OpenLB – Open Source Lattice Boltzmann Code › Forums › on OpenLB › General Topics › About ConvectionBC › Re: About ConvectionBC July 12, 2017 at 9:50 am #2660 mathiasKeymaster The value *uAv should be the actual value of the average velocity at the outflow area. That means you must set it to a desiged value or compute it with the e.g. flux functor every time step.