Topological optimization design method for volute and air duct of high-air-volume fan

Abstract

The invention belongs to the field of fan air ducts, and provides a topological optimization design method for a fan volute and an air duct, which comprises the following steps of: 1, calculating the speed and direction of the periphery of a fan in a free space field through simulation; 2, setting an entrance boundary condition of a topological calculation domain based on the calculated speed size and speed direction; and 3, carrying out topological optimization calculation on the fan air duct. And 4, model reconstruction and flow field analysis are carried out based on the air duct and volute form of topological optimization. And 5, carrying out flow field analysis on the original fan air duct. And 6, comparing the air volumes before and after topological optimization of the fan volute air duct, if the topological optimized air duct and the volute conform to the expected lifting air volume, completing the designed fresh air duct, and if the lifting amount is insufficient or deteriorated, expanding the iteration step number and repeating the optimization process. The optimization method has the advantage of automatic optimization. The optimized fresh air ventilator volute and air duct have the advantages of low energy consumption, low vorticity and high air volume.

Description

Technical Field

[0001] The invention belongs to the field of design of fan volutes and air ducts, and relates to a topological optimization design method for a fan volute and air duct with a high air volume. Background Art

[0002] The fan duct system is used to transport air and is an important part of the ventilation system. Its design requirement is to transport a certain amount of air to a designated location through the duct at the speed required by the design. The air volume directly determines the ventilation efficiency. With the increasing requirements for energy efficiency and environmental comfort in the industrial and residential fields, optimizing the design of the fan duct system is particularly critical. This paper uses topology optimization technology to optimize the design method of the refrigeration fan volute and duct of a certain refrigerator, aiming to design a volute form and duct layout method. This structure can increase the flow rate of the air outlet while reducing energy loss.

[0003] The traditional fan volute air duct design, on the one hand, relies on the experience of the staff and requires multiple attempts of design, simulation, and verification. This greatly increases the working time and investment cost of the design product. On the other hand, the designed fan volute and air duct layout is often not optimal, which is prone to small air volume, high energy consumption, and even backflow at the air outlet. In order to solve this problem, a fan volute air duct topology optimization design method is proposed.

[0004] The topology optimization method is a technology that uses mathematical methods to determine the optimal distribution of materials in a structure under given loads, support conditions and material properties. It has a wide range of applications in the fields of engineering design and manufacturing, especially in situations where weight reduction, performance improvement and cost reduction are required. The present invention mainly applies topology optimization technology to the optimal design of the fan volute and air duct, using the least time and labor costs to get rid of the dependence on human experience. A layout form of a new fan volute and air duct with the advantages of low energy consumption, low vortex and high air volume is designed. The new fan volute and air duct optimized by the present invention have the advantages of low energy consumption, low vortex and high air volume. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of backflow, high energy consumption and low air volume in the fan volute air duct in the engineering field, and to propose a topological optimization design method for the fan volute air duct. Through the topological optimization technical means, the optimal form of the fan volute and the automatic optimization layout of the air duct can be performed by only giving the outlet position and the inlet position. The new fan volute and air duct optimized by the topological optimization method of the fan volute air duct proposed in the present invention have the advantages of low energy consumption, low vortex and high air volume, and include the following steps:

[0006] Step 1: A method for obtaining the inlet boundary conditions of the topology optimization, wherein the boundary conditions obtain the tangential velocity and normal velocity of the fan through the rated speed of the fan in the free field;

[0007] Step 2: Establishment of topology optimization model of fan volute air duct

[0008] 2.1 Setting of inlet and outlet boundary conditions;

[0009] In step 2.1, the inlet boundary condition is the velocity boundary condition, and the inlet velocity is expressed as u x with u y Indicates that u x with u y is defined as Formula 9; the outlet boundary condition is set to pressure boundary condition, and the static pressure is 0Pa.

[0010] 2.2 Structural design of fan volute air duct topology optimization model;

[0011] Step 3: Reconstruct the three-dimensional model of the fan volute air duct topology optimization model and analyze the flow field, use the grid filter to obtain the new air duct volute contour, and use the finite element method to calculate the air volume of the optimized air duct volute;

[0012] Step 4: Use the finite element method to calculate the air volume of the initial air duct volute;

[0013] Step 5: Compare the air volume before and after optimization and calculate the increase in air volume.

[0014] The working principle of the technical solution of the present invention is: the flow field analysis part uses a steady-state model for calculation, and the duct wall is set as a no-slip boundary condition. Due to the complexity of the flow inside the duct, especially the complexity of the wall, the flow characteristics may be significantly affected. For example, flow separation, turbulent transition or flow blockage may occur inside the pipeline. In order to accurately simulate its internal flow, it is crucial to choose the correct turbulence model. Compared with other turbulence models, the k-ω model, as a low Reynolds number model, can resolve the flow near the wall, even to the wall itself. This model shows better performance when dealing with complex flow conditions such as internal flow, strong curvature flow, separated flow and jet, and is particularly suitable for simulating the flow conditions inside the fan duct; the optimization process of the topology optimization part is to start from the original duct, broaden the design space, construct the optimization design domain, and perform mesh discretization. In the early stage of duct topology optimization design, we usually have no preset concept of the specific layout of the duct, and only know the location of the fan and the outlet. The density method of topology optimization is a technology widely used in structural topology optimization. This method introduces a pseudo-density variable to describe whether the material exists in the design space. These design variables are usually defined in each unit or at each node of the grid. This method has the advantages of high design freedom, simple program design and high clarity of optimization results. The material density of the duct structure is used as the design variable (θ k ), taking the minimum energy consumption as the objective function of topology optimization, applying the size constraint of the fluid domain (L), the optimization formula is as follows:

[0015] Find: θ k ,(1)

[0016]

[0017] f(x i ,y i )≤L(x,y), (4)

[0018]

[0019] In the topology optimization design of fan duct, in order to more accurately control the path and speed of the fluid to obtain a better design layout, laminar flow is used to study it. For laminar flow problems, the fan duct calculation domain is calculated with the help of the finite element software k-ω turbulence model, and the fluid flow is described by the Navier Stokes equation as:

[0020]

[0021] F=-α(θ)u, (7)

[0022]

[0023] Where ρ is the fluid density, u is the fluid velocity, p is the fluid pressure, η is the fluid dynamic viscosity, is a gradient operator defined on the computational domain Ω, α(θ) is the inverse of the local permeability, and q is a positive real number. The realization of duct topology optimization is based on the Darcy interpolation model of the density model, and the resistance term F is introduced into the Stokes equation. The larger the value of the resistance term, the more difficult it is for the fluid to be transmitted in this computational domain, which has the effect that the solid material fluid cannot be transmitted in the computational domain. Among them, θ is the volume factor of the boundary control material, and the value range is 0≤θ≤1. When θ=1, the resistance term is 0, representing the air domain, and the fluid will not be hindered. When θ=0, huge resistance will be generated, which is the solid domain.

[0024] In order to better implement the method of the present invention, further, in step 1, the rated speed RPM of the fan is 1080r / min, and the tangential speed u x0 is 1.4671m / s, and the normal velocity is u y0 It is 1.285m / s.

[0025] Furthermore, in step 2.1, the inlet velocity is expressed as u x with u y express.

[0026]

[0027] Furthermore, in step 2.2, the number of iteration steps is initially set to 100 steps.

[0028] Furthermore, in step 3, in the flow field calculations before and after optimization in steps 3 and 4, the fan speed is set to 1080 r / min, and the speed before and after optimization is kept the same.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The present invention uses topological optimization technology to optimize the layout of the fan volute and air duct, including the establishment of an objective function, the acquisition of boundary conditions of the topological calculation domain, the application of a variable density method, and the analysis of the flow field before and after optimization, thereby ensuring that the optimized new fan volute air duct has low energy consumption and low vortex, thereby achieving an effect of increasing the outlet air volume.

[0031] (2) The method of the present invention gets rid of the empirical dependence in the traditional fan volute and air duct design, as well as the high time cost and large workload in the traditional design. The method of the present invention can automatically optimize the layout of the fan volute and air duct.

[0032] (3) The new fan volute air duct optimized by the method of the present invention avoids the backflow problem of the original fan volute air duct, and the air volume after optimization is increased by 173.17L / min, and the air volume increase rate is 34.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the method of the present invention;

[0034] Figure 2 The calculation domain of the fluid in the initial fan volute air duct of the embodiment;

[0035] Figure 3 The calculation result of the initial fan volute air duct flow field information of the embodiment;

[0036] Figure 4 The calculation results of the speed direction and magnitude of the fan around the embodiment when the fan speed is 1080r / min in free space;

[0037] Figure 5 The calculation domain and the location of each outlet of the wind duct topology optimization calculation domain of the fan volute domain of the embodiment;

[0038] Figure 6 The topology optimization result of the wind duct in the volute domain of the fan in the embodiment;

[0039] Figure 7 The calculation information of the wind duct flow field in the volute domain of the fan is reconstructed after optimization based on the embodiment;

[0040] Figure 8 The pressure distribution diagram of the fan volute and the air duct inside before and after optimization of the embodiment;

[0041] Fig. 9 The vorticity distribution diagram of the fan volute and the air duct before and after optimization of the embodiment. DETAILED DESCRIPTION

[0042] In order to make the purpose, calculation method and advantages of the present invention clearer, the specific implementation of the present invention is further described in detail in conjunction with the following implementation examples, but the implementation and applicable objects of the present invention are not limited thereto. Without departing from the technical idea of ​​the present invention, various replacements and changes made according to the common technical knowledge and customary means in the field should be included in the scope of the present invention. The specific implementation examples described here are only used to explain the present invention and are not used to limit the present invention.

[0043] Example:

[0044] Take the volute air duct of a refrigerator refrigeration fan as an example. Figure 2 shown. Figure 2The figure shows the fluid domain of the initial fan volute and duct before optimization. The fan duct contains 5 air outlets and one air inlet. The fan is located in the rotating domain. The rotation of the fan creates a negative pressure zone inside the rotating domain, which in turn draws air into the duct.

[0045] The velocity field distribution and streamline diagram of the fan speed at 1080r / min before optimization were obtained through finite element simulation, as shown in Figure 3 As shown in the figure, the unreasonable design of outlet 2 causes backflow.

[0046] In order to accurately describe the speed and direction around the fan after the fan rotates at the rated speed, the fan flow field distribution state under free field is constructed. Figure 4 As shown in Figure 2, it provides the most realistic velocity distribution state for the inlet boundary condition in topology optimization.

[0047] Constructing topological computing models such as Figure 5 As shown in the figure, the boundary conditions at the inlet are obtained by the velocity and size around the fan in the free field, and the velocity boundary conditions are loaded into the model using Formula 9. The outlet position and number in the topology optimization model are consistent with the fan duct before optimization.

[0048] Figure 6 This is the optimization result of the fan volute and air duct. It can be seen from the figure that compared with before optimization, the fan volute form and air duct layout have changed significantly after topology optimization.

[0049] The optimized fan volute and air duct are subjected to flow field analysis. Figure 7 is the optimized velocity field distribution diagram, Figure 8 and Fig. 9 The pressure distribution and vortex size of the fan volute and air duct before and after optimization are shown respectively. It can be seen from the figure that the pressure pulsation and vortex of the fan volute and air duct after optimization are reduced, which means that the fluidity performance of the fluid in the air duct is improved, the vortex loss is reduced, and the energy consumption is reduced.

[0050] Table 1 is a comparison of the air volume at each outlet before and after optimization. It can be seen from the table that the air volume is greatly improved after optimization, and the air volume increase rate reaches more than 34%.

[0051] Table 1

[0052]

[0053]

Claims

1. A topological optimization design method for a high-volume fan volute and air duct, characterized in that: The following steps are involved: Step 1: A method for obtaining the inlet boundary conditions of the topology optimization, wherein the boundary conditions obtain the tangential velocity and normal velocity of the fan through the rated speed of the fan in the free field; Step 2: Establishment of topology optimization model of fan volute air duct 2.1 Setting of inlet and outlet boundary conditions; In step 2.1, the inlet boundary condition is the velocity boundary condition, and the inlet velocity is expressed as u x with u y Indicates that u x with u y The definition of is formula 9; 2.2 Structural design of fan volute air duct topology optimization model; In step 2.2, the objective function of the fan volute air duct topology optimization model is: The volume constraint is The governing equations used Where F = -α(θ)u, ρ is the fluid density, u is the fluid velocity, p is the fluid pressure, η is the fluid dynamic viscosity, is the gradient operator defined on the computational domain Ω, is the inverse of the local permeability, q is a positive real number; Step 3: Reconstruct the three-dimensional model of the fan volute air duct topology optimization model and analyze the flow field, use the grid filter to obtain the new air duct volute contour, and use the finite element method to calculate the air volume of the optimized air duct volute; Step 4: Use the finite element method to calculate the air volume of the initial air duct volute; Step 5: Compare the air volume before and after optimization and calculate the increase in air volume.

2. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 1, characterized in that: In step 2.2, the implementation of duct topology optimization is based on the Darcy interpolation model of the density model, and a resistance term F is introduced into the Stokes equation; the larger the value of the resistance term, the more difficult it is for the fluid to be transmitted in this calculation domain, which has the effect of preventing the fluid from being transmitted when solid materials appear in the calculation domain.

3. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 1 or 2, characterized in that: In the step 2.2, θ is the volume factor of the boundary control material, and its value range is 0≤θ≤1.

4. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 1 or 2, characterized in that: In step 1, the rated speed of the fan RPM is 1080r / min, and the tangential speed of the fan in the free field is u x0 is 1.4671m / s, and the normal velocity is u y0 It is 1.285m / s.

5. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 3, characterized in that: In step 1, the rated speed of the fan RPM is 1080r / min, and the tangential speed of the fan in the free field is u x0 is 1.4671m / s, and the normal velocity is u y0 It is 1.285m / s.

6. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 1 or 2, characterized in that: In step 2.1, the outlet boundary condition is set as a pressure boundary condition, and the static pressure is 0Pa.

7. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 3, characterized in that: In step 2.1, the outlet boundary condition is set as a pressure boundary condition, and the static pressure is 0Pa.

8. The method for topological optimization design of volute and air duct of a high air volume fan according to claim 4, characterized in that: In step 2.1, the outlet boundary condition is set as a pressure boundary condition, and the static pressure is 0Pa.

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