A method for determining icing zones based on water droplet coverage

Abstract

The present invention discloses a method for determining icing zone based on water droplet coverage rate, belonging to the technical field of icing simulation in visual measurement. It solves the problem of low accuracy of icing numerical simulation in the prior art due to the traditional icing model being unable to distinguish between continuous icing area and discontinuous icing area; the present invention defines a calculation formula for water droplet coverage rate; according to the magnitude relationship between the water droplet coverage rate and a typical characteristic constant value, a relational expression for determining the zoning of the icing surface is obtained; by making the water droplet coverage rate equal to a typical characteristic constant value, a critical value of the water droplet collection coefficient corresponding to the typical characteristic constant value is obtained; through experimental measurement or simulation calculation, the distribution characteristics of the water droplet collection coefficient in the water droplet impact area are obtained, and the position where the critical value of the water droplet collection coefficient is located, that is, the zoning boundary between the continuous icing area and the discontinuous icing area, is determined. The present invention effectively improves the accuracy of icing numerical simulation, can judge the boundary position between the two icing areas, and can be applied to icing numerical simulation.

Description

Technical Field

[0001] The present invention relates to a method for determining icing zones, in particular to a method for determining icing zones based on water droplet coverage, and belongs to the field of icing simulation technology for visual measurement. Background Art

[0002] Under specific meteorological conditions, there are a large number of supercooled water droplets in clouds. Although the temperature of supercooled water droplets is below zero degree, they still exist in liquid form. When an aircraft flies in the above clouds, the supercooled water droplets hitting the aircraft surface will freeze. Under different icing conditions, frost ice, clear ice or mixed ice may be formed on the aircraft. When frost ice is formed, all the supercooled water droplets freeze into ice after hitting; when clear ice is formed, not all the supercooled water droplets freeze, and the unfrozen liquid water forms a thin water film on the icing surface, and the water film flows along the icing surface and gradually freezes at different rates; but no matter which type of icing situation, there is a certain zoning phenomenon on its surface.

[0003] In the prior art, the icing surface is usually divided into a rough ice formation area, a feathery ice formation area and the boundary between them; the icing in the rough ice formation area is continuous, and the roughness is evenly distributed on its surface, while the icing in the feathery ice formation area is discontinuous, and ice particles or ice protrusions with discontinuous distribution are formed at the initial stage of icing and continue to grow to form feathery ice. At the initial stage of icing, a relatively obvious demarcation is formed between the rough ice formation area and the feathery ice formation area; for the rough ice formation area, since the icing is continuous, a relatively mature icing model has been established, while for the feathery ice formation area, there is no effective numerical simulation method. Although the icing in the feathery ice formation area cannot be numerically simulated, the determination of the demarcation position between the rough ice formation area and the feathery ice formation area plays a very crucial role in improving the accuracy of icing numerical simulation. At present, there is no simple and rapid method for determining the demarcation position between the rough ice formation area and the feathery ice formation area.

[0004] In summary, a method for determining icing zones based on water droplet coverage is needed. Summary of the Invention

[0005] A brief overview of the present invention is given below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is only to present some concepts in a simplified form as a prelude to the more detailed description to be discussed later.

[0006] In view of this, to solve the problem of low accuracy of ice accretion numerical simulation caused by the inability of traditional ice accretion models in the prior art to distinguish between the continuous ice accretion area and the discontinuous ice accretion area, the present invention provides an ice accretion zone determination method based on the water droplet coverage rate.

[0007] The technical solution is as follows: An ice accretion zone determination method based on the water droplet coverage rate, comprising the following steps:

[0008] S1. Define the water droplet coverage rate calculation formula as the ratio of the sum of the cross-sectional areas of all water droplets per unit time to the impact area thereof;

[0009] S2. Divide the ice accretion surface into a continuous ice accretion area, a discontinuous ice accretion area, and a partition boundary between the continuous ice accretion area and the discontinuous ice accretion area, and obtain a relational expression for determining the ice accretion surface partition according to the magnitude relationship between the water droplet coverage rate and the typical characteristic constant value;

[0010] S3. According to the relational expression for determining the ice accretion surface partition, make the water droplet coverage rate equal to the typical characteristic constant value to obtain the critical value of the water droplet collection coefficient corresponding to the typical characteristic constant value;

[0011] S4. Obtain the distribution characteristics of the water droplet collection coefficient in the water droplet impact area through experimental measurement or simulation calculation, and determine the position where the critical value of the water droplet collection coefficient is located, that is, the partition boundary between the continuous ice accretion area and the discontinuous ice accretion area.

[0012] Further, in S2, the relational expression for determining the ice accretion surface partition is expressed as: when the water droplet coverage rate is equal to the typical characteristic constant value , that is , the position where it is located represents the partition boundary between the continuous ice accretion area and the discontinuous ice accretion area; when the water droplet coverage rate is greater than the typical characteristic constant value , that is , the position where it is located belongs to the continuous ice accretion area; when the water droplet coverage rate is less than the typical characteristic constant value , that is , the position where it is located belongs to the discontinuous ice accretion area.

[0013] Further, in S3, make the water droplet coverage rate equal to the typical characteristic constant value , and the critical value of the water droplet collection coefficient corresponding to the typical characteristic constant value is expressed as:

[0014] ;

[0015] wherein, is the liquid water content, and its unit is g / m3 , where \(d\) is the water droplet diameter in \(\mu m\), and \(v\) is the air flow velocity in \(m / s\);

[0016] When the water droplet collection coefficient equals the critical value of the water droplet collection coefficient , i.e., , its position represents the partition boundary between the continuous icing region and the discontinuous icing region; when the water droplet collection coefficient is greater than the critical value of the water droplet collection coefficient , i.e., , its position belongs to the continuous icing region; when the water droplet collection coefficient is less than the critical value of the water droplet collection coefficient , i.e., , its position belongs to the discontinuous icing region.

[0017] The beneficial effects of the present invention are as follows: By defining the concept of water droplet coverage rate and its calculation formula, the specific value of the water droplet coverage rate is calculated under given icing conditions, and a specific quantitative determination criterion for the position of the partition boundary between the continuous icing region (rough region) and the discontinuous icing region (feathery region) on the object surface is established, which is used to determine the partition boundary between the continuous icing region and the discontinuous icing region on the object surface. The present invention can be applied to fields such as icing mechanism research, icing test analysis, and icing simulation calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 is a schematic flow chart of an icing partition determination method based on water droplet coverage rate;

[0020] Figure 2 is a schematic diagram of the water droplet collection coefficient distribution of the NACA0012 airfoil under given icing conditions;

[0021] Figure 3 is a schematic diagram of the position of the critical value of the water droplet collection coefficient under given icing conditions;

[0022] Figure 4 is a comparison schematic diagram of the 3 - minute icing surface of the NACA0012 airfoil in the icing wind tunnel and the position of the critical value of the water droplet collection coefficient under given icing conditions. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the technical solutions and advantages in the embodiments of the present invention clearer and more understandable, the following further elaborates on the exemplary embodiments of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than an exhaustive list of all embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0024] Reference Figures 1 - 4 A method for determining icing zones based on water droplet coverage rate will be described in detail in this embodiment. Specifically, it includes the following steps:

[0025] S1. Define the water droplet coverage rate calculation formula as the ratio of the sum of the cross-sectional areas of all water droplets within a unit time to their impact area. The specific value of the water droplet coverage rate depends on the air flow, icing conditions, and the water droplet impact position.

[0026] S2. Divide the icing surface into an icing continuous zone (rough zone), an icing discontinuous zone (feathery zone), and the partition boundary between the icing continuous zone and the icing discontinuous zone. According to the magnitude relationship between the water droplet coverage rate and the typical characteristic constant value, obtain the relational expression for determining the icing surface partition.

[0027] S3. According to the relational expression for determining the icing surface partition, set the water droplet coverage rate equal to the typical characteristic constant value to obtain the critical value of the water droplet collection coefficient corresponding to the typical characteristic constant value.

[0028] S4. Obtain the distribution characteristics of the water droplet collection coefficient in the water droplet impact area through experimental measurement or simulation calculation, and determine the position where the critical value of the water droplet collection coefficient is located, which is the partition boundary between the icing continuous zone and the icing discontinuous zone.

[0029] Further, in S2, the relational expression for determining the icing surface partition is expressed as: when the water droplet coverage rate equals the typical characteristic constant value i.e., , its position represents the partition boundary between the icing continuous zone and the icing discontinuous zone; when the water droplet coverage rate is greater than the typical characteristic constant value i.e., , it represents that the number of water droplets in the air flow can completely cover the impact area, and its position belongs to the icing continuous zone, and the icing surface mainly presents a relatively uniform roughness distribution pattern; when the water droplet coverage rate is less than the typical characteristic constant value i.e., it represents that the number of water droplets in the air flow cannot completely cover the impact area, and its position belongs to the icing discontinuous zone, and the icing is mainly composed of feathery ice.

[0030] Further, in S3, set the water droplet coverage rate Equal to the typical feature constant value , the typical feature constant value The corresponding critical value of the water droplet collection coefficient is expressed as:

[0031] ;

[0032] Among them, is the liquid water content, and its unit is g / m 3 , is the water droplet diameter, and its unit is μm, is the air flow velocity, and its unit is m / s;

[0033] When the water droplet collection coefficient is equal to the critical value of the water droplet collection coefficient , that is , the position where it is located represents the partition boundary between the continuous icing area and the discontinuous icing area; when the water droplet collection coefficient is greater than the critical value of the water droplet collection coefficient , that is , the position where it is located belongs to the continuous icing area; when the water droplet collection coefficient is less than the critical value of the water droplet collection coefficient , that is , the position where it is located belongs to the discontinuous icing area.

[0034] Specifically, the water droplet collection coefficient varies with the change of the water droplet impact position, and there is a one-to-one correspondence between the water droplet coverage rate and the water droplet collection coefficient ;

[0035] Under general icing conditions, assuming the typical feature constant value , then the corresponding critical value of the water droplet collection coefficient is expressed as:

[0036] ;

[0037] In this embodiment, it is assumed that the liquid water content is 0.47 g / m 3 , the water droplet diameter is 19.2 μm, and the air flow velocity is 75 m / s, then the critical value of the water droplet collection coefficient corresponding to the water droplet coverage rate equal to 1;

[0038] Reference Figure 2, showing the water droplet collection coefficient distribution and the critical value of the water droplet collection coefficient of the NACA0012 airfoil under given icing conditions, where S is the arc length coordinate of the airfoil surface, with the unit of m;

[0039] Reference Figure 3 , showing the positions of the critical value of the water droplet collection coefficient on the upper and lower surfaces of the NACA0012 airfoil under given icing conditions, which respectively represent the specific positions of the partition boundaries between the continuous icing regions and the discontinuous icing regions on the upper and lower surfaces of the NACA0012 airfoil;

[0040] Reference Figure 4 , showing the comparison between the 3-minute icing surface of the NACA0012 airfoil icing wind tunnel and the position of the critical value of the water droplet collection coefficient under given icing conditions. The red dot part is the partition boundary between the continuous icing region and the discontinuous icing region.

[0041] Although the present invention has been described in terms of a limited number of embodiments, those skilled in the art in this technical field will appreciate that other embodiments can be contemplated within the scope of the present invention as thus described. In addition, it should be noted that the language used in this specification has been primarily selected for readability and teaching purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those of ordinary skill in the art in this technical field without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure made of the present invention is illustrative, not restrictive, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for determining ice partitions based on water drop coverage, characterized in that: The following steps are involved: S1. Water drop coverage The calculation formula is defined as the ratio of the sum of the cross-sectional areas of all water droplets per unit time to their impact area; S2. The ice surface is divided into ice continuous area, ice discontinuous area and the partition boundary between ice continuous area and ice discontinuous area. With typical characteristic constant The relationship between the size of the ice surface is obtained to obtain the relationship between the determination of the ice surface partition; S3. According to the relationship for determining the ice surface partition, let the water drop coverage Equal to the typical characteristic constant , and obtain the typical characteristic constant The corresponding critical value of the droplet collection coefficient; S4. Obtain the distribution characteristics of the water droplet collection coefficient in the water droplet impact area through experimental measurement or simulation calculation, and determine the location of the critical value of the water droplet collection coefficient, that is, the partition boundary between the ice continuous area and the ice discontinuous area; In S3, let the water drop coverage ratio Equal to the typical characteristic constant , typical characteristic constant Corresponding critical value of droplet collection coefficient It is expressed as: ； in, is the liquid water content, its unit is g / m 3 , is the water droplet diameter, its unit is μm, is the air flow speed, the unit is m / s; When the droplet collection coefficient Equal to the critical value of the droplet collection coefficient When , its location represents the partition boundary between the continuous freezing zone and the discontinuous freezing zone; when the droplet collection coefficient Greater than the critical value of the droplet collection coefficient When , its location belongs to the continuous ice zone; when the water droplet collection coefficient Less than the critical value of the droplet collection coefficient When , and its location belongs to the ice discontinuous zone.

2. The method for determining ice partitions based on water drop coverage according to claim 1, characterized in that: In S2, the relationship for determining the ice surface partition is expressed as: when the water droplet coverage Equal to the typical characteristic constant When , its location represents the partition boundary between the continuous freezing zone and the discontinuous freezing zone; when the water drop coverage Greater than the typical characteristic constant When , its location belongs to the continuous ice zone; when the water drop coverage Less than the typical characteristic constant ,Right now When , its location belongs to the icing discontinuous zone.

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