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International Journal on Mechanical Engineering and Robotics (IJMER)

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ISSN (Print) : 2321-5747, Volume-2, Issue-2,2014 12

Investigation Study on Fluid Flow Modelling and Damping Response of Automobile Hydraulic Damper

1Kautkar Nitin Uttamrao, ²S.T Satpute, ³L.M Jugulkar

1Post Graduate Student , ²Associate Professor, ³Assistant Professor,

1Automobile Engineering Department, R.I.T. Islampur (M.S.), India

2,3Rajarambapu Institute of Technology, Rajaramnagar, Sangli, Maharashtra Email: ¹[email protected], ²[email protected], ³[email protected]

Abstract -Automobile shock absorber consists of a dissipative element connected in parallel with an elastic element. Fluid damper are most reliable to be used as a dissipative elements in the vehicle shock absorber.

Damping action in fluid shock absorbers is obtained by throttling viscous fluid through an orifice. Fluid shock absorbers offer sufficient damping force with compact size, also the damping force is linear in nature. Damping force of the fluid damper depends on orifice properties and on the physical properties of oil used.

This case study carry out on fluid flow modelling and damping response of hydraulic damper also Computational Fluid Dynamics (CFD) trial study method is used to investigation fluid flow pressure in moped (Luna) hydraulic damper. Averaged Navier-Stokes equations are solved by the SIMPLE method and the RNG k- ε is used to model turbulence.

Keywords –Shock absorber, Hydraulic damper, Hydraulic valve, CFD simulation

I. INTRODUCTION

Isolation from forces transmitted by external excitation is the fundamental task of any suspension system. In case of a vehicle a classical car suspension aim to achieve isolation from the road by means of spring-type element and viscous damper (shock absorber) dampers are also called shock absorbers, shocks or spring energy dissipaters and contemporarily to improve road holding and handling. Dampers are an integral part of any suspension system. The main function of the dampers is to control the transient behaviour of the sprung and unsprung masses of the vehicle. This is accomplished by damping the energy stored in the springs from suspension movement. The elastic element of suspension is constituted by spring (coil spring but also air spring and leaf spring), where as the damping element is typically of the viscous type. Shock absorbers are compact, light weight suspension struts which reduce the suspension play and they can be used in very

heavy load applications such as heavy military vehicles, landing gear suspension in aircrafts and space shuttles.

The liquid flow through orifices produces larger damping where as the cushioning effect comes from the fluid’s compressibility. The liquid spring design is subject to constant high pressure necessary to achieve required forces, which drastically increases during dynamic operation. These peak dynamic pressures which may propagate fluid leakage the shock transmissibility and the suspension play are the critical design parameters. [6] Unlike automobile suspension design where the trade OFF between the driving comfort and manoeuvrability is the principal design concern robustness and reliability are key design aspects in defence systems. Theoretical studies have long back shown that liquid springs are very effective in isolating large shocks high-rate input loading [3]. The basic schematic of a liquid spring is shown in Fig.1 where variables H, ht, Ap, Ar, M, W, g and V(t), respectively, represent the overall internal height of the device, thickness of the piston, piston cross-section area, piston- rod cross-section area, supported mass its weight, gravity and the velocity excitation from the ground.

Primary suspension is the term used to designate those suspension components connecting the axle and wheel assemblies of a vehicle to the frame of the vehicle. This is in contrast to the suspension components connecting the frame and body of the vehicle, or those components located directly at the vehicle’s seat, commonly called the secondary suspension. There are two basic types of elements in conventional suspension systems. These elements are springs and dampers. The role of the spring in a vehicle’s suspension system is to support the static weight of the vehicle. The role of the damper is to control the input from the road that is transmitted to the vehicle. The basic function and form of a suspension is the same regardless of the type of vehicle or suspension.

Primary suspensions will be divided into passive, active adjustable and semiactive systems, as will be discussed next, within the context of this study.

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Fig, 1.1: (a) Schematic of the liquid shock absorber and (b) top view of the oriﬁces in the piston [6]

II. ANALYSIS OF DAMPING:

Rebound valve consists of rebound slice which locates piston underside and piston under-surface, the basic components include piston orifice, throttle slice, throttle holes and down-check ring. Schematic diagram is shown in Figure 2. In Figure 2, d_h is diameter of piston orifice, n_h is the number; p is pressure on throttle slice; f_rk0 is pre- deformation of throttle slice which is decided by the fixing size to ensure right valve-opening velocity; r_b is outer radius of slice, r_kis valve mouth radius, r_a is inner radius of slice (taking the fixing size into account); $_k is the opening size of rebound slice, and it is equal to difference between total deformation f_rk and pre deformation f_rk0of slice. For the design of throttle holes area, it should take the piston orifice, the piston slot and local throttle loss with suddenly expansion, and shrinkage and direction change into account.[4]

Fig.2.1: Schematic diagram of rebound valve [4]

The damping force of shock absorber is determined by the forces acting on the both sides of the piston. And the friction forces are another factor that determines damping force. Nevertheless, in this study, the friction forces are ignored to simplify the analysis. Fig.1.3 shows free body diagram of the piston considering the damping force [10]

Fig.2.2: Free body diagram of the piston [10]

By considering the forces acting on the piston, the damping force can be obtained as follows:

F _damping=P_r._.A_r-P_c.A_c± F_friction ………. 1 [10]

A_r= A_p- A_rod Where,

F_dampingis a damping force. F_friction is the friction force, that is acting on piston rod.[10]

2.1Piston orifice:

Orifices are distributed on the piston uniformity. The diameter dh and number n_h are both serialization, and dh is in series, such as 1.5 mm, 1.75 mm, 2.0 mm, n_h is in series too, such as 2, 4, 6, 8. For single piston orifice with diameter dh and length L_h, its type can be selected by the ratio L_h / d_h. Due to L_h / d_h > 4, according to the definition of orifice sort, piston orifice can be regarded as slim orifice. So the throttle pressure of piston orifice as follows

P_h= ... 2 [4]

Where, p_h is the pressure of pisto+n orifice; L is the equivalent Length the value is equal to sum of the physical length and the local loss calibrated length, that is L = L_h + L_e; µ_t is the dynamic viscosity of fluid. [4]

III. THE 3D ANSYS:

3.1Fluent Simulations:

Fluent Simulations In order to capture the fluid flow pressure behaviour in CFD analysis have been performed. The ANSYS Fluent solver has been used to run a set of steady-state simulations for the parametric design moped (Luna) geometries. The hydraulic damper have been analysed in two separate chamber which is rebound and compression chamber.

Mass flow inlets/pressure outlets boundaries are chosen in order to cover the known operating range main settings for the performed steady-state CFD analysis.

This model is used in many practical engineering flow calculations, thanks to its robustness, economy and accuracy for a wide range of turbulent flows.

Additionally, the realizable version, compared to

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standard k-ε models, improves the mathematical formulations around the definition of the critical Reynolds stresses, leading to a better prediction over flows characterized by strong streamline curvature, vortices and rotations.

Fig 3.1: Fluid domain in ANSYSE FLUENT 3.2 MASS FLOW CALCULATIONS:

Density of Fluid *Area * Velocity of Fluid Where, Density of fluid (p) = 860 kg/m³

TABLE 3.2.1- PARAMETRIC DIMENSION FOR MOPED (LUNA)

Parameter Value Unit

Cylinder Diameter 18.9 mm

Piston Diameter 18.6 Mm

Rod diameter 8.8 mm

Rod length 142 mm

Piston height 8 Mm

Cylinder height 118 Mm

Area Consideration for Rebound stroke while Mass Flow Calculation for 2 Orifice= Area of Piston –Area of Rod

= -

=π*9.3^2-π*4.4²

=210.895 mm²

Area Consideration for Compression stroke while Mass Flow Calculation Orifice for 2 Orifice =

Area of Piston = =π*9.3² =271.176 mm²

Velocity of fluid which is basic mineral oil as given below (calculate Mass flow for each Velocity for given Velocity range by considering Area and Density constant) 0.1, 0.2

TABE 3.2.2: MASS FLOW VALUE FOR DIFRANT VELOCITY

Sr.

No

Velocity of fluid

Mass flow for Rebound stroke (kg/s)

Mass flow for Compression stroke(kg/s)

1 0.1 0.018130 0.023367576

2 0.2 0.03627 0.046735152

Typical CFD analysis results from simulation are shown by Figure where the complexity of the fluid flow and its influence on the hydraulic pressure build up can be noticed.

Fig 3.2: ANSYSE FLUENT result for fluid pressure pattern at 0.01813kg/s mass flow in rebound stroke

Fig 3.3: ANSYSE FLUENT result for fluid pressure pattern at 0.023367576 kg/s mass flow in compression

stroke

VI. CONCLUSIONS

Fluid flow modelling of the shock absorber/hydraulic damper which contains rebound chamber, compression chamber, orifice, assembly is given in this paper, then a trial CFD simulation model is established using ANSYS software, whole study describe that damping force or response is the distributed parameter modelling/design is not only necessary to understand the impact of key design features, but also to extract physical variables associated with the fluid flow. In particular, flow pattern and static pressure distributions on the piston are studied.

Finally, based on a investigation study evaluation of the information obtained from all the cases examined, it was concluded that while fluid passes through one chamber

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to another orifice region is the influence region from where pressure losses are going to start, however pressure difference is the function of damping force moreover damping response depend on pressure difference .

REFERENCES

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Sawant (2013),“Fluid flow modelling of a fluid damper with shim loaded relief valve”, International Journal of Mechanical Engineering (IJME), Vol. 2, pp 65-74.

[2] L.M. Jugulkar,Dr. Shankar Singh, Nitin Satpute(2011), “Developments in suspension a review ”, International Journal of Research in IT

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[3] Branislav Titurus , Jonathan du Bois, Nick Lieven, Robert Hansford (2010), “A method for the identiﬁcation of hydraulic damper characteristics from steady velocity inputs.”, Mechanical Systems and Signal Processing, Elsevier, pp 2868–2887.

[4] Changcheng Zhou , Zhiyun Zheng and Xueyi Zhang (2009), “Design method for throttle holes area of telescopic shock absorber for small electric vehicles”, Journal of Asian Electric Vehicles, Volume 7, pp1191-1197.

[5] Yanqing Liu,Hiroshi Matsuhisa, Hideo Utsuno (2008), “Semi-active vibration isolation system with variable stiffness and damping control,”Journal of Sound and Vibration, Elsevier, pp16–28.

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[8] G. Verros,s. Natsiavas, C. Papadimitriou (2005),

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[9] Yanquing Liu,Hiroshi Matsuhisa,Hideo Utsuno (2005), “Vibration Isolation by a Variable Stiffness and Damping System”,JSME International Journal Series C,Vol.48,No.2,2005, pp 305-310.

[10] Choon-TaeLeea,Byung-YoungMoonb

(2004),“Simulation and experimental validation of vehicle dynamic characteristics for displacement-sensitive shock absorber using ﬂuid-ﬂow modelling”, Mechanical Systems and Signal Processing, Elsevier, pp373-388.

[11] R. D. Eyres, A.R. Champneys, N.A. J .Lieven (2003),“Modellig and Dynamic Response of a Damper with Relief Valve”, Bristol Laboratory for Advanced Dynamic Engineering, University of Bristol, Elsevier, pp1-51.

[12] L.F.P. Etman, R.C.N. Vermeulen,(2002),“Design of a stroke dependent damper for the front axle suspension of a truck using multi body system dynamics and numerical optimization”, Vehicle System Dynamics, Vol. 38, No. 2, pp 85-101.

[13] John C. Dixon (2007),“The shock absorber handbook ,”Second edition” Professional Engineering Publication, ISBN 978-0-470- 51020-9,pp1-445.

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