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-   -   stationary flow - transient temperature (https://www.cfd-online.com/Forums/siemens/53332-stationary-flow-transient-temperature.html)

 Nicola June 2, 2003 08:00

stationary flow - transient temperature

Hey all,

I have a complex geometry with two separated fluids with constant velocities and

1.) the same temperature which differs from the solid temperature. I want to calculate the heating up of the solid

2.) one fliud with constant temperature and the other with a varying temperature ramp. I also want to calculate the heating up of the solid

As I get a maximum time step of 0.02 s for my flow condition it is quite uncomfortable to calculate fully transient. Is there a possibility to treat the flow as stationary and only the conjugate heat transfer as transient? How can I do the set-up for this calculation?

Regards,

Nicola

 Joern Beilke June 2, 2003 11:04

Re: stationary flow - transient temperature

If you are sure that the flow does not change anymore you can switch off the calculation of velocity, pressure ... and only solve for the temperature with a much larger time step.

Later you can switch on the flow for some time steps ...

 Nicola June 3, 2003 08:39

Re: stationary flow - transient temperature

Thanks a lot, it's running much faster. Is there an equation for the max time step for conjugate heat transfer equivalent to the equation for the transient piso? Do you know how the convective heat transfer is solved without solving the velocity? Is the existing velocity from the restart file used?

Regards,

Nicola

 Joern Beilke June 10, 2003 10:11

Re: stationary flow - transient temperature

You dont need to stop the calculation every time. Just define some load steps and use different settings for the solve command and the time step size.

 Nicola June 16, 2003 05:04

Re: stationary flow - transient temperature

I tried to switch on the flow and pressure calculation for some time steps, with the transient file, in which only the energy equation is solved, as restart file. But it didn't work. Prostar accepts the switch, but in the calculation, it is not solved for neither velocities nor pressure...

Havew I to change anything in the previous set-up, or in the .prob file, or somewhere else?

Thanks for help,

Nicola

 Joern Beilke June 16, 2003 05:44

Re: stationary flow - transient temperature

time trans
trfi init

! solve all for 10 time steps
solve,y,y,y,y,n,n,y,n,n,n,n,n,
lstep,1,10,cons,1e-5,N,0,0
lssave,1

! solve temperature for 100 steps
solve,n,n,n,n,n,n,y,n,n,n,n,n,
lstep,2,100,cons,1,N,0,0
lssave,2

! solve all for 10 time steps
solve,y,y,y,y,n,n,y,n,n,n,n,n,
lstep,2,10,cons,1e-5,N,0,0
lssave,2

lsra 1 3
...

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