Hi Mohammadali, In the velocity correction scheme you have to specify boundary conditions for both pressure and velocity. An example of the type of boundary condition you wish to impose can be found in the IncNavierStokesSolver regression tests. Please have a look at $NEKTAR/solvers/IncNavierStokesSolver/Tests/ChanFlow_m3.xml where $NEKTAR is where you have installed the codes. You will see there is a boundary condition of the form. <REGION REF="2"> <N VAR="u" VALUE="0" /> <N VAR="v" VALUE="0" /> <D VAR="p" VALUE="0" /> </REGION> Cheers, Spencer. On 22 Jul 2016, at 15:58, mohammadali alidoost <alidoost.ma@gmail.com<mailto:alidoost.ma@gmail.com>> wrote: Dear Nektar++ Developers, We are going to use a Traction-Free boundary condition as an outflow in our simulation. In addition, we intend to use “Velocity Correction Scheme” of “Incompressible Navier-Stokes Solver”. As far as we know, the Traction-Free boundary condition contains two parts which should be satisfied simultaneously: zero velocity gradient and zero pressure. Based on the scheme we are going to use, we are wondering if you could tell us if it is necessary to implement both conditions in Nektar++ or we just need to set zero pressure condition alone. Kind Regards Mohammadali Alidoost _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk<mailto:Nektar-users@imperial.ac.uk> https://mailman.ic.ac.uk/mailman/listinfo/nektar-users Spencer Sherwin McLaren Racing/Royal Academy of Engineering Research Chair, Professor of Computational Fluid Mechanics, Department of Aeronautics, Imperial College London South Kensington Campus London SW7 2AZ s.sherwin@imperial.ac.uk<mailto:s.sherwin@imperial.ac.uk> +44 (0) 20 759 45052