Simulation analysis method for tobacco leaf air separation process

Abstract

The invention relates to the technical field of tobacco leaf air separation, in particular to a tobacco leaf air separation process simulation analysis method. A tobacco leaf geometric model is established, a tobacco leaf movement initial field and a wind field initial field are calculated based on a discrete element method and a computational fluid mechanics method, and coupling calculation is performed on wind field movement and tobacco leaf movement; the rolling motion of the tobacco leaves in a wind field, the positive pressure and shear stress of the wind field on the upper and lower surfaces of the tobacco leaves, the gravity borne by the tobacco leaves, the acting force between the tobacco leaves and the acting force between the tobacco leaves and wind field equipment are fully considered to calculate the linear acceleration and the rotation angle acceleration of the tobacco leaves, so that the mass center position and the azimuth angle of the tobacco leaves can be updated; and the motion posture of the tobacco leaves in the wind field is obtained. By the adoption of the simulation analysis method, the motion posture of the tobacco leaves in the wind field is more accurate, and errors of simulation analysis results are small.

Description

Technical Field

[0001] The invention relates to the technical field of tobacco leaf wind fractionation, and in particular to a tobacco leaf wind fractionation process simulation analysis method. Background Art

[0002] The air separation process is a key link in the production of leaf threshing and redrying, and the air separation efficiency directly affects the economic benefit indicators of leaf threshing and redrying. The air separation technology of tobacco leaves after threshing mainly uses the different physical properties of tobacco leaves, tobacco stems and leaves with stems to separate tobacco leaves, tobacco stems and leaves with stems under the action of wind.

[0003] In order to investigate the movement characteristics of tobacco leaves in the air separation chamber and how to improve the air separation efficiency and reduce the proportion of leaves containing stems, there have been many studies on tobacco leaf air separation technology in recent years. By improving the structure of the air separation chamber, the air separation efficiency has been improved to a certain extent. However, the dynamic behavior of tobacco leaves was not considered during the improvement process, and the movement state and force changes of tobacco leaves in the air separation chamber could not be obtained. In addition, the tobacco leaf air separation process is in an unobservable closed space, and there is a complex environment with multiple fields coupled inside, such as fluid field, gravity field, and collision between materials. The collision force between tobacco leaves and between tobacco leaves and tobacco stems causes the movement trajectory of tobacco leaves in the air separation chamber to be more complicated.

[0004] At present, when dealing with the forces on tobacco leaves in the wind field, tobacco leaves are considered as particles (this is reasonable when the particle size is smaller than the fluid calculation grid size), and the force of the wind field on the tobacco leaves is calculated with the help of the resistance calculation formula of the empirical relationship. However, since most tobacco leaves are oblate and large in size, treating tobacco leaves as particles will not allow for the tumbling motion of tobacco leaves under the action of the wind field, which is inconsistent with the actual movement of tobacco leaves in the wind field, resulting in large errors in the simulation analysis results. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for simulating and analyzing tobacco leaf wind separation process, so as to solve the problem of large errors in the simulation analysis results of the movement posture of tobacco leaves in the wind field during the tobacco leaf wind separation process in the prior art.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a tobacco leaf wind separation process simulation analysis method, the simulation analysis method comprising:

[0007] Measure the geometric parameters of tobacco leaves and wind field equipment, and establish geometric models of tobacco leaves and wind field;

[0008] Obtaining the initial information of tobacco leaf movement to perform initial field calculation of tobacco leaf movement based on discrete element method. The initial information of tobacco leaf movement includes determining the calculation area of ​​tobacco leaf movement, tobacco leaf force model, physical parameters of tobacco leaves, and tobacco leaf flow and position under the working condition under study;

[0009] Obtaining preliminary wind field information to perform preliminary wind field calculation based on computational fluid dynamics methods. The preliminary wind field information includes creating a computational grid for the wind field, determining a flow model, physical parameters of the gas, boundary information of the wind field, and initial information of the wind field, and calculating the wind field;

[0010] The wind field motion and tobacco leaf motion are coupled and calculated, and the tobacco leaf posture position variables are output to the wind field. The wind field uses the input position of the tobacco leaf to calculate the normal pressure and shear stress of the wind field on the upper and lower surfaces of the tobacco leaf, and obtains the resultant force and torque on the tobacco leaf through the normal pressure and shear stress on the upper and lower surfaces of the tobacco leaf. The force and torque on the tobacco leaf in the wind field are output, and the discrete element method is used to simultaneously consider the gravity on the tobacco leaf, the force between the tobacco leaves, and the force between the tobacco leaf and the wind field equipment, and calculate the linear acceleration and angular acceleration of the tobacco leaf, thereby updating the posture position of the tobacco leaf;

[0011] Data extraction and analysis of calculation results were performed.

[0012] Optionally, the tobacco leaf force model includes a normal contact force model and a tangential contact force model.

[0013] Optionally, the physical properties of the tobacco leaf include thickness, density, Young's modulus and Poisson's ratio.

[0014] Optionally, the physical property parameters of the gas include density and viscosity of the gas.

[0015] Optionally, the boundary information of the wind farm includes inlet conditions, outlet conditions of the wind farm and wall conditions of wind farm equipment.

[0016] Optionally, the initial information of the wind field includes initial velocity distribution, pressure distribution and calculation time step of the wind field.

[0017] Optionally, the calculation of the wind field includes selecting a continuity equation, a momentum equation space discretization method and a time marching format, setting a suitable relaxation factor and a velocity-pressure coupling calculation method to calculate the velocity and pressure on the wind field calculation grid.

[0018] Optionally, the wind farm equipment is a wind compartment, and the flow model is a turbulence model.

[0019] Optionally, the tobacco leaf in the wind field is a single tobacco leaf, and by changing the working conditions of the wind field or the tobacco leaf, recalculation and analysis are performed to obtain the change of the centroid height of different tobacco leaves over time under different wind field conditions.

[0020] Optionally, there are multiple tobacco leaves in the wind farm, and the wind farm equipment is a wind separation bin, and data extraction and analysis are performed on the calculation results to obtain movement trajectories of different types of tobacco leaves in the wind separation bins;

[0021] The simulation analysis method also includes conducting a tobacco leaf wind distribution experiment under the same working conditions, and comparing the calculated results with the experimental results to verify the simulation model.

[0022] In a tobacco leaf wind separation process simulation analysis method of the present invention, by establishing a tobacco leaf geometric model, the initial field of tobacco leaf movement and the initial field of wind field are calculated based on discrete element method and computational fluid dynamics method, and the wind field movement and tobacco leaf movement are coupled and calculated, and the rolling movement of tobacco leaves in the wind field, the positive pressure and shear stress of the wind field on the upper and lower surfaces of tobacco leaves, the gravity of tobacco leaves, the forces between tobacco leaves, and the forces between tobacco leaves and wind field equipment are fully considered to calculate the linear acceleration and rotational angular acceleration of tobacco leaves, so that the center of mass position and azimuth of tobacco leaves can be updated, and then the movement posture of tobacco leaves in the wind field can be obtained. The above simulation analysis method is used to make the movement posture of tobacco leaves in the wind field more accurate, and the error of simulation analysis results is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an overall flow chart of a tobacco leaf wind separation process simulation analysis method according to an embodiment of the present invention;

[0024] Figure 2 is a schematic diagram of a geometric model of a tobacco leaf in one embodiment of the present invention;

[0025] Figure 3 is a flowchart of the steps of initial field calculation of tobacco leaf motion in one embodiment of the present invention;

[0026] Figure 4 is a flow chart of the steps of initial wind field calculation in one embodiment of the present invention;

[0027] Figure 5 is the change of the centroid height of tobacco leaves over time under different wind field conditions in one embodiment of the present invention;

[0028] Figure 6 It is a comparison chart of the calculated results and the experimental results of the tobacco leaf wind separation process in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] Refer to the following Figures 1 to 6To describe a tobacco leaf wind fractionation process simulation analysis method of the present invention. In the description of this embodiment, it should be understood that the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features, that is, include one or more of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. When a feature "includes or contains" one or some of the features it covers, unless otherwise specifically described, this indicates that other features are not excluded and may further include other features.

[0030] Unless otherwise clearly defined and limited, the terms "set", "install", "connect", "connect", "fix", "couple" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. A person skilled in the art should be able to understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0031] In addition, in the description of this embodiment, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. That is, in the description of this embodiment, the first feature being "above", "above", and "above" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. The first feature being "below", "below", or "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0032] In the description of the present embodiment, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0033] like Figure 1-Figure 4 As shown, an embodiment of the present invention provides a tobacco leaf wind separation process simulation analysis method, the simulation analysis method comprising:

[0034] Step S10, measuring geometric parameters of tobacco leaves and wind farm equipment, such as the shape of tobacco leaves and the outline of wind farm equipment, and establishing geometric models of tobacco leaves and wind farm, such as geometric CAD models.

[0035] Step S20, obtaining the initial information of tobacco leaf motion, so as to perform initial field calculation of tobacco leaf motion based on discrete element method. The specific steps include:

[0036] Step S21, determining the calculation area of ​​tobacco leaf movement, for example, the movement calculation area of ​​tobacco leaves can be selected as the wind bin.

[0037] Step S22, determining the tobacco leaf force model, which specifically includes a normal contact force model and a tangential contact force model.

[0038] Step S23, determining the physical parameters of the tobacco leaf, the physical parameters of the tobacco leaf include thickness, density, Young's modulus and Poisson's ratio. Optionally, the tobacco leaf thickness is 0.2 mm, the tobacco leaf density is 450 kg / m3, the tobacco leaf Young's modulus is 1e7 N / m2, and the tobacco leaf Poisson's ratio is 0.3.

[0039] Step S24, determine the tobacco leaf flow rate and position of the working condition under study. For the suspension simulation of a single tobacco leaf, the tobacco leaf can be set at the center of the wind field, and the spatial orientation of the tobacco leaf can be determined at the same time. For the simulation of the wind separation process of multiple tobacco leaves in the wind separation bin, a conveyor belt is set at the air inlet of the wind separation bin, and tobacco leaves of a certain mass flow rate enter the wind separation bin through the conveyor belt, and the flow rate and position of the tobacco leaves are determined according to this working condition.

[0040] Step S30, obtaining the initial wind field information, so as to perform the initial wind field calculation based on the computational fluid dynamics method. The specific steps include:

[0041] Step S31, creating a computational grid for the wind farm, and discretizing the wind farm geometric model to generate a computational grid.

[0042] Step S32, determine the flow model, and select a suitable flow model based on the flow characteristics under the studied working condition. The wind separation process of multiple tobacco leaves in the wind separation bin is usually carried out in turbulence, so the turbulence model is selected as the flow model for calculation.

[0043] Step S33, determining the physical parameters of the gas, the physical parameters of the gas include the density and viscosity of the gas. Optionally, the density of the gas is 1.125 kg / m 3 , the viscosity is 1.83mPa·s.

[0044] Step S34, determine the boundary information of the wind farm, which includes the inlet conditions, outlet conditions and wall conditions of the wind farm equipment. Optionally, the inlet wind speed of the wind farm is 1m / s, the outlet pressure is 1atm, and the wall of the wind farm equipment is a non-slip wall.

[0045] Step S35, determining the initial information of the wind field, the initial information of the wind field including the initial velocity distribution, pressure distribution and calculation time step of the wind field. Optionally, the calculation time step of the transient flow field is defined as 0.001s.

[0046] Step S36, calculating the wind field, specifically including selecting the continuity equation, the momentum equation space discretization method and the time advancement format, setting the appropriate relaxation factor and the velocity-pressure coupling calculation method, so as to calculate the velocity and pressure on the wind field calculation grid. Among them, the velocity-pressure coupling calculation method can select the SIMPLE algorithm.

[0047] Step S40, coupling calculation of wind field motion and tobacco leaf motion. At a certain wind field calculation moment, the attitude position variables (such as the center of mass position and azimuth) of the tobacco leaf are output to the wind field. The wind field uses the input position of the tobacco leaf to use the immersed boundary method to calculate the normal pressure and shear stress of the wind field on the upper and lower surfaces of the tobacco leaf, and obtains the resultant force and torque on the tobacco leaf through the normal pressure and shear stress on the upper and lower surfaces of the tobacco leaf. The force and torque on the tobacco leaf in the wind field are output, and the discrete element method is used to calculate the linear acceleration and angular acceleration of the tobacco leaf by considering the gravity on the tobacco leaf, the force between the tobacco leaves, and the force between the tobacco leaf and the wind field equipment, so as to update the center of mass position and azimuth of the tobacco leaf.

[0048] Furthermore, the model equation for coupling calculation of wind field motion and tobacco leaf motion is:

[0049] In the discrete element calculation framework, particles in the calculation domain are tracked and calculated using the Lagrangian method. By solving Euler's first and second laws that control the translation and rotation of particle motion, the spatial information and motion state of the particle at each moment can be determined. The particle model equation is as follows:

[0050]

[0051] Among them, m p is the mass of the tobacco leaf, g is the gravitational acceleration vector, F c is the contact force considering the leaf-leaf and leaf-wall interactions, ω p is the angular velocity vector, is its moment of inertia tensor, M c is the net torque generated by the tangential force that causes the tobacco leaf to rotate. To take into account the interaction between the tobacco leaf and the fluid, two additional terms are added to the equation: Ff→p is the additional force of the fluid on the tobacco leaves, M f→p is the additional torque due to the fluid velocity gradient.

[0052] The fluid motion is described by the volume-averaged Navier-Stokes equations. The average mass conservation equation is given by:

[0053]

[0054] The averaged momentum conservation equation is:

[0055]

[0056] Among them, α f represents the fluid volume fraction, p is the fluid pressure, ρ f is the fluid density, u is the fluid velocity vector, is the stress tensor of the fluid, which is defined as:

[0057]

[0058] In the momentum conservation equation, F p→f represents the momentum source term interacting with the particle phase and is calculated according to the following expression:

[0059]

[0060] Among them, V c is the volume of the calculation unit, N is the number of particles inside the calculation unit, and F p→f Represents the force exerted by the fluid on the particles.

[0061] Step S50, extracting and analyzing the calculation results. Figure 5 For the suspension simulation of a single tobacco leaf, by changing the working conditions of the wind field, the change of the centroid height of the tobacco leaf over time under different wind field conditions can be obtained, and then the suspension speed of the tobacco leaf can be analyzed. By changing the working conditions of the tobacco leaf, the change of the centroid height of different tobacco leaves over time can be obtained, and then the suspension speed of different tobacco leaves under different wind field conditions can be analyzed. For the simulation of the wind separation process of multiple tobacco leaves in the wind separation bin, according to the calculation results, the centroid position and azimuth of the tobacco leaves at different times can be obtained, so as to obtain the movement trajectory of the tobacco leaves over a period of time, and then analyze the distribution of different types of tobacco leaves at the upper and lower outlets of the wind separation bin.

[0062] By establishing a tobacco leaf geometric model, the initial field of tobacco leaf motion and the initial field of wind field are calculated based on the discrete element method and computational fluid dynamics method, and the wind field motion and tobacco leaf motion are coupled. The rolling motion of tobacco leaves in the wind field, the normal pressure and shear stress of the wind field on the upper and lower surfaces of tobacco leaves, the gravity of tobacco leaves, the forces between tobacco leaves, and the forces between tobacco leaves and wind field equipment are fully considered to calculate the linear acceleration and rotational angular acceleration of tobacco leaves, so that the center of mass position and azimuth of tobacco leaves can be updated, and the motion posture of tobacco leaves in the wind field can be obtained. The above simulation analysis method makes the motion posture of tobacco leaves in the wind field more accurate, and the error of simulation analysis results is small.

[0063] At the same time, by analyzing the simulation results, we can obtain the suspension speed of a single tobacco leaf under different wind field conditions, as well as the wind separation process of multiple tobacco leaves in the wind separation bin.

[0064] Further, refer to Figure 6 For the simulation of the air separation process of multiple tobacco leaves in the air separation bin, the simulation analysis method also includes conducting a tobacco leaf air separation experiment under the same working conditions, and comparing the simulation results with the experimental results to verify the simulation model. By continuously verifying the simulation model, the results of the simulation analysis can be made more accurate. According to the verified simulation model, the operating conditions and structure of the air separation bin can be optimized to improve the air separation efficiency and reduce the proportion of leaves containing stems.

[0065] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A tobacco leaf wind separation process simulation analysis method, characterized in that: The simulation analysis method comprises: Measure the geometric parameters of tobacco leaves and wind field equipment, and establish geometric models of tobacco leaves and wind field; Obtaining the initial information of tobacco leaf movement to perform initial field calculation of tobacco leaf movement based on discrete element method. The initial information of tobacco leaf movement includes determining the calculation area of ​​tobacco leaf movement, tobacco leaf force model, physical parameters of tobacco leaves, and tobacco leaf flow and position under the working condition under study; Obtaining preliminary wind field information to perform preliminary wind field calculation based on computational fluid dynamics methods. The preliminary wind field information includes creating a computational grid for the wind field, determining a flow model, physical parameters of the gas, boundary information of the wind field, and initial information of the wind field, and calculating the wind field; The wind field motion and tobacco leaf motion are coupled and calculated, and the tobacco leaf posture position variables are output to the wind field. The wind field uses the input position of the tobacco leaf to calculate the normal pressure and shear stress of the wind field on the upper and lower surfaces of the tobacco leaf, and obtains the resultant force and torque on the tobacco leaf through the normal pressure and shear stress on the upper and lower surfaces of the tobacco leaf. The force and torque on the tobacco leaf in the wind field are output, and the discrete element method is used to simultaneously consider the gravity on the tobacco leaf, the force between the tobacco leaves, and the force between the tobacco leaf and the wind field equipment, and calculate the linear acceleration and angular acceleration of the tobacco leaf, thereby updating the posture position of the tobacco leaf; Perform data extraction and analysis on the calculation results.

2. The tobacco leaf wind separation process simulation analysis method according to claim 1 is characterized in that: The tobacco leaf force model includes a normal contact force model and a tangential contact force model.

3. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The physical properties of the tobacco leaf include thickness, density, Young's modulus and Poisson's ratio.

4. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The physical property parameters of the gas include density and viscosity of the gas.

5. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The boundary information of the wind farm includes the inlet conditions, outlet conditions of the wind farm and the wall conditions of the wind farm equipment.

6. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The initial information of the wind field includes the initial velocity distribution, pressure distribution and calculation time step of the wind field.

7. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The calculation of the wind field includes selecting a continuity equation, a momentum equation space discretization method and a time advancement format, setting a suitable relaxation factor and a velocity-pressure coupling calculation method to calculate the velocity and pressure on the wind field calculation grid.

8. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: If the wind farm equipment is a wind compartment, the flow model is a turbulence model.

9. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: The tobacco leaf in the wind field is a single tobacco leaf. By changing the working conditions of the wind field or the tobacco leaf, recalculation and analysis are performed to obtain the change of the centroid height of different tobacco leaves over time under different wind field conditions.

10. The tobacco leaf wind separation process simulation analysis method according to claim 1, characterized in that: There are multiple tobacco leaves in the wind farm, and the wind farm equipment is a wind separation bin. Data extraction and analysis are performed on the calculation results to obtain the movement trajectories of different types of tobacco leaves in the wind separation bins. The simulation analysis method also includes conducting a tobacco leaf wind distribution experiment under the same working conditions, and comparing the calculated results with the experimental results to verify the simulation model.

Images