Flow Over a Backward Facing Step

The geometry of a Backward Facing Step is imported to converge and dimensions are scaled down from metre to millimetre to aviod any errors. The normals should point inwards so that the flow runs inside the geometry.

The boundaries are assigned to different region of the geometry by flagging them and assigning each with a name.

The case is setup by beginning case setup problem and defining the parameters required for the geometry. In a backward facing step, the flow is continuous but very disturbed initially, which reaches a steady state later; so the case is run using a pressure based steady state solver. The base grid is set according to the problem given, i.e, 2e-4 for dx, 1.5e-4 for dy & 1e-4 for dz respectively.

In boundary conditions, a boundary type is selected for each boundary. The Inlet pressure flows with 1.1 atm of air and outlet pressure flows with 1 atm air so that there is a pressure difference of 10000 pascals which drives the flow.

The Input files are exported to a folder from where the simulation is to be run. The simulation is run using Cygwin in serial and parallel.

In Converge Studio, Line Plotting tool is selected to view the output files of the simulation.

The Mass average flow through inlet & outlet is viewed.

The cell count rank is also shown with total cell count and cell count of each rank.

The output files are post processed by converting all the cell variables and choosing the format in which the output files are to be viewed. The Ensight format is selected which can also be viewed in Paraview.

In Paraview, the output file is opened and the velocity view or pressure view is selected to show the velocity or pressure difference throughout the flow.

Static pressure increases due to increase in area, whereas velocity decreases due to flow separation.