[RobBanks]

Hello to anyone who might read this, thank you for any possible help you may provide.

I have the following issue, I'm not sure it is a real problem or not because I'm an ANSYS-CFX starter user.

I'm running some airflow simulations on a mesh corresponding to a solar collector.

I'm running 2 simulations for the study, using the results of the first as the input file for the second (the only reason for this is to aid the process into reaching convergence faster because the conditions in both sims are alike).

Both have the exact same parameter setup, only changing the parameters values.

These are a:

Transient Analysis, Thermal Energy as heat transfer option, with a Turbulent Prandtl Number of 0.9 sims

The most influential parameters are, as follow:

- Inlet: Mass flow rate & air temperature at the inlet.
- Opaque Plate: Heat Flux (Heat transfer option)
- Transparent glass: Heat Transfer Coefficient & Outside air temperature, Boundary Source: Energy Flux.

For the first simulation, the code will be Sim1 and Sim2 for the second. This is to easily explain the concern.

Inlet: Mass Flow Rate_Sim1 < Mass Flow Rate_Sim 2
Opaque Plate: Heat Transfer Coeff < Heat Transfer Coeff_Sim 2
Transparent Glass: Outside air_Sim 1 < Outside air_Sim 2

For all the other parameters, the values are Sim1 > Sim2.

So, the concern is: For the first simulation, I'm using a file from the mesh independence study as the input file, then I get the .res and the .trn files for Sim1. That simulation went on for 1 day and some 20 hours.

For the second simulation "Sim 2", I used as an input file, the "Sim_1.res", that simulation takes about 8 minutes, then it ends normally, generates the .res file but no .trn files.

Both simulations have as "Total Time" 15 seconds, 0.01 timesteps and the initial time for both is 0 s.

Question: Is this difference in the duration of the simulations due to a possible error? because in the second one I don't get any .trn files, it finishes too soon and I believe it is not simulating the whole 15 seconds it should. It only runs 1 timesteps of 10 coefficient iteration loops, and that's it.

I've read around that it could possibly be because the variation in the conditions set doesn't affect much the functioning and/or results of the simulation. Another possible answer could be: the increase in the mass flow rate, Heat Transfer Coefficient and Outside air temperature from Sim 1 to Sim 2 don't affect the functioning as much as the decrease of the rest of the values from Sim 1 to Sim 2... I've read many vague, possible answers but yet nothing convincing nor helpful to sort this issue out.

The fact is: I need more data to analyse and it is not providing it. I don't know why though.

I was hoping any of you could explain what is happening in this case scenario and what could be the possible solutions.

I hope the explanation was clear and thorough enough.

Thank you, so much for any possible reply!

RobBanks