I tested waLBerla's TRT collision model with the compressible D3Q19 velocity set in waLBerla's free surface LBM module (not yet open source), . When using the `GuoConstant` force model, I noticed two things that are not present when using the `SimpleConstant` force model: 1. the physical results significantly differ from SRT (same even order relaxation rate, arbitrary "Magic" parameter) 2. the physical results change significantly with small changes in TRT's (even order) relaxation rate These observations should not be related to the free surface LBM implementation and we should therefore - [x] create a simple test case to validate the `GuoConstant` force model when using the TRT/MRT collision operators (without free surface LBM) - [x] try to reproduce this issue (without free surface LBM) - [ ] check if the `GuoConstant` and `GuoField` force models are implemented correctly for TRT/MRT collision operators