This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

This paper describes the multi-physics FSI simulation approach to study the valve flutter which happens in reciprocating compressor reed valve. Area of study involves the compact variable compression (CVC) compressor which is operated by swash plate mechanism i.e., the rotation of the engine shaft is converted into reciprocating motion of the piston by swash plate. Both inlet and outlet valves have reeds which operate based on the difference in pressure between manifold and cylinder. During suction stroke, the piston movement increases the volume of the compression chamber. When the pressure inside the cylinder drops below the suction pressure, gas enters the cylinder via the inlet valves. The piston reaches the lower dead centre, reverses its movement and starts to compress the cylinder gas. Inlet valves closes and the gas undergoes an isentropic compression. When the piston approaches the top dead centre the pressure inside the compression chamber forces the outlet reed valves to open and the gas is delivered to the discharge pipe. Finally, the piston reaches the top dead centre, outlet valves close and the cycle starts again. In this simulation, real-time thermodynamic behaviour of fluid inside the cylinder and structural behaviour of the reed valve is predicted using coupling between ANSYS Mechanical and FLUENT. When FSI occurs, fluid flow deforms a physical structure, which in turn changes the fluid flow. This 2-way interaction loop continues through multiple cycles, which helps in predicting the more realistic fluid flow across valves and helps in studying the flutter behaviour. The fluid pressure causes the reed valve to deflect which in turn will influence the flow structure and again the change in flow structure will influence the deflection of reed valve. This phenomenon is taken care by setting up the problem as FSI (Fluid Structure Interaction) simulation. This 2-way interaction is carried out every time step to make the simulation more realistic and accurate. In the process we can capture the fluttering of the valve if it happens for given conditions. Traditional fluid flow doesn’t account for this interaction, so simulation results may be incomplete and even misleading. The resulting prototype from traditional flow would not perform as expected, and it is an expensive and time-consuming. That’s why Fluid-Structure Interaction (FSI) approach is important to study the valve flutter phenomena.