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-   -   Steady or transient? (https://www.cfd-online.com/Forums/fluent/95314-steady-transient.html)

 SerSe December 13, 2011 10:02

Steady or transient?

Dear all,

I am analysing the flowfield of an air nozzle inserted into a hot gas pipe. Temperature of the gas is about 1000K, temperature of air is about 400K. Fluids move by pressure differences. Both materials are modelled as AIR and GAS with ideal gas behaviour and same properties (viscosity, specific heat, etc.) changing with temperature. Given the large differences in pressure, velocity, temperature, etc., I have two materials and two domains to initialize the solution with air in the nozzle and gas in the pipe. It is a 2d axisym steady problem with k-e turbulent model ON, solved by the density-based solver.
When I calculate the solution (I have tried with mass flow inlets as well as pressure inlets), it tends to converge but I get strange results (such as step changes in temperature at the nozzle exit, low Mach number in the nozzle though it should be 1 at the throat from manual calculations, etc.).
I am wondering if changing the model to transient might help!

Moreover, as I am interested in air-gas mixing, I wonder if I have to use the species model! From the "mixing elbow" tutorial, it seems that I could study mixing phenomena without species model ON.

Thank you very much for your help!

Regards,

Serse

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