[bial]

i am new to gambit and fluent
i have modelled a flush intake with a square duct , now i have to analyze the flow that pass through this intake at subsonic/ supersonic mach numbers
i run it @ mach 0.4 and results come quite good
but when i run it at mach 0.8,, certaien errors are coming, like absolute pressure limited to 1 and temperature exceeded to 5000K,
i have make my mesh more finer,, but same problems are coming
i am using a density solver and steady state
what should i do now??

can u please help me

Thnx

[bial]

i am new to gambit and fluent
i have modelled a flush intake with a square duct , now i have to analyze the flow that pass through this intake at subsonic/ supersonic mach numbers
i run it @ mach 0.4 and results come quite good
but when i run it at mach 0.8,, certaien errors are coming, like absolute pressure limited to 1 and temperature exceeded to 5000K,
i have make my mesh more finer,, but same problems are coming
i am using a density solver and steady state
what should i do now??

can u please help me

Thnx

[Chris D]

A few things to try:

1) Set reasonable solution limits to help keep the code stable. For example, if you expect temperatures to be around 300K, set the temperature limits at 200K and 400K. Also, do the warnings go away as the solution progresses?

2) Find out where the solution is going unstable, and make sure that the grid is ok in that region. One way to do this is to go to Adapt->Iso value, adapt by temperature, and then set the range such that the cells outside of the range will be adapted. Then, set the range to be what you would reasonably expect for your calculation, and select "Mark". If you then go to manage, display, it will show the problem cells (make sure to also select "draw grid", and display any wall zones, also.)

3) Try running at a lower CFL number.

4) Use FMG initialization to get a better initial condition for the flow.

This may not solve your problem, but it's what I would do without knowing anything else about what you're doing. Good luck!

[bial]

thanx Chris

i am getting the same messages as absolute pressure limited to 1e10 and temperature exceeded to 5000K, also divergence is detected
and i am running a steady state

if u want i can upload the model of my geometry

skewness is not high
i mean the worse element is 0.94

[bial]

this is the geometry of my model

[Chris D]

I think a cell with skewness of 0.94 in a region with high flow gradients could cause you some problems. Have you tracked down exactly where in your domain the solution is going blowing up? Setting better solution limits?

[bial]

how can i know that where in my domain the solution is blowing up...........

THANKS

[Chris D]

See 2) from my post on May 14.

[bial]

actually i have done steady runs of fluent at mach 0.4 and mach 0.6
the results are coming good..

but when i put the values for mach 0.8.. it is not running

the residulas suddenly goes up.................and showing that divergence is detected

so wat may be the possible reason behind that..........and how can i correct my errors

THANX

[bial]

thnx alot for ur help, CHRIS

i have started my cfd run at mach 0.8,,
now after 10800 iteartions ,,,,,i have started unsteady

but the following error is coming

Error: add_memory_block: failed to allocate memory block-926 0.000976563MB. (..\..\src\amg.c:620)
Error Object: ()


is it possible that i can start unsteady without being converged at steady????????

size of my mesh is 1.1 million ...i am using a dual core 2.4GHz wd 2GB of RAM

plz help me,,,,and suggest some solution........