International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 5, May 2018, pp. 717 724, Article ID: IJMET_09_05_079 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=9&itype=5 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed OPTIMAL DESIGN OF CLUTCH PLATE BASED ON HEAT AND STRUCTURAL PARAMETERS USING CFD AND FEA Akash Porwal, Abhishek Tripathi and Tript Agrawal Undergraduate Students, Department of Mechanical Engineering, VIT University, Vellore, India Baskar. P Assistant Professor (SG), Automotive Research Centre, VIT University, Vellore, India ABSTRACT The energy transfer during the friction clutch operation is followed by dissipative process through convection at friction surface. To improve the performance of the friction clutch, it is important to analyze maximum temperature rise at the friction surface different design variants of grooves on the clutch plate were analyzed using CFD and FEA techniques to determine the optimum design which has good air flow around grooves and bears considerable amount of load which is imposed at the time of engagement. According to the results, a new clutch plate design is suggested, which has tapered groove geometry. The results shows improvement of the convection between air and friction surface in new design, resulting in reduced maximum temperature rise. The software ANSYS 18 and Starccm+ 12.0 are used for the numerical computation and analysis in this paper. Keywords: convection, grooves, computational fluid dynamics, Finite element analysis, ANSYS 18, Starccm+ 12.0 Cite this Article: Akash Porwal, Abhishek Tripathi, Tript Agrawal and Baskar. P, Optimal Design of Clutch Plate Based on Heat and Structural Parameters using CFD and FEA, International Journal of Mechanical Engineering and Technology, 9(5), 2018, pp. 717 724 http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=9&itype=5 1. INTRODUCTION The friction clutch system consists of pressure plate, clutch disc and flywheel. When the clutch start to engage slipping occurs between contact surfaces due to the difference in the velocities between them depending on engine speed and engaged gear ratio. Due to slipping between the surfaces a high amount of kinetic energy converted into heat energy at interfaces according to the first law of thermodynamics. The heat generated between contact surfaces http://www.iaeme.com/ijmet/index.asp 717 editor@iaeme.com
Optimal Design of Clutch Plate Based on Heat and Structural Parameters using CFD and FEA will dissipate by the conduction between friction clutch components and by convection to environment. These heat loads may be significant during traffic jam or hill starts. During such events, the temperature periodically rises. While the temperature reaches a high value, close to 300 C, the friction coefficient, which is related to the temperature, can drop suddenly, thus making the vehicle unusable, as engine cannot transmit its torque to the gearbox. To dissipate the heat generated during the engagement time, different grooves geometry is made on the friction surface to provide path for air flow. This helps in increase in air flow at the surface because of increase in the surface area thus reducing the maximum temperature rise. 2. MATHEMATICAL MODEL Convective heat transfer is the transfer of thermal energy by the combined effects of random molecular motion (diffusion) within the fluid, and the overall movement of the fluid from one place to another. It is case of free convection. The density of a fluid typically decreases with increasing temperature and thus warm fluid will tend to rise. As warm fluid rises from a hot object, thermal energy is convected away. Figure 1 Fluid Domain Fluid domain used for analysis is cylindrical, as the model is the rotating disc so the flow will be uniform and symmetrical around it. All different design variants are modelled in Solidworks 2017. The mathematical model for the vertical rotating disc is determined by checking whether flow is laminar or turbulent. Ra = Gr * Pr Rex = Ω µ Pr = µ ( ) Gr = For the flow to be laminar Reynolds number should be less than 5*10 5 else the flow will be turbulent. http://www.iaeme.com/ijmet/index.asp 718 editor@iaeme.com
Akash Porwal, Abhishek Tripathi, Tript Agrawal and Baskar. P Considering the constant circumferential wall temperature for the model Ω= 150rad/sec, =0.09m Dynamic viscosity of air at 30 C = 18.63* 10-6 β = 3.3*10-3, and =16*10-6 At x =, Rex = 6.52*104 << 5*105 Gr = 3.8*/1014 Pr = 0.701 Gr/Rex2 = 8.9*104 >>1, Hence it is natural or free convection at 30 temperature. For temperature of air equal to 300 C dynamic viscosity is equal to 29.71*10-6, β =1.75*10-3, and = 48.2*10-2 Pr= 0.0674 Rex = 4*104 << 5*105 Gr/ Rex2 = 2*105 >>1 At temperature 300 C also it is satisfies condition of free convection. Therefore for both the extremities of temperature the flow is laminar and only free convection takes place. for lamilar flow (Nu) x =0.332*Re x 0.5 *Pr 0.333 By calculating Nusselt number, convective heat transfer coefficient can be calculated by the formula (Nu) x = h x L/k f. Convective heat transfer at a surface is governed by Newton s law of cooling: Q = h ( ) h = ( )! ( )" # $ $ ( ) 2.1. Air Flow Field Steady state computation can be achieved for velocity field within the rotating frame of the clutch disc. The Navier-Stokes equations govern the motion of fluids in the rotating frame. In the case of a compressible Newtonian fluid, %&' (" () *+&.-... = -& + -(µ(-. +-. ) 0 1 µ(-.).2) + 3 4 1 This equation is solved with the continuity equation to determine the velocity vector field. % 56 57 + -(&..) = 0 4 2 The velocity relative to the moving reference frame (relative velocity). transforms from the velocity in the stationary laboratory reference frame (absolute velocity) by u:. =.. 9 =. (. : + ; < ) 3 http://www.iaeme.com/ijmet/index.asp 719 editor@iaeme.com
Optimal Design of Clutch Plate Based on Heat and Structural Parameters using CFD and FEA 3. NOMENCLATURE Rex Reynolds number at distance x - L Circumference m Inner radius of friction lining 0.0625 m 0 Outer radius of friction lining 0.090m D Depth of the radial groove 0.00112m d Depth of circumferential groove 0.0005m t Thickness of the clutch plate 0.008m T Thickness of cushioning plate 0.001m ω Angular velocity of the clutch plate 139 rad/s Pr Prandtl Number - µ Dynamic viscosity >?/A 0 n Number of grooves 12 Kinematic viscosity A 2 /?CD Cp Specific heat of friction lining 1420 EJ/kq*k Thermal conductivity of layer of air adjacent to k topmost layer of friction lining A 0 F β Coefficient of thermal expansion 1/K. Velocity vector at a point r m/s p Fluid pressure N/A 0 ρ Fluid density g/da 1 4. CFD SIMULATION The Mesh Type used for the model is Trimmed Mesh with Surface repair mesher. The Physics Model used for rotating disc system is K- Omega with Reynolds Averaged Navier Stroke Model (RANS) under implicit unsteady analysis. conjugate heat transfer model is used to determine convective heat transfer coefficient on the complete surface of the disc. To apply the conditions of the time of engagement for heat source, temperature data is input as function of time as shown in Table2. The relative rotation rate of the clutch plate about its axis is 139 rad/s. The boundary condition applied for the model is Stagnation inlet and Pressure outlet as no clutch assembly is completely enclosed so no surrounding air would enter into the system. The complete model was simulated for 1.1 s. Velocity flow and convective heat transfer coefficient around the friction is studied through the simulation. Figure 2 Angular Radial Grooves Figure 3 Straight Radial Grooves http://www.iaeme.com/ijmet/index.asp 720 editor@iaeme.com
Akash Porwal, Abhishek Tripathi, Tript Agrawal and Baskar. P Figure 4 Tapered radial and circumferential Grooves Grooves Figure 5 Straight radial and circumferential Figure 6 Heat Transfer Coefficient of angular grooves Maximum velocities in different variants are found to be as: Straight radial grooves - 11.570 m/s, Angular radial grooves - 12.245 m/s Tapered radial and circumferential grooves - 15.5701m/s, Radial and circumferential grooves 11.701m/s. Tapered radial and circumferential grooves has the maximum air velocity so it will give best cooling of all the grooves geometries, air entering from inside disc will have more area exposed for flow at the inner radius of the disc while area decreases at the outer radius of the disc.so the velocity of air will increase as shown in Fig 3. The radial grooves have more impact on increase in velocity as compared to the circumferential grooves. The convective heat transfer coefficient is maximum along the grooves region which shows maximum cooling by the groove region of the surface and reduces the maximum temperature rise. Table 2 Time-temperature data Time (s) Temperature(K) 0 0 0.1 300 0.2 310 0.3 323 0.4 350 0.5 396 0.6 425 0.7 450 0.8 475 0.9 490 1 520 1.1 560 http://www.iaeme.com/ijmet/index.asp 721 editor@iaeme.com
Optimal Design of Clutch Plate Based on Heat and Structural Parameters using CFD and FEA Table 3 Material Properties Components Cushioning Plate Friction lining Material Structural Steel Kevlar 49 Density (g/da 1 ) 7.85 1.44 Young s Modulus 2 x 10 Pa 1.24 x 10 Pa Tensile yield Strength 2.5 x 10 I Pa 337.6 x 10 J Pa Tensile Ultimate Strength 4.6 x 10 I Pa 3 x 10 K Pa Poisson s ratio 0.3 0.36 Isotropic thermal Conductivity 60.5 WA L 0.04WA L Specific Heat 434 JFM L 1418 JFM L 5. FINITE ELEMENT FORMULATION Finite element method is matrix method of analysis. The analysis is done through stiffness methods of which displacement of points on body are unknown. The set of equations used in stiffness method are equilibrium equations. The Rayleigh-Ritz method is used to derive the equilibrium equation. Static analysis is time independent, the equations for static structural analysis are found to be: {e} = [B]{u}, {σ} = [D]{e} [K] = [O ] [D] [B] dv {F} = [K]{u} Where, [K] is the stiffness matrix, {u} the vector of nodal displacements, and {F} element force vectors. {e} is strain matrix, [B] is strain displacement relation matrix, [D] is stress strain relation matrix which is Young s Modulus of the material used, {σ} is stress matrix. In order to determine stress distribution of this static structural problem, the fine mesh element was essential. Moreover, when the iterative method of the given problem is employed, then a relatively short time is needed for the calculations. ANSYS software is used to investigate static thermomechanical analysis of dry friction clutch. Equivalent (von misses ) stress Figure 7 Straight radial grooves Figure 8 Angular radial Grooves http://www.iaeme.com/ijmet/index.asp 722 editor@iaeme.com
Akash Porwal, Abhishek Tripathi, Tript Agrawal and Baskar. P Figure 9 Tapered radial and Circumferential grooves Figure 10 Circumferential grooves The Mesh type for discretization of model is tetrahedral mesh. loads applied are Pressure normal to the surface equal to 0.25 MPa under the thermal Condition of 300 C and a torque of 120Nm. the constraint applied is Fixed Support at Cushioning plate surface. Analysis type for the model is Static structural. These Conditions are at the time of engagement of clutch plate and pressure plate at which temperature rises to maximum in relatively short time. The maximum stress value is large in case of angular grooves as compared to straight grooves. But there is very less maximum stress region in angular grooves. Therefore angular grooves can bear better load than straight grooves. All the four design variants are within the safety limit of the component. Graph of stress v/s distance from inner radius Straight radial grooves Straight grooves with circumferential grooves http://www.iaeme.com/ijmet/index.asp 723 editor@iaeme.com
Optimal Design of Clutch Plate Based on Heat and Structural Parameters using CFD and FEA Stress Peak is large in case of straight grooves as compared to angular grooves. From Fig5. There is much larger region of high stress (green colour) in straight grooves while angular grooves have less large stress regions as shown in Fig6 6. CONCLUSION A parametric variation of different groove geometries has been performed on friction clutch using CFD and FEA. The results show that tapered groove geometry has maximum velocity of air flow as compared with all different design variants. These will reduce the maximum temperature rise on the friction surface. Also, a radial groove has more impact than circumferential grooves on increasing the velocity of air flow. Convective heat transfer coefficient is maximum around the groove region so maximum cooling will do through groove area. The strength of different design variants is analyzed using FEA, tapered groove and radial groove have smaller stress peak than the straight groove. After optimization, grooves number equal to 12 can hold the pressure applied to the clutch plate during its operation. The tapered groove with radial and circumferential groove is best design of all geometries considered as shown in Fig9. REFERENCES Figure 11 New Structure of Clutch Plate [1] Abd Al-Sahb, W. and Abdullah, O., "A Three Dimensional Finite Element Analysis for Grooved Friction Clutches," SAE Technical Paper 2015-01-0688, 2015, doi: 10.4271/2015-01-0688. [2] Levillain, A., Brassart, P., and Patte-Rouland, B., "Numerical Computation of the Air Flow and the Thermal Behavior of a Double Dry Clutch Automotive Transmission," SAE Int. J. Engines 8(4):2015, doi: 10.4271/2015-01-1661. [3] Starccm+ 12.0 Theory guide [4] Robert Cook: Finite Element Modeling for Stress Analysis, John Wiley & Sons, 1995. [5] Oday I. Abdullah and Josef Schlattmann: The Effect of Disc Radius on Heat Flux and Temperature Distribution in Friction Clutches, J. Advanced Materials Research, Vol. 505, pp. 154-164, 2012. [6] Oday I. Abdullah and Josef Schlattmann, Contact Analysis of a Dry Friction Clutch System, ISRN Mechanical Engineering, vol. 2013, Article ID 495918, 9 pages, 2013. doi:10.1155/2013/495918 http://www.iaeme.com/ijmet/index.asp 724 editor@iaeme.com