Two-phase problem simulation method for liquid drop impinging net structure based on phase field method

Abstract

The invention discloses a two-phase problem simulation method for liquid drop impact net structure based on a phase field method, and relates to the technical field of liquid drop impact simulation. Gas-liquid parameters corresponding to a liquid film formed by the liquid drops are obtained through experimental literatures; drawing a silk screen structure model and a liquid drop model based on gas-liquid parameters, describing the movement of the liquid drop in a gas phase by using an Euler model, describing the initial shape and position of the liquid drop by using a Navier-Stokes equation and a laminar flow initialization equation, and describing the surface tension and phase change process of the liquid drop by using a phase field control equation; drawing a liquid drop impact silk screen structure model, dividing a plurality of grid adaptive areas, and carrying out simulation calculation; and according to the obtained simulation result, performing post-processing to obtain a speed cloud picture, a pressure cloud picture, a phase volume fraction cloud picture and an animation of the liquid drop impacting the silk screen structure. According to the method, a phase field control equation and an Euler model are utilized to simulate the coalescence and dispersion process of the liquid drop impacting a net structure, and complicated experiment operation is not needed.

Description

Technical Field

[0001] The invention relates to the technical field of droplet impact simulation, in particular to a two-phase problem simulation method of a droplet impacting a mesh structure based on a phase field method. Background Art

[0002] Droplet impact on mesh structures is widely used in the fields of physics, fluid mechanics and materials science, and is mainly used in a variety of application scenarios, such as spray cooling, coating technology, biomedical experiments, industrial sprayers, atomizers or atomizing nozzles. The core of this technology is to understand the interaction between droplets and mesh structures (such as grids, pores or mesh-like surfaces), including droplet breakup, dispersion, adsorption and flow behavior.

[0003] Numerical simulation has been favored by many scholars for its advantages of fast speed, high efficiency and low cost, but a technical problem that urgently needs to be solved is: a simulation method for droplet impact on mesh structure is needed to explore the flow and heat transfer characteristics of droplet impact on liquid film dynamics and promote its application value in related fields. The phase field module is a powerful numerical simulation tool, mainly used to solve problems involving phase change, diffusion and interface dynamics. Based on phase field theory, complex physical processes are simplified into a continuous field, which can describe the continuous transition between different phases, such as solid-liquid, solid-gas, liquid-liquid, solid-solid phase change, and interface evolution during diffusion.

[0004] However, the behavior of droplets impacting mesh structures is currently affected by many factors, and its dynamic behavior is relatively complex, which makes prediction difficult and has a huge impact on the research on its heat and mass transfer efficiency. At the same time, it also hinders the research on physical phenomena such as the evolution of fluid flow after droplet impact and heat conduction between fluids and at the fluid-solid interface. Summary of the invention

[0005] In order to address the shortcomings of the background technology, the present invention provides a two-phase problem simulation method of droplet impacting a mesh structure based on the phase field method, which utilizes the phase field control equation and the Euler model to realize the simulation of the coalescence and discrete process of droplet impacting a mesh structure without the need for complicated experimental operations.

[0006] To achieve the above object, the present invention adopts the following technical solution: a two-phase problem simulation method of a droplet impacting a mesh structure based on a phase field method, comprising the following steps:

[0007] S1. Obtain the gas-liquid parameters corresponding to the formation of liquid film by droplets by reading relevant experimental literature;

[0008] The gas-liquid parameters include liquid phase inlet flow rate u, absolute pressure p, thermal conductivity K, body force source term F, gravity vector g, liquid phase temperature T, position vector r, reference position vector rref , the density of the gas phase and the liquid phase ρ1 and ρ2, the dynamic viscosity of the gas phase and the liquid phase μ1 and μ2, the interface thickness control parameter ε, the surface tension coefficient σ and the phase content φ;

[0009] S2. Draw the screen structure model and droplet model based on the gas-liquid parameters;

[0010] The droplet model and the wire mesh structure model include the following governing equations:

[0011] a. Euler model of a droplet falling in a gas phase

[0012]

[0013] In the formula, is the gradient operator, the subscripts i = 1, 2 correspond to the gas phase and liquid phase respectively, t is the time, α is the volume fraction, v is the velocity field, P is the local pressure, F g,I It is the interphase force between gas and liquid;

[0014] b. Navier-Stokes equation

[0015]

[0016] c. Laminar flow initialization equation

[0017]

[0018] In the formula, is the Laplace operator, f is the external force;

[0019] d. Phase field governing equations

[0020]

[0021] Among them, the Euler model represented by formula (1) and formula (2) is used to describe the movement of the droplet in the gas phase, the Navier-Stokes equation and laminar initialization equation represented by formula (3) and formula (4) are used to describe the initial shape and position of the droplet, and the phase field control equation represented by formula (5)-formula (8) is used to describe the surface tension of the droplet and the phase change process;

[0022] S3, draw a droplet impact screen structure model, divide it into multiple grid adaptive areas, and perform simulation calculations;

[0023] According to the actual size of the droplet and the wire mesh structure, the droplet impact wire mesh structure model is drawn in proportion, and multiple grid adaptive regions are divided. The gas-liquid parameters measured by S1 are set as the inlet boundary conditions respectively. The liquid phase inlet flow rate u, absolute pressure p, liquid phase temperature T and the droplet particle size at the initial injection are set at the inlet end. The gravity vector g, surface tension coefficient σ, gas phase density ρ1 and dynamic viscosity μ1 are set for the simulation area. The outlet parameters are obtained using formulas (1) to (8) in S2. It is assumed that the calculation is completed when the droplet reaches the outlet end.

[0024] S4. Based on the simulation results obtained in S3, post-processing is performed to obtain the velocity cloud map, pressure cloud map, phase volume fraction cloud map and animation of the droplet impacting the wire mesh structure, and the results are compared and analyzed with the experimental literature to determine whether they are similar. If not, return to S3 to repeat the operation. If so, output the calculation results.

[0025] Furthermore, when dividing the multiple grid adaptive regions in S3, free quadrilateral grid division is performed on the droplet domain, and free triangle grid division is performed on the range of 0.05 cm above and below the screen structure.

[0026] Furthermore, the outlet parameters in S3 include the velocity field v1 of the gas phase, the velocity field v2 of the liquid phase, and the absolute pressure p.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention explores the dynamic behavior of droplets under different concentrations, impact speeds, and different positions of the impact network structure based on phase interface tracking and adaptive dynamic grid technology, and the physical mechanism of the corresponding impact phenomenon, which is conducive to further revealing the role of droplet impact in heat and mass transfer efficiency, and understanding the physical phenomena such as the fluid flow evolution morphology after droplet impact and heat conduction between fluids and at the fluid-solid interface, thereby providing a solution for controlling heat and mass transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the method of the present invention;

[0029] Figure 2 is a phase volume fraction cloud diagram obtained in Example. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] like Figure 1As shown, a two-phase problem simulation method of a droplet impacting a mesh structure based on a phase field method includes the following steps:

[0032] S1. Obtain the gas-liquid parameters corresponding to the formation of liquid film by droplets by reading relevant experimental literature;

[0033] The gas-liquid parameters related to the formation of liquid film by droplets are obtained, and the gas-liquid parameters include liquid phase inlet flow rate u, absolute pressure p, thermal conductivity K, body force source term F, gravity vector g, liquid phase temperature T, position vector r, reference position vector r ref , densities of the gas phase and liquid phase ρ1 and ρ2, dynamic viscosities of the gas phase and liquid phase μ1 and μ2, interface thickness control parameter ε, surface tension coefficient σ and phase content φ.

[0034] S2. Draw the screen structure model and droplet model based on the gas-liquid parameters;

[0035] After the droplets collide with the wire mesh structure, they pass through the wire mesh structure, during which the droplets form a liquid film on the surface of the wire mesh structure, accompanied by coalescence and fragmentation.

[0036] The droplet model and the wire mesh structure model include the following governing equations:

[0037] a. Euler model of a droplet falling in a gas phase

[0038]

[0039] In the formula, is the gradient operator, the subscripts i = 1, 2 correspond to the gas phase and liquid phase respectively, t is the time, α is the volume fraction, v is the velocity field, P is the local pressure, F g,I It is the interphase force between gas and liquid;

[0040] b. Navier-Stokes equation

[0041]

[0042] c. Laminar flow initialization equation

[0043]

[0044] In the formula, is the Laplace operator, f is the external force;

[0045] d. Phase field governing equations

[0046]

[0047] Among them, the Euler model represented by formula (1) and formula (2) is used to describe the movement of droplets in the gas phase, the Navier-Stokes equation and laminar initialization equation represented by formula (3) and formula (4) are used to describe the initial shape and position of the droplets, and the phase field control equation represented by formula (5)-formula (8) is used to describe the surface tension of the droplets and the phase change process.

[0048] S3, draw a droplet impact screen structure model, divide it into multiple grid adaptive areas, and perform simulation calculations;

[0049] According to the actual size of the droplet and the screen structure, the droplet impact screen structure model is drawn in proportion and divided into multiple mesh adaptive areas. The droplet domain is divided into free quadrilateral meshes, and the screen structure is divided into free triangle meshes within 0.05 cm above and below.

[0050] The gas-liquid parameters measured by S1 are set as the inlet boundary conditions respectively. The liquid phase inlet flow rate u, absolute pressure p, liquid phase temperature T and droplet size at the time of initial injection are set at the inlet. The gravity vector g, surface tension coefficient σ, gas phase density ρ1 and dynamic viscosity μ1 are set for the simulation area. The outlet parameters are obtained using formulas (1) to (8) in S2. The outlet parameters include the velocity field v1 of the gas phase, the velocity field v2 of the liquid phase and the absolute pressure p. It is assumed that the calculation is completed when the droplet reaches the outlet.

[0051] S4. Based on the simulation results obtained in S3, post-processing is performed to obtain the velocity cloud map, pressure cloud map, phase volume fraction cloud map and animation of the droplet impacting the wire mesh structure, and the results are compared and analyzed with the experimental literature to determine whether they are similar. If not, return to S3 to repeat the operation. If so, output the calculation results.

[0052] Example

[0053] The parameters obtained from experimental literature are used as the initial conditions for numerical simulation, as shown in Table 1:

[0054] Table 1 Parameter settings

[0055] parameter value Liquid phase inlet velocity u / (m / s) 0.4(m / s) Absolute pressure p / (N) 1(pa) Thermal conductivity K / (W / (m·K)) 0.025(W / (m·K)) Body force source term F / (N) 0.0098(N) Gravity vector g / (N / kg) 9.8(N / Kg) Liquid phase temperature T / K 293.15(K) Position vector r (0,0,7) <![CDATA[Reference position vector r ref > (0,0,0) <![CDATA[Density ρ1 of the gas phase / (kg / cm 3 )]]> <![CDATA[1.2(kg / m 3 )]]> <![CDATA[Density ρ2 of the liquid phase / (kg / cm 3 )]]> <![CDATA[1000(kg / m 3 )]]> <![CDATA[Dynamic viscosity μ1 of the gas phase / (mPa·s)]]> 1.81×10^(-5)(Pa·s) <![CDATA[Dynamic viscosity μ2 of the liquid phase / (mPa·s)]]> 0.001(Pa·s) Interface thickness control parameter ε / (mm) 0.00036(mm) Surface tension coefficientσ / (N / m) 0.0728(N / m) Phase content φ 0.3 <![CDATA[The mutual force F between gas and liquid g,I > <![CDATA[9800(N / M 3 )]]>

[0056] The phase volume fraction cloud map obtained by combining Figure 2 shown.

[0057] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other forms of assembly without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0058] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A two-phase problem simulation method for droplet impact on a mesh structure based on a phase field method, characterized by: The following steps are involved: S1. Obtain the gas-liquid parameters corresponding to the formation of liquid film by droplets by reading relevant experimental literature; The gas-liquid parameters include liquid phase inlet flow rate u, absolute pressure p, thermal conductivity K, body force source term F, gravity vector g, liquid phase temperature T, position vector r, reference position vector r ref , the density of the gas phase and the liquid phase ρ1 and ρ2, the dynamic viscosity of the gas phase and the liquid phase μ1 and μ2, the interface thickness control parameter ε, the surface tension coefficient σ and the phase content φ; S2. Draw the screen structure model and droplet model based on the gas-liquid parameters; The droplet model and the wire mesh structure model include the following governing equations: a. Euler model of a droplet falling in a gas phase Where ▽ is the gradient operator, the subscripts i=1 and 2 correspond to the gas phase and the liquid phase respectively, t is the time, α is the volume fraction, v is the velocity field, P is the local pressure, and F g,I It is the interphase force between gas and liquid; b. Navier-Stokes equation c. Laminar flow initialization equation In the formula, ▽ 2 is the Laplace operator, f is the external force; d. Phase field governing equations ▽·u＝0 (6) Among them, the Euler model represented by formula (1) and formula (2) is used to describe the movement of the droplet in the gas phase, the Navier-Stokes equation and laminar initialization equation represented by formula (3) and formula (4) are used to describe the initial shape and position of the droplet, and the phase field control equation represented by formula (5)-formula (8) is used to describe the surface tension of the droplet and the phase change process; S3, draw a droplet impact screen structure model, divide it into multiple grid adaptive areas, and perform simulation calculations; According to the actual size of the droplet and the wire mesh structure, the droplet impact wire mesh structure model is drawn in proportion, and multiple grid adaptive regions are divided. The gas-liquid parameters measured by S1 are set as the inlet boundary conditions respectively. The liquid phase inlet flow rate u, absolute pressure p, liquid phase temperature T and the droplet particle size at the initial injection are set at the inlet end. The gravity vector g, surface tension coefficient σ, gas phase density ρ1 and dynamic viscosity μ1 are set for the simulation area. The outlet parameters are obtained using formulas (1) to (8) in S2. It is assumed that the calculation is completed when the droplet reaches the outlet end. S4. Based on the simulation results obtained in S3, post-processing is performed to obtain the velocity cloud map, pressure cloud map, phase volume fraction cloud map and animation of the droplet impacting the wire mesh structure, and the results are compared and analyzed with the experimental literature to determine whether they are similar. If not, return to S3 to repeat the operation. If so, output the calculation results.

2. According to claim 1, a two-phase problem simulation method of a droplet impacting a mesh structure based on a phase field method, characterized in that: When dividing a plurality of grid adaptive regions in S3, free quadrilateral grid division is performed on the droplet region, and free triangle grid division is performed on the range of 0.05 cm above and below the screen structure.

3. The two-phase problem simulation method of droplet impacting a mesh structure based on a phase field method according to claim 1, characterized in that: The outlet parameters in S3 include the velocity field v1 of the gas phase, the velocity field v2 of the liquid phase and the absolute pressure p.

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