[FLASH-USERS] Flow Reversal for Windtunnel with Gravity

[Nitesh Attal]

Hello,
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?
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.
      (ii) I would get back on that
      (iii) I would get back on that
3) I am using FLASH4-beta but observed this in the previous releases 
also(FLASH3.3 and FLASH4-alpha)
On 5/2/2012 1:06 PM, dongwook at flash.uchicago.edu wrote:
> Hi Nitesh,
>
> I am not sure if anyone has replied to your email, but if not, I am sorry
> that your email has not been anwered yet.
>
> Just few questions to understand your issue:
>
> (1) To what direction do you apply your constant gravity? Is this to the
> negetive x-direction, and as a result, do you see flow reversal at the
> xl-boundary?
>
> The Windtunnel uses inflow boundary condition at the xl-boundary, and this
> should not allow any matter to leave across the boundary. But if your
> gravity is applied to the negative x-direction, it may as well be the case
> that flow reversal would happen (depending on how strong your gravity is
> relative to the inflow velocity), but the inflow boundary condition at the
> xl-boundary doesn't seem to be a sensible thing to have.
>
> (2) In case that your gravity is NOT to the negative x-direction but still
> experiencing the flow reversal, it could be useful for you to understand
> your problem by trying several things:
>
>    (i) change gravity directions and identify which one has the flow reversal,
>    (ii) change the magnetitude of gravity and identify the problems as a
> function of its magnitude,
>    (iii) use an alternative solver, for example, if you use the split PPM
> then use the unsplit hydro solver, or vice versa.
>
> (3) By the way, what FLASH do you use? Do you use the most recent release?
>
> Hope this helps.
>
> Best,
> Dongwook
> =========================================
> Dongwook Lee, Ph.D., Research Scientist
> The Flash Center for Computational Science
> The University of Chicago
> 5747 S. Ellis Ave., Room 319
> Chicago, IL 60637
> (773) 834-6830
>
>> Hello All,
>> I intend to perform a Multi-species laminar buoyant Jet simulation.
>> I began with the turning on Gravity in the Supplied Windtunnel test
>> problem.
>> The Windtunnel test problem when ran with constant Gravity results into
>> complete flow reversal (towards xl-boundary). Even when the xl-boundary
>> is made outflow flow reversal is observed.
>> Is this a known issue? Could some one suggest how to overcome this?
>> Thanks,
>> Nitesh
>>
>