The figures and mpeg animation below show the flow velocity and temperature distribution in a 2D model of gas flow due to moving boundary. The gas is compressible and satisfies the ideal gas state equation. The geometry in this case is a vessel containing fluid with one moving wall so that the fluid is driven into motion, and inner pressure and temperature differences appear. The dimensions of the model are in a millimeter scale and the movement of the wall is sinusoidal with an amplitude of 0.5mm and a frequency of 1kHz. The downloadable animation shows the variation of temperature during a cycle in a state where the system has been running a for a while. The moving wall is fixed in the temperature 300K.

The movement of the wall is so large that the element mesh has to be updated on every timestep. This is done by deforming the original mesh elastically and using ALE-formulation (Arbitrary Lagrangian-Eulerian) of the Navier-Stokes equations for solving the flow velocity. The ALE formulation takes into account that the mesh is not stationary and calculates the fluid velocity seen by a stationary observer.

The following two pictures present the flow velocity in a time instant when the wall is moving downwards.