KR20140115835A - Method for simulating ice accretion around an air intake - Google Patents

Abstract

The present invention discloses a method for simulating surface freezing of an air inlet. The method for simulating surface freezing of an air intake port according to the present invention comprises the steps of defining a grid topology and a boundary condition of an ice wind tunnel test section for modeling an air flow flowing into an air intake port and an air intake port, A step of setting the size of the wind tunnel test section, a velocity of the air introduced into the air intake port, a temperature of the air and an air pressure are respectively set to predetermined values, and the surface pressure distribution and the surface velocity distribution applied to the peripheral surface of the air intake port are calculated Calculating an accumulation rate of droplets accumulated on a peripheral surface of the air inlet according to a predetermined droplet amount and a droplet size based on the calculated surface pressure distribution and surface velocity distribution; And analyzing the icing growth on the peripheral surface of the air inlet using the accumulation rate of the droplets.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for simulating surface freezing of an air intake port,

More particularly, the present invention relates to a method for simulating surface freezing of an air intake port for simulating freezing occurring around an engine intake port of a rotor blade airplane.

Freezing in flight is closely related to aircraft and engine production, aircraft certification and operation in terms of aircraft safety. In particular, freezing on the aircraft surface is one of the most threatening environmental factors in flight safety. Changes in shape due to freezing of the surface of the aircraft, that is, changes in the shape of the wing shape occurring on the main wing and tail wing surface, are factors that hinder aerodynamic characteristics such as the maximum lift coefficient directly related to the safety of the aircraft. In addition, the icing around the engine air intake causes a decrease in the flow separation and intake air, and may lead to a decrease in the voltage recovery rate and an increase in the distortion rate, which may lead to deterioration of the engine performance. Flight safety can cause serious situations. Meanwhile, the ice and ice maker developed to prevent such a performance deterioration maintains the surface temperature above the freezing point by using the hot gas generated from the engine of the aircraft or the electric hot wire, thereby eliminating the surface freezing.

Freezing occurs during the collision with the surface of the aircraft during the movement of the supercooled droplet along the air at low atmospheric temperature and high relative humidity. In particular, freezing around the aircraft engine intake hinders the flow of air into the engine and negatively affects fuel injection and vaporizer systems. In the 1950s, the influence of aerodynamics on freezing, which is the basis of current freezing research, was mainly analyzed based on wind tunnel tests and flight tests. Hardy, Messinger, Langmuir and Blodgett have developed and used freezing propagation simulation techniques and computational fluid dynamics simulation techniques that have been developed since the 1970s. Initially, experimental and theoretical analysis of aircraft icing phenomenon was carried out by NASA Glenn Research Center, DERA permanent, and ONERA of France. In the late 1990s, research on freezing computer simulation It is actively proceeding.

Computational analysis and Icing Wind Tunnel tests can be considered to demonstrate safety by surface freezing of the aircraft. In the case of the freezing wind tunnel test, it is very difficult to control the similarity to the droplet and the flow conditions outside the aircraft, compared with the general wind tunnel test. This is because it is difficult to meet sophisticated laws that depend on many variables such as convection, conduction, sublimation, evaporation, latent heat exchange and surface heat transfer. In addition, while freezing wind tunnel tests take a lot of time and cost, the current simulation of ice using the latest computational fluid dynamics is relatively cost and time efficient, and consideration of droplet and aircraft similarity is not an issue. Therefore, the icing simulation method can be a good tool to substitute or supplement the freezing wind tunnel test which is limited to the actual various flight environments.

In addition, computer simulations can be applied immediately to the actual wind conditions as well as the freezing wind tunnel test conditions. In this case, consideration should be given to the relative size of the test model and the wind tunnel. Typically, the United States developed the IRT (Icing Research Tunnel) wind tunnel experiment and the LEWICE freezing simulation code for NASA.

Therefore, there is a need for a method for simulating the influence of the surface generated freezing region, the absolute amount of freezing growth, the freezing wind speed and the relative size of the test model before performing the freezing wind tunnel test.

The present invention, which is devised in view of the above-mentioned necessity, is to analyze the influence of the surface-generated freezing region, the absolute amount of icing propagation, the freezing wind speed and the relative size of the test model before performing the freezing wind tunnel test on the rotary- And to provide a method for simulating surface freezing of an air intake port.

According to another aspect of the present invention, there is provided a method of simulating surface freezing of an air intake port for an ice-making wind tunnel test of a rotary wing, the method comprising: performing freezing wind tunnel test for modeling air flow entering the air inlet and the air inlet A method of controlling the freezing wind tunnel test apparatus includes the steps of defining a negative grid structure and a boundary condition, setting a size of the freezing wind tunnel test unit, a velocity of air flowing into the air intake port, Calculating a surface pressure distribution and a surface velocity distribution applied to a peripheral surface of the air intake port and analyzing the flow field of the air intake port based on the calculated surface pressure distribution and the surface velocity distribution, The droplet accumulating on the peripheral surface of the air inlet according to the defined droplet volume and droplet size By using a step and the accumulation rate of the liquid for calculating the enemy jeokyul comprises the step of interpreting the ice growth on the peripheral surface of the air inlet.

In this case, the step of setting the size of the freezing wind tunnel testing section may be such that the cross-sectional area of the freezing wind tunnel testing section is set to the first type or the second type, and the size of the cross-sectional area of the first type is larger than the cross- Small size can be set.

In this case, the step of setting the size of the freezing wind tunnel test section may be such that the cross-sectional area of the first type is 1.2 meters in width and 1.5 meters in length.

Meanwhile, in the step of setting the size of the freezing wind tunnel testing unit, the cross-sectional area of the second type may be 2.6 meters in width and 3.8 meters in length.

Meanwhile, in the step of calculating the flow field of the air inlet, the number of lattices of the lattice structure of the freezing wind tunnel test portion may be set to 200,000.

Meanwhile, the step of calculating the flow field of the air intake port may be such that the velocity of the air is 72 m / s, the temperature of the air is -10 ° C, and the air pressure can be set to atmospheric pressure.

Meanwhile, in the step of calculating the accumulation rate of the droplets, the size of the droplets may be mono-disperse.

Meanwhile, the step of calculating the accumulation rate of the droplets may be performed by setting the droplet amount to 0.9 g / m ^3, and setting the droplet size to at least one of 20, 30, and 40 탆, The rate distribution can be calculated.

에 의해서 상기 액적의 축적율(β)을 연산하고, 여기서, α는 액적의 체적비,

는 액적의 속도 벡터,

는 수직 단위 벡터일 수 있다.In this case, the step of calculating the accumulation rate of the droplet may include:

To calculate the accumulation rate (beta) of the liquid droplet by the following equation, where alpha is the volume ratio of the droplet,

Is the velocity vector of the droplet,

May be a vertical unit vector.

에 의해서 상기 결빙 증식을 해석하고,여기서,

는 기 결정된 지점에서 액적의 속도이고, LWC는 액적량이며, β은 액적의 축적율일 수 있다.In this case, the step of analyzing the ice-

To analyze the frost growth,

Is the velocity of the droplet at the predetermined point, LWC is the droplet volume, and? Is the droplet deposition rate.

A computer-readable recording medium recording a code relating to a method for simulating surface freezing of an air intake port for a freezing wind tunnel test of a rotary wing according to another embodiment of the present invention is characterized in that the method for simulating the surface freezing of the air intake port comprises: And defining a grid topology and a boundary condition of the freezing wind tunnel testing unit for modeling an air flow flowing into the air inlet, setting a size of the freezing wind tunnel testing unit, Calculating a surface pressure distribution and a surface velocity distribution applied to a peripheral surface of the air intake port by setting a velocity of the introduced air, a temperature of the air, and an air pressure at predefined values, and analyzing the flow field of the air intake port, Based on the calculated surface pressure distribution and the surface velocity distribution, Calculating an accumulation rate of droplets accumulated on a peripheral surface of the air intake port in accordance with a droplet volume and a droplet size of the droplet; and analyzing ice growing on a peripheral surface of the air intake port using the accumulation rate of the droplet Code.

The method for simulating the air inlet surface freezing according to various embodiments of the present invention is characterized in that before performing the freezing wind tunnel test for the rotating air intake air inlet, the influence of the surface generated freezing region, the absolute amount of freezing growth, It is effective in terms of analysis cost and time and applicable to various flight environments.

FIG. 1 is a flowchart for explaining a method of simulating an air inlet surface freezing according to an embodiment of the present invention;
2 is a view for explaining a lattice structure and a boundary condition of an icemaking wind tunnel testing unit according to an embodiment of the present invention,
3 is a view for explaining a first type and a second type wind tunnel according to the sectional area of the freezing wind tunnel test portion shown in FIG. 2;
4 is a view for explaining surface pressure distribution around the air inlet port of the freezing wind tunnel test section according to the number of grids of the grid structure shown in FIG. 2,
FIGS. 5 and 6 are views for explaining surface pressure distribution and velocity distribution according to the first type and the second type shown in FIG. 3;
FIG. 7 is a view for explaining the distribution of the accumulation rate of droplets according to the first type and the second type shown in FIG. 3; and
FIG. 8 is a view for explaining the thickness of the freezing growth on the peripheral surface of the air inlet according to the first time and the second type shown in FIG. 3; FIG.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flowchart for explaining a method of simulating an air inlet surface freezing according to an embodiment of the present invention.

Referring to FIG. 1, the method for simulating the air inlet surface freezing defines a grid topology and a boundary condition of the freezing wind tunnel testing unit for modeling the air flow introduced into the air inlet and the air inlet (S110 ). If the lattice structure and boundary condition of the freezing wind tunnel test section are defined, the size of the freezing wind tunnel test section is set (S120). The air velocity, the temperature of the air, and the air pressure are set to predetermined values according to the size of the freezing wind tunnel test portion, the surface pressure distribution and the surface velocity distribution applied to the peripheral surface of the air intake port are calculated, (S130). The storage rate of the droplet accumulated on the peripheral surface of the air inlet is calculated according to the predetermined droplet amount and droplet size based on the calculated surface pressure distribution and the surface velocity distribution (S140). Next, the frost growth is analyzed on the peripheral surface of the air inlet using the liquid deposition rate (S150).

Define grid structure and boundary conditions

The lattice structure and boundary conditions of the freezing wind tunnel test section will be described in more detail with reference to the drawings shown in Fig.

2 is a view for explaining a lattice structure and a boundary condition of the freezing wind tunnel testing unit according to an embodiment of the present invention.

2, the model of the freezing wind tunnel testing unit according to the present invention is a model for modeling the air flowing into the air inlet and the air inlet of the rotating wing. The model of the freezing wind tunnel test section is a lattice structure and can be composed of Tetra grid system. The model of the freezing wind tunnel test part is a rectangular parallelepiped structure, and an air intake port model can be included inside.

Since the air intake port of the rotating wing unit to which the air intake surface surface freezing simulation method according to the present invention is applied can be disposed symmetrically with respect to the center axis, symmetry conditions can be imparted to the cross section of the central axis to reduce computation time. A separate small intake for the ECS (Environment Control System) and Nacelle can be placed below the engine air intake (see right drawing in FIG. 2).

In the model of the freezing wind tunnel test part, air can flow in direction A and air can flow in direction B. The air introduced into the freezing wind tunnel test section can be modeled as air flowing into the air intake port inside.

Then, modeling and computational grids for the analytical shape can be generated to calculate the freezing occurring at the air intake of the rotating wing. Grid creation can be done using ANSYS-GAMBIT, a grid-only generation program, and can be configured with a Tetra grid system. In order to compare the influence of the pressure distribution around the air intake port according to the number of lattices, it is possible to generate 200,000 grid and 600,000 grid.

frost wind tunnel Testing Department  Set size

After defining the lattice structure and boundary conditions of the freezing wind tunnel test section, the size of the modeled freezing wind tunnel test section is set.

Specifically, calculations can be performed on the air flow field in which no droplet is present prior to performing droplet collision and icing propagation calculations. In other words, the governing equations for the flow field calculations can be used to accurately simulate the atmospheric air flow, and the three-dimensional compressible Navier-Stokes equations can be used to account for viscosity and compressibility effects. As a numerical technique, it is possible to use the Cell-Centered-based finite volume method and the implicit time advance method (Implicit). The Roe method can be used for the space term in the flow field calculation and the second order accuracy flux calculation method can be applied. The Spalart-Allmaras model, which is simple but relatively accurate, can be applied to the turbulence model. Also, in order to efficiently handle complicated three-dimensional flow around the air inlet, FLUENT 6.3, a commercial CFD code, can be used.

 In order to analyze the flow field and ice growth characteristics due to the size of the freezing wind tunnel test section, two types of wind tunnel tunnels of different sizes can be considered. Two types of air intake port model sizes will be described in more detail with reference to FIG.

FIG. 3 is a view for explaining a first type and a second type wind tunnel according to the sectional area of the freezing wind tunnel test portion shown in FIG. 2. FIG. The left side of FIG. 3 shows a first type of wind tunnel and the right side of FIG. 3 shows a second type of wind tunnel. That is, the freezing wind tunnel test section can be set as the first type or the second type. For example, the size of the first type of freezing wind tunnel test section can be set to 1.2 m (width), 1.5 m (length), and 6.3 m (length). The size of the second type of the freezing wind tunnel test portion can be set to 2.6 meters in width, 3.8 meters in length, and 9.9 meters in length. According to the result of checking the blockage level according to the size of the wind tunnel test portion, the first type is about 5 times larger than the second type. This blockage difference can affect the freezing shape and the area that occur during freezing analysis.

In FIG. 3, it can be seen that there is a difference in speed of air applied to the air intake port depending on the size of the wind tunnel. In FIG. 3, it can be seen that the periphery of the air inlet is marked with a darker color than the periphery of the air inlet in the right side of FIG.

In other words, it can be confirmed that the color around the air intake port is displayed in a darker color as compared with the case where the wind tunnel having the narrow cross-sectional area (the first type) has the wind tunnel with the wide cross-sectional area (the second type). It can be seen that the air velocity at the air intake port becomes faster as the cross-sectional area of the wind tunnel becomes narrower. The cross sectional area of the first type of freezing wind tunnel test section may be designed to be smaller than the size of the cross sectional area of the second type freezing wind tunnel test section in order to compare the air speed difference of the air intake port with the cross sectional area of the wind tunnel. Therefore, by designing the size of the freezing wind tunnel test section in two types, it is possible to analyze the flow field and the ice growth characteristics according to the cross-sectional area size.

Flow field calculation of air inlet

When the size of the freezing wind tunnel test portion is set, a step of calculating the flow field of the air intake port is performed. At this time, the main factors determining the surface-generated freezing phenomenon in the freezing problem may be Liquid Water Contents (LWC), Mean Volume Diameter (MVD), aircraft flying speed, temperature of the icing environment and exposure time .

In this case, the droplet volume (LWC) means the mass of the droplet contained per unit volume, and the size of the droplet means the diameter of the droplet assumed to be spherical. Considering only the influence of air on the motion of droplets on the assumption that the multiphase flow in which the droplet and the air exist at the same time in order to perform the freezing analysis, the influence of the droplet of several tens of microns on the flow of the air is not great Multiphase flow calculations can be performed. In other words, based on the information obtained from the simulation of the air flow field and droplet movement, it is possible to carry out calculations on the ice growth.

In carrying out the step of calculating the flow field, the velocity of the air introduced into the air inlet, the temperature of the air and the air pressure are respectively set to predefined values. Then, the surface pressure distribution and the surface velocity distribution applied to the peripheral surface of the air intake port are calculated to perform the flow field analysis of the air intake port.

According to one embodiment of the present invention, the number of lattice structures of the lattice structure of the freezing wind tunnel test portion can be set to 200,000 or 600,000 to simulate the surface pressure distribution in the vicinity of the rotary air intake port (see FIG. 4).

The left side of FIG. 4 shows simulation of the surface pressure distribution of the air inlet port based on the lattice structure having 200,000 grid points. The right figure of FIG. 4 shows simulation of the surface pressure distribution of the air intake port based on the lattice structure having 600,000 grids.

As shown in FIG. 4, the surface pressure distribution around the rotating blade air inlets according to the number of grids of 200,000 or 600,000 pieces can exhibit a very similar tendency quantitatively. Therefore, in order to reduce computation time, liquid deposition and icing propagation calculation are performed on the basis of 200,000 grid lines.

As shown in FIG. 4, it can be seen that the upper portion of the air inlet of the rotary wing has a higher pressure than the other surface. It can be seen that this is directly related to the stagnation point of the flow. That is, when the size of the supercooled droplet is small, the droplet flows along the stream of air, so that there is a high possibility that the droplet collides with the surface of the air inlet around the stagnation point of the flow. Also, the calculation of the pure flow field with no droplet can affect the surface pressure distribution of the air intake port depending on the wind tunnel size.

3, it can be seen that the area where the air intake port shown in the left side is darker than the air intake port shown in the right side is more widely distributed. In other words, it can be seen that as the cross-sectional area of the wind tunnel is smaller, the high-pressure area of the air pressure applied to the air inlet surface is wider than the low-pressure area.

The pressure and velocity distribution at the cross section of the air intake port will be described with reference to FIGS. 5 and 6 according to the cross-sectional area of the wind tunnel.

Referring to FIGS. 5 and 6, the pressure and velocity distributions for the same point (area indicated by circles in the drawing) in the first and second types of wind tunnel models are shown. It can be confirmed that the first type is lower in pressure near the stagnation point at the upper end of the air inlet than the second type and the flow field is formed at a higher speed in the same influent flow condition.

This means that wind tunnel magnitude can cause substantial flow field differences. Calculating the velocity based on the mass flow rate of the air at the outlet area of each wind tunnel and at the exit, it can be seen that the velocity of the first type increases about 1.4 times as compared with the second type.

In addition to the effect of the size of the wind tunnel, the flow around the air intake port of the rotating wing is generally influenced by the turbulence-induced downward current. However, in the present invention, in order to derive a critical icing condition in which the interference effect by the main is neglected, the wake by the rotor blades is not considered. This is because wakes caused mainly by turbo blades are difficult to realize in the freezing wind tunnel, and even in the case of theoretical analysis, complicated wake calculation is required.

Therefore, according to an embodiment of the present invention, it is possible to perform an analysis for a pure flow field without a droplet at the previous stage of the freezing calculation. According to the simulation method for freezing air around the air inlet, the surface velocity distribution and the surface velocity distribution around the air inlet are calculated by setting the velocity of the air flowing into the air inlet, the temperature of the air and the air pressure at predetermined values, Can be calculated.

Droplet Accumulation rate  calculate

After calculating the flow field of the freezing wind tunnel test section, it is possible to calculate the accumulation rate of the droplet accumulated on the peripheral surface of the air intake port based on the calculated surface pressure distribution and the surface velocity distribution, have. The DROP3D module can be used to calculate the accumulation rate of droplets according to an embodiment of the present invention.

In this way, we can investigate the characteristics of the atmospheric droplet to quantitatively show the ratio of droplets impacting the surface of the aircraft after the flow field calculation. The atmospheric condition during icing can be regarded as a space physically mixed with air and water.

The supercooled clouds in the atmosphere are composed of droplets of various sizes, and the droplet distribution is known as the Langmuir D distribution. In Langmuir D distribution, the size of the largest droplet is 2.2 times larger than the mean value and the size of the smallest droplet is 3.2 times smaller than the mean value. In actual atmospheric conditions, the Langmuir D distribution has a non-uniform droplet size. However, when the droplet size is not large, the position where the droplet collides with the solid surface and the accumulation rate tend to be similar to Mono-Disperse.

When the accumulation rate of the solid surface is calculated by using the Langmuir D distribution, a considerable computation time may be required since the droplet field calculation must be performed considering all the probabilistic distribution of the droplet size.

Therefore, for efficient computation, we suppose that Mono-Disperse has a constant droplet size with similar tendency of accumulation rate instead of Langmuir D distribution.

Under this assumption, a more specific method for calculating the accumulation rate is as follows. It is possible to set at 0.9 g / m < ³ > as a predefined droplet amount, and to set at least one of 20, 30 and 40 mu m as the predefined droplet size. The storage rate is calculated by the DROP3D module according to the following method according to the calculation conditions set in the liquid amount and liquid size defined in the first and second types of freezing wind tunnel test sections.

First, the Eulerian-based droplet motion equation can be used to calculate the supercooled droplet field in the atmosphere. It was proposed by Bourgault et al. As a multiphase flow model in which air and liquid droplets are mixed, and can be constituted by a continuity equation for liquid droplets and a momentum dynamics equation. This is a numerical technique based on a finite volume method and can be expressed as Equation 1 below.

는 보존변수이며,

는 대류항,

는 용출항(Source Term)을 나타낸다. 구체적으로 보존변수, 대류항, 용출항은 다음의 수학식 2 내지 4와 같이 표현될 수 있다.In Equation (1)

Is a conservative variable,

The convection term,

Indicates the source term. Specifically, the conservation variables, the convection term, and the release term can be expressed by the following equations (2) to (4).

Here, α indicates a volume ratio of the droplets (Volume Fractiion), _D u, _D v is enemy speed liquid, _a u, _a v is the velocity, ρ _a is the density of air, ρ _w is the density of water in the air. C _D represents the drag coefficient of a droplet assuming a spherical shape.

The number of drag of such a droplet can be expressed by the following equations (5) and (6).

In the above equation (5), the Reynold's number (Re _d ) related to the liquid droplet can be expressed by the following equation (7).

In Equation (7), d represents the diameter of the droplet and μ represents the dynamic viscosity of the air. The K and Froude dimensionless can be expressed as Equation (8).

The equation relating to the accumulation rate indicating the rate at which the liquid droplet collides with the surface after calculating the droplet impingement equation can be expressed by the following equation (9). That is, Equation (9) is a value quantitatively indicating the ratio of the droplet colliding with the solid surface, and means the accumulation rate.

는 액적의 속도 벡터이고,

는 수직 단위 벡터이다.In Equation (9),? Is the volume ratio of the droplet,

Is the velocity vector of the droplet,

Is a vertical unit vector.

For example, the velocity of the air may be 72 m / s, the temperature of the air may be -10 ° C, and the air pressure may be set to atmospheric pressure in the above-described Equations 1 to 9 according to an embodiment of the present invention.

In Equations (1) to (9), a predefined value of the velocity of the air introduced into the air inlet, the temperature of the air, and the air pressure are input to calculate the surface pressure distribution and surface velocity distribution applied to the peripheral surface of the air inlet. Based on the calculated surface pressure distribution and surface velocity distribution, the rate of accumulation of droplets accumulated on the peripheral surface of the air inlet is calculated using the droplet amount and the droplet size.

The accumulation rate of the droplets accumulated around the air inlet according to the above-described method is as shown in Fig.

7 is a simulation result of the first type of accumulation rate, and the right side is a simulation result of the accumulation rate of the second type. The upper drawing in the left drawing shows a case where the droplet size is 20 탆, the intermediate drawing shows the case where the droplet size is 30 탆, and the lower drawing shows the case where the droplet size is 40 탆. Likewise, in the upper part of the right drawing, the lower drawing shows a case in which the droplet sizes are 20 탆, 30 탆 and 40 탆.

As shown in FIG. 7, as the droplet size increases, the magnitude of the accumulation rate and the droplet collision region tend to increase. In addition, it can be seen that the accumulation rate distribution of the first type is larger than that of the second type and the absolute value thereof is large.

It can be seen that the accumulation rate difference is caused by the velocity difference of the air according to the wind tunnel size because the rate of the air obtained through the flow field calculation is applied to the droplet impingement equation to calculate the accumulation rate at which the droplet impinges on the surface. In addition, the smaller the cross-sectional area of the freezing wind tunnel test portion, the more the freezing and thawing may occur on the surface of the air inlet. That is, it can be seen that the accumulation rate is high in the stagnation point region where the pressure distribution on the upper side of the rotating air intake air inlet is higher than the pressure distribution shown in FIG.

Surface freezing propagation analysis

After computing the droplet deposition rate, it is possible to analyze the ice growth on the peripheral surface of the air inlet using the calculated deposition rate of droplets. Specifically, the freezing and thawing analysis can be performed by setting the atmospheric temperature to -10 DEG C and setting the exposure time of the droplet to 15 minutes to analyze the freezing growth of droplets around the air inlet.

The type of ice growth after droplet impact calculation can be divided into Rime freezing and Glaze freezing according to atmospheric conditions. Rime icing can be a droplet of cloudy clouds with small droplet size and occurring predominantly at low, low, and low LWC conditions.

This is due to the very low atmospheric temperature, which causes the liquid to rapidly freeze at the moment it collides with the aircraft surface, and the air is drawn between the first freezing layer and the continuously accumulating ice layer. On the other hand, Glaze freezing occurs in cumulus clouds with an atmospheric temperature near 0 ° C, and occurs mainly at relatively high temperatures and high velocity, high LWC. Glaze icing can be freezing as it flows along the streamline without being frozen immediately after impact with the aircraft surface due to the large droplets and high temperatures.

The shear force and the heat flux distribution are not important because Rime freezing occurs at the moment of collision with the solid surface, but the shear force and heat flux must be considered to analyze Glaze freezing. In the case of Rime freezing, the ice growing shape is smoothly formed along the surface of the aircraft. On the other hand, Glaze ice shows a very irregular shape. For this reason, Glaze freezing can have more serious aerodynamic effects than Rime freezing.

Therefore, the Glaze model is applied to analyze the influence of ice on the surface of the aircraft. In general, the continuity equation concerning the thickness of the film and the energy spinning equation relating to the temperature, which describe the process in which the droplet is attached to the object and the freezing is proliferated, can be expressed as the following equations (10) and (11).

는 다음의 수학식 12와 같이 표현될 수 있다.In the above equations (10) and (11)

Can be expressed by the following equation (12).

는 다음의 수학식 13과 같이 표현될 수 있다.here,

Can be expressed by the following Equation (13).

는 매개변수들을 나타내며, 결빙 조건에 따라 결정될 수 있다. Rime 결빙의 경우, 액적이 표면에 충돌과 동시에 결빙되므로 액적은 시간(t)에서 공간에 대한 액적의 이동은 없고 시간에 대한 변환만 존재하므로, 에너지 방정식을 필요로 하지 않는다. 이때 결빙 높이에 대한 시간에 대한 변화율은 액적의 속도, 액적량 및 축적율로 표현될 수 있다. 즉, 상기 수학식 10과 같은 연속 방정식은 다음의 수학식 14와 같이 간단하게 표현될 수 있다.In the equations (10) to (13)

Represents the parameters and can be determined according to the freezing condition. In the case of Rime freezing, since the droplet is freezing at the same time as the surface collides with the surface, the droplet does not need energy equation because there is no shift of the droplet to space at time (t) At this time, the rate of change with respect to time with respect to the ice height can be expressed by the velocity of the droplet, the droplet amount, and the accumulation rate. That is, the continuity equation as shown in Equation (10) can be simply expressed as Equation (14).

는 무한 지점의 액적 속도이고, LWC는 액적량이며, β는 액적의 축적율을 의미한다. 상기 수학식 14를 참고하면, 결빙 증식은 액적의 축적율을 이용하여 해석할 수 있다. 즉, 액적의 축적율(β), 액적량 및

을 이용하여 공기 흡입구 표면 결빙 증식을 해석할 수 있다.here,

Is the droplet velocity at an infinite point, LWC is the droplet volume, and β is the droplet accumulation rate. Referring to Equation (14), the icing propagation can be analyzed by using the accumulation rate of the droplet. That is, the accumulation rate (?) Of droplets,

It is possible to analyze the surface freezing growth on the air inlet surface.

In the above, equations (1) to (14) are equations concerning the droplet accumulation rate and the surface freezing growth. This can be implemented using the sub-modules DROP3D and ICE3D of the FENSAP-ICE package, which is numerically implemented freezing simulation code based on finite volume method and finite element method.

For verification of the operation code, it is possible to carry out the accumulation rate and ice growth calculation for NACA64 (2) 45 and NACA0012, and compared with the results of the experiment and the LEWICE code, the similar tendency can be confirmed quantitatively and qualitatively.

FIG. 8 is a view for explaining the thickness of the freezing growth on the peripheral surface of the air inlet according to the first time and the second type shown in FIG. 3; FIG.

Referring to FIG. 8, it can be seen that the ice frost propagation analysis results show a difference in predicted ice frost growth depending on the cross-sectional area of the pond test section. That is, when comparing the predicted result value of the part where the frost is grown, it can be seen that the first type exhibits about 1.5 times larger ice thickness than the second type.

This is because when the viscosity and heat flux obtained from the accumulation rate calculated by the droplet impingement equation and the velocity of the droplet and the flow field are applied to the icing propagation equation, The difference may be generated. In order to obtain the accurate ice distribution and expansion amount in the freezing wind tunnel test, it is necessary to determine the size of the wind tunnel test section in comparison with the model size. have.

The method of simulating the air inlet surface freezing simulation according to the present invention simulates the influence of the surface freezing region, the absolute amount of freezing growth, the freezing wind speed and the relative size of the test model before performing the freezing wind tunnel test on the rotating air intake air inlet And such a simulation approach can be more efficient in terms of analysis cost and time.

The above-described methods according to various embodiments of the present invention may be stored as a code in a computer-readable storage medium. The code for performing the above-described methods according to various embodiments of the present invention may be stored in a memory such as a random access memory (RAM), a flash memory, a ROM (Read Only Memory), an EPROM (Erasable Programmable ROM), an Electrically Erasable and Programmable ROM ), A register, a hard disk, a removable disk, a memory card, a USB memory, a CD-ROM, and the like.

Although illustrative embodiments and applications of the present invention have been shown and described, many changes and modifications may be made without departing from the scope of the present invention, and such modifications may be made by one of ordinary skill in the art to which the present invention pertains It can be clearly understood. Accordingly, the described embodiments are illustrative and not restrictive, and the invention is not limited by the accompanying detailed description, but is capable of modifications within the scope of the claims.

Claims (11)

A method of simulating surface freezing of an air intake port for a freezing wind tunnel test of a rotating wing,
Defining a grid topology and a boundary condition of the freezing wind tunnel testing unit for modeling an air flow flowing into the air inlet and the air inlet;
Setting a size of the freezing wind tunnel testing unit;
The air velocity, the temperature of the air, and the air pressure introduced into the air intake port are set to predefined values, and the surface pressure distribution and the surface velocity distribution applied to the peripheral surface of the air intake port are calculated to calculate the flow field of the air intake port Computing;
Calculating an accumulation rate of a droplet accumulated on a peripheral surface of the air inlet according to a predetermined droplet amount and a droplet size based on the surface pressure distribution and the surface velocity distribution calculated; And
And analyzing freezing growth on a peripheral surface of the air intake port using the accumulation rate of the liquid droplet. The method according to claim 1,
Wherein the step of setting the size of the freezing wind tunnel testing unit includes:
Wherein the cross-sectional area of the freezing wind tunnel test section is set to a first type or a second type, and a cross-sectional size of the first type is set to be smaller than a cross-sectional size of the second type. . 3. The method of claim 2,
Wherein the step of setting the size of the freezing wind tunnel testing unit includes:
Wherein the cross-sectional area of the first type is 1.2 meters in width and 1.5 meters in length. 3. The method of claim 2,
Wherein the step of setting the size of the freezing wind tunnel testing unit includes:
Wherein the cross-sectional area of the second type is 2.6 meters in width and 3.8 meters in length. The method according to claim 1,
Wherein calculating the flow field of the air inlet comprises:
Wherein the number of lattices of the lattice structure of the freezing wind tunnel test portion is set to 200,000. The method according to claim 1,
Wherein calculating the flow field of the air inlet comprises:
Wherein the speed of the air is 72 m / s, the temperature of the air is -10 DEG C, and the air pressure is set to atmospheric pressure. The method according to claim 1,
Wherein the step of calculating the accumulation rate of the droplets comprises:
Wherein the size of the liquid droplet is mono-disperse. The method according to claim 1,
Wherein the step of calculating the accumulation rate of the droplets comprises:
Wherein the liquid droplet amount is set to 0.9 g / m < ³ >, and the liquid droplet size is set to at least one of 20, 30, and 40 mu m. 9. The method of claim 8,
Wherein the step of calculating the accumulation rate of the droplets comprises:
The following equation

(?) Of the liquid droplet by the liquid-liquid separator
Here,? Is the volume ratio of the droplet,

Is the velocity vector of the droplet,

Is a vertical unit vector. 10. The method of claim 9,
The step of analyzing the ice-
The following equation

To analyze the frost growth,

Is a droplet velocity at a predetermined point, LWC is a droplet volume, and? Is an accumulation rate of a droplet. A method of simulating a surface freezing of an air intake port for a freezing wind test of a rotary wing aircraft, the method comprising the steps of:
Defining a grid topology and a boundary condition of the freezing wind tunnel testing unit for modeling an air flow flowing into the air inlet and the air inlet;
Setting a size of the freezing wind tunnel testing unit;
The air velocity, the temperature of the air, and the air pressure of the air introduced into the air inlet are set to predetermined values, the surface pressure distribution and the surface velocity distribution applied to the peripheral surface of the air inlet are calculated, ;
Calculating an accumulation rate of a droplet accumulated on a peripheral surface of the air inlet according to a predetermined droplet amount and a droplet size based on the surface pressure distribution and the surface velocity distribution calculated; And
And analyzing the ice growth on the peripheral surface of the air inlet using the accumulation rate of the droplets.

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