Turbulence control-based centrifugal barrel key geometric structure design method

Abstract

The invention belongs to the technical field of aramid honeycomb paper mechanical equipment, and discloses a turbulent flow control-based centrifugal barrel key geometric structure design method, which comprises the following steps of: simulating interaction between gas-liquid two-phase fluids simultaneously existing in an equipment centrifugal barrel through an Euler method; capturing a gas-liquid free interface in the upper space of the centrifugal barrel of the equipment by using a fluid volumetric method; fluid in the centrifugal barrel of the equipment is driven by the rotor to form a flow field; unsteady tracking particle simulation fibrid and unsteady tracking particle parameters are established, and visual distribution of particles in the centrifugal barrel is obtained; and S4, according to the calculation result of the step S5, taking the average strain rate of the whole field, the average strain rate in the rotation domain, the maximum vorticity and whether flocculation exists or not as evaluation indexes, and carrying out optimization design on the geometric structure of the centrifugal barrel established in the step S1. According to the invention, design and manufacturing by virtue of experience are avoided, a large amount of design time and resources are saved, and fine simulation of effective mixing volume and flow field structure in the centrifugal barrel is realized.

Description

Technical Field

[0001] The invention relates to the technical field of aramid honeycomb paper mechanical equipment, and in particular to a method for designing a key geometric structure of a centrifugal barrel based on turbulence control. Background Art

[0002] As an important raw material for lightweight structure, advanced composite materials have been widely used in important engineering fields such as aerospace, rail transportation, and shipbuilding. The aramid honeycomb sandwich composite material structure prepared with aramid paper as the main material has become the main structure of scientific and technological equipment such as aircraft, automobiles, ships, and weapons. As an important raw material for aramid paper, the quality of precipitated fibrils directly affects the mechanical properties of the final paper. In the preparation process of aramid honeycomb paper, the precipitated fibrils need to be washed with pulp washing equipment, and finally qualified precipitated fibrils are obtained through pulping and refining. The fiber surface has poor hydrophilicity, large length, low surface activity, and poor wettability. The fibers are easy to entangle and flocculate in the slurry suspension system, and the secondary dispersion of the floccules is extremely difficult, which seriously affects the forming uniformity and strength of the material. It is precisely because the fibers are easy to flocculate that a large amount of water is required for dilution during the fiber forming process. The degree of dispersion of precipitated fibrils in water is one of the important factors affecting the structure and performance of the finished paper, which has an important influence on the uniformity, pore size and distribution of the finished paper. The geometric design of the beating equipment directly determines the flow field inside the equipment. A flow field with a higher average strain rate will obtain more evenly dispersed fibrils. However, the currently commonly used fibrillation beating equipment in China has not been designed with its geometric structure. The flow field inside the centrifugal barrel of the equipment is not enough to evenly disperse the fibrils, which is not conducive to the full swelling and stretching of the fibrils, resulting in insufficient mechanical properties and poor consistency of the aramid honeycomb paper. Therefore, it is necessary to design a reasonable geometric structure for the beating equipment to obtain a flow field that allows the fibrils to be evenly dispersed, so as to improve the mechanical properties of the final paper and obtain good consistency.

[0003] However, there is still a lack of good design methods for the structure of pulping equipment. Existing structural design methods are usually based on the designer's past knowledge and data obtained from actual projects, and the structural design scheme is determined after a continuous iteration of the design-manufacturing-trial and error process. This process is not able to directly evaluate the flow field during the pulping process, which not only consumes a lot of time and resources, but also the final design scheme is not the optimal one.

[0004] The existing design methods are all designed for the mechanical, power and other structures of the pulping equipment. There is still a lack of corresponding design methods for the geometric structure design of the centrifugal barrel of the pulping equipment. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for designing the key geometric structure of a centrifugal barrel based on turbulence control, which can directly obtain the flow field distribution in the centrifugal barrel of a pulping device, without the need for the designer to repeatedly iterate the physical object of the pulping device to obtain the final design. Only the geometric structure of the centrifugal barrel can be given to perform analysis and optimization design. The designed pulping device can obtain more uniformly dispersed and larger specific surface area precipitated fibers. In order to achieve the above-mentioned purpose and other advantages according to the present invention, a method for designing the key geometric structure of a centrifugal barrel based on turbulence control is provided, comprising the following steps: S1. Establish the centrifugal bucket geometry model, flow field grid model, calculation model boundary conditions and calculation model parameters of the pulping equipment; S2. Setting a turbulence model to calculate the strong turbulence field inside the centrifugal barrel of the equipment; S3. The interaction between the gas-liquid two-phase fluids coexisting in the centrifugal bucket of the equipment is simulated by the Euler method, and the volume of fluid (VOF) method is used to capture the gas-liquid free interface in the upper space of the centrifugal bucket of the equipment to track the interfacial flow of the gas-liquid two-phase flow; S4. Calculate the flow field formed by the fluid inside the centrifugal barrel of the equipment driven by the rotor until the flow field is stable; S5, establishing non-steady-state tracking particle simulation fibrillation and non-steady-state tracking particle parameters, and adding the non-steady-state tracking particles into the stable flow field formed in step S4 to obtain a visualized distribution of particles in the centrifuge barrel; S6. According to the calculation result of step S5, the average strain rate of the whole field, the average strain rate in the rotating domain, the maximum vorticity and the presence or absence of flocculation are taken as evaluation indicators to optimize the geometric structure of the centrifuge bucket established in step S1.

[0006] The present invention realizes the optimization of the geometric structure of the centrifugal barrel based on the simulation results by constructing an internal flow field simulation model of the centrifugal barrel of the pulping equipment.

[0007] The present invention simulates the interaction between gas-liquid two-phase fluids coexisting in the centrifugal barrel of the equipment through the Euler method, captures the gas-liquid free interface in the upper space of the centrifugal barrel of the equipment, and tracks the interface flow of the gas-liquid two-phase flow.

[0008] The present invention simulates the movement of fibrides in a centrifugal barrel by establishing non-steady-state tracking particles, visualizes the distribution of particles inside the centrifugal barrel, and directly observes whether flocculation of fibrides will occur under the current geometric structure design.

[0009] The present invention realizes the prediction of the gas-liquid-solid three-phase complex flow field in the centrifugal barrel by solving the internal flow field simulation model of the centrifugal barrel, and can simultaneously obtain the flow field phase diagram, velocity cloud diagram, velocity vector distribution, fiber analysis distribution, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A centrifugal bucket geometric model and a rotor model diagram of a centrifugal bucket key geometric structure design method based on turbulence control according to the present invention; Figure 2 A grid division diagram of a computational model of a method for designing a key geometric structure of a centrifugal bucket based on turbulence control according to the present invention; Figure 3 The flow field phase distribution diagram and cloud diagram are calculated according to the key geometric structure design method of the centrifugal bucket based on turbulence control of the present invention; Figure 4 A diagram of the geometric structure of the agitator after optimization according to the method for designing the key geometric structure of the centrifugal bucket based on turbulence control of the present invention; Figure 5 It is the optimized flow field phase distribution diagram and cloud diagram of the key geometric structure design method of the centrifugal bucket based on turbulence control according to the present invention. DETAILED DESCRIPTION

[0011] 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.

[0012] Reference Figure 1 , a method for designing key geometric structures of centrifugal barrels based on turbulence control, comprising: Step 1: Establish the geometric model of the centrifugal barrel of the pulping equipment, including the protrusion inside the centrifugal barrel, the concave cone of the barrel body, and the centrifugal barrel rotor.

[0013] Step 2: Establish a flow field mesh model, divide the internal rotating domain and non-rotating domain of the centrifugal barrel of the equipment, and use sliding mesh to process the interface.

[0014] Step 3: Establish the boundary conditions of the calculation model, including the boundary conditions at the junction of the barrel mouth and the air, the boundary conditions of the barrel wall, etc.

[0015] Step 4: Establish the calculation model parameters, including the rotation speed and direction of the rotor, the initial water phase liquid level inside the centrifugal bucket of the equipment, etc.

[0016] Step 5: Set the turbulence model to the RNG k-epsilon two-equation turbulence model to calculate the strong turbulence field inside the centrifugal bucket of the equipment. The k equation (turbulent kinetic energy equation) in the RNG k-epsilon two-equation turbulence model is shown in Equation 1: (1) in, is the fluid density, is the turbulent kinetic energy, It's time. are the velocity vector components, are the spatial coordinate components, is the dynamic viscosity, is the turbulent viscosity, is the turbulent kinetic energy transport term, is the turbulent kinetic energy generated by buoyancy, is the turbulent kinetic energy dissipation rate, is the effect of wave expansion on the turbulent dissipation rate, The default constant is 1.0.

[0017] The epsilon equation (turbulent dissipation rate equation) in the RNG k-epsilon two-equation turbulence model is shown in Equation 2: (2) in, is the default constant 1.39, is the default constant 1.3, is the empirical constant 1.42, is a constant correction term.

[0018] For turbulent viscosity , there is formula 3: (3) in, The default constant is 0.0845.

[0019] For the constant correction term , there is formula 4: (4) in, is the default constant 1.68, is the default constant 4.377, The default constant is 0.012. is the calculation parameter, which is calculated by formula 5: (5) Step 6: The Euler method is used to simulate the interaction between the gas-liquid two-phase fluids coexisting inside the centrifugal bucket of the equipment, and the volume of fluid (VOF) method is used to capture the gas-liquid free interface in the upper space of the centrifugal bucket of the equipment to track the interfacial flow of the gas-liquid two-phase flow.

[0020] Step 7: Calculate the flow field formed by the fluid inside the centrifugal barrel of the equipment driven by the rotor until the flow field is stable.

[0021] Step 8: Establish a non-steady-state tracking (DPM) particle simulation fiber precipitation, ignoring the particle volume and the interaction between particles. The DPM particles and the flow field are unidirectionally coupled, that is, the influence of particles on the flow field is not considered, and the influence of turbulence on particle diffusion is considered.

[0022] Step 9: Establish DPM particle parameters, including total particle mass, number of particles, initial velocity of individual particles, and boundary conditions.

[0023] Step 10: Add the DPM particles created in steps 8 and 9 to the stable flow field formed in step 7 to obtain a visualized distribution of the particles in the centrifuge bucket.

[0024] Step 11: Based on the calculation results of step 10, take the average strain rate (shear rate) of the entire field, the average strain rate in the rotation domain (i.e., the area where the slip grid is located), the maximum vorticity, and the presence or absence of flocculation as evaluation indicators to optimize the geometric structure of the centrifuge bucket established in step 1.

[0025] Step 12: Based on the optimized centrifuge bucket geometry, repeat steps 1-11 until the maximum full-field average strain rate, the average strain rate in the rotating domain, the maximum vorticity, and no flocculation are obtained.

[0026] Example 1, step 1. Figure 1 As shown in the figure, the centrifuge bucket geometric model and the corresponding rotor model are established. The centrifuge bucket is 1.3 m high and has a bottom radius of 0.6 m. The maximum radius of the rotor blade is 0.3 m and the radius of the turntable is 0.26 m.

[0027] Step 2. Use Figure 2 The 980,000 grids shown in the figure are used to discretize the geometric model. In view of the motion characteristics of the rotating domain and the non-rotating domain inside the agitator, and taking into account the instantaneous characteristics of the flow field changes driven by the blades when the rotor rotates, the sliding grid model is used to process the interface between the rotating domain and the non-rotating domain. The specific operation is to divide an area of ​​appropriate size around the rotor as the active rotating domain, and use the sliding grid to process the interface between the rotating domain and the non-rotating domain ( Figure 2 The yellow grid part in the middle), and the rest of the area is divided into non-rotating domains. There is an interface between the rotating domain and the non-rotating domain. The data of the internal rotating domain is transmitted to the external static area through the interface, realizing the stirring function of the convection field of the rotor blades in the agitator.

[0028] Step 3. According to the physical model of the pulping equipment, the calculation boundary conditions are set. The opening of the centrifugal bucket is set as the pressure outlet boundary condition, and only air is allowed to enter and exit freely. The wall of the centrifugal bucket is set as the no-slip wall boundary condition.

[0029] Step 4. Set the calculation parameters according to the actual working conditions of the pulping equipment. The rotor rotates at 260 rpm in a clockwise direction. The initial setting of the water level inside the agitator is 0.85 m, that is, water occupies 65% of its effective volume.

[0030] Step 5. The RNG k-epsilon two-equation turbulence model is used to calculate the strong turbulence field in the centrifuge bucket, the Euler method is used to simulate the interaction between the gas-liquid two-phase fluids coexisting inside the centrifuge bucket of the equipment, and the fluid volume (VOF) method is used to track the interfacial flow of the gas-liquid two-phase flow.

[0031] Step 6. Add DPM particles, with a total mass of 0.99 kg, a number of 300 particles, and a single particle mass of 0.0033 kg. The particles are thrown above the water area with an initial negative z-axis velocity of 0.2 m / s and a gravitational acceleration of 9.81 m 2 / s, and after 1.06 s, it falls on the water surface. Then, when it enters the water, the flow field begins to affect the movement of the particles, and the particles rotate and fall to the bottom, rotating with the flow field. The calculation results are as follows: Figure 3 The two-dimensional phase distribution diagram and velocity cloud diagram of the flow field are shown.

[0032] Step 7. Considering the increase in strain rate of the flow field in the barrel to make the precipitated fibers disperse more uniformly, Figure 4 As shown, a protrusion is set on the side wall of the cylindrical barrel of the agitator for structural optimization, and the height of the protrusion is 60 mm.

[0033] Step 8. Repeat steps 2-6 to obtain Figure 5 The phase distribution diagram and velocity cloud diagram are shown in Table 1. The comparison of the average strain rate in the whole field, the average strain rate in the rotation domain, and the maximum vorticity before and after optimization is shown in Table 1.

[0034] Table 1 Strain rate and maximum vorticity before and after optimization <![CDATA[全场平均应变率(s -1 )]]> <![CDATA[Average strain rate in the rotation domain (s -1 )]]> <![CDATA[Maximum vorticity (s -1 > Before structural optimization 3.92 43.26 6629.08 After structural optimization 4.11 45.08 18835.40 It can be seen that after optimization, the average shear rate of the entire field, the average strain rate in the rotation domain, and the maximum vorticity were successfully increased, which is beneficial to the fiber stretching and uniform dispersion of the precipitated fibers.

[0035] In summary, 1. The present invention realizes the optimization of the centrifugal bucket geometry based on the simulation results by constructing the internal flow field simulation model of the centrifugal bucket of the pulping equipment, which can avoid designing and manufacturing based on experience, thus saving a lot of design time and resources.

[0036] 2. The present invention simulates the interaction between the gas-liquid two-phase fluids coexisting inside the centrifugal barrel of the equipment through the Euler method, successfully captures the gas-liquid free interface in the upper space of the centrifugal barrel of the equipment, and realizes the refined simulation of the effective mixing volume and flow field structure inside the centrifugal barrel.

[0037] 3. The present invention simulates the movement and distribution of precipitated fibers in a centrifuge barrel by non-steady-state tracking particles, and obtains information such as velocity, phase distribution, and vorticity of the flow field in the barrel, thereby realizing the prediction of the gas-liquid-solid three-phase complex flow field in the centrifuge barrel, and can effectively and quickly and reliably evaluate the geometric structure design of the centrifuge barrel.

[0038] The number of devices and processing scales described here are used to simplify the description of the present invention, and the application, modification and variation of the present invention will be obvious to those skilled in the art.

[0039] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for designing key geometric structures of centrifugal barrels based on turbulence control, characterized in that: The following steps are involved: S1. Establish the centrifugal bucket geometry model, flow field grid model, calculation model boundary conditions and calculation model parameters of the pulping equipment; S2. Setting a turbulence model to calculate the strong turbulence field inside the centrifugal barrel of the equipment; S3. The interaction between the gas-liquid two-phase fluids coexisting in the centrifugal bucket of the device is simulated by the Euler method, and the gas-liquid free interface in the upper space of the centrifugal bucket of the device is captured by the fluid volume method to track the interfacial flow of the gas-liquid two-phase flow; S4. Calculate the flow field formed by the fluid inside the centrifugal barrel of the equipment driven by the rotor until the flow field is stable; S5, establishing non-steady-state tracking particle simulation fibrillation and non-steady-state tracking particle parameters, and adding the non-steady-state tracking particles into the stable flow field formed in step S4 to obtain a visualized distribution of particles in the centrifuge barrel; S6. According to the calculation result of step S5, the average strain rate of the whole field, the average strain rate in the rotating domain, the maximum vorticity and the presence or absence of flocculation are taken as evaluation indicators to optimize the geometric structure of the centrifuge bucket established in step S1.

2. A method for designing a key geometric structure of a centrifugal bucket based on turbulence control as claimed in claim 1, characterized in that: The geometric model of the centrifugal barrel of the pulping equipment in step S1 includes a protrusion inside the centrifugal barrel, a concave cone of the barrel body, and a centrifugal barrel rotor.

3. A method for designing a key geometric structure of a centrifugal bucket based on turbulence control as claimed in claim 1, characterized in that: The flow field grid model in step S1 is divided into a rotating domain and a non-rotating domain inside the centrifuge barrel, and a sliding grid is used to process the interface.

4. A method for designing a key geometric structure of a centrifugal bucket based on turbulence control as claimed in claim 1, characterized in that: The calculation model boundary conditions in step S1 include the boundary conditions at the junction of the barrel mouth and the air and the boundary conditions of the barrel wall.

5. A method for designing a key geometric structure of a centrifugal bucket based on turbulence control as claimed in claim 1, characterized in that: The calculation model parameters in step S1 include the rotation speed and direction of the rotor and the initial water phase liquid level inside the centrifugal bucket of the equipment.

6. A method for designing a key geometric structure of a centrifugal bucket based on turbulence control as claimed in claim 1, characterized in that: The turbulence model in step S2 is a RNG k-epsilon two-equation turbulence model, and the k equation in the RNG k-epsilon two-equation turbulence model is as follows: ； in, is the fluid density, is the turbulent kinetic energy, It's time. are the velocity vector components, are the spatial coordinate components, is the dynamic viscosity, is the turbulent viscosity, is the turbulent kinetic energy transport term, is the turbulent kinetic energy generated by buoyancy, is the turbulent kinetic energy dissipation rate, is the effect of wave expansion on the turbulent dissipation rate, The default constant is 1.0.

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