 1.

[0029] The third step is to calculate the density of the ice. In this example, the ice wind tunnel test temperature is -20℃, so the density of the ice is taken as 0.82 g / cm³. 3 .

[0030] The third step is to test the frequency change per unit ice thickness of the resonant vibrating head. In the example, the icing detector used corresponds to a frequency change of 350Hz per unit ice thickness. Therefore... Let it be 350.

[0031] The fourth step involves acquiring data on the frequency change of the icing detector over time under specific ice wind tunnel conditions. In this example, the ice wind tunnel test conditions are -20℃ and a water content of 0.6 g / m³. 3 The wind speed was 56.6 m / s. The frequency dropped by 240 Hz, corresponding to a time of 61 seconds.

[0032] Fifth step, substitute the above values ​​into the LWC calculation formula:

[0033] The liquid water content (LWC) was found to be approximately 0.67 g / m³. 3 .

Claims

1. A method for calculating liquid water content using a resonant icing detector, characterized in that: The output frequency of the resonant icing detector and the aircraft's flight speed are collected. ; Calculate the frequency change value within each cycle of the output frequency change. and freezing time; The timing start point t1 is taken after the typical frequency value of the peak descent. This is then used as the timing endpoint t2; Freezing time t = t2 - t1; Calculate the liquid water content using the following formula: In the formula: t represents the timing time, and the unit is seconds; is the freezing coefficient, and is a dimensionless constant; The total collection coefficient; This represents the frequency variation corresponding to a unit thickness of ice. Liquid water content, in g / m³ 3 ; The frequency change over the time interval; This is the density of ice, expressed in g / cm³. 3 .

2. The method according to claim 1, characterized in that: Freezing coefficient Temperature-related The value ranges from 0 to 1, determined through simulation calculations, and is set to 1 for values ​​below -18℃.

3. The method according to claim 2, characterized in that: The density of ice is selected based on temperature, using the following formula: Where T [-5℃~-18℃], when T>-5℃, is taken as 0.82-0.82 g / cm³. 3 When T < -18℃, the concentration is 0.917 g / cm³. 3 .

4. The method according to claim 3, characterized in that: The aircraft speed required for a resonant icing detector to calculate liquid water content Information, measurement, or reception of aircraft input.

5. The method according to claim 4, characterized in that: The frequency range is 350Hz to 400Hz.

6. The method according to claim 5, characterized in that: The value range is 200 Hz to 550 Hz.

7. The method according to claim 6, characterized in that: The value range of A2 is 40000Hz to 39800Hz.

8. The method according to claim 7, characterized in that: The value range of A3 is 39800Hz to 39400Hz.

9. The method according to claim 8, characterized in that: A3 is 39660Hz, and A2 is 39830Hz.

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