HP-RTM process resin stirring time prediction simulation method

Abstract

The invention discloses an HP-RTM process resin stirring time prediction simulation method which comprises the following steps: constructing a physical model of a resin stirring tank, and dividing a fluid domain in the physical model into a rotating domain and a static domain according to a stirrer structure and size parameters arranged in the stirring tank; performing steady-state simulation on a resin stirring process in the physical model by using a VOF model, and determining that a flow field of resin stirring is stable; the method comprises the following steps: adding a tracer agent to the bottom of a stable flow field of resin stirring in a unit region marking manner to replace resin precipitation, setting an initial position and concentration, and then carrying out transient simulation by using an SIMPLE algorithm; a plurality of monitoring points are arranged in a transient simulation flow field, and when the precipitation concentration of the resin replaced by the tracer displayed by the plurality of monitoring points meets the 95% mixing principle, the uniform resin precipitation mixing time is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of high pressure resin transfer molding technology, and in particular to a HP-RTM process resin stirring time prediction simulation method. Background Art

[0002] High-pressure resin transfer molding (HP-RTM) is a derivative process of traditional resin transfer molding (RTM). HP-RTM equipment is generally in a circulating working state, and the stirring tank is always working, but some uncontrollable factors such as power failure will cause the equipment to stop working. The resin will precipitate and impurities will agglomerate if it is left at room temperature for too long. As part of the HP-RTM equipment, the resin stirring tank is used to stir the resin so that the resin impurities and precipitation are mixed evenly.

[0003] However, there is no specific parameter standard for how long it takes to achieve a uniform mixing state after the equipment is started. The time is controlled based on work experience. The uncertainty of the stirring state can easily lead to the resin not being able to enter the mold in a relatively ideal mixed uniform state or the resin being over-stirred, both of which can easily lead to deviations in product performance. Summary of the invention

[0004] The purpose of the present invention is to provide a HP-RTM process resin mixing time prediction simulation method to solve the technical problems caused in the actual production process due to the lack of precise time control of the resin precipitation mixing uniformity in the shutdown state in the existing high-pressure resin transfer molding process.

[0005] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0006] A method for predicting and simulating the mixing time of resin in a HP-RTM process comprises the following steps:

[0007] Step 100, constructing a physical model of a resin stirring tank, and dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the stirrer set in the stirring tank;

[0008] Step 200: Use the VOF model to perform steady-state simulation on the resin stirring process in the physical model, and determine whether the flow field of the resin stirring reaches stability;

[0009] Step 300, adding a tracer to the bottom of the stable flow field of resin stirring to replace the resin precipitation by means of unit area marking, setting its initial position and concentration, and then performing transient simulation using SIMPLE algorithm;

[0010] Step 400: multiple monitoring points are set in the transient simulated flow field, and when the concentration of the resin precipitate replaced by the tracer displayed by the multiple monitoring points meets the 95% mixing principle, the time for the resin precipitate to be mixed uniformly is obtained.

[0011] As a preferred solution of the present invention, a method for dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the agitator set in the stirring tank includes:

[0012] By performing Boolean operations on the physical model, the interface between the agitator and the space inside the agitator tank is extracted, and the remaining area obtained by suppressing the agitator entity model in the physical model is the fluid domain;

[0013] The rotating domain is determined according to the meshing of the stirring paddles in the same layer of the stirrer, and the rest of the fluid domain is set as the stationary domain.

[0014] As a preferred solution of the present invention, in the process of suppressing the remaining area obtained by the agitator solid model in the physical model as a fluid domain, the top surface of the fluid domain is agreed to be a free liquid surface.

[0015] As a preferred embodiment of the present invention, the stirrer comprises a rotating shaft and a stirring paddle, a plurality of the stirring paddles are evenly distributed along the same circumference of the rotating shaft to form a stirring body, and a plurality of stirring bodies are arranged on the rotating shaft;

[0016] Before the meshing of the stirring paddles of the stirring body determines the rotation domain, the number of the stirring paddles distributed in the stirring body is increased, and a boundary layer is inserted between the stirring paddles and the fluid domain.

[0017] As a preferred embodiment of the present invention, a specific method for achieving stability of the flow field of resin stirring by steady-state simulation includes:

[0018] By setting monitoring points in the flow field and ensuring that the speed of the monitoring points does not increase with the number of iterations;

[0019] Obtain the vertical plane velocity distribution cloud map of the model and obtain the maximum stirring velocity of the flow field; calculate the blade tip velocity through the formula and make it the same as the maximum stirring velocity of the flow field.

[0020] As a preferred embodiment of the present invention, the agitator structure and size parameters include but are not limited to: the distance between two adjacent stirring bodies, the diameter of the stirring body, the diameter of the rotating domain formed by the stirring body, and the distance from the bottom stirring body to the bottom of the stirring tank.

[0021] As a preferred solution of the present invention, the stirring and mixing uniformity time data corresponding to each experimental parameter at different parameter values ​​is analyzed by controlling a single variable;

[0022] Select at least three groups of orthogonal experiments for each experimental parameter to determine the optimal combination of experimental parameters.

[0023] As a preferred solution of the present invention, the diameter of the rotating domain is set to be the diameter of the stirring body plus 10 mm.

[0024] As a preferred solution of the present invention, a fluid inflow boundary condition and a fluid outflow boundary condition of the rotating domain are constructed, and the stationary domain and the rotating domain exchange data through the fluid inflow boundary condition and the fluid outflow boundary condition.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention utilizes a tracer instead of resin precipitation to perform a steady-state simulation and a transient simulation in the resin stirring process to simulate the state of the stirring tank and the agitator during the stirring process. The study reveals the connection between the relevant parameters of the stirring tank and the stirring time, effectively reducing the problem of the operator's mixing time being too short, and realizing the transformation from "mixing experience" to "determined by data". BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0028] Figure 1 This is a schematic diagram of the physical model structure of a stirring tank according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of a structure for dividing a fluid domain into a physical model according to an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of the vertical velocity distribution of a flow field simulated by a physical model of an embodiment of the present invention;

[0031] Figure 4 A graph showing the number of iterations of the speed of a monitoring point according to an embodiment of the present invention;

[0032] Figure 5 A schematic diagram of constructing a tracer deposition phase according to an embodiment of the present invention;

[0033] Figure 6 It is a schematic diagram of the overall process of an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] There are many numerical simulation software on the market, such as Ansys Fluent, COMSOL Multiphysics, OpenFOAM, CFX, SIMULIA Abaqus, etc., which can realize numerical simulation of agitators. Among them, Ansys Fluent is widely used in academia and industry, has a rich user community and document support, and provides a variety of turbulence models to adapt to different flow characteristics. Among them, the multiphase flow model is suitable for processing reactions in the mixing process, and the post-processing function is also relatively powerful. This patent uses Ansys Fluent as an example to explain the mixing simulation method.

[0036] The agitator simulation theory of this embodiment mainly involves the following aspects:

[0037] 1. Use the Navier-Stokes equations to describe fluid flow, taking into account the nonlinearity, viscosity and incompressibility of the flow

[0038] 2. Since the stirring process is usually turbulent, the turbulence model used is the k-ε or k-ω model to simulate the energy transfer and eddy characteristics of turbulence. The k-ε model describes turbulence by solving the turbulent kinetic energy (k) and the turbulent kinetic energy dissipation rate (ε), which is suitable for most industrial flow conditions. This model is relatively simple to calculate and has high stability, but the prediction ability for low Reynolds number flow and strong rotation flow is poor, and the simulation of turbulent behavior near the wall is not accurate enough. The k-ω model describes turbulence by solving the turbulent kinetic energy (k) and the turbulent kinetic energy frequency (ω), which is suitable for low Reynolds number flow and boundary layer flow. This model has better simulation of flow characteristics near the wall and is suitable for complex boundary layer flow. It has strong prediction ability for strong rotation flow, but under certain flows, it is numerically unstable. This patent uses the k-ε model with higher stability for solution.

[0039] 3. The VOF (Volume of Fluid) model is suitable for simulating multiphase flow, especially when the fluid interface is significant and immiscible, such as the separation process of precipitation and liquid. This model can effectively capture the flow characteristics of the two phases and is suitable for use in complex multiphase flow scenarios. This patent is to check the distribution of precipitation in the resin, so it is believed that the interface between the two is significant and immiscible, and the VOF model can be used for multiphase flow simulation.

[0040] 4. Accurately set the boundary conditions of the reactor, such as inlet and outlet flow rates, agitator speed, etc., to ensure the authenticity and accuracy of the simulation. The model involved in this patent has no inlet and outlet, so only the agitator speed and the rotation domain speed need to be set, which will be explained in detail in the following process.

[0041] 5. Regardless of whether a pressure-based solver or a density-based solver is used, fluid flow requires solving the momentum equation, continuity equation, and turbulence equation, and then solving the energy equation and component equation according to the operation settings. The difference is that the pressure-based separation solver solves the momentum equations in the three directions of U, V, and W separately, and then solves the continuity equation. This will cause it to ignore other conditions when calculating some equations, so the solution speed is faster; the pressure-based coupling solver solves the momentum equation and the continuity equation in one set of equations, and then solves the energy equation and the component equation separately; the density-based coupling solver solves all equations together, and finally solves the turbulence equation separately, which has the highest accuracy, but is not easy to converge and takes a long time. Regardless of the type of solver, the mass conservation equation and the momentum conservation equation need to be satisfied. This patent uses a pressure-based solver for solution.

[0042] The mass conservation equation:

[0043]

[0044] Where: u, v, w—velocity vectors along the x, y, z directions.

[0045] Momentum conservation equation:

[0046]

[0047] Where: f i —component of the unit mass volume force in the i direction; τ mn —The projected component of the viscous stress in the n direction onto the plane perpendicular to the m axis.

[0048] like Figures 1 to 6 As shown, the present invention provides a HP-RTM process resin stirring time prediction simulation method, comprising the following steps:

[0049] Step 100, constructing a physical model of a resin stirring tank, and dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the stirrer set in the stirring tank;

[0050] Step 200: Use the VOF model to perform steady-state simulation on the resin stirring process in the physical model, and determine whether the flow field of the resin stirring reaches stability;

[0051] Step 300, adding a tracer to the bottom of the stable flow field of resin stirring to replace the resin precipitation by means of unit area marking, setting its initial position and concentration, and then performing transient simulation using SIMPLE algorithm;

[0052] Step 400: multiple monitoring points are set in the transient simulated flow field, and when the concentration of the resin precipitate replaced by the tracer displayed by the multiple monitoring points meets the 95% mixing principle, the time for the resin precipitate to be mixed uniformly is obtained.

[0053] The method of dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the agitator set in the stirring tank includes:

[0054] By performing Boolean operations on the physical model, the interface between the agitator and the space inside the agitator tank is extracted, and the remaining area obtained by suppressing the agitator entity model in the physical model is the fluid domain;

[0055] The rotating domain is determined according to the meshing of the stirring paddles in the same layer of the stirrer, and the rest of the fluid domain is set as the stationary domain.

[0056] In the process of suppressing the agitator solid model in the physical model to obtain the remaining area as the fluid domain, the top surface of the fluid domain is agreed to be the free liquid surface.

[0057] The stirrer comprises a rotating shaft and a stirring paddle, a plurality of the stirring paddles are evenly distributed along the same circumference of the rotating shaft to form a stirring body, and a plurality of stirring bodies are arranged on the rotating shaft;

[0058] Before the meshing of the stirring paddles of the stirring body determines the rotation domain, the number of the stirring paddles distributed in the stirring body is increased, and a boundary layer is inserted between the stirring paddles and the fluid domain.

[0059] The specific methods for achieving stability through steady-state simulation and determining the flow field of resin stirring include:

[0060] By setting monitoring points in the flow field and ensuring that the speed of the monitoring points does not increase with the number of iterations;

[0061] Obtain the vertical plane velocity distribution cloud map of the model and obtain the maximum stirring velocity of the flow field; calculate the blade tip velocity through the formula and make it the same as the maximum stirring velocity of the flow field.

[0062] The agitator structure and size parameters include but are not limited to: the distance between two adjacent agitating bodies, the diameter of the rotating shaft, the diameter of the rotating domain formed by the agitating bodies, and the distance from the bottommost agitating body to the bottom of the agitating tank.

[0063] The diameter of the rotating domain is set to the diameter of the stirring body plus 10 mm.

[0064] The fluid inflow boundary condition and the fluid outflow boundary condition of the rotating domain are constructed, and the stationary domain and the rotating domain exchange data through the fluid inflow boundary condition and the fluid outflow boundary condition.

[0065] In order to more clearly illustrate the above implementation, this implementation provides a specific example:

[0066] The agitator is selected according to the viscosity range and flow state of the medium. Taking a certain fast-curing resin from Huntsman as an example, the viscosity is 6.5-9.0pas at room temperature; the flow state is divided into axial flow type, radial flow type and mixed type. Considering the size of this mixing tank, a mixed type agitator is selected, typically a six-fold blade open turbine agitator.

[0067] Combined with the existing equipment, determine the structure of the mixing tank Figure 1 As shown, the inner diameter is 400mm, the outer diameter is 460mm, the tank height is 900mm, the liquid height is 600mm, the blade angle is 45°, the distance from the lower stirrer to the bottom of the stirring tank is 1h, the distance between the two layers of stirrers is 2h, the stirrer diameter is 1d, and the rotating domain diameter is 2d (Note: the stirrer diameter should be equal to the rotating domain diameter, but considering the inconvenience of dividing the grid, the rotating domain diameter is increased by 10mm). The density of the resin in the stirring tank is 11503 / Kgm, the viscosity is 7pas, and the stirring paddle rotates at a constant speed of 80 / minr around the Y axis.

[0068] Whether using a pressure-based solver or a density-based solver, fluid flow requires solving the momentum equation, continuity equation, and turbulence equation, and then solving the energy equation and component equation according to the operation settings. The difference is that the pressure-based separation solver solves the momentum equations in the three directions of UVW,, and then solves the continuity equation, which will cause it to ignore other conditions when calculating some equations, so the solution speed is faster; the pressure-based coupling solver solves the momentum equation and the continuity equation in one set of equations, and then solves the energy equation and the component equation separately; the density-based coupling solver solves all equations together, and finally solves the turbulence equation separately, which has the highest accuracy, but is not easy to converge and takes a long time. Regardless of the type of solver, the mass conservation equation and the momentum conservation equation must be satisfied.

[0069] For physical model division of fluid domain:

[0070] The purpose of this numerical simulation is to check the mixing uniformity of the agitator. There is no subsequent calculation of the fluid's force on the structure. Therefore, after extracting the interface using Boolean operations, the agitator solid model is suppressed, and the rest is all fluid domain. The fluid domain is divided into a rotating domain and a stationary domain. Interface1-out and interface1-in create an interface, and interface2-out and interface2-in create an interface. The rotating domain and the stationary domain exchange data through the internal interface, such as Figure 2 shown.

[0071] Meshing: Before meshing, the size is adjusted, the blades in the two dynamic domains are encrypted, the boundary layer is inserted between the blades and the dynamic domain, and the mesh is divided using tetrahedral meshes.

[0072] Boundary condition settings:

[0073] The multiphase flow model uses the VOF model; the viscosity model uses the K-epsilon turbulence model; the wall surface is processed using the standard wall surface function; the Coupled algorithm is used in steady state, and the transient default is the SIMPLE algorithm. The model calculation uses the multiple reference system method to rotate the rotating domain. When setting, the rotation direction must be determined according to the blade, and the right-hand rule is used to determine whether the rotation speed is positive or negative. The top surface of the fluid domain is a free liquid surface, which is set as a symmetric boundary condition (Note: Under this model condition, a numerical simulation is performed on it, and no vortex is generated in the middle of the liquid after stabilization, indicating that it is less disturbed); the rotating axis wall selects the moving wall surface, and for the adjacent static domain, the rotating axis is moving, and the rotation speed is -80 / minr; the blade wall selects the moving wall surface, and the blade is relatively static relative to the adjacent rotating domain; the remaining walls are static walls.

[0074] Research methods for mixing processes:

[0075] Through the VOF model, the steady-state simulation of resin stirring is first performed. After the flow field is stable, the component transmission is turned on, the precipitation area is marked, and the tracer is added to calculate the component transmission equation. Six equidistant monitoring points are set to monitor the tracer concentration and perform transient simulation. Among them, the convergence of the steady-state simulation is determined by the velocity field and the flow velocity at a certain point. When the flow velocity fluctuates little over time and almost forms a straight line, it can be considered that the steady state converges, and then the tracer transient simulation is performed; the time used for uniform mixing is an important basis for judging the uniform mixing performance, which is expressed by 95% mixing time. 95% mixing time refers to the time required for the modifier to reach a stable concentration error of ±5% from the time it is just added to the stirring tank to the time it is mixed in the stirring tank.

[0076] Specific simulation prediction and analysis process:

[0077] Take the following model size as an example to analyze the velocity field and convergence. The analysis methods of other models are the same. Model size: agitator diameter 1d is 200mm, rotation domain diameter 2d is 210mm, 1h is 150mm, 2h is 300mm, other dimensions remain unchanged, and a monitoring point A (0, 500, 150) close to the upper surface is selected. The plumb surface velocity distribution cloud diagram of this model is as follows Figure 3 As shown, the speed of monitoring point A changes with the number of iterations as follows Figure 4 As shown;

[0078] Depend on Figure 3 It can be seen that the maximum stirring speed is 0.879m / s, which occurs at the end of the blade. The blade end speed can be calculated by the formula v=πnd, where n is the rotation speed in m / s and d is the rotation domain diameter in m.

[0079] Substitute the parameters of the model size into the formula to calculate the blade end; Figure 4 It can be seen that the speed of monitoring point A basically does not change with the increase of iteration number. Combining the above two points, it is believed that the steady-state result calculation is accurate.

[0080] Resin initial position calibration and monitoring:

[0081] After the steady-state calculation is completed, switch to transient calculation, open component delivery on its basis, add tracer, and mix it only with resin. Here, tracer is used to replace resin precipitation, so the tracer viscosity and density are the same as resin. Define the initial position and concentration of tracer by unit area marking. Combined with experience, precipitation generally gathers at the bottom of the stirring tank. Assume that the precipitation at the bottom of the stirring tank is 100mm high and the mass volume fraction is 1. Use the patch function to add precipitation to the bottom of the stirring tank, such as Figure 5 As shown, the red area is the resin precipitation and the blue area is the resin.

[0082] In this embodiment, simulation can also be performed by controlling single-factor variables, where the single factors include but are not limited to: the distance between two adjacent stirring bodies, the diameter of the rotating shaft, the diameter of the rotating domain formed by the stirring body, and the distance from the bottom stirring body to the bottom of the stirring tank.

[0083] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A simulation method for predicting the mixing time of resin in a HP-RTM process, characterized in that: The steps include: Step 100, constructing a physical model of a resin stirring tank, and dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the stirrer set in the stirring tank; Step 200: Use the VOF model to perform steady-state simulation on the resin stirring process in the physical model, and determine whether the flow field of the resin stirring reaches stability; Step 300, adding a tracer to the bottom of the stable flow field of resin stirring to replace the resin precipitation by means of unit area marking, setting its initial position and concentration, and then performing transient simulation using SIMPLE algorithm; Step 400: multiple monitoring points are set in the transient simulated flow field, and when the concentration of the resin precipitate replaced by the tracer displayed by the multiple monitoring points meets the 95% mixing principle, the time for the resin precipitate to be mixed uniformly is obtained.

2. The HP-RTM process resin stirring time prediction simulation method according to claim 1, characterized in that: The method of dividing the fluid domain in the physical model into a rotating domain and a stationary domain according to the structure and size parameters of the agitator set in the stirring tank includes: By performing Boolean operations on the physical model, the interface between the agitator and the space inside the agitator tank is extracted, and the remaining area obtained by suppressing the agitator entity model in the physical model is the fluid domain; The rotating domain is determined according to the meshing of the stirring paddles in the same layer as the stirrer, and the rest of the fluid domain is set as the stationary domain.

3. A HP-RTM process resin stirring time prediction simulation method according to claim 2, characterized in that: In the process of suppressing the agitator solid model in the physical model to obtain the remaining area as the fluid domain, the top surface of the fluid domain is agreed to be the free liquid surface.

4. The HP-RTM process resin stirring time prediction simulation method according to claim 3, characterized in that: The stirrer comprises a rotating shaft and a stirring paddle, a plurality of the stirring paddles are evenly distributed along the same circumference of the rotating shaft to form a stirring body, and a plurality of stirring bodies are arranged on the rotating shaft; Before the meshing of the stirring paddles of the stirring body determines the rotation domain, the number of the stirring paddles distributed in the stirring body is increased, and a boundary layer is inserted between the stirring paddles and the fluid domain.

5. A HP-RTM process resin stirring time prediction simulation method according to claim 4, characterized in that: The specific methods for achieving stability through steady-state simulation and determining the flow field of resin stirring include: By setting monitoring points in the flow field and ensuring that the speed of the monitoring points does not increase with the number of iterations; Obtain the vertical plane velocity distribution cloud map of the model and obtain the maximum stirring velocity of the flow field; calculate the blade tip velocity through the formula and make it the same as the maximum stirring velocity of the flow field.

6. A HP-RTM process resin stirring time prediction simulation method according to claim 5, characterized in that: The experimental parameters are determined by the structural dimensions of the agitator and the relative structural dimensions between the agitator and the stirring tank. The experimental parameters include but are not limited to: the distance between two adjacent stirring bodies, the diameter of the stirring body, the diameter of the rotation domain formed by the stirring body, and the distance from the bottom stirring body to the bottom of the stirring tank.

7. A HP-RTM process resin stirring time prediction simulation method according to claim 6, characterized in that: By controlling a single variable, the stirring and mixing uniformity time data corresponding to each experimental parameter at different parameter values ​​are analyzed; Select at least three groups of orthogonal experiments for each experimental parameter to determine the optimal combination of experimental parameters.

8. The HP-RTM process resin stirring time prediction simulation method according to claim 6, characterized in that: The diameter of the rotating domain is set to the diameter of the stirring body plus 10 mm.

9. The HP-RTM process resin stirring time prediction simulation method according to claim 6, characterized in that: The fluid inflow boundary condition and the fluid outflow boundary condition of the rotating domain are constructed, and the stationary domain and the rotating domain exchange data through the fluid inflow boundary condition and the fluid outflow boundary condition.

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