<!-- This form is for bug reports ONLY! If you're looking for help check out the [readme](/README.md). --> **Bug report** The `test_ff_navierstokes_sincos` fails (only!) on buildbot **What happened / Problem description**: The `convergencetest.py` includes numpy, but numpy is not available on buildbot. We should try to get rid of numpy in this case. I did not look into the files yet, but the other convergence tests do not need numpy and were desigend to work without numpy. According to @timok installing numpy on buildbot is not wanted because it is quite large. **Environment**: - Dune version: master - DuMux version: master - Others: gcc, Python version: 2.7.9