Bounca back

Hi dear all
I decided to simulate heat and fluid flow in a 2-d channel with a single square obstacle placed in it. at the first stage of my simulation I simulated the hydrodynamic using d2q9 with mid-plane bounce back but I have velocity on solid boundaries surely, this non-zero velocities can affect the heat transfer problem in the second stage of my simulation so i have 2 questions:
1- how much it will be accurate if we force the velocities on the solid boundaries to be zero right after simulation ?
2- are the half-way bounce back is significantly accurate than mid-plane bounce back?

thanks in advance