Why results differs between upwind and vanLeerV
I have been experimenting with different schemes for a pipe case, and have been running upwind and vanLeerV for the initial phase for two almost identical cases. A two phase flow w/ alpha = 0.5 with different velocities is used.
In setup 1 I used this setup for div schemes:
divSchemes... and for setup 2:
divSchemesBut the results from the two setups are quite different, and I believe the only difference in my setup is the different schemes. After 10 seconds, the pipe exit looks very different in the two setups - see attached photos. And it is the vanLeer-case which is "delayed". Does anybody have an explanation to this? I suppose the two schemes should yield the same results?
the difference between upwind and vanLeer is, that vanLeer is a scheme composed of upwind and central differencing. Of course, you can have different results, because upwind is alway first order accurate whereby vanLeer can have second order accuracy - when no step gradients occur. For a better understanding, I recommend to read Versteeg (Chapter about upwind, QUCIK etc.). He does a very good analysis about the different schemes.
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