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Nitesh,<br>
<br>
From your description it sounds like the simulation is doing just
what it is supposed to, just the gravity you are applying is much
stronger than what you might have expected.<br>
<br>
In order for the fluid to remain static when a simulation is
started, it must be initialized in hydrostatic equilibrium -- i.e.
it must have a pressure/density/temperature gradient of the
appropriate size and direction. Without this the fluid will just
start to "fall" toward such an equilibrium as soon as the simulation
starts.<br>
<br>
There is some discussion of initializing fluid in hydrostatic
equilibrium in Zingale et al. (<a
href="http://adsabs.harvard.edu/abs/2002ApJS..143..539Z">2002ApJS..143..539Z</a>),
though it is in the astrophysical context. This also discusses
relevant boundary conditions to support the fluid.<br>
<br>
If the gravity is too strong, it is possible for an inlet boundary
condition to be inconsistent, i.e. the imposed pressure may not be
high enough to actually support the material in the domain against
gravity. In this situation the pressure is not consistent with
sustained inflow and things will just get weird.<br>
<br>
I have implemented a top-to-bottom flow-through hydrostatic domain,
but it is pretty touchy and it doesn't sound like this is what you
are looking for. For a buoyant jet it seems like you want the
hydrostatic background to be mostly static, not steadily flowing.
Though honestly I'm unsure what you are trying to reproduce. Maybe
if you have a reference for an example?<br>
<br>
Dean<br>
<br>
<br>
On 05/02/2012 12:43 PM, Nitesh Attal wrote:
<blockquote cite="mid:4FA1725D.2070800@uncc.edu" type="cite">Hello,
<br>
1) I use a constant acceleration of gravity (-981.0) along x
direction. The x-velocity decreases throughout the domain at early
time and as time progress the rate at which it decreases
increases. Also, pressure inside the domain increases where as we
are fixing the pressure at the inlet boundary (xl). This causes
the reverse flow, and I am wondering if it has anything to do with
the gravity implementation or its compatibility with the inlet
boundary. What should I use for the inflow boundary?
<br>
2) (i)When I changed constant of gravitational acceleration to
+981.0 along x direction. The velocity inside the domain rises
rapidly and there is no flow reversal.
<br>
(ii) I would get back on that
<br>
(iii) I would get back on that
<br>
3) I am using FLASH4-beta but observed this in the previous
releases also(FLASH3.3 and FLASH4-alpha)
<br>
On 5/2/2012 1:06 PM, <a class="moz-txt-link-abbreviated" href="mailto:dongwook@flash.uchicago.edu">dongwook@flash.uchicago.edu</a> wrote:
<br>
<blockquote type="cite">Hi Nitesh,
<br>
<br>
I am not sure if anyone has replied to your email, but if not, I
am sorry
<br>
that your email has not been anwered yet.
<br>
<br>
Just few questions to understand your issue:
<br>
<br>
(1) To what direction do you apply your constant gravity? Is
this to the
<br>
negetive x-direction, and as a result, do you see flow reversal
at the
<br>
xl-boundary?
<br>
<br>
The Windtunnel uses inflow boundary condition at the
xl-boundary, and this
<br>
should not allow any matter to leave across the boundary. But if
your
<br>
gravity is applied to the negative x-direction, it may as well
be the case
<br>
that flow reversal would happen (depending on how strong your
gravity is
<br>
relative to the inflow velocity), but the inflow boundary
condition at the
<br>
xl-boundary doesn't seem to be a sensible thing to have.
<br>
<br>
(2) In case that your gravity is NOT to the negative x-direction
but still
<br>
experiencing the flow reversal, it could be useful for you to
understand
<br>
your problem by trying several things:
<br>
<br>
(i) change gravity directions and identify which one has the
flow reversal,
<br>
(ii) change the magnetitude of gravity and identify the
problems as a
<br>
function of its magnitude,
<br>
(iii) use an alternative solver, for example, if you use the
split PPM
<br>
then use the unsplit hydro solver, or vice versa.
<br>
<br>
(3) By the way, what FLASH do you use? Do you use the most
recent release?
<br>
<br>
Hope this helps.
<br>
<br>
Best,
<br>
Dongwook
<br>
=========================================
<br>
Dongwook Lee, Ph.D., Research Scientist
<br>
The Flash Center for Computational Science
<br>
The University of Chicago
<br>
5747 S. Ellis Ave., Room 319
<br>
Chicago, IL 60637
<br>
(773) 834-6830
<br>
<br>
<blockquote type="cite">Hello All,
<br>
I intend to perform a Multi-species laminar buoyant Jet
simulation.
<br>
I began with the turning on Gravity in the Supplied Windtunnel
test
<br>
problem.
<br>
The Windtunnel test problem when ran with constant Gravity
results into
<br>
complete flow reversal (towards xl-boundary). Even when the
xl-boundary
<br>
is made outflow flow reversal is observed.
<br>
Is this a known issue? Could some one suggest how to overcome
this?
<br>
Thanks,
<br>
Nitesh
<br>
<br>
</blockquote>
<br>
</blockquote>
<br>
<br>
</blockquote>
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