Hello,

I have written a code for compressible (varable density, ideal gas for example) flow in a pipe using SIMPLE. When the condition is isothermal I observe no problem. When I include the energy equation in the model (inlet temperature is fixed and I set the pipe wall temperature equal to Ta<T_inlet) all my problems start. The steady state solution is correct while in the transient part I observe negative pressure, back flow. Is is because of initial condition? I am sure the energy code is correct. The major problem is for the transient part. Can anyone help me with this? Is there any free code for such a simple problem?

Many many thanks for your help.

Where is your simple question?

Sorry it seems part of the message was somehow omitted.

So here is the question one more time:

I have written a code for compressible (variable density, ideal gas for example) flow in a pipe using SIMPLE. When the condition is isothermal I observe no problem. When I include the energy equation in the model (inlet temperature is fixed and I set the pipe wall temperature equal to Ta< T_inlet) in the transient result I observe negative pressure (with respect to outlet pressure) and some back flow. my question: Do you think the back flow and negative pressure is due to my incorrect (incompatible) boundary condition? Is there any free code similar to this problem so I can verify or compare the results? Many many thanks for your help.