Computer Life (CPL) ISSN: 1819-4818 Delivering Quality Science to the World Fluid-structure Coupling Simulation Analysis of Wavy Lip Seals Linghao Song a, Renpu Deng b and Chaonan Huang c College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Shandong, China a 139305897@qq.com, b 10837165@qq.com, c 95343518@qq.com Abstract: The wavy lip seal is widely used in the sealing process. In order to realize the use of the wavy lip seal. firstly, this paper analyzes the structure and sealing theory of wavy lip seal, and determines the factors which affects the seal performance of the lip shape oil seal in the initial assembly, the internal travel and the outside stroke, and then, the ANSYS software is used to model and simulate the wavy lip seal and the ordinary lip seal accurately. The results show that the maximum flow velocity, maximum fluid pressure, minimum fluid pressure and maximum deformation of the wavy lip seal are greater than the ordinary lip seal, but the minimum velocity and maximum stress of the wavy lip seal are smaller than the ordinary lip oil seal s minimum flow velocity and maximum stress. This is consistent with the actual working situation of the wave lip seal. Therefore, the results are of great significance not only to the study of the lip rotating oil seal, but also for the study of the sealing performance of the lip rotating lip oil seal. Keywords: Wavy Lip Seals, Fluid-structure Coupling, deformation, stress. 1. INTRODUCTION During the normal operation of the oil seal, there is a thin layer of lubricating oil film between the lip of the seal and the rotating shaft. The oil film can reduce the friction between the gap. The fluid pressure in the oil film is affected by the dynamic pressure effect of the fluid, and the fluid pressure in the oil film will affect the change of the lip of the wavy lip seal. The deformation of the wavy seal lip will in turn affect the thickness of the oil film, thus the pressure and velocity of the oil film is changed. [1,] With the development of finite element analysis technology, finite element analysis technology has been widely applied to the research of the wavy lip seal. Kim C K[3] and others use the finite element technique to calculate the two-dimensional simplified model of ordinary lip oil seal. The calculated results are in agreement with the test results. Gorrino A [4] and so on through the static simulation analysis of the section of the rotating lip seal with two-way sinusoidal reflux lines to calculate the contact pressure at different positions of the oil seal. in the above finite element analysis, the three-dimensional model is used to be represented by the two dimensional simplified model. This method has certain limitations. With the development of computer technology, Tasora A [5] established a three-dimensional model of ordinary lip seal and studied the contact pressure and 1
overall deformation of ordinary lip oil seal in different assembly positions with the help of ABAQUS finite element software. Maoui A [6], respectively, carried out the numerical value of two dimensional axisymmetric and three-dimensional model of radial lip seal. The deformation of the lip of the seal is simulated, and the results shown that there are differences in the lip deformation between two dimensional axisymmetric and three-dimensional models. Therefore, in the finite element analysis of rotating seals, it is not necessary to simplify the two-dimensional axisymmetric model as far as possible. This paper will continue to analyze the wave lip seal by using the three-dimensional model. In order to make up the shortage of the above research, through the analysis of the structure and sealing mechanism of the rotating oil seal of the corrugated lip, the finite element software is used to simulate and compare the wave rotating lip seal and the ordinary rotating lip seal. The comparison results are of great value to the design of the lip rotating oil seal and the improvement of the sealing performance.. THEORETICAL BASIS OF FLUID-STRUCTURE COUPLING FOR WAVE LIP SEALS The fluid-structure coupling analysis of wave lip seals involves two major disciplines: fluid mechanics and structural mechanics. In order to study the coupling effect between wave lip seals and fluid, we make some assumptions here. (1) Incompressibility of fluid; () Non rotation of fluid; (3) Fluid is ideal. (4) The initial oil film thickness between the lip and the seal is constant. The equilibrium equations and continuous equations of fluid in rectangular coordinates are shown in expressions (1) and () respectively. u v w 0 x y z (1) p u u u u ρ u v w 0 x t x y z p v v v v ρ u v w 0 y t x y z p w w w w ρg ρ u v w 0 z t x y z () φ p ρ t (3) p p p x y z p 0 In the expressions (1) and (), u v and w are the velocity components in the direction of x y and z axis respectively. Among them, the fluid pressure can be expressed by the formula (3). (4)
For the formula (1), we obtain the first derivative (4), (4) as the basic equation, and the boundary condition of the basic equation (5). Free surface: Fixed surface: p ρgh p 0 n p u Coupled surface: ρ n n t Infinity: (5) (6) (7) p 0 (8) It is known from the boundary condition (7) that the basic equation of the fluid medium is coupled with the solid, and the fluid pressure load is included in the structural equation, which makes the solid medium equation coupled with the fluid. 3. THE PROCESS OF FLUID-STRUCTURE COUPLING SIMULATION ANALYSIS OF WAVE LIP SEALS Since the ANSYS Workbench software has powerful analysis function in structure, fluid and mutual coupling, this paper uses it to analyze the fluid-structure coupling static analysis of seals. The analysis process mainly includes the establishment of fluid-structure coupling model of seals, then the calculation of the fluid part. The result is mapped to the structural part, then the structural part is calculated, and finally the result is read. 3.1 Establishment of three-dimensional model of fluid-structure coupling When the wave lip seal and the rotating shaft are assembled, the lip will deform and form a plane contact area with a certain width with the rotation axis. When the oil seal works normally, the oil seal lip and the rotating shaft will be filled with a layer of lubricating oil film, and the fluid pressure of the oil film will lift the oil seal lip to the surface of the rotation axis. According to this principle, we assume that the thickness of the lubricant film is 0.mm, i.e., the gap between the corrugated lip seal and the rotary shaft is 0.mm. The 3D solid model of wave lip seals fluid-structure coupling is established as shown in Fig. 1. In Fig.1, model 1 is spring and model is rotation axis, model 3 is fluid, model 4 is skeleton, model 5 is rubber body. Among them, the circumferential boundary of the fluid model coincides with the surface of the rotating shaft, the lip surface of the seal, the lip surface of the air side and the lip surface of the oil side. 1 3 4 5 Fig.1 3D fluid-solid coupling model for oil seal 3
3. Hydrodynamics calculation Fluid mechanics calculation of fluid solid coupling of the seal is carried out in project A. Firstly, the cell length is set and the fluid is meshed. The fluid model after mesh is shown in Fig.. Finally, the solution parameters and fluid boundary conditions are solved for the fluid selection material. The flow of the fluid in the seal region of the lip oil seal is mainly caused by the attraction between the fluid molecules, the adsorption and the inertia between the fluid and the solid boundary. Among them, the main function is the attraction between the fluid molecules and the adsorption between the fluid and the solid boundary. Therefore, the flow of the lip seal area is laminar flow, so the Standard k-epsilon model of two parameters is chosen, the parameters C 1 and C are 144, 19. Fig. Mesh model of fluid Respectively, and the density of the lubricating oil is set to 887kg/m 3 and the viscosity is set. For 0.kg/m 3. When the rotating shaft is stationary, the inlet of the fluid is only affected by the pressure of the fluid, the fluid pressure is set to 0.1MPa, the outlet of the fluid is affected by the pressure of the atmosphere, and the outlet is set free flow, and the surface of the fluid and the oil seal and the rotating shaft are set to the boundary. 3.3 Structural mechanics calculation After the fluid solution is completed, the solid structure of the seal is solved. Firstly, the structural steel model is selected for the skeleton, spring and rotation axis, and the mooney-rivlin rubber model with parameters is selected for the oil seal. After that, the fluid geometry model, which is independent of the solid structure calculation, is suppressed, and the material attributes are assigned to the seal, spring, skeleton and axis of rotation. The element length is set to mesh the solid geometry model. The meshed model is shown in fig.3. Fig. 3 Mesh model of lip oil seal Fig.4 Lip oil seal model after applied load 4
A fixed constraint is imposed on the outer circumference of the seal, the inner surface of the skeleton and the outer surface of the spring; afterwards, an angular velocity rotating around the z axis is applied to the axis of rotation; and the fluid calculation results are then mapped to the solid structure of the seal. The fluid surface of the fluid-solid interface is selected in the column CFD surface, and the model after the load is applied is shown in fig.4. Finally, setting the parameters to solve the problem. 3.4 Analysis of Fluid-structure Coupling Simulation results for Wave Lip Seal The fluid-structure coupling analysis method is used to analyze the fluid-structure coupling of the same profile lip and the ordinary lip seal, respectively. The period of the seal is 4 and the amplitude of the wave is 0.065 mm. 3.4.1 Flow field analysis After the simulation analysis is completed, the flow velocity vector and pressure vector cloud of the lip fluid of the waveform lip oil seal and the ordinary lip oil seal are read respectively as shown in fig.5 and 6. (a) Wavy lip seal Fig. 5 Velocity vector cloud (a) Wavy lip seal Fig. 6 Pressure vector cloud It can be seen from the figure that the maximum flow velocity and the maximum fluid pressure of the wave lip seal are both higher than those of the ordinary lip seal, and the minimum velocity of the wave lip seal is less than the minimum velocity of the ordinary lip seal. However, the minimum fluid 5
pressure of the wave lip seal is greater than that of the ordinary lip seal, which indicates that the oil film thickness of the wave lip seal is greater than the ordinary one [7]. Because the thickness of the lip oil film is related to the lip deformation of the seal, the deformation of the wavy lip seal is larger than that of the ordinary lip seal, which is consistent with the actual operation results. 3.4. Structural simulation analysis On the basis of the fluid calculation results, the static structure of the wave lip seal and the ordinary lip seal are analyzed. The deformation and stress cloud images of the wave lip seal and the ordinary lip seal are shown in figs. 7 and 8, respectively. (a)wavy lip seal Fig.7 Deformed cloud of lip seal (a) Wavy lip seal Fig.8 Equivalent stress cloud of lip seal It can be seen from the diagram that the maximum deformation of the wave lip seal is greater than that of the ordinary lip seal under the action of fluid, but the maximum stress of the wave lip seal is smaller than the ordinary. The above results are consistent with the actual operation results, but under the action of the fluid, the equivalent effect force is much smaller than that in the nonlinear static simulation analysis [8], which shows that the interaction between the oil seal and the fluid can reduce the equivalent stress. Thus, prolonging the service life of oil seal. 4. CONCLUSION In this paper, by introducing the theoretical basis of fluid solid coupling analysis, the interaction between oil seal and lubricating oil is analyzed. After that, the detailed process of transient analysis of fluid solid coupling is introduced in detail. Then, through the analysis of fluid solid coupling flow field and the result of structural field analysis of wave lip seals and ordinary lip seals, the results of the 6
analysis of the fluid-structure coupling flow field and the results of the structural field analysis are analyzed. The maximum flow velocity, maximum fluid pressure, minimum fluid pressure and maximum deformation are greater than ordinary lip seals, but the minimum flow velocity and maximum stress of the corrugated lip seal are smaller than the minimum flow velocity and maximum stress of the ordinary lip seal. REFERENCES [1] Jagger E T. Rotary shaft seals: the sealing mechanism of synthetic rubber seals running at atmospheric pre-sure [J]. Proceedings of the Institution of Mechanical Engineers, 1957, 171: 597-616. [] Renliang Cai, Fluid seal technology[m]; Beijing, Chemical Industry Press,013.5. [3] Kim C K, Shim W J. Analysis of contact force and thermal behavior of lip seals[j]. Tribology International, 1997, 30(): 113-119. [4] Gorrino A, Angulo C, Canales J. Theoretical analysis of the pumping effect of rotary hydrodynamic seals with elastomeric lips[j]. tribology international, 007, 40(5): 896-905. [5] Tasora A, Prati E, Marin T. A method for the characterization of static elastomeric lip seal deformation[j]. Tribology International, 013, 60: 119-16. [6] Maoui A, Hajjam M, Bonneau D. Effect of 3D lip deformations on electrohydrodynamic lip seals behavior[j]. Tribology International, 008, 41(9 10): 901-907. [7] Müller H K, Nau B S. Fluid sealing technology: principles and applications[m]. New York: M. Dekker, 1998. [8] Dandan Zhao, Research on Precise Modeling and Sealing Performance of Wavy Lip Seal, China: Shandong University of Science and Technology,018. 7