OpenLB – Open Source Lattice Boltzmann Code › Forums › on OpenLB › General Topics › olb1.6 bifurcation3d › Reply To: olb1.6 bifurcation3d November 6, 2023 at 11:48 am #7891 AdrianKeymaster The explanation is right there in the output you shared: ERROR: Subgrid particles can only be used with MPI! You need to compile this example using MPI as the inter-block communication of subgrid particles requires MPI.