Hello,
I’m trying to implement LBM for velocity driven poiseuille flow (zero pressure gradient) with a D2Q9 model. A free stream velocity is applied at the inlet and full-bounce-back boundary conditions at top and bottom walls. As of now, I haven’t specified any specific boundary condition for the outlet but the streaming process ensures a zero gradient condition there. My problem is that the final maximum value of the x-direction velocity is smaller than the value I’ve specified as the magnitude of the free-stream velocity. The analytical solution says Umax should be 1.5 times U(free stream). Is this because I haven’t specified any boundary condition for the outlet? The problem persists even if I give periodic boundary condiditon at inlet and outlet. Your help is really appreciated.
Thanks in advance and in anticipation,
Aswathy Nair K.
IIT Madras
India