Simulation Example: Isentropic Compression in a Piston-Cylinder Assembly


A piston-cylinder assembly is an integral part of many mechanical systems such as engines, pumps, compressors etc. The most famous and well-known application for the piston-cylinder assembly is the reciprocating engine, where the compression and expansion of the gases leads to a linear motion of the piston, which is converted to a rotating motion that can be used for turning wheels. In these engines, the compressible nature of the gases allows for their compression and expansion, which in a typical reciprocating engine can be generally considered to be isentropic, i.e., both adiabatic and reversible. For such isentropic flows, there are established theoretical formulas that can help in estimating the fluid variables at different states, which is extremely helpful during the preliminary design phase.




In this example, you will learn how to set up a 2D simulation to model the thermodynamics of air during the compression stroke of a piston-cylinder assembly. You will learn how to prescribe the piston motion using the dynamic meshing approach of Ansys Fluent. You will finally compare the results from simulation with the analytical results obtained from the isentropic relations.


Download the Mesh file needed for setting up the simulation and the associated Case & Data files here. Follow the instructions below to set up this simulation in Ansys Fluent starting with the Mesh file. In case you face any issues setting up or running the simulation, refer to the corresponding initial and final Case and Data files.

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Results and Discussion

Let's take a look at some results and understand the isentropic compression process of a piston-cylinder assembly.