Hi, i am simulating the airflow over a diffusor in the compressor of a turbocharger with fluent 3d.

I select the option density =ideal gas in material properties, and i dont know how to initialize the problem.

I have the following boundary conditions:inlet massflow, and the outlet pressure.

I already tried to initialize with both, massflow and pressure outlet, with pressureoutlet and introducing my own values. I always get this error:

divergence detected in AMG solver

If i use the constant density model i dont find any problem.

if anyone can help me, i would thank you

the error was divergence of temperature. Sorry

Usually when dealing with ideal gas, I initially disable the energy equation in Solve/Controls/Solution. Once the problem tends to converge, I enable the energy again. This procedure is also recommended in the Fluent manual and it works most of the time.

I have had a similar problem and substituted my own polynomials for the gas properties, which eliminated the divergence error. Also, for some reason I don't understand (and have a request in to tech support for), Fluent's model for air seems to give half the conductivity and 1/3 the specific heat that it should.

[Daryun]

Originally Posted by kafka
;129536

Usually when dealing with ideal gas, I initially disable the energy equation in Solve/Controls/Solution. Once the problem tends to converge, I enable the energy again. This procedure is also recommended in the Fluent manual and it works most of the time.

what can you say about the accuracy of the results when trying it? it mentions about 50 iterations in the user guide and also discusses under relexation parameters. After converging this, what kind of change makes the energy equation active? I have a thesis on the pipe at the turbocharger outlet where I work with compressible flow. I've used what you said and it works. If not used, the continuity equation diverges and gives a floating point error. this is my experience. But what do you think is the difference between the results?

thanks

[Daryun]

Originally Posted by Ana
;129531

the error was divergence of temperature. Sorry

You just change the density to ideal gas. You leave Cp, thermal conductivity and viscosity constant. That's why you get an error. Determine these values as a function of temperature with the help of an equation as polynomial. The error will be solved and you will get more accurate values Polynomial equation in excel table, then add as a graph. Generate equations from the graph, usually a fourth-degree polynomial.