Investigation of Gas Compression Process inside Oleo-Pneumatic Shock-Absorber with Two-Phase Flow Simulation Method

The Oleo-Pneumatic shock absorber has a dual function in suspension systems. Compressibility of gas plays the role of spring and oil passing through the orifice plays damper role. Shock absorber response to various excitation depends on Fluids (gas and oil) and their internal flow. Prediction of the flow behavior inside the shock absorber can reduce cost of experimental during design and optimization process and performance analysis. Numerical Fluids flow has been simulated with assumption of axisymmetric and two-phase flow. Primary phase is compressible and Redlich-Kwang-Soave equation of state has been used to describe the compressible gas behavior. Volume of fluid model (VOF) has been described the relationship between two phases. k-ε model and Scalable wall function has been chosen for modeling turbulence. The piston's movement has been simulated using dynamic mesh (layering method). The way of gas-oil mixing and temperature change during stroke, has been shown an increase in temperature about 50-degree for largest gas bubble because of compressing. However, temperature of small bubbles has been reduced to oil temperature because of higher heat exchange. In polytropic description of gas process, the polytropic expansion has been found to describe with polynomial function of stroke. Polytropic expansion value starts from 1.3, rises to 1.4, and reduces again after mixing two phases.