An engineering approximation method based on the calculation of aircraft water collection coefficient

Abstract

The present invention discloses an engineering approximation method based on the calculation of the water collection coefficient of an aircraft, and relates to the field of numerical technology for aircraft icing. The engineering approximation method for calculating the water collection coefficient searches for the characteristic length of the aircraft and the geometric parameters of the aircraft surface according to the selected aircraft type, searches for the corresponding water droplet parameters and air parameters according to the meteorological conditions required for the water collection coefficient calculation, calculates the maximum water collection coefficient of the aircraft surface, calculates the inner normal of each surface on the aircraft according to the geometric parameters of the aircraft surface, finds the angle between the inner normal and the incoming air velocity vector, calculates the cosine value of the angle, finds the water collection coefficient, and obtains the water collection coefficient distribution on the aircraft surface. The engineering approximation method based on the calculation of the aircraft water collection coefficient of the present invention has the advantages of simple form, fast calculation, and obvious effect, and can effectively improve the efficiency of water collection coefficient calculation in the preliminary design stage of the aircraft.

Description

Technical Field

[0001] The present invention relates to the field of numerical technology of aircraft icing, and in particular to an engineering approximation method based on calculation of aircraft water collection coefficient. Background Art

[0002] Icing poses a serious threat to aircraft flight safety and is a key concern in the civil aviation sector. Predicting droplet trajectories and impact characteristics is an input for icing prediction and anti-icing system design. The prediction results influence the accuracy of icing range and amount simulations.

[0003] The water collection coefficient β is the most important parameter in calculating water droplet impact characteristics. The water collection coefficient (also known as the local water collection coefficient) is the ratio of the water flow rate collected by a microelement on the surface to the maximum possible collection volume. The water collection coefficient varies at different locations and is related to the incoming flow conditions, droplet parameters, and surface geometry. The water collection coefficient can be used to determine the quality of a droplet impacting a surface. Therefore, determining the water collection coefficient on a surface is fundamental to numerical simulations of icing and the design of anti-icing and de-icing systems.

[0004] The water collection coefficient is calculated based on the water droplet trajectory, which mainly includes the Lagrangian method and the Euler method.

[0005] The Lagrangian method takes a single water droplet as the research object. By establishing the force equation of the water droplet, the change law of the water droplet position and physical quantity over time is obtained. By calculating a large number of water droplet trajectories in space, the starting position of each water droplet and its corresponding water droplet impact point are obtained. The distance between the initial positions of the two water droplet trajectories is S0, and the distance between the impact positions is S i The calculation formula of the water collection coefficient in the Lagrangian method can be expressed as:

[0006]

[0007] Where θ is the incoming flow angle of attack.

[0008] The Euler method constructs the equation of motion for water droplets based on Euler two-phase flow. During the modeling process, the water droplets are treated as a continuously distributed phase. By establishing and solving the equation for the motion trajectory of the water droplets, the mass and velocity distribution of the water droplets in space are obtained, and thus the motion trajectory of the water droplets is obtained. In the Euler method, the water collection coefficient can be expressed as:

[0009]

[0010] Among them, α ∞ represents the volume fraction of the water drop at infinity, V ∞ represents the velocity of water droplets, α n represents the volume fraction of the water droplet that hits the surface, represents the velocity of the water droplet upon impact, Represents the cell normal vector of the impact surface.

[0011] At present, the water collection coefficient mainly adopts the above-mentioned Lagrangian method and Euler method, and the calculation results of these two methods are consistent. In the calculation process of these two methods, it is necessary to mesh the calculation object and calculate the flow field, and then calculate the water droplet motion trajectory, and finally obtain the water collection coefficient of the object surface. Regardless of which method is used, it requires relatively complex numerical calculations, which consumes more computing resources and computing time. Usually, it may take several days to calculate the water collection coefficient of the surface of a three-dimensional large civil aircraft in a calculation state. In the preliminary design stage of an aircraft, it is obviously not cost-effective to spend a lot of time on numerical calculations for an aircraft that has not been finalized and may be repeatedly modified. Therefore, an engineering method of water collection coefficient is needed to achieve rapid prediction of water collection coefficient to help engineering designers better carry out icing and anti-icing system design.

[0012] At the same time, icing is also one of the important problems faced by wind turbines. The shape of wind turbine blades is relatively complex, and how to quickly predict the surface water collection characteristics in the preliminary design stage of the anti-icing system is also an important issue. Summary of the Invention

[0013] To address the challenges of existing technologies, the present invention provides an engineering approximation method based on the calculation of an aircraft's water collection coefficient. This method offers a simple calculation process, reasonable results, and significant effectiveness. Furthermore, it addresses practical engineering needs and can be used by aircraft designers and design teams during the initial design phase to assess aircraft icing and prevent deicing.

[0014] To achieve the above technical objectives, the present invention adopts the following technical solution: an engineering approximation method based on the calculation of the aircraft water collection coefficient, specifically comprising the following steps:

[0015] (1) According to the selected aircraft type, find the aircraft characteristic length and aircraft surface geometric parameters, and calculate the required meteorological conditions based on the water collection coefficient, and find the corresponding water droplet parameters and air parameters;

[0016] (2) Calculate the maximum water collection coefficient β on the aircraft surface based on the aircraft characteristic length, water droplet parameters, and air parameters found in step (1) max ;

[0017] (3) Calculating the inner normal of each curved surface on the aircraft based on the geometric parameters of the aircraft surface found in step (1), finding the angle γ between the inner normal and the incoming air velocity vector, and calculating the cosine value cosγ of the angle γ;

[0018] (4) When cosγ>(1-β max ), the water collection coefficient on the surface is β=cosγ-(1-βmax ); otherwise, the water collection coefficient on the surface is β = 0;

[0019] (5) Traverse each curved surface on the aircraft and repeat step (4) to obtain the water collection coefficient of each curved surface on the aircraft and obtain the distribution of the water collection coefficient on the aircraft surface.

[0020] Furthermore, the water droplet parameters include: water droplet density and water droplet diameter.

[0021] Furthermore, the air parameters include: incoming air velocity, air density and air dynamic viscosity.

[0022] Furthermore, the maximum water collection coefficient β of the aircraft surface max The calculation process is:

[0023]

[0024] Among them, K0 is the corrected inertia factor.

[0025] Furthermore, the calculation process of the modified inertia factor is specifically as follows:

[0026]

[0027] Among them, ρ w is the water droplet density, ρ a is the air density, d is the water droplet diameter, V is the incoming air velocity, L is the characteristic length of the aircraft, μ a is the dynamic viscosity of air.

[0028] Furthermore, the incoming air velocity vector includes the magnitude of the incoming air velocity and the direction of the incoming air velocity. The magnitude of the incoming air velocity is represented by the Mach number, and the direction of the incoming air velocity is represented by the angle of attack.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The engineering approximation method for calculating the water collection coefficient of an aircraft in the present invention takes into account the influence of water droplet parameters, air parameters, and aircraft surface geometric parameters on the calculation results of the water collection coefficient, and can be used to calculate the water collection coefficient under different meteorological conditions;

[0031] (2) The engineering approximation method for calculating the aircraft water collection coefficient of the present invention obtains the distribution of the aircraft surface water collection coefficient through simple calculation, avoiding complex numerical calculations and saving a lot of time;

[0032] (3) The error between the calculated result of the water collection coefficient based on the engineering approximation method of the present invention and the experimental value is within 20%, which can meet the engineering requirements;

[0033] The engineering approximation method for calculating the water collection coefficient of an aircraft according to the present invention has the advantages of simple form, fast calculation, obvious effect, etc., and can effectively improve the efficiency of calculating the water collection coefficient in the preliminary design stage of an aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of the engineering approximation method for calculating the aircraft water collection coefficient based on the present invention; (Flow chart missing)

[0035] Figure 2 is a schematic diagram of the angle between the inner normal and the incoming air velocity vector;

[0036] Figure 3 It is a graph of the cosine value of the angle between the normal line of each curved surface of the aircraft and the velocity vector of the incoming air;

[0037] Figure 4 This is a comparison chart of the calculation results of the water collection coefficient of Example 1 of the present invention and the Euler method;

[0038] Figure 5 3 is a comparison chart of the calculation results of the water collection coefficient of Example 2 of the present invention and the Euler method. DETAILED DESCRIPTION

[0039] In order to make the essential features and practicality of the present invention easier to understand, the technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0040] like Figure 1 The flowchart of the engineering approximation method for calculating the water collection coefficient of an aircraft according to the present invention is shown in FIG. The engineering approximation method for calculating the water collection coefficient includes the following steps:

[0041] (1) Based on the selected aircraft type, the aircraft characteristic length and aircraft surface geometric parameters are searched, and based on the meteorological conditions required for calculating the water collection coefficient, the corresponding water droplet parameters and air parameters are searched. The water droplet parameters used in the present invention include: water droplet density and water droplet diameter; the air parameters used include: incoming air velocity, air density, and aerodynamic viscosity. By considering the influence of water droplet parameters, air parameters, and aircraft surface geometric parameters on the calculation results of the water collection coefficient, the present invention can carry out the calculation of the water collection coefficient under different meteorological conditions.

[0042] (2) Calculate the maximum water collection coefficient β on the aircraft surface based on the aircraft characteristic length, water droplet parameters, and air parameters found in step (1) max :

[0043]

[0044] Among them, K0 is the corrected inertia factor;

[0045]

[0046] Among them, ρ w is the water droplet density, ρ a is the air density, d is the water droplet diameter, V is the incoming air velocity, L is the characteristic length of the aircraft, μ a is the dynamic viscosity of air.

[0047] Since the aircraft types have different geometric shapes and different flight states, resulting in different maximum water collection coefficients, the above method needs to be used to calculate and adjust the water collection coefficient. At the same time, the method of the present invention can quickly and effectively calculate the maximum water collection coefficient, and the calculation result error meets engineering requirements.

[0048] (3) Calculate the internal normals of each surface on the aircraft based on the geometric parameters of the aircraft surface found in step (1), and find the angle γ between each internal normal and the incoming air velocity vector, as follows: Figure 2 , and calculate the cosine value of the angle γ, cosγ. The cosine value represents the deviation between the incoming air flow direction and the inner normal direction of the aircraft's curved surface, and can preliminarily indicate the deviation between the incoming water droplet flow direction and the impact direction of the aircraft's curved surface. In the present invention, the magnitude of the incoming air velocity is represented by the Mach number, and the direction of the incoming air velocity is represented by the angle of attack.

[0049] (4) The cosine value calculated in step (3) is shifted downward according to the maximum water collection coefficient. When the calculated result is greater than 0, that is, when cosγ>(1-β max ), the water collection coefficient on the surface is β=cosγ-(1-β max ); otherwise, the water collection coefficient on the surface is β = 0;

[0050] (5) Traverse each curved surface on the aircraft and repeat step (4) to obtain the water collection coefficient of each curved surface on the aircraft and obtain the distribution of the water collection coefficient on the aircraft surface.

[0051] The engineering approximation method for calculating the aircraft water collection coefficient in the present invention obtains the distribution of the aircraft surface water collection coefficient through simple calculation, avoiding complex numerical calculations and saving a lot of time. The method has the advantages of simple form, fast calculation and obvious effect, and can effectively improve the efficiency of water collection coefficient calculation in the preliminary design stage of aircraft.

[0052] In addition, the engineering approximation method for calculating the water collection coefficient of the present invention can be applied not only to aircraft, but also to other fields such as wind turbines, transmission lines, and motor vehicles.

[0053] Example 1

[0054] The aircraft is selected as a NACA0012 wing, and its model chord length 1.0m and the aircraft surface geometric parameters are found. According to the required meteorological conditions, the air velocity vector (angle of attack 0°, incoming Mach number 0.2) and the water droplet diameter are found to be 40μm. The maximum water collection coefficient β of the aircraft surface is calculated by the engineering approximation method based on the aircraft water collection coefficient calculation of the present invention. max is 0.83. Based on the geometric parameters of the aircraft surface, the inner normal of each surface on the aircraft is calculated. The angle γ between the inner normal and the incoming air velocity vector is obtained. The cosine value of the angle γ, cosγ, is calculated, as follows: Figure 3 As shown, when cosγ>(1-β max ), the water collection coefficient on the surface is β=cosγ-(1-β max ); otherwise, the water collection coefficient on the surface is β = 0, and the water collection coefficients of the various surfaces on the aircraft are traversed to obtain the distribution of the water collection coefficients on the aircraft surface.

[0055] like Figure 4 A comparison chart of the water collection coefficient calculated by the method of the present invention and the water collection coefficient calculated by the Euler method is given in the above embodiment. The error between the calculated result and the Euler method is within 20%, which meets the engineering requirements.

[0056] Example 2

[0057] For the aircraft selected as NACA0012 wing, find its model chord length 1.0m and the aircraft surface geometric parameters. According to the required meteorological conditions, find the air velocity vector (angle of attack 0°, incoming Mach number 0.4), the water droplet diameter 20μm, and refer to the method in Example 1 to obtain the water collection coefficient distribution on the aircraft surface, as shown in Figure 1. Figure 5 As shown in the figure, the error between the calculation result and the Euler method is within 20%, which meets the engineering requirements.

[0058] Therefore, the engineering approximation method for calculating the aircraft water collection coefficient of the present invention can calculate the water collection coefficient under different meteorological conditions, and the calculated results have an error within 20% of the Euler error, which can meet engineering requirements. However, in terms of computational time, the present invention does not require complex numerical calculation methods. On a home computer, the entire calculation can be completed in just a few minutes. In contrast, the Euler method, without considering programming time, requires two hours to complete the series of steps from meshing, flow field calculation, to water droplet impact characteristics calculation. This shows that the engineering approximation method for calculating the aircraft water collection coefficient of the present invention can save a lot of computing resources and time, and can meet the needs of preliminary engineering design.

[0059] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. An engineering approximation method based on the calculation of the aircraft water collection coefficient, characterized in that: The specific steps include: (1) According to the selected aircraft type, find the aircraft characteristic length and aircraft surface geometric parameters, and calculate the required meteorological conditions based on the water collection coefficient, and find the corresponding water droplet parameters and air parameters; (2) Calculate the maximum water collection coefficient β on the aircraft surface based on the aircraft characteristic length, water droplet parameters, and air parameters found in step (1) max ; (3) calculating the inner normal of each curved surface on the aircraft based on the aircraft surface geometric parameters found in step (1), finding the angle γ between the inner normal and the incoming air velocity vector, and calculating the cosine value cosγ of the angle γ; the incoming air velocity vector includes the magnitude of the incoming air velocity and the direction of the incoming air velocity, the magnitude of the incoming air velocity is represented by the Mach number, and the direction of the incoming air velocity is represented by the angle of attack; (4) When cosγ>(1-β max ), the water collection coefficient on the surface is β=cosγ-(1-β max ); otherwise, the water collection coefficient on the surface is β = 0; (5) Traverse each curved surface on the aircraft and repeat step (4) to obtain the water collection coefficient of each curved surface on the aircraft and obtain the distribution of the water collection coefficient on the aircraft surface.

2. The engineering approximation method for calculating the aircraft water collection coefficient according to claim 1, characterized in that: The water drop parameters include: water drop density and water drop diameter.

3. The engineering approximation method for calculating the aircraft water collection coefficient according to claim 1, characterized in that: The air parameters include: incoming air velocity, air density and air dynamic viscosity.

4. The engineering approximation method for calculating the aircraft water collection coefficient according to claim 1, characterized in that: The maximum water collection coefficient β of the aircraft surface max The calculation process is: Among them, K0 is the corrected inertia factor.

5. The engineering approximation method based on the calculation of the aircraft water collection coefficient according to claim 4 is characterized in that: The calculation process of the modified inertia factor is specifically as follows: Among them, ρ w is the water droplet density, ρ a is the air density, d is the water droplet diameter, V is the incoming air velocity, L is the characteristic length of the aircraft, μ a is the dynamic viscosity of air.

Images