Cylinder Piston Motion

Cylinder Piston Motion (Dynamic Mesh) — ANSYS Fluent CFD Simulation

Description

This project simulates the motion of a four-stroke engine's cylinder-piston system using ANSYS Fluent's Dynamic Mesh capabilities. Inside an internal combustion engine, the piston moves up and down through four stages — intake, compression, power, and exhaust — while the valves open and close in sequence, and the mesh must continuously deform and regenerate to follow that reciprocating motion. This project captures the complete cycle: the piston descending and the valve opening on the intake stroke, the flow compressing as the piston ascends, the piston reaching top dead center at the power stroke, and the exhaust valve opening as the piston descends again. Within the Dynamic Mesh: Beginner CFD Training Package, this project introduces classic reciprocating in-cylinder motion — the workhorse dynamic-mesh application at the heart of engine simulation.

Methodology

The geometry is created in Design Modeler and meshed in ANSYS Meshing. The Dynamic Mesh model is applied through the In-Cylinder option for the piston motion, defining the key parameters — crank radius, connecting-rod length, and piston stroke cutoff — with the full-piston function driving the boundary movement. Rigid body motion is set up for the piston surface and valves, profiles are used to describe the valve-lift changes, and deforming mesh zones and stationary options are assigned appropriately. The reciprocating motions are defined with time-dependent flow behavior, and a transient solver with suitable settings resolves the evolving in-cylinder flow.

Analysis

Post-processing focuses on the pressure and velocity contours through the engine cycle, along with animations of the mesh changes and flow behavior that verify the correct operation of the cylinder-piston system. From these results you can follow how the flow is drawn in, compressed, and expelled across the four strokes, and confirm the dynamic mesh handles the piston and valve motion correctly. By the end of this project, you'll be able to set up a Dynamic Mesh simulation using the In-Cylinder option, define reciprocating piston and valve motion through crank parameters and lift profiles, apply deforming and rigid-body mesh zones, and interpret the time-dependent pressure and velocity fields of a four-stroke engine cycle.