<div dir="ltr"><div class="gmail_extra">Thanks Ammar for the help. My channel is quite long so I can use the 'ON' boundary condition at outlet for the passive scalar. I have a scalar equation </div><div class="gmail_extra">
<br></div><div class="gmail_extra">c_t + u.grad(c) = div(D*grad(c))</div><div class="gmail_extra"><br></div><div class="gmail_extra">with </div><div class="gmail_extra"><br></div><div class="gmail_extra">c = 1 as initial condition</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">I want to use inlet bc</div><div class="gmail_extra"><br></div><div class="gmail_extra">c = 0 at x=0 (inlet)</div><div class="gmail_extra"><br></div><div class="gmail_extra">
but this leads to a discontinuous initial condition. Is it ok to use such bc ?</div><div class="gmail_extra"><br></div><div class="gmail_extra" style>To avoid specifying such dirichlet bc, I tried to use zero flux bc for c at inlet but then c did not change with time at all.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">Thanks</div><div class="gmail_extra">praveen</div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Oct 13, 2013 at 12:34 AM, <span dir="ltr"><<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">If you are to use outflow BCs' at the channel exit plane it should be located sufficiently far from the inlet (i.e. the channel length long enough) to allow the flow and scalars to be fully developed d phi /dx =0 <div>
Insulation is usually used at solid walls where there is no gradient in the wall normal direction (no heat or mass flow across the boundary) so it works for temperature and scalars.</div><div><br></div><div>try to at least check on mass conservation in an integral sense..</div>
<div><br></div><div>Ammar</div></div></blockquote></div><br><br></div></div>