What cells can be called Small cells

In FlowVision uses Cartesian grid that can be automatically locally downscaled. Grid cells intersecting computational domain boundaries and computational subregions are clipped by boundary surfaces.

fig1 cutcell

Fig.1. Splitting cells by geometry surface

After such clipping it is possible that size of new cells will be in many times smaller than initial cell:

fig2 smallcells

Fig. 2. Small cells

At present moment, usage of PrePostprocessor (PPP) is officially supported only for Windows. However, sometimes it is necessary to run PPP on Linux too. Actually, customers of FlowVision have such possibility due to special software for running of windows applications on Linux, like Wine. Let us consider, how to run PPP on Linux using Wine, on the example of Ubuntu 16.04.1, and you will be convinced how easily it is.

PPP on Linux

Too quick changing of variable can give divergence or make convergence worse, because fast changes will give large gradients of physical variables.

For example, in tasks about turbines and compressors we have rotor which has large velocity of rotation. When we start simulation we can’t specify initial velocity for gas between blades of rotor, because structure of flow too complex. It means that during first time step we will have quick changes of velocity from zero (initial velocity of gas) to some large velocity of blades.

hydroturbine

If we will solve this task for incompressible liquid, we will have divergence. It is possible to make convergence better if we will exclude too quick changes, for example, we can change speed of rotation smoothly from zero.

FlowVision allow to specify very complex equations for any user’s variables. Below you will find some formula template which useful to use every time when you need specify some smooth changing of variable.

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